ICONE23-1356 CREEP-FATIGUE CRACK GROWTH ASSESSMENTS OF AUSTENITIC 316H WELDS

Abstract

In a Nuclear Power Station, some austenitic 316H boiler platen support beams have been identified as potentially susceptible to reheat cracking, because their welds did not receive post weld heat treatment and they have been operated at sufficiently high temperatures. To ensure the integrity of these support beams, creep-fatigue crack growth assessments and creep deformation calculations for postulated extended, surface-breaking defects at the welds have been carried out using the latest R5 procedures, the plant operating temperature histories and welding residual stresses that had been calculated by finite element analysis. Limiting defect sizes have been calculated following the R6 procedure. The crack growth assessment has assumed a lifetime of 350,000 hours, and has conservatively assumed defect initiation at 510 hours in operation and an initiation crack depth of 2.3mm. Two base cases and three sensitivity studies have been investigated for all material regions including 316H parent material and Heat Affected Zone. The assessment results show that for this postulated initiation time and defect depth, integrity of the weld has been demonstrated to the lifetime of 350,000 hours.