Stress on the High-frequency Straight Seam Resistance Welding Pipe Trench Corrosion

The roll-formed steel direct high-frequency resistance welding technique is a rapid production of pipeline technology, currently in many areas such as: downhole casing, oil and gas gathering pipe has been widely used.

However, this pipe weld area than the base metal and the heat affected zone has higher activity, so the weld zone determines the service life of the pipe trench etching is a special pipe joints for crevice corrosion phenomena, usually It will form a trench in the weld zone. Under natural conditions, the formation of the trench easily inseam corrosive medium in the state of stagnation, leading to reduced oxygen concentration in the joints gradually oxygen concentration cell and outer seam formed to accelerate the corrosion of the metal seam.

High-frequency electric resistance welded (ERW) pipe as a whole without heat treatment, to achieve circumferential weld residual stress around 350MPa, close to the yield strength of the pipe. When the weld processing into working electrode, the residual stress is reduced to 100MPa or less. Circumferential tensile stress can reduce the corrosion potential of welds, accelerated corrosion, corrosion sensitivity increases trench coefficient and the welded pipe after the heat treatment, the tensile residual stress in the weld circumferential small as 10 ~ 100MPa, processed into a working electrode after its circumferential tensile stress is little change. Such conventional measurement methods can not characterize the welded pipe products in the practical application of corrosion resistance, and can not distinguish between real or not heat treatment on the corrosion resistance of welded pipe.