Points to note when connecting stainless steel pipes to other pipe fittings or flanges

In the actual application of stainless steel pipes, it is indispensable to butt to other stainless steel pipes or flanges. At this time, if you want to meet the corresponding use requirements, you must ensure that the butt quality between the stainless steel pipe fittings and the butt fittings reaches a certain standard. Let’s talk about it below. A few points to note in this regard.

One is the butt joint between stainless steel pipes. When the pipe groups are aligned, the inner walls should be aligned, and the gap between them should be less than 0.1mm. In order to ensure the assembly size and prevent welding deformation and misalignment, which will affect the normal welding and weld formation, most of the welding is done with positioning welding. The spacing of the positioning welding points is determined according to the grade, thickness and joint type of the material to be welded. Because stainless steel has a larger linear expansion coefficient than low carbon steel and greater welding deformation, spot welding should be smaller. For thinner and easily deformable weldments, the spacing should also be small. For weldments with greater rigidity and greater tendency to crack, in order to avoid solder joint cracking, long solder joints should be used and the size of the positioning solder joints should be shortened.

The tack welding should ensure complete penetration and reliable connection. The welding points should be low and flat, and should not be too long, too wide, or too high to avoid affecting the normal welding and weld formation. In order to avoid oxidation of the tack welding points, spot welding should be done during spot welding. Let the argon gas stay at the spot weld until the solder joint solidifies and is not oxidized. If spot welding cracks are found, they should be dealt with in time to prevent defects from remaining in the weld and affecting the welding quality.

During welding, because stainless steel pipes have a high affinity with oxygen, the inside of the pipe must be protected by hydrogen gas to ensure that the inner wall formed weld is not oxidized. In order to prevent welding defects caused by over-burning of the molten welding metal, for pipes with small diameters, the entire pipe can be filled with argon. This argon filling method is relatively simple. However, as the length of the pipeline increases, argon gas is wasted. Generally, segmented assembly welding is used. A small amount of middle welds are blocked on both sides of the welded pipe mouth with soluble paper. During the hydraulic pressure test, the soluble paper Dissolve on its own.

The intersection is the butt joint between thick and thin tubes. The butt joints of stainless steel pipes with different thicknesses will appear due to the wall thickness of the equipment pipe head and the wall thickness of the assembled pipes. If not handled properly, problems such as incomplete penetration, welding spots, or failure to weld will occur. The main reason is that the thin-walled pipes have been welded during welding. melts, while the thick wall has not yet reached the melting point temperature. In order to prevent the occurrence of such problems, thick-walled pipes must be ground into 45-degree bevels, and thin pipes must be ground into 20-degree bevels. In this way, the quality requirements can be fully met after welding.

The third is to weld the trifurcated pipe. The key point at this time is to cut the material accurately; the assembly must be reasonable; the groove must be processed; otherwise, the requirements cannot be met. When blanking, the diameter of the opening should be equal to the inner diameter of the connecting pipe, and then beveled. The connecting pipe must also be beveled. When assembly spot welding is carried out after processing, it should be carried out by welders with better skills. Each time we weld a l/4 of the trident, there are four angle changes, and the wire feeding speed is different each time. When the angle between the two tubes is 90 degrees, It is a critical part. The welding speed here should be slow to achieve penetration, and then the welding speed should be accelerated accordingly to keep the angle between the workpiece and the workpiece between 75-80 degrees. The interior must be smooth and flat after welding to meet quality requirements.

The last step is flange welding. At this time, a looper flange type connection is used. The flange is welded to the pipe. During welding, two points are spot welded at 180 degrees. Only after the flange is concentric with the pipe can other spots be welded. fixed point.