Post weld heat treatment on the stress corrosion resistance welded steel pipe impact

Welded steel pipe stress corrosion only in certain circumstances take place, it also has some of the following characteristics: (a) only if there is stress (especially tensile stress) only when the stress corrosion cracking. This stress can be applied stress, T or introduced during welding and processing the residual stress corrosion products can also be caused by the action of the expansion wedge stress. (2) Stress corrosion cracking is a lag time-related damage, which is completely similar to delayed cracking and hydrogen. (3) Stress corrosion cracking is a low-stress brittle fracture.Stress corrosion cracking is a petrochemical equipment, especially oil pipeline - a common cause of failure of welded tube. Due to stress corrosion cracking occurred unpredictability, so the petrochemical industry, the biggest hidden dangers. Stress corrosion cracking is a necessary condition for coexistence of tensile stress and corrosive media, the tensile stress is an important condition for stress corrosion. In the petrochemical and nuclear industries such as equipment, most of the stress caused by stress

Corrosion cracking is caused by the residual tensile stress, it is often superimposed on stress at work. Mainly from the device residual stresses produced during the welding residual stresses. Currently, the project is widely used welding cooling after annealing treatment to eliminate residual stress, while cooling after welding residual stress is an important process, this approach is not only a waste of energy and easy to produce larger welding residual stresses. Heat treatment after welding is a new technique to eliminate the residual stress. Preheated before welding the material to a heat treatment temperature after the welding process and welding pieces of heating was continued to maintain this temperature, the soldering is completed using heat insulation cotton to its slow cooling. This method can effectively reduce residual stress and improve the stress corrosion resistance of metals.

Heat treatment after welding can reduce the residual stress, and heat treatment temperature is higher, the better to eliminate the residual stress. PWHT welded steel pipe can effectively improve the resistance to stress corrosion, after the heat treatment temperature is higher, increasing resistance to stress corrosion is more significant.