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Precautions when connecting stainless steel pipe to other fittings or flanges

In the practical application of stainless steel pipes, there will be no other stainless steel pipes or flanges, fittings. At this time to meet the requirements of the use, it is necessary to ensure that the quality of the butt joint between the stainless steel pipe and the butt parts reaches a certain standard, and the following points are concerned.
One is the connection between the stainless steel pipe, tube group pair, inner Nezi gap should be less than 0.1mm. In order to ensure the size of the group, prevent welding deformation and dislocation, affect the normal welding and weld formation, most of the positioning welding is carried out. The distance between the location of the welding spot depends on the number, thickness and type of the welded joint. Because stainless steel has larger linear expansion coefficient and larger welding distortion than that of low carbon steel, spot welding should be small. For thinner and easily deformable weldments, the spacing should be small. For the welded parts with large steel and large cracks, long welding points should be used to avoid the cracking of the solder joints, and the size of the welding spot should be shortened.
Positioning welding should ensure complete penetration and reliable connection, low level of solder joints and not too long, too wide and too high to prevent the influence of normal welding and weld formation. In order to avoid oxidation of the spot welding point, the argon gas should stay at the spot welding spot to solidify without oxidation during spot welding. If spot weld cracking is found, it should be disposed in time to prevent defects from remaining in the weld and affect the welding quality.
During welding, because the affinity between stainless steel tube and oxygen is very large, the inner side of the pipe must be protected by hydrogen, so as to ensure that the inner wall weld is not oxidized. It also prevents welding defects from overheating of molten metal, and can be filled with argon by whole pipe, which is relatively simple. However, with the increase of the length of the pipeline, the waste of argon is much more wasteful. In general, subsection assembly and welding are adopted, and a small amount of intermediate joints are blocked by soluble paper on both sides of the welded pipe, and the soluble paper is dissolved in water pressure test.
Its intersection is the butt of the thick and thin tubes. The butt of stainless steel pipes with different thickness appears on the wall thickness of the pipe head of the equipment. If the treatment is not appropriate, there will be problems of unweld, welding or welding. The main reason is that the thin wall tube has been melted when welding, and the thick wall still does not reach the melting point temperature. To prevent such problems, it is necessary to grind the thick wall tube into 45 degree groove and add the thin pipe to 20 degree groove, so that after welding, it can completely meet the quality requirement.
The third is to weld the Trident pipe. The key point is to cut the material accurately, assembly is reasonable, and the groove must be machined, otherwise it will not meet the requirement. When the material is cut off, the aperture of the opening should be equal to the inner diameter of the connecting pipe, and then the groove must be made for connecting pipe. After the process of assembly spot welding, it should be carried out by a better welder with a better welder, L / 4 each of the three forked ports, four angle changes, the speed of the wire feeding is different, the key position is 90 degrees at the two pipe angle. The welding speed here should be slower to be welded, then the welding speed should be accelerated and the angle of the workpiece is kept from 75- to 80. Between degrees. After welding, the inner surface should be smooth and smooth.
Finally, the flange and stub end welding, at this time the use of looped flange connection, stub end and pipe welding, welding, spot welding point 180 degrees, find stub end and pipe concentric, can spot welding other fixed points.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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