Mechanical Behavior of Multipass Welded Joint during Stress Relief Annealing

Abstract

An investigation into mechanical behavior of a multipass welded joint of a pressure vessel during stress relief annealing was conducted. The study was performed theoretically and experimentally on idealized research models.
In the theoretical analysis, the thermal elastic-plastic creep theory developed by the authors was applied. The behavior of multipass welded joints during the entire thermal cycle, from welding to stress relief annealing, was consistently analyzed by this theory. The results of the analysis show a good, fundamentally coincidence with the experimental findings.
The outline of the results and conclutions is as follows.
(1) In the case of the material (21/4Cr-lMo steel) furnished in this study, the creep strain rate during stress relief annealing below 575°C obeys the strain-hardening creep law using the transient creep and the one above 575°C obeys the power creep law using the stational creep.
(2) In the transverse residual stress (σx) distribution after annealing, the location of the largest tensile stress on the top surface is about 15 mm away from the toe of weld, and the largest at the cross section is just below the finishing bead. These features are similar to those of welding residual stresses. But the stress distribution after annealing is smoother than one from welding.
(3) The effectiveness ofstress relief annealing depends greatly on the annealing temperature. For example, most of residual stresses are relieved at the heating stage with a heating rate of 30°C/hr. to100°C/hr. if the annealing temperature is 650°C, but if the annealing temperature is 550°C, the annealing is not effective even with a longer holding time.
(4) In the case of multipass welding residual stresses studied in this paper, the behaviors of high stresses during annealing are approximated by ones during anisothermal relaxation.