Tensile Properties of Boiler Materials for FAD Based Failure Analysis

Failure assessment of components with crack-like flaws are performed using the Failure Assessment Diagram (FAD) approach. Both fracture toughness and tensile properties of the component material are required for the analysis. The temperature dependence for the tensile properties of yield strength, flow stress, and ratio of yield strength to ultimate tensile strength were studied. The yield/tensile ratio is used to estimate the strain hardening exponent. The materials include carbon steel, 1/2Cr to 9Cr-1Mo steels, 1CrMoV rotor material, and 422 stainless steel bolting material. The tensile data was from the NRIM data compilation. Least squares regression was performed for log of the tensile property as the dependent variable and a sixth order Chebyshev polynomials in temperature. In general, the fits were good based on comparisons of the observed and calculated, specifically the mean at each temperature, the standard deviation, and the R² value. The distribution function was shown to be normal. Values for the regression coefficients and standard deviation in log Y are tabulated.