Abstract
In the author's recent work, effects of pH, chlorides, and sulfides on local anodic acidification has been modeled by coupling electrochemical polarization and phase precipitation inside occluded cells of nickel and iron. In the present work, the model is experimentally verified and extended to demonstrate the capability of accumulated and reduced hydrogen ions to provide critical conditions for local hydrogen-assisted crack propagation. Based on experimentally determined crack critical hydrogen reduction charge densities and crack initiation strains from small scale slow strain rate testing (SSRT), the model explains quantitatively the effects of chlorides, hydrogen sulfide (H2S), pH, and global mechanical stress on cracking by hydrogen that is locally produced by ion reduction at the tip of an advancing anodic corrosion path. In particular, the known effects of pH, chlorides, and H2S on cracking of metallic materials applied in the oil and gas industry are reflected by the results of the calculations.
