Three Common Welding Processes For Square And Rectangular Tubes

Welded square rectangular pipes can be divided into arc welded pipes, high and low-frequency resistance welded pipes, gas-welded pipes, and furnace-welded pipes according to the process. According to the welding seam, they can be divided into straight seam pipes and spiral pipes. Next, we will introduce to you three common welding processes for rectangular tubes:

(1) Spiral welding

The welds are distributed in a spiral shape. Generally speaking, the weld area of square and rectangular pipes, including the weld heat affected zone, is the part of the steel pipe with poor mechanical properties. While the maximum internal stress of the pressure pipe is distributed along the axial direction, spiral welding will separate the weaker parts. The location avoids the direction of maximum internal stress, thereby improving the performance of the square and rectangular tubes. In addition, due to the spiral weld formation and the reinforced height of the weld, it is more difficult to perform external anti-corrosion, and gaps may be formed on both sides of the weld. Currently, some manufacturers use the process of lateral winding and coating of three layers of PE or two layers of PE. , which can solve the anti-corrosion problem of square and rectangular pipes.

(2) Straight seam submerged arc welding

Because it uses a post-weld cold expansion process to expand the pipe, the geometric dimensions of the UOE pipe are relatively accurate, and the quality of the butt joints is good to ensure the welding quality. Part of the internal stress is eliminated to a certain extent through the pipe expansion process. In addition, multi-wire welding is used when welding square and rectangular pipes. This welding process generates small linear energy and has a small impact on the heat-affected zone of the base metal. The rear welding wire of multi-wire welding can eliminate the stress generated during welding on the front welding wire, thereby improving the mechanical properties of the pipe. Compared with spiral welded pipes, straight seam submerged arc welded pipes have a shorter weld length, so welding defects and impacts are relatively small. In high-pressure pipelines, the base material of straight-seam pipes can be 100% ultrasonic tested for steel plates one by one, meeting the requirements for base materials of high-pressure pipelines. However, although the overall performance of straight-seam square and rectangular pipes is better than that of other pipes, its price is relatively high.

(3) High-frequency resistance welding

Because its welding process is compared with submerged arc welding, this process does not add any welding materials during the welding process, and the weld seam formation does not go through a thermal melting state, but the weld metal undergoes a recrystallization process, so the weld seam formed is different from the base metal. The chemical composition is exactly the same. The square and rectangular pipes are annealed after welding, and the internal stress of the cold working process and the internal stress of the welding are improved. Therefore, the comprehensive mechanical properties of the high-frequency resistance welded pipes are better.