Indentation energy method for evaluating the effect of local PWHT on pressure vessels

Abstract

Post weld heat treatment (PWHT) is widely applied to improve the performance and eliminate residual stresses of the welded joint in the field of pressure vessels. However, a significant challenge arises in conducting in-situ evaluations of the local PWHT effectiveness during the manufacturing. The absence of reliable testing methods and instructive assessment cases make it difficult to carry out in engineering practice. In this work, two real-size 12Cr2Mo1V steel cylindrical shells were butt-welded together as an experimental product, which was then used for local PWHT and followed evaluation experiments. The Indentation Energy (IE) method was utilized to assess the residual stress and strength of the welded joint both before and after local PWHT. To verify its reliability, X-ray diffraction method, hole-drilling method and finite element analysis were also adopted. The results obtained from these methods show a great agreement. According to the test results, the residual stresses are redistributed after local PWHT, the peak stresses of the outer wall are reduced by about 70 % on average, and that of the inner wall are reduced by about 60 %. Particularly, there are still about 200 MPa axial tensile stresses on the inner surface due to the shrinkage deformation. After local PWHT, the tensile properties of the welded joint become uniform. The decrease in tensile properties of the weld metal is much greater than that of the base metal, but both within the standard range.