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In the rolling of seamless steel pipe, especially in the production process of seamless steel pipe, how does the pickling process go on, today it will open this mysterious veil for you immediately! Summary of seamless steel pipe pickling The method of removing oxide scale and rust from steel surface by acid solution is called acid pickling. Iron oxides (Fe3O4, Fe2O3, FeO, etc.), such as oxide scales and rust, react with acid solutions to form salts dissolved in acid solutions and are removed. Sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid and mixed acid are used for acid pickling. The common medium for pickling of seamless steel pipe: Sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid. Acid pickling inhibitor must be added in acid pickling to prevent acid from corroding metal. Seamless steel pipe pickling process The main methods are pickling acid washing, spraying acid washing and acid ointment removing. In general, impregnation acid washing is widely used, and injection method can be used in mass production. Iron and steel parts are usually pickled in 10% to 20% (volume) sulfuric acid solution at a temperature of 40 degrees Celsius. When the iron content in solution exceeds 80g/L and ferrous sulfate exceeds 215g/L, acid pickling fluid should be replaced. At room temperature, 20% ~ 80% (volume) of hydrochloric acid is used to pickle steel, which is not easy to cause corrosion and hydrogen embrittlement. Because of the corrosive effect of acids on metals, corrosion inhibitors are needed. After cleaning, the surface of the metal is silver white, and the surface is passivated to improve the corrosion resistance of the stainless steel. In order to eliminate the adsorption on the surface of diatomite support and reduce the tailing of chromatographic peaks, the carrier should be pickled or washed before being used. Pickling is to carry the carrier with 6mol/L hydrochloric acid to boil 2H or concentrated hydrochloric acid to heat to dip and boil 30min, filtering, washing with water to neutral, drying. Pickling can remove impurities such as Fe, Al, Ca and Mg on the surface, but can not remove silanol. Acid pickling carrier is suitable for the analysis of acid samples. The effect of pickling of seamless steel pipe The surface of seamless steel pipe is degreasing and rust removing, so as to prepare for the next process. In the process of production, the process of acid pickling is to remove the surface oxide skin, after the lubrication treatment (carbon steel – phosphorus saponification, stainless steel – calf lime, copper aluminum tube – oiling), the old process – copper plating), and then drawing deep processing. If the steel pipe is not pickled and the surface may contain oxide and oil, the phosphating solution can not remove nuclear energy and the quality of phosphating will be reduced. Source: China Seamless Steel Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1 Application of Stainless Steel in Petroleum and Petrochemicals The most commonly used classification of stainless steel is classified according to the structure of the steel and can generally be pided into ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, duplex stainless steel, and precipitation hardened stainless steel. In petroleum and petrochemical applications, austenite stainless steel, ferritic stainless steel, and duplex stainless steel account for a large proportion. Ferritic stainless steel generally has a Cr content of between 13% and 30% and a C content of less than 0.25%. In general, ferritic stainless steels have lower corrosion resistance than austenitic stainless steels and duplex steels, but are higher than martensitic stainless steels. However, due to its lower production cost compared to other stainless steels, it has a wide range of applications in the areas of chemical and petrochemical applications where corrosion resistance and strength requirements are not high. Martensitic stainless steel generally has a Cr content of between 13% and 17%, and a high C content of between 0.1% and 0.7%. It has higher strength, hardness and wear resistance, but lower corrosion resistance. It is mainly used in petroleum and petrochemical fields in environments where corrosive medium is not strong, such as components requiring higher toughness and impact loads, such as turbine blades, bolts, and other related parts. Austenitic stainless steels have Cr contents between 17% and 20%, Ni contents between 8% and 16%, C contents generally below 0.12%, and the austenite transformation area is mainly expanded by the addition of Ni elements, thus at room temperature. Under the austenite structure. Austenitic stainless steels are superior to other stainless steels in terms of corrosion resistance, plasticity, toughness, processability, weldability, and low temperature performance. Therefore, their application in various fields is the most extensive. Their use accounts for approximately all stainless steels. About 70% of the volume. In the petroleum and petrochemical field, austenitic stainless steels have a greater advantage for strong corrosive media and low temperature media. Duplex stainless steel is developed on the basis of single-phase stainless steel. Its Ni content is generally about half that of austenitic stainless steel, which reduces the cost of the alloy. Austenitic stainless steel has excellent corrosion resistance and high overall performance. It solves the shortcomings of poor corrosion resistance of ferritic and martensitic stainless steels and insufficient strength and wear resistance of austenitic stainless steels. In the petroleum and petrochemical field, it is mainly used in offshore oil platforms that are resistant to seawater corrosion, acidic components and equipment, and particularly in components that are resistant to pitting corrosion. Precipitated-strengthened stainless steels mainly obtain high-strength properties through precipitation strengthening mechanism. At the same time, they sacrifice their own corrosion resistance. Therefore, they are used less in corrosive media and are generally used in petrochemical machinery mining and other industries. 2 Application of Stainless Steel Pipe in Petroleum and Petrochemicals In the past 20 years, both stainless steel pipes and welding pipes have been greatly improved in terms of production technology. Stainless steel pipes produced by some domestic manufacturers have reached the level that can completely replace imported products, and have achieved localization of steel pipes. In petroleum and petrochemical industries, stainless steel pipes are mainly used in pipeline transportation systems, including high-pressure furnace pipes, piping, petroleum cracking pipes, fluid transportation pipes, and heat exchange pipes. Requires stainless steel to perform well under wet and sour service conditions. 2.1 The application of stainless steel seamless pipe with large diameter thick wall high pressure hydrogen In order to meet the requirements for processing low-quality crude oil and meeting environmental protection requirements, domestic refining companies continue to optimize the processing structure of the refinery equipment and adjust the product structure. High-pressure hydrogenation units such as hydrocracking and hydrotreating have developed rapidly in recent years, and the processing capacity of the equipment has been improved. It is also constantly improving. Hydrogen pipelines are characterized by a large diameter and a thick wall. For the selection of high-pressure hydrogen-imparting materials, TP321/H, TP347/H, etc. are generally used at home and abroad as the material for high-pressure hydrogen-infiltrating pipes because of their high-temperature and high-pressure working conditions. Both stainless steel materials are stable due to the addition of Ti, Nb, etc. Chemical elements have high temperature corrosion resistance and high temperature mechanical properties. At present, domestic large-caliber thick-walled hydrogen-producing pipelines are mainly produced by hot perforation + cold rolling/cold drawing. The hot-perforated + cold-rolled/cold-drawing tubes are superior to the steel tubes produced by other methods in that they have a good surface, high dimensional accuracy, and uniform wall structure. For high-pressure hydrogen-free steel pipes, due to the special nature of the working medium, the requirements for the steel pipe raw materials are relatively high. Therefore, the design requirements for the high-pressure hydrogen-producing pipes are: S ≤ 0.015%, P ≤ 0.030%, Non-metallic inclusions A Classes B, C, and D are not higher than 1.5. Ultrasonic inspection is required for the finished tube, and the artificial contrast defect is not more than 5% of the nominal wall thickness of the tube. 2.2 Application of Stainless Steel Welded Pipe for Low Temperature LNG Due to the development of society, people’s awareness of environmental protection has increased and more and more attention has been paid to clean energy. LNG is a clean and efficient energy source and plays an important role in the production and life of the people. Therefore, LNG receiving stations and LNG carriers have mushroomed. LNG is to cool gaseous natural gas to -162°C under normal pressure and condense it into a liquid. Therefore, the pipeline for LNG transportation must have high low temperature performance. For low-temperature LNG conveying pipes, ultra-pure, low-carbon, low-sulfur, and low-phosphor stainless steels are mostly used at home and abroad. In recent years, the dual-grade stainless steels are very popular among LNG users, among which TP304/304L, TP316/316L and other applications are particularly extensive. Double-certified steel not only has L-level corrosion resistance and low-temperature properties, but also has high mechanical properties. At present, domestic and foreign mainstream welding stainless steel tubes for low temperature LNG are generally processed by using automatic unit welding forming process, UOE forming process, and JCO forming process. The automatic welding unit is a fast, efficient and automatic welding pipe production method used in the case of not thick wall thickness. At present, most of the rollers are used to form the plate, and then the welding and heat treatment are performed online. Some welding units also Integrated advanced technology such as on-board ultrasonics for plates, on-line weld ultrasonics, and automatic weld seam tracking technology can provide high-efficiency manufacturing operations for LNG long-distance pipeline manufacturing and reduce the production deadlines of manufacturers. UOE molding technology is currently the most widely used, most mature, and most recognized quality of a low-temperature LNG welded pipe production process, the main process technology has been established. The JCO molding process is a fresh molding process in recent years. This molding technology is an organic combination of step-wise pre-bending and pipe NC bending. For the LNG stainless steel welded pipe, because its use environment is in a low temperature environment of -162°C, it is necessary for the LNG tube to have a high low temperature impact performance. At present, most design institutes, research institutes, and manufacturers require LNG tubes to have low-temperature impact performance of not less than 80 J, and lateral expansion volumes of not less than 0.38 mm according to ASME B 31.3. For stainless steel welded pipes, as the weak link of the pipe, the quality of the weld directly affects the safety of the pipeline and even the pipeline. The welding coefficient is one of the important factors for evaluating the quality of the weld. For low temperature LNG welded pipes, the welding coefficient is Ej = 1.0 and the welded joint must be a full penetration welded joint. After welding joints are completed, all welds must undergo 100% ray inspection. The welds must have no defects such as incomplete penetration, no weld inclusion, no undercut, and no cracks to ensure the stability of welded joints at low temperatures. 3 Outlook Petroleum pipelines are the bulk of consumption of stainless steel pipes. Stainless steel pipes play an important role in equipment manufacturing, oil recovery, oil refining, and transportation in the oil industry. In recent years, the state has increased the development of petroleum resources. At the same time, as the world’s largest net oil importing country, as the rigid oil demand increases, the oil-related industries will further develop, and the demand for stainless steel pipelines will continue to increase. increase. In 2018, the Chinese steel industry has shown signs of recovery. Domestic stainless steel pipe leading companies have increased their cooperation with relevant oil pipelines between PetroChina and Sinopec to increase market share. At the same time, domestic steel pipe enterprises have also started activities with foreign oil companies to push China’s stainless steel pipe manufacturing to the world platform. Source: China Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Structural detailed solution of shell and tube heat exchanger The shell-and-tube heat exchangers mainly include structural types such as fixed tube-plate heat exchangers, floating-head heat exchangers, U-tube heat exchangers, and packing-type floating-head heat exchangers. The structure of the fixed-tube heat exchanger is simple. The low manufacturing cost can obtain a smaller shell inner diameter. The tube process can be pided into multiple types. The shell process can also be pided into multiple passes by longitudinal partitions. The advantages such as wide range of specifications are widely used in the project. Today, we took everyone together to take the structure of the fixed tube-plate heat exchanger as an example to understand the structure of the shell-and-tube heat exchanger. Fixed tube heat exchanger. Structure diagram of fixed tube plate heat exchanger Tube box Pipe box structure The common pipe box structure can be roughly pided into the following categories, as shown above. A-type pipe box can be used for single pipe and multiple pipe runs. The advantage is that it is easy to clean the tube of the heat exchanger; the disadvantage is that there are many materials for the pipe cover structure. When the size is large, it needs forgings, so it is recommended that the A-type tube box Suitable for DN ≤ 900mm. B-type pipe box is used for single pipe and multiple pipe, the advantage is that the structure is simple, easy to manufacture; the disadvantage is that when the inspection and cleaning tube heat exchange tube, the pipe flange on the pipe and the equipment flange need to be disassembled And remove the overall tube box. C-type pipe box The pipe box is the return pipe box of a multi-tube heat exchanger. D-type pipe box The pipe box is used for the inlet and outlet of a single-tube heat exchanger. The flat cover of the pipe box is an important part of the pipe box. Different flat covers can be selected according to the use, material cost, and convenience of cleaning. Pipe box flat cover structure as shown a) Figure 1 shows the overall structure of the tube box cover, mainly used when the tube box is carbon steel or low alloy steel material. Figure 1 Tube cover of the overall structure b) Figure 2 shows the lid of the composite structure for the case of stainless steel or corrosion-resistant alloys. Figure 2 Composite tank cap c) Figure 3 shows the lid of the tank cap welded with a lining plate, but it is not suitable for applications in a vacuum state. Fig. 3 Casing plug cap welding The effective thickness of the overall structure of the pipe box cover should be equal to the actual thickness of the pipe box cover minus the corrosion margin of the pipe box or the corrosion margin of the pipe box and the large value of the partition plate groove depth. For composite tank caps and liner tank caps, the composite or liner thickness is not included in the effective thickness. Tube sheet According to the connection structure between the tube sheet, the tube box and the shell, the tube sheet can be pided into: a) The extension part doubles as a fixed tube plate for the flange. b) Fixed tube plates that do not double as flanges and that are welded together with shell and tube barrels. As shown below: According to the use function (use) of the tube sheet, the tube sheet is pided into: a) Fixed tubesheets for fixed tubesheet heat exchangers; b) Fixed tube plates and floating tube plates of floating head heat exchangers; c) fixed tube plates of U-tube heat exchangers; d) Double tube sheet heat exchanger double tube plate; e) Thin tube sheet. Wave expansion joint In the fixed tube plate heat exchanger, in order to avoid the tensile failure of the shell and the heat exchange tube, the heat exchange tube is unstable, and the heat exchange tube is pulled off from the tube plate. Therefore, a flexible compensating element must be provided in the middle of the housing. – Expansion joints to reduce the axial load of the shell and the heat transfer tubes, and to reduce the stress of the tube sheet caused by the difference in thermal expansion, thereby appropriately thinning the thickness of the tube sheet. Type of expansion joint for heat exchanger There are many types of expansion joints. According to the cross-sectional shape, there are U-shaped, Ω-shaped, and S-shaped. In the fixed tube-plate heat exchanger, the U-shaped wave expansion joint is the most common and most common. U-shaped expansion joints are mainly composed of two parts: a corrugated tube and a straight edge section. If necessary, liners may be provided to reinforce the ring, as shown in the figure: Expansion joints for heat exchangers can also be pided into single-layer and multi-layer expansion joints. a) For fixed tube sheet heat exchangers, under the premise of ensuring the bearing capacity required by the design and compensating stiffness and fatigue life, single-layer wave expansion joints should be preferred. b) In the following cases, multi-layer waveform expansion joints can be used 1) Must withstand higher pressures and require greater displacement compensation capability; 2) requirements to withstand higher fatigue life; The features of the multi-layered waveform expansion joint structure are as follows: 1) Good flexibility and high compensation capability; 2) Fatigue life is higher than single-layer structure (foreign data is 6 times that of single layer); 3) Compact structure, saving material; 4) In the case of high pressure, it will not burst suddenly and it is not easy to be dangerous. Heat exchange tube The heat exchange tube is the core part of the heat exchanger. Different diameters, shapes, and arrangements of heat exchange tubes will affect the efficiency of the heat exchanger. Pipe diameter The recommended lengths of the heat transfer tubes are 1.5, 2.0, 2.5, 3.0, 4.5, 6.0, 7.5, 9.0, 12.0m. Common specifications of heat exchange tubes are shown in Table 1 below Table 1 Common specifications of heat exchange tubes Shape U-shaped heat exchange tube The bend radius R (as shown in the figure below) of the U-tube bend section shall not be less than twice the outer diameter of the heat exchange tube. The minimum bend radius R min of the commonly used heat exchange tube shall be selected according to Table 2. Table 2 Minimum bending radius of heat exchange tubes Heat exchange tube outer diameter 10 14 19 25 32 38 45 57 R   min 20 30 40 50 65 76 90 115 When the flow rate in the U-shaped tube is too high or there is corrosion, the wall thickness of the U-shaped tube with a small radius of the curved tube should be appropriately thickened. Heat exchange tube arrangement The heat exchanger tube standard arrangement form sees a) Triangle arrangement The triangular arrangement (including the arrangement of the regular triangles and the arrangement of the corner triangles) is the most common form of arrangement, particularly in fixed tube-plate heat exchangers where the shell-side medium is relatively clean and the heat exchange tubes do not need to be cleaned. b) Square arrangement The square arrangement is generally used in floating head heat exchangers and U-tube heat exchangers that need to be cleaned outside the heat exchange tubes. c) Arrangement of regular triangles and squares of corners (see figs. a and d). It is called staggered on heat transfer, and turbulence can be formed when the medium flows, which is beneficial to heat transfer. The corner triangles and square arrays (see Figures b, c) are called in-line in terms of heat transfer. When the medium flows, part of it is laminar, which has an adverse effect on heat transfer. Therefore, for heat exchangers with no phase transition, there is a large relationship between heat transfer and the flow state of the medium. Therefore, it is better to use a regular triangle or a corner square arrangement. For the condenser with phase change, because the relationship between the heat transfer and the flow of the medium is small, and only the relationship of the direction of the condensate flow in the pipe wall is relatively large, generally a corner triangle and a square arrangement can be used. Shell structure Common typical shell side components are shown in Table 3. Table 3 Common typical shell side components Baffle The role of baffles a) Increase the flow rate of the medium between the shell side tubes to improve the heat transfer effect. b) Support the heat exchange tubes. c) Adjust the baffle spacing to play a role in avoiding tube bundle induced vibration. Baffle shape The commonly used baffle plates and support plates have two types of bow-shaped and disk-annular shapes. In addition, there are other types of baffles and supporting plates as required, such as rectangular hole circular plates and rectangular baffles, as shown in the figure: a) Single bow baffle (figure a): is the most commonly used form. Its form is simple, but the pressure drop is large. 1) Arranged up and down (horizontal incision) means that the material inlet and arcuate notch are vertically arranged to cause severe disturbance of the medium to increase the heat transfer coefficient. 2) Arranged in the right and left (vertical gap) means that the material inlet and the arcuate gap are arranged in parallel. Mostly used for horizontal condensers or evaporators to facilitate the flow of condensate and gases. 3) The corner arrangement is generally used for the square arrangement of the heat exchange tubes, which can form turbulence in the fluid to improve the heat transfer efficiency. b) Double bow (figure b) and three bowed baffles (figure c): This applies to flows with a relatively large shell-side flow, or when the shell-side fluid is a low density, low pressure drop. The decrease in the heat transfer coefficient is much smaller; at the same time, this form is also conducive to preventing the vibration induced during the flow of the medium. c) Disc – Circular annular baffle (Fig. d): The disc is arranged in a staggered arrangement with the ring. The media flow characteristics are symmetrical to the axis. d) Rectangular baffles (figure e): The rectangular baffles can be placed horizontally or vertically, while the horizontal flow is generally used when the shell-side medium is in the gas phase, and the vertical flow is used for the shell-side medium in the liquid phase or with condensation. Liquid occasions. These two forms are usually used in large diameter and large flow conditions. Pull rod and distance tube The baffle plate and the support plate are generally fixed by tie rods or tie rods and distance tubes and tube plates. There are two commonly used fixed structures, namely the distance between the rod and the spot welding structure, as shown in the figure: a) Tie rod distance tube structure, used for tube bundles with an outside diameter of the heat exchange tube greater than or equal to 19mm. b) Rod and baffle spot welding structures for tube bundles with outer diameters less than or equal to 14mm. 1 Rod size The tie rod connection dimensions are as shown in the figure and Table 4. Table 4 Tie rod size 2 Rod arrangement Pull rods should be arranged as evenly as possible on the outer edge of the tube bundle. For large diameter heat exchangers, a suitable number of tie rods should be placed in or near the baffle notch. Double shell structure In the shell, a rectangular flat plate parallel to the axis of the heat exchange tube is installed, that is, a longitudinal partition, and the shell process is pided into two, that is, the double shell process, as shown in the figure. This structure can increase the flow rate of the shell material and improve the heat transfer effect, that is, increase the heat transfer coefficient. From the economic point of view, a double-shell heat exchanger is cheaper than two single-tube heat exchangers. Today we mainly introduced the fixed tube-plate heat exchangers in shell-and-tube heat exchangers. Because many of the heat transfer parts and components are common, some of the parts and components that we do today are not very detailed, and we hope that users will work together to improve them. More parts structure. Source: China Heat Exchanger Tubes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

What is penetrant testing (PT)? Penetrant Testing (PT), also called Liquid Penetrant Inspection (LPI) or Dye Penetrant Inspection (DPI), is one of the oldest and simplists NDT methods where its earliest versions (using kerosene and oil mixture) dates back to the 19th century. NDT methods can generally be classified into two categories: conventional and advanced. Each method has its own characteristic advantages and limitations. More information on each test can be found in their respective Integripedia definitions. The oil and whiting method used in the railroad industry in the early 1900s was the first recognized use of the principles of penetrants to detect cracks. The oil and whiting method used an oil solvent for cleaning followed by the application of a whiting or chalk coating, which absorbed oil from the cracks revealing their locations. Soon a dye was added to the liquid. By the 1940s, fluorescent or visible dye was added to the oil used to penetrate test objects. Experience showed that temperature and soak time were important. This started the practice of written instructions to provide standard, uniform results. The use of written procedures has evolved, giving the ability for design engineers and manufacturers to get the high standard results from any properly trained and certified liquid penetrant testing technician. Liquid penetrant inspection is used to detect any surface-connected discontinuities such as cracks from fatigue, quenching, and grinding, as well as fractures, porosity, incomplete fusion, and flaws in joints. Principles DPI is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed, a developer is applied. The developer helps to draw penetrant out of the flaw where an invisible indication becomes visible to the inspector. Inspection is performed under ultraviolet or white light, depending upon the type of dye used – fluorescent or nonfluorescent (visible). Materials Penetrants are classified into sensitivity levels. Visible penetrants are typically red in color, and represent the lowest sensitivity. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Since Fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to defects. When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surface finish of the specimen, and the size of defects sought. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradation. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some lint free cloths, and adequate visible light. Stationary systems with dedicated application, wash, and development stations, are more costly and complicated, but result in better sensitivity and higher samples through-put. Inspection steps PRE-CLEANING: The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may “work over” small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment. APPLICATION OF PENETRANT: The penetrant is then applied to the surface of the item being tested. The penetrant is allowed “dwell time” to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant. EXCESS PENETRANT REMOVAL: The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering your ability to do a proper inspection. APPLICATION OF DEVELOPER: After excess penetrant has been removed a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water soluble. Choice of developer is governed by penetrant compatibility (one can’t use water-soluble or suspendable developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface. The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience. INSPECTION: The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after 10 to 30 minute development time, depends of product kind. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws. POST CLEANING: The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled. Advantages and Disadvantages The primary advantages and disadvantages when compared to other NDT methods are: ADVANTAGES High sensitivity (small discontinuities can be detected). Few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and conductive and nonconductive materials may be inspected). Rapid inspection of large areas and volumes. Suitable for parts with complex shapes. Indications are produced directly on the surface of the part and constitute a visual representation of the flaw. Portable (materials are available in aerosol spray cans) Low cost (materials and associated equipment are relatively inexpensive) DISADVANTAGES Only surface breaking defects can be detected. Only materials with a relatively nonporous surface can be inspected. Pre-cleaning is critical since contaminants can mask defects. Metal smearing from machining, grinding, and grit or vapor blasting must be removed. The inspector must have direct access to the surface being inspected. Surface finish and roughness can affect inspection sensitivity. Multiple process operations must be performed and controlled. Post cleaning of acceptable parts or materials is required. Chemical handling and proper disposal is required. Standards INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) ISO 3452-1, Non-destructive testing – Penetrant testing – Part 1. General principles ISO 3452-2, Non-destructive testing – Penetrant testing – Part 2: Testing of penetrant materials ISO 3452-3, Non-destructive testing – Penetrant testing – Part 3: Reference test blocks ISO 3452-4, Non-destructive testing – Penetrant testing – Part 4: Equipment ISO 3452-5, Non-destructive testing – Penetrant testing – Part 5: Penetrant testing at temperatures higher than 50°C ISO 3452-6, Non-destructive testing – Penetrant testing – Part 6: Penetrant testing at temperatures lower than 10°C ISO 3059, Non-destructive testing – Penetrant testing and magnetic particle testing – Viewing conditions ISO 12706, Non-destructive testing – Penetrant testing – Vocabulary ISO 23277, Non-destructive testing of welds – Penetrant testing of welds – Acceptance levels EUROPEAN COMMITTEE FOR STANDARDIZATION (CEN) EN 1371-1, Founding – Liquid penetrant inspection – Part 1: Sand, gravity die and low pressure die castings EN 1371-2, Founding – Liquid penetrant inspection – Part 2: Investment castings EN 10228-2, Non-destructive testing of steel forgings – Part 2: Penetrant testing EN 10246-11, Non-destructive testing of steel tubes – Part 11: Liquid penetrant testing of seamless and welded steel tubes for the detection of surface imperfections AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM) ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry ASTM E 1417, Standard Practice for Liquid Penetrant Testing AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) ASME Boiler and Pressure Vessel Code, Section V, Art. 6, Liquid Penetrant Examination ASME Boiler and Pressure Vessel Code, Section V, Art. 24 Standard Test Method for Liquid Penetrant Examination SE-165 (identical with ASTM E-165)

In the process of smelting or hot processing, the internal or surface defects of steel are caused by some factors (such as non-metallic inclusions, gas and process of improper operation, etc.), which seriously affect the quality of the material or product, and sometimes it will cause material or product to be scrapped. The porosity, bubble, shrinkage residual, non-metallic inclusions, segregation, white spots, cracks and various abnormal fracture defects of the steel can be found by macro test. The macroscopic inspection method consists of two methods: acid leaching test and fracture inspection. The common macro defects shown by acid leaching are summarized below. Segregation Cause of formation During the solidification process, some elements are aggregated due to the selection of crystallization and diffusion, resulting in uneven chemical composition. According to the different locations of distribution, they can be pided into ingot shape, center and dot segregation. Macro characteristics In the acid leaching sample, when the segregation is an erosive material or gas inclusion, it is dark dark, irregular in shape, slightly concave, flat at the bottom and a lot of dense microporous spots. If the elements are gathered for corrosion resistance, they are slightly colored, irregular and smooth. Loose Cause of formation In the course of solidification, the steel can not be welded in the hot working process due to the final solidification and contraction of the low melting point material and the voids generated by the gas emission. According to its distribution, it can be pided into two categories: Center and general loose. Macro characteristics On the transverse hot acid soaking surface, the pores are irregular polygons and dimples at the bottom, which usually occur in segregation spots. In serious cases, there is a tendency to be spongy. Inclusion Cause of formation (1) foreign metal inclusion During casting, metal strips, blocks and sheets fall into the ingot mold or the iron alloy added at the end of smelting is not melted. Macro characteristics On the etched sheet, there are many distinct shapes with distinct edges and different colors. Cause of formation (2) Foreign non-metallic inclusions During casting, there is no time to come out of the slag or the refractory material that is spalling into the lining of the molten steel and the inner wall of the pouring system. Macro characteristics The larger non-metallic inclusions are well identified, while smaller inclusions are spalling after corrosion, leaving tiny circular pores. Cause of formation (3) The semi solidified film on the surface of the bottom ingot is embedded in the molten steel. Macro characteristics On the acid leaching samples, the color is different from the surrounding area, and the irregular curved narrow strip is surrounded by oxide inclusions and pores. Shrinkage hole Cause of formation When the ingot or casting is poured, the liquid in the core can not be replenished due to the volume contraction at the last condensing, and the macro hole is formed in the ingot head or casting. Macro characteristics On the transverse acid leaching sample, the shrinkage cavity is located at the central part, which is often surrounded by segregation, inclusion or loose density. Sometimes holes or gaps can be seen before etching. After etching, the holes become darker and appear irregular wrinkled holes. Bubble Cause of formation Defects caused by gas generated and released during ingot casting. Macro characteristics On the transverse specimen, there are cracks that are approximately perpendicular to the surface and slightly oxidizing and decarburization nearby. Beneath the surface there is a hypodermic bubble, and a deep subcutaneous bubble is called pinhole. During the forging process, the pores which are not oxidized and not welded are extended into thin tubes, and the cross sections are isolated small pinholes. The cross section is similar to the punctate segregation of the arrangement, but the deeper color is the inner honeycomb bubble. White spot Cause of formation It is generally believed that hydrogen and tissue stress play an important role in the segregation and inclusion of steel. Macro characteristics In the transverse hot acid leaching sample, there is a fine short crack. On the vertical fracture surface, it is a coarse crystalline silver white spot. Crack Cause of formation Axial intergranular cracks: when the dendrites are serious, large cracks occur along the main stem and branch of the twigs. Internal crack: cracking due to improper forging process. Macro characteristics On the cross section, the axis position is intergranular crack, which appears spider net, and radially dehiscence is serious. Fold Cause of formation The surface of the steel or ingot is uneven and the edge angle of the tip. It is superimposed on the steel during the forging and rolling, or the ears are produced due to the improper design or operation of the pass. Macro characteristics On the transverse hot acid leaching sample, there is a diagonal crack on the surface of the steel, and there is more serious decarburization near it. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Burr is found in metal casting, milling or electroplating process. The surface of metal pipe fittings are fine or tiny metal particles. The appearance of burrs will greatly reduce the quality standard of metal pipe fittings, so we should try to prevent them or try to remove burrs. There are ten simple ways to deburr. Artificial deburring The operator uses tools such as files, sandpaper, grinding head and so on to polish the workpiece and remove the burr. This method is not very high in technical requirements for workers, with small burrs and simple product structure, so it is also a common method to remove burrs in general enterprises. The file is pided into two kinds: artificial file and pneumatic file. The cost of artificial file is more expensive, the burr efficiency is not very high, and it is difficult to remove complex cross holes. Die deburring The burrs are removed by making punch and punch press. It is necessary to make rough die and fine blanking for stamping burrs, and it may be necessary to make plastic moulds. For the simpler products, the efficiency and effect of burr removal are better than manual methods. Grind and deburring Grinding deburring is a way to remove burrs by means of vibration, sand blasting and roller. It is widely used by enterprises. The problem of grinding burrs is that sometimes removal is not very clean, and may require subsequent manual processing or other way to burr. This method is suitable for large quantities of small pieces. Frozen deburring This is the way to make burr quickly embrittlement and plunge projectile to remove burrs by sudden drop in temperature. Frozen deburring is suitable for products with smaller burr wall thickness and smaller workpiece. The price of the whole set of equipment is not low, about RMB 2.3 million yuan. Hot detonating deburring Hot detonating deburring is also known as heat energy deburring, explosion deburring, this is some easy gas, into a equipment furnace, and then through a number of media and conditions, the gas exploded in a flash, using the energy produced by the explosion to dissolve the burr removal method. The equipment required by this method is expensive, and it usually reaches more than RMB million yuan, and the requirements for operation technology are also very high. The efficiency of removing burrs is low, and it also causes rust, deformation and other side effects. Thermal explosion burr removal is mainly used in some high precision parts and components, such as automotive and aerospace precision parts. Engraving machine deburring With the engraving machine to remove the burr on the workpiece, the equipment is not very expensive, usually only tens of thousands of yuan, suitable for the removal of simple space structure, simple and regular burr position. Chemical deburring Chemical deburring is the process of automatically and selectively removing burrs from parts made of metal materials by means of electrochemical reaction. It is suitable for internal burrs which are difficult to remove, especially suitable for removing small burrs on pump body and valve body. Electrolysis deburring The method of removing burrs from metal pipe fittings by electrolysis. This method has some side effects, because the electrolyte is corrosive, and the burr is also affected by electrolysis. The surface will lose its gloss and even affect the dimensional accuracy. Therefore, after deburring, the workpiece should be cleaned and rust treated. This method is suitable for the removal of burrs of the cross hole or complex parts of the parts. The production efficiency is high, and the operation only takes only a few seconds to dozens of seconds in one operation. It is suitable for removing burrs, such as gear, connecting rod, valve body and crankshaft oil hole, and so on. High pressure water jet deburring This is the way to remove burrs and flashes by using the instantaneous impact force of water, and at the same time, achieve the purpose of cleaning. This set of equipment is expensive, mainly used in the car’s heart part and the hydraulic control system of construction machinery. Ultrasonic deburring The propagation of ultrasonic waves can also produce instantaneous high pressure, which can be used to remove burrs on parts. This method is of high precision and is mainly used to remove some microscopic burrs which can only be observed by microscope. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

First, the concept of surface roughness Surface roughness refers to the roughness of the machined surface with small spacing and small peak valley. The distance between the two peaks or two wave valleys is very small (below 1mm), and it belongs to the microscopic geometric error. It refers to the S level of Z. Generally according to S: S < 1mm is surface roughness; 1 < S < < 10mm > waviness; S > 10mm is the shape of F. VDI3400, Ra, Rmax control table VDI3400 Ra（μm） Rmax（μm） 0 0.1 0.4 6 0.2 0.8 12 0.4 1.5 15 0.56 2.4 18 0.8 3.3 21 1.12 4.7 24 1.6 6.5 27 2.2 10.5 30 3.2 12.5 33 4.5 17.5 36 6.3 24 Three. Formation factors of surface roughness The surface roughness is usually formed by the processing methods and other factors, such as the friction between the tool and the surface of the parts during the processing, the plastic deformation of the surface metal when the chip separation is separated, and the high frequency vibration in the process system and the discharge pits of the electric machining. Because of the difference between processing methods and workpiece materials, the depth, density, shape and texture of the machined surface are different. Four. The influence of surface roughness on parts is mainly manifested. It affects wear resistance. The coarser the surface is, the smaller the effective contact area is, the greater the pressure, the greater the friction resistance, and the faster the wear. It affects the stability of the coordination. For the gap coordination, the roughness of the surface, the more easy to wear and the increase of the middle gap in the working process; for the interference fit, the actual effective interference is reduced and the connection strength is reduced because of the extrusion of the micro convex peak in the assembly. It affects the fatigue strength. The surface of rough parts has large trough, which is very sensitive to stress concentration, such as sharp notches and cracks, which affects the fatigue strength of parts. It affects corrosion resistance. The surface of rough parts can cause corrosive gas or liquid to penetrate into the inner layer of metal through the surface concave Valley, causing surface corrosion. Influence the seal. The rough surface can not be tightly adhered, and the gas or liquid leaks through the gap between the contact surfaces. Influence the contact stiffness. Contact stiffness is the ability of the joint surface to resist contact deformation under external force. The stiffness of a machine depends largely on the contact stiffness between the parts. It affects the accuracy of measurement. The surface roughness of the measured surface of the parts and the measuring tools will directly affect the accuracy of the measurement, especially when the precision is measured. In addition, surface roughness has varying degrees of influence on the coating, thermal conductivity and contact resistance, reflection and radiation, resistance of liquid and gas flow, and flow of current on the surface of the conductor. Five. The basis for evaluating the surface roughness 1. Sampling length The length of sampling is the length of a reference line for evaluating the surface roughness. According to the formation and texture features of the actual surface of the parts, the length of the section which can reflect the surface roughness should be selected and the length of the sample should be taken according to the general direction of the actual surface profile. The length of sampling is specified and selected to limit and weaken the effect of surface waviness and shape error on the measurement results of surface roughness. 2. Evaluation length The length of assessment is a length necessary to evaluate the contour, which can include one or several sampling lengths. Because the surface roughness of the parts of the parts is not very uniform, it is often not reasonable to reflect the characteristics of a surface roughness on a sampling length, so several sampling lengths need to be taken on the surface to evaluate the surface roughness. The evaluation length generally contains 5 sampling lengths. 3. Datum line The datum line is the contour line used to evaluate the surface roughness parameters. There are two kinds of datum lines: the least square middle line of the Outline: within the sampling length, the square of the contour of the contour of each point on the contour is the smallest, and has the shape of the geometric contour. The arithmetic mean midline of a contour: the length of the upper and lower sides of the middle line is equal in the sampling length. In theory, the least square middle line is an ideal datum line, but it is difficult to obtain in practical application, so it is usually replaced by the arithmetic mean line of the contour and can be replaced by a straight line with an approximate position in the measurement. Six. Evaluation parameters of surface roughness 1. Height characteristic parameters Ra arithmetic mean deviation: the arithmetic mean of the absolute value of the contour offset in the sampling length (LR). In actual measurement, the more the number of measuring points, the more accurate Ra is. The maximum height of the Rz contour: the distance between the contour peak line and the valley bottom line. Ra is preferred in the range of amplitude parameters. In the national standard before 2006, one of the evaluation parameters was the “ten point height of micro unevenness”, which was expressed by Rz. The maximum height of the contour was expressed by Ry. The ten point height of the micro unevenness was cancelled in the national standard after 2006, and the maximum height of the contour was expressed by Rz.

The surface of stainless steel pipe fitting is not uniform. When heat treatment is heated, it is necessary to make the oxide skin evenly. To reach the first, the quality of the surface of the stainless steel pipe fitting is mainly determined by the acid washing process after heat treatment. This article focuses on the relationship between surface quality and heat treatment of stainless steel pipe fitting. I If the surface of the pipe fitting is attached to oil when heated, the thickness of the oxide scale and the thickness and composition of the oxide scale of the oil attachment part will be different and produce carburizing. The oxidized carburized part of the matrix metal will be severely eroded by acid. The oil droplets ejected from the heavy oil burner when burning first, if attached to the pipe fitting fittings, will also have a great influence. The fingerprints of the operator will also be affected when they are attached to the pipe fitting fittings. So, do not touch the stainless steel directly by hand, do not touch the tube on the surface of the new oil pipe fitting, such as the lubricating oil that is attached to cold processing. It must be cleaned with warm water after the degreasing agent, caustic sodium solution is fully defatted, and then the heat is then carried out. II If there is any debris on the surface of the pipe fitting, and when it is not organic or ash attached to the pipe fitting, heating will certainly affect the oxide scale. III Gas or oil flame directly contacts the stainless steel surface and does not touch the place produced by the oxide scale is different. Therefore, when heating, the processing parts must not be directly exposed to the flame port. IV If there is a residual oxide skin in the part of the processing part before heat treatment, the remaining parts of the oxide skin and the part without the oxide skin after heating, the thickness and the difference in the composition of the oxide skin will appear, and the surface is not uniform after the acid washing, so the final heat treatment should be paid attention to, but also the intermediate heat treatment and the acid washing should be paid attention to. V If the surface finish is different, if the surface finish is different, even if the same heat is applied, the surface roughness and fine oxide scale are different. For example, the condition of forming oxide scale is different in the place where the partial defects are cleared and uncleaned, resulting in uneven surface of the pipe fitting after pickling. VI The difference of the atmosphere in the furnace is different from that in the furnace. The formation of the oxide scale will also change. This is also the reason why the acid washing is uneven. Therefore, when heating, the atmosphere in all parts of the furnace must be the same. So it is necessary to consider the cycle of the atmosphere. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. How to classify the defects and quality of finished steel pipes? Defects and quality problems of finished steel pipes are checked according to their inspection methods. 1) the chemical composition found in chemical analysis is not qualified. 2) the physical properties, mechanical properties, process properties and metallographic structure of the test found that the performance and organization failed; 3) size, shape and surface defects detected by size measurement and surface inspection. If the section size is too poor, the shape is not right, the length of the steel pipe is very poor, and other surface defects. The surface defects here refer to the surface defects caused by rolling process. This kind of defect has different characteristics in different products. The surface defects can be pided into the reasons for their production. 1) the surface defects caused by smelting and ingots are left on the steel pipes because of the unclean surface of the billet. 2) surface defects caused by rolling process are mostly produced on the surface of steel pipes. Such as straightening crack, internal crack and so on. 2. What steel pipe defects can be found in fracture inspection? Fracture inspection is one of the methods to determine the quality of steel pipe. The fracture specimen can check the defect of the steel pipe with the transverse macrostructure. The fracture can directly show the defects such as white spots, inclusions, bubbles, internal cracks and shrinkage holes in tapping. By identifying the size and characteristics of the grain on the fracture surface, the overheating or overheating of the steel pipe can be determined. The fracture characteristics of the steel pipe (ductile fracture and brittle fracture) can be determined and the fracture cause of the steel pipe (part) can be judged, such as fatigue fracture and stress fracture. The fracture types are: ductile fracture, brittle fracture, porcelain fracture, lamellar fracture, (coating) fracture, stone fracture and graphite fracture. In the course of use, broken zero, parts and broken pieces of pieces caused by some reason in the production and manufacturing process, as well as the fracture of test sample for tensile force and force, no longer need any preparation processing, can be directly observed and tested. Direct observation on these natural surfaces can obtain direct capital. Material. According to the variety of steel pipe and the different inspection requirements, the fracture test specimen should be heat treated in different ways before breaking. According to the different heat treatment methods, the fracture can be pided into annealing fracture and quenching and tempering fracture. 3. What are the contents of the finished product size and shape inspection of the steel pipe? The inspection contents of the size and shape of the steel pipe are as follows: 1 check whether the section size of the steel pipe exceeds the deviation specified in the corresponding standard (including the withdrawal of square steel and the roundness of round steel). 2 check whether the length of the steel pipe meets the delivery length stipulated by the corresponding standard. 3 check whether the shape of the steel pipe has obvious bending (sickle or wave bending). 4 measure the bending degree and total bending degree of the steel pipe. 5 what is the size super difference? What is the unequal thickness of the thick and thin? What is the wrong shape? The tolerance of dimension is the allowable deviation of the size of the workpiece. These include the upper limit and the lower limit of the specified size. The uneven thickness is the phenomenon that the thickness of the steel pipe is different from each other on the cross section and longitudinal section. The uneven thickness of the steel pipe is called the uneven thickness of the wall. In fact, the thickness of a piece can not be equal everywhere. In order to control this inhomogeneity, some standards specify the three point difference of the section, the same plate difference, and the standard of the steel pipe, which stipulate the allowable range of uneven wall thickness. The geometric shape of the cross section of the rolled material is not positive. This kind of defect is varied according to the variety of the rolled material, such as square steel, flat steel, six angle steel and six sides. In a broad sense, bending, twisting, breaking waves and lacking meat are all wrong in shape. 4. What is the degree of roundness? What is the nominal size and the actual size? What is the tolerance? Circular cross section rolling materials such as round steel and round steel pipe appear on the same section; two different diameters are called roundness. The degree of roundness is expressed by the difference between the maximum and minimum diameters on the same section. Nominal size refers to the nominal size specified in the standard, which is the desired size desired in the production process. The actual size obtained in production is called actual size, and the actual size of the steel pipe is usually larger than or smaller than the nominal size. Because the actual size of the steel pipe is hard to reach the nominal size, the standard stipulates that there is a allowable difference between the actual size and the nominal size, which is called tolerance. Negative difference is called negative bias, positive value is called positive deviation. 5. What is the delivery length? The delivery length of steel pipes is as follows: 1. Usually the length is also called the indefinite length. Where the length of the steel pipe is within the standard limits and has no fixed length, it is called the normal length. For example, the usual length of high quality steel is 2-6mm. 2. The length of the length of the length of the fixed length is fixed to the fixed length according to the order. For example, the fixed length of rail is 12.5mm and 25mm. The length of the fixed length steel pipe also permits the positive deviation of the length. 3. The length of the length of the steel pipe is cut into the integral multiple equal to the order length. If the length is 1000mm, the double ruler is 2000mm, and the three cup ruler is 3000mm. The same standard or technical condition should also provide positive deviation and cutting allowance for double length. 4. The length of a short ruler is shorter than that of the standard, but not less than the minimum allowable length. In addition, the length of the gauge is the development of the normal length, requiring the same length of the steel pipe in each bundle, allowing a certain deviation. China’s export steel pipes are mostly delivered on the same length. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. how can the heat exchange equipment be classified? Answer: can be pided into: (1) tube shell heat exchanger (2) casing heat exchanger (3) water immersion heat exchanger (4) spray heat exchanger (5) rotary (snake tube) heat exchanger (6) plate heat exchanger (7) plate fin heat exchanger (8) tube fin heat exchanger (9) heat exchanger tubes (10) other 2. how does the heat exchanger heat the heat? Answer: in the most common wall type heat exchangers, there are mainly two ways of conduction and convection. The heat transfer is first passed to one side of the tube wall by convection heat transfer, then the heat passes through the side of the tube wall through the way of conduction, and the heat transfer is passed to the cold fluid on the other side of the tube wall, and the heat transfer process of the heat exchanger is completed. 3. medium velocity on the heat transfer effect? Answer: the greater the velocity of the medium in the heat exchanger, the greater the heat transfer coefficient. Therefore, increasing the velocity of the medium in the heat exchanger can greatly improve the heat transfer effect, but the negative effect of increasing the flow rate is to increase the pressure drop through the heat exchanger and increase the energy consumption of the pump, so it is necessary to have a certain suitable range. 4. how does the surface structure of the heat exchanger affect the heat transfer effect? Answer: the special design of heat transfer tube surface structure, such as fin tube, nail head tube, thread tube and so on, on the one hand increase the heat transfer area, on the other hand, the disturbance of the special surface greatly increases the turbulence level of the fluid outside the tube, which can increase the overall heat transfer effect of the heat exchanger in two aspects, so these surface structures are better than light. The performance of the tube surface is excellent. 5. what are the usual ways to remove fouling on the surface of heat exchanger tubes? Answer: the common methods of descaling on the surface of heat exchange tube are: Mechanical descaling: manual cleaning of steel drill and scaling of pressure water Chemical descaling 6. are there any methods for anti scaling on the surface of the heat exchange tube? Answer: (1) nickel phosphorus plating (2) chemical coating, 847 coating 7. what are the commonly used methods to enhance heat transfer in heat exchangers? Answer: the main method of heat transfer enhancement in heat exchange equipment One is to use the structure of increasing the heat transfer surface, such as 1 use finned tube, nail head pipe, screwed pipe, bellows and so on. 2 the surface of the pipe is machined: spiral pipe, spiral grooved tube, screwed pipe, etc. 3 small tube diameter can increase the number of tubes on the same tube plate area and increase the heat transfer area. The two is to increase the flow rate of fluid in the heat exchanger, which can greatly improve its heat transfer coefficient, such as: 1 adding spoiler, such as inserting spiral belt in the tube, setting baffle outside the tube, false pipe, etc. 2 increase the number of tube or shell process. In addition, the use of materials with good thermal conductivity to make heat exchangers, good heat and corrosion prevention measures, and timely scaling are all means to improve the heat transfer effect. 8. what is the requirement for the number of pipe plugging when the tubular heat exchanger is overhauled? Answer: the tube holes are allowed to be blocked by a metal plunger with a conical degree of 3~5 degrees. Generally speaking, the number of tubes that are blocked in the same pipe range will not exceed 10% of the total number of pipes, but can be appropriately increased according to the technological requirements. 9. why does the gasket on both sides of the tubesheet have to choose the same material? Answer: because the flange bolts on both sides of the tubesheet are the same bolts, the specific pressure applied to the gaskets on both sides of the tubesheet is the same. If the gaskets on both sides of the two sides choose different materials, it will cause the sealing failure of one side gasket not enough and the sealing failure of the gasket on the other side is too large, so the gasket on both sides of the tube must choose the same material. Why does the 10. cooling water heat exchanger produce scale? Answer: the scale is formed by the crystallization of dissolved salts in the water and attached to the wall of the heat exchanger tube. Its characteristics are dense and hard, firmly attached and difficult to remove. A large number of suspended particles in water can become crystal species. Other impurity ions, bacteria and rough metal surface all have a strong catalytic effect on the crystallization process, which greatly reduces the supersaturation required by the crystallization. Therefore, the cooling water heat exchanger is very easy to produce scale. What are the main components of the 11. float heat exchanger? Answer: the main components are: tube bundle, baffle plate, drawing bar, fixed distance pipe, shell, tube box, tube plate, inlet flange, outlet flange, floating head flange, float head cover, float head hook ring, float head gasket, outer cover flange, outer lid flanges, outer cover, outer lid gasket, exigents, draining mouth Pipe box flange, pipe box side flange, pipe box gasket, pipe box side gasket, fixed saddle, movable saddle. 12. what are the main components of the fixed tube sheet heat exchanger? Answer: the main components are: tube bundle, baffle plate, pull rod, fixed distance pipe, shell, tube box (top cover), tube plate, inlet flange, outlet flange, pipe box flange, tube box gasket, fixed saddle, active saddle, ear type support, expansion joint. What are the main components of the 13.U tube heat exchanger? Answer: the main components are: U tube bundle, baffle plate, punching plate (inner guide tube), pull rod, fixed distance pipe, shell, tube box, tube plate, inlet flange, outlet flange, pipe box flange, tube box flanges, tube box gasket, tube box side gasket, fixed saddle, moving saddle. What are the main components of the 14. casing heat exchanger? Answer: the main components of the sleeve type heat exchanger are: inner tube, outer pipe and back elbow. 15. what are the main components of a water immersion heat exchanger? Answer: the main components of the water flooding heat exchanger are: inlet pipe, outlet pipe, collecting pipe, snake pipe and cooling water tank. What are the main components of the 16. spray heat exchanger? Answer: the main components of the spray heat exchanger are: tube bundle, fan, water nozzle, drainage pipe, feed water pump. What are the main components of the 16. spray heat exchanger? Answer: the main components of the spray heat exchanger are: tube bundle, fan, water nozzle, drain pipe and feed water pump. 17. what are the characteristics of fixed tube sheet heat exchangers, U tube heat exchangers and floating head heat exchangers? Answer: the characteristics of the fixed tube plate heat exchanger are compact, simple, low cost, the largest number of tubes in the same shell diameter, convenient maintenance of the single tube, convenient cleaning in the tube, but difficult to clean out of tube, and the high stress of tube and shell body temperature. The U type tube heat exchanger is characterized by its simple structure, no temperature difference stress problem, high flow velocity, low metal consumption and high temperature and high pressure fluid. The tube bundle can be easily removed to clean the shell and pipe, but the elbow is not easy to sweep, the tube number is few, the tube spacing is large, the tube center has gap, and the fluid outside the tube is easily short circuited. . The float head type heat exchanger is characterized by the free movement of the tube bundles, no temperature difference stress problem, the free extraction of the tube bundles, the convenience of cleaning the pipe and the tube bundle, but the structure of the float head is complex, the cost is high, the sealing requirement of the float head is more strict, the float head is easy to leak and is not easy to check and find in operation. 18. where are the fixed tube sheet heat exchangers applicable? Answer: fixed tube sheet heat exchangers are suitable for occasions where shell side medium is clean, it is not easy to scale, and medium temperature difference is relatively small. Where is the 19.U type tube heat exchanger? Answer: U type tubular heat exchangers are suitable for high temperature and high pressure applications in the tubes. 20. where do the float heat exchangers apply? Answer: floating head heat exchangers are suitable for occasions where the temperature difference between the shell and tube is large, the medium is not clean and needs frequent cleaning. 21. the arrangement of tubular heat exchangers is arranged in triangle and square to 45 degrees. Why? Answer: triangle arrangement and square rotation to 45 degree angle have their advantages and disadvantages. The advantages of triangle arrangement are compact and high heat transfer efficiency. The number of pipe rows on the same tube plate area is the most, which is about 15% more than square arrangement, but it is not easy to clean the outer surface of the tube, while the square to 45 degree angle is more convenient to arrange the surface of the tube, but the number of pipe row is much less than that of the triangle row. 22. what are the materials commonly used in tubular heat exchangers? Answer: materials commonly used for pipes are: 10#, 20#, 12CrMo, 15CrMo, 0Cr13, 1Cr13, 1Cr5Mo, 0Cr18Ni9Ti, 1Cr18Ni9Ti, titanium tube, 410321, etc. 23. in tube heat exchangers, why are diameters of 32, 25, 19 and 16? Answer: the size of the pipe will directly affect the performance of the heat exchanger. The diameter of the tube is small, the heat transfer coefficient is large, and the effective heat transfer area is large in the same volume. This can not only make the structure compact, but also save the material. The smaller the diameter of the fluid with the same flow rate, the smaller the diameter, the greater the resistance to the flow and the increase of the pressure loss. In addition, the thin tubes are also easily blocked by the dirt, making the cleaning difficult, so the diameter of the heat exchanger is usually 16 mm to 32 mm. 24. why does the bolt hole of the heat exchanger support have circular and long circular ones? Answer: the bolt hole on the fixed support is circular, so that the shell can be firmly fastened to the foundation. The bolt holes on the movable support are long and round, the purpose is to make the shell free and telescopic when the temperature changes, and avoid the large stress to protect the equipment. 25. what are the commonly used heat exchanger gaskets? Answer: commonly used heat exchanger gaskets are oil resistant asbestos mats, iron pads, wave tooth mats, metal mats. 26. what should we pay attention to when choosing the bolts for floating heads of floating head heat exchangers? (1) length (2) wet H2S stress corrosion (3) temperature 27. what is the function of baffles (baffles) in tubular heat exchangers? Answer: the baffle (baffle) in the heat exchanger can change the flow direction of the fluid in the shell, increase the flow velocity in the shell, increase the turbulence level of the medium, improve the heat transfer efficiency and support the function of the tube bundle. 28. why does tube heat exchanger have single tube, two tube, four tube, six tube, eight pipe? Answer: when the number of heat exchangers is at the same time, increasing the number of tubes can increase the flow rate in each pipe, so it can increase the heat coefficient and reduce the required heat transfer area. But at the same time, the pressure drop is also increased, and the fluid can not be completely reheated by countercurrent, and the heat exchanger structure is more complicated. Therefore, the general number of pipe runs should be no less than 2, not greater than 8, and should be chosen according to the actual process requirements. 29. what are the causes of leakage in tubular heat exchangers? Answer: there may be the following reasons for the leakage in the heat exchanger: Corrosion perforation, or fracture of heat transfer tube Leakage of pipe mouth cause leakage Loosening of heat transfer tube and tube plate expansion joint Cracks, holes or corrosion holes on the weld of heat exchanger tubes and tubesheet. Loosening or breaking of small float bolt Small float gasket damage Seal damage of small float or floating tube plate 30. why should the water pressure be tried after the heat exchanger is overhauled? Answer: the purpose of the test water pressure of the heat exchanger is to check whether the heat exchanger has the ability to withstand the design pressure (i. e. pressure strength), tightness, the quality of the interface or joint, the quality of the welding and the tightness of the sealing structure. In addition, the residual deformation of the welding seam of the parent material and the pipe after pressure can be observed, and the problems existing in the material can be found in time. 31. what are the installation positions of tubular heat exchangers, some of them are upright, and others are horizontal (horizontal)? Answer: the tubular heat exchangers are set up and some are lying, mainly from the following aspects: (1) the production process requirements: if some reboiler needs a certain height of the medium liquid level, if the displacement heater is used, that is, the height of the liquid level can not be reached, so the selection of the replacement heat exchanger must be selected; 2. A process unit needs thousands of square meters of heat exchange area. If a heat exchanger with a heat pipe length of 6 meters is selected, a number of heat exchangers may be needed. It occupies a large area and is not conducive to the space effective arrangement of the device. If a vertical replacement heat exchanger with a length of 12 meters of heat transfer tube is selected, 1 sets can solve the problem; 3. Reduce the pressure drop: some students reduce the pressure drop. The production process is required to minimize the pressure drop in the medium transport process, select the vertical displacement heat exchanger and arrange it together with the tower, so that it can shorten the connection line with the tower and reduce the pressure drop. 32. why do some places choose casing heat exchangers and water immersed heat exchangers, while others use tubular heat exchangers? Answer: at present, most of the heat exchanger selected for oil refining and chemical production equipment are tubular heat exchangers, but in some production devices, there are still a small amount of casing heat exchangers and water immersed heat exchangers. Although tubular heat exchanger has compact structure and high heat exchange efficiency, it is easy to cause blockage if it is used in medium containing solid particles due to its smaller heat exchanger tubes. Therefore, in the medium containing solid particles, the casing heat exchanger or the water immersion heat exchanger is usually selected. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

GH536 alloy is a kind of nickel based superalloy with high iron content, which is mainly reinforced by solid solution of chromium and molybdenum. It is suitable for the manufacture of aeroengine flame tube, combustor component and other high temperature components. The alloy pipe made of GH536 alloy is mainly used for the fuel main pipe or sub fuel pipe of the aero engine. The specification of a batch of alloy pipes is 8.3mm 2.3mm, which is qualified by the reexamination of the alloy pipe. The intergranular corrosion is qualified, and the grain size is 8 to 7.5, which meets the standard requirements. However, it was found that the white ring appeared on the outer wall of the alloy tube. The researchers sampled and analyzed the alloy tubes that found white circles. At the lower multiple, there was a white layer on the edge of the tube. The enlargement observation revealed that the outer wall of the tube was less precipitated than the matrix, and the outer wall grain was larger than the matrix grain. Compared with the qualified pipe material, it is found that the alloy tube with “white ring” has fine grain, and the small precipitation phase is more than that of the qualified tube, and the large precipitation phase is equivalent to that of the qualified pipe. The tubes were heat treated at three, 1130, 1150 and 1190 degrees respectively for 12min and water cooling. It is found that the higher the solid solution temperature is, the less the precipitation phase is. The grain size did not grow significantly at 1150, and the grain grew obviously at 1190. It can be seen from the microstructure analysis that there are a small amount of precipitated phases and grain boundaries in the “white circle” organization, but compared with the qualified pipe structure, it is a normal organization. That is to say, the matrix structure is abnormal, which shows fine grains and precipitates, and the outer wall of the reverse alloy tube appears white ring. The essence of the “white ring” is the nonuniformity of the tube wall. The standard heat treatment system for GH536 alloy pipes is 1130~1170 C, fast cooling, and holding time is less than 30min. The alloy pipes were treated by solid solution at 1130 degree x 10min, and the tube billets were rolled by multiple passes, once each rolling, solid solution once, and the accumulated deformation was larger. The higher the heating temperature is, the larger the grain size is. When the heating temperature is constant, the longer the holding time will make the grain grow. The lower limit of the standard heat treatment system is adopted for the alloy pipes. The holding time is 10min, which is not solid enough for the 2.3mm thick wall, so the grain is finer. At relatively low solid solution temperature, there are more precipitates in the tube billet. The final deformation process of the tube is cold dial, and the cold drawing allowance is usually certain, that is to say, the deformation of the outer wall of the alloy tube is not very different from that of the qualified alloy tube, then the problem is the tube blank. The heat preservation time of producing 1.0mm thick pipes is 10min. The thermal insulation time of the alloy tube producing 2.3mm is still 10min, which will lead to the uneven heating of the thick alloy tubes and the inadequately solid solution in the internal structure, which is also one of the reasons for the uneven microstructure of the alloy tubes. It is considered that the phenomenon of “white ring” of alloy tube is caused by the low temperature of solid solution and the short holding time during the rolling process, which is caused by the uneven structure of the matrix and the outer wall. On the basis of the constant rolling path and the reasonable deformation amount, the solid solution temperature is adjusted to 1150 degrees C, the heat preservation time is 20min, and the tube structure has been improved, and no “white ring” phenomenon appears. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Metal fatigue is commonly used to describe the accidental failure of metal parts in the course of using. Metal fatigue is directly related to the number of stress cycles and stress levels exerted on parts. The research shows that if the local stress in the part is kept below the well-defined limit, the infinite life of the metal component is possible. Fatigue failure will increase if parts are stressed, or parts with stress concentration such as notches, holes and keyways. There is also a relationship between the ultimate tensile strength and hardness of metals. The higher the tensile strength and hardness, the higher the wave load of the metal component, the easier fatigue. Typical fatigue fracture The general explanation for the fatigue mechanism of metals is based on dislocation theory. Theoretically, atomic arrangements in metallic crystals are imperfect and contain many missing atoms. The missing atoms create gaps, resulting in a great deal of stress. When the metal is loaded, the stress rising gap is cut and aggregated through the grain. When sufficient atomic interspaces are clustered together, micro cracks occur. If the load is increased, the initial crack opens. If the load fluctuates from the minimum value to the maximum near the limit of the metal load, the new micro crack expands from the position of the first micro crack. Each crack becomes the stress lift of the next crack. Continue to develop until the remaining metal is no longer bearing the load, and it suddenly fails.