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The steel strip or steel plate selected for the stainless steel welded pipe is first considered for its thickness. Use reasonable and correct thickness to ensure and meet the basic requirements of the product. The thickness of the selected steel strip or sheet is determined by the minimum allowable wall thickness of the stainless steel welded pipe, but it must also consider the factors affecting the wall thickness of the stainless steel welded pipe during the production process, such as forming, welding, weld grinding, etc. It is possible to make the thickness of the stainless steel welded pipe thinner. Therefore, the determination of the thickness of the material used for stainless steel welded pipe should consider the following various factors: Standard for the production of stainless steel welded pipes Nominal (standard) size (diameter × wall thickness) of stainless steel welded pipe; Stainless steel welded pipe wall thickness tolerance; The thickness tolerance level of the steel strip; Stainless steel welded pipe weld grinding margin; Safety factors. The strip thickness obtained from the above factors is: T=t-k%t+∮+0.04+0.05 Where t: standard wall thickness of stainless steel welded pipe K%: wall thickness tolerance (maximum k value is 10%) ∮: for steel strip thickness tolerance Grinding allowance: 0.04mm Safety factor margin: 0.05mm Example: Stainless steel welded pipe standard size: 51 × 2.0mm Standard for the production of stainless steel welded pipes: GB/T12770 Stainless steel welded pipe wall thickness tolerance: 10% t 2.00×10%=0.2mm Steel strip thickness tolerance level: +0.14mm Safety factor margin: +0.05mm Welded pipe weld grinding allowance: +0.04mm Minimum thickness of steel strip: 2.03mm (2.0 positive tolerance) The calculation of the width of the stainless steel welded pipe is a very complicated problem, because in the production process of the stainless steel welded pipe, the factors affecting its outer shape are many, the change is large, and the law is difficult to grasp, and these are related to the width of the material used. The dimensions of the stainless steel welded pipe are closely related to the material of the selected stainless steel, mechanical properties, material thickness, elongation of the material, forming method of the welded pipe production process and welding method. In this way, in calculating the width of the stainless steel welded pipe, the above factors must be considered. The width of the stainless steel welded pipe shall be calculated from the required diameter and the pre-calculated wall thickness of the welded pipe, together with the influencing factors mentioned above. The most basic size is to give the theoretical width of the material. The theoretical width is the average diameter remaining in π, that is: π × (OD-t); where OD is the standard outer diameter of the stainless steel welded pipe, and t is the wall thickness of the stainless steel welded pipe, as shown in the following figure: L=π(OD-t)+14%t+0.5√ ̄OD Where the theoretical width: π (OD-t) Welding allowance: 14%t Sizing allowance: 0.5√ ̄OD L: width of stainless steel welded pipe t: steel strip thickness (mm) OD: Standard outer diameter (mm) of stainless steel welded pipe Source: China Welded Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The weld of the welded elbow must be inspected, which is also an important measure to ensure the quality of the weld. After the completion of the elbow welding, the weld joint shall be inspected according to the technical requirements of the product. Any defects that do not meet the technical requirements shall be repaired in time (such as direct disposal that cannot be repaired if it is seriously unqualified). Common inspections of welding quality include visual inspection, non-destructive testing and mechanical performance testing. These three are complementary to each other, and they are mainly based on non-destructive testing. 1. Visual inspection: generally based on the naked eye observation, sometimes with a 5-20 times magnifying glass for observation. Through visual inspection, surface defects of weld elbow welds, such as undercuts, welds, surface cracks, pores, slag inclusions, and weld penetration, can be found. The dimensions of the weld can also be measured using a weld detector or template. 2. Non-destructive testing: Inspection of defects such as slag inclusions, pores and cracks hidden inside the weld. At present, the most common use is X-ray inspection, as well as ultrasonic flaw detection and magnetic flaw detection. The X-ray inspection uses X-rays to photograph the weld seam, and judges whether there are defects, the number and type of defects in the interior based on the image of the film. Then, according to the technical requirements of the product, the weld is qualified. The basic principle of ultrasonic flaw detection is shown in the figure below. The ultrasonic beam is emitted by the probe and transmitted to the metal. When the ultrasonic beam is transmitted to the metal-air interface, it is refracted and passed through the weld. If there is a defect in the weld, the ultrasonic beam is reflected to the probe and accepted, and a reflected wave appears on the screen. Based on the comparison and discrimination of these reflected waves with normal waves, the size and position of the defects can be determined. Ultrasonic flaw detection is much simpler than X-ray photography and is therefore widely used. However, ultrasonic flaw detection often can only be judged based on operational experience, and can not leave a test basis. For internal defects that are not deep from the surface of the weld and extremely small cracks on the surface, magnetic flaw detection can also be used. 3. Hydraulic test and air pressure test: For pressurized containers requiring sealing, hydraulic pressure test and/or air pressure test shall be carried out to check the sealing and pressure bearing capacity of the weld. The method is to inject 1.25-1.5 times working water or a working pressure gas (mostly air) into the container for a certain period of time, then observe the pressure drop in the container and observe whether there is leakage outside. According to these, it can be assessed whether the weld is qualified. 4. the mechanical performance test of the elbow: non-destructive testing can find the inherent defects of the weld, but can not explain the mechanical properties of the metal in the heat affected zone of the weld, so sometimes the welded joint should be subjected to tensile, impact, bending and other tests. These tests were performed by the test panels. The test panels used are preferably welded together with the longitudinal joints of the cylinder to ensure consistent construction conditions. The test panels were then tested for mechanical properties. In actual production, only welded joints of new steel grades are generally tested in this respect. Source: China Stainless Steel Elbows Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steel is a high-alloy steel material with a variety of alloying elements. According to the organization, stainless steel can be pided into a variety of types such as austenitic system, ferritic system, martensitic system, biphasic system and precipitation hardening system. Austenitic stainless steel is widely used in the market, commonly known as 304, 304 is a representative steel of austenitic stainless steel. Austenitic stainless steel is superior in processability, weldability and corrosion resistance, accounting for about 60% of the world’s stainless steel consumption. It has very economic value and use value. This stainless steel is magnetic. The representative steel of the austenitic stainless steel is SUS304 (18Cr-8Ni-0.05C). SUS304 is also the most widely used stainless steel. The crystal structure is FCC (face-centered cubic), and since the process-induced martensite is formed, the elongation is about 60%. (→Because of the material, you must have a set of martensitic stainless steel knife!) In the daily life environment, it has sufficient corrosion resistance, but in order to further improve the corrosion resistance, Mo is often added, and the biggest disadvantage is that stress corrosion cracking is relatively easy to occur. By increasing or decreasing the Ni content, it is possible to control the formation of martensite in the process, and it is also possible to use steel grades such as SUS301 (17Cr-7Ni) which have both high strength and high toughness. In order to suppress intergranular corrosion at the welded portion, the C content was reduced to about 0.02%, and an L type steel such as SUS304L or SUS316L was developed. In addition, in recent years, the price of Ni raw materials has risen and the cost has increased. Therefore, the development of the 200-series SUS201 (17Cr-4.5Ni-6.5Mn-0.2N) in which Ni is replaced with Mn and the resource-saving stainless steel such as the high corrosion-resistant iron system SUS have been developed. This 200 series is also austenitic stainless steel and is also non-magnetic. Another type of ferritic stainless steel is used. The representative ferritic stainless steel is SUS430 (16Cr-0.05C), which is a magnetic stainless steel, sometimes called “stainless iron”. Although magnetic, it does not mean rust. In order to improve corrosion resistance, workability and weldability, a plurality of steel grade ferritic stainless steels have been developed. This steel grade is basically free of Ni, so the price is relatively cheap, and it is widely used as ordinary stainless steel. Industrially produced stainless steel has a Cr content of 11% to 30%. SUS430 is a two-phase structure of α phase (ferrite phase) and γ phase (austenite phase) in the high temperature zone of the hot rolling process. In the cold rolling annealing process, heat treatment of α single phase region is performed, which is ferrite single phase. organization. It is also possible to pass high Cr and low C, high temperature gamma phase, and alpha single phase structure in the full temperature region. The crystal structure is BCC and the elongation is about 30%. The deep value of r is important. In order to improve the workability, low C, N (high purity) and Ti, Nb (stabilized) elements are added. The addition of Ti and Nb is also effective for improving weldability. Ferritic stainless steel is mostly used in construction. The most common ones are handrails, escalators, railings, etc. It is the eyeball of the bloggers. There are also such stainless steels marked with “304” on the stainless steel. That is the “Li Gui” stainless steel. Types of stainless steel such as martensitic, biphasic and precipitation hardening systems or with slightly magnetic properties, containing more ferrite in the structure, are more magnetic. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

U-bolts are also called U-shaped wire, U-shaped bolts, U-shaped pipe clamps, mostly used for pipe installation and fixing, u-shaped bolts, that is, horse-riding bolts. The English name of riding bolts is U-bolt, which is a non-standard part and has a U shape. Therefore, it is also called U-bolt. The two ends are threaded and can be combined with the nut. It is mainly used to fix tubular objects such as water pipes or sheets, such as the leaf spring of a car. Because the object is fixed like a person riding on the horse, it is called For riding bolts. The two ends are respectively composed of a hanging ring and a threaded rod, and a U-shaped fitting connected to the tower. U-bolts are widely used, mainly for construction and installation, mechanical parts connection, vehicle ships, bridge tunnels, etc. Main shapes: semi-circular, square right angle, triangle, oblique triangle, etc. 1. Material properties Density, flexural strength, impact toughness, compressive strength, modulus of elasticity, tensile strength, temperature resistance, and color are determined according to the use environment. 2. The material is commonly used carbon steel Q235A Q345B alloy steel stainless steel and so on. Among them, stainless steel has 201 304, 321, 304L, 316, 316L. 3. The national standard for u-type screws: JB/ZQ4321-1997 4. U-shaped screws are pided into carbon steel Q235, Q345 alloy steel, stainless steel 201 304 316, etc., which is the difference between carbon steel and stainless steel. There are many sizes of u-screws, u-type screws have many standards, and there are many non-standard parts according to the drawings, so u-type screws are too large in size. Regarding the description of U-bolts, most people say a few points or a few inches. The size mentioned here refers to the nominal diameter of the fixed pipe, which is DN. Common u-type screw size: 4 points == DN15 = = inner diameter 20mm 6 points == DN20 = = inner diameter 25mm 1 inch == DN25 = = inner diameter 32mm 1.2 inch == DN32 = = inner diameter 40mm 1.5 inch == DN40 = = inner diameter 50mm 2 inch == DN50 = = inner diameter 63mm 2.5 inch == DN65 = = inner diameter 75mm 3 inch == DN75 = = inner diameter 89mm 4 inch == DN100 = = inner diameter 120mm 5 inch == DN125 = = inner diameter 140mm 6 inch == DN150 = = inner diameter 175mm 8 inch == DN200 = = inner diameter 219mm Conversion between different descriptions in use and procurement 1. This refers to the size of the unit and the specification of the unit when purchasing the specification. The first step is to convert the inch into millimeters 1”=DN25. After the unit conversion, the outer diameter of the steel pipe corresponding to the engineering diameter should be found. 2. In the same way, when you get a U-bolt, you can find the value of the corresponding tube outer diameter by measuring the inner diameter value. Check the standard to know the nominal diameter and then convert the millimeter into inches. Source: China U-bolts Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

304 stainless steel industrial pipe has great differences in physical properties and chemical composition from structural steel, so the welding process of 304 stainless steel industrial pipe has its own characteristics. Welding method and specification selection: 304 stainless steel industrial pipe can be welded by TIG, MIRG, PAW and SAW. 304 stainless steel industrial pipe welding, because of its low melting point, small thermal conductivity, large resistivity, the base metal and welding materials are easily heated and melted during welding, so the welding current used is relatively small, only about 80% of ordinary carbon steel. At the same time, narrow welds and narrow weld beads should be used to reduce the high temperature residence time, prevent carbide precipitation from affecting corrosion resistance, reduce weld shrinkage stress and reduce hot crack sensitivity. Selection of 304 stainless steel industrial pipe welding materials There are many varieties of austenitic stainless steel, the use environment is complex and changeable, and the choice of welding materials is a cautious and important work. The main basis for selecting welding materials for 304 stainless steel industrial pipes is: Select welding consumables according to the main chemical composition of stainless steel industrial pipe base material The composition of the welding consumables, especially the Cr and Ni alloying elements in the welding material is higher than that of the industrial pipe base material, for example, 18-8 welding using 19-9 welding materials, etc. Under the possible conditions, a welding material containing a small amount (4%-12%) of ferrite should be used to ensure good crack resistance of the weld. When the ferrite phase is not allowed or impossible in the weld of stainless steel industrial pipe, the welding consumables should use welding materials containing alloying elements such as Mo and Mn. C, S, P, Si, Nb of welding consumables should be as low as possible, especially C, S, P and other elements. Nb causes solidification cracks in pure austenitic welds, but there is a small amount of ferrite in the weld, which can effectively avoid Welding structures that need to be stabilized or stress-relieved after welding, usually using Nb-containing soldering materials. Filling metals such as welding rods, welding wire, etc. should be selected according to the variety, specifications and matching welding processes of industrial pipes. The 304 stainless steel industrial pipe has high thermal cracking sensitivity, which requires the weld metal composition to be roughly matched with the base material composition, and the ferrite content in the weld should be controlled. For weldments working at high temperatures for a long time, the ferrite content in the weld should be no more than 5%. Most of the 304 stainless steel tubes can be submerged arc welded. The welding wire should be made of low Si, low S, low P, and similar to the base metal. For austenitic stainless steel tubes with Cr and Ni content greater than 20%, in order to improve their crack resistance, high Mn (6%-8%) welding wire can be used. The flux should be alkaline or neutral flux to prevent welding to the weld. Increase Si. Austenitic stainless steel special flux increases Si, and can also transfer alloy to the weld to compensate for the burning of alloying elements, which can meet the requirements of weld performance and chemical composition. When submerged arc welding of 304 stainless steel industrial pipe, attention should be paid to selecting a thinner wire and a smaller welding line energy. Source: China Stainless Steel Industrial Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. When welding stainless steel welded pipe, the grinding wheel used for grinding can only be used for grinding stainless steel welded pipe; the wire brush used and the tool for removing welding slag are all made of stainless steel; the surface of stainless steel welded pipe is not allowed to be exposed to flame processing. Otherwise, the corrosion resistance of the stainless steel welded pipe will be damaged. 2. When welding stainless steel welded pipe, apply short arc. In the case of gas shielded welding, inert gas protection must be good. When the solid wire is used as the molten-welded stainless steel welded pipe, the shielding gas should not be mixed with carbon dioxide; the resistant core wire is not protected by slag, and the carbon content of the stainless steel welded pipe weld is not increased by the carbon dioxide gas. 3, generally do not preheat, only thicker stainless steel welded pipe is preheated 100-150 degrees before welding. 4. In the welding, the interlayer temperature should be strictly controlled, less than 150 degrees. 5. Welding with a small amount of wire energy should be used as much as possible. 6. Gas shielded welding of reverse surface molding, the root side must be protected with reducing gas or pure argon. 7. Considering the pre-determined ferrite content in the weld of the stainless steel welded pipe, the actual ferrite content in the weld should be re-tested with a ferrite tester. Generally, the melting amount of the base metal should be controlled below 35% of the cross-sectional area of the entire stainless steel welded pipe. 8. For austenitic stainless steel welded pipes with stabilizer added to stabilize carbon, it is recommended to use ultra-low carbon fillers without stabilizers and vice versa to prevent intergranular corrosion. 9. Due to the large shrinkage deformation of the austenitic stainless steel welded pipe, it should be strengthened on both the clamping device and the positioning welding. 10. It is not allowed to have traces of arc scratching of the base metal at the groove of the stainless steel welded pipe. 11. In order to ensure the corrosion resistance of the welded joint, the surface should be bright, and the color of the residue and weld should be removed. The removal method is grinding, pickling, shot blasting, brushing or polishing. The smaller the surface roughness, the higher the corrosion resistance. For surface pickling, various pickling solutions or pickling pastes can be used, and rinsed with clean water according to the prescribed pickling time. When removing the color after welding, the best way is to use quartz sand for grinding. 12. Before repairing the weld, the surface of the groove should also be pickled. However, since the surface of the old component is rough, it is preferable to passivate the surface after pickling, and then rinse it with water. 13. Only quartz sand or stainless steel granules are allowed for shot peening. After the shot peening, the surface has a metallic luster, but if the surface is too rough, it should be passivated. 14. In the welding of stainless steel welded pipes, in order to speed up the cooling speed of stainless steel welded pipe welds, it is recommended to use quenching copper pads. Source: China Stainless Steel Welded Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Fasteners are the most common parts in mechanical equipment, and they are also very important to function. Machines that operate like air compressors are particularly large, and the role of fasteners can be imagined. However, corrosion is the most common problem during the use of fasteners. In order to prevent the corrosion of fasteners during use, the manufacturer will surface the fasteners after the fasteners are produced. So, which surface treatments can improve the corrosion resistance of fasteners? In industrial manufacturing, there are mainly four surface treatment methods to prevent corrosion of fasteners. When purchasing air compressors, we can combine the actual working conditions and pay attention to the anti-rust treatment method of fasteners.

There are many types of valves, each with its own advantages and disadvantages. The following small series lists the advantages and disadvantages of the five major valves, including gate valves, butterfly valves, ball valves, globe valves and plug valves, I hope to help you. gate The gate valve refers to a valve in which the closing member (gate) moves in the vertical direction of the channel axis, and is mainly used as a cutting medium in the pipeline, that is, fully open or fully closed. In general, gate valves are not available for regulated flow. It can be applied to low temperature pressure or high temperature and high pressure, and can be made according to different materials of the valve. However, gate valves are generally not used in pipelines for conveying media such as mud. Advantage: 1 fluid resistance is small; 2 The required torque for opening and closing is small; 3 can be used on the ring flow of the medium flowing in both directions, that is to say, the flow direction of the medium is not limited; 4 When fully open, the sealing surface is less affected by the working medium than the shut-off valve; The shape of the body is relatively simple and the manufacturing process is good; 6 structure length is relatively short. Disadvantages: 1 The external dimensions and opening height are large, and the required installation space is also large; 2 During the opening and closing process, the sealing surface is relatively frictional, the friction is large, and even the high temperature is likely to cause scratches; 3The general gate valve has two sealing faces, which adds some difficulties to processing, grinding and maintenance; 4 The opening and closing time is long. Butterfly valve The butterfly valve is a valve that opens and closes and adjusts the fluid passage by reciprocating about 90° with a disc type opening and closing member. Advantage: 1The structure is simple, the volume is small, the weight is light, the consumables are saved, and it is not used in large-diameter valves; 2 rapid opening and closing, small flow resistance; 3 can be used for media with suspended solid particles, and can also be used for powdery and granular media depending on the strength of the sealing surface. It can be applied to the two-way opening and closing and adjustment of ventilation and dust removal pipelines. It is widely used in gas pipelines and waterways of metallurgy, light industry, electric power and petrochemical systems. Disadvantages: 1 The flow adjustment range is not large. When the opening is up to 30%, the flow rate will be more than 95%; 2 Due to the structure of the butterfly valve and the limitation of the sealing material, it is not suitable for use in high temperature and high pressure piping systems. The general working temperature is below 300 ° C, below PN40; 3 Sealing performance is relatively poor compared to ball valves and globe valves, so it is not used for sealing requirements. Ball valve The ball valve is evolved from a plug valve. Its opening and closing member is a ball that is opened and closed by rotating the ball 90° around the axis of the valve stem. The ball valve is mainly used to cut, distribute and change the flow direction of the medium on the pipeline. The ball valve designed as a V-shaped opening also has a good flow regulation function. Advantage: 1 has the lowest flow resistance (actually 0); 2 It can be reliably applied to corrosive media and low boiling liquids because it will not get stuck during work (in the absence of lubricant); 3 can achieve complete sealing within a large pressure and temperature range; 4 can achieve fast opening and closing, the opening and closing time of some structures is only 0.05~0.1s, to ensure that it can be used in the automation system of the test bench. When the valve is quickly opened and closed, the operation has no impact; 5 spherical closures can be automatically positioned at the boundary position; 6 working medium is sealed reliably on both sides; 7 When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed does not cause erosion of the sealing surface; 8 compact and lightweight, it can be considered as the most reasonable valve structure for low temperature media systems; 9 valve body symmetry, especially the welded valve body structure, can well withstand the stress from the pipeline; 10 closing parts can withstand the high pressure difference when closing. (11) The ball valve of the fully welded valve body can be buried directly in the ground, so that the valve internals are not eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines. Disadvantages: 1Because the most important seat seal material of the ball valve is PTFE, it is inert to almost all chemicals, and has a small friction coefficient, stable performance, not easy to aging, wide temperature range and excellent sealing performance. Comprehensive features. However, the physical properties of Teflon, including higher coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the design of the seat seal must be centered around these characteristics. Therefore, when the sealing material is hardened, the reliability of the sealing is broken. Moreover, PTFE has a low temperature resistance and can only be used at less than 180 °C. Above this temperature, the sealing material will age. In the case of long-term use, it is generally not used at 120 °C. 2 Its adjustment performance is worse than the shut-off valve, especially the pneumatic valve (or electric valve). Shut-off valve Globe valve: A valve that moves the closure (valve) along the centerline of the seat. Depending on the form of movement of the flap, the change in the seat opening is proportional to the flap travel. Due to the relatively short opening or closing stroke of the valve stem of this type of valve, and the very reliable cutting function, and because the change of the valve seat opening is proportional to the stroke of the valve flap, it is very suitable for the adjustment of the flow rate. Therefore, this type of valve is very cooperative for cutting or regulating and throttling. Advantage: 1 During the opening and closing process, the friction between the valve flap and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant. 2 The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than the gate valve; 3 Usually there is only one sealing surface on the valve body and the valve flap, so the manufacturing process is better and easy to repair; 4 Because the filler is generally a mixture of asbestos and graphite, the temperature resistance level is higher. Generally, steam valves use a shut-off valve. Disadvantages: 1 Since the flow direction of the medium through the valve changes, the minimum flow resistance of the shut-off valve is also higher than most other types of valves; 2 Due to the long stroke, the opening speed is slower than the ball valve. Plug valve Plug valve: refers to a rotary valve in which the closing member is in the shape of a plunger. The valve opening on the valve plug communicates with or separates from the passage opening on the valve body by 90° rotation to realize a valve that opens or closes. The shape of the valve plug can be cylindrical or conical. The principle is basically similar to that of the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used for oil field exploitation and also used in petrochemical industry. Advantage: 1, for frequent operation, opening and closing quickly and lightly. 2. The fluid resistance is small. 3, simple, relatively small size, light weight, easy to repair. 4, the sealing performance is good. 5. Due to the limitation of the installation direction, the flow direction of the medium can be arbitrary. 6, no vibration, low noise. Disadvantages: 1. The cover is too large, resulting in too much torque and not flexible enough. 2, the weight of the body, the size of the caliber is limited. 3. In actual use, if a large-size valve is used, the inverted plug structure must be used, which easily affects the sealing effect. Source: China Valves Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Welding defects in stainless steel welded pipes can lead to stress concentration, reduced load carrying capacity, shortened service life, and even brittle fracture. General technical regulations stipulate that cracks, incomplete penetration, unfusion and surface slag are not allowed; defects such as undercut, internal slag and pores cannot exceed certain allowable values, and must be thoroughly removed and welded for excessive defects. Make up. The causes, hazards and preventive measures of welding defects of common stainless steel welded pipes are briefly described below. First, the weld size does not meet the requirements The weld seam size does not meet the requirements mainly refers to the weld height and residual height difference, the weld width and width difference, the wrong side amount, the post-weld deformation amount, etc., which are not in conformity with the standard. The weld is uneven, uneven, and deformed. Larger and so on. The weld width is inconsistent, in addition to causing the weld bead to be unsightly, it also affects the bond strength between the weld and the base metal; if the weld height is too large, resulting in stress concentration, and the weld is lower than the base metal, there is not enough Joint strength; if the wrong side and deformation are too large, the force transmission will be distorted and stress will be concentrated, resulting in a decrease in strength. Causes: improperly angled or unblind edge of stainless steel welded pipe and uneven assembly clearance; unreasonable selection of welding process parameters; low skill level of welders. Precautionary measures: select the appropriate groove angle and assembly clearance; improve the assembly quality; select the appropriate welding process parameters; improve the welder’s operating technology level. Second, undercut Due to incorrect selection of welding process parameters or incorrect operation process, the grooves or depressions formed by burning along the base material of the weld toe are called undercuts. The undercut not only weakens the strength of the welded joint of the welded pipe, but also causes cracks due to stress concentration. The cause is: the current is too large, the arc is too long, the angle of the electrode is not correct, and the method of transporting the strip is improper. Preventive measures: When welding arc welding, it is necessary to select the appropriate welding current and welding speed, the arc can not be pulled too long, the angle of the electrode should be appropriate, and the method of transportation should be correct. Third, not welded Incomplete penetration refers to the phenomenon that the root of the welded joint is not completely penetrated during the welding of the stainless steel welded pipe. Incomplete penetration can cause stress concentration and can easily cause cracks. Important weld joints are not allowed to pass through. The reason is: the groove angle or gap is too small, the blunt edge is too large, the assembly is poor; the welding process parameters are improperly selected, the welding current is too small, the welding speed is too fast; the welder has poor operation technique. Precautionary measures: Correctly select and process the groove size, properly assemble, ensure the clearance, select the appropriate welding current and welding speed, and improve the technical level of the welder. Fourth, not fused Unfused refers to the portion of the weld bead and the base metal or between the weld bead and the weld bead that is not completely melted during fusion welding. Unfused directly reduces the mechanical properties of the joint, and severe unfused causes the welded structure to be unsupportable at all. Causes: Mainly when welding stainless steel welded pipe, the speed is fast and the welding current is small, the welding heat input is too low; the welding rod is eccentric, the angle between the welding rod and the welding piece is improper, the arc is deflected; the sidewall of the groove has rust and dirt, and the layer The slag is not completely cleaned. Preventive measures: Correctly select the welding process parameters, carefully operate, strengthen the interlayer cleaning, and improve the technical level of the welder. Five, welding tumor A weld bead is a metal tumor formed by a molten metal flowing into an unmelted base metal outside the weld during welding. The weldment not only affects the formation of the weld of the stainless steel welded pipe, but also often has slag inclusions and no penetration in the weld. The reason is: the blunt edge is too small and the root gap is too large; the welding current is large and the welding speed is fast; the welder’s operation skill level is low. Preventive measures: According to different welding positions, it is necessary to select appropriate welding process parameters, strictly control the size of the molten holes, and improve the technical level of the welder. Six, crater The depressed part of the industrial grade stainless steel welded pipe weld end is called the crater. The crater not only severely weakens the strength of the weld at that location, but also causes crater cracks due to the concentration of impurities. Cause: The main reason is that the arc extinguishing time is too short; the current is too large when the thin plate is welded. Preventive measures: When welding arc welding, the welding rod should be slightly stopped at the molten pool or used as an annular moving strip. After the molten metal is filled, it will be led to one side to extinguish the arc. When tungsten argon arc welding is required, there should be enough The residence time, after filling the weld, decays the arc. Seven, stomata When welding industrial grade stainless steel welded pipes, the holes formed by the gas in the molten pool that cannot escape during solidification and remain are called pores. Pores are a common weld defect that is pided into internal welds and external air holes. The pores are round, elliptical, worm-shaped, needle-shaped, and dense. The presence of pores not only affects the tightness of the weld, but also reduces the effective area of the weld and reduces the mechanical properties of the weld. Causes: There are oil, rust, moisture and other contaminants on the surface and groove of industrial grade stainless steel welded pipe; when the welding rod is arc welding, the coating strip is damp, not dried before use; the arc is too long or partial blow, the molten pool protection effect is not Well, the air invades the molten pool; the welding current is too large, the welding rod is red, the coating peels off in advance, and the protection is lost; the operation method is improper, such as the arcing action is too fast, the shrinkage hole is easy to occur, the joint arcing action is incorrect, and it is easy to produce Dense pores, etc. Preventive measures: Remove the oil, rust and moisture in the range of 20~30mm on both sides of the groove before welding; strictly bake according to the temperature and time specified in the specification of the welding rod; correctly select the welding process parameters and operate correctly; try to use short arc Welding, wind-proof facilities in the field construction; failure to use welding rods, such as corrosion of the core, cracking of the coating, peeling, excessive eccentricity, etc. Eight, inclusions and slag inclusions Inclusions are non-metallic inclusions and oxides that are produced by metallurgical reactions in the weld metal. The slag inclusions are slag remaining in the weld. Stainless steel welded pipe slag can be pided into two types: point slag and strip slag. The slag inclusion weakens the effective section of the weld and reduces the mechanical properties of the weld. The slag inclusion also causes stress concentration, which easily causes the welded structure to be damaged during loading. Cause: The slag cleaning in the welding process is not clean; the welding current is too small; the welding speed is too fast; the welding process is improper; the welding material and the parent metal chemical composition are not properly matched; the groove design and processing are not suitable. Preventive measures: Select the welding rod with good slag removal performance; carefully remove the interlayer slag; reasonably select the welding process parameters; adjust the welding rod angle and the moving strip method. Nine, burn through During the welding process, the molten metal flows out from the back of the groove, and the defect in which the stainless steel welded pipe forms a perforation is called burn through. Burn through is one of the common defects of electrode arc welding. Cause: The welding current is large, the welding speed is slow, and the welded pipe is overheated; the groove gap is large, the blunt edge is too thin; the welder has poor operation skill. Preventive measures: select the appropriate welding process parameters and the appropriate groove size; improve the welder’s operating skills. Ten, crack Industrial grade stainless steel welded pipe cracks can be pided into cold cracks, hot cracks and reheat cracks according to the temperature and time of their generation; according to the different parts they produce, they can be pided into longitudinal cracks, transverse cracks, root cracks, crater cracks, Fuse line cracks and heat affected zone cracks. Cracks are one of the most dangerous defects in a welded structure, which not only causes the product to be scrapped, but may even cause serious accidents. (a) hot crack During the welding process, the weld cracks generated by the weld and the heat-affected zone metal cooling to the high temperature zone near the solidus line are called hot cracks. It is a dangerous soldering defect that is not allowed to exist. According to the mechanism, temperature interval and shape of the hot crack of the welded pipe, the hot crack can be pided into crystal crack, high temperature liquefaction crack and high temperature low plastic crack. Causes: mainly the low melting point eutectic and impurities in the molten pool metal during the crystallization process, forming severe intragranular and intergranular segregation, and under the action of welding stress. It is pulled apart along the grain boundary to form a thermal crack. Hot cracks generally occur in austenitic stainless steels, nickel alloys, and aluminum alloys. When low carbon steel is welded, it is generally not easy to generate hot cracks, but as the carbon content of the steel increases, the hot cracking tendency also increases. Preventive measures: Strictly control the content of harmful impurities such as sulfur and phosphorus in stainless steel welded pipes and welding materials, reduce the sensitivity of hot cracks; adjust the chemical composition of weld metal, improve weld microstructure, refine grains, improve plasticity, and reduce Or disperse the degree of segregation; use alkaline welding materials to reduce the content of impurities in the weld and improve the degree of segregation; select appropriate welding process parameters, appropriately increase the weld forming coefficient, and adopt multi-layer multi-pass welding method; Use the same lead plate as the base material, or gradually extinguish the arc and fill the crater to avoid hot cracks in the crater. (2) Cold crack Cracks that are generated when the welded joint is cooled to a lower temperature (below M. for steel) are called cold cracks. Cold cracks can occur immediately after welding, and may occur after a period of time (hours, days, or even longer). This crack is also called delayed crack. It is a common form of cold crack and has more Great danger. Causes: The hardened structure formed by martensite transformation, the welding residual stress formed by the large degree of restraint, and the hydrogen remaining in the weld are the three major factors that cause cold cracking. Preventive measures: Use low-hydrogen type welding materials, strictly follow the instructions in the instructions before use; remove the oil and moisture on the weldments before welding, reduce the hydrogen content in the weld; select reasonable welding process parameters and heat input to reduce The tendency of hardening of the weld; the hydrogen dehydration treatment is carried out immediately after the welding to allow hydrogen to escape from the welded joint; for the stainless steel welded pipe with high tendency to harden, preheating before welding and heat treatment after welding to improve the structure and performance of the joint ; Various process measures to reduce welding stress. (3) Reheat crack After welding, the crack generated by the stainless steel welded pipe reheating in a certain temperature range (stress-relieving heat treatment or other heating process) is called reheat cracking. Cause: Reheat cracks generally occur in low-alloy high-strength steels, pearlitic heat-resistant steels and stainless steels containing alloying elements such as vanadium, chromium, molybdenum and boron. After undergoing a thermal cycle of welding, they are heated to a sensitive area (550). ~ 650 ° C) produced. Most of the cracks originate from the coarse-grained areas of the heat affected zone of the weld. Most of the reheat cracks occur in stainless steel welded pipes and stress concentrations, and reheat cracks sometimes occur in multilayer welding. Preventive measures: Under the premise of meeting the design requirements, select low-strength welding materials, so that the weld strength is lower than the base metal, the stress is loose in the weld, avoid cracks in the heat-affected zone; minimize welding residual stress and stress concentration; Control the welding heat input of the welded pipe, reasonably select the preheating and heat treatment temperature, and avoid the sensitive area as much as possible. Source: China Welded Pipe Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The selection of the welding method for stainless steel industrial pipes should be selected according to the material and wall thickness of stainless steel industrial pipes. Different welding methods have different characteristics because of different welding methods with different arc heat and arc forces. For example, tungsten argon arc welding is characterized by low current density, stable arc combustion, good weld formation, especially suitable for thin plate welding, and thick plate welding is not preferred; plasma arc is characterized by high arc column temperature and energy density. Large, plasma arc has good straightness, its rigidity and flexibility have a wide adjustment range, and the work is stable, but the operation is more complicated; submerged arc welding has the characteristics of deep penetration ability and high efficiency of welding wire, so welding The speed can be greatly improved, the welding cost is low, but the working conditions and environment are relatively poor. It can be seen that different welding methods have different capabilities and different operating costs. According to the material and wall thickness of the stainless steel industrial pipe, the reasonable selection of the welding method is a very important task to ensure the welding quality, increase the productivity and reduce the cost. In addition, the same welding method, the type and size of the welding current, the arc voltage, the welding speed, and the welding materials used have a great influence on the arc heat and the arc force. Therefore, different welding methods can only be applied to welding of different materials and thicknesses. The following figure shows the different welding methods for stainless steel welding speed ranges of different thicknesses. Welding method for stainless steel industrial pipe The selection of welding methods for stainless steel industrial pipes and the determination of process parameters should be based on the material and wall thickness, and efforts should be made to meet the following requirements: Ensure that the welding quality meets the requirements of relevant standards; The welding process should be stable and reliable (less faults and welding defects); The welding speed should be fast, that is, the production efficiency should be high; Welding costs and consumption are the lowest. As can be seen from the above figure, tungsten argon arc (TIG) filler wire welding, stainless steel industrial pipe thickness between 0.2mm-4.5mm, speed between 10cm/min-100cm/min. TIG welding, TIG welding stainless steel industrial pipe thickness between 0.2mm-5.5mm, speed between 10cm/min-150cm/min. MIG, the thickness of the weldable stainless steel industrial pipe is between 2.0mm and 6.5mm and the speed is between 35cm/min and 110cm/min. Plasma arc welding (PAW), weldable stainless steel industrial pipe thickness between 2.0mm-8.0mm, speed between 10cm/min-90cm/min. Because all welding methods have their maximum output energy limit, its weldable thickness is also limited. Therefore, it can be flexibly selected according to thickness and production practice, such as combination welding of various welding methods. Stainless steel industrial pipe thickness between 0.5mm-4.0mm, can be TIG welding (only for strip continuous forming welding unit); thickness ≧ 2mm, can also be used PAW welding (suitable for strip continuous forming welding unit and discontinuous Welding unit) Stainless steel industrial pipe thickness between 1.5mm-4.0mm, can also be used multi-cathode TIG welding (suitable for strip continuous forming welding unit); Stainless steel industrial pipe thickness between 4.0mm-8.0mm, can be welded once by PAW welding (suitable for strip continuous forming welding unit); Stainless steel industrial pipe thickness ≧ 8.0mm, can be covered by PAW welding and other welding methods, such as TIG welding cover, SAW welding surface, flux cored wire welding cover (for non-continuous welding units). In addition, the use of laser welding for the welding of stainless steel industrial pipes is also a development direction of stainless steel welded pipes. Source: China Industrial Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The forming process of the stamping elbow is complicated, and it needs to be welded according to different materials and uses, and gradually formed under a certain pressure. The forming of the stamping elbow needs to be carried out according to a certain process, and the corresponding process is strictly followed, otherwise the quality of the stamping elbow produced will be produced. If required, a circular ring shell can be cut into 4 90 ° elbows or 6 60 ° elbows or other specifications of elbows. This process is suitable for making any elbow and elbow inner diameter ratio greater than 1.5D. Specifications Large stamping elbows are an ideal way to make large stamping elbows. This process molding method is used in the production of different elbows and exhibits good use value in different fields, so that the process has a good value in different elbow production. The advantages of the forming process of large punching elbows are mainly reflected in the following aspects: (1) It is not necessary to use the tube blank as a raw material, which can save the cost of the pipe making equipment and the mold, and can obtain a stamping elbow of any large diameter and relatively thin wall thickness. The material of the stamping elbow is special, and it is not necessary to add the raw material of the tube blank, and it is easy to control during processing. (2) The blank for processing the punching elbow is a flat plate or a developable curved surface, so the material is simple to cut, the precision is easy to ensure, the assembly and welding are convenient, the raw materials are easily controlled during processing, the operation is relatively simple, there is no complicated process, and the welding and assembly are convenient. (3) Due to the above two reasons, the manufacturing cycle can be shortened and the production cost is greatly reduced. Because it does not require any special equipment, it is especially suitable for processing large punching elbows on site. The material of the stamping elbow is made of carbon steel, stainless steel or alloy steel. The carbon steel stamping elbow is cheap and large in use. The elbow of alloy steel is used in a special position. The surface quality and mechanical properties are basically the same as the tube. For the convenience of welding, the steel grade of the pipe to be connected is the same. Requirements for packaging: For small pipe fittings, such as export, you need to make a wooden box, about 1 cubic meter. The number of elbows in this box is about no more than one ton. The standard allows suits, that is, large sets, but total The weight generally cannot exceed 1 ton. For large pieces, a single package, like a 24″, must be a single package. The other is the packaging mark, the mark is to indicate the size, steel number, batch number, manufacturer’s trademark. On the stamping elbow to be stamped with Packing list and other documents. Any large-scale stamping elbow that produces a bend with a median diameter of elbow and an inner diameter of the elbow greater than 1.5D is an ideal way to make large stamping elbows. This process molding method is used in the production of different elbows and exhibits good use value in different fields, so that the process has a good value in different elbow production. Source: China Stamping Elbows Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Butt welding flange is a kind of flange. The flange is a part that connects the pipe to the pipe and is connected to the pipe end. There are holes in the flange, and the bolts make the two flanges tightly connected. Butt weld flanges and their gaskets and fasteners are collectively referred to as flange joints. Flange joints are an essential component in equipment and equipment components, and are also indispensable parts in piping design and pipe fittings. Butt welding flange is not easy to be deformed, sealed well, widely used, suitable for pipelines with high pressure or temperature fluctuations or high temperature, high pressure and low temperature pipelines. The advantage is that the price is relatively cheap, the nominal pressure does not exceed 2.5MPa; also used for conveying price On the pipeline of expensive, flammable and explosive medium, the nominal pressure is around PN16MPa. The welding flange connection is easy to use and can withstand large pressures. The welding flange pads are made of different materials according to different grades of pressure. From low-pressure asbestos pads, high-pressure asbestos pads to metal mats. Butt welding flange Production process of butt welding flange: 1. Whether the annealing temperature reaches the specified temperature. The welding flange treatment is generally a solution heat treatment, which is commonly called “annealing”, and the temperature range is 1040~1120 °C (Japanese standard). You can also observe through the observation hole of the annealing furnace. The flanged pipe fittings in the annealing zone should be in an incandescent state, but there is no softening and sagging. 2. The welding flange is used to process the water vapor in the casting furnace. On the one hand, check whether the material of the furnace body is dry. When the furnace is installed for the first time, the material of the furnace body must be dried. Second, whether the flanged pipe fittings entering the furnace have excessive water stains. If there are holes on the flange pipe fittings, do not leak water. Go in, or else destroy the atmosphere of the stove. 3. The furnace body sealability. The soldering flange bright annealing furnace should be closed and isolated from the outside air; if hydrogen is used as the shielding gas, only one exhaust port is open (used to ignite the discharged hydrogen). The inspection method can be applied to the gaps of the joints of the annealing furnace with soapy water to see if it runs. The most easy place to run the gas is the place where the annealing furnace enters the pipe and the place where the pipe is discharged. The sealing ring in this place is particularly easy to wear. Always check frequently. 4. Protect the gas pressure. In order to prevent micro-leakage on the welding flange, the protective gas in the furnace should maintain a certain positive pressure. If it is hydrogen shielding gas, it generally requires more than 20kBar. 5. The annealing atmosphere. For the welding flange, pure hydrogen is generally used as the annealing atmosphere, and the purity of the atmosphere is preferably 99.99% or more. If another part of the atmosphere is an inert gas, the purity can be lower, but it must not contain too much oxygen or water vapor. Source: China Butt Welding Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)