TY - GEN
T1 - Methodology of creep data analysis for advanced high Cr ferritic steel
AU - Maruyama, Kouichi
AU - Yoshimi, Kyosuke
PY - 2008
Y1 - 2008
N2 - Long term creep rupture life is usually evaluated from short term data by a time-temperature parameter (TTP) method. The apparent activation energy Q for rupture life of steels sometimes changes from a high value of short term creep to a low value of long term creep. However, the conventional TTP analyses ignore the decrease in Q, resulting in the overestimation of rupture life recognized recently in advanced high Cr ferritic steels. A multi region analysis of creep rupture data is applied to a creep data set of Gr. 122 steel; in the analysis a creep rupture data is divided into several data sets so that Q value is unique in each divided data set. The multi region analysis provides the best fit to the data and the lowest value of 105 h creep rupture strength among the three ways of data analysis examined. The conventional single region analysis cannot correctly represent the data points and predicts the highest strength. A half of 0.2 % proof stress could not be an appropriate boundary for dividing data to be used in the multi region analysis. In the 2001 Edition of ASME Code an F average concept has been proposed as a substitution for the safety factor of 2/3 for average rupture stress. The allowable stress of Gr. 122 steel may decrease significantly when the F average concept and the multi region analysis are adopted.
AB - Long term creep rupture life is usually evaluated from short term data by a time-temperature parameter (TTP) method. The apparent activation energy Q for rupture life of steels sometimes changes from a high value of short term creep to a low value of long term creep. However, the conventional TTP analyses ignore the decrease in Q, resulting in the overestimation of rupture life recognized recently in advanced high Cr ferritic steels. A multi region analysis of creep rupture data is applied to a creep data set of Gr. 122 steel; in the analysis a creep rupture data is divided into several data sets so that Q value is unique in each divided data set. The multi region analysis provides the best fit to the data and the lowest value of 105 h creep rupture strength among the three ways of data analysis examined. The conventional single region analysis cannot correctly represent the data points and predicts the highest strength. A half of 0.2 % proof stress could not be an appropriate boundary for dividing data to be used in the multi region analysis. In the 2001 Edition of ASME Code an F average concept has been proposed as a substitution for the safety factor of 2/3 for average rupture stress. The allowable stress of Gr. 122 steel may decrease significantly when the F average concept and the multi region analysis are adopted.
KW - Allowable stress
KW - ASME P122
KW - Overestimation of rupture life
KW - Time-temperature parameter metnod
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U2 - 10.1115/CREEP2007-26150
DO - 10.1115/CREEP2007-26150
M3 - Conference contribution
AN - SCOPUS:43449118070
SN - 0791842878
SN - 9780791842874
T3 - 2007 Proceedings of the ASME Pressure Vessels and Piping Conference - 8th International Conference on Creep and Fatigue at Elevated Temperatures - CREEP8
SP - 631
EP - 636
BT - 2007 Proceedings of the ASME Pressure Vessels and Piping Conference - 8th International Conference on Creep and Fatigue at Elevated Temperatures - CREEP8
T2 - 2007 ASME Pressure Vessels and Piping Conference - 8th International Conference on Creep and Fatigue at Elevated Temperatures, PVP-2007/CREEP8
Y2 - 22 July 2007 through 26 July 2007
ER -