An analysis of published creep rupture data for modified 9%Cr steel weldments

TWI Industrial Member Report Summary 598/1997

K Bell

This report (prepared in March 1992) considers the crossweld creep rupture strength of modified 9%Cr steel (a candidate material for high temperature pressurised components in conventional and advanced thermal and nuclear power generation plant).

Background

Modified 9%Cr steel (ASTM T91 and P91) offers considerable creep strength advantages over other low alloy ferritic steels, offering material and fabrication cost savings. However, welds in this material have been found to be susceptible to a particular form of creep failure known as Type IV cracking, characterised by locally intense cavitation damage in the HAZ outer regions. Typically the Type IV region in modified 9%Cr steel weldments has a creep rupture strength 20-30% lower than the parent. This reduction in strength leads to creep rupture lives being reduced by approximately an order of magnitude.