A STATISTICAL FAILURE DISTRIBUTION AND LIFETIME ASSESSMENT OF THE HSLA STEEL PLATES IN H2S CONTAINING ENVIRONMENTS

lbSteel plates of JIS-G-3115SPV-50Q were found to be susceptible to su lphide stress corrosion cracking (SSCC) and hydrogen induced cracking (HIC) under the wet H2S service environments. The mixed failure modes of SSCC and HIC make it difficult to predict the failure time after th e crack growth measurements. Statistical analysis of the failure time from constant load tests in H2S saturated NACE solution (0.5% acetic a cid + 5% NaCl) is a method to solve this problem. The experimental res ults indicate that the Weibull distribution fits the H2S failure mode. The shape parameter, m, related to the hazard function in the Weibull distribution increased when the applied stress was changed from 80 to 90% of the yield stress in 100% H2S environment. With decreasing H2S concentration, a range of maximum m values between 30 and 3% H2S-N-2 g as mixture was observed at 90% yield stress. This phenomenon can be in terpreted as the characteristics of iron sulphide film from the result s of hydrogen permeation measurement. The acceleration factor for the NACE TM-01-77 test was estimated to be about 10(2) in this HSLA steel.