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research-article

A Post Assessment Test of 100,000 Hours Creep Rupture Strength of Grade 91 Steel at 600 oC

[+] Author and Article Information
Kouichi Maruyama

Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
kouichi.maruyama@tohoku.ac.jp

Nobuaki Sekido

Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
nobuaki.sekido.b7@tohoku.ac.jp

Kyosuke Yoshimi

Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
yoshimi@material.tohoku.ac.jp

1Corresponding author.

ASME doi:10.1115/1.4037446 History: Received April 30, 2017; Revised July 11, 2017

Abstract

Predictions as to 105 hrs creep rupture strength of grade 91 steel have been made recently. The predicted values are examined with long-term creep rupture data of the steel. Three creep rupture databases were used in the predictions: data of tube products of grade 91 steel reported in NIMS Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an ASME code committee. Short-term creep rupture data points were discarded by the following criteria for minimizing overestimation of the strength: selecting long-term data points with low activation energy (multiregion analysis), selecting data points crept at stresses lower than a half of proof stress (?0.2/2 criterion), and selecting data points longer than 1000 hrs (cut-off time of 1000 hrs). In the case of NIMS T91 database, a time-temperature parameter (TTP) analysis of a dataset selected by multiregion analysis can properly describe the long-term data points and gives the creep rupture strength of 68 MPa at 600 oC. However, TTP analyses of datasets selected by ?0.2/2 criterion and cut-off time of 1000 hrs from the same database overestimate the data points and predict the strength over 80 MPa. Datasets selected by the same criterion from the three databases provide similar values of the strength. The different criteria for data selection have more substantial effects on predicted values of the strength of the steel than difference of the databases.

Copyright (c) 2017 by ASME
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