Determination of Material Coefficients for SA-317 and for 2.25 Cr-1 Mo at 450 °C in Chaboche Unified Model

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Thermal fatigue is widely recognized as an important damage mechanism in mixing points of hot and coldfluids. This phenomenon is an important subject in the life-time management of piping components ofrefineries and power plants. In particular, high frequency temperature fluctuations in tee connections as a resultof mixing the hot and cold fluids may cause material degradation with consequence of cracking and thus affectthe system integrity.In order to predict failure caused by cyclic thermal loading, a strain base fatigue curve is needed. In particular,two group of pipeline steels will be targeted, the 300series stainless steel and 2.25 Cr-1Mo steel. For the formerones, strain-based fatigue tests will be conducted at different temperatures to extend the application of ASMEcode for fatigue design for higher strain ranges at higher temperature. For the latter, the temperature range ofthe ASME code will be extended to account for the elevated temperature as seen at the mixing tees.The results of the proposed research will be used to capture the Chaboche viscoelastic material model whichwill be used in the finite element code to predict thermal fatigue failure of pipeline steels at the mixing tees.This will help minimize the likelihood of fatigue failure, and therefore, improve the structural integrity ofpiping components of refineries and power plants.