Identification of corrosion mechanisms on 13% Cr martensitic stainless steel in thiosulphate containing chloride solution by acoustic emission technique

The use of brine containing thiosulphate solution to simulate the sour gas environment was recently evaluated in the scientific literature to overcome the problems related to H2S use for laboratory testing of corrosion-resistant alloy (CRA) for Oil and Gas industry. However, corrosion attacks on stainless steel alloys are strongly influenced by thiosulphate to chloride concentration ratio. The identification of a reliable non destructive monitoring technique that can allow to distinguish between the different corrosion mechanisms is a big issue and it is the main aim of the present paper. Corrosion behaviour under tensile load of 13% Cr martensitic stainless steel in a modified NACE TM0177 standard solution at room temperature in presence of thiosulphate ions at different concentration (from 10-3 to 10-1 M) was evaluated by acoustic emission technique. By microstructural observations and a bivariate analysis it was possible to evidence how some acoustic emission patterns can clearly identify specific corrosion mechanisms.