Creep properties and failure assessment of new and fully repaired P91 pipe welds at 923 K

Abstract

A creep testing programme was conducted at 923 K to identify the properties for new and repaired welds fabricated in a 9CrMoNbV grade P91 steel using a 9CrMoNbV weld metal. The material data obtained were assessed and used to determine the material creep and damage constitutive equations for the parent material (PM), weld metal (WM) and heat-affected zone (HAZ) materials in the P91 welds. Steady state creep and continuum damage finite element analyses were performed to assess the failure behaviour of the circumferential welds in the pipes, under two internal pressures and a range of end load levels. A full post-weld heat treatment is assumed to have been carried out, and any effects of welding-induced residual stresses were neglected. The results obtained have illustrated the main features of life reduction of a P91 pipe owing to the presence of welds, an additional life reduction due to repair and the more limited life reduction due to geometry difference, for the particular set of material properties used.