Estimation of material properties and maintenance of pressure parts of thermal power plant boilers under long-term service of 300,000 hours

Tensile and creep properties were investigated of 2 1/4 Cr–1Mo steel (A335 P22) taken from a main steam pipe operated for 300,000 hours for examining the effect of long-term operation. The test specimens in this study were taken from the circumferential welded joint of a Y-piece having been operated as a main steam pipe in a power plant for 302,188 hours at 839 K under 293 start–stop cycles. Creep test of a welded joint taken from this component was carried out and the remaining life prediction was performed considering Type IV damage. In this prediction, finite element creep analysis was combined with a microscopic damage simulation considering the effect of increase of number density of creep voids in the fine-grained heat-affected zone. Thus, the fracture time of the welded joint was predicted.