Long term creep–rupture behaviour of 813 K exposed 2.25–1Mo steel between 773 and 873 K

Samples machined from 17-year service-exposed 2.25Cr–1Mo steel superheater and reheater tubes from a thermal power plant boiler were creep–rupture tested in air between 773 and 873 K at various stress levels. Analysis of the steady state creep rate and time to rupture data indicated that both quantities could be described by normal temperature compensated power laws and the Monkman–Grant equation. The stress exponent and activation energy for creep suggest that deformation is the result of a dislocation climb controlled mechanism. Comparison of the time to rupture data to the acceptable ASME range for virgin 2.25Cr–1Mo using a Larson–Miller Parameter analysis indicated that the exposed alloy was essentially equivalent to that of the virgin material for stresses ≥60 MPa; however at lower stresses the exposed alloy is somewhat weaker than new steel. In spite of this decrease, it is predicted that the tubing could easily withstand another 100,000 h at current service conditions.