Chemical studies of polythionic acid stress-corrosion cracking

Abstract

Low temperature stress corrosion cracking of sensitized stainless steel, promoted by aqueous solutions of polythionates S xO 6 2−, and related sulfur compounds, particularly thiosulfates, has been a long known problem in the petroleum industry and more recently has cropped up in the nuclear power industry. Membrane permeation results presented here show that S 4O 6 2− and S 2O 3 2− do not function simply as sources of sulfide to promote hydrogen permeation and embrittlement. They do promote anodic dissolution, also generating an unusual adsorption-related anodic spike in voltammetric scans. The oxidation of iron sulfide scales, said to be the source of the substances in petroleum refineries, has been shown to give rise mostly to Fe 2O 3 and elemental sulfur, with low yields of both S 4O 6 2− and S 2O 3 2−.