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Research Papers: Materials and Fabrication

A Postassessment Test of 100,000 h Creep Rupture Strength of Grade 91 Steel at 600 °C

[+] Author and Article Information
K. Maruyama

Department of Materials Science,
Graduate School of Engineering,
Tohoku University,
6-6-02 Aramaki-Aoba, Aoba-ku,
Sendai 980-8579, Japan
e-mail: kouichi.maruyama@tohoku.ac.jp

N. Sekido, K. Yoshimi

Department of Materials Science,
Graduate School of Engineering,
Tohoku University,
Sendai 980-8579, Japan

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 30, 2017; final manuscript received July 11, 2017; published online August 23, 2017. Editor: Young W. Kwon.

J. Pressure Vessel Technol 139(5), 051404 (Aug 23, 2017) (7 pages) Paper No: PVT-17-1077; doi: 10.1115/1.4037446 History: Received April 30, 2017; Revised July 11, 2017

Predictions as to 105 h 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 National Institute for Materials Science (NIMS) Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an American Society of Mechanical Engineers (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 (σ0.2/2 criterion), and selecting data points longer than 1000 h (cutoff time of 1000 h). 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 °C. However, TTP analyses of datasets selected by σ0.2/2 criterion and cutoff time of 1000 h 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.

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Copyright © 2017 by ASME
Topics: Creep , Databases , Rupture , Steel
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References

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Figures

Grahic Jump Location
Fig. 1

Correlation between data band (gray band) and its regression line (thin solid line) determined by OSD analysis of the creep rupture data

Grahic Jump Location
Fig. 2

Comparisons of regression lines for NIMS T91 database with long-term creep rupture data points measured. Solid line obtained from the data points belonging to region L2, dashed line from the dataset selected by σ0.2/2 criterion, and dashed-dotted line from the dataset selected by cutoff time of 1000 h.

Grahic Jump Location
Fig. 5

A comparison among regression lines obtained from the following datasets. All the datasets were selected by cutoff time of 1000 h from ASME type I database (dotted line), ASME type II database (dashed-dotted line), NIMS type I database (dashed line), and NIMS type II database (solid line). The symbols are long-term creep rupture data points of NIMS type II materials.

Grahic Jump Location
Fig. 3

Comparisons of regression lines obtained from the following datasets with long-term creep rupture data points measured. All the datasets were selected by σ0.2/2 criterion from ASME Gr.91 database (solid line), NIMS T91 database (dashed line), and Japan T91 database (dashed-dotted line).

Grahic Jump Location
Fig. 4

Comparisons of regression lines obtained from the following datasets with long-term creep rupture data points measured. The datasets were selected by cutoff time of 1000 h from ASME Gr.91 database (solid line) and NIMS T91 database (dashed-dotted line).

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