Creep Behaviour of P92 and P92 Welds at 675°C

Abstract

The results of an accelerated creep test programme on the leading new build high temperature power plant pipework ferritic steel P92 and two P92 welds are presented. Tests were performed at 675°C, which is above the service operating temperature range recommended for P92, but allowed for more realistic operating stresses to be used. Comparison with similar tests of P92 at lower temperatures has shown that testing at 675°C produces the same general creep behavior, and can therefore be used for component life assessments in the service operating temperature range. Axially loaded parent P92 material uniaxial round bar and notched bar specimens, given a heat treatment equivalent to that given post-welding, are compared with weld metal specimens and cross-weld specimens extracted from welds made using both a similar P92 consumable and a dissimilar IN625 nickel alloy consumable. Both welds exhibited typical premature ferritic steel weld failure at the heat-affected zone (HAZ) and parent material interface, known as Type IV. The creep crack growth behavior of parent material, weld metal and the HAZ was studied using compact tension specimens. Impression testing was performed to determine the relative creep behavior of the HAZ. The HAZ was found to have the highest minimum creep strain rates and creep crack growth rates, indicating the relative weakness of this region.