LSAW steel pipe after heat treatment is a new technology to eliminate residual stress. After the material is preheated before welding to heat treatment temperature and the butt welding process to maintain the temperature of the continuously heated member, after the welding is completed using its thermal insulation cotton allowed to cool slowly. This method can effectively reduce the welding residual stress and improve resistance to stress corrosion of metals.

Internal weld NDT since the large steel pipes in water supply project belongs, especially the thickness t = 30mm steel is used as a pipe bridge, both to withstand water pressure inside, but also the burden of its own weight and the water formed by a steel pipe moment, so the welding quality requirements are particularly high. For pipe bridge with a thickness t = 30mm large-diameter pipe, the longitudinal seam and girth weld belong to a class, require 100% of X-ray film examination and 100% ultrasonic flaw detection; and thickness t = 24mm buried pipe, longitudinal seam welding belongs to a class for 20% of the X-ray film examination and 50% of the ultrasonic flaw inspection.

Post weld heat treatment can effectively reduce the welding residual stress, and heat treatment temperature is higher, residual stress better. Large-diameter pipe post weld heat treatment can effectively improve the stress corrosion resistance of large diameter pipe, the higher the heat treatment temperature, resistance to stress corrosion increased more significant. Diffusion method metal carbide coating technology is the workpiece placed in special medium, formed by diffusion of metal carbide layer of a few microns to tens of microns on the workpiece surface. Anti-corrosion anti-corrosion of buried large diameter steel pipe and clear tubes are used to hang galvanized wire, spraying compressive strength of not less than 30N / mm2 of cement mortar lining.