Consumed creep life fraction assessment of critical locations of an in-service super heater outlet header under surveillance programme

Abstract

Boilers and turbines including high-energy piping and headers are operated round-the-clock in the creep regime. For the integrity of such components and equipments, it is essential to have a real-time monitoring system to identify and monitor the critical locations. As per statutory requirement of IBR Act 391A of 1998, a component is to be taken for surveillance programme, if its design life is exhausted. One such exercise was conducted at locations in close proximity to the header-stub weld joints of higher heat-flux zone after 1,12,547 hours of operation. The in-situ metallography technique developed indigenously within the country (i.e., cryogenic in-situ metallography) was adopted for assessment of locations closest to the identified weld joints of a superheater outlet header (SHOH) of a 210 MW unit of a super thermal power station. The qualitative assessment done using high resolution microscopy has indicated that the creep cavities correspond to stage-II of Neubauer’s classification diagram. Subsequently image analysis of in-situ replicated photomicrographs extracted from the investigating locations was carried out. The accrued creep damages (cavitation) at the locations were quantified for cavitated grain boundaries and correspondingly ldA” parameters were derived to evaluate the extent of life exhaustion of respective locations.