Effect of Stress on Groove Corrosion of Electric Resistance Welded Pipe
Date:2018-05-09 View:1062 Tag:Effect of Stress on Groove Corrosion of Electric Resistance Welded Pipe
The direct rolling technology of resistance welding is a rapid production line technology, which is widely used in many fields, such as underground casing, oil and gas gathering and so on, but its welding activity is higher than that of matrix metal and heat affected zone. Therefore, the welding area determines the service life of the welded pipe. Weld corrosion is a special crevice corrosion phenomenon of welded pipe, usually forming groove in weld area. Under natural conditions, the formation of the groove can cause the corrosion medium to be in a stagnant state, and the concentration of dissolved oxygen is reduced, and the oxygen concentration in the seam and seam seam is gradually formed, and the corrosion of the metal in the coal seam is accelerated. At the same time, the residual metal ions were observed during the corrosion process, and the neutral Sodium Chloride Solution was observed in the gap, and the chloride contained in the main solution was 3 to 10 times. With corrosion, the corrosion products accumulated around the weld, such as Fe2 +, and often produced excessive H + at the joint, and the stagnation effect made the metal in the joint. The pH value can reach 2 ~ 3, so that the metal in the seam is kept activated and the corrosion is accelerated. When the anode is polarized, the corrosion rate of the substrate and weld depends mainly on its electrochemical activity.
If the resistance welded pipe (ERW) is not heat treated through the pipe, the residual tensile stress around the weld is about 350MPa, which is close to the yield strength of the pipe. When the weld enters the working electrode, the residual stress falls below 100MPa. The circumferential tensile stress can reduce the corrosion potential of the weld, accelerate corrosion and increase the sensitivity of groove corrosion. After heat treatment, the residual tensile stress in the weld is small, which is 10 ~ 100MPa. In this way, the traditional measurement method can not characterize the corrosion resistance of welded pipe products in practical application, and can not really distinguish the effect of heat treatment on corrosion resistance of welded pipe.