A statistical failure distribution and lifetime assessment of the hsla steel plates in H 2S containing environments

Abstract

1bSteel plates of JIS-G-3115 SPV-50Q were found to be susceptible to sulphide stress corrosion cracking (SSCC) and hydrogen induced cracking (HIC) under the wet H 2S service environments. The mixed failure modes of SSCC and HIC make it difficult to predict the failure time after the crack growth measurements. Statistical analysis of the failure time from constant load tests in H 2S saturated NACE solution (0.5% acetic acid + 5% NaCl) is a method to solve this problem. The experimental results indicate that the Weibull distribution fits the H 2S 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% H 2S environment. With decreasing H 2S concentration, a range of maximum m values between 30 and 3% H 2S-N 2 gas mixture was observed at 90% yield stress. This phenomenon can be interpreted as the characteristics of iron sulphide film from the results 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.