Large diameter steel pipe

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Large Diameter Steel Pipe

Large diameter steel pipe with an outer diameter more than 100MM and the ratio of wall thickness to diameter greater than 0.2. Mechanical properties of large diameter steel pipe is to ensure that large-diameter steel pipe end-use properties (mechanical properties) are an important indicator, it depends on the chemical composition of the steel pipe and heat treatment system. 

Large diameter steel pipe welding heat treatment is a new technique to eliminate residual stress. After the material is preheated before welding to heat treatment temperature and in the butt welding process to maintain the temperature of the heating element continuously, after the welding is completed using its thermal insulation cotton allowed to cool slowly. This method can effectively reduce the welding residual stress, increase resistance to stress corrosion of metals. NDT weld inside the pipe due to pipe in water supply projects are large, especially the thickness t = 30mm steel tube is used as a pipe bridge, both within withstand water pressure, but also the burden of weight and water is formed from steel pipe moment, so the quality of the welding requirements are particularly high. For pipe bridge with the t = 30mm thick, large diameter pipe, its longitudinal seam and girth welds belong to a class, called for 100% of the X-ray film examination and 100% ultrasonic flaw detection; while the thickness t = 24mm buried pipe, belong to a class of longitudinal seam welding, carried 20 percent of the X-ray film examination and 50% of the ultrasonic flaw detection. 

Heat treatment after welding can effectively reduce the welding residual stress, and heat treatment temperature is higher, the better the effect of residual stress relief. Large diameter steel heat treatment after welding can be effectively improved stress corrosion resistance of large diameter pipe, the higher the heat treatment temperature, stress corrosion resistance increased more significant. Diffusion method metal carbide coating technology is placed in special medium workpiece, the diffusion layer to form a metal carbide layer a few microns to tens of microns to the workpiece surface. Corrosion inside the large diameter steel pipe corrosion of buried pipes and clear tubes are used to hang galvanized wire, spraying compressive strength of not less than 30N / mm2 cement mortar lining.