| P92 steel was designated by adding vanadium (V), niobium (Nb) and 1.8% tungsten (W) into chromium-molybdenum (Cr-Mo) steel as matrix, which is a kind of frequently-used material in ultra-supercritical units steam pipe, because of its excellent high temperature performance, such as creep resistance, thermal conductivity and so on. However, P92 has creep behavior under high-temperature and high-pressure of long-time service, and is failure caused by grain boundary creep holes. Hence, the accurate prediction of rupture life and endurance strength is significance for designing high temperature furnace tubes; sequentially guarantee the safety of high-temperature components. Traditional TTP method,θ projection method and modification method based on creep behavior have been proposed. But the research of influencing factor of TTP parameter and parameter sensitivity is rare reported. Creep rupture life prediction based on creep extrapolating depends mainly on how well the prediction equation is relative to the creep test curve. On the other side, the comment of extrapolation effect is insufficient. At the same time, life prediction based on stress relaxation test (SRT) in the P92 steel is rare reported. The current paper took P92 steel data as research objects, comparative analyzed the accuracy of different TTP parameters methods and studied the difference of different influence factors of life prediction based on M-H method; Meanwhile, analyzed the discrepancy of life prediction using different creep model in creep rupture life extrapolation based on creep curve; analyzed the result of creep rupture life prediction used by polynomial fitting in different sections methods based on creep rate. Ultimately, creep rupture life prediction by SRT data transforms the creep data, and objectively analyzed the strengths and weaknesses of three different methods.The main conclusions were drawn as follows:(1) The life prediction was small affected by creep rupture life, the result of extrapolation 100000h based on the data of short-term rupture life has no difference with all data. The influence factors of stress has an important effect on the accuracy of life predictive, the more temperature compensation of stress data segment, the more accurate of life prediction, and vice versa. The prediction value was higher than the real value. Traditional TTP method can unify and predict the data well. The accuracy of life prediction based on different TTP method has almost no difference; The change of constant B of M-S and P of OSD have significant influence on extrapolated results of life prediction。(2) Comparative analysis of the extrapolation of creep ruptures life based on different creep model. The results showed that the composite model have a higher accuracy than the theta projection method to describe the creep behavior of P92 steel; When extrapolate creep strain rate, the extrapolation result of the theta projection method have error at some extent, while the predict result of the composite model was consistent with the real tendency; The value of creep strain between 5% and 50% has little effect on the extrapolation of creep rupture life, The values of endurance life extrapolated by the two models are approximately the same, while the value of life prediction were much higher than the real one at 600 degree; The result of piecewise fitting based on curves of creep rate was consistent with the extrapolation of creep rupture life based on the composite model; The extrapolation curve of creep rupture life based on creep model combined with the relationship of Monkman-Grant were much higher than the experimental value.(3)The extrapolation of creep rupture life based on stress relaxation method combined with TTP method was analyzed. The results showed that the high accuracy of prediction at high temperature, and vice versa. The values of stress exponent observed between 9.6 and 11.6 at different temperature. The activation energy was about 412 KJmol-1. Based on this, it was suggested the creep behavior was controlled of slip of dislocations; through the calculation of the activation volume, the increase of the value of the activation volume with the increase of temperature. |
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