Self-catalytic Action in Pitting Propagation Process of Low Alloy Steels

Four kinds of low alloy steels had been selected and the effects of solution conditions in the occluded area on corrosion of occluded anode had been studied by means of occluded corrosion cell (OCC) testing.The results indicated that with the increase of FeCl2 concentration and decrease of pH the corrosion rate of anodic metal decreased.Self-catalytic acidification action could be explained as follows: the surface activation of the metal was maintained by the solution acidification,which made the metal dissolve and hydrolyze continuously.Consequently,the corrosion was concentrated in the pit and the pit propagated.The necessary condition was that the potential of cathode out of the pit was more positive than that of anode in side of the pit.