An analysis of creep damage in a welded low alloy steel rotor

An assessment of commonly used creep-rupture extrapolation techniques on weldments was undertaken. Gas tungsten arc and submerged arc welds were fabricated using 1.0Cr-1Mo-0.25V rotor steel as base metal. Crossweld samples, which includes base metal, heat-affected zone and weld metal, were machined and submitted to isostress creep-rupture tests at 83.0 MPa between 690 and 620 °C. Larson-Miller and Monkman-Grant plots were produced from these data; the parameters associated with the Larson-Miller method were estimated and extrapolations were done to the service temperatures. The actual lives of the submerged arc crosswelds were shorter than predicted. Monkman-Grant predictions were more conservative than Larson-Millerʹs for the gas tungsten arc welds. The discrepancies are attributed in part to the heterogeneous microstructures in a crossweldment leading to different creep rates. Application of extrapolation methods to weldments should be done prudently; the heterogeneous microstructure of the heat-affected zone makes them less reliable.