Steel direct rolling resistance welding technology is a fast production pipeline technology, which is widely used in downhole casing, oil and gas gathering and transportation and other fields. However, the welding activity of the pipe is higher than that of base metal and heat affected zone, so the service life of the welded pipe is determined by the welding zone. Groove welding is a special phenomenon of crevice corrosion, which usually forms a groove in the weld zone. Under natural conditions, the formation of grooves easily makes the corrosion medium stagnate, leading to the decrease of dissolved oxygen concentration, and gradually forms the oxygen concentration of the battery seams and seams, accelerating the corrosion of the metal in the seams. At the same time, the residual metal ions in the corrosion process, observed in neutral sodium chloride solution gap, chloride in the main solution contains 3-10 times, with corrosion, corrosion products accumulated in the surrounding welds, such as Fe2+, often produce excessive H+, and stagnation effect makes metal in the welds, pH value. It can reach 2 to 3, so that the metal in the joint remains unchanged activation and promotes corrosion. When subjected to anodic polarization, the corrosion rate of substrate and weld mainly depends on its electrochemical activity.


Residual circumferential tensile stress of resistance welded pipe (ERW) is about 350 MPa, which is close to the yield strength of the pipe without heat treatment. When the welding enters the working electrode, the residual stress decreases to less than 100 MPa. The circumferential tensile stress can reduce the corrosion potential of the weld, accelerate the corrosion and increase the groove corrosion sensitivity coefficient. After heat treatment, the residual tensile stress in the weld is small, ranging from 10 MPa to 100 MPa, and the circumferential tensile stress is small when the working electrode is machined. In this way, the traditional measurement methods can not characterize the corrosion resistance of welded pipe products in practical application, nor can they really distinguish the effect of heat treatment on the corrosion resistance of welded pipe.