Electrochemical Aspects of Cold Work Effect on Corrosion of Mild Steel in Sour Gas Environments

Experimental results of the effects of cold work on the corrosion of mild steel in a simulated, aqueous sour gas well environment are reported. The steel was cold rolled from 10% to 70% in increments of 10%. Detailed electrochemical kinetic analysis of the experimental data was conducted in an attempt to understand the electrochemical corrosion behavior. The results indicated that the effect of cold work on the corrosion behavior is associated with hydrogen coverage (θ) on the corroding electrode and FeS2 formation. The cathodic current density increases with cold work. The cold working causes a steady and continuous increase in corrosion rate and corrosion potential. The formation of FeS2 on the surface is promoted by conditions of cold working in excess of 20%. This, in turn, results in some corrosion retardation. The anodic polarization of steel is independent of cold work. The hydrogen saturation in the steel from long-term immersion prior to initiating a polarization scan causes a major alteration in corrosion rate and corrosion potential as compared to materials tested without achieving hydrogen saturation.