Welded steel compressive corrosion can occur only in a specific environment, it also has the following characteristics: firstly, the presence of only the stress (tensile stress in particular) is to stress corrosion cracking. This stress can be applied stress or residual stress introduced during the welding and processing of T, it can be expanded to stress corrosion products caused by the wedge effect. Secondly, stress corrosion cracking is a time lag of about destruction, which delayed cracking and hydrogen completely similar. Thirdly, compressive corrosion cracking is a low-pressure brittle fracture.
Compressive corrosion cracking is a petrochemical equipment, especially oil pipeline is a common cause of failure of welded steel pipe. Due to the unpredictability of compressive corrosion cracking occurred, and therefore the largest petrochemical industry hazards. A necessary condition for the occurrence of compressive corrosion cracking and corrosion medium tensile strength coexistence, the tensile strength is an important condition for compressive corrosion. In the petrochemical and nuclear industries equipment, most of the stress caused by corrosion cracking is caused by the residual tensile strength, it is often superimposed on job. Mainly from tensile residual stress generated in the device during welding. Currently, the project is widely used to eliminate residual stress annealed after welding cooling, and cooling after welding is an important process, this approach is not a waste of energy and easy to produce larger welding residual stresses. Post weld heat treatment is a new technique to eliminate residual stress. After the material is preheated before welding to heat treatment temperature and the welding process to maintain continuous heating of the weld member that temperature after soldering using its thermal insulation cotton allowed to cool slowly. This method can effectively reduce the welding residual stress, improve resistance to compressive corrosion of metals.
Post weld heat treatment can effectively reduce the welding residual stress, and heat treatment temperature is higher, it will be more better. Heat treatment after welding can be effectively improved compressive corrosion resistance welded steel pipe, the higher the heat treatment temperature, compressive corrosion resistance increased more significant. Post weld heat treatment is a new technique to eliminate residual stress. After the material is preheated before welding to heat treatment temperature and the welding process to maintain continuous heating of the weld member that temperature after soldering using its thermal insulation cotton allowed to cool slowly. This method can effectively reduce the welding residual stress. Heat treatment after welding can be effectively improved stress corrosion resistance welded steel pipe, the higher the heat treatment temperature, stress corrosion resistance increased more significant. With the continuation of the electrolysis reaction, the solution is close to the anode interface layer, the electrolyte concentration may develop into a saturated or supersaturated state. After the coating is applied to the steel material pretreatment ri indirectly affect the quality of the coating off the force attached to compete.
