Abstract
Advanced power plant alloys must endure high temperatures and pressures for durations at which creep data are often not available, necessitating the extrapolation of creep life. A recently developed creep life extrapolation method is the Wilshire equations, with which multiple approaches can be used to increase the goodness of fit of available experimental data and improve the confidence level of calculating long-term creep strength at times well beyond the available experimental data. In this article, the Wilshire equation is used to extrapolate the creep life of Inconel 617 and Nimonic 105 to 100,000 h. The use of (a) different methods to determine creep activation energy, (b) region splitting, (c) heat- and processing-specific tensile strength data, and (d) short-duration test data were investigated to determine their effects on correlation and extrapolation. For Inconel 617, using the activation energy of lattice self-diffusion as resulted in a poor fit with the experimental data. Additionally, the error of calculated rupture times worsened when splitting regions. For Nimonic 105, the error was reduced when heat- and processing-specific tensile strengths were used. Extrapolating Inconel 617 creep strength to 100,000 h life gave conservative results when compared to values calculated by the European Creep Collaborative Committee.
Highlights
Innovations in power generation require materials that are capable of withstanding high temperatures and stresses for at least 100,000 h of operation time
The longest creep rupture test of a nickel-based superalloy known to the authors—an Inconel 617 specimen last reported at 90,936 h—is ongoing and is the result of a joint effort led by the U.S Department of Energy and the Ohio Coal Development
Creep rupture data for Inconel 617 and Nimonic 105 were split into two data sets for each alloy; one consisted of all data, while the other was limited to data with rupture times less than 10,000 h
Summary
Innovations in power generation require materials that are capable of withstanding high temperatures and stresses for at least 100,000 h of operation time. Data regarding creep of new advanced power plant alloys are often not available at times relevant to the required design life. Nickel-based superalloys—promising alloys for ultra-supercritical power plant applications—have no creep rupture data at 100,000 h in the literature. The Wilshire equations [5] are a recently-developed extrapolation method that has been used to predict long-term creep behavior of high-temperature, creep-resistant alloys [6]. Different approaches have been used to fit the Wilshire equation to creep rupture data. The Wilshire equation for time to rupture and the Larson–Miller parameter (LMP) equation are used to correlate and extrapolate the creep life of two nickel-based superalloys, Inconel 617 and Nimonic 105. The error of the calculated rupture times resulting from the use of different creep activation energy ∗ , split stress regions, and how Larson–Miller fitting parameters were obtained; Section 4 to obtain QC outlines the calculations and results of the study; and the final section presents conclusions
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