Creep rupture analysis and remaining life assessment of 2.25Cr–1Mo steel tubes from a thermal power plant

Abstract

Superheater and reheater 2.25Cr–1Mo steel boiler tubes from a thermal power plant after 17 year of service at nominally 540 °C and 40 MPa were studied to predict their remnant life. The investigation included dimensional, hardness and tensile measurements in addition to accelerated stress rupture tests between 625 and 700 °C and microstructural examination. The microstructure of the service-exposed alloy was free from any signs of deterioration, and the hardness was within the expected ranges; however, tensile testing revealed an apparent loss of strength from room temperature to 600 °C. Accelerated rupture testing, on the other hand, did not reveal any degradation of rupture behaviour compared to that of the virgin alloy. Analysis of the stress rupture data predicted that the 17 years exposed superheater and reheater tubes could remain in continued service for at least 12 more years at the current stress–temperature conditions.