No abstract

No abstract

In the current study, simulating residual stress distributions has been investigated for an AISI 316H austenitic stainless steels weld header and compared to actual measured residual stresses. These welds connect the outlet nozzle to the archetypal header 1B1/1 which was ex-serviced from Heysham power plant in UK. Finite element (FE) analyses of different load and boundary conditions have been performed to predict the optimum stress distribution around the cracking region to compare with available measured residual stress distributions in the literature. The FE predictions show that a remote displacement control tensile load on the nozzle with fixed vertical movement of cylinder can best fit the measured residual stress distribution. Hardness profile across the weld cross section indicates that the hardness gradually decease from HV 210 in weld metal to HV 160 in base metal, however, in the fusion away from 3 mm, the hardness were over HV 240. The facts indicate that the primary crack is likely to initiate at high hardness boundary and propagate in the direction of the highest principal stress regardless of the material hardness. Hypothesis of mechanism to the crack propagation is considered and proposals to predict damage and cracking in the header using FEM are presented.

Determination of long-term creep rupture properties for 316H steel is both costly and time-consuming and given the level of scatter in the data would need substantial number of tests to be performed. The primary objective of this study is to estimate the long-term creep properties of cross-weld (XW) and as-received (AR) 316H stainless steel by performing accelerated tests on pre-compressed (PC) material. In this work, uniaxial creep rupture tests have been performed on XW specimens and the results have been used to establish a correlation with accelerated test results on the PC material. Moreover, tensile tests have been performed on XW specimens at room temperature and 550 °C to examine the pre-conditioning effects on the mechanical response of the material. Similar power-law creep properties have been found for the creep strain rate and rupture time behaviour of the XW and PC specimens. It also has been found that the creep ductility data points obtained from XW and PC specimens fall upon the estimated trend for the AR material at 550 °C when the data are correlated with the applied stress normalised by 0.2% proof stress. The results show that the long-term creep properties of the XW and AR material can be estimated in much shorter time scales simply by performing tests on the PC material state.