1.High frequency straight seam welded pipe after welding, the heat treatment is a new elimination of residual stress technology. Before welding, the material is preheated to the post-heat treatment temperature and the weld is continuously heated during the welding process to maintain this temperature. After the welding is completed, it is warmed by the heat-insulating cotton to cool it slowly. This method can effectively reduce the welding residual stress, improve the metal resistance to stress corrosion.
2.Non-destructive testing of the weld due to the pipeline in the water supply project is a large steel pipe, especially the thickness of t = 30mm steel pipe is used as a pipe bridge, it is necessary to bear the water pressure, but also bear the weight of the steel pipe and water bending moment, so the quality of the welding requirements are particularly high. For the pipe with t = 30mm thick large diameter steel pipe, the longitudinal seam and ring joints are belong to a class of welds, requiring 100% X-ray film inspection and 100% ultrasonic inspection; and the thickness t = 24mm buried steel pipe, longitudinal seam is a class of welding, 20% of the X-ray film inspection and 50% of the ultrasonic testing.
3.After welding, the heat treatment can effectively reduce the welding residual stress, and the higher the heat treatment temperature, the better the residual stress elimination effect. The 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 remarkable the improvement of stress corrosion resistance. Diffusion method Metal carbide coating technology is the workpiece placed in a special medium, the role of diffusion on the surface of the workpiece to form a layer of micron to tens of microns of metal carbide layer. Large diameter steel pipe within the anti-corrosion buried pipe and the tube of the anti-corrosion, are used galvanized iron wire mesh, spraying compressive strength of not less than 30N / mm2 cement mortar lining.
