Yuanzineng kexue jishu (Feb 2023)
Analysis and Discussion of Constitutive Equation for High Temperature Creep of 316H Stainless Steel of ASME Code
Abstract
ASME 2021 code provides constitutive equation for high temperature creep of 316H stainless steel. The paper aims to help engineers and researchers correctly evaluate the strain and creep damage of high-temperature equipment by using the equation. Firstly, the physical mechanism of the items was explained. Secondly, the relationship between crucial parameters with temperature and stress was analyzed. Thirdly, the applicable stress and time range of the 316H creep constitutive equation was briefly introduced. And fourthly, the prediction values of the constitutive equation was compared with the data value from the isochronous stress-strain curve in ASME code. Results show that the constitutive equation is described by three items, in which the first creep stage is described by the rapid initial transient and transient items, and the second creep stage is described by the steady-state creep item. The equation’s applicability of evaluating the strain and creep damage of high-temperature equipment is limited by the starting time of the third creep stage. Moreover the key parameters of the equations, such as εs, εr, decay too rapidly to be accurately predicted at high stress. This research finds that due to item n increases with increasing temperature, the minimum creep rate m and transient creep rate constant r decrease in 1 000-1 075 ℉. Meanwhile, based on contrasting the rapid transient creep rate constants s of the original paper and ASME code, item D of parameter s is incorrect in the latter. Based on comparing predicted strain obtained by equation and data from ASME code isochronous stress-strain curves, the paper finds that predicted values at 950, 1 050 and 1 150 ℉ will agree with isochronous stress-strain curves, but larger than the datum from curve at 1 000 ℉, resulting in a relatively conservative strain prediction. Based on above four research and results, the paper concludes that the high temperature creep constitutive equation of 316H stainless steel in the ASME code can be used to evaluate high-temperature equipment structural integrity at 950, 1 050 and 1 150 ℉, but the result of 1 000 ℉ is conservatism.
