LSAW steel pipe after heat treatment is a new technology to eliminate residual stress. Before welding, the material is preheated to the heat treatment temperature and butt welding process to maintain the temperature of the continuous heating component. After welding, the insulating cotton is used to cool it slowly. This method can effectively reduce the welding residual stress and improve the stress corrosion resistance of metals.


Non-destructive testing of internal welding is very important for large steel pipes in water supply engineering, especially for steel pipes with thickness of T = 30mm, which can withstand not only internal water pressure, but also its own weight and the moment of water piping formed by molten steel. For large diameter pipelines with thickness t = 30mm, longitudinal seam and circumferential seam belong to one category, which requires 100% X-ray film detection and 100% ultrasonic flaw detection; for buried pipelines with thickness t = 24mm, longitudinal seam welding belongs to 20% X-ray film inspection and 50% ultrasonic flaw detection.


Postweld heat treatment can effectively reduce welding residual stress, and the heat treatment temperature is higher, the residual stress is better. The post-weld heat treatment of large diameter pipelines can effectively improve the stress corrosion resistance of large diameter pipelines. The higher the heat treatment temperature, the better the stress corrosion resistance. The diffusion method of metal carbide coating is to place the workpiece in a special medium and form a layer of metal carbide by diffusing several microns to tens of microns on the workpiece surface. Anti-corrosion and anti-corrosion of buried large diameter steel pipes and transparent pipes are used for hanging galvanized steel wires. The compressive strength of spraying is not less than 30N/mm2 of cement mortar lining.