Failure analysis of a reheater tube dissimilar metal weld failure in a 500 MW power plant

Abstract

Dissimilar metal welding (DMW) finds extensive use in final sections of reheater tubing where the expected temperatures reach the maximum. Dissimilar weld failures are reported to occur at the weld interface, the heat affected zone and in the base metal depending on the operating parameters and stress level experienced during service. This paper presents a failure investigation of a reheater tube dissimilar weld failure, where the observed crack path cannot be described by any previously reported literature. The investigation leads to find the combination of i) tube restraint ii) shallow weld angle and iii) overheating conditions to be the root cause of failure. Recommendations are made based on the observations to prevent recurrence of reheater tube dissimilar weld failure.