Creep Damage Development of a 1.25Cr-0.5Mo Steel Weldment Exposed to Long Term Service

Abstract

Most of mechanical problems take place at weldment especially for the components operated in the creep regime. In the present paper, creep damage development of a service exposed 1.25Cr-0.5Mo steel weldment containing the service induced damage at HAZ associated with high temperature operation for 23 years has been examined. The components fabricated from a 1.25Cr-0.5Mo steel tend to suffer premature Type III damage at the early stage of operations. Though the similar tendency has been observed in the current work, the ultimate failure mode has been predominantly Type IV. The Type IV failure was generated in a relatively short period of time by applying spirally notched specimens. The transition of a failure mode from ductile transgranular rupture at a parent material to brittle intergranular cracking at Intercritical HAZ (ICZ) took place with the increase in time to failure. And the difference in the susceptibility to damage at HAZ between two materials (a pipe fabricated from plates and a forged flange) constituting welds was found. Despite lower creep strength of a pipe parent, HAZ generated on the pipe side has been almost immune to both Type III and Type IV damage in the testing conditions examined, suggesting that the creep life of weldment is not necessarily determined by creep strength of parent materials.