Stress corrosion Cause
Large diameter oil pipeline stress corrosion cracking is a lag time-related damage, this hydrogen delayed cracking completely similar. Stress corrosion cracking (SCC) is a low-stress brittle fracture. Q345B spiral steel stress corrosion can occur only in specific circumstances, only the presence of stress (tensile stress) in particular, in order to stress corrosion cracking. Such stress can be applied stress, or the introduction of residual stress in the weld processing T process, the expansion stress can be caused by the wedging action of the corrosion product. Stress corrosion cracking in petrochemical equipment, in particular, is a common cause of failure in oil pipeline with spiral steel. Unpredictability due to stress corrosion cracking occurred, it is the biggest hidden trouble in the petrochemical industry. Equipment of petrochemical and nuclear power plants and other industries, most of the stress caused by stress corrosion cracking is caused by the residual tensile stress, it is often superimposed on the work stress. The tensile residual stress is mainly derived from the residual tensile stress generated by the device during the welding process. The necessary conditions for stress corrosion cracking is the tensile stress and corrosive media coexist, the tensile stress is important to stress corrosion.
Protective measures
Annealing treatment to eliminate residual stress, widely used in engineering welding cooling, cooling after welding residual stress generated important process, this approach is only a waste of energy and prone to large welding residual stress. The post weld heat treatment is a new eliminate residual stress technique. Before welding, the material is preheated to the heat treatment temperature and weldments continued heating to maintain this temperature, after completion of welding using cotton insulation its insulation to slow cooling during the welding process. This method can effectively reduce the welding residual stress, improve the metal resistance to stress corrosion. Post weld heat treatment can effectively reduce residual stresses, and the higher the heat treatment temperature, the better to eliminate the effect of residual stress. Post weld heat treatment can also effectively improve the stress corrosion resistance of large diameter steel pipe, the higher the heat treatment temperature, the more significant the resistance to stress corrosion ability.
Post time: Oct-29-2019