Stress corrosion of erw pipe

Stress corrosion of erw pipe only in a specific environment can occur, it also has the following characteristics: (1) Only in the presence of stress (especially tensile stress) to produce stress corrosion cracking. This stress can be applied stress, or the residual stress introduced during welding, as well as the expansion stress caused by the wedging effect of corrosion products. (2) Stress corrosion cracking is a time-dependent hysteresis failure that is completely similar to hydrogen hysteresis cracking. (3) Stress corrosion cracking is a kind of low stress brittle fracture.

Stress corrosion cracking is a common cause of failure of petrochemical equipment, especially for welded oil pipelines. Due to the unpredictability of stress corrosion cracking, it is the biggest hidden danger in the petrochemical industry. The necessary conditions for stress corrosion cracking are the coexistence of tensile stress and corrosion medium, and tensile stress is an important condition for stress corrosion. In petrochemical and nuclear plants, most of the stresses that cause stress corrosion cracking are caused by residual tensile stress, which is often superimposed on the working stress. Residual tensile stress mainly from the equipment in the welding process of residual tensile stress. At present, the engineering is widely used after welding cooling annealing treatment to eliminate residual stress, and cooling after welding is an important process of residual stress, this approach is a waste of energy and easy to produce greater welding residual stress. Heat treatment after welding is a new technique to eliminate residual stress. The material is preheated to a post-heat treatment temperature prior to welding and the weldment is continuously heated to maintain this temperature during the welding process. After the welding is completed, the material is soaked with insulation wool to allow it to cool slowly. This method can effectively reduce the welding residual stress and improve the metal's stress corrosion resistance.

After welding, heat treatment can effectively reduce welding residual stress, and the higher the heat treatment temperature, the better the residual stress elimination effect. Post-weld heat treatment can also effectively improve the resistance to stress corrosion resistance of erw pipe, post-heat treatment temperature is higher, the more significant increase in anti-stress corrosion resistance