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Natural gas pipeline refers to the pipeline that transports natural gas (including associated gas produced in oil field) from the production site or treatment plant to urban gas distribution center or industrial enterprise users, also known as gas transmission pipeline. Using natural gas pipeline to transport natural gas is a way to transport natural gas on land. Natural gas pipelines account for about half of the world’s total pipelines. China’s modern natural gas pipeline industry is mostly concentrated in Sichuan Province, the main natural gas producing area. In 1963, the first Bayu gas transmission pipeline with a diameter of 426 mm and a total length of 54.7 km was completed. By 1983, it had built a gas transmission pipeline network from east Sichuan to Chengdu, Deyang and other places through Chongqing, Luzhou, Weiyuan, etc., with a diameter of 426-720mm, a total length of more than 2200km, 178 gas gathering and distribution stations and an annual capacity of 5-6 billion cubic meters. In addition, in Daqing, Shengli, North China and other oilfields, there are pipelines to transport associated gas to petrochemical plants. Welding Technology of Natural Gas Pipeline I. Universal Welding Method Generally, semi-automatic welding is the main method of Engineering welding, and manual arc welding downward welding can be used for locally difficult sections and joints. The downward welding operation rules must conform to the stipulations of the Downward Welding Procedure Regulations for Pipelines. 1. AWS_E6010 cellulose electrode is used for manual arc welding, AWS_E8010 electrode is used for filling, and AWS_E8018G low hydrogen electrode is used for cap. 2. Semi-automatic root welding adopts AWS_E6010 electrode, filling and capping adopts E71T8-Ni1 or 71T8-K6 flux cored wire. II. Welders 1. Establish a welding quality management system according to the welding process before construction. Train and test the welders according to the requirements of the welding process approved by the owner, so that the technical quality and technical level of the welders can meet the relevant regulations of the construction acceptance criteria of this project. 2. All welders participating in the construction of this project must have the “Welder Qualification Certificate” issued by the State General Administration of Technical Supervision or the provincial and municipal technical supervision bureaus and the “Work Certificate” issued by the pre-job supervisor, so as to hold the certificate to work. III. Major Welding Equipment Power supply: Semi-automatic welding power supply is DZ-80 mobile power station produced by Pipeline Machinery Equipment Company. The power station is equipped with DC-400 Lincoln multi-system welding machine, which can meet manual welding at the same time. IV. GENERAL REQUIREMENTS 1. Pipeline welding with X70 material needs preheating before welding. Ring heater and baking handle are used for preheating. Pre-heating width: the groove on both sides (> 50mm), preheating temperature, interlayer heating temperature: according to the temperature specified in the welding procedure for heating treatment. The preheating temperature is measured by infrared thermometer 50 mm away from the pipe orifice. There is no preheating requirement for other materials. 2. The arc initiation or closure of weld beads are staggered for more than 30 mm. Welding arc initiation is carried out in groove, and arc initiation on groove outside welding layer is not allowed, let alone on pipe wall outside groove. Every arc-starting point and joint must be repaired before welding. After the first welding layer is completed, the next welding layer is started. 3. After the root welding is completed, angular polishing machine is used to grind and clean up the slag, spatter, defects and weld protrusion on the outer surface of the root welding. The groove shape on the outer surface of the pipe shall not be damaged by grinding, and the time interval between root welding and filling shall not exceed 10 minutes. 4. All beads should be welded continuously and the interlayer temperature of beads should meet the required requirements. After the weld is finished, the splash and slag on the surface of the joint must be cleaned up. Before the completion of the weld bead on that day, more than 50% of the whole weld bead should be completed at each weld joint and not less than three layers. In welding construction, the “welding process record” should be filled in carefully according to the regulations. 5. Dry, waterproof and heat-insulating materials should be used to cover the unwelded joints on that day. Before welding the next day, the temperature required by the welding procedure should be preheated. For the unused welding wire on the same day, the wire feeder should be removed from the wire feeder or put together with the wire feeder into the warehouse equipped with dehumidifier at the construction site for dehumidification treatment. The next day after arriving at the construction site, immediately remove the tape wrapped on the pipe mouth, grind the root, and then use the annular heater to heat the left mouth. The heating temperature requirements are the same as the temperature of the pipe mouth group. The heating quality must be approved by the on-site supervision engineer. 6. In the welding process, the rubber protective layer with a width of 800mm is wound around the two ends of the anti-corrosion layer to prevent welding splash and burn. 7. Welding material requirements (1) Each batch of welding materials must have a certificate of quality, a certificate of conformity and a report of reexamination. Imported materials should also have a certificate of commodity inspection. (2) The appearance of welding materials should be smooth, clean, crack-free, rust-free, oil and other contaminants. (3) Welding materials are strictly prohibited from being eroded by dampness, rainwater and oil. They should be stored in dry and ventilated rooms with humidity less than 60%. (4) The shelf of welding material is more than 300 mm above ground, more than 300 mm away from wall, and the stacking height does not exceed the specified number of layers. (5) Damage to welding materials and packaging should be avoided during storage and handling. After opening the package, it should be protected from deterioration. Welding materials with signs of damage or deterioration should not be used in engineering. (6) Set up a special person to keep and distribute welding materials, and make good records of distribution and recovery, meteorological records and baking records. (7) When using the electrode, it should be placed in the barrel of the electrode. When the relative humidity of the environment is greater than 80%, the usage of the electrode should be limited for two hours, and when the relative humidity of the environment is less than 80%, the usage of the electrode should be limited for four hours. (8) The unused electrodes on that day shall be retrieved and stored. Low hydrogen type electrode should be used first after re-drying, and the number of re-drying should not exceed two times. (9) Each electrode should be welded continuously, and the welder should avoid the occurrence of arc breaking as far as possible. (10) Welding wire can not be dried. It should be stored in a dry and ventilated room and kept dry. (11) If the eccentricity of the electrode is large, the coating cracks, dropping and other phenomena affecting the welding quality, they shall not be used for welding. (12) After the completion of welding, the remaining electrodes shall not be discarded at will, and special persons shall be responsible for recovery and centralized treatment. V. Welding Environment Welding is strictly prohibited in the following cases, such as without effective protective measures (such as shelter, heater, etc.). When the wind speed exceeds the requirements of the welding procedure, special windshield shall be provided to ensure the sealing requirements of the welding site. When the ambient wind speed affects the welding operation, effective wind-proof measures should be taken to protect the welding area. According to the past construction experience, we usually adopt the method of wind-proof. Ⅵ. Welding inspection 1. Visual inspection After welding, repair or repair, visual inspection shall be carried out in time. Before inspection, slag, splash and other dirt on the surface shall be removed. The weld appearance shall meet the acceptance standard specified in welding and acceptance of steel pipeline. Non destructive testing shall not be carried out for welds that fail to pass the visual inspection. The weld appearance inspection shall meet the following requirements. (1) The appearance of the weld is uniform, and the surface of the weld and its heat affected zone shall be free of defects such as cracks, lack of fusion, air holes, slag inclusions, splashes, clamp welds, etc (2) The weld surface shall not be lower than the base metal surface, and the weld reinforcement shall not be greater than 1.6mm. (3) The width of each side of the weld surface shall be 0.5-2mm wider than the groove surface. (4) The unfitness after welding shall be less than 2mm (5) The maximum size of undercut shall meet the requirements. (6) The arc burn mark shall be polished off, and the remaining pipe wall thickness shall not be reduced less than the minimum thickness allowed by the material standard after grinding. Otherwise, the whole section of the pipe with arc burn mark shall be cut off. 2. Non destructive testing of welds All butt welds shall be subject to 100% radiographic testing, and the ultrasonic testing retest (commonly known as double hundred testing) shall be conducted according to the following requirements. The design requirements are to test according to the actual requirements: （1） Perform 100% ut on the following welds: a. All pipe joints in class III and class IV areas; b. Pipeline welded junction crossing large and medium-sized rivers, mountain tunnels, swamps, reservoirs, highways and railways above class III; c. Pipeline welded junction crossing underground pipeline, cable and optical cable; d. Welded junction of straight pipe and elbow; e. Butt weld after sectional pressure test; f. The first 100 welds initially welded by each unit; (2) After 100% radiographic inspection, 10% of all welded joints completed on the same day of each unit shall be subject to ultrasonic flaw detection: the unqualified welded joints shall be repaired as required, and the defect repair times of the same part shall not exceed 1, and the repaired parts shall be subject to 100% ultrasonic re inspection. Ⅶ. Repair 1. The non crack defects in the weld bead can be repaired directly. If the repair process is different from the original welding process, the qualified repair welding process must be used. 2. When the crack length is less than 8% of the weld length, the qualified repair welding procedure shall be used for repair. When the crack length is more than 8%, all welds with cracks must be cut off from the pipeline. 3. The repair times of defects in the same part shall not exceed 1 time, otherwise the weld shall be cut off. After repair, test according to the original standard. Source: China Natural Gas Pipelines Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What are the characteristics of the 14 kinds of metal materials commonly used in gaskets? We will give you an analysis one by one. If you have any related questions, you can also call the ship seal. Let’s discuss it together. 1. Carbon steel The recommended maximum operating temperature does not exceed 538 ° C, especially when the medium is oxidizing. High-quality thin carbon steel sheets are not suitable for use in equipment for the production of inorganic acid, neutral or acidic salt solutions. If carbon steel is subjected to stress, the equipment accident rate under hot water conditions is very high. Carbon steel gaskets are commonly used for high concentrations of acids and many alkaline solutions. The Brinell hardness is about 120. 2. 304 stainless steel 18-8 (chromium 18-20%, nickel 8-10%), the recommended maximum operating temperature does not exceed 760 °C. In the temperature range of -196~538 °C, stress corrosion and grain boundary corrosion are prone to occur. Brinell hardness of 160. 3. 304L stainless steel The carbon content does not exceed 0.03%. The recommended maximum operating temperature does not exceed 760 °C. Corrosion resistance is similar to 304 stainless steel. The low carbon content reduces the precipitation of carbon from the crystal lattice, and the resistance to intergranular corrosion is higher than that of 304 stainless steel. The Brinell hardness is about 140. 4. 316 stainless steel 18-12 (chromium 18%, nickel 12%), adding about 2% molybdenum in 304 stainless steel, when the temperature increases its strength and corrosion resistance. It has higher creep resistance than other common stainless steels when the temperature is increased. The recommended maximum operating temperature does not exceed 760 °C. The Brinell hardness is about 160. 5. 316L stainless steel The recommended maximum continuous operating temperature does not exceed 760 ° C ~ 815 ° C. The carbon content does not exceed the stress resistance and grain boundary corrosion of 316 stainless steel. The Brinell hardness is about 140. 6. 20 alloy 45% iron, 24% nickel, 20% chromium and a small amount of molybdenum and copper. The recommended maximum operating temperature does not exceed 760 ° C ~ 815 ° C. It is especially suitable for the manufacture of equipment resistant to sulfuric acid corrosion with a Brinell hardness of approximately 160. 7. Aluminum Aluminum (content not less than 99%). Aluminum has excellent corrosion resistance and processing properties and is suitable for the manufacture of double-clamp gaskets. The Brinell hardness is about 35. The recommended maximum continuous operating temperature does not exceed 426 °C. 8. Copper The composition of copper is close to pure copper, which contains traces of silver to increase its continuous operating temperature. The recommended maximum continuous operating temperature does not exceed 260 °C. The Brinell hardness is about 80. 9. Brass (66% copper, 34% zinc), it has good corrosion resistance under most working conditions, but it is not suitable for acetic acid, ammonia, salt and acetylene. The recommended maximum continuous operating temperature does not exceed 260 °C. The Brinell hardness is about 58. 10. Hastelloy B-2 (26-30% molybdenum, 62% nickel and 4-6% iron). The recommended maximum operating temperature does not exceed 1093 °C. It has excellent heat resistance and hydrochloric acid corrosion performance. It also has excellent resistance to wet hydrogen chloride gas corrosion, sulfuric acid, phosphoric acid and reducing salt solution corrosion. It has high strength under high temperature conditions. The Brinell hardness is about 230. 11. Hastelloy C-276 16-18% molybdenum, 13-17.5% chromium, 3.7-5.3% tungsten, 4.5-7% iron, and the rest are nickel). The recommended maximum operating temperature does not exceed 1093 °C. Has excellent corrosion resistance. It has excellent corrosion resistance for various attempts of cold nitric acid or boiling nitric acid with a concentration of 70%, good resistance to hydrochloric acid and sulfuric acid corrosion and excellent stress corrosion resistance. The Brinell hardness is about 210. 12. Inconel 600 Nickel based alloy (77% nickel, 15% chromium and 7% iron). The recommended maximum operating temperature does not exceed 1093 °C. It has high strength under high temperature conditions and is usually used in equipment that needs to solve stress corrosion problems. Excellent low processing performance at low temperatures. The Brinell hardness is about 150. 13. Monel 400 (Copper 30%, nickel recommended maximum continuous working temperature does not exceed 815 ° C. In addition to strong oxidizing acid, it has excellent corrosion resistance to most acids and bases. Stress corrosion is easy to occur in hydrofluoric acid, mercuric chloride, mercury medium Cracks, therefore, are not suitable for use in the above media. They are widely used in the manufacture of hydrofluoric acid. The Brinell hardness is about 120. 14. Titanium The recommended maximum operating temperature does not exceed 1093 °C. Excellent corrosion resistance at high temperatures. It is well known that it is resistant to chloride ions and has excellent resistance to nitric acid corrosion over a wide range of temperatures and concentrations. Titanium is used in most alkaline solutions and is suitable for use in oxidizing conditions. The Brinell hardness is about 216. Source: China Stainless Steel Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Natural gas pipeline refers to the pipeline that transports natural gas (including associated gas produced in oil field) from the production site or treatment plant to urban gas distribution center or industrial enterprise users, also known as gas transmission pipeline. Using natural gas pipeline to transport natural gas is a way to transport natural gas on land. Natural gas pipelines account for about half of the world’s total pipelines. I. Common Safety Problems In the construction process of general natural gas pipeline, there are some safety problems in environment, construction and management, and these three potential safety hazards will be explained in detail. 1. Environmental factors The main potential safety hazard in the environment comes from the destruction of soil structure caused by the excavation of pipelines, which leads to a higher degree of soil looseness. In addition, the stacking of solid waste at the construction site, the noise in the construction process, the emission of harmful gases and so on. If bad weather or natural disasters, such as earthquakes, floods, debris flows, are encountered in the construction process, it will cause secondary damage to the already fragile soil, and will increase the difficulty of construction, threatening the personal safety of construction personnel. 2. Construction factors The state has formulated a set of relatively perfect construction standards for natural gas pipeline engineering, which involves specific construction technology, construction technology, operation process, etc. It can be used as a reference basis for each construction unit in the actual construction process, and can effectively ensure that the potential safety hazards are minimized. However, many enterprises fail to clarify these indicators to technicians in the construction process, resulting in frequent irregular construction, or lack of comprehensive consideration of the overall project, resulting in omissions on some details, which will bring some potential safety hazards to the follow-up construction process. 3. Management factors According to the survey, more than half of natural gas pipeline accidents are caused by poor management in the construction process. The level of management has a direct relationship with the quality of the project, and directly determines the safety factor of the construction site. Management involves all aspects of construction, from the management of construction materials, machinery and equipment to the management of construction personnel, we should pay more attention. If any one of the management is not in place, it may lead to safety problems on the construction site, especially the electricity problem on the construction site, which is closely related to the personal safety of the site personnel. It is a arduous and complicated task to manage all the elements in the whole process of natural gas pipeline construction. The most common safety problems are as follows: (1) Safety measures are not in place In the construction under ditches, if the working surface is not thoroughly cleaned, or the safety measures such as escape ladders, protective nets are not placed correctly, or the lack of enclosure, it may cause pipe rolling accidents. (2) Negligent management of electricity consumption In the process of pipeline construction, it is necessary to inspect the distribution equipment regularly. If the equipment fails and is not repaired in time, it is very likely to cause short circuit or leakage. In addition, if the site line is unreasonable, it is easy to cause short-circuit, the direct consequence of short-circuit is to burn down electrical equipment, and even cause explosions and fires. (3). Management of Dangerous Goods In the pipeline construction process, the following inflammable and explosive materials may be introduced into the site. Attention should be paid to the decentralized handling of these items when they are preserved, and to ensure that the containers for storing these dangerous goods have a good appearance and no damage, otherwise it is very likely to lead to the spillover of the goods. In order to reduce the cost, some construction units use plastic containers to store these chemically prone items without authorization, which may lead to fire and explosion accidents. Ⅱ. Preventive and control measures 1. Strengthen the training of construction personnel The construction personnel are the main body of the construction site, the most active factor, and the breakthrough of maintaining the safety of the construction site. Therefore, the primary task is to strengthen the education and management of the construction personnel, improve their safety awareness, so that they can work in accordance with the standard technology in the construction, and avoid accidents in the construction caused by factors considered. Therefore, construction units can use technical training, safety education and responsibility system to manage employees, so that they can continuously improve their operational ability and professional ethics. In the training process, attention should be paid to follow up the training process of construction personnel in real time, so as to adjust their post responsibilities, so that construction projects are not affected by external factors. In addition, construction units must give necessary humanistic care to employees, organize regular physical examinations, and conduct psychological counseling to enhance their work enthusiasm and attention, so as to effectively guarantee the construction efficiency and construction quality. 2. Deepening territorial management According to the actual situation of the project, it can be pided into specific territorial responsibility areas, and the responsibilities in each area can be refined to specific positions and inpiduals, so that each employee has its own exclusive responsibility areas, responsible for their own positions, and accept the supervision of others. In daily work, employees should investigate the potential safety hazards in the area they are responsible for one by one, and then report them to the team leader to ensure that on-site risk control measures are in place, and make safety technical submissions. 3. Risk Prevention and Control and Emergency Management When carrying out high-risk project operations, such as excavation, welding technology of natural gas pipeline and blasting operations, it is necessary to carry out risk assessment and safety analysis, and formulate reasonable construction risk response measures, urge these measures to be implemented, so that each post can clearly define its actual responsibilities, and each employee should put safety awareness first, starting from itself, to ensure the operation ring. Security and stability of the environment. In addition, it is necessary to organize emergency drills regularly so that employees can grasp the response measures in various emergencies and improve their ability to identify and avoid risks. Source: China Stainless Steel Natural Gas Pipelines Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Spiral-wound gaskets are made of steel strips and graphite and other materials are wound by a winding machine. The manufacturing process is not very complicated, but the quality of the products is a nationally certified customer can purchase and use. Manufacturing process of spiral wound gasket The spiral wound gasket is wound on a special winding machine. The winding machine is processed according to the precision of the machine tool and consists of a main machine, a feed system, a gas source and a control system. Using special motor, the metal winding gasket has no inertia and can be stopped instantaneously. The spindle speed can be adjusted in 4 steps, so that the gaskets of different diameters can be wound at similar linear speeds. Adjusting the handwheel can change the position of the pressure roller to adapt Winding diameter of gaskets of different specifications. The feed system consists of a wheel train bracket and a belt pulley, a transition wheel, a guide wheel, a packing reel and a forming metal reel which are connected thereto by a movable rocker arm, and has the same positioning reference with the pressing wheel to ensure the same. The wheels are located in the same central plane. Gas source is generated by an air compressor, and the pressure reducing valve is filtered to the electromagnetic reversing valve, and then the pressure regulating valve is pushed to the cylinder to push the piston and the pressing wheel connected to the piston rod, thereby generating compression. force. Spiral-wound gasket manufacturing process The tangential tensile force of the metal strip is generated by the friction torque of the electromagnetic clutch connected to the steel reel, controlled by the excitation voltage supplied to the electromagnetic clutch by the controller, and the multi-stop excitation voltage attenuation is set on the controller. The coefficient can be selected as needed. During the winding process of the gasket, the dimensions are measured online by a displacement sensor. The Spiral wound gasket manufacturing process sensor converts the displacement of the spacer width into a corresponding voltage signal, which is sent to the first preset zero point of the controller and displayed, and compared with the two set values, when any one of them is reached. When the value is set, the relay acts to release the contactor and the motor stops, thereby automatically controlling the width of the gasket winding. The new winding machine features high precision, automatic feeding of packing belt, process parameters display and control, and automatic measurement of dimensions. Therefore, the influence of manual operation is eliminated, and the quality of the gasket and the production efficiency are remarkably improved. Source: China Stainless Steel Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Many customers have always expressed more or less confusion when they inquire about the purchase of metal-wound gaskets. There are technical uncertainties, quality concerns, and manufacturers and after-sales distrust. Here, wilsonpipeline technical department Write a small article to teach you how to avoid pits in the purchase of metal wound gaskets. First point: It is necessary to purchase metal wound gaskets suitable for the current working conditions according to the conditions of the working conditions and the flange sealing surface type. The second point: When purchasing, try to use the products of the production enterprise with sound and effective operation of the quality management system. It is best to use the products of the enterprise that hold the manufacturing license for special equipment (pressure piping components) and the effective type test report. The third point: the surface of the metal wound gasket main body is not allowed to have flaws, voids, irregularities and rust spots which affect the sealing performance. The non-metallic strip on the surface of the metal wound gasket should be evenly and appropriately raised beyond the metal strip. The texture between the layers should be clear, but the metal strip should not be exposed. The spacing of the solder joints of the metal wound gasket should be uniform, and there should be no defects such as unfusion or over-melting. The surface of the reinforcing ring shall be free from defects such as burrs, irregularities, rust spots, etc. The spacing between the upper and lower sealing surfaces of the metal wound gasket main body and the upper and lower surfaces of the reinforcing ring shall be equal. The inner side of the reinforcing ring and the metal wound gasket body shall be tightly fixed and shall not be loosened; The outer reinforcing ring and the metal wound gasket main body should be positioned and loose. The fourth point, compression ratio, rebound rate and sealing performance are important performance indicators for sealing metal wound gaskets. Generally speaking, under the premise of meeting the compression ratio requirements, the higher the rebound rate, the better; Under the premise of the rate standard requirements, the test value of the compression ratio is also larger. Products with good sealing performance, moderate compression ratio and maximum resilience should be selected. Dear customers, please keep in mind the above four points, you can perfectly avoid the various pits encountered in the procurement process of metal wound gaskets. Source: China Stainless Steel Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Duplex stainless steel is a kind of stainless steel which has both austenite and ferrite structure and two phases are independent and contain a large amount. The third generation duplex stainless steel is also called super duplex stainless steel pre (CR% + 3.3 × (Mo + 0.5W)% + 16N%) ≥ 40. UNS S32750 (022cr25ni7mo4n) is a typical super duplex stainless steel with high content of Cr, Mo and N, which has good resistance to pitting and crevice corrosion. It is suitable for the fields of petrochemical industry, oil refining, vacuum salt making, flue gas desulfurization and other more severe corrosion environment. UNS S32750 (022cr25ni7mo4n) super duplex stainless steel has low plasticity and high resistance to hot deformation. According to the characteristics of steel grades, the hot extrusion process of sms-meer 6000 extruder was studied. The main research contents are preheating heat treatment system, expanding deformation, induction heating system, hot extrusion deformation, cooling system and hot extrusion tube blank performance. The test material is smelted in electric furnace + AOD + LF furnace. After radial forging, it is turned to Φ 219mm. See Table 1 for the main components of UNS S32750. Table.1 Chemical composition of UNS S32750ElementCSiMnPSCrNiMoNStandard requirements≤0.030≤0.80≤1.20≤0.035≤0.02024.00～26.006.00～8.003.00～5.000.24～0.32Actual0.0220.0541.030.0290.00124.947.153.930.28 Process flow: tube preparation → ring furnace preheating → primary induction heating → reaming → secondary induction heating → extrusion → cooling. The extrusion equipment is 6000 ton horizontal extruder. According to the size requirements of the finished pipe, the extrusion barrel is Φ 230mm, the extrusion needle is Φ 75mm, the extrusion die is Φ 89mm, and the specification of the finished steel pipe is Φ 89 × 7mm. The maximum safe load of this extruder is 38mn. At the same time, special glass powder lubrication pad and glass powder for extrusion duplex stainless steel are prepared. In this hot extrusion process, UNS S32750 is extruded and the surface quality is good. Take the head and tail of the UNS S32750 super duplex stainless steel seamless pipe for tensile test according to ASTM A370 standard, and the test results meet the requirements of the standard. According to different composition design, the strength increases with the increase of ferrite, the toughness increases with the increase of austenite, and the strength decreases. However, for the same steel, the influence of the example on the mechanical properties has no obvious change. The metallographic analysis of the extruded tube shows that the ferrite and austenite are banded, the proportion of ferrite is 49.52%, and the grain boundary is pure without precipitation, which meets the requirements of ASME code. The hardness and corrosion test results of the UNS S32750 super duplex stainless steel seamless pipe meet the requirements of the standard. The results show that: 1) UNS S32750 (022cr25ni7mo4n) super duplex stainless steel σ phase harmful phase precipitation interval is 800-1020 ℃, preheating is 750 ℃, 2.75h, no harmful phase precipitation, temperature uniformity; 2) The hot working temperature is 1100-1200 ℃, the elongation coefficient is 1.056, the extrusion ratio is 19.9, and the surface quality of hot extrusion is good; 3) After extrusion, it cools rapidly and has good structure; 4) The hot extrusion state performance meets the standard requirements and can be delivered directly. Source: China Super Duplex  Seamless Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In view of the difficulty in the disassembly of the spiral wound gasket, the wilsonpipeline Technology Department summarized the following points and the disassembly sequence for your reference. 1. Unloading method Symmetrical, uniform, take turns to loosen the flange bolts 1/4 to 1 turn, and then officially remove the bolts. 2. Derusting method The thread is saturated with kerosene or rust remover, removes rust, increases lubrication, and facilitates the removal of parts. 3. Expansion method Use a tool such as wedge iron to insert between the flanges and loosen the flange to be unloaded. 4. Pole method For the rust-dead, bonded gasket, first remove the bolt, then close the valve, and open the valve cover with the valve stem. 5. Knocking method Use a copper rod, a hammer, etc. to tap the valve body to loosen the parts and washers. 6. Wetting method Soak the gasket with solvent, kerosene, etc. to soften or peel off the sealing surface and remove it. 7. Punching method It is fixed by four open loops, and the gap between the ring grooves is small and there is no wrench position. It is difficult to disassemble after the four open loops of the candle. The hole can be removed from the groove outside the valve, and the four open rings can be removed with a flat head. 8. Scraping Use the blade to sharpen the sealing surface and remove the gasket and its residue. This method is especially suitable for rubber gaskets and rubber asbestos gaskets. spiral-wound gasket removal sequence: Remove the pre-tightening force on the spiral-wound gasket, open the static sealing device, take out the spiral-wound gasket, and remove the spiral-wound gasket residue. Source: China Stainless Steel Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In the modern industry, as long as we carefully observe, we will find an unremarkable thing, playing an important role in the industry, that is, spiral wound gasket. In the industry, it is probably because of such a small metal-wound gasket that causes a big accident. For example, in the petrochemical industry, once there is a problem with the spiral wound gasket, it will affect the environmental problem of the whole ocean, or the same in the shipbuilding industry. If there is a problem with the spiral wound gasket, it may lead to the whole boat. The safety of the ship. So a small metal-wound gasket is inconspicuous in the device and can’t even be seen, but it is really crucial. In fact, spiral wound gaskets have been used in many industries, such as pipes, pressure vessels, lifting equipment, etc. in the machinery industry, as well as many municipal engineering and community fire protection. Of course, the most used ones are the mechanical industry. Most of the equipments use metal-wound gaskets. Of course, there are still very few parts that are not used. For example, some equipments require frequent maintenance and often choose to save metal-wound gaskets. this part. In fact, in the industry regulations, all flanges are required to be in direct contact with each other. Metal-wound gaskets must be used. Metal-wound gaskets not only play a buffering role, but also play a good sealing role. For example, if the flanges are in direct contact with each other in the pressure vessel, they will become steel-to-steel contact. There will be gaps in the middle, and air leaks. The sealing performance of the metal-wound gasket can prevent steam. The leak. spiral wound gaskets have been used more and more widely in modern industry. In order to ensure a safer environment and avoid unnecessary accidents, wilsonpipeline recommends not to ignore spiral wound gaskets. Pay attention to the following points when purchasing spiral wound gaskets: 1. Select the gasket according to the working conditions of the spiral wound gasket and the flange sealing surface type. 2. For the gaskets of the production enterprises that are sound and effective in the quality management system, it is best to use the metal-wound gaskets of the enterprises with valid type test reports. 3. The surface of the spiral wound gasket main body is not allowed to have flaws, voids, irregularities and rust spots that affect the sealing performance. The non-metallic strip on the surface of the spiral wound gasket should be evenly and appropriately raised beyond the metal strip. The texture between the layers should be clear, but the metal strip should not be exposed. The spacing of the solder joints of the spiral wound gasket should be uniform, and there should be no defects such as unfusion or over-melting. The surface of the reinforcing ring shall be free from defects such as burrs, irregularities, rust spots, etc. The spacing between the upper and lower sealing surfaces of the spiral wound gasket main body and the upper and lower surfaces of the reinforcing ring shall be equal. The inner side of the reinforcing ring and the gasket main body shall be tightly fixed and shall not be loosened; The ring and the spiral wound gasket body should be positioned and loosened properly. 4. Compression ratio, rebound rate and sealing performance are important performance indicators of the gasket. Generally speaking, under the premise of meeting the compression ratio requirements, the higher the rebound rate, the better; and meet the requirements of the rebound rate standard. Under the premise, the test value of the compression ratio is also larger. spiral wound gaskets with good sealing performance, moderate compression ratio and maximum resilience should be selected. Pay attention to the following points when installing spiral wound gaskets: 1. Carefully check the quality of flanges, bolts, nuts and gaskets before installation, carefully check the installation of flanges or interfaces, and have defects such as eccentricity, misalignment, opening, and wrong holes. 2. The surface of the flange or sealing part must be cleaned. The surface of the spiral wound gasket and the bolts and threads are not allowed to adhere to mechanical impurities. 3, spiral wound gasket can not be biased, should ensure uniform pressure. 4. When the nut is tightened, the applied force is uniform, and the bolt should be symmetrically evenly pided into 2 to 3 times to make the spiral wound gasket evenly pressed. Source: China Spiral Wound Gaskets Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is quenching medium? The medium used for quenching and cooling the workpiece is called quenching cooling medium (or quenching medium). The ideal quenching medium should have the condition that the workpiece can be quenched into martensite without causing too much quenching stress. This requires slow cooling above the “nose” of the C curve to reduce the thermal stress generated by rapid cooling; the cooling rate at the “nose” should be greater than the critical cooling rate to ensure that the undercooled austenite does not undergo non martensitic transformation; under the “nose”, especially when Ms points the temperature, the cooling rate should be as small as possible to reduce the stress of structural transformation. The common quenchants are water, aqueous solution, mineral oil, molten salt, molten alkali, etc. Water Water is a quenching medium with strong cooling capacity. It has a wide range of sources, low price, stable composition and is not easy to deteriorate. The disadvantage is that in the “nose” region of C curve (about 500-600 ℃), water is in the steam film stage, and if it is not cooled fast enough, it will form a “soft point”; in the martensite transformation temperature region (300-100 ℃), water is in boiling stage, and cooling is too fast, which will easily cause martensite transformation speed to be too fast and produce great internal stress, resulting in deformation and even cracking of the workpiece. When the water temperature rises, there are more gases in the water or insoluble impurities (such as oil, soap, mud, etc.) in the water, the cooling capacity will be significantly reduced. Therefore, water is suitable for quenching and cooling of carbon steel workpieces with small section size and simple shape. Saline and alkaline water After the high temperature workpiece is immersed in the cooling medium by adding appropriate amount of salt and alkali in the water, the crystals of salt and alkali precipitate in the steam film stage and burst immediately. The steam film is destroyed and the oxide skin on the surface of the workpiece is also blasted. In this way, the cooling capacity of the medium in the high temperature region can be improved. Its disadvantage is that the medium is corrosive. In general, the concentration of brine is 10% and that of caustic soda solution is 10% ～ 15%. It can be used as quenching medium for carbon steel and low alloy structural steel workpiece. The service temperature should not exceed 60 ℃. After quenching, it should be cleaned and antirust treated in time. Oil Mineral oil (mineral oil) is generally used as cooling medium. Such as oil, transformer oil and diesel oil. Generally, No. 10, No. 20 and No. 30 engine oils are used. The larger the oil number, the higher the viscosity, the higher the flash point, the lower the cooling capacity and the higher the service temperature. At present, there are three kinds of new quenching oil: high speed quenching oil, bright quenching oil and vacuum quenching oil. High speed quenching oil is a kind of quenching oil whose cooling rate is increased in high temperature region. There are two basic ways to obtain high-speed quenching oil. One is to select different types of mineral oil with different viscosity and mix them with appropriate ratio to improve the cooling capacity of high-temperature zone by increasing the characteristic temperature; the other is to add additives to ordinary quenching oil to form powdery ash like plankton in the oil. The additives are barium salt, sodium salt, calcium salt, phosphate, stearate, etc. The production practice shows that the cooling rate of high-speed quenching oil in the unstable region of undercooled austenite is obviously higher than that of ordinary quenching oil, while the cooling rate of high-speed quenching oil in low-temperature martensitic transformation zone is close to that of ordinary quenching oil. In this way, high hardenability and hardenability can be obtained, and deformation is greatly reduced. It is suitable for quenching alloy steel workpieces with complex shapes. Bright quenching oil can keep the bright surface of workpiece after quenching. Bright quenching oils with different cooling rates can be obtained by adding polymer additives with different properties into mineral oil. The main component of these additives is brightener, which is used to suspend aging products insoluble in oil and prevent accumulation and precipitation on the workpiece. In addition, the additives of bright quenching oil also contain antioxidants, surfactants and refrigerants. Vacuum quenching oil is a cooling medium for vacuum heat treatment and quenching. Vacuum quenching oil must have low saturated vapor pressure, high and stable cooling capacity, good brightness and thermal stability, otherwise the effect of vacuum heat treatment will be affected. Salt bath and alkali bath quenchants are generally used in step quenching and isothermal quenching. New quenchant There are polyvinyl alcohol aqueous solution and three nitrate aqueous solution. The co cooling capacity of polyvinyl alcohol (PVA) aqueous solution with mass fraction of 0.1% – 0.3% is between water and oil. When the workpiece is quenched into the solution, a layer of vapor film and a gel film are formed on the surface of the workpiece, and two layers of film are used to cool the heating workpiece. After entering the boiling stage, the film is broken and the workpiece cooling is accelerated. When the temperature reaches low, the PVA gel film is formed again, and the workpiece cooling rate decreases. Therefore, the solution has low cooling capacity in high and low temperature regions, high cooling capacity in the middle temperature zone and good cooling characteristics. The Trinitro nitrate aqueous solution is composed of 25% sodium nitrate + 20% sodium nitrite + 20% potassium nitrate + 35% water. At high temperature (650 ～ 500 ℃), due to the precipitation of salt crystals and the formation of steam film, the cooling capacity is close to that of water. At low temperature (300-200 ℃), because of its high concentration, poor fluidity and cooling capacity close to that of oil, it can replace water oil double medium quenching. Cooling method The most widely used quenching classification in production practice is based on different cooling methods. There are mainly single liquid quenching, double liquid quenching, step quenching and isothermal quenching. Single liquid quenching It is a quenching operation method that the austenitic chemical parts are immersed in a certain kind of quenching medium and cooled to room temperature. Single liquid quenching medium includes water, brine, alkali water, oil and specially prepared quenchant. In general, carbon steel is quenched and alloy steel is quenched with oil. The operation of single liquid quenching is simple, which is conducive to the realization of mechanization and automation. Its disadvantage is that the cooling rate is limited by the cooling characteristics of the medium, which affects the quenching quality. For carbon steel, single liquid quenching is only suitable for the workpiece with simple shape. Double liquid quenching It is to immerse the austenitic chemical parts into a medium with strong cooling capacity, take out the steel parts before reaching the quenching medium temperature, and immediately immerse them in another medium with weak cooling capacity for cooling, such as water before oil, water before air, etc. Double liquid quenching can reduce the tendency of deformation and cracking. The operation is not easy to master, so it has some limitations in application. Martensite step quenching It is a quenching process in which the austenitic chemical parts are immersed in the liquid medium (salt bath or alkali bath) with the temperature slightly higher or lower than the martensitic point of the steel for a proper time. After the inner and outer layers of the steel parts reach the medium temperature, they are taken out for air cooling to obtain the martensitic structure, which is also called graded quenching. The results show that the staged quenching can effectively reduce the phase transformation stress and thermal stress, and reduce the quenching deformation and cracking tendency because the staged temperature stays at the same internal and external temperature of the workpiece. Step quenching is suitable for alloy steel and high alloy steel workpieces with high deformation requirements, and can also be used for carbon steel workpieces with small section size and complex shape. Bainite austempering It is a quenching process, sometimes called austempering, in which steel parts are austenitized and rapidly cooled to the bainite transformation temperature range (260-400 ℃) and kept isothermal to transform austenite into bainite. The general holding time is 30-60min. Compound quenching The workpiece is quenched below MS to obtain 10% – 20% martensite, and then isothermal in the lower bainite temperature region. The results show that the M + B structure can be obtained by this cooling method. The martensite formed during pre quenching can promote bainite transformation and temper martensite at isothermal temperature. Compound quenching can avoid the first kind of temper brittleness and reduce the residual austenite volume, that is, the tendency of deformation and cracking. Special parts are also compressed air quenching, spray quenching and jet quenching. Source: China Pipe Fitting Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.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

Effect of titanium on Microstructure and heat treatment of steel ① Titanium has strong affinity with nitrogen, oxygen and carbon. It is a good deoxidizer and an effective element for fixing nitrogen and carbon. ② Titanium and carbon compounds (TIC) have strong binding force and high stability. Only when heated above 1000 ℃ can it slowly dissolve into the solid solution of iron. TiC particles can prevent the grain growth and coarsening of steel. ③ Titanium is one of the forming elements of strong ferrite, which makes the austenite phase area narrow. Solid solution titanium improves the hardenability of steel, while the presence of TiC particles reduces the hardenability of steel. ④ When titanium content reaches a certain value, precipitation hardening can be produced due to dispersion precipitation of tife2. Effect of titanium on mechanical properties of steel ① When titanium exists in ferrite as a solid solution, its strengthening effect is higher than that of aluminum, manganese, nickel, molybdenum, etc., and lower than that of beryllium, phosphorus, copper and silicon. ② The influence of titanium on the mechanical properties of steel depends on its morphology, the ratio of Ti to C and the heat treatment method. When the content of Ti is in the range of 0.03% ~ 0.1%, the yield strength can be increased, but when the ratio of Ti to C is more than 4, the strength and toughness of Ti decrease sharply. ③ Titanium can improve the endurance strength and creep resistance. ④ Titanium can improve the toughness of steel, especially the impact toughness at low temperature. Effect of titanium on physical, chemical and technological properties of steel ① Improve the stability of steel in high temperature, high pressure and hydrogen. ② Titanium can improve the corrosion resistance of stainless and acid resistant steel, especially the resistance to intergranular corrosion. ③ In low carbon steel, when the ratio of Ti to C is more than 4.5, because oxygen, nitrogen and carbon are all fixed, it has good stress corrosion resistance and alkali embrittlement resistance. ④ The oxidation resistance of the steel at high temperature can be improved by adding titanium to the steel with chromium content of 4% – 6%. ⑤ Titanium can promote the formation of nitriding layer and obtain the required surface hardness quickly. Titanium containing steel is called “fast nitriding steel” and can be used to make high-precision screws. ⑥ Improve the weldability of low carbon manganese steel and high alloy stainless sodium. Application of titanium in steel Titanium alloy aircraft turbine ① When the mass fraction of titanium exceeds 0.025%, it can be considered as alloy element. ② Titanium, as an alloy element, is widely used in common low alloy steel, alloy structural steel, alloy tool steel, high-speed tool steel, stainless and acid resistant steel, heat-resistant and non peeling steel, permanent magnet alloy and cast steel. ③ Titanium has been used as a variety of advanced materials and has become an important strategic material, accounting for more than half of the use in the aerospace industry, such as aerospace vehicles, power machinery, etc.

What is a flat welding flange? A flat welded flange is a type of flange that is joined to a vessel or pipe by a fillet weld. It is an arbitrary type of flange. According to the degree of integrity of the connection between the flange ring and the straight section, the design is checked according to the integral or loose flange. The flange ring is available in both neck and neck. Compared with the neck-welded flange, the flat-welded flange has a simple structure and is material-saving, but the joint is not as good as the neck-welded flange. Flat welded flanges are widely used in the connection of medium and low pressure vessels and pipes. Flat welding flange features: The flat welded flange not only saves space, reduces weight, but more importantly ensures that the joint is not leaked and has good sealing performance. The reduced size of the compact flange is due to the reduced diameter of the seal which will reduce the cross-section of the seal face. Second, the flange gasket has been replaced by a seal ring to ensure that the seal faces the sealing surface. In this way, only a small amount of pressure is required in order to press the cover tightly. As the required pressure is reduced, the size and required number of bolts can be reduced accordingly, so a new design that is small in size and light in weight (70% to 80% lighter than conventional flanges) is designed. product. Therefore, the flat welding flange type is a relatively high quality flange product, which reduces the quality and space and plays an important role in industrial use. Sealing of flat welding flange: The sealing problem of the flat welding flange has always been a hot issue related to the production cost or economic benefit of the enterprise, so the sealing principle of the flat welding flange has been improved and improved. However, the main design defect of the flat welding flange is that it can not be leak proof. This is a defect in design: the connection is dynamic and periodic loads, such as thermal expansion and fluctuating loads, will cause mutual movement of flange faces, affect the function of the flange, thus damage the integrity of the flange, and eventually lead to leakage. No product can be free of defects, but try to minimize the defects of the product, so the company improves the performance of the product as much as possible and plays the largest role in the production of flat welding flange. Sealing principle of flat welding flange: The two sealing faces of the bolt squeeze the flange gasket to form a seal, but this can also cause seal damage. In order to keep the seal, you have to maintain a large bolt force, in order to do this, you have to make the bolt larger. Larger bolts match larger nuts, which means larger bolt diameters are needed to create the conditions for tightening the nuts. However, the larger the bolt diameter, the flange will be bent, the only way is to increase the wall thickness of the flange part. The sealing problem of the flat welding flange has always been a hot issue related to the production cost or economic benefit of the enterprise, so the sealing principle of the flat welding flange has been improved and improved. However, the main design defect of the flat welding flange is that it can not be leak proof. This is a defect in design: the connection is dynamic and periodic loads, such as thermal expansion and fluctuating loads, will cause mutual movement of flange faces, affect the function of the flange, thus damage the integrity of the flange, and eventually lead to leakage. No product can be free of defects, but try to minimize the defects of the product, so the company improves the performance of the product as much as possible and plays the largest role in the production of flat welding flange. Features of flat welding flange: flat welding flange not only saves space and weight, but also ensures no leakage at the joint and good sealing performance. By reducing the seal diameter, the size of the compact flange is reduced, so the seal section is reduced. Secondly, replace the flange gasket with a sealing ring to ensure that the confidential cover matches the sealing surface. In this way, the sealing surface can be tightened with only a small amount of pressure. With the decrease of the required pressure, the size and quantity of the bolts are reduced accordingly. Therefore, a new product with small volume and light weight is designed, which can reduce the weight of the traditional flange by 70% ー 80%. Therefore, the plate welding flange is a relatively high-quality flange product, which reduces the quality and space, and plays an important role in the industrial application. The two sealing faces of the bolt squeeze the flange gasket to form a seal, but this can also cause seal damage. In order to keep the seal, you have to maintain a large bolt force, in order to do this, you have to make the bolt larger. Larger bolts match larger nuts, which means larger bolt diameters are needed to create the conditions for tightening the nuts. However, the larger the bolt diameter, the flange will be bent, the only way is to increase the wall thickness of the flange part. Common production process for flat welding flange Round forging process of round steel pure material; Finished forging and cutting forming process; Steel plate cutting and blanking processing technology; Rough forging, expansion machine thermal expansion production process; Steel plate rolling production process, generally for large diameter flanges, such as flanges above DN600; The above is the type of flange raw material production process, but high-precision CNC lathe turning, CNC rocker drilling, final flange forming, packaging workshop for flange printing stencil marking and packaging, the company quality inspection department to carry out inspection, The inspection report is issued and the final flange is taken out of the warehouse. Forging of flat welded flanges can be pided into free forging, upsetting, extrusion, die forging, closed die forging, and closed upsetting. Closed die forging and closed upset forging have high material utilization due to the absence of flash. Finishing of complex forgings is possible with one or several processes. Since there is no flash, the area of force applied to the forging is reduced and the required load is also reduced. However, care should be taken not to completely limit the blank. To this end, the volume of the blank is strictly controlled, the relative position of the forging die is controlled, and the forging is measured to reduce the wear of the forging die. According to the movement mode of the forging die, the flat welding flange can be pided into pendulum, pendulum swivel, roll forging, cross wedge rolling, boring ring and cross rolling. Swing, swivel and shackle can also be used for precision forging. In order to improve the utilization of materials, roll forging and cross rolling can be used as a front-end process for slender materials. The same rotary forging as free forging is also partially formed, which has the advantage that it can be formed in the case of a smaller forging force than the forging size. In this forging method including free forging, the material expands from the vicinity of the mold surface to the free surface during processing. Therefore, it is difficult to ensure the accuracy of the flat welding flange. Therefore, the moving direction of the forging die and the swaging process are controlled by a computer. flat welding flanges can be used to obtain products with complex shapes and high precision with low forging force. Flat welding flange connection application The smooth flat welding flange is the most widely used. The flat welded steel flange is suitable for the nominal pressure not exceeding 2.5MPa. The carbon steel pipe connection. The sealing surface of the flat welding flange can be made smooth. It is more suitable for medium conditions. In the case, such as low-pressure non-purified compressed air and low-pressure circulating water, the advantage is that the price is relatively cheap. The structure is reasonable, and the welded steel flange is used for the opposite welding of the flange and the pipe. The strength and rigidity are large, and the high temperature can withstand. High pressure and repeated bending and temperature fluctuations, reliable sealing. Nominal pressure is 0.25 2.5MPa. The butt welding flange adopts concave and convex sealing surface. The flat welding flange gasket is placed between the two flange sealing surfaces. After tightening the nut, the specific pressure on the surface of the gasket reaches a certain value and then deforms, and fills the unevenness on the sealing surface, so that the joint is tight. A flanged joint is a detachable joint. There are holes in the flange, bolts can be worn to make the two flanges tightly connected, and the flanges are sealed with gaskets. According to the connected parts, it can be pided into container flange and pipe flange. flat welding flanges are often used when the medium temperature and pressure are not high and the medium is corrosive. When the medium is corrosive. Rare integral flanges have flat and butt weld flanges. Flange fittings are flanged (flange or splicing) fittings. It can be cast, and the flat welded flange is mainly a part that connects the pipe and the pipe to each other. According to the structure type. It can also be constructed by screwing or welding. Flange joints consist of a pair of flanges, a gasket and a number of bolts and nuts. Source: China Flat Welding Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Recently contacted with a batch of long cylinder workpieces (see Fig. 1). During the acceptance of finished products, cracks were found on the surface of inner holes of four products. One of the most typical samples was cut and analyzed, as shown in Fig. 2 and Fig. 3. Fig.1 Long barrel workpiece Figure.2 Sectioning Fig.3 Cracks and sampling positions found by MT after sectioning Physical and chemical test and results Chemical composition The chemical composition of H1 sample was detected by direct reading spectrometer, and the results are shown in Table 1. Table.1 results of spectral chemical composition analysis of H1 sample (mass fraction) (%) Element C Si Mn P S Cr Mo Ni Cu Standard EN10083-3 0.38～0.45 ≤0.40 0.60～0.90 ≤0.025 ≤0.025 0.90～1.20 0.15～0.30 — — Actual measurement 0.40 0.22 0.74 0.010 — 1.14 0.225 0.13 0.03 Hardness Use Rockwell hardness tester to test the hardness value of H1 and B1 samples in the direction of wall thickness, and the results are shown in Table 2. Table.2 Hardness distribution in the direction of wall thickness of H1 and B1 samples (HRC) Hardness Sample 1 2 3 4 5 Average value H1 29.0 25.8 26.3 27.7 28.0 27.4 B1 30.3 30.6 28.7 29.1 23.6 28.5 Microstructure Grind and polish H1 specimen along n-PLANE and k-plane (see Fig. 4) (n-PLANE is the surface of inner hole, k-plane is the grinding and polishing surface along the direction of wall thickness), and observe in turn with microscope. The crack morphology of n-PLANE after polishing is as shown in Figure 5. Then, the polishing surface was eroded with 4% nitric acid alcohol solution, and the microstructure near the crack was observed, as shown in Fig. 6. The crack morphology and microstructure after erosion of surface k after polishing are shown in Fig. 7. Figure.4 Grinding and polishing of H1 sample Fig.5 Crack morphology (50x) after polishing the inner hole surface of H1 sample Fig.6 Microstructure near inner hole surface crack of H1 sample (500X) Figure.7 K-plane crack and microstructure of H1 specimen The B1 specimen (see Figure 8) was polished and eroded along the n-PLANE and the k-plane respectively (n is the inner hole surface, K is the polishing surface along the wall thickness direction), and the crack morphology and microstructure nearby were observed under the microscope. Fig.8 Grinding and polishing of B1 specimen along n-PLANE and k-plane respectively There are many cracks on the inner hole surface of B1 sample. Under the microscope, its morphology is shown in Figure 9. Then, 4% nitric acid alcohol was used for erosion, and the microstructure near the surface crack of the inner hole was observed, as shown in Figure 10. Figure.9 N-PLANE crack morphology of B1 sample (50x) Fig.10 Microstructure near n-PLANE crack of B1 sample After polishing in the direction of wall thickness of B1 sample, the crack morphology is as shown in Figure 11. Figure.11 N-PLANE crack morphology of B1 sample After etching the k-plane with 4% nitric acid alcohol solution, observe the microstructure near the crack, as shown in FIG. 12. Fig.12 Microstructure near k-plane crack of B1 sample Result analysis From the above analysis results, it can be seen that the chemical composition of the raw material used for this part meets the requirements of 42CrMo4 in en 10083-3, and no element exceeding the standard is found. According to the hardness test results of the cut-off test block, there is no obvious gradient change in the hardness of the pipe sleeve along the thickness direction, which indicates that the workpiece has been hardened thoroughly and tempered fully during quenching. According to the actual heat treatment process of the pipe sleeve, the actual heat treatment process curve is shown in Figure 13, and no abnormality is found in the production process. Fig.13 Quenching and tempering curve of pipe sleeve From the crack morphology observed after grinding, the crack tip on the inner hole surface and wall thickness direction of sample H1 and sample B1 is relatively sharp, and its propagation path is transgranular, which is a typical quenching crack. According to the microstructure after erosion, the microstructures near the cracks of the two samples are tempered sorbite, no massive ferrite and long strip ferrite are found, and no obvious oxide decarburization layer is found on both sides of the cracks. This shows that the cracks are formed in the process of heat treatment. In fact, for the finished long tube parts, the wall thickness is 40mm (thin wall end) and 52mm (thick wall end), respectively. In general, the inner hole is relatively long, the inner diameter is small and the wall thickness belongs to 42CrMo4 steel, which can be fully quenched, and the structure stress is relatively large during quenching. At the same time, for the deep hole parts with small inner diameter, because the cooling speed of the inner surface is much smaller than that of the outer surface and the effect of residual thermal stress is small, the tensile stress on the inner surface is larger than that on the outer surface, and it is easy to form longitudinal cracks on the inner surface, or even multiple parallel cracks (see Figure 14). Figure.14 Distribution and crack of quenching residual stress of deep hole parts Conclusion and preventive measures (1) Through the body sampling analysis, it can be seen that the pipe sleeve crack belongs to a typical quenching crack, which is caused by the excessive internal stress of the workpiece during quenching, especially the excessive tensile stress on the surface of the inner hole. (2) In order to avoid this kind of cracks, measures can be taken to reduce quenching temperature, increase the speed and efficiency of quenching medium flowing along the inner hole, and increase the final cooling temperature, so as to reduce quenching stress and avoid workpiece cracking. Source: China Pipe Sleeve Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)