Heat treatment is a new technique for eliminating residual stress after welding of high frequency straight seam welded pipe. Before welding, the material is preheated to the post-heat treatment temperature, and the weld is continuously heated during the welding process to maintain the temperature. After welding, heat it with insulating cotton to cool it slowly. This method can effectively reduce the welding residual stress and improve the stress corrosion resistance of metals.


Because the non-destructive inspection of the weld of the pipeline in the water supply project is a large steel pipe, especially the steel pipe whose thickness is t = 30mm is used as the pipe bridge. It bears not only the water pressure, but also the weight of the steel pipe and the bending moment of the water, so the welding quality requirement is particularly high. For large diameter steel pipe with T = 30mm thickness, longitudinal seam and circumferential seam belong to one kind of weld, requiring 100% X-ray film inspection and 100% ultrasonic inspection; while for buried steel pipe with T = 24mm thickness, longitudinal seam is a kind of welding, 20% X-ray inspection and 50% ultrasonic inspection.


After welding, heat treatment can effectively reduce welding residual stress. The higher the heat treatment temperature, the better the effect of residual stress elimination. Heat treatment of large diameter steel pipe can also effectively improve the stress corrosion resistance of large diameter steel pipe. The higher the temperature after heat treatment, the more significant the improvement of stress corrosion resistance. The diffusion method of metal carbide coating is to place the workpiece in a special medium and diffuse it on the surface of the workpiece to form a layer of metal carbide from micron to tens of micron. Galvanized wire mesh is used for the anticorrosive buried and anticorrosive pipes in large diameter steel pipes. The compressive strength of the cement mortar lining is not less than 30N/mm2.