Extrapolation of 100 000 h Rupture Strength of P91 Steel Pipe Based on Confidence and Survival Probability

The endurance strength test at 625 ℃ and seven stress levels with stress ranging from 80 MPa to 140 MPa were conducted on the P91 steel pipes produced by a steel plant in China. The unary linear regression of the breaking time under each stress was carried out, and the correlation coefficient of the results were checked. Finally, the 100 000 h endurance strength based on a certain confidence and survival probability was extrapolated. The results show that when the test temperature was 625 ℃, and the confidence γ was 95% and the survival probability was 99. 9%, extrapolated the 100 000 h endurance strength of P91 steel pipe was 71. 38 MPa. With the extension of the breaking time, the standard deviation of different fracture times under the same stress decreased gradually, which may be related to the change of creep mechanism.