Chloride Limits for Pitting and Cracking of 300 Stainless Steels Series on an Acid Gas Removal Plant

The effect of chloride on the pitting and cracking propagation of 304L and 316L exposed to sour service was studied. Laboratory testing to simulate the extreme ends of process conditions found in our acid gases removal plant were conducted. The typical gas process conditions vary from 110^oF to 300^oF with high and low loads of H₂S and CO₂ in equilibrium with a solution of an acid gas selective solvent and water. This study covered a range of chlorides from 0 to 500 ppm. Cyclic polarization and potentiostatic electrochemical techniques were used to determine the limits of chlorides required to cause stable pitting leading to cracking. Cracking was confirmed by means of 30-days exposure testing of stressed coupon. An algorithm based on published models for pitting stability and crack growth rate was built to estimate the likelihood of cracking and its variation with the applied stress. Preliminary cracking data collected for this study seem to back up the predictions of likelihood of cracking but more data is needed to statistically validate the model.