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There are many processing methods for stainless steel elbows, many of which are mechanical processing. The most used ones are stamping method, forging method, roller processing method, rolling method, bulging method, stretching method, bending method, and combined processing method. . Stainless steel elbow processing and metal force processing are combined organically. Here are some ways to share the processing of stainless steel elbows as follows: Forging method of stainless steel elbow: The end of the pipe or a section is punched by a swaging machine to reduce the outer diameter. The common type forging machine has a rotary type, a link type and a roller type. Rolling method: Generally, the mandrel is not used, and it is suitable for the inner edge of the thick-walled tube. The core is placed in the tube, and the outer circumference is pressed by a roller for round edge processing. Stamping method: The pipe end is expanded to the required size and shape with a tapered core on the punching machine. Bending forming method: There are three methods that are more commonly used. One method is called stretching method, the other method is called pressing method, the third method is roller method, there are 3-4 rollers, two fixed rollers, one adjusting roller, and adjustment. With the fixed roll distance, the finished pipe is curved. Inflating method: one is to place rubber in the tube, and the upper part is compressed by a punch to make the tube protrude and formed; the other method is to form a hydraulic bulge, fill the middle of the tube with liquid, and the liquid pressure drums the tube into the required The shape, the bulk of the production of bellows is used in this way. The processing method of the stainless steel elbow is mainly the above five methods, and everyone can choose the processing method suitable for their own processing. Source: China Stainless Steel Elbows Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

1. Flange and pipe assembly connection The assembly quality of the flange and the pipe not only affects the strength and density of the pipe joint, but also affects the eccentricity of the entire pipeline. Therefore, in assembling the flange to the pipe, the following basic requirements must be met. The center of the flange should be in line with the center of the tube. The flange sealing surface should be perpendicular to the center of the tube. The position of the screw hole on the flange of the pipe shall be consistent with the position of the flange screw hole on the matching equipment or pipe fitting. The screw hole positions of the flanges at both ends of the same pipe shall be consistent. Flat welding flange and pipe assembly When assembling the flat welding flange and the pipe, first insert the flange into the pipe end, and a certain distance (usually 1.5 times the pipe wall thickness) should be left between the pipe mouth and the flange sealing surface. At this time, spot welding can be performed on either side of the pipe, and then the flange is bent or squared on the opposite side of the spot welding, and then spot welding is performed at the curved rule. Rotate the pipe at an angle of 90° so that the spot welding position is placed above and below. At this time, use the curved ruler to align on either side of the pipe, and then spot weld on the left and right sides. When PN<1.6Mpa, only the outer port is welded; Internal and external welding is possible when PN ≥ 1.6Mpa. Welding flange and pipe assembly The welding flange and the pipe are assembled by butt welding. The welding method and requirements are the same as the welding method of the pipe. 2. Flange gasket The gasket acts as a seal in the flange connection and is in contact with the medium being sealed, directly affected by the physical properties, temperature and pressure of the medium. In general, flanges of the same pressure class should be used on the same pipeline for the same type of gaskets for interchangeability. For water pipelines, medium-pressure asbestos rubber sheets are generally used. Due to the long service life of rubber, rubber gaskets should be used for infrequent disassembly and long service life. The correct choice of gaskets, in order to ensure that the gasket will not be crushed, in order to reduce the excessive bolt tightening force, it is a principle to take a small width gasket. 3. Flange connection 3. Check and handle flanges, bolts and gaskets before installation: First, the flange dimensions should be checked, including the outer diameter, inner diameter, groove, bolt hole center distance, flange height, etc., which should meet the design requirements. The flange sealing surface should be smooth and smooth, without burrs and radial grooves. The threaded portion of the threaded flange shall be intact and free of damage; the convex and concave flanges shall be naturally fitted, and the height of the convex surface shall not be lower than the depth of the groove. Rubber asbestos board, rubber sheet, plastic and other hose gaskets should be flexible, without aging deterioration and delamination; the surface should not have defects such as defects and wrinkles. The material should match the design selected. The processing dimensions, precision, surface roughness and hardness of the metal gasket shall meet the requirements, and the surface shall be free of defects such as cracks, burrs, grooves, radial scratches and rust spots. Metal wound gaskets should not have defects such as radial scratches, looseness, warpage, and the like. Before the flange is assembled, the rust, oil and other debris on the surface and the sealing surface must be removed until the metallic luster is exposed. The sealing line of the flange sealing surface must be clearly clarified. Flange assembly When installing the flat flange, the end of the tube should be inserted into the flange 2/3. Since the flat welding flange is subjected to mechanical stress and thermal stress, the entire joint is suddenly broken at the time of fracture. Therefore, the flat welding flange should adopt the reinforced welding method on both the inner and outer sides under the condition of condition. After welding, the slag should be cleaned, the inner hole should be smooth, and the flange surface should be free of spatter. The flange face must be perpendicular to the pipe centerline. The skewness is allowed to be 1 mm when DN < 300 mm and 2 mm when DN > 300 mm. The flange connection should be kept coaxial, and the center deviation of the bolt hole should generally not exceed 5% of the hole diameter, and the bolt should be allowed to penetrate freely. The flange connection should be the same size bolts, the installation direction is the same, that is, the nuts should be on the same side. The bolts and nuts that connect the valves should generally be placed on the side of the valve. When tightening the bolts, it should be symmetrical and evenly elastic. The tightened bolts shall not exceed 5mm or 2~3 buckles outside the exposed nut. Bolt hole position on the flange: The bolt hole of the horizontal pipe, the uppermost two should be kept horizontal; the bolt hole on the vertical pipe, the two holes closest to the wall should be parallel to the wall. At the same time, the two connecting flanges should be parallel and natural, and the parallelism deviation should be no more than 2mm. The flange on the branch pipe is 100mm or more from the outer wall of the riser, or the bolt can be worn. For ease of disassembly, the distance between the flange and the edge of the bracket or building should be more than 200mm. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Flange connection is to fix two steel pipes, pipe fittings or equipment on a flange, and between the two flanges, with flange pads, bolted together to complete the connection. Some fittings and equipment have their own flanges and are also flanged. The welding quality of the flange and the pipe not only affects the eccentricity of the entire pipe, but also affects the strength and density of the pipe joint. The center of the flange should be in line with the center of the tube. The sealing surface of the flange flat welding flange shall be perpendicular to the center of the pipe. When the DN is less than 300 mm, the deflection is allowed to be 1 mm, and when the DN is > 300 mm, it is 2 mm. The flange connection should be the same size bolts, the installation direction is the same, that is, the nuts should be on the same side. The bolts and nuts that connect the valves should generally be placed on the side of the valve. When tightening the bolts, it should be symmetrical and evenly elastic. The tightened bolts shall not exceed 5mm or 2~3 buckles outside the exposed nut. The flange connection should be kept coaxial. The center deviation of the bolt hole should not exceed 5% of the hole diameter, and the bolt should be allowed to penetrate freely. The position of the screw holes of the flanges at both ends of the same pipe shall be consistent. The position of the screw holes on the flange of the pipe shall be consistent with the position of the flange hole of the flange on the matching equipment or pipe fittings. Bolt hole position on the flange: The bolt hole on the vertical pipe, the two bolt holes closest to the wall should be parallel to the wall surface; the bolt holes of the horizontal pipe, the uppermost two bolt holes should be kept horizontal. At the same time, the two connecting flanges should be parallel and natural, and the parallelism deviation should be no more than 2mm. The main features of the flange connection are easy disassembly, high strength and good sealing performance. When installing the flange, the two flanges must be kept parallel, the sealing surface of the flange should not be damaged, and it should be cleaned. The gasket used for the flange shall be selected according to the design regulations. Flange threaded connection (wire connection) flange and welded flange. Low-pressure small-diameter wire-bonded flanges, high-pressure and low-pressure large diameters are all welded flanges. The thickness of the flanges of different pressures and the diameter and number of connecting bolts are different. Source: China Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The flange manufacturer‘s process of producing flanges is mainly pided into four types: forging, casting, cutting and rolling. Cast flange and forged flange Casting flange, the shape of the blank is accurate, the processing volume is small, the cost is low, but there are casting defects (pores, cracks, inclusions); the internal flow of the casting is poor (if it is a cutting part, the streamline type is worse); Forged flanges generally have lower carbon content than cast flanges and are less prone to rust. Forgings have better streamlined shape, denser structure and better mechanical properties than cast flanges; If the forging process is improper, the grain will be large or uneven, and the hardening crack will occur. The forging is higher than the casting flange. Forgings can withstand higher shear and tensile forces than castings. The advantage of the casting is that it can produce a more complicated shape and the cost is relatively low; The advantage of the forging is that the internal structure is uniform, and there are no harmful defects such as pores and inclusions in the casting; Different from the production process, the difference between the cast flange and the forged flange, such as the centrifugal flange, is one of the cast flanges. Centrifugal flange is a precision casting method production flange. This kind of casting is much thinner than ordinary sand casting structure, and the quality is improved a lot. It is not easy to have problems such as loose structure, pores and trachoma. First of all, we need to understand how the centrifugal flange is produced and processed by centrifugal casting to produce a flat welded flange. The product is characterized by the following process steps: The selected raw material steel is smelted in a medium frequency electric furnace to make the molten steel temperature reach 1600-1700 ° C; Preheating the metal mold to 800-900 ° C to maintain a constant temperature; Start the centrifuge, and inject the molten steel in step 1 into the metal mold after preheating in step 2; Castings are naturally cooled to 800-900 ° C for 1-10 minutes; Cool with water to near normal temperature, demoulding to remove the casting. Let’s take a look at the production process of forged flanges: The forging process generally consists of the following steps: selecting high-quality billet blanking, heating, forming, and forging cooling. Forging processes include free forging, die forging and film forging. At the time of production, different forging methods are selected according to the quality of the forgings and the number of production batches. The free forging productivity is low, the machining allowance is large, but the tool is simple and the versatility is large, so it is widely used for forging a single piece and a small batch of forgings with a simple shape. Free forging equipment includes air hammers, steam-air hammers and hydraulic presses, which are suitable for the production of small, medium and large forgings. Die forging has high productivity, simple operation, and easy mechanization and automation. The die forgings have high dimensional accuracy, small machining allowance, and reasonable distribution of the fiber structure of the forgings, which can further improve the service life of the parts. The basic process of free forging: When free forging, the shape of the forging is gradually forged by some basic deformation process. The basic processes of free forging are upsetting, lengthening, punching, bending and cutting. Upsetting Upsetting is an operation process in which the raw material is forged in the axial direction to reduce its height and increase the cross section. This type of process is commonly used for forging gear blanks and other disc-shaped forgings. The ups and downs are pided into two types: all upsetting and partial forging. Pulling out Lengthening is a forging process that increases the length of the blank and reduces the section. It is usually used to produce shaft blanks, such as lathe spindles and connecting rods. Punching A forging process in which a punch punches a through hole or a through hole without using a punch. Bending A forging process that bends the billet into a certain angle or shape. Torting A forging process that rotates a portion of a blank relative to another portion by a certain angle. Cutting The forging process of piding the blank or cutting the material. Second, die forging The die forging is collectively referred to as model forging, and the heated billet is placed in a forging die fixed to the die forging device to be forged. The basic process of die forging The process of die forging: cutting, heating, pre-forging, final forging, punching, trimming, quenching and tempering, shot peening. Commonly used processes are upsetting, lengthening, bending, punching, and forming. Common die forging equipment Common die forging equipment includes die forging hammer, hot die forging press, flat forging machine and friction press. Generally speaking, forged flanges are of better quality, generally produced by die forging, with fine crystal structure and high strength, and of course the price is more expensive. Whether it is cast flange or forged flange, it is a common method of manufacturing flanges. See the strength requirements of the parts to be used. If the requirements are not high, you can also use turning flanges. Third, the cutting flange The inner and outer diameters of the flange and the thickness of the disc are cut directly on the middle plate, and the bolt holes and water lines are processed. The flange thus produced is called a cut flange, and the maximum diameter of such a flange is limited to the width of the middle plate. Fourth, the rolling flange The process of cutting the strips with the middle plate and then rolling them into a circle is called rolling, and is used for the production of some large flanges. After the winding is successful, the welding is performed, and then the flattening is performed, and then the process of the water line and the bolt hole is processed. Source: China Stainless Steel Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

A stainless steel elbow is a pipe fitting that changes the direction of the pipe. According to the angle, there are three common types, such as 45°, 90°, and 180°. The processing methods of stainless steel elbows are generally mechanical processing such as: stamping method, forging method, roller processing method, rolling method, bulging method, stretching method, bending method, and combined processing method; However, in the current production and processing, there are not many common methods for processing stainless steel elbows. There are three commonly used forming methods for stainless steel elbows: stretching, stamping, and roller. Forging method: The end portion or a part of the stainless steel pipe is punched by a swaging machine to reduce the outer diameter. The common type forging machine has a rotary type, a link type, and a roller type. Stamping method: The end of the tube is expanded to the required size and shape with a tapered core in the stainless steel elbow. The stamping forming of stainless steel elbows is the earliest forming process for mass production of elbows. At present, it has been replaced by hot push or other forming processes in the production of seamless elbows of common specifications, but in some specifications of elbows It is still used because of the small amount of production, excessive wall thickness or special requirements of the product. The stamping elbow is formed by using a tube blank equal to the outer diameter of the elbow, and is directly press-formed in the mold using a press. Before the stamping, the tube blank is placed on the lower mold, the inner core and the end mold are loaded into the tube blank, the upper mold is moved downward to start pressing, and the punching elbow is formed by the constraint of the outer mold and the support of the inner mold. Compared with the hot push process, the appearance quality of stamping is not as good as the former; when the punch elbow is in the stretched state when forming, there is no excess metal in other parts to compensate, so the wall thickness at the outer arc is about 10% thinner. . However, due to the characteristics of single-piece production and low cost, the stamping elbow process is mostly used for the manufacture of small batches and thick-walled elbows. Stamping elbows are pided into cold stamping and hot stamping. Cold stamping or hot stamping is usually selected according to material properties and equipment capabilities. The forming process of the cold extrusion elbow is to use a special elbow forming machine to put the tube blank into the outer mold. After the upper and lower molds are closed, the blank is reserved along the inner and outer molds under the push of the push rod. The gap moves to complete the forming process. The elbow manufactured by the inner and outer mold cold extrusion process has beautiful appearance, uniform wall thickness and small dimensional deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbow forming, is mostly manufactured by this process. The precision of the inner and outer molds used in the stamping elbow process is high; the wall thickness deviation of the billet is also demanding. Roller method: The core is placed in the tube of the stainless steel elbow, and the outer circumference is pressed by the roller for the round edge processing. Source: China Stainless Steel Elbows Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Inside the pressure vessel and pressure vessel components such as boiler tubes, there are often defects that are not easily found, such as unfused, incomplete penetration, slag inclusions, pores, cracks, etc. in the weld. In order to know the location, size and nature of these defects, it is impossible to perform a destructive inspection of each boiler or pressure vessel. For this purpose, non-destructive testing is required. That is, physical deformation of the workpiece or structure is inspected and measured by physical methods without damaging the structure to infer the internal tissue condition and defects of the workpiece or structure. The purpose of nondestructive testing is to: (1) Improve the manufacturing process to ensure product quality. (2) In the manufacturing process of the product, defects can be found in advance to avoid product scrapping, thereby saving man-hours and costs, and reducing the cost of manufacturing the product. (3) Improve the reliability of the product, ensure the safety of the use of the product, and avoid accidents. Apply non-destructive testing to all aspects of product design, manufacturing, installation, use and maintenance; through a series of tests, determine the design, raw materials, manufacturing processes and operation, and identify the factors that may cause damage, and then Improve to improve product reliability. Commonly used non-destructive testing methods are: radiographic flaw detection, ultrasonic flaw detection, magnetic particle inspection, penetrant inspection, and eddy current inspection. There are also leak detection, acoustic emission detection, stress testing, visual inspection and so on. Radiographic inspection The method of examining the quality of a weld by the ability of the ray to penetrate metals and other materials is called radiographic inspection. The basic principle of radiographic inspection is the projection principle. When the ray passes through the weld metal, when there are defects in the weld metal (such as cracks, slag inclusions, pores, incomplete penetration, etc.), the radiation is attenuated differently in the metal and the defect, and the sensitivity is different on the film. The ray decays rapidly in the metal, and the ray decays slowly in the defect. Therefore, the use of radiographic inspection can determine the size, shape and position of defects in the weld. Since radiographic inspection is a projection principle, this method is sensitive to volumetric defects such as slag inclusions. Because this method can record and save, China’s boiler pressure vessels have more confidence in this method. China’s boiler regulations stipulate that the longitudinal steam seam of the boiler drum with the rated steam pressure of 0.1MPa or more and less than 3.8MPa, the longitudinal joint of the header and the joint of the head shall be 100% radiographic inspection; For a .8 MPa boiler, 100% ultrasonic flaw detection plus at least 25% radiographic inspection is required. (1) Since the flaw detection result can be directly output by the electric signal, automatic detection can be performed. (2) Since the non-contact method (the probe does not directly contact the workpiece to be inspected), the detection speed can be fast. (3) Suitable for surface or near surface defect detection. (4) A wide range of applications, in addition to the detection of damage, but also to detect changes in materials, changes in size and shape. Acoustic emission detection The probe is used to detect the sound wave emitted by the deformation or crack initiation due to the applied stress, so as to infer the position and size of the defect. The ultrasonic flaw detection method is that the ultrasonic signal emitted by the probe is reflected back and received after encountering the defect. The function of the defect in this process is to passively reflect the ultrasonic signal back. The acoustic emission detection enables the object (defect) to be actively involved in the detection process. The sound emission is generated due to the development of the defect, so the acoustic emission Detection is a dynamic non-destructive testing method. According to the characteristics of the emitted sound waves and the external conditions that cause the acoustic emission, it is possible to check the location of the sounding (the location of the defect) and the microscopic structural characteristics of the acoustic emission source. This detection method can not only understand the current state of the defect, but also understand the defect. The formation process and the tendency to develop and increase under actual use conditions. Acoustic emission detection can be pided into single channel detection, dual channel detection and multi-channel detection according to the number of detection probes. Single-channel detection can only detect the presence or absence of defects in the object, and the position of the defect cannot be determined. The two-channel detection can only be used for linear positioning, and is generally used for the detection of known condition welds. Multi-channel detection is generally 4 channel, 8 channel, 16 channel, 32 channel acoustic emission detection, mainly used for acoustic emission detection of large components, not only can detect the existence of acoustic emission source, but also can locate the acoustic emission source. Source: China Stainless Steel Boiler Tubes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The flange is placed between the sealing surfaces of the two flanges. After tightening the nut, the specific pressure on the surface of the gasket reaches a certain value and then deforms, and fills the unevenness on the sealing surface to make the joint tight. A flanged joint is a detachable joint. There are holes in the flange, bolts can be worn to make the two flanges tightly connected, and the flanges are sealed with gaskets. According to the connected parts, it can be pided into container flange and pipe flange. Flanges are often used when the medium temperature and pressure are not high and the medium is corrosive. When the medium is corrosive. Rare integral flanges have flanges and butt weld flanges. Flange fittings are flanged (flange or splicing) fittings. It can be cast, and the flange is mainly a part that connects the pipe to the pipe. According to the structure type. It can also be constructed by screwing or welding. Flange joints consist of a pair of flanges, a gasket and a number of bolts and nuts. The main functions of the flange are pided into the following categories: The pipeline has a fault, which is easy to disassemble and detect. Connect the pipeline and maintain a good sealing performance of the pipeline; If there is a problem with a certain section of pipeline, it is convenient to replace a certain pipeline; Flange has certain technical requirements and technical parameters in production and use, and is produced and processed according to certain methods and methods: The butt weld of the ring shall be subjected to post-weld heat treatment and 100% ray or ultrasonic flaw detection, and the radiographic inspection conforms to the Class II requirements of JB4730, and the ultrasonic flaw detection meets the Class I requirements of JB4730. The welding flange is manufactured and processed with certain welding standards and techniques, in line with the corresponding production standards and requirements of the country. The steel plate of the production flange should be ultrasonically flawed, no delamination defects, to ensure good quality and performance problems, production and inspection according to certain quality requirements, to ensure that there is no quality problem in the production and use of steel plates; It should be cut into strips along the rolling direction of the steel, and be welded into a ring shape by bending, and the surface of the steel will form a cylindrical surface. In the production of butt welding flanges, steel plates shall not be directly machined into neck flanges, and they shall be fabricated and processed by a certain process. Source: China Stainless Steel Flanges Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Channel steel is the most commonly used type of steel in engineering construction. Like angle steel, they are mainly used for corrosion resistance and weight requirements. The theoretical weight calculation of channel steel is also a basic knowledge that engineers must know. This article focuses on the specification of the channel steel and the theoretical weight table of the channel steel. a) theoretical calculation method of channel steel The calculation formula of the channel steel (kg/m) W=0.00785x[hd+2t(b-d)+0.349(R^2-r^2)], where: h= high b= leg length d= waist thickness t= average leg thickness R= inner arc radius r= end arc radius Note: R^2 represents the square of R Schematic diagram of channel steel: Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

One, overview Stainless steel bellows are widely used and have applications in oil, water and gas pipelines, and most of them still have some pressure. Such thin corrugated tubes are often welded, and because of the thinness (about 0.2 mm), welding is difficult. Welding methods include welding, brazing, and the like. Here, the tungsten argon arc welding of stainless steel bellows and stainless steel flanged tubes is introduced. The key to welding is to prevent burn through. Clean the stainless steel corrugated pipe to be welded and the oil on the flange pipe. If it is cracked and leaked at the weld, the original weld bead should be cleaned off, and the metal luster should be ground at the straight pipe of the flange pipe. The straight pipe of the bellows is too thin to be ground and polished, and the sand is brightened by hand sand. Just fine. Welding assembly: the best assembly clearance is 0, due to processing error, sometimes the gap is too large, the welding is easy to burn through, the solution can be overlapped on the straight pipe of the flange pipe (usually 3 ~ 5mm) heap One layer of welding, machined to 0 ~ 0.05mm gap or hand grinding. If the sleeve does not go up, the small outer diameter of the straight tube of the flange tube should be small or small until it is suitable. Welding machine selection: WS315 type, using DC positive connection. Welding consumables selection: ER308, Ø0.8mm Third, the welding operation Welding parameters: welding current 25 ~ 30A, protective gas flow 4 ~ 7L / min. The arc must be carried out on the flange tube, the arc should be on the thick tube, the arc outer flame is used to heat the bellows, and the wire is used to block the edge of the bellows, and the bellows is melted with the molten stainless steel wire. Welding time strip must be carried out on thick tubes, using short weld welding or spot welding for welding. When welding, it is necessary to observe the melting condition of the bellows at all times. Generally, one to three molten pools are melted at a time, which is not suitable for continuous welding, especially when the gap is large. In summary, the arc welding of stainless steel bellows and stainless steel flanged tubes (or other tubes) is based on the fact that the arc cannot directly point to the bellows, and the bellows is used to weld the bellows.

The corrosion resistance of stainless steel generally increases with increasing chromium content. The basic principle is that when there is enough chromium in the steel, a very thin to dense oxide film is formed on the surface of the steel, which prevents further oxidation or corrosion. An oxidizing environment can strengthen the film, while a reducing environment inevitably destroys the film, causing corrosion of the steel. (1) Corrosion resistance in various environments Atmospheric corrosion The atmospheric corrosion resistance of stainless steel is basically a function of the amount of chloride in the atmosphere. Therefore, corrosion of stainless steel near the ocean or other chloride sources is extremely important. A certain amount of rainwater is important only if it acts on the chloride concentration of the steel surface. Rural environment 1Cr13, 1Cr17 and austenitic stainless steel can be used for a variety of purposes, and there will be no significant changes in appearance. Therefore, stainless steel exposed in rural areas can be selected based on price, market availability, mechanical properties, processability and appearance. Industrial environment In an industrial environment without chloride pollution, 1Cr17 and austenitic stainless steel can work for a long time, basically keep no rust, and may form a foul film on the surface, but when the dirt film is removed, it still maintains the original Bright appearance. In industrial environments with chlorides, stainless steel will be rusted. Marine environment 1Cr13 and 1Cr17 stainless steel will form a thin rust film in a short period of time, but will not cause obvious dimensional changes. Austenitic stainless steels such as 1Cr17Ni7, 1Cr18Ni9 and 0Cr18Ni9 may appear when exposed to the marine environment. Corrosion. Corrosion is usually shallow and can be easily removed. 0Cr17Ni12M02 molybdenum-containing stainless steel is basically corrosion-resistant in the marine environment. In addition to atmospheric conditions, there are two other factors that affect the resistance of stainless steel to atmospheric corrosion. That is, the surface state and the manufacturing process. The finishing level affects the corrosion resistance of stainless steel in chloride-containing environments. Matte surfaces (matte) are very sensitive to corrosion. That is, normal industrial finishing surfaces are less sensitive to corrosion. Surface finishing levels also affect the removal of dirt and rust. It is easy to remove dirt and rust from highly finished surfaces, but it is difficult to remove from a matte surface. For matte surfaces, frequent cleaning is required if the original surface condition is to be maintained. 2. Various acidic water When stainless steel is used in a halide solution, especially a chloride solution, it should be considered that even if the corrosion rate is generally low, pitting and/or stress corrosion cracking may occur under certain conditions. Although there are many excellent effects in the use of stainless steel in the presence of chlorides (such as food processing equipment and seawater flowing under relatively low temperature conditions), various uses must be considered separately. Whether pitting or stress corrosion cracking occurs depends on many factors and factors such as the environment and equipment design and operation. (2) Corrosion Pitting As mentioned earlier, the excellent corrosion resistance of stainless steel is due to the formation of an invisible oxide film on the surface of the steel, making it passive. The passivation film is formed as a result of the reaction of the steel with oxygen when exposed to the atmosphere or due to contact with other oxygen-containing environments. If the passivation film is destroyed, the stainless steel will continue to corrode. In many cases, the passivation film is only destroyed on the metal surface and in local places. The effect of the corrosion is to form fine holes or pits, resulting in irregularly distributed small pit-like corrosion on the surface of the material. 2. Factors causing pitting Pitting corrosion is likely to be the presence of chloride ions in combination with depolarizers. Pitting corrosion of passive metals such as stainless steel is often caused by localized destruction of the passivation film by some aggressive anions, and protection of passive states with high corrosion resistance. An oxidizing environment is usually required, but this is also the condition for pitting. The medium in which pitting occurs is a heavy metal ion such as FE3+, Cu2+, Hg2+ or a chloride solution containing Na+, Ca2+ alkali and alkaline earth metal ions of H2O2, O2 or the like in a C1-, Br-, I-, Cl04-solution. The pitting rate increases with increasing temperature. For example, in a solution having a concentration of 4% to 10% sodium chloride, the weight loss caused by pitting corrosion is maximized at 90 ° C; for a more dilute solution, the maximum value occurs at a higher temperature. 3. Methods to prevent pitting Avoid concentration of halogen ions. To ensure the uniformity of the oxygen or oxidizing solution, stir the solution and avoid small areas where the liquid does not flow. Either increase the concentration of oxygen or remove oxygen. Increase the pH. Compared to neutral or acidic chlorides, the apparently alkaline chloride solution causes less pitting or is completely absent (the hydroxide ions act as an anticorrosive). Work at the lowest possible temperature. Add a passivating agent to the corrosive medium. Low concentrations of nitrate or chromate are effective in many media (preventing ions from preferentially absorbing on the metal surface, thus preventing chloride ions from damaging and causing corrosion). Using cathodic corrosion protection. There is evidence that stainless steel cathodically protected with low carbon steel, aluminum or zinc does not cause pitting in seawater. Austenitic stainless steel containing 2%-4% molybdenum has good pitting resistance. The use of molybdenum-containing austenitic stainless steels can significantly reduce pitting or general corrosion, such as sodium hydride solution, seawater, sulfurous acid, sulfuric acid, phosphoric acid and formic acid. 3. Intergranular corrosion Unstable austenitic stainless steels containing less than 0.03% carbon (titanium-free or niobium-free grades) are prone to intergranular corrosion in certain environments if not properly heat treated. Intergranular corrosion occurs when these steels are heated between 425 and 815 ° C or slowly cooled through this temperature range. Such heat treatment causes carbides to precipitate at the grain boundaries (sensitization) and causes the chromium depletion in the nearest region to make these regions susceptible to corrosion. Sensitization can also occur during welding, causing localized corrosion in the heat affected zone of the weld. The most common method for checking the sensitivity of stainless steel is the 65% nitric acid corrosion test method. During the test, the steel samples were placed in a boiling 65% nitric acid solution for a period of 48 hours for a total of 5 cycles, and the weight loss was measured in each cycle. Generally, the average corrosion rate for 5 test cycles should be no more than 0.05mm/month. Intergranular corrosion of austenitic stainless steel welded structures can be prevented by: Use low carbon grade 00Cr19Ni10 or 00Cr17Ni14Mo2, or stable grade 0Cr18Ni11Ti or 0Cr18Ni11Nb. Use these grades of stainless steel to prevent the precipitation of carbides during welding to cause harmful effects. If the face structure is small and can be heat-treated in the furnace, heat treatment may be performed at 1040-1150 ° C to dissolve the chromium carbide, and rapid cooling in the interval of 425-815 ° C to prevent rumination. Welded ferritic stainless steel may also exhibit intergranular corrosion in certain media. This is caused by precipitation of carbides or oxides and metal lattice strain when steel is rapidly cooled from above 925 ° C. Stress-relieving heat treatment after welding can eliminate stress and restore corrosion resistance. Adding more than 8 times the carbon content of titanium to 1Cr17 stainless steel generally reduces the intergranular corrosion of the welded steel structure in some media. However, the addition of titanium is not effective in concentrated nitric acid. 4. Stress corrosion crack Stress corrosion cracking is a combination of static stress and corrosion that causes cracks and metal embrittlement. Only tensile stress causes this form of damage. In fact, all metals and alloys (except for very few metals) are prone to stress corrosion cracking in certain environments. The damage to certain metals is either “stress corrosion” or “hydrogen embrittlement” (eg high There are also some different opinions on the cracking of strength steel in hydrogen sulfide. For the sake of discussion, all such damage caused by the external environment is included in the stress corrosion cracking. Hardened (quenched and tempered) martensitic stainless steels are sensitive to stress corrosion cracking in solutions containing chlorides, thermal hydroxides or nitrates, or hydrogen sulfide. For austenitic stainless steels, the hydroxide solution of concentrated chloride is the main medium causing stress corrosion cracking. It has been shown that several other environments can also cause stress corrosion cracking in austenitic and martensitic stainless steels. However, it should be noted that in many such environments, the presence of impurities may have caused cracks. Sensitized austenitic stainless steels are sensitive to intergranular forms of stress corrosion cracking. If the sensitivity is severe and/or the stress is high, this form of crack may be produced in an environment considered to be weak. Sensitized and austenitic stainless steels must not be used for stress conditions unless sufficient tests are performed to demonstrate that the environment encountered does not cause intergranular stress corrosion cracking. The environment in which stress corrosion cracking occurs is often quite complex. E.g. The stress involved is usually not just the working stress, but the combination of residual stresses in the metal that are produced, welded, or heat treated. This situation can often be mitigated by the method of stress relief after fabrication. In the same gear, as mentioned above, the corrosive medium causing the crack is often only an impurity in the product being processed. In the overall solution, the amount of corrosive medium present may not be sufficient to cause cracking, but at the crack or in the splash zone above the liquid, the local concentration of the medium may cause damage. Although there are several general methods for preventing stress corrosion cracking, the best method is to use materials that are resistant to stress corrosion cracking in this environment. Therefore, 0Cr18Ni13Si4 (American AISLX M15) or ferritic stainless steel should be used in the hot chloride environment. The use of ferrite and austenitic stainless steels in a hydrogen sulfide environment is generally suitable, and hardened martensitic stainless steels cannot be used. Source: China Pipe Fittings Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The wide range of surface finishes in stainless steel broadens its field of application – different surface finishes make stainless steel surfaces different, making them unique in their applications. In the field of architectural applications, the surface processing of seamless stainless steel pipes is important for a number of reasons. A corrosive environment requires a smooth surface because the surface is smooth and not easily fouled. The deposition of dirt can rust or even cause corrosion of the stainless steel. In the spacious hall, stainless steel is a commonly used material for elevator decorative panels. Although the surface fingerprint can be wiped off, it affects the appearance, so it is good to choose a suitable surface to prevent fingerprints. Hygienic conditions are important in many industries, such as food processing, catering, brewing, and chemicals. In these applications, the surface must be easily cleaned daily, and chemical cleaners are often used. Stainless steel is a good material for this. In public places, the surface of stainless steel is often ridiculed, but one of its important characteristics is that it can be washed away, which is a remarkable feature of stainless steel over aluminum. The surface of aluminum tends to leave traces and is often difficult to remove. When cleaning the stainless steel surface, it should be cleaned along the lines of stainless steel, because some surface processing lines are unidirectional. Seamless stainless steel tubing is suitable for hospitals or other areas where hygienic conditions are critical, such as food processing, catering, brewing and chemicals, not only because it facilitates daily cleaning, but sometimes with chemical cleaners, and because it is not easy Breeding bacteria. Tests have shown that stainless steel has the same properties as glass and ceramics in this respect. 1. Natural appearance of stainless steel Stainless steel gives a natural, sturdy, natural feel that gently reflects the color of the surroundings. 2. Basic types of surface processing There are roughly five types of surface finishes that can be used for stainless steel, which can be combined to transform more end products. There are five types: rolling surface processing, mechanical surface processing, chemical surface processing, textured surface processing, and colored surface processing. There are also some special surface finishes, but regardless of which surface finish is specified, the following steps should be followed: 1 Work with the manufacturer to agree on the required surface finish, and prepare a sample as a standard for future mass production. 2 When using in large area (such as composite board, it must be ensured that the same type of base coil or coil is used. 3 In many architectural applications, such as the interior of the elevator, although the fingerprint can be wiped off, it is not beautiful. If you choose a textured surface, it is not so obvious. Mirror stainless steel pipes must not be used in these sensitive areas. Mirror stainless steel pipe Mirror stainless steel seamless pipe 4 When selecting the surface processing, the manufacturing process should be considered. For example, in order to remove the beads, it is necessary to repair the weld and restore the original surface processing. The tread plate is difficult or even impossible to meet this requirement. 5 For some surface processing, grinding or polishing lines are directional, known as one-way. If the texture is made to be vertical rather than horizontal, the dirt is less likely to adhere to it and is easy to clean. 6 No matter which kind of finishing is used, it is necessary to increase the process steps, so increase the cost, so choose the surface plus Work hours should be cautious. Therefore, architects, designers, and manufacturers need to have an understanding of the surface finish of stainless steel. Through friendly cooperation and mutual communication with each other, we will surely achieve the desired results. 7 Based on our experience, we do not recommend the use of alumina as an abrasive unless careful during use. It is good to use silicon carbide abrasives. 3. Standard surface processing Many types of surface processing have been represented by numbering or other classification methods, and they have been incorporated into relevant standards such as “British Standard BS1449” and “American Iron and Steel Association Stainless Steel Producers Committee Standard”. 4. Rolling surface processing There are three basic rolling surface finishes for sheet and strip, which are expressed by the production process of the sheet and the village. No. 1: Hot rolled, annealed, pickled, and descaled. The treated steel sheet surface is a dull surface and is somewhat rough. No.2D: It is better than the surface of N0.1 and is also a dull surface. After cold rolling, annealing, descaling, and then light rolling with a matte roll. No.2B: This is commonly used in architectural applications. It is the same as 2D except for the subsequent cold rolling with a polishing roller after annealing and descaling. The surface is slightly illuminated and can be polished. No. 2B Bright Annealing: This is a reflective surface that is rolled by a polishing roll and subjected to a final annealing in a controlled atmosphere. Bright annealing still maintains its reflective surface and does not produce scale. Since the oxidation reaction does not occur during the bright annealing process, it is not necessary to perform pickling and passivation treatment. 5. Polished surface processing No. 3: It is represented by 3A and 3B. “ 3A: The surface is uniformly ground, and the abrasive grain size is 80 to 100. 3B: The matte surface is polished, and the surface has a uniform straight line. Usually, it is formed by polishing the belt with a particle size of 180-200 on the 2A or 2B board. No.4: Unidirectional surface processing, low reflectivity, this surface processing may be versatile in architectural applications. The process steps are first polished with a coarse abrasive and then with an abrasive having a particle size of 180. No.5: A further improvement to No. 4, which is polished with a Tampico polishing brush in abrasive and oil media. 4 surface. This surface finish is not available in “British Standard 1449”, but can be found in the US standard. No.6: Known as bright polishing, it polishes the surface that has been ground very fine but still has scratch marks. Typically 2A or 2B plates are used, with fiber or cloth polishing wheels and corresponding polishing pastes. No.7: Mirror-finished surface with high reflectivity, often referred to as mirror-surface finish, because the image it reflects is sharp. The stainless steel pipe is continuously polished with a fine abrasive and then polished with a very fine polishing paste. It should be noted in architectural applications that such surfaces can be left handprints if used in places where people are heavily mobile or where people often touch them. The fingerprint can of course be erased, but sometimes it affects the appearance.  Source: China Seamless Stainless Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The stainless steel seamless tube is softened by solution treatment. Generally, the stainless steel seamless tube is heated to about 950 to 1150 ° C for a period of time, so that the carbide and various alloy elements are sufficiently uniformly dissolved in the austenite, and then rapidly quenched. Water cooling, carbon and other alloying elements are too late to precipitate, to obtain pure austenite structure, called solid solution treatment. There are three points in the role of solution treatment: Make the uniformity and composition of the stainless steel seamless pipe uniform, which is especially important for the raw materials, because the rolling temperature and cooling rate of each section of the hot rolled pipe are different, resulting in inconsistent structure. At high temperatures, atomic activity is intensified, the σ phase dissolves, the chemical composition tends to be uniform, and a uniform single-phase structure is obtained after rapid cooling. Eliminate work hardening to facilitate further cold work. Through the solution treatment, the lattice recovery of the twist, the elongated and broken crystal grains recrystallize, the internal stress is eliminated, the tensile strength of the steel wire is lowered, and the elongation is increased. Restore the inherent corrosion resistance of stainless steel tubes. Due to the precipitation of carbides caused by cold working, the lattice defects cause the corrosion resistance of the stainless steel tube to decrease. After the solution treatment, the corrosion resistance of the stainless steel seamless tube is restored to a good state. For stainless steel seamless pipes, the three elements of solution treatment are temperature, holding time and cooling rate. The solution temperature is mainly determined based on the chemical composition. Generally speaking, the number of alloying elements is high, and the solid solution temperature is correspondingly increased. In particular, steels with high manganese, molybdenum, nickel, and silicon content can only achieve a softening effect by increasing the solid solution temperature and allowing them to be fully dissolved. However, stabilized steel, such as 321 stainless steel tube, has a high solid solution temperature and the carbide of the stabilizing element is sufficiently dissolved in the austenite, and precipitates at the grain boundary in the form of Cr23C6 in the subsequent cooling, causing intergranular corrosion. In order to prevent the carbides (TiC and NbC) of the stabilizing element from decomposing or being solid-solved, the lower limit solid solution temperature is generally employed. Source: China Steel Pipes Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)