applied fracture mechanics

Structural Reliability Improvement Using In-Service Inspectionfor Intergranular Stress Corrosion of Large Stainless Steel Piping 3352.2.1. Crack initiation model2.2.1.1. Time to initiationTime to initiation of stress corrosion crack is considered as a function of damage parameter,Dsigma, which represent effects of loading, environment and material variables on IGSCC. Thedamage parameter is given bysigmawhere f1, f2 and f3 are given by D f material f environment f looding(1)1 2 3Cf C Pa(2)1 1 2where Pa is a measure of degree of sensitization, given by Electrochemical PotentiokineticReactivation (in C/cm 2 ).C C22 3 exp4273 log56f OC TC (3)where O2 is oxygen concentration in ppm, T is temperature in degrees centigrade, and γ iswater conductivity in μs/cm. The loading term f3 is considered to be a function of stress. Forconstant applied load case, f3 is given byCC 793C8f (4)where σ is stress in MPa. C1 to C9 are constants whose values depend on type of material.Values for these constants are presented in Table1.Constant C1 C2 C3 C4 C5 C6 C7 C8 C9Value 23.0 0.51 0.18 −1123.0 8.7096 0.35 0.55 2.21 ×10 −15 6.0Table 1. Numerical values of constants Ci used for predicting the initiation and propagation of SCC forAISI304 (Harris et al., 1992).The time to initiation tI for a given Dsigma is considered as a random variable followinglognormal distribution. The mean and standard deviation of Log (tI) are given by:Mean value ofLog t I3.10 4.21 logDsigmaStandard deviation ofLogtI 0.3081(5)