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The long weld neck flange of pressure vessel is optimized through two specific examples, and the effects of cone neck height and flange thickness on the three main stresses of flange axial stress, radial stress and tangential stress are analyzed. The calculation results show that when the flange thickness and cone neck height are adjusted to be similar, the three main stress values are close to the full stress value. This optimized design makes the flange compact in structure, reasonable in force, reduces the weight, and can significantly reduce the flange cost. For long weld neck flanges with small diameter and low pressure, on the premise of ensuring that the slope of flange cone neck section is less than 1:3, the flange can not have straight edge section. Optimal design of long weld neck flange Long weld neck flange is the most commonly used equipment flange in pressure vessels. Although NB/T 47023-2012 standard [7] gives the long weld neck flange of carbon steel and low alloy steel pressure vessels with nominal pressure of 0.6 ~ 6.4MPa and working temperature of – 70 ° C ~ 450 ° C, the flange, stud, nut and backing sheet materials need to be fully implemented according to the matching table and correction table in the standard, which is subject to many restrictions, Moreover, in engineering practice, many long weld neck flanges are beyond the scope of NB/T 47023-2012 standard, such as stainless steel flange or long weld neck flange with working temperature exceeding 450C, which shall be in accordance with GB/T 150 3-2011 design and calculation of non-standard flange. Through two specific calculation examples, the author optimizes the design of UNS S30408 long weld neck flange and 15crmo long weld neck flange, analyzes the effects of cone neck height and flange thickness on the three main stresses of flange axial stress, radial stress and tangential stress, and gives suggestions on the optimal design of long weld neck flange, which can be used as a reference for relevant designers of pressure vessels. In addition, the author also draws lessons from the flange design schemes of some large design institutes and engineering coMPanies. For the long weld neck flange with small diameter and low pressure, it is recommended that the flange design should not have straight edge section, but according to GB/T 150 3-2011 it is required to ensure that the slope of flange cone neck section is 31:3, which can significantly reduce the flange cost. The flange material of a vessel is s30408 and the design temperature is 300C; Design pressure: 2.6MPa; The specification of butt barrel is dn1000x14mm, and the winding pad is selected: M = 3.0, y = 69MPa; The allowable stress of flange under normal temperature [0] = 137MPa, the allowable stress of flange under design temperature [0] / = 85MPa, the material of stud is 35CrMoA, the specification is M30, the quantity is 48, and the corrosion allowance is not considered. Firstly, the author designs and calculates with reference to the overall dimensions of NB/T 47023-2012 standard equipment flange. The outer diameter of the flange is 1215mm, the inner diameter of the flange is $1000mm, the diameter of the bolt circle is 1155mm, the effective thickness of the flange is 100mm, the height of the cone neck is h = 42mm, the effective thickness of the large end of the neck is G1 = 36mm, and the effective thickness of the small end of the neck is G0, which is taken as the thickness of the butt cylinder 14mm. After preliminary calculation, the axial stress 0h = 199.25MPa > 1.5 [called /, comprehensive stress max (0.5 (0h + 0r), 0.5 (0h + 0t)) = 136.01MPa > [0h] /, and the flange strength is unqualified. At this time, some designers will blindly increase the flange thickness until it is qualified, which is not desirable. Blindly thickening the flange will cause material waste and unreasonable stress on the flange. When the axial stress is too large or too small, the method of adjusting the size of the cone neck shall be adopted, and the thickness or height of the cone neck can be adjusted. The maximum value of the axial stress is usually located on the section of the small end of the cone neck, which can be judged from the coefficient F. the coefficient f is the stress at the small end of the cone neck. When f is greater than 1, the maximum stress is at the small end of the cone neck. When f is less than or equal to 1, the maximum stress is at the large end of the cone neck. In this example, in order to facilitate docking with the cylinder, the thickness of the small end of the cone neck is taken as the thickness of the cylinder without adjustment; the effective thickness of the large end of the cone neck shall be in accordance with the provisions of the minimum value of La in table.1 in GB/T 150.3. Table.1Cone neck heighth/ mmAxial stress is calculated/MPaAllowable axial stress value/MPaRadial stress is calculated/MPaAllowable radial stress value/MPaThe tangential stress is calculated/MPaAllowable tangential stress value/MPaComprehensive stress calculation value/MPaCombined allowable stress value/MPaCheck the results55167.82127.518.298564.8585116.3485Unqualified65143.75127.519.278559.7185101.7385Unqualified75120.8127.520.118555.348588.0785Unqualified78114.22127.520.348554.168584.1985Qualified It can be seen from the stress calculation results in Table.1 that after increasing the cone neck height, the axial stress value decreases significantly, the tangential stress value also decreases, and the radial stress value increases slightly. When the cone neck height increases to 78mm, the flange is checked and qualified, but is this the optimal design? In the above calculation process, the author only increases the cone neck height, and the flange thickness is not adjusted. The flange design should follow According to the full stress design principle, the axial stress and radial stress in the above calculation are close to the full stress value. Through further adjustment and calculation of the flange thickness and cone neck height, the author concludes that when the flange thickness is 90mm and the cone neck height is 84mm, the axial stress 0h = 116.04MPa, the tangential stress 0t = 52.25MPa, the axial stress and tangential stress value and the flange thickness are 100mm and the cone neck height is 78m M is basically the same, the radial stress 0r = 27.92MPa, and the radial stress value increases slightly. The flange thickness is reduced, the flange weight is significantly reduced, the flange cost can be significantly reduced, and the stress is reasonable. In the process of pressure vessel design and verification of several projects, the author found that some large design institutes and engineering coMPanies do not have straight edge segments in flange design, especially for long weld neck flanges with small diameter and low pressure. According to the provisions of GB/T 150.3 and JB4732 standards, long weld neck flanges can not have straight edge segments on the premise of ensuring the slope of flange cone neck section of 2:3, which is difficult to calculate The effective thickness of the small end of the flange neck is the thickness of the butt cylinder. The author also understands that the main purpose of the design institute’s design is to save flange materials, which is particularly important for the pressure vessel manufacturer. If the flange structure can be optimized, the flange cost can be significantly reduced. Moreover, in the actual production and manufacturing process, the groove type of the flange is often determined by the welding process , if there is no straight edge section, the thickness of the small end of the flange neck can be the same as that of the butt cylinder. In this way, whether the outer slope or the inner groove is adopted, it can ensure the inner flush during assembly, which is conducive to welding and does not need thinning treatment, which greatly improves the production efficiency. Flange optimization design is a complex and tedious process, and different designers often have different calculation results, but flange design must follow the principle of full stress, and give full play to the strength performance of flange materials through full stress optimization design. Through the above two examples, the author analyzes the three main stress values of flange, and adjusts the cone neck size and flange thickness respectively The design results that each stress value is close to the full stress are obtained. This optimal design makes the flange coMPact, reasonable stress and light weight. Therefore, the optimal design of the flange has obvious economic benefits. Source: China Stainless Steel Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Flange is the main connecting equipment of process pipeline in petrochemical enterprises. It has a large number and plays a very important role in production and operation. Most of Fujian coastal petrochemical enterprises are located in coastal areas. The high salt and high humidity marine corrosive atmosphere accelerates the corrosion rate of station flanges, resulting in a wide range of flange corrosion, especially flange clearance and flange gasket corrosion, which will not only cause equipment damage and shorten service life, but also cause management medium leakage, and bring great potential safety hazards to production safety. Flange corrosion mechanism By analyzing the mechanism of flange corrosion, there are mainly the following: The flange clearance space is narrow (the common flange clearance size is about 2 ~ 20mm, which is easy to accumulate dust and salt in the air, which are the inducing factors of corrosion and will lead to rapid corrosion; The flange has a gap structure, which is a typical structure of crevice corrosion and a prerequisite for the formation of crevice corrosion. A narrow flange gap will cause different oxygen concentrations inside and outside the gap, forming an oxygen concentration difference battery, greatly accelerating the occurrence of corrosion; Some petrochemical enterprises are located in coastal areas. The coastal air is high in humidity and salt. The water, gas and salt rich in the air are very easy to damage the flange coating and cause local corrosion; In the design stage, attention is not paid to the anti-corrosion part or anti-corrosion structure design, resulting in the connection of flange surfaces of different materials and the selection of metal gaskets with different materials from the flange surface during construction, resulting in galvanic corrosion. Flange anti-corrosion method The most appropriate anti-corrosion process shall be selected according to the corrosion environment and corrosion severity of the flange. The details are as follows: The anti-corrosion design avoids the design of narrow gap structure, resulting in gap corrosion and impurity accumulation, and the same metal is designed for the same flange surface to avoid galvanic corrosion; Strengthen the construction quality control during construction and strictly control the substrate bottom; Treatment and coating construction quality; Consider using non-metallic gaskets to reduce the probability of galvanic corrosion of gaskets. If sacrificial anode protection is provided, consider flange bridging; The new coating anti-corrosion process is adopted, and the coating material with excellent anti-corrosion performance is selected to completely fill and cover the flange gap, isolate the corrosion sources such as water, air and impurities, and contact the inner surface and gasket of the flange gap, so as to realize long-term anti-corrosion. The flange is coated with anti-corrosion materials In the case that the traditional coating anti-corrosion can not effectively prevent the flange from corrosion, through investigation, a variety of new coating materials are selected and tested on the flange, and their anti-corrosion processes are tested and improved. Some flange coating anti-corrosion processes have achieved good anti-corrosion effects. Wax magnetic anti-corrosion material is an excellent anti-corrosion protection material. Wax Tape anti-corrosion material mainly includes wax tape and wax magnetic primer, which can well isolate water and air. It can be applied to the anti-corrosion of various irregular pipelines, valves, flanges, bolts and other equipment in various corrosive environments. In 2006, NACE formulated the standards related to wax magnetic anti-corrosion materials. Viscoelastic anti-corrosion material is a new type of high molecular polymer anti-corrosion material originated in the Netherlands. Its state is between liquid and solid. At room temperature, it can remain in a state of no flow and no solidification for a long time. In addition, viscoelastic has very good bonding performance, waterproof and air isolation performance. According to the experience of equipment anti-corrosion maintenance in many petrochemical enterprises along the coast of Fujian, the traditional coating anti-corrosion can not meet the increasingly severe demand for station flange anti-corrosion. According to the characteristics of coastal and long-term marine corrosive atmosphere with high humidity and high salt, the disadvantages of the traditional coating anti-corrosion method are analyzed, and two coating anti-corrosion materials with excellent anti-corrosion performance are selected to be used in Fujian After several years of experience accumulation, it is considered that the wax magnetic anti-corrosion material and viscoelastic anti-corrosion material have good applicability and good anti-corrosion effect on the process flange equipment of petrochemical enterprises. Several solutions to flange corrosion The integrity of the flange connection is very important for the fluid piping system. Since the sealing surface of the flange connection can only be visually inspected when the whole system is closed, the inspection process should be as simple as possible. First, external corrosion should be eliminated. If it cannot be stopped, only ultrasonic technology can be used for detection. If external corrosion cannot be controlled, the process will be more complex and cannot be controlled Therefore, in order to monitor the whole system and provide effective and feasible quality control and maintenance procedures, the external corrosion protection of flanges and fasteners is very important. The ideal solution should take into account excellent corrosion resistance and simple construction procedures. It is suitable for flanges of various sizes and shapes. It is easy to operate bolts during maintenance. At present, the following solutions are commonly used in the market. 1. Maintenance paint solution Maintenance paint is a hard film that can be directly bonded to the substrate, usually epoxy or polyurethane paint. The flange has many corners and edges. Due to the effect of edge thinning, it is difficult for the traditional coating system to effectively cover the edge. Although the thickened coating can solve the problem of edge protection, it will seal the fasteners and cannot be removed for future maintenance. 2. Mechanical solutions The gap between flange and flange surface is mainly sealed by protective cover, usually made of stainless steel or plastic clamp, and equipped with rubber sealing strip. This protection method is not flexible, and it is necessary to store covers or fixing devices that fully match flanges of various sizes. 3. Tape or semi-solid anti-corrosion tape solution Roll packaged tape (such as Vaseline tape, wax tape or elastic polymer bandage) is protected by winding on the surface of the substrate. Since the semi-solid polymer is waterproof, this protection method can provide reliable protection. However, if the flange shape is complex, this material is not only time-consuming, but also difficult to construct. 4. Hot melt plastic solutions Hot melt plastic is essentially a waxy fusible polymer heated at high temperature, which can be sprayed on the substrate surface through professional hot melt equipment. The advantage of this protection method is that it can be remelted and reused, saving cost. However, although it can be reused, it still needs hot work, professional equipment and construction services, but it is not easy to open and close during maintenance Seal. 5. Polymer sealed bag solution The sealing bag can completely cover the flange. Its composition is composed of low permeability polymer, corrosion inhibitor steam and desiccant. It is easy to install, but the two ends of the bag are only sealed with tape instead of long-term effective mechanical bonding. The steam space has a large area, it is easy to accumulate a large amount of water, and the corrosion inhibitor will be consumed over a period of time. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The intergranular corrosion tendency test of stainless steel is a common content in design documents, and the relevant content in standards such as HG/T 20581 is relatively clear. The water pressure test or the chloride ion content in the operating medium is also the basic content of the austenitic stainless steel equipment design. In addition to chloride ions, wet hydrogen sulfide, polythionine and other environments that may generate sulfides can also cause stress corrosion cracking of austenitic stainless steel. It is worth mentioning that although austenitic stainless steel is not mentioned in the chapter of HG/T 20581 wet hydrogen sulfide corrosion, the reference points out that although austenitic stainless steel has a much greater ability to dissolve atomic hydrogen than ferritic stainless steel, But hydrogen-induced wet hydrogen sulfide stress corrosion cracking will still occur, especially after cold work hardening appears deformed martensite structure transformation. Cold work hardening increases stress corrosion cracking sensitivity Austenitic stainless steel has excellent cold working properties, but its work hardening is very obvious. The greater the degree of cold working deformation, the higher the hardness rise. The increase in hardness caused by work hardening is also an important reason for the stress corrosion cracking of stainless steel, especially those where the base material is not welded. There are some cases: The first type of case is the cold spinning of austenitic stainless steel oval or dish-shaped head, the cold deformation of the transition zone is the largest, and the hardness also reaches the highest. After commissioning, chloride ion stress corrosion cracking occurred in the transition zone, resulting in equipment leakage. The second type of case is a U-shaped corrugated expansion joint made by hydroforming after the stainless steel sheet is rolled. The cold deformation is the largest at the wave crest, and the hardness is the highest. The stress corrosion cracking occurs along the wave crest the most, and even cracking along the wave crest occurs. Explosion accident with low stress and brittle fracture. The third case is the stress corrosion cracking of the corrugated heat exchange tube. The corrugated heat exchange tube is cold-extruded from a stainless steel seamless tube. The wave crests and troughs are subjected to different degrees of cold deformation and thinning. The crests and troughs may cause several stress corrosion cracks. The essence of cold work hardening of austenitic stainless steel is to produce deformed martensite. The greater the cold work deformation, the more deformed martensite and the higher its hardness. At the same time, the greater the internal stress within the material. In fact, if solution heat treatment is carried out after its processing and forming, the effect of reducing the hardness and greatly reducing the residual stress can be achieved, and the martensite structure can also be eliminated, thereby avoiding stress corrosion cracking. The embrittlement problem of long-term service under high temperature At present, the container and pipe materials at 400～500℃ are mainly Cr-Mo steel with higher high temperature strength, and at 500～600℃ or even 700℃, various austenitic stainless steels are mainly used. In the design, people often pay more attention to the high temperature strength of austenitic stainless steel, and require its carbon content not to be too low. The allowable stress at high temperature is basically obtained by the extrapolated high temperature endurance strength test, which can ensure that no creep rupture occurs under the design stress of 100,000 hours of service. However, the ageing embrittlement problem of austenitic stainless steel at high temperature cannot be ignored. After long-term service at high temperature, austenitic stainless steel will have a series of changes in the structure, which will seriously affect a series of mechanical properties of steel, especially the brittleness Significantly rise, resilience drops significantly. The embrittlement problem after long-term service at high temperature is generally caused by two factors, one is the formation of carbides, and the other is the formation of σ phase. The carbide phase and σ phase continue to precipitate along the crystal after long-term service of the material, and even form a continuous brittle phase on the grain boundary, which is very easy to form intergranular fracture. The formation temperature range of σ phase (Cr-Fe intermetallic compound) is about 600-980 ℃, but the specific temperature range is related to the alloy composition. As a result of the precipitation of σ phase, the strength of austenitic steel is greatly increased (the strength may be doubled), and it becomes hard and brittle. High chromium is the main reason for the formation of high-temperature σ phase, and Mo, V, Ti, Nb, etc. are alloy elements that strongly promote the formation of σ phase. The formation temperature of carbide (Cr23C6) is in the sensitization temperature range of austenitic stainless steel, which is 400～850 ℃. Cr23C6 will dissolve above the upper limit of the sensitization temperature, but the dissolved Cr will promote the further formation of σ phase. Therefore, when austenitic steel is used as a heat-resistant steel, the understanding and prevention of high-temperature aging embrittlement should be strengthened. Like the metal monitoring of thermal power plants, the metallographic structure and hardness changes can be checked regularly. If necessary, samples can be taken out for metallographic and hardness inspections, and even comprehensive mechanical properties and endurance strength tests can be performed. Source: China Stainless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.steeljrv.com) (wilsonpipeline Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. wilsonpipeline products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.) If you want to have more information about the article or you want to share your opinion with us, contact us at sales@wilsonpipeline.com

Bolt pre-tightening force An important factor affecting sealing. The pre-tightening force must compress the gasket to achieve the initial seal. Properly increasing the bolt pre-tightening force can increase the sealing ability of the gasket, because increasing the pre-tightening force can make the gasket retain a larger contact surface pressure under normal working conditions. However, the pre-tightening force should not be too large, otherwise the gasket will yield as a whole and lose its resilience, or even extrude or crush the gasket. In addition, the preload should be applied to the gasket as evenly as possible. Measures are usually taken to reduce the bolt diameter, increase the number of bolts, and take appropriate pre-tightening methods to improve the sealing performance. Gasket performance The gasket is an important component of the seal. The function of the gasket is to seal the gap between the sealing surfaces of the two flanges and prevent fluid leakage. The types of gaskets include non-metal gaskets, non-metal and metal combination gaskets and metal gaskets. Appropriate gasket material requires that the gasket can produce the necessary elastic deformation under the action of appropriate pre-tightening force without being crushed or squeezed out; the distance between the flange sealing surface is increased during operation, and the gasket material should It has sufficient resilience to keep the gasket surface in close contact with the flange surface to continue to maintain good sealing performance; The working medium and working temperature should also be considered when selecting gasket materials. The width of the gasket is also an important factor affecting the seal. The wider the gasket, the greater the pre-tightening force required, and the larger the size of bolts and flanges is required. ① Non-metallic gaskets such as rubber, asbestos rubber, polytetrafluoroethylene, etc. are commonly used on medium and low pressure equipment and pipeline flanges. They have good corrosion resistance and flexibility, but their strength and temperature resistance are poor. They are usually cut from the entire gasket sheet. The shape of the entire gasket is a ring with a rectangular cross section. ② In order to improve the strength and heat resistance of the gasket, thin steel belts and asbestos belts (or PTFE belts or flexible graphite belts) are wound together to form spiral wound gaskets, or asbestos or other non-metallic materials are wrapped with metal sheets made of metal-clad gaskets have multiple sealing effects and good resilience. They are used in higher temperature and pressure ranges, and can maintain good sealing under pressure and temperature fluctuations, so they are widely used. Spiral wound gaskets are made by winding steel belts with asbestos, polytetrafluoroethylene or flexible graphite and other filling belts. To prevent looseness, weld the beginning and end of the metal strip. In order to increase the elasticity and resilience of the gasket, both the metal strip and the non-metal strip are rolled into a wave shape. There are two wave shapes: V-shaped and W-shaped. There are 4 types of V-shaped structures. Type A-also known as basic type, without reinforcement ring, used for tongue and groove sealing surface. Type B-with inner strengthening ring for concave and convex sealing surface. Type C-with outer reinforcement ring for flat sealing surface. Type D–there are reinforced rings inside and outside for flat sealing surfaces. ③ The metal cladding gasket is made of asbestos rubber sheet as the inner core, and the outer thickness is 0.2～0.5mm thick thin metal plate (as shown below). The material of the metal plate can be aluminum, steel and its alloys, stainless steel or high-quality carbon steel. Metal-clad gaskets are also only used on flanges of Type B flat welding and long-neck butt welding. ④ Metal gaskets are commonly used on flanges of high-pressure equipment and pipelines. The materials include soft aluminum, copper, mild steel and stainless steel. In addition to metal gaskets with rectangular cross-sections, there are also metal ring gaskets with elliptical or octagonal cross-sectional shapes and other special shapes. When the operating pressure is very high or the leakage rate is very strict, and the temperature is very high or the corrosiveness is very strong, metal gaskets can be used. The specific pressure value of the metal gasket is very large. In order to reduce the bolt force, the pressing surface must be very narrow, relying on the extremely narrow pressing surface to maintain a good seal, and must have a small surface roughness, Ra≤2.5μm to Ra ≤0.63μm. Types of sealing surface The contact surface where the gasket is inserted between the flanges and pressed to achieve a sealing effect is called the flange sealing surface or the pressing surface. The selection of the sealing surface type is related to the operating conditions, the consequences of leakage and the nature of the gasket. The common structure types are as follows. ① Flat sealing surface: Its structure is shown in the figure (a) below. The sealing surface is not a smooth plane. There are often 2 to 4 concentric triangular cross-section grooves (ie flange waterline) on the plane. The flat sealing surface has a simple structure, is convenient to manufacture, and is convenient for anti-corrosion lining. Secondly, the width of the sealing surface of this structure is large, so non-metal or metal soft gaskets are often used in use. But after the bolts are tightened, the gasket material is easy to stretch to both sides. Used in occasions where the required pressing force is not high and the medium is non-toxic. ② Concave-convex sealing surface: The structure of the sealing surface is shown in the figure (b) below. It is equivalent to a pair of flat sealing surface flanges, one of which is made as a pressing surface with a raised platform, and the flange is called a convex flange, and the other correspondingly made concave is called a concave flange. The gasket with the same size as the concave is embedded in it, and the gasket is easy to center. The height of the convex plane is slightly greater than the depth of the concave surface, and it is tightly pressed with bolts to play a sealing role. This structure can limit the radial deformation of the gasket, prevent the gasket from being extruded, and improve the sealing performance to a certain extent. Suitable for occasions with higher pressure. ③ Tongue and groove sealing surface: in the middle of a pair of flat sealing surfaces in the width direction, one is made into a cross-section like a tenon, and the other cross-section is like a groove. The pressing surface is paired, as shown in the following figure (c), the former is called a tenon surface flange, the latter is called groove flange. The groove-shaped pressing surface can limit the radial deformation of the embedded gasket, with good sealing performance, and the gasket can be less eroded and corroded by the medium. But the tenon part is easy to damage. It is often used in flammable, explosive, toxic media and higher pressure occasions. In addition, there are trapezoidal groove sealing surfaces and tapered sealing surfaces. The former uses an elliptical cross-section annular metal gasket, and the latter uses a lens-type annular metal gasket. The above two structures are forced sealing, which are commonly used on high-pressure pipelines. The form and surface properties of the flange sealing surface play a vital role in the influence of the sealing effect. The flatness of the flange sealing surface and the perpendicularity between the sealing surface and the flange centerline directly affect the uniformity of the gasket force and the good contact between the gasket and the flange. The roughness of the flange sealing surface should match the gasket requirements. Radial knife marks or scratches on the surface are not allowed, let alone surface cracks. Flange stiffness Excessive warpage due to insufficient flange rigidity (as shown in the figure below) is often one of the main reasons for the failure of the bolt flange connection seal in actual production. A flange with a large rigidity is small in deformation, and the bolt pre-tightening force can be evenly transmitted to the gasket, thereby improving the sealing performance of the flange. The rigidity of the flange is related to many factors. Appropriately increasing the thickness of the flange ring, reducing the diameter of the bolt center circle and increasing the outer diameter of the flange ring can increase the rigidity of the flange. Use a necked flange or increase the size of the tapered neck part. , Can significantly improve the bending resistance of the flange. However, if the rigidity of the flange is increased without principle, the flange will become bulky and the cost will increase. Operating conditions The influence of pressure, temperature and the physical and chemical properties of the medium on the sealing performance is very complicated. The influence of pure pressure and medium on the sealing is not significant, but under the combined action of temperature, especially under fluctuating high temperatures, it will seriously affect the sealing performance , and even make the seal completely fail due to fatigue. Because at high temperatures, the viscosity of the medium is small, the permeability is large, and it is easy to leak; the corrosive effect of the medium on gaskets and flanges is intensified, increasing the possibility of leakage; flanges, bolts and gaskets will all produce greater high temperatures creep and stress relaxation make the seal ineffective; certain non-metallic gaskets will also accelerate aging, deterioration, and even burn. Source: China China Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The differences of normalizing, tempering, annealing and quenching lie in different processes, different changes of material structure and different results of material properties. What is quenching? Quenching of Steel is to heat the steel to the critical temperature above Ac3 (hypoperformances steel) or Ac1 (hyperperformances steel), and keep it warm for a period of time to refine all or part of it, then conduct the heat treatment process of martensite (or baine) transformation with the cooling speed which is higher than the critical cooling speed to be cooled below Ms (or the isothermal around Ms). Generally, solid solution treatment of aluminum alloy, copper alloy, titanium alloy, steel glass and other materials or thermal treatment process with rapid cooling process are also called quenching. Purpose of quenching: 1) improve the mechanical properties of metal materials or parts. For example: improve the hardness and wear resistance of tools, bearings, etc., improve the elastic limit of the spring, improve the comprehensive mechanical properties of shaft parts, etc. 2) improve the material properties or chemical properties of some special steel. Such as improving the corrosion resistance of stainless steel, increasing the permanent magnetism of magnetic steel, etc. When quenching and cooling, in addition to reasonable selection of quenching medium, there must be correct quenching methods. The common quenching methods mainly include single-Liquid Quenching, double-Liquid Quenching, graded quenching and isothermal quenching, local quenching, etc. The steel workpiece has the following characteristics after quenching: ① unbalanced (I .e. unstable) structures such as martensite, bainitic and retained austenite are obtained. ② there is a large internal stress. ③ mechanical properties cannot meet the requirements. Therefore, steel workpieces generally have to be tempered after quenching. What is tempering? Tempering is a heat treatment process that heats the quenched metal materials or parts to a certain temperature and cools them down in a certain way after holding for a certain period of time, tempering is an operation that is followed after quenching. It is usually the last process for thermal treatment of the workpiece. Therefore, the combined process of quenching and tempering is called the final process. The main purpose of quenching and tempering is: 1) reduce internal stress and reduce brittleness. Quenching parts have great stress and brittleness. If they are not tempered in time, they will often deform or even crack. 2) adjust the mechanical properties of the workpiece, after the workpiece is quenched, the hardness is high and the brittleness is large, in order to meet the different performance requirements of various workpieces, it can be adjusted by tempering, hardness, strength, plasticity and toughness. 3) stabilize the size of the workpiece. Tempering can stabilize the metallographic structure to ensure that no deformation will occur in the future use process. 4) improve the cutting performance of some alloy steel. The role of tempering is: ① improve the stability of the tissue, so that the workpiece will not be changed in the process of use, so that the geometric size and performance of the workpiece remain stable. ② eliminate internal stress in order to improve the performance of the workpiece and stabilize the geometric size of the workpiece. ③ adjust the mechanical properties of steel to meet the use requirements. The reason why tempering has these effects is that with the temperature rising, the atomic mobility will be enhanced, and the atoms of iron, carbon and other alloying elements in steel can be diffused faster, thus realizing the rearrangement and combination of atoms, so as to gradually transform the unstable and unbalanced organization into a stable and balanced organization. The elimination of internal stress is also related to the decrease of metal strength when the temperature rises. Generally, when steel is tempered, the hardness and strength decrease and the plasticity increases. The higher the tempering temperature, the greater the change of these mechanical properties. For the alloy steel with high alloying elements, when tempering at a certain temperature range, some metallic compounds with fine particles will be precipitated out to increase the strength and hardness. This phenomenon is called secondary hardening. Tempering requirements: workpieces with different uses should be tempered at different temperatures to meet the requirements in use. ① tools, bearings, carburizing and quenching parts, surface quenching parts are usually tempered at a low temperature below 250℃. After tempering at low temperature, the hardness changes little, the internal stress decreases, and the toughness increases slightly. ② the spring can obtain higher elasticity and necessary toughness by tempering at medium temperature of 350 ~ 500℃. ③ parts made of medium carbon structural steel are usually tempered at 500 ~ 600℃ to obtain a good coordination of appropriate strength and toughness. When steel is tempered at about 300℃, its brittleness is often increased. This phenomenon is called the first class of tempering brittleness. Generally should not temper in this temperature range. Some medium carbon alloy structural steel after high temperature tempering, if slowly cooled to room temperature, also easy to become brittle. This phenomenon is called the second class of tempering brittleness. Adding molybdenum to steel, or cooling in oil or water when tempering, can prevent the second class of tempering brittleness. Reheating the steel of the second type of tempering brittleness to the original tempering temperature can eliminate this brittleness. In production, it is often based on the requirements of workpiece performance. According to different heating temperatures, tempering is pided into low temperature tempering, medium temperature tempering and high temperature tempering. The heat treatment process combined with quenching and subsequent high temperature tempering is called quenching and tempering, that is, it has high strength and good plastic toughness. 1. Low temperature tempering: 150-250 ℃ ,M loop, reduce internal stress and brittleness, improve plastic toughness, and have higher hardness and wear resistance. It is used to make measuring tools, cutting tools and rolling bearings. 2. Medium temperature tempering: 350-500 ℃ ,T back, with high elasticity and certain plasticity and hardness. Used to make springs, forging dies, etc. 3. High temperature tempering: 500-650℃ ,S back, with good comprehensive mechanical properties. Used to make gears, crankshaft, etc. What is normal fire? Normalizing is a heat treatment that improves the toughness of steel. After heating the steel members to the temperature of Ac3 above 30~50 ℃, heat the temperature for a period of time to cool the air. The main feature is that the cooling rate is faster than annealing but lower than quenching. When normalizing can refine the crystalline grains of the steel in the faster cooling, not only can obtain satisfactory strength, moreover, the toughness (AKV value) can be obviously improved and the cracking tendency of components can be reduced. The comprehensive mechanical properties of materials can be greatly improved, and the cutting properties can also be improved after normalized treatment for low alloy hot rolled steel plates, low alloy steel forgings and castings. Normalizing has the following purposes and uses: ① for hypoeutectic steel, normalizing is used to eliminate the over-heated coarse crystal structure and widthhouse structure of casting, forging and welding parts, and the band structure in rolled material; Refine the crystal grain; and can be used as pre-heat treatment before quenching. ② as for hyperdialysis steel, normalizing can eliminate remullated carbonized body and refine pearlite, which not only improves mechanical property, but also is beneficial to later spheroidization annealing. ③ for low carbon deep drawing thin steel plates, normalizing can eliminate free cementite at grain boundary to improve their deep drawing performance. ④ for low carbon steel and low carbon and low alloy steel, using normalizing can get more fine flake pearlite structure, increasing the hardness to HB140-190, and avoiding the “sticking” phenomenon during cutting, improve machinability. For medium carbon steel, it is more economical and convenient to use normalizing in the situation where normalizing and annealing are available. ⑤ for ordinary medium carbon structural steel, under the occasion of low requirement of mechanical property, use normalizing instead of quenching and tempering high temperature, which is not only easy to operate, but also stablize the structure and size of the steel. ⑥ high temperature normalizing (150 ~ 200℃ above Ac3) due to the high diffusion velocity at high temperature, composition segregation of castings and forgings can be reduced. Coarse and large grains after high temperature normalizing can be refined by the following second lower temperature normalizing. ⑦ as for some low-carbon and middle-carbon alloy steels used for steam turbine and boiler, normalizing is usually used to obtain bainitic structure, and then after tempering at high temperature, they have good creep resistance when temperature is between 400℃ and 550℃. ⑧ in addition to steel and steel, normalizing is also widely used in the heat treatment of ductile iron to obtain pearlite matrix and improve the strength of ductile iron. Because the characteristic of normalizing is air cooling, the environment temperature, stacking mode, air flow and workpiece size have influence on the organization and performance after normalizing. Normalizing structure can also be used as a classification method for alloy steel. Usually, the microstructure obtained by air cooling after heating the sample with a diameter of 25mm is pided into pearlite steel, balanced steel, martensite steel and austenitic steel. What is annealing? Annealing is a metal heat treatment process that slowly heats the metal to a certain temperature, maintains enough time, and then cools at an appropriate rate. Annealing heat treatment is pided into complete annealing, incomplete annealing and stress relief annealing. The mechanical properties of annealed materials can be tested by tensile test or hardness test. Many steels are supplied in the state of annealing heat treatment. For steel hardness test, Rockwell hardness meter can be used to test HRB hardness. For thinner steel plate, steel strip and thin steel tube, surface Rockwell hardness meter can be used, HRT hardness was detected. The purpose of annealing is: ① improve or eliminate all kinds of microstructure defects and residual stress caused by steel in the process of casting, forging, rolling and welding, and prevent deformation and cracking of workpieces. ② soften the workpiece for cutting. ③ refine the grain and improve the structure to improve the mechanical properties of the workpiece. ④ prepare for the final heat treatment (quenching and tempering). Commonly used annealing processes are: ① complete annealing. Used to refine medium and low carbon steel with poor mechanical properties after casting, forging and welding. The workpiece is heated to a temperature above 30 ~ 50℃ that ferrite will all transform into austenite, kept warm for a period of time, and then cooled slowly with the furnace. During the cooling process, austenite changes again, the structure of the steel can be thinned. ② spheroidization annealing. Used to reduce the hardness of tool steel and bearing steel after forging. The workpiece is heated to a temperature of 20 ~ 40℃ When austenite begins to form in steel, and then cooled slowly after heat preservation. During the cooling process, the lamellar cementite in pearlite becomes spherical, thus reducing the hardness. ③ isothermal annealing. It is used to reduce the high hardness of some alloy structural steel with high content of nickel and chromium to be cut. Generally, it is cooled to the most unstable temperature of austenite at a relatively fast speed first, and when it is kept at a suitable time, austenite is converted into torchian or Sorbite, and the hardness can be reduced. ④ recrystallization annealing. It is used to eliminate the hardening phenomenon (increase in hardness and decrease in plasticity) of metal wire and sheet in the process of cold drawing and cold rolling. The heating temperature is generally the steel began to form austenite temperature below 50~150 ℃, only in this way can eliminate work hardening effect to soften the metal. ⑤ graphitization annealing. It is used to turn cast iron containing a large amount of cementite into malleable cast iron with good plasticity. The process operation is to heat the casting to about 950℃ and cool down after holding for a certain period of time, so that the cementite can decompose into bulk graphite. ⑥ diffusion annealing. It is used to homogenize the chemical composition of alloy castings and improve their performance. The method is, on the premise of no melting, to heat the casting to the highest temperature as much as possible, and keep the heat for a long time, and then after the various elements in the alloy diffusion tend to uniform distribution, slow cooling. ⑦ stress relief annealing. It is used to eliminate internal stress of steel castings and welding parts. For steel products after heating began to form austenite temperature below 100~200 ℃, after the heat insulation in the air cooling, can eliminate internal stress. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Valve is the basic element used to control the flow direction, pressure and flow of fluid in pipeline. The valve is the control component in the pipeline fluid delivery system, which is used to change the section of the access and the medium flow direction, and has the functions of persion, cut-off, adjustment, throttling, check-back, persion or overflow pressure relief, etc. The valve used for fluid control, from the simplest stop valve to various valves used in extremely complex automatic control system, has many varieties and specifications, the nominal diameter of the valve is from the extremely tiny instrument valve to the industrial pipeline valve with a diameter of 10m. Classification of valves Classification by use and role (1) block valves are mainly used to cut off or connect medium flow. Including gate valve, stop valve, diaphragm valve, ball valve, plug valve, butterfly valve, plunger valve, ball plug valve, needle type instrument valve, etc. (2) control valve is mainly used to adjust medium flow, pressure, etc. Including regulating valve, throttle valve, pressure reducing valve, etc. (3) check valves are used to prevent dielectric from flowing backwards. Including check valves of various structures. (4) shunt valve type is used to separate, distribute or mix media. It includes the distribution valve and the trap valve of various structures. (5) safety valves are used for safety protection when medium overpressures. Including various types of safety valves. Classification by main parameters Classification by pressure (1) vacuum valve working pressure is lower than the standard atmospheric pressure of the valve. (2) the low pressure valve nominal pressure pn≤1. 6 mpa. (3) the valve whose nominal pressure PN of medium pressure valve is 2.5, 4.0 or 6.4 MPa. (4) high Pressure Valve nominal pressure PN is 10.0~80.0 MPa valve. (5) super High Pressure Valve nominal pressure pn≥100 MPa. Classification by medium temperature (1) high temperature valve is used for the valve with medium working temperature t> 450℃. (2) medium temperature valve is used for medium working temperature 120 ℃ valve. (3) normal temperature valve is used for valves with medium working temperature of-40℃ ≤t≤120℃. (4) low temperature valve is used for the valve of medium working temperature-100℃ ≤t≤40 ℃. (5) ultra low temperature valve is used for the valve with medium working temperature t <-100℃. Classification by valve body material (1) non-metallic material valves: such as ceramic valves, FRP valves, plastic valves. (2) metal material valves: such as copper alloy valve, aluminum alloy valve, lead alloy valve, hastelloy alloy valve, monel alloy valve, cast iron valve, carbon steel valve, stainless steel valve, low alloy steel valve, high alloy steel valve. (3) metal valve body lining valve: such as lead lining valve, plastic lining valve and enamel lining valve. General classification This kind of classification method is pided according to both the principle and function, which is currently the most commonly used classification method at home and abroad. It is generally pided into gate valve, stop valve, throttle valve, instrument valve, plunger valve, diaphragm valve, plug valve, ball valve, butterfly valve,globe valves,check valve, reducing valve, safety valve, trap valve, bottom valve, filter, drain valve, etc. Characteristics of valve Operating Characteristics It determines the main performance and scope of use of the valve. The use characteristics of valves include: Valve category (closed-circuit valve, regulating valve, safety valve, etc.); Product Type (gate valve, stop valve, butterfly valve, ball valve, etc.); Main parts of valve (valve body, material of bonnet, valve stem, disc and sealing surface); Valve transmission mode, etc. Structural characteristics It determines some structural characteristics of Valve installation, maintenance, maintenance and other methods. Belonging to the structural characteristics: the structural length and overall height of the valve, and the connection form with the pipeline (flange connection, threaded connection, clamp connection, external threaded connection, welding end connection, etc.); the form of sealing surface (insert ring, thread ring, overlaying, spray welding, valve body); Structure of valve stem rotating rod, lifting rod) and so on. Steps and basis of valve selection Steps for selecting valves (1) specify the use of the valve in the equipment or device, determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc. (2) determine the nominal diameter and connection method of the pipe connected with the valve: flange, thread, welding, etc. (3) determine the mode of operating the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc. (4) determine the materials of the shell and internals of the selected valve, gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc. (5) select the types of valves: Closed-circuit valves, regulating valve, safety valves, etc. (6) determine the form of the valve: gate valve, stop valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap valve, etc. (7) determine the parameters of the valve: for the automatic valve, according to different needs, first determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole. (8) determine the geometric parameter structure length of the selected valve, flange connection form and size, size of valve height direction after opening and closing, size and quantity of connected bolt holes, external dimensions of the whole valve, etc. (9) use the existing information, such as product catalog of valves and samples of valve products, to select appropriate valve products. Basis of valve selection (1) the purpose, working condition and control mode of the selected valve. For example, the choice of the pump house water pump outlet valve, first need to meet the water pump can close the valve start and stop to reduce the start current and stop the impact on the water pump; Second need to be equipped with a check valve, when the pump unit is accidentally shut down, the valve can be quickly closed to prevent the pump from being reversed for a long time; Thirdly, the valve to eliminate the water hammer should be equipped to ensure the operation safety of the pump unit. After understanding the purpose of the selected valve, it is necessary to understand the installation site and use conditions to correctly select the valve. If electric butterfly valve + micro stop check valve is selected, electric butterfly valve can meet the requirements of start-up and shutdown of the closed valve. Micro retarding closed check valve is used to prevent water pump reversal and water hammer. Due to its relatively simple structure, the failure rate is lower, but the installation length is longer and the water resistance is larger, so it is suitable for large installation space, the pump station which does not have high energy consumption requirements, such as the use of small pump station; The choice of the hydraulic slowly-closing type check valve can meet the three necessary functions of the pump outlet valve at the same time, and the installation length can be very small, and the water resistance is, however, due to the complicated structure, a set of high-pressure hydraulic system is needed, so the failure rate is high and the maintenance is difficult. Therefore, it is suitable to be installed in the large pumping station where there are many spare units; multi-function pump control valve is also available for pump outlet, and its installation length is shorter than that of electric butterfly valve + micro stop closed check valve, so there is no need for electric or hydraulic system vacancy, with the simplest structure and the lowest failure rate, and the water hammer has the best removal, however, the water resistance is the highest, which is suitable for the use of water hammer in severe or unattended pumping stations. (2) properties of working medium working pressure, working temperature, corrosion performance, whether it contains solid particle medium, whether it is toxic, whether it is the viscosity of flammable and explosive medium, etc. (3) requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc. (4) installation dimension and outer dimension requirements: nominal diameter, connection method and connection dimension of the pipe, outer dimension or weight limitation, etc. (5) additional requirements for the reliability, service life and explosion-proof performance of electric devices of valve products. Attention should be paid to when selecting parameters: if the valve is to be used for control purpose, the following additional parameters must be determined: Operation method, maximum and minimum flow requirements, normal flow pressure drop, pressure Drop when closed, maximum and minimum inlet pressure of valve. According to the above-mentioned basis and steps for selecting valves, the internal structure of various types of valves must also be understood in detail when selecting valves reasonably and correctly, so as to make the right choice for the preferred valves. The final control of the pipeline is the valve. The valve hoist controls the medium in the pipeline flow way the shape of the valve passage makes the valve have certain flow characteristics, which must be taken into account when choosing the most suitable valve for installation in the pipeline system. Principles that must be followed when choosing valves Valves for cut-off and open media The channel is a through-through valve, commonly used butterfly valve, gate valve, etc., whose flow resistance is relatively small, usually choose as the cut-off and open medium valve. The downward closed valve (stop valve, plunger valve) is seldom used because its channel is tortuous and its flow resistance is higher than other valves. In the occasion allowing a higher flow resistance, such as the transport medium is gas, you can choose to use the downward closed valve. When choosing butterfly valve, when there are more impurities in the transport medium, such as raw water or sewage, horizontal butterfly valve should be selected, because its valve shaft is horizontal, the bottom of the flow channel is not easy to accumulate debris and scale, which is conducive to the protection of the valve plate seal ring. Choose the type of gate valve that has no groove at the bottom of the valve runner to avoid valve leakage due to the accumulation of sundries in the groove. The valve used for flow control Generally, a valve that is easy to adjust the flow is selected to control the flow. A downward closed valve (such as a stop valve) is suitable for this purpose because its valve seat size is proportional to the stroke of the closing piece. Rotary Valve Rotary plug valve, butterfly valve, ball valve) and flexible valve body type valve (clamp valve, diaphragm valve) can also be used for throttling control, but usually only in a limited range of valve diameter. Gate valve is a disc-shaped disc disc to make a cross-cutting movement of the circular valve seat. It can control the flow well only when it is close to the closed position, so it is usually not used for flow control. Reversing shunt valve According to the need of reversing shunt, this valve can have three or more channels. Plug valves and ball valves are more suitable for this purpose. Therefore, most of the valves used for reversing and shunt are one of these valves. However, in some cases, other types of valves, as long as two or more valves are properly connected to each other, can also be used for reversing persion. Valve for medium with suspended particles When the medium has suspended particles, it is most suitable to use its closing parts along the sealing surface to slide the valve with wiping effect. If the back and forth movement of the closing piece to the valve seat is vertical, it is possible to clamp the particles. Therefore, this valve is only suitable for basic clean media unless the sealing surface material can allow embedded particles. Ball valve and plug valve in the opening and closing process on the sealing surface are wiping effect, so it is suitable to be used in the medium with suspended particles. Valve installation The installation of the valve should be carried out in accordance with the valve instruction and relevant provisions. During the construction process, it should be carefully checked and carefully constructed. Before installing the valve, install it after the pressure is tested to be qualified, carefully check whether the specification and model of the valve are consistent with the drawings, check whether the parts of the valve are intact, and whether the opening and closing valve can rotate flexibly, whether the sealing surface is damaged or not can be installed after confirmation. When installing the valve, the operation mechanism of the valve should be at about 1.2m away from the operation ground and be in conformity with the chest. When the center of the valve and the hand wheel are more than 1.8m away from the operating ground, an operating platform should be set for valves and safety valves that are frequently operated. For pipelines with more valves, the valve should be concentrated on the platform as far as possible for easy operation. For a single valve exceeding 1.8m and not frequently operated, Sprocket, extension rod, movable platform, movable ladder and other equipment can be used. When the valve is installed under the operation surface, stretching rod should be set, and the ground valve should be set up in the ground well. For the sake of safety, the ground well should be covered. For the valve stem of the valve on the horizontal pipe, it is best to vertically up, and it is not suitable to install the valve stem down. The valve stem is installed downward, which is inconvenient to operate, inconvenient to repair, and easy to corrode the valve. The floor valve should not be installed in a crooked way to avoid inconvenience. Valves on the pipelines which are side by side should have vacancy for operation, maintenance and disassembling, and the net distance between the hand wheels should not be less than 100mm. If the distance between the pipes is narrow, the valves should be staggered. For those valves which have big opening force, low strength, high brittleness and heavy weight, the valve frame should be set to support the valve before installation to reduce starting stress. When installing the valve, the pipe near the valve uses the pipe wrench, while the valve itself uses a common wrench. At the same time, during installation, the valve should be semi-closed to prevent valve rotation and deformation. The correct installation of the valve should make the internal structure form conform to the flow direction of the medium, and the installation form conform to the special requirements and operation requirements of the valve structure. In particular, pay attention to the valve with medium flow requirements should be installed according to the requirements of the process pipeline. The arrangement of the valve should be convenient and reasonable, and it is easy for the operator to get access to the valve. For the lift stem type valve, the operating space should be reserved. Installation of valve connection surface When installing the valve connected with thread at the end, the thread should be screwed into the valve at a proper depth, and the thread should be screwed into a too deep and compressed valve seat, which will affect the good coordination between the valve seat and the Ram, and screwed into the shallow, it will affect the sealing reliability of the joint and easily introduce leakage. At the same time, the thread sealing material should use tetrafluoroethylene green tape or sealant. For the valve connected by the end of the flange, first find the connection surface of the positive flange, the cover is perpendicular to the pipeline, and the bolt holes should be aligned. The valve flange should be parallel to the pipe flange, the flange clearance is moderate, and the phenomena such as misopening and tilting should not occur. The center gasket between the flanges should be placed in the middle, without deflection, and the bolts should be tightened symmetrically and evenly. Prevent the tightening of the forced connection during the installation of the valve and produce an additional residual force. Before installation, it is necessary to thoroughly remove the dirt from the inner wall of the pipe and the external thread; Remove the burr and foreign matter that block the flow of the medium and may affect the operation of the equipment, and blow out the dirt in the pipe before connecting the pipe, slag and other sundries. To prevent damage to the sealing surface of the valve or blockage of the valve. When installing the welding end connection valve, the two ends of the valve should be opened after spot welding, and then the weld is welded according to the welding process card, and the appearance of the weld and the quality of the inner weld are inspected after welding, make sure that there are no pores, slag, cracks, etc., and the welding lines should be checked by ray or override when necessary. Heavy valve installation When installing heavier valve (DN>100), lifting tools or equipment should be used. The lifting rope should be tied to the flange or bracket of the valve, and should not be tied to the handle-type valve stem of the valve, to avoid damaging the valve. What are the general requirements for valve installation? The general requirements of valve installation, the most suitable installation height, the direction of the valve and the valve stem on the horizontal pipe are as follows: The valve should be set in a place that is easy to access, easy to operate and maintain. Valves on rows of pipes (such as pipes for receiving and discharging devices) should be arranged in a centralized manner, and the setting of operation platform and ladder should be considered. The central line of the valve on the pipe in parallel layout should be taken as close as possible. The net distance between the hand wheels should not be less than 100mm. In order to reduce the pipeline spacing, the valves can be staggered; The installation position of frequently operated valve should be easy to operate, and the most suitable installation height should be 1.2m or so away from the operation surface. When the height of the center of the valve hand wheel exceeds 2m of the operation surface, platform should be set for the central arrangement of the valves, the frequently operated inpidual valves and the safety valve, appropriate measures should also be taken for inpidual valves that are not frequently operated (e.g. sprocket, extension rod, movable platform and movable ladder, etc.). The chain of the sprocket should not hinder traffic. Pipelines of the dangerous media and valves of the equipment should not be installed within the height range of the head to avoid bumping and damaging the head or directly damaging people’s face due to valve leakage; The valve used for partition equipment should be directly connected with or close to the nozzle of equipment. The valve connecting the pipe with extremely harmful and highly harmful toxic medium should be directly connected with the equipment port, and the valve should not be operated by chain wheel; Accident handling valves such as fire water valve and fire steam valve should be arranged in separate places, and the safe operation in the accident should be considered. This kind of valve should be arranged in the control room. There are safety zones behind the safety wall, outside the factory gate, or within certain distance from the accident site; So that the operators can operate safely when there is a fire accident; Except for special requirements of craft, valves on the bottom pipelines of tower, reactor, vertical vessel and so on should not be arranged in skirt; The cut-off valve of the horizontal branch that leads out from the main pipe should be set on the horizontal pipe section near the root; Lifting check valves should be installed on the horizontal pipe, and vertical lifting check valves should be installed on the vertical pipe where media flows from bottom to top. Swing check valve should be preferentially installed on the horizontal pipe, or installed on the vertical pipe in which medium flows from bottom to top; Bottom valve should be installed on the installation height of centrifugal pump suction butterfly check valve can be selected; when the diameter of pump outlet is different from that of the connected pipe, reducing check valve can be used; The center distance between the hand wheel of the valve arranged around the operation platform and the edge of the operation platform should be no larger than 450mm. When the valve stem and the hand wheel stretch into the above of the platform with the height less than 2 meters, it should not affect the operation and transportation of the operator; The valve of underground pipeline should be set in the trench or valve well, and the extension rod of the valve should be set when necessary. Fire valve well should have obvious sign; For the valve on the horizontal pipe, the direction of the valve stem can be determined according to the following order: vertically up; Horizontally; Up to 45 °; Down to 45 °; Not vertically down; The stem is horizontally installed open-lever valve. When the valve is open, the stem shall not affect the passage. Technical requirements for valve installation Direction. On the valve body of general valve, the direction indicated by the arrow is the direction in which the gas flows forward. Special attention must be paid to the fact that it must not be reversed. Because there are various valves requiring one-way gas circulation, such as safety valve, pressure reducing valve, check valve, throttle valve, etc. For the stop valve, in order to facilitate opening and maintenance, gas is also required to pass through the valve seat from bottom to top, but the gate valve, when installing the cock, it is not limited by the flow direction. Installation location. The long-term operation and maintenance of the valve should be considered, making it as convenient as possible to operate and maintain, and at the same time, attention should be paid to the beautiful appearance when assembling. The valve handle can be turned vertically to the above direction, and can also be tilted to a certain angle or placed horizontally, but the hand wheel can not be downward to avoid the operation of looking up; The hand wheel of the landing valve should be best close to the chest to facilitate the opening and closing; the open bar gate valve cannot be used underground to prevent the valve stem from being corroded. The installation position of some valves has special requirements, such as the pressure reducing valve is required to be installed vertically on the horizontal pipe and cannot be tilted. The lift check valve requires that the valve clack is vertical swing check valve and the pin shaft is required to be horizontal. In short, the installation position should be determined according to the principle of the valve, otherwise the valve will not work effectively or even will not work. Installation of the cock. Check the specifications and models, identify whether there is any damage, clean the sealing cap of the threaded opening and excessive grease and sundries in the thread, and check the sealing performance of the cock. Proper strength must be applied when installing the gas cock. According to the size of the cock, different specifications of pipe tongs or spanners should be chosen to install. When installing the valve with screw thread, the valve company should ensure that the thread is intact and intact; When the wrench can be used, do not use the pipe wrench to avoid damage to the appearance of the valve body. The installation of flange valve must ensure that the two flange sections are parallel to each other and on the same axis. When tightening the bolt, it should be carried out in a cross way to make the valve end face evenly stressed. The valve connected by flange and thread should be installed in the closed state. When the butt welding valve is connected with the pipe, the bottom weld should be argon welded to ensure the internal clean welding, and the valve should not be closed to prevent heating deformation. Under normal circumstances, the valve is directly connected with the corrugated expansion joint, so the pipes on both sides of the valve and the corrugated expansion joint should be cut off according to the size of the valve and the corrugated expansion joint as well as the flange and the gasket to set aside the installation position. When the valve is hoisted, the rope should not be tied to the first wheel or valve stem to prevent damage. When placed on the pier, according to the requirements of the elevation pad is stable and balanced. There must be a solid pier or bracket under the valve to hold the valve, and the valve is not allowed to generate stress. Pipe valve installation 35 professional tips 1. Pay attention to the direction of medium flow during installation. 2. Check valve should be installed before condensate water enters the recycling main pipe after steam trap to prevent condensate water from returning. 3. The open bar valve cannot be buried to prevent the stem from rusting. In the trench with cover plate, the valve should be installed in a convenient place for maintenance, inspection and operation. 4. For pipelines that require to be closed with small water hammer impact or no water hammer, it is best to choose slow-closing butterfly check valve and slow-closing swing check valve. 5. When installing the threaded valve, it is necessary to ensure that the thread is intact, and the filler is coated according to the different media. When tightening, it is necessary to use even force to avoid damage to the valve and valve parts. 6. When installing the socket-welded valve, the socket-welded valve should have a gap of 1-2m to prevent the thermal stress from exceeding the ambassador during welding. 7. When installing on the horizontal pipe, the valve stem should be vertically upward, or inclined to a certain angle, and the valve stem is not allowed to be installed downward. 8. The bottom layer of welding seam connecting the docking valve and pipe should adopt argon arc welding, and the valve should be opened during welding to prevent overheating and deformation. 9. Before installing the steam trap, the pipeline must be blown with pressure steam to remove sundries in the pipeline. 10. Do not install the steam trap in series. 11. Diaphragm type check valve is often used in pipelines which are easy to generate water hammer, because the diaphragm can well eliminate the water hammer generated when the medium is countercurrent, but it is limited by the temperature and pressure, generally used on low pressure normal temperature pipes. 12. Filter should be installed before the steam trap to ensure that the steam trap is not blocked by pipeline sundries, and the filter should be cleaned regularly. 13. The valve connected with flange and thread should be closed during installation. 14. The direction of condensate water should be consistent with the sign of the arrow installed on the trap. 15. The steam trap should be installed at the lowest place of the equipment outlet, and the condensed water should be discharged in time to avoid steam resistance in the pipeline. 16. When installing flange valve, it should be ensured that the two flange end faces are parallel and concentric with each other. 17. The valve should be installed before and after the trap, so that the trap can be repaired at any time. 18. The mechanical trap should be installed horizontally. 19. If the drain valve is found to run steam, it should be discharged in time and the filter should be cleaned according to the actual use situation, and repaired at any time in case of failure. 20. Do not make the check valve bear the weight in the pipeline. Large check valve should be supported independently, so that it is not affected by the pressure generated by the pipeline system. 21. After the drain valve, the condensate recovery main pipe cannot climb, which will increase the back pressure of the drain valve. 22. If there is no trap installed at the lowest point of the equipment, a reverse water bend should be added at the lowest point of the water outlet to raise the condensation water level before installing a trap to avoid steam resistance. 23. The outlet pipe of the trap should not be soaked in water. 24. If condensate is recycled after the steam trap, the outlet pipe of the drain valve should be connected to the main pipe from above the recovery main pipe to reduce back pressure and prevent backflow. 25. Each equipment should be installed with traps. 30. Lift type level flap check valve should be installed on the level pipe. 31. Install a drain valve on the steam pipe. In the main pipe, a condensate water-collecting well which is close to the radius of the main pipe should be set, and then use a small tube to lead to the drain valve. 32. If there is condensate recovery after the trap, it needs to be recovered separately by pipelines with different levels of pressure. 33. Lift-type vertical flap check valve needs to be installed vertically. 34. When the mechanical trap is not in use for a long time, it is necessary to remove the sewage screw and let the water inside go to prevent freezing. 35. Before the thermostatic type steam trap, a subcooled pipe that does not keep warm is needed for more than one meter. Other types of steam trap should be as close as possible to the equipment. Conclusion At present, whether in municipal water supply, petrochemical, or in other industries, the application, operating frequency and service of pipeline system valves are ever-changing, it is most important to control or eliminate even low leakage, the most critical equipment is the valve. The final control of the pipeline is that the service and reliable performance of the valve in various fields are unique. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is a breather valve? Breather valve is a kind of valve which can not only keep the tank space isolated from the atmosphere within a certain pressure range, but also connect with the atmosphere (breathing) when the pressure range is higher or lower. Its function is to prevent the tank from being damaged due to overpressure or vacuum, and to reduce the evaporation loss of the storage liquid. It is mainly composed of valve seat, valve cover, protective cover and two groups of opening and closing devices controlled by vacuum and pressure. The opening and closing device includes valve disc, guide rod, spring, spring seat and sealing ring. When the pressure in the tank reaches the rated exhaled positive pressure, the pressure valve flap opens and the steam in the tank is discharged; when the vacuum degree in the tank reaches the rated suction negative pressure, the vacuum valve flap opens and the air enters. Structure characteristics of breather valve The breather valve is made of cast iron, cast steel, aluminum alloy and stainless steel with good corrosion resistance. The valve disc and seal ring are made of stainless steel tetrafluoroethylene. The breather valve has good low temperature resistance and antifreeze performance. The breather valve is a ventilation device installed on the fixed roof tank to reduce the evaporation loss of oil and control the pressure of the tank. The breather valve has the advantages of large ventilation, small leakage, corrosion resistance and good antifreeze performance. It can automatically adjust the pressure inside and outside the oil tank. Function of breather valve The internal structure of the breather valve is essentially a combination of a pressure valve disc (that is, an exhalation valve) and a vacuum valve disc (that is, an inhalation valve). The pressure valve disc and the vacuum valve disc can be arranged side by side or overlapped. The working principle of the breather valve is that when the pressure in the tank reaches the rated positive exhalation pressure, the pressure valve flap opens and the vapor in the tank is discharged; when the vacuum in the tank reaches the rated suction negative pressure, the vacuum valve flap opens and air enters. 1. When the pressure of the medium in the tank is within the control operating pressure range of the breather valve, the breather valve does not work to maintain the tightness of the oil tank; 2. When the medium is added to the tank to increase the pressure in the upper gas space of the tank and reach the positive operating pressure of the breather valve, the pressure valve is opened and the gas escapes from the breather valve exhalation outlet, so that the pressure in the tank does not continue increase; as shown in the figure below: 3. The atmosphere outside the tank will open the negative pressure valve disc of the breather valve and suck in air; as shown in the figure below: The breather valve plays a sealing role under normal conditions. It can only work under the following conditions: (1) When the storage tank outputs materials, the breather valve begins to suck air or nitrogen into the tank. (2) When the material is filled into the tank, the breather valve starts to exhale the gas from the tank to the outside. (3) Due to climate change and other reasons, the vapor pressure of materials in the tank increases or decreases, and the breather valve exhales steam or inhales air or nitrogen (usually called thermal effect). (4) In case of fire, the evaporation of liquid in the tank increases sharply due to the heat of exhaled gas, and the breather valve begins to exhale out of the tank, so as to avoid the damage of the tank due to overpressure. (5) In other working conditions, such as the pressurized transportation of volatile liquid, chemical reaction of internal and external heat transfer devices, misoperation, etc., the breather valve will exhale or inhale accordingly, so as to avoid damage to the storage tank due to overpressure or ultra vacuum. Working principle of breather valve The internal structure of the breather valve is essentially composed of a pressure valve disc (i.e. exhalation valve) and a vacuum valve disc (i.e. suction valve). The pressure valve disc and vacuum valve disc can be arranged side by side or overlapped. Its working principle: when the pressure of the tank is equal to the atmospheric pressure, the disc and seat of the pressure valve and vacuum valve are closely matched, and the sealing structure on the side of the seat has “adsorption” effect, so that the seat is tight without leakage. When the pressure or vacuum degree increases, the valve disc starts to open, because there is still “adsorption” effect on the seat edge, so it can still maintain a good seal. When the pressure in the tank rises to the constant value, the pressure valve is opened, and the gas in the tank is discharged into the outside atmosphere through the exhalation valve (pressure valve). At this time, the vacuum valve is closed due to the positive pressure in the tank. On the contrary, when the pressure in the tank drops to a certain degree of vacuum, the vacuum valve opens due to the positive pressure of atmospheric pressure, and the external gas enters the tank through the suction valve (i.e. vacuum valve), and the pressure valve is closed. At any time, the pressure valve and vacuum valve cannot be opened at the same time. When the pressure or vacuum in the tank drops to the normal operating pressure, the pressure valve and vacuum valve are closed, and the process of exhalation or inhalation is stopped. Common standards for Breather valves Commonly used standards for Breather valves are: SY/T 0511.1-2010 “Petroleum Storage Tank Accessories Part 1: Breather valve” TB/T 3319-2013 “Breathing safety valve for railway tank car” QC/T 1064-2017 “Tank Vehicle Breather valve for Road Transport of Flammable Liquid and Dangerous Goods” DIN EN 14595-2016 “Dangerous Goods Transport Tank, Tank Operating Device Pressure and Vacuum Breather valve” Classification of breather valve Tight breather valve The tight breather valve is usually used in low-pressure straight-through pipelines. The sealing performance depends entirely on the goodness of the fit between the plug and the plug body. The compression of its sealing surface is achieved by tightening the lower nut. Generally used for PN≤0.6Mpa. Packed breather valve Packing type breather valve realizes the sealing of plug and plug body by pressing the packing. Due to the packing, the sealing performance is better. Usually, this kind of breather valve has a packing gland, and the plug does not need to extend out of the valve body, thus reducing a leakage path of the working medium. This kind of breather valve is widely used for the pressure of PN≤1Mpa. Self-sealing breather valve The self-sealing breather valve realizes the compression and sealing between the plug and the plug body through the pressure of the medium itself. The small head of the stopper extends upwards out of the body, and the medium enters the big head of the stopper through the small hole at the entrance to press the stopper upwards. This structure is generally used for air medium. Oil-sealed breather valve The scope of application of breather valves continues to expand, and oil-sealed breather valves with forced lubrication appear. Due to forced lubrication, an oil film is formed between the plug and the sealing surface of the plug body. In this way, the sealing performance is better, the opening and closing is labor-saving, and the sealing surface is prevented from being damaged. Classified by material Cast iron breather valve, carbon steel breather valve, cast steel breather valve, stainless steel (304, 304L, 316, 316L) breather valve, aluminum alloy breather valve, plastic (PVC, PP) breather valve; Classified by working principle The first is to exhale or inhale when a certain pressure is reached; the other is designed to only exhale but not inhale, which can be understood as replacing it with two check valves with appropriate pressure. The second type of breather valve is similar to a one-way check valve. It can only breathe out, not inhale. When the pressure in the system rises, the gas will pass through the breather valve to vent outwards to ensure a constant pressure in the system. For storage tanks that store toxic substances, there is no breather valve, and treatment devices such as activated carbon filters can be added. breather valves are generally used on normal pressure or low pressure storage tanks, that is, only normal pressure and low pressure storage tanks have breather discharge (the low pressure tank often has a steam recovery system), and the high pressure storage tank has no discharge, no breather loss and work loss . The main emissions of fixed roof tanks are pided into breather loss (small breather discharge) and work loss (large breather discharge). Installation of Breather valve 1. Remove the packaging, it is very important to read the product description. 2. When hoisting the breather valve, appropriate lifting tools should be used to avoid damage to the protective cap of the breather valve disc. 3. Check the coaxiality and verticality of the pipe flange on the tank or water tank, which is essential for the normal use of the pressure and vacuum relief valve (Breather valve). 4. Check the waterline surface of the pipe flange on the tank or water tank. It must be clean, free of scratches, corrosion, tool marks, and flat. 5. Remove the flange port protection cover and other packing materials. 6. Check the gasket; make sure the material is suitable for the application. 7. Use the bolt circle to center the washer. Installation points of Breather valve (1) The Breather valve should be installed at the highest point on the top of the tank. Theoretically speaking, from the viewpoint of reducing evaporation loss and other exhaust gas, the breather valve should be installed at the highest point of the gas phase space of the tank in order to smoothly provide the most direct and largest passage to the breather valve. (2) When the volume of the storage tank is large or the storage tank is more important, in order to prevent the risk of overpressure or negative pressure in the storage tank due to failure of a single Breather valve, two Breather valves can be installed at this time. In order to avoid two Breather valves operating at the same time and increasing the probability of failure, during process design, the suction and discharge pressure gradients of the two Breather valves are usually designed. Normally, the next one works and the other is standby. (3) If the breather volume is too large and the breather volume of a single Breather valve cannot meet the requirements, more than two Breather valves can be set. When installing two Breather valves, their distance from the center of the tank top should be equal, that is, they are arranged symmetrically on the tank top. (4) If the breather valve is installed on a nitrogen-sealed storage tank, the position of the nitrogen gas supply pipe must be far away from the breather valve interface and inserted into the storage tank from the top of the tank for about 200mm, so that the nitrogen is not directly discharged after entering the tank. Nitrogen sealing effect. (5) If there is a flame arrestor in the breather valve, the influence of the pressure drop of the flame arrestor on the discharge pressure of the breather valve must be considered to avoid overpressure in the storage tank. (6) When the average temperature of the coldest month in the tank building area is lower than or equal to 0, the breather valve must have anti-freezing measures to prevent freezing or blocking of the breather valve valve disc, resulting in poor exhaust or insufficient air supply of the storage tank , Which leads to overpressure drum or low pressure deflated tank. Breathing discharge calculation of breather valve The respiratory emissions of the fixed roof tank can be estimated by the following formula: LB=0.191×M(P/(100910-P))^0.68×D^1.73×H^0.51×△T^0.45×FP×C×KC In the formula: LB-respiratory discharge volume of fixed top tank (Kg/a); M-the molecular weight of the vapor in the tank; P-In a large amount of liquid state, the true vapor pressure (Pa); D-The diameter of the tank (m); H-average vapor space height (m); △T- the average temperature difference within a day (℃); FP-coating factor (dimensionless), the value is between 1 and 1.5 according to the paint condition; C-Adjustment factor for small diameter tanks (dimensionless); For tanks with a diameter between 0-9m, C=1-0.0123(D-9)^2; C=1 for tanks with a diameter greater than 9m; KC-product factor (Petroleum crude oil KC is 0.65, other organic liquids are 1.0). Working discharge calculation of Breather valve Work emissions are losses due to man-made loading and unloading. As a result of charging, when the pressure in the tank exceeds the release pressure, the vapor is forced out of the tank; while the discharge loss occurs when the liquid is discharged, and the air is drawn into the tank, and the air becomes a gas saturated with organic vapor and expands. Therefore, the capacity of the vapor space is exceeded. The working emissions of the fixed roof tank can be estimated by the following formula: LW=4.188×10^-7×M×P×KN×KC In the formula: LW-Work loss of fixed roof tank (Kg/m3 input); KN-Turnover factor (dimensionless), the value is determined by the number of annual turnover (K). Turnover times=annual input/tank capacity K<=36,KN=1 36 K>220, KN=0.26 Pressure test of Breather valve 1. Test preparation Install the fire-stop Breather valve on the test bench correctly, the device should not leak, and the inner wall of the test tube should be flat and smooth. 2. Detection medium The detection medium for the opening pressure, ventilation and leakage of the fire resistance Breather valve is air, the absolute pressure is 0.1Mpa, the temperature is 20℃, the relative humidity is 50%, and the density is 1.2kg/m3. If the air is not in this state, Should be converted to gas in this state. The detection medium for the pressure of the flame retardant Breather valve body is 5-35 ℃ clean water. 3. Air pressure detection First detect its leakage, and then detect its sensitivity and ventilation volume one by one. 4. Water pressure detection The water pressure test of the fire retardant Breather valve is 0.2Mpa, and the pressure holding time is 10min. 5. Pressure detection Install the fire-resistance Breather valve on the connecting flange of the gas storage tank, adjust the valve to gradually increase or decrease the pressure in the gas storage tank, adjust the valve disc to make it open, and read from the connected micromanometer Output the pressure value, read the value once every minute, and then rotate the valve disc by 90° and 180° respectively, repeat the above test, repeat each working condition three times, and take the average value. 6. Leakage detection The leak detection pressure is 0.75 times the operating pressure, and this value is read on the micromanometer. The value of the leakage is read from the flowmeter (the accuracy of the flowmeter is 0.5-1.0 level). Read each measurement value once per minute for a total of three readings, and take the average. 7. Low temperature detection fire resistance Breather valve. Install the fire resistance Breather valve on the test frame and put it in the low temperature box. The temperature in the low temperature box will drop to 4-15℃, and the continuous input relative temperature of the low temperature box should not be less than 70%. The air at room temperature reaches the end of the breather valve before the end of the valve disc is opened, and then the temperature in the low temperature box is reduced to -30 ℃, after 24 hours of constant temperature, connect one side of the test frame to the micromanometer, and the other side passes through A surge tank containing room temperature air is connected to the aerodynamic force. When the valve disc of the breather valve is in the open state, read the pressure value. repeat three times. Maintenance of Breather valve The Breather valve is maintained and maintained once a month and twice a month in winter. The method: first slightly open the valve cover, take out the vacuum valve disc and the pressure valve disc, check the valve disc and valve disc seal, valve disc guide rod and guide rod sleeve for oil and dirt, such as oil and dirt The objects should be cleaned up, then put back in place, and pull up and down a few times to check whether the opening is flexible and reliable. If everything is normal, then tighten the valve cover. In the maintenance and maintenance, if there is any abnormal phenomenon such as scratches or wear on the valve disc, it should be replaced immediately or contact the supplier company to solve it in time. How to choose the right breather valve Breather valve selection should first follow the four principles of safety, reliability, applicability, and economy in sequence, and then follow the six aspects of on-site working conditions (namely, pipeline parameters, fluid parameters, pressure parameters, action methods, and special requirements). select). The following factors are mainly considered when selecting the breather valve: 1. For the requirements of the installation location and temperature range, such as cold areas, all-weather Breather valves should be used, and pipeline breather valves should be used for installation in pipelines. 2. The control pressure of the mechanical Breather valve should be compatible with the relevant pressure bearing capacity. 3. The specifications (flange diameter) of the mechanical Breather valve should meet the requirements of the maximum flow rate of breather gas in and out of the oil tank. 4. Consider the exhalation volume caused by the increase in the evaporation of liquid in the tube caused by the heating of the tank during a fire. 5. Under the influence of climate, the increase of vapor pressure in the tank decreases, resulting in the thermal effect of breather. 6. Anti-freeze Breather valve should be selected for selection in northern cold regions. 7. The maximum amount of liquid in and out of the tank. First, determine the breather volume of the breather valve according to the working conditions of the specific occasions where the breather valve is set up and the prescribed calculation method or formula, and then select the breather valve according to the various specified performance curves of different constant pressure values ​​provided by the breather valve manufacturer size. It also determines the take-off pressure and ventilation pressure of the breather valve. When a single breather volume cannot meet the requirements, more than two Breather valves can be set. Confirm the minimum pressure of the vessel design and the maximum allowable pressure of the vessel, that is, the determination of negative pressure and positive pressure, and the operating pressure range. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Effect of forging on microstructure and properties of metal In forging production, in addition to ensuring the required shape and size of forged flanges, it must also meet the performance requirements of parts in the process of use, which mainly include: strength index, plasticity index, impact toughness, fatigue strength and initial fracture degree For parts working at high temperature, there are also high temperature instantaneous tensile property, endurance property, anti creep property and thermal fatigue property. The raw materials for forged flanges are ingot, rolling stock, extrusion stock and forging stock. Rolling stock, extrusion stock and forging stock are semi-finished products formed by rolling, extrusion and forging respectively. In forging production, the structure and properties of raw materials can be improved by adopting reasonable process and process parameters: 1. The results show that the columnar crystal is broken, the macrosegregation is improved, the as cast structure is changed into the forged structure, and the internal pores are welded under the appropriate temperature and stress conditions to improve the density of the material; 2. The fiber structure of ingot is formed by forging, and reasonable fiber direction distribution is obtained by rolling, extrusion and die forging; 3. Controlling the size and uniformity of grains; 4. Improve the distribution of the second phase (such as alloy carbide in ledeburite steel); 5. It can strengthen the structure by deformation. Because of the improvement of the above-mentioned structure, the plasticity, impact toughness, fatigue strength and endurance properties of the forging are also improved, and then through the final heat treatment of the parts, the good comprehensive properties such as hardness, strength and plasticity required by the parts can be obtained. However, if the quality of raw materials is poor or the forging process is unreasonable, the forging defects may occur, including surface defects, internal defects or unqualified performance. Influence of raw materials on forging quality Good quality of raw materials is a prerequisite to ensure the quality of forged flanges. If there are defects in raw materials, the forming process and final quality of forged flanges will be affected. If the chemical elements of raw materials exceed the specified range or the content of impurity elements is too high, it will have a great impact on the forming and quality of forged flanges, for example, s, B, Cu, Sn and other elements are easy to form low melting point phase, which makes forgings prone to hot embrittlement. In order to obtain essentially fine grain steel, the residual aluminum content in the steel should be controlled within a certain range, such as 0.02% – 0.04% (mass fraction) of A1 acid. If the aluminum content is too small, it can’t control the grain size, so it is easy to make the essential grain size of forged flanges unqualified; if the aluminum content is too high, it is easy to form wood grain fracture and tear mark fracture under the condition of forming fiber structure during pressure processing. For another example, in austenitic stainless steel, the more N, Si, Al and Mo are contained, the more ferrite phases are, the easier it is to form banded cracks during forging and make the parts magnetic. If there are some defects in the raw materials, such as residual shrinkage, blistering under the skin, serious carbide segregation, coarse non-metallic inclusions (slag) and so on, the forging is easy to produce cracks. The defects in raw materials, such as dendrite, serious porosity, non-metallic inclusion, white spot, oxide film, segregation band and mixture of different metals, are easy to cause the performance degradation of forgings. The surface cracks of forgings are easily caused by surface cracks, folds, scabs and coarse-grained rings of raw materials. Influence of forging process on forging quality The forging process generally consists of the following processes: blanking, heating, forming, cooling after forging, pickling and heat treatment after forging. If the forging process is improper, a series of forging defects may occur. The heating process includes charging temperature, heating temperature, heating speed, holding time, furnace gas composition, etc. Improper heating, such as too high heating temperature and too long heating time, will cause decarbonization, overheating, overburning and other defects. If the heating speed is too fast and the holding time is too short, the temperature distribution is often uneven, resulting in thermal stress and cracking of forging blank. Forging forming process includes deformation mode, deformation degree, deformation temperature, deformation speed, stress state, die condition and lubrication condition. If the forming process is not proper, coarse grains, uneven grains, various cracks, folding, flow through, eddy current and residual as cast structure may be caused. During the cooling process after forging, if the process is not proper, it may cause cooling cracks, white spots, network carbides and so on. Effect of forging microstructure on Microstructure and properties after final heat treatment Austenitic and ferritic heat-resistant stainless steel, superalloy, aluminum alloy, magnesium alloy and other materials without isomerism transformation during heating and cooling, as well as some copper alloy and titanium alloy, can not be improved by heat treatment. In the process of heating and cooling, some structural defects caused by improper forging process or some defects left by raw materials have great influence on the quality of forged flanges after heat treatment. Examples are as follows: 1. The microstructure defects of some forged flanges can be improved during post forging heat treatment, and satisfactory microstructure and properties can be obtained after final heat treatment. For example, coarse grain and widmanstatten structure in general overheated structural steel forgings, slight network carbide in hypereutectoid steel and bearing steel due to improper cooling, etc. 2. The structure defects of some forged flanges are difficult to be eliminated by normal heat treatment, which can be improved by high temperature normalizing, repeated normalizing, low temperature decomposition, high temperature diffusion annealing and other measures. 3. The structure defects of some forgings can’t be eliminated by general heat treatment process, resulting in the performance degradation or even disqualification of forgings after final heat treatment. For example, severe stone fracture and edge fracture, overburning, ferrite band in stainless steel, carbide net and band in ledeburite high alloy tool steel, etc. 4. The structure defects of some forgings will be further developed in the final heat treatment, and even cause cracking. For example, if the coarse-grained structure of alloy structural steel forgings is not improved during post forging heat treatment, the coarse martensite and unqualified properties are often caused after carbonitriding and quenching; the coarse banded carbide in high-speed steel often causes cracking after quenching. Different forming methods have different stress and strain characteristics, so the main defects may be different. For example, the main defects during upsetting are longitudinal or 45 ° cracks on the side surface, and only the upper and lower ends of the ingot usually have as cast structure; the main defects during drawing rectangular section billet are transverse cracks and corner cracks on the surface, diagonal cracks and transverse cracks inside; the main defects during open die forging are underfill, folding and dislocation. Different kinds of materials, due to their different composition and microstructure, have different microstructure changes and mechanical behaviors in the process of heating, forging and cooling. Therefore, when forging process is not appropriate, the possible defects also have their particularity. For example, the main defects of ledeburite high alloy tool steel forgings are coarse carbide particles, uneven distribution and cracks; the main defects of high temperature alloy forgings are coarse grains and cracks; the main defects of austenitic stainless steel forged flanges are poor intergranular chromium, reduced intergranular corrosion resistance, ferrite banded structure and cracks; the main defects of aluminum alloy forgings are coarse grains, folding, eddy current, etc And so on. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is sand blasting? Sand blasting is a surface treatment process that uses compressed air as power to form a high-speed jet beam to spray sand at high speed to the workpiece surface to be treated. The compressed air is used as the power to form a high-speed jet beam to spray the sprayed materials (copper ore, quartz sand, emery, iron sand and steel sand) to the workpiece surface to be treated at high speed, so as to change the appearance or shape of the outer surface of the workpiece surface. Due to the impact and cutting effect of abrasive on the workpiece surface, the workpiece surface can obtain certain cleanliness and different roughness, The mechanical properties of the workpiece surface are improved, so the fatigue resistance of the workpiece is improved, the adhesion between it and the coating is increased, the durability of the coating film is prolonged, and it is also conducive to the leveling and decoration of the coating. Sand blasting can remove all dirt such as rust on the surface of the workpiece, and establish a very important foundation on the surface of the workpiece (usually the so-called rough surface). Moreover, it can achieve different degrees of roughness by exchanging abrasives with different particle sizes, greatly improve the adhesion between the workpiece and coatings and plating, or make the bonding parts more firm and better quality. Sand blasting process Sand blasting process is dry sand blasting. The abrasives can be steel sand, alumina, quartz sand, silicon carbide, etc., but quartz sand is the most widely used in China. Abrasives of different substances can be selected according to the requirements of part materials, surface conditions and processing. Dry sand blasting process conditions for different parts Part type Degree of quartz sand (mm) Compressed air pressure (MPA) Large steel parts with thickness over 3 mm. 2.5~3.5 0.3~0.5 Medium sized steel parts with thickness of 1 ~ 3mm. 1.0~2.0 0.2~0.4 Small thin brass parts. 0.5~1.0 0.15~0.25 Steel sheet metal parts and aluminum alloy parts with thickness less than 1 mm. 0.5 ~ down 0.1~0.15 There are two kinds of dry sand blasting: mechanical sand blasting and air pressure sand blasting. Each method is pided into manual, non automatic or continuous automatic modes. Manual air pressure sand blasting machine is widely used in China, and it also uses various complex shapes of small and medium-sized parts. Wet spray Sand technology The abrasive used in wet sand blasting is the same as that of dry sand blasting. The abrasive can be mixed with water to form mortar. The abrasive is usually 20% – 35% and stirred continuously to prevent sinking. Compressed air is used to press into the nozzle and sprayed to the parts. Sand and water can be put into the tank respectively and mixed before flowing to the nozzle before spraying to the parts. In order to prevent corrosion of steel parts, sodium nitrite and other corrosion inhibitors must be added in water, Sand should be dried before next use. There are many kinds of equipment for wet sand blasting machine, and the most commonly used one is sand blasting chamber. Spray Pill Technology (1) General On Shot peening is similar to sand blasting, but steel shot or glass shot is used instead of abrasive for sand blasting. Shot peening can produce compressive stress on parts, and there is no dust pollution containing silicon. This process is mainly used for: (1) The fatigue strength and stress corrosion resistance of the parts are improved by compressive stress. (2) Straighten the twisted thin-walled parts. (3) Instead of the general cold and hot forming process, the large thin-walled aluminum parts are processed, which can avoid the high residual on the surface of the parts Tensile stress And the favorable compressive stress is formed. It should be noted that the service temperature of the parts after shot peening should not be too high, otherwise, the compressive stress will be eliminated and the expected effect will be lost. The limit of using temperature depends on the material of the parts. For example, the temperature of steel parts is about 260 ~ 290 ℃, and that of aluminum parts is about 170 ℃. (2) Types of pills 1. Cast steel shot: its hardness is generally 40-50HRC. When processing hardware metal, the hardness can be increased to 57-62HRC. Cast steel shot has good toughness and is widely used. Its service life is several times that of cast iron shot. 2. Cast iron shot: its hardness is 58-65HRC. It is brittle and easy to be broken. It has short life and is not widely used. It is mainly used in occasions with high strength without shot peening. 3. Glass pill: hardness is lower than the former two, mainly used in stainless steel. Titanium, aluminum, magnesium and other materials that do not allow iron contamination can also be used for secondary processing after shot peening to remove iron contamination and reduce surface roughness of parts. (3) Shot blasting technology For shot peening, which requires compressive stress on the surface of parts, it must have enough coverage, which is difficult. In addition, it is difficult to make quantitative judgment. Therefore, the method of controlling shot peening strength is often adopted, that is, the method requiring a certain sandblasting degree is required, that is, the required stress value can be obtained after reaching a certain sandblasting strength. The shot peening strength is mostly in accordance with the American SAE standard J442. Almen arc altimeter was used for measurement Almen arc height meter uses 1070 cold rolled steel with thickness of 0.8 mm, 1.3 mm or 2.4 mm. Compared with 70 carbon steel in China, its hardness is 44-50 HRC. The shot peening strength can be obtained by measuring the arc height of bent steel bar. The shot peening strength is mainly affected by the following factors: (1) Shot size: the larger the shot peening, the greater the impact energy, the greater the shot peening intensity, and the shot peening coverage. Therefore, on the premise of producing the required shot peening strength, it is beneficial to reduce the shot size as much as possible. In addition, the selection of shot peening size is also limited by the shape of shot peening parts, and its diameter should not exceed half of the radius of the inner circle of the groove. The particle size of shot peening is generally 2.00-0.30mm (2) Hardness of Shot Peening: when the hardness is greater than the hardness of parts, the change of shot peening hardness value does not affect the shot peening strength, otherwise, the decrease of shot peening hardness will reduce the shot peening strength. (3) Shot peening speed: when the shot peening speed is increased, the shot peening intensity will be increased, but if the shot peening speed is too high, the crushing amount will increase. (4) Spray angle: when it is vertical, the shot peening intensity is the highest. Therefore, shot peening is generally carried out in this state. If it is necessary to peen at a small angle due to the shape of the parts, the size and speed of shot peening shall be appropriately increased. (5) Shot peening fragmentation: the shot peening strength of crushing shot blasting is low, so the shot peening should be removed frequently to ensure that the integrity of shot peening is not less than 85%. In addition, the shot with sharp angle will scratch the parts. Function and application of sand blasting (1) Pretreatment of workpiece coating and workpiece bonding Sand blasting can remove all dirt such as rust on the workpiece surface, and establish a very important basic schema (commonly known as rough surface) on the workpiece surface. Moreover, it can achieve different degrees of roughness by exchanging abrasives with different particle sizes, such as flying abrasives and abrasives of abrasives, so as to greatly improve the binding force between the workpiece and coatings and plating materials. Or make the bonding parts bond more firmly and have better quality. (2) Cleaning and polishing of casting rough surface and workpiece after heat treatment Sand blasting can clean all dirt (such as oxide scale, oil stain and other residues) on the surface of castings and forgings and workpieces after heat treatment, polish the surface of workpieces, improve the smoothness of workpieces, expose uniform and consistent metal color, and make the appearance of workpieces more beautiful and good-looking. (3) Burr cleaning and surface beautification of machined parts Sand blasting can clean the micro burrs on the workpiece surface, make the workpiece surface more flat, eliminate the harm of burrs and improve the grade of the workpiece. And sand blasting can make a small fillet at the junction of the workpiece surface, making the workpiece more beautiful and more precise. (4) Improve the mechanical properties of parts, mechanical parts After sandblasting, uniform and fine concave convex surfaces can be generated on the surface of parts to store lubricating oil, so as to improve lubrication conditions, reduce noise and improve mechanical service life. (5) Gloss effect For some special purpose workpieces, sandblasting can realize different reflection or matte at will. Such as the polishing of stainless steel workpieces and plastics, the polishing of jade, the matte surface of wooden furniture, the pattern pattern on the surface of frosted glass, and the texturing of cloth surface. ▲ the left is the effect after sandblasting Sand blasting is the most thorough, universal, rapid and efficient cleaning method. Sand blasting treatment can be arbitrarily selected between different roughness, but other processes cannot achieve this. Manual grinding can make rough surface, but the speed is too slow. Chemical solvent cleaning is too smooth, which is not conducive to coating bonding. Type of sand blasting machine Sand blasting machine is the most widely used product of abrasive jet. Sand blasting machine is generally pided into dry sand blasting machine and liquid sand blasting machine. Dry sand blasting machine can be pided into suction type and press in type. Suction dry sand blasting machine 1. General composition A complete suction dry sand blasting machine is generally composed of six systems, namely structure system, medium power system, pipeline system, dust removal system, control system and auxiliary system. 2. Working principle The suction dry sand blasting machine is powered by compressed air and forms a negative pressure in the spray gun through the high-speed movement of air flow. The abrasive is sucked into the spray gun through the sand conveying pipe, shot out through the nozzle and sprayed to the machined surface to achieve the expected processing purpose. In the suction dry sand blasting machine, compressed air is not only the feeding power, but also the accelerating power. Press in dry sand blasting machine 1. General composition The working unit of a complete press in dry sand blasting machine is generally composed of four systems, namely pressure tank, medium power system, pipeline system and control system. 2. Working principle of press in dry sand blasting machine. The press in dry sand blasting machine is powered by compressed air. Through the working pressure established in the pressure tank by compressed air, the abrasive is pressed into the sand conveying pipe through the sand discharge valve, shot out through the nozzle, and sprayed onto the machined surface to achieve the expected machining purpose. In the press in dry sand blasting machine, compressed air is not only the feeding power, but also the accelerating power. Liquid sand blasting machine Compared with dry sand blasting machine, the biggest feature of liquid sand blasting machine is to well control the dust pollution in the process of sand blasting and improve the working environment of sand blasting operation. 1. General composition A complete liquid sand blasting machine is generally composed of five systems, namely structure system, medium power system, pipeline system, control system and auxiliary system. 2. Working principle The liquid sand blasting machine takes the grinding fluid pump as the feeding power of the grinding fluid, and the evenly stirred grinding fluid (mixture of abrasive and water) is transported to the spray gun through the grinding fluid pump. As the acceleration power of grinding fluid, compressed air enters the spray gun through the gas transmission pipe. In the spray gun, compressed air accelerates the grinding fluid entering the spray gun, and shoots out through the nozzle to the machined surface to achieve the expected processing purpose. In the liquid sand blasting machine, the grinding liquid pump is the feeding power and the compressed air is the accelerating power. Grade of sand blasting That is, cleanliness. There are two representative international standards: one is “SSPC -” formulated by the United States in 85; The second is “SA -” formulated by Sweden in 76. It is pided into four levels: SA1, SA2, Sa2.5 and SA3. It is an international common standard. The details are as follows: SA1 – equivalent to sspc-sp7 in the United States. The general simple manual brushing and abrasive cloth grinding methods are adopted, which is the lowest level of the four kinds of cleanliness, and the protection of the coating is only slightly better than that of the untreated workpiece. Technical standard for SA1 treatment: the workpiece surface shall be free of oil, grease, residual oxide scale, rust spots, residual paint and other dirt. Grade SA1 is also called manual brushing and cleaning grade（ Or cleaning level). SA2 – equivalent to SSPC-SP6 in the United States. Sand blasting is the lowest level of sand blasting, that is, general requirements, but the protection of the coating is much higher than manual brushing. Technical standard for SA2 level treatment: the workpiece surface shall be free of greasy, dirt, oxide scale, rust scale, paint, oxide, corrosion and other foreign substances (except defects), but the defects shall not exceed 33% per square meter of surface, including slight shadows; A small amount of slight discoloration caused by defects and corrosion; Oxide scale and paint defects. If there is a dent on the original surface of the workpiece, slight rust and paint will remain at the bottom of the dent. SA2 grade is also called commodity cleaning grade (or industrial grade). Sa2.5 level – it is widely used in industry and can be used as the acceptance technical requirements and standards. Sa2.5 level is also called near white cleaning level (near white level or out of white level). Technical standard for Sa2.5 treatment: the same as the first half of SA2 requirements, but the defects are limited to no more than 5% per square meter of surface, including slight shadow; A small amount of slight discoloration caused by defects and corrosion; Oxide scale and paint defects. SA3 – equivalent to sspc-sp5 in the United States, is the highest treatment level in the industry, also known as white cleaning level (or white level). Technical standard for SA3 treatment: the same as Sa2.5, but 5% of shadows, defects, rust, etc. shall not exist. Sandblasting raw materials Sand blasting: that is to spray the pattern part into a very fine frosted surface with metal sand particles of different sizes and models on the production mold of gold and silver coins. When producing gold and silver coins, a layer of beautiful silver appears in the pattern part, which increases the sense of three-dimensional and hierarchy. Refined quartz sand Quartz sand, ordinary quartz sand and refined quartz sand for sand blasting (refer to derusting or plating on metal surface): high hardness, good derusting effect, and physical and chemical indexes are as follows: SiO2 ≥ 88-99.8% Fe2O3 ≤ 0.1-0.005%, fire resistance 1450-1800 ℃, uniform appearance particles, common particle sizes of 1-3mm and 0.1-0.3mm, pure white. The particle size range is mostly 5-220 mesh, which can be produced according to the user’s requirements. Main uses: metallurgy, ink, silicon carbide, glass and glass products, enamel, cast steel, water filtration, bubble alkali, chemical industry, sand blasting and other industries. Sandblasting rubber hose: the inner and outer rubber of sandblasting pipes are usually made of wear-resistant materials, mostly NBR (acrylonitrile butadiene copolymer), SBR (oil filled styrene butadiene rubber), or there is a kind of paralubber (clover rubber) with better service performance of imported hose. The common wear resistance coefficient is 60 ~ 75 cubic mm. Operating procedures for sand blasting Wear protective equipment before work, and do not work with bare arms. At least two people shall work. The air storage tank, pressure gauge and safety valve shall be calibrated regularly. The air storage tank discharges dust every two weeks, and the filter in the sand tank is checked once a month. Check whether the ventilation pipe and sandblasting machine door are sealed. Five minutes before work, the ventilation and dust removal equipment must be started. When the ventilation and dust removal equipment fails, the sand blasting machine is prohibited to work. The compressed air valve shall be opened slowly, and the air pressure shall not exceed 0.8MPa. The sand blasting particle size shall adapt to the work requirements, generally between No. 10 and No. 20, and the sand shall be kept dry. When the sand blasting machine is working, irrelevant personnel are not allowed to approach. When cleaning and adjusting the operating parts, stop the machine. Do not blow dust or joke with compressed air. After work, the ventilation and dust removal equipment shall continue to operate for five minutes and then shut down to discharge indoor dust and keep the site clean. In case of personal and equipment accidents, the site shall be protected and reported to relevant departments.

What is shot blasting? Shot blasting is a process that uses compressed air as power to spray shot onto the workpiece surface and clean or strengthen the workpiece surface. The medium used for shot blasting is round particles without edges and corners, such as steel shot, iron shot, glass shot and ceramic shot. Shot blasting relies on the strong impact force of shot particles to make the workpiece surface closer, so as to make the workpiece more wear-resistant, ductile and corrosion-resistant. Shot blasting, also known as shot blasting strengthening, is one of the effective methods to reduce fatigue and improve service life of parts. Shot blasting is to spray high-speed projectile flow onto the surface of parts, resulting in plastic deformation on the surface of parts, forming a strengthening layer with a certain thickness. High residual stress is formed in the strengthening layer. Due to the existence of compressive stress on the surface of parts, When the parts bear load, it can offset part of the stress, so as to improve the fatigue strength of the parts. Shot blasting is a surface strengthening process widely used in factories, that is, the cold working process of bombarding the workpiece surface with shot particles and implanting residual compressive stress to improve the fatigue strength of the workpiece. It is widely used to improve the mechanical strength, wear resistance, fatigue resistance and corrosion resistance of parts. The advantages of shot blasting are simple equipment, low cost, not limited by workpiece shape and position, and convenient operation. The disadvantages are poor working environment, low unit output and lower efficiency than shot blasting. The types of shot blasting include steel shot, cast iron shot, glass shot, ceramic shot, etc. Types of pills Pills are generally spherical particles without edges and corners, such as steel wire cut pills. Cast steel shot Its hardness is generally 40 ~ 50HRC. When processing hard metals, the hardness can be increased to 57 ~ 62HRC. Cast steel shot has good toughness and is widely used. Its service life is several times that of cast iron shot Cast iron shot Its hardness is 58 ~ 65HRC, brittle and easy to break. Short service life and not widely used. It is mainly used for occasions requiring high shot blasting strength Glass pellet The hardness is lower than the first two. It is mainly used for stainless steel, titanium, aluminum, magnesium and other materials that do not allow iron pollution. It can also be used for secondary processing after steel shot blasting to remove iron pollution and reduce the surface roughness of parts. Ceramic pill The chemical composition of ceramic pellets is approximately 67% ZrO2, 31% SiO2 and 2% Al2O3 inclusions, which are made by melting, atomizing, drying, rounding and screening, and the hardness is equivalent to HRC57 ~ 63. Its outstanding properties are higher density and hardness than glass. It was first used for aircraft parts strengthening in the early 1980s. Ceramic pellets have higher strength, longer service life and lower price than glass pellets. Now they have been extended to the surface strengthening of non-ferrous metals such as titanium alloy and aluminum alloy. Therefore, there are four categories of shot: cast steel shot, cast iron shot, glass shot and ceramic shot Special note: Glass shot for shot blasting and glass shot for other purposes are two different concepts. The biggest feature of shot peened glass shot is that its minimum hardness is not less than 6-7 Mohs, and it has certain toughness, and the minimum rounding rate is not less than 90%. The road reflective glass shot has no requirements for hardness. Generally, ordinary glass can be used as raw material, and the rounding rate is required to be at least 75%. The two prices are very different, but the appearance is almost the same. If ordinary glass shot is used for shot blasting, it seems that the cost is low. When shot blasting, the crushing rate is high and the workpiece with high strength is almost broken at one time. In contrast, the total cost is much higher. Characteristics of shot blasting 1) Metallic or non-metallic projectiles can be used arbitrarily to meet the different requirements of cleaning the workpiece surface; 2) The cleaning is flexible, easy to clean the inner and outer surfaces of complex workpieces and the inner wall of pipe fittings, and is not limited by the site. The equipment can be placed near super large workpieces; 3) The equipment has simple structure, less investment, less vulnerable parts and low maintenance cost; 4) A high-power air compressor station must be equipped, which consumes more energy under the condition of the same cleaning effect; 5) The cleaned surface is prone to moisture and rust regeneration; 6) Low cleaning efficiency, many operators and high labor intensity. ▲ strong shot blasting machine The advantages of shot blasting are simple equipment, low cost, not limited by workpiece shape and position, and convenient operation. The disadvantages are poor working environment, low unit output and lower efficiency than shot blasting. The types of shot blasting include steel shot, cast iron shot, glass shot, ceramic shot, etc. Gear shot blasting strengthening: it is mainly to impact the surface of parts with the help of high-speed bullets to make them undergo elastic-plastic deformation, resulting in favorable changes such as residual compressive stress, work hardening and microstructure refinement, so as to improve the bending fatigue strength and contact fatigue strength of gears. It is an important way to improve the anti bite ability of gears and improve the service life of gears. During shot blasting, the small-size spherical steel shot strikes the surface of the workpiece to form a compressive stress. The impact of each shot will produce a certain plastic deformation of the metal, and the final surface can not completely recover to form a permanent compressive stress state. As a surface strengthening process, shot blasting can form residual compressive stress on the surface, which is equivalent to 55% ~ 60% of the tensile strength limit of the material, and the workpiece surface is the place where cracks are easy to initiate. For carburized and quenched gears, the compressive stress can reach 1177 ~ 1725mpa, which can greatly improve the fatigue performance. Improving surface hardness of carburized gear by gear shot blasting For example, the shot blasting equipment of FAW heat treatment branch adopts German tr5svr-1 stress shot blasting equipment. Shot blasting process: use steel shot with diameter of ￠ 0.8mm, shot blasting time of 9min and shot blasting speed of 2800r / min. The gear material is 22CrMoH steel, which is carburized, Quenched and tempered. After shot blasting, the surface structure of the gear is refined. The residual austenite content of the surface is about 10% lower than that of the workpiece without shot blasting, and the change is obvious within 0.15mm from the surface; The surface hardness of the gear after enhanced shot blasting is increased by 0.5 ~ 2hrc. Shot blasting improves the fatigue life of gears For example, FAW carried out the fatigue life test on the first gear of “Jiefang” automobile transmission by using the enhanced shot blasting process, which significantly improved the fatigue life of the gear. In order to improve the fatigue life of the “Jiefang” brand driving helical gear, the large arc hob is used to cut the teeth. Increasing the gear fillet can increase the service life of the driving helical gear from 208300 times to 695400 times. If enhanced shot blasting is used, the fatigue life can be increased to 2109000 times. Classification of shot blasting Shot blasting is pided into shot blasting and sand blasting. The surface treatment with shot blasting has great striking force and obvious cleaning effect. However, the treatment of thin plate workpiece by shot blasting is easy to deform the workpiece, and the steel shot strikes the workpiece surface (whether shot blasting or shot blasting) to deform the metal substrate. Because Fe3O4 and Fe2O3 are not plastic, they are stripped after crushing, and the oil film is deformed together with the substrate, shot blasting and shot blasting cannot completely remove the oil stain on the workpiece with oil stain. Among the existing workpiece surface treatment methods, sand blasting has a good cleaning effect. Sand blasting is suitable for cleaning the workpiece surface with high requirements. However, the general sand blasting equipment in China is mostly composed of original heavy sand conveying machinery such as hinged dragon, scraper and bucket elevator. Users need to build a deep pit and make a waterproof layer to install machinery. The construction cost is high, the maintenance workload and maintenance cost are great, and a large amount of silicon dust generated in the sand blasting process cannot be removed, which seriously affects the health of operators and pollutes the environment. Shot blasting is pided into general shot blasting and stress shot blasting. During general treatment, when the steel plate is in a free state, the inside of the steel plate is hit with high-speed steel shot to produce preloading stress on its surface. To reduce the tensile stress on the steel plate surface and increase the service life. Stress shot blasting is the pre bending of the steel plate under a certain force, and then shot blasting. Application of shot blasting Shot blasting is used to remove oxide scale, rust, molding sand and old paint film on medium and large metal products with a thickness of not less than 2mm or not required to maintain accurate size and contour, as well as castings and forgings. It is a cleaning method before surface coating (plating). It is widely used in large shipyards, heavy machinery factories, automobile factories, etc. Shot blasting is a cold treatment process, which is widely used to improve the fatigue resistance of metal parts in long-term service under high stress conditions, such as aircraft engine compressor blades, fuselage structural parts, automobile transmission system parts and so on. Shot blasting strengthening is to spray the medium called steel shot at a high speed and continuously in a fully controlled state and hammer it to the surface of the part, so as to produce a residual compressive stress layer on the surface. Because when each steel shot hits the metal part, it is like a miniature rod hammering the surface, hammering out small indentation or depression. In order to form a depression, the metal surface must be stretched. Under the surface layer, the compressed grains try to restore the surface to its original shape, resulting in a hemisphere under the action of high compressive force. Numerous depressions overlap to form a uniform residual compressive stress layer. Finally, under the protection of compressive stress layer, the fatigue strength of parts is greatly improved and the safe working life is prolonged. Difference from shot blasting and sand blasting Difference between shot peening and shot blasting Shot peening uses high-pressure air or compressed air as power, and shot blasting is generally a high-speed rotating flywheel to shoot out the steel sand at high speed. Shot blasting has high efficiency, but there will be dead corners, while shot blasting is more flexible, but the power consumption is large. Although the two processes have different spraying power and methods, they both aim at high-speed impact on workpieces, and their effects are basically the same. In comparison, shot peening is relatively fine and easy to control accuracy, but the efficiency is not as high as shot blasting. It is suitable for small workpieces with complex shapes. Shot blasting is more economical and practical, easy to control efficiency and cost, and can control the particle size of shot to control the spraying effect, However, there will be dead corners, which is suitable for batch processing of workpieces with single shape and surface. The selection of the two processes mainly depends on the shape of the workpiece and the machining efficiency. Difference from sand blasting Both shot blasting and sand blasting use high-pressure air or compressed air as power to blow it out at high speed and impact the workpiece surface to achieve cleaning effect, but the effect is also different due to different media. After sand blasting, the dirt on the workpiece surface is removed and the surface area is greatly increased, thus increasing the bonding strength between the workpiece and the coating. The surface of the workpiece after sand blasting is of the natural color of metal, but because the surface is rough and the light is refracted, it has no metal luster and is a darkened surface. After shot blasting, the dirt on the workpiece surface is removed, and the workpiece surface is slightly damaged, which is not easy to be damaged. The surface area has increased. Because the workpiece surface is not damaged in the machining process, the excess energy generated during machining will lead to the surface strengthening of the workpiece matrix. The surface of the workpiece after shot blasting is also the natural color of metal, but because the surface is spherical and the light is partially refracted, the workpiece is processed into matte effect. Quality evaluation of shot blasting Cleaning quality level a. Most thorough cleaning level (SA3) The cleaned steel surface is completely silver gray, with a certain surface roughness to improve the adhesion of the coating. b. Very thorough cleaning level (SA2.5) The cleaned steel surface shall be free of grease, dirt, scale, rust, corrosion products, oxides and other impurities. Shadows and color differences due to incomplete cleaning are allowed, but at least 95% of the surface per square inch shall reach the level of the most thorough cleaning, and only slight shadows and color differences shall appear in the rest. c. More thorough cleaning level The cleaned steel surface shall be free of grease, dirt, rust scale and other impurities. The oxide scale, rust and old paint shall be removed. Light shadows and color differences due to incomplete removal of rust and oxide scale are allowed, and the area shall not exceed 33% per square inch; If pitting corrosion has occurred on the steel surface, a small amount of rust and old paint are allowed at the depth of the corrosion point. d. Non thorough cleaning level After the surface is completely cleaned, grease, dirt, loose oxide skin and loose paint skin are removed. Oxide skin, rust, paint and coating that are firmly bonded to the substrate and cannot be removed with a very sharp blade are allowed to remain on the surface after cleaning. A large number of evenly distributed metal spots appear on the surface. Surface roughness Surface roughness and surface cleanliness are produced at the same time. Determining the appropriate surface roughness is as important as determining the correct cleanliness requirements. Effect of surface roughness 1) The actual bonding area between the coating and the workpiece surface is increased, which is conducive to improving the bonding force of the coating; 2) The coating will produce great internal stress during curing. The existence of roughness can effectively eliminate the stress concentration in the coating and prevent the coating from cracking; 3) The existence of surface roughness can support the quality of some coatings and help to eliminate sagging, especially for vertically coated surfaces. The factors affecting roughness are as follows: 1) Abrasive particle size, hardness and particle shape; 2) Hardness of workpiece material; 3) Pressure and stability of compressed air; 4) The distance between the nozzle and the workpiece surface and the included angle between the nozzle and the workpiece surface. Several problems related to surface roughness: 1) The cleaning time is almost independent of the surface roughness; 2) The angle between the nozzle and the surface will affect the surface roughness, but the change is not obvious between 45 degrees and 90 degrees; 3) Cleaning the difficult surface with large particle abrasive can improve the work efficiency, but the surface roughness will be high. The research shows that the roughness value caused by abrasive with particle size greater than 1.2mm is high. The surface with high roughness can be cleaned again with small grain abrasive to reduce the roughness to the specified requirements. Shot blasting produces greater compressive stress on the surface than sand blasting. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Selection of heat exchanger type and scaling treatment method 1. When the temperature difference is large, floating head heat exchanger, U-shaped tube heat exchanger, stuffing box heat exchanger and sliding tube sheet heat exchanger can be selected. When the shell side is often mechanically cleaned, the structure with withdrawable tube bundle can be selected. Under high temperature and high pressure, U-tube heat exchanger can be selected. When the shell side medium is flammable, explosive, toxic or volatile, and the service pressure and temperature are high, the stuffing box heat exchanger should not be used. When the tube side medium and shell side medium are not allowed to be mixed, the heat exchanger with double tubesheet structure can be used. 2. Types and selection principles of tubular heat exchangers (1) Tubular heat exchangers can be pided into the following main types: ① The tubesheets at both ends of the tube bundle of the tubular heat exchanger are connected with the shell as a whole, with simple structure, but it is only applicable to the heat exchange operation when the temperature difference between cold and hot fluids is small and the shell side does not need mechanical cleaning. When the temperature difference is slightly large and the shell side pressure is not too high, an elastic compensation ring can be installed on the shell to reduce the thermal stress. ② The tube sheet at one end of the floating head heat exchanger tube bundle can float freely, which completely eliminates the thermal stress, and the whole tube bundle can be extracted from the shell, which is convenient for mechanical cleaning and maintenance. Floating head heat exchanger is widely used, but its structure is complex and its cost is high. ③ Each heat exchange tube of the tubular heat exchanger is bent into a U shape, and both ends are respectively fixed in the upper and lower areas of the same tube plate, which is pided into inlet and outlet chambers with the help of the diaphragm in the tube box. The heat exchanger completely eliminates the thermal stress and has a simpler structure than the floating head sheet type, but the tube side is not easy to clean. For the heat exchange of highly corrosive fluids in chemical production, non-metallic materials such as ceramics, glass, polytetrafluoroethylene and graphite need to be used to make shell and tube heat exchangers. This kind of heat exchanger has poor heat exchange performance and is only used in occasions with low pressure, low vibration and low temperature. (2) For the cold and hot fluids for heat exchange, the flow channel shall be selected according to the following principles: ① Unclean and easy to scale fluids should go through the pipe side, because it is more convenient to clean in the pipe. ② Corrosive fluid should go through the tube side to avoid corrosion of tube bundle and shell at the same time. ③ The fluid with high pressure should go through the pipe side to avoid pressure on the shell. ④ The saturated steam should go through the shell side, because the heat transfer coefficient of steam condensation has nothing to do with the flow rate, and the condensate is easy to discharge. 3. Precautions and working principle of fixed tubesheet heat exchanger Precautions for fixed tubesheet heat exchanger during operation include: (1) The heat exchanger can only be used after pressure test after new installation or maintenance. (2) When starting the heat exchanger, the cold flow shall be followed by the heat flow, and when stopping the work, the heat flow shall be stopped first and then the cold flow. To prevent leakage or damage caused by uneven thermal expansion and cold contraction. (3) The fixed tubesheet heat exchanger is not allowed to be heated in one direction, and the temperature difference on both sides of the tube and shell of the floating heat exchanger is not allowed to be too large. (4) During startup, the exhaust valve shall be kept open to discharge all air, and shall be closed after startup. (5) If hydrocarbons are used, the air in the heat exchanger shall be removed with inert gas before loading hydrocarbons to avoid explosion. (6) During shutdown and purging, the condensate must be drained before steam introduction, and the air shall be ventilated slowly to prevent water hammer. When one side of the heat exchanger is ventilated, the vent valve on the other side must be opened to avoid damage to the pressure. When the heat exchanger is closed, the exhaust valve and drain valve shall be opened to prevent the equipment from being damaged by vacuum caused by cooling. (7) When using the air cooler, pay attention to the uniform flow of some parts to ensure the cooling effect. (8) Always pay attention to monitoring to prevent leakage. Working principle of fixed tubesheet heat exchanger: It is the structure of fixed tubesheet heat exchanger. A fluid flows into the housing from the connecting pipe 1 and flows out from the connecting pipe 2 through the pipe. B fluid flows in from the connecting pipe 3 and out of the connecting pipe 4 through the pipe. If the temperature of fluid a is higher than that of fluid B, heat is transferred from fluid a to fluid B through the pipe wall; On the contrary, it is transferred from fluid B to fluid a through the pipe wall. The area inside the shell and outside the pipe and pipe box is called the shell side, and the fluid passing through the shell side is called the shell side fluid (a fluid). The area inside the pipe and the pipe box is called the pipe pass, and the fluid passing through the pipe pass is called the pipe pass fluid (B fluid). Shell and tube heat exchanger is mainly composed of tube box, tube plate, tube, shell and baffle. Generally, the shell is cylindrical and the pipe is straight or U-shaped. In order to improve the heat transfer efficiency of the heat exchanger, threaded tubes and finned tubes can also be used. The arrangement of pipes has many forms, such as equilateral triangle, square, square skew 45 ° and concentric circle. The first three are the most common. When arranged in a triangle, more tubes can be arranged in the shell with the same diameter to increase the heat transfer area, but it is difficult to clean the tubes mechanically and the fluid resistance is large. The overall of tubesheet and tube is called tube bundle. There are two types of connection between the end of the pipe and the tubesheet: welding and expansion. Some baffles are set transversely in the tube bundle to guide the shell side fluid to change the flow direction for many times and effectively scour the tube, so as to improve the heat transfer efficiency and support the tube at the same time. The shapes of baffles include bow, circle and rectangle. In order to reduce the flow cross section of shell side and tube side fluid, speed up the flow rate and improve the heat transfer efficiency, split partition plates can be set longitudinally in the tube box and shell, pide the shell side into 2 passes and the tube side into 2 passes, 4 passes, 6 passes and 8 passes. 4. Type and connection mode of floating head heat exchanger One end of the tubesheet at both ends of the floating head heat exchanger is not connected with the shell, and this end is called floating head. When the tube is heated, the tube bundle and the floating head can expand and contract freely along the axial direction, completely eliminating the temperature difference stress. The floating head heat exchanger has a tubesheet at one end fixed with the shell, while the tubesheet at the other end can float freely in the shell. The shell and tube bundle are free from thermal expansion, so when the temperature difference between the two media is large, there will be no temperature difference stress between the tube bundle and the shell. The floating head end is designed into a detachable structure, so that the tube bundle can be easily inserted or pulled out, which provides convenience for maintenance and cleaning. This type of heat exchanger is especially suitable for working conditions where the temperature difference stress between the shell and the heat exchange tube is large and both the shell side and the tube side are required to be cleaned. (1) Advantages of floating head heat exchanger: A the tube bundle can be pulled out to facilitate the cleaning of the tube and shell side. B. the temperature difference between media is not limited. C. It can work under high temperature and high pressure. Generally, the temperature is less than or equal to 450 degrees and the pressure is less than or equal to MPa. D. It can be used in occasions with serious scaling. E. it can be used in places where the pipe side is easy to corrode. (2) Disadvantages of floating head heat exchanger: A small floating head is prone to internal leakage. B the consumption of metal materials is large and the cost is 20%. C complex structure. (3) Selection requirements for parts and materials of floating head heat exchanger. (4) Connection mode of heat exchange tube and tubesheet: the connection mode of heat exchange tube and tubesheet includes expansion, welding, expansion and welding, etc. A. Expansion joint Expansion joint formation can be pided into sticking expansion and strength expansion according to expansion tightness. Sticking expansion refers to the slight expansion to eliminate the gap between heat exchange tube and tubesheet. Strength expansion refers to the expansion joint to ensure the sealing performance and tensile strength of the connection between heat exchange tube and tubesheet. B. Welding The welding connection between heat exchange tube and tubesheet is pided into strength welding and sealing welding. Strength welding refers to the welding to ensure the sealing performance and tensile strength of the connection between heat exchange tube and tubesheet. Seal welding refers to the welding to ensure the sealing performance of the connection between heat exchange tube and tubesheet. The welding of heat exchange tube and tube sheet generally adopts manual arc welding, manual sub arc welding and automatic rotating argon arc welding. C. Expansion and welding In terms of expansion welding connection process, it can be pided into expansion before welding and welding before expansion. Expansion and welding are suitable for occasions with high sealing performance requirements; Occasions bearing vibration or fatigue load; Occasions with interstitial corrosion; Where composite tubesheet is used. (5) Selection of connection type between heat pipe and tubesheet The application scope of strength expansion specified in GB150 pressure vessels is: the design pressure is less than or equal to 4MPa; Design temperature is less than or equal to 300 ° C; There is no violent vibration, excessive temperature change and obvious stress corrosion during operation. The application scope of strength welding is: it can be used for the design pressure specified in this standard, but it is not suitable for occasions with large vibration and interstitial corrosion. Expansion and welding are suitable for occasions with high sealing performance requirements; Occasions bearing vibration or fatigue load; Occasions with interstitial corrosion; Where composite tubesheet is used. 5. Reasonable selection of heat exchange medium and preliminary treatment method Generally, scale inhibitor and algicide are added. If necessary, sulfuric acid is added to adjust the pH value. Pay attention to the hardness and pH value of circulating water, and timely adjust the dosage of scale inhibitor and sulfuric acid. Algicide is generally added by impact method. Pay attention to sewage discharge 1-2 days after algicide is added. If possible, the soft water treatment system can be used, but algicide must be added. Even so, some biological slime will adhere to the heat exchanger, and high-pressure water can be considered for cleaning. The agents added in the circulating water system are mainly bactericidal algicide and corrosion and scale inhibitor, which aims to improve the circulating water quality, slow down the corrosion of equipment and pipelines and prevent scaling in the heat exchanger, To increase the fouling thermal resistance, we should strictly control the relevant process parameters in the actual production process, hang hanging pieces at different points in the circulating water system, and properly adjust the agent according to the hanging piece corrosion. 6. Reduce and eliminate scale formation from the process control of heat exchanger operation The process conditions of heat exchanger include heat transfer, thermodynamic parameters of fluid (temperature, pressure, flow, phase state, etc.) and physicochemical properties (density, viscosity, corrosivity, etc.). While ensuring heat transfer efficiency, minimize the conditions for scaling formation; The operation shall be carried out in strict accordance with the specifications. The general practice is: (1) Increase the heat transfer coefficient. On the premise of comprehensively considering the fluid resistance and no fluid induced vibration, the high flow rate shall be selected as far as possible. (2) Increase the average temperature difference. For the fluid without phase change, the heat transfer mode close to countercurrent shall be adopted as far as possible. Because this can not only improve the average temperature difference, but also help to reduce the temperature difference stress in the structure. Under allowable conditions, the inlet temperature of hot fluid can be increased or the inlet temperature of cold fluid can be reduced. (3) Properly arrange the heat transfer surface. For example, heat exchangers, cold disks, etc. adopting appropriate tube spacing or arrangement can not only increase the heat transfer area in unit space, but also improve the fluid flow characteristics. The heat transfer mode of staggered tube bundle is better than that of parallel tube bundle. (4) Cleaning method of formed scale ① Chemical method The chemical method is to remove the scale by chemical reaction or loosen the scale by chemical reaction, and then remove it by external force. Of course, for chemical cleaning, it is best to ask an experienced professional company for cleaning. The cleaning cost is low. Before cleaning, analyze the scaling composition and formulate a detailed construction scheme. During cleaning, ensure that the chemical solution will not erode the heat exchange pipe and process pipeline. ② Mechanical method (a) High pressure water jet cleaning: generally, 1-5mpa pressure is used to form a strong jet through the spray gun nozzle, and the water volume reaches 80-120l / min to break and scour the scale layer to achieve the purpose of cleaning. At present, the manual hand-held flexible or rigid spray gun is basically used to flush the inner side of the heat transfer tube one by one, and the outer side of the tube bundle is rotated section by section to flush from multiple directions. In order to improve efficiency and reduce labor intensity, different spraying instruments shall be used according to the scale conditions, such as improving the nozzle (nozzle size, shape, quantity and angle). For some insoluble scale and blockage, special cleaning methods shall be adopted, such as high-pressure water jet drill bit or ultra-high-pressure water jet > 70MPa. Combined cleaning can also be carried out by reagent or heating. (b) Manual cleaning or pipeline mechanical cleaning brush: manual cleaning or pipeline mechanical cleaning brush is used to clean the inner wall of the pipe. This method has good adaptability and can be cleaned for many times, but attention must be paid not to damage the pipe wall. ③ Regular cleaning In order to eliminate the scaling during the operation of the heat exchanger, the flow can be increased periodically and temporarily or countercurrent operation can be carried out, which can effectively eliminate the light attachments on the inner wall of the pipe, but the backwash pipeline shall be preset on the equipment. It can also be cleaned with rubber balls. Appropriate chemicals can also be injected according to the type of fluid to remove the dirt. Timely cleaning shall be carried out during each shutdown and maintenance, and the effect is the best. ④ Cleaning during parking The shutdown cleaning of heat exchanger shall adopt different methods for different types of heat exchangers and scaling conditions, mainly including high-pressure water jet cleaning, chemical cleaning and mechanical cleaning. Mechanical cleaning is to manually pull through the strip or rotate the heat transfer pipe one by one with an electric drill bit. If the compressed oil cooler is overhauled, it shall be cleaned in time. It is not easy to clean for a long time, with high labor intensity and easy to damage the inner wall of the steel pipe. Source: China Stainless Steel Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Valve is an important component in the piping system of petrochemical plant. It is one of the main leakage sources in the plant with many kinds and large quantity. Therefore, the leakage requirement of valve is very important. Valve sealing performance refers to the ability of each sealing part of the valve to prevent medium leakage. The main sealing parts of the valve are: the matching surface between the opening and closing parts and the valve seat, the matching of the packing and the valve stem and the stuffing box, and the connection between the valve body and the valve cover. The first leakage is called internal leakage, which directly affects the ability of the valve to cut off the medium and the normal operation of the equipment. The leakage of the last two places is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve, which directly affects the safe production, causes the loss of working medium and enterprise economic loss, environmental pollution, and even causes production accidents in serious cases. Especially for high temperature and high pressure, flammable and explosive, toxic or corrosive media, the leakage of the valve is not allowed, because the consequences are more serious than the internal leakage, so the valve must have reliable sealing performance, to meet the requirements of its use conditions on the leakage. 1. Classification standard of valve sealing grade in China At present, there are two common classification standards of valve sealing grade in China. 1.1 Classification of valve sealing grade in Chinese national standard GB / T 13927 pressure test for industrial valves. 1.2 Classification of valve sealing grade in China mechanical industry standard JB / T 9092 inspection and test of valves. 2. International valve seal classification standard At present, there are five commonly used classification standards of valve sealing grade. 2.1 Classification of valve sealing grade in former Soviet Union In order to select the products according to the sealing degree and the specified use of the valves, the valves are classified according to the sealing degree. 2.2 ISO classification of valve sealing grade ISO 5208 pressure testing of industrial valves and metal valves. 2.3 American Petroleum Institute (APL) classification of valve sealing grade American Petroleum Institute standard API 598-2004 inspection and testing of valves. 2.4 Classification of valve sealing class by MSS the allowable valve leakage requirements of MSS SP61 are as follows: (1) If one sealing surface of the valve sealing pair is made of plastic or rubber, there shall be no visible leakage during the duration of the sealing test. (2) The maximum allowable leakage on each side when closing shall be: the liquid is 0.4ml/mm and 0.4ml/h of nominal size (DN); The gas is nominal size (DN) 120 ml per millimeter per hour. (3) The allowable leakage of check valve can be increased by 4 times. 2.5 Classification of control valve sealing class in ANSI / FCI ANSI / FCI 70-2 (ASME b16.104) control valve seat leakage. 2.6 Classification of valve sealing grade in European standard European standard EN 12266-1 testing of industrial valves Part 1. Pressure tests, test methods and acceptance criteria – mandatory requirements. 3. Selection of valve sealing grade 3.1 Selection of domestic valve sealing grade (1) The national standard GB / T 13927 (pressure test for industrial valves) implemented on July 1, 2009 is formulated with reference to the European standard ISO 5208. It is suitable for inspection and pressure test of industrial metal valves, including gate valve, globe valve, check valve, plug valve, ball valve and butterfly valve. The classification and maximum allowable leakage of sealing test are the same as those specified in ISO 5208. This standard is a revision of GB / T 13927 (pressure test for general purpose valves). Compared with GB / t13927, it adds AA, CC, e, EE, F and G grades. The new version of the standard stipulates that “the selection of leakage grade shall be one of the strict requirements in the relevant valve product standard or order contract. If there is no special provision in the product standard or order contract, the non-metallic elastic sealing valve shall meet the requirements of class A, and the metal sealing auxiliary valve shall meet the requirements of class D. ” Generally, class D is suitable for general valves, and the leakage class above class D should be selected for key valves. (2) Mechanical industry standard JB / t9092 “inspection and test of valves” is a revision of zbj16006. The maximum allowable leakage of sealing test is made according to API 598-1996. It is suitable for inspection and pressure test of gate valve, globe valve, plug valve, ball valve, check valve and butterfly valve used in petroleum industry, including metal sealing pair, elastic sealing pair and non-metal sealing pair (such as ceramic). At present, GB / T 9092 is being revised. (3) It should be noted in engineering design that the national standard GB / T 19672 (technical specifications for pipeline valves) is formulated with reference to European standard ISO 14313 and American Petroleum Institute standard API 6D. The national standard GB / T 20173 “pipeline valves for petroleum and natural gas industries” is formulated with reference to the European standard ISO 14313. Both GB / T 19672 and GB / T 20173 have the same acceptance criteria for valve leakage as ISO 5208 class A and D. Therefore, the leakage requirement higher than the standard in the engineering design should be given in the order contract. 3.2 Selection of foreign valve sealing grade (1) The former Soviet Union mainly used the classification of valve sealing grade in the 1950s. With the disintegration of the former Soviet Union, most countries do not use this classification of valve sealing grade, but use European and American standards seal grade classification. European standard EN 12266-1 seal grade classification conforms to ISO 5208, but lacks AA, CC and EE. Compared with the 1999 edition, the ISO 5208 has added AA, CC, e, EE, F and G grades. ISO 5208 standard gives the comparison of several seal grades with API 598 and EN 12266 standards. The comparison of other nominal size seal grades can be obtained by calculating the leakage according to the diameter. (2) API 598 is the most commonly used inspection and pressure test standard for American Standard valves. The manufacturer’s standard msssp61 is often used for the inspection of “fully open” and “fully closed” steel valves, but it is not applicable Not suitable for control valves. Msssp61 is not usually used for American Standard valves. API598 is applicable to the sealing performance test of valves manufactured according to the following API standards: Flange type, lug type, clip type and butt welded check valve API 594; Flange, thread and butt welding metal plug valve API 599; DN l00 and below steel gate valve, globe valve and check valve API 602 for petroleum and natural gas industry; Flange and butt welded corrosion-resistant bolted bonnet gate valve API 603; Flange, thread and butt welding metal ball valve API 608; Double flange, lug and wafer butterfly valve API 609. Attention should be paid in engineering design: API 598-2004 cancels the inspection and pressure test of API 600 (bolted bonnet steel gate valve for petroleum and natural gas industry) compared with 1996 edition. API 600-2001 (ISO 10434-1998) stipulates that the sealing performance test of valves shall refer to ISO 5208, but the leakage in Table 17 and table 18 of the standard is the same as that of API 598-1996, instead of ISO 5208. API 600 standard implemented in September, 2009 corrected this contradiction in 2001 edition, which stipulated that the sealing performance test of valves should be carried out in accordance with API 598, but there was no specified edition, which was in contradiction with API 598-2004. Therefore, when selecting API 600 and API 598 standard for sealing performance test in engineering design, the version of the standard must be clear to ensure the consistency of the content of the standard. (3) American Petroleum Institute standard API 6D (ISO 14313) Petroleum and natural gas industries – pipeline transportation systems – pipeline valves: the acceptance criteria for valve leakage are as follows: “the leakage of soft seal valve and oil seal plug valve shall not exceed ISO 5208A (no visible leakage), and the leakage of metal seat valve shall not exceed ISO 5208 (1993) d, but according to the sealing test described in b.4, The leakage shall not be more than twice of ISO 5208 (1993) class D unless otherwise specified. ” Note in the standard: “special applications may require leakage less than ISO 5208 (1993) class D ¨ J.” Therefore, the leakage requirement higher than the standard in engineering design should be given in the order contract. API 6D-2008 Appendix B additional test requirements specifies the additional test requirements of valve FJ to be conducted by the manufacturer when specified by the buyer. Seal test includes low pressure and high pressure gas seal test. High pressure seal test with inert gas as test medium will replace liquid seal test and liquid seal test. According to the type, diameter and pressure level of the valve, the selection of sealing test can refer to the provisions of ISO 5208 standard. It is suggested that low pressure sealing test should be used for valves on gal and GCL of long distance pipeline to improve the qualified rate of valves. When selecting high pressure sealing test, it should be noted that the sealing performance of elastic sealing valve under low pressure condition may be reduced after high pressure sealing test. The production cost of valve can be effectively reduced by reasonably selecting the valve sealing test requirements according to the actual working conditions of medium. (4) American national standard ANSI / FCI 70-2 (ASME B16.104) is applicable to control valve sealing class. In engineering design, metal elastic seal or metal seal should be selected according to the characteristics of medium and the opening frequency of valve. The sealing grade of metal sealing control valve shall be specified in the order contract. According to experience, for metal seal control valve, the requirements of grade I, II and III are relatively low, and the selection in engineering design is relatively small. Generally, grade IV is the lowest for metal seal control valve, and grade V or VI is the most critical control valve. The control valve of the flare system of an ethylene plant is designed to meet the requirements of grade IV metal seal, which runs well. (5) In addition, attention should be paid in engineering design: API 6D stipulates that the chloride ion content of water used in austenitic stainless steel valve sealing test shall not exceed 30ug/g, and ISO 5208 and API 598 both stipulate that the chloride ion content of water used in austenitic stainless steel valve sealing test shall not exceed 100ug/g. Due to the different requirements of each standard, it is suggested that the chloride ion content of water used in sealing test should be specified in the valve order contract. 4. Classification standard for sealing grade of low leakage valve Low leakage valve refers to the valve actual leakage is very small, rely on conventional water pressure, air pressure seal test has been unable to determine, need to use more advanced means and instruments to detect the small leakage. The tiny leakage of the valve to the external environment is called low leakage. At present, there are three standards commonly used to detect low leakage of valves in the world (1) EPA method 21, leakage detection of volatile organic components. (2) ISO 15848 (industrial valves: low leakage measurement, testing and qualification procedures). (3) Shell MESC SPE 77 / 312 “industrial valves: low leakage measurement, classification system, qualification procedures and type approval and product testing of on-off and control valves”. EPA method 21 standard of the United States Environmental Protection Agency only specifies the detection method, but does not pide the leakage level. It belongs to the local standard regulations, and is rarely used. According to ISO 15848 and shell MESC SPE 77 / 312, the performance of valves is evaluated from three aspects: tightness grade, durability grade and temperature grade. According to the leakage of valve stem and valve body seal, the tightness grade is pided into a, B and C. for iso15848 standard, the leakage requirement of valve body seal is ≤ 50 em3/m3, while the leakage of valve stem is calculated according to the diameter of valve stem. The sealing grade of ISO 15848A is the highest, and that of B and C is the same as shell MESC SPE 77/312. Generally, the sealing grade of low leakage valve is lower than grade B, while the sealing grade of bellows seal valve is lower than grade a due to the metal bellows seal used in the sealing part of valve stem. 5. Selection of low leakage valve Bellows seal valve is one of the low leakage valves. In the past, bellows sealing valve was generally used in the working conditions with special requirements for valve leakage grade. However, due to the great difficulty and high technical requirements of bellows sealing valve f-jjm, its bellows material can not be completely localized and the cost is too high, which restricts its extensive application in petrochemical industry. At present, with the continuous enhancement of people’s awareness of safety and environmental protection, the increase of technical cooperation with foreign countries, and the continuous strengthening of domestic valve manufacturers’ own technical strength, domestic technical personnel’s understanding of low leakage valves is also constantly improving, so that its application scope is constantly expanding. If the valves selected for inflammable, explosive and toxic media in petrochemical enterprises can meet the low leakage standard, it will undoubtedly greatly reduce the emission of toxic, combustible and explosive media in the device, and avoid fire, explosion, poisoning and other accidents endangering life safety caused by valve leakage. Compared with bellows valves, low leakage valves meeting ISO 15848 and shell MESC SPE 77/31 standards have simple structure and easy manufacturing, and their cost is about 10% – 20% higher than that of general valves. According to the previous analysis and comparison of the two standard sealing grades, the leakage of tight grade B valve can generally meet the low leakage requirements of some special working conditions, the machining accuracy requirements are relatively easy to achieve, and the manufacturing cost is not much increased. It can replace part of the bellows valve. At present, low leakage valve has more practical significance for purification system of oil and gas field with high content of hydrogen sulfide. Because hydrogen sulfide is a highly toxic and combustible gas, heavier than air, and can gather in low-lying areas. Inhaling a certain concentration of hydrogen sulfide will harm the body and even lead to death. Therefore, the requirements for leakage of such natural gas purification facilities are more stringent. 6. Conclusion When selecting the sealing grade and the specified allowable leakage, it should be noted that the leakage of medium between the sealing surfaces of high-pressure valves will cause surface erosion. If there is leakage of corrosive medium, the metal at the leakage place will be corroded. With the increase of leakage gap, the leakage volume will also increase rapidly, so that the valve will be scrapped. Therefore, for the high pressure or corrosive medium working condition of the valve, in ensuring the sealing should put forward higher requirements. In the pipeline conveying flammable, explosive and toxic media, the leakage of media between valve sealing surfaces may cause personal harm, economic loss and even accidents. Therefore, for the valves conveying flammable, explosive and toxic media, the requirements for sealing should be reasonably put forward according to the dangerous level of the media. Any seal sometimes allows a small amount of leakage, if the leakage does not play a practical role, it can be considered as sealed. The technical standard of valve manufacturing usually stipulates that metal to metal seal is allowed to have a certain amount of leakage when sealing performance test is carried out under closed state. In order to ensure the high sealing performance of the valve, it is necessary to grind the sealing surface carefully, increase the specific pressure on the sealing surface, but it should be less than the allowable specific pressure of the sealing surface material, and improve the structural stiffness. The application experience of valves shows that in many cases, it is unnecessary to put forward too high requirements on the sealing performance of valves, because some working conditions completely allow a small amount of medium leakage, because the leakage is not enough to affect the use of valves. On the contrary, improving the sealing performance of these valves will complicate the manufacturing process, increase the cost and cause unnecessary waste. The structural design and manufacturing process of the valve itself have the most obvious impact on its external leakage. For low leakage valves, the design, manufacturing and processing requirements of key components such as valve body, stem and stuffing box are more stringent, such as: (1) The quality of valve body and cover, especially in forging or casting, should avoid folding, slag inclusion, porosity, microstructure evacuation, hidden cracks and other defects and uneven composition. (2) The processing quality of the parts at the connection of valve stem and valve body, especially the roughness of valve stem and stuffing box, the straightness of valve stem, the verticality of valve cover stuffing box hole and the processing accuracy. (3) The structure selection of the valve stuffing box, because the seal at the valve stem is dynamic seal, the packing is easy to wear during the rotation or sliding of the valve stem. It is necessary to select a special low leakage packing seal and packing seal combination, and strictly control the gap between the packing and the valve stem, and between the packing and the packing box. To sum up, the selection of valve type should not only meet the process conditions and standards, but also fully consider various working conditions. In the engineering design, the valve sealing grade should meet the principles of safety, rationality and economy. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)