THE INFLUENCE OF TEMPERATURE, APPLIED POTENTIAL, BUFFER AND INHIBITOR ADDITION ON THE PASSIVATION BEHAVIOR OF A COMMERCIAL GRADE 316L STEEL IN AQUEOUS HALIDE SOLUTIONS

The influence of factors which can increase or decrease the rate of pH reduction and halide ion build up in a developing pit solution are evaluated for pits nucleated on the surface of a commercial grade 316L steel in chloride, bromide and fluoride solutions. Temperature and applied potential are shown to have a significant influence on these processes for the steel immersed in Cl- and Br- solution, but not in F-. Additions of appropriate buffers to chloride test solutions is shown to alter quite considerably the extent of pH reduction in growing pits and in a number of cases to increase the pitting potential also. In chloride solutions containing suitable amounts of sodium dichromate the passivation behaviour of 316L is shown to alter considerably with the almost total elimination of activation-repassivation events on the oxide surface as evidenced by the absence of current peaks or fluctuations on potentiostatic current time plots. Removal of surface inclusions by immersion of the steel in HNO3 solutions results in a short term improvement in film stability for 316L. © 1990.