The Role of Solution Treatment of LSAW Steel Pipe

Straight seam steel pipes are steel pipes whose welds are parallel to the longitudinal direction of the steel pipe. Usually divided into metric electric welded steel pipe, electric welded thin-walled pipe, transformer cooling oil pipe and so on. Longitudinal welded pipe has simple production process, high production efficiency, low cost and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. A narrower blank can be used to produce welded pipes with larger pipe diameters, and a billet with the same width can also be used to produce welded pipes with different pipe diameters. However, compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower.

What is the effect of LSAW steel pipe solution treatment:
1. Make the structure and composition of the longitudinally welded pipe uniform, which is especially important for the raw materials, because the rolling temperature and cooling rate of each section of the longitudinally welded pipe are different, resulting in inconsistent structure. At high temperatures, the atomic activity intensifies, dissolves, and the chemical composition tends to be uniform. After rapid cooling, a uniform single-phase structure is obtained.

2. Eliminate work hardening to facilitate continued cold working. Through solution treatment, the distorted crystal lattice is restored, the elongated and broken crystal grains are recrystallized, the internal stress is eliminated, the tensile strength of the steel wire is reduced, and the elongation rate is increased.

3. Restore the inherent corrosion resistance of the longitudinally welded pipe. Due to the precipitation of carbides and lattice defects due to cold working, the corrosion resistance of longitudinally welded pipes is reduced. After solution treatment, the corrosion resistance of the longitudinally welded pipe is restored to a good state.

The solid solution temperature is mainly determined according to the chemical composition. Generally speaking, the solid solution temperature should be increased correspondingly for the grades with various alloying elements and high content. Especially for straight seam welded pipes with high content of manganese, molybdenum, nickel and silicon, the softening effect can only be achieved by increasing the solid solution temperature and making it fully dissolved. But for stabilized steels, such as longitudinally welded pipes, when the solid solution temperature is high, the carbides of the stabilizing elements are fully dissolved in austenite, and will precipitate in the grain boundaries in the form of Cr23C6 during subsequent cooling, causing intergranular corrosion. In order to prevent the carbides of stabilizing elements from decomposing or solid solution, the lower limit solid solution temperature is generally adopted.

Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat 

treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces.