Analysis on microstructure and properties evolution and life prediction of P92 steel in high temperature service

Abstract

P92 steel (10Cr9MoW2VNbBN) is widely used in high-temperature steam piping and high-temperature header fabrications of ultra-supercritical units. In this paper, a follow-up study on the microstructure, mechanical properties and life of P92 steel steam pipes which are virgin, 31,000 h in service, 49,000 h in service and 71,000 h in service was carried out. The results show that the mechanical properties of the P92 steel drop significantly after 31,000 h of service, then decrease slowly with the increase of the service time. When the service time reaches 71,000 h, the high temperature yield strength, percentage elongation, and impact absorbed energy are all close to the lower limit regulated by the ASME standard. Moreover, the morphology of lath martensite becomes fragmentary, the width of the martensitic lath increases and carbide particles cluster and grow at the grain boundary. M23C6 phase coarsens and local Laves phase precipitates. Meanwhile, the dislocation density decreases to some degree. Furthermore, there is a good corresponding relationship between the room temperature hardness and the high temperature tensile strength of the P92 steel after a long period of service. The prediction model of the remaining endurance life of P92 components is proposed on the basis of the room temperature hardness.