Structural metastability of “cold” repair welds in 2.25Cr-1Mo (P22) steel under elevated temperature and stress conditions

This paper investigates the effects of accelerated creep testing of a temperbead (TB) repair weld for a P22 pressure vessel component that was produced without post-weld heat-treatment (PWHT). The mechanical properties of the “cold” (non-PWHT) weld metal were superior to those of aged parent metal and the original fabrication welds for all tests, with the notable exception of creep performance. The creep performance of the TB repair weld material was inferior to that of the aged parent metal, due to the metastability of the weld metal microstructure relative to restoration processes occurring at the “accelerated” temperatures used for testing. It is concluded that the test conditions induced structural changes that are unlikely to occur under the actual service conditions and resulted in a creep life assessment that was highly conservative. The reported results are relevant to the security and integrity of non-PWHT repair welding of high-energy piping components.