Effect of Cl~- Concentration on Corrosion Behavior of Austenitic Stainless Steel under Sour environment

摘要

Effect of Cl~- concentration on pitting susceptibility of UNS S31603 stainless steel was evaluated by immersion testing. Initiation and growth of pitting on austenitic stainless steel exposed to a sour environment was studied by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and electrochemical measurement. The results show that the pitting potential of UNS S31603 steel decreases with a rise of Cl~- concentration, and the pitting susceptibility increases significantly. In pit initiation, there exist competitive adsorption between Cl~- and H_2S. When Cl~- concentration reaches a certain level, Cl~- occupies most of the adsorption sites on the surface of passive film. This can impede the reaction between H_2S and the passive film, however, the corrosion process is inhibited. With the further increases of the Cl~- concentration, due to the formation of soluble complexes via the reaction between Cl~- and the metal, the dissolution of passive film increases and the corrosion process is accelerated. The pitting depth of UNS S31603 stainless steel increases with the increasing Cl~-concentration under a sour environment, and the pitting grows inward.