High Temperature Relaxation of Residual Stress in SA213-T92 Welded Pipe

Welded SA213-T92 pipes were annealed at 600-750 ℃ for different times. The residual stresses in welded pipes before and after annealing were tested, and the thermal relaxation behaviors of residual stress were analyzed. The relaxation activation energy was obtained by calculation based on high temperature relaxation kinetic curves. The results show that the residual stress along longitudinal direction was higher than along the transverse direction before annealing. But both of them had similar distributions that tensile residual stress became smaller with increasing the distance from the welding line. The residual stress of the surface of welded pipe after annealing at different temperatures decreased compared with before annealing. With the increase of temperature, the tensile residual stress decreased. According to the relaxation kinetic curves at different annealing temperatures, the coefficient B in creep equivalent equation was 5.07×104, the stress exponent n was 4.4 and the relaxation activation energy was 242 kJ·mol-1 by calculation.