Long-Term Creep Life Estimation for Manaurite XM Material, Using a Constrained Monkman-Grant Plot and Proportional Similitude

Abstract

The present paper revisits a constrained use of Monkman-Grant coordinates, a relatively little employed or appreciated method for estimation of long-term creep life. This method is based on a logarithmic plot of remaining life versus the steady creep rate. A procedure, here called proportional similitude, is also discussed as a means to estimate the steady creep rate or time to rupture at an early stage of a test. Numerous studies as yet mostly unpublished increasingly demonstrate for many steel samples from prior creep service that a combination of these two methods permits extrapolations at least as soon, as accurate, and at overall cost similar to other popular procedures. One of the advantages of this procedure is that short term creep test results can be extrapolated to long-term creep life in a transparent manner without complex mathematical maneuvers or need for typical reference properties or initial behavior of the sample. Results now available for a variety of widely-employed materials suggest that these methods may have more-general validity for remaining creep life evaluations than industry has recognized. This paper presents remaining creep lives obtained though a combination of four procedures, i.e., Monkman-Grant, proportional similitude, Larson-Miller, and curve fit methods, for exposed hydrogen reformer tube samples. Results are compared with those of previous Omega analyses performed independently for the same sample.