Complexities of In-Service Failures in Dissimilar Metal Welds Between Grade 91 and Austenitic Stainless Steels

Abstract

The efficiency of thermal power plants is related to operating steam pressure and temperature. The desire to maximize performance, while minimizing emissions, provides a large incentive to introduce new power generating plants with higher temperature and pressure. Improvements to design can offer important benefits, but, a key enabling technology to greater thermal efficiency is the development and acceptance of engineering materials with superior properties. Next generation heat recovery steam generators (HRSGs) are expected to require the use of thick-section dissimilar metal welds (DMWs) due a competitive market that is rapidly pushing increases in efficiency (and therefore an increase in steam temperature). There is an increasing concern that the current, “conventional practice” for fabricating DMWs is ill-established and not optimized for applications where the ferritic material is Grade 91 steel. To address the complexity of issues associated with the performance of DMWs, a series of research studies are underway with the Electric Power Research Institute. This paper reviews a number of in-service failures arising from DMWs between Grade 22 and austenitic stainless steels and Grade 91 and austenitic stainless steels.