Electrochemical Aspects of Stress Corrosion of Steels in Alkaline Solutions

The existing theories of initiation and propagation of stress corrosion cracking (SCC) are examined with particular reference to their applicability to steels in caustic solutions. The electrochemical theory which considers cracking to be due to local active dissolution at the crack tip, and passivation of the walls, is developed into a model which explains the observed potential dependence of cracking rate and aspect ratio, and the existence of an anodic potential above which cracking ceases. The current distribution during stress corrosion at the rest potential is calculated, and it is shown that the cathodic current, unlike the anodic current, is not highly localized. The efficacy of anodic and cathodic polarization of a stress corrosion specimen is also examined, and it is shown that anodic control can be effective at the crack tip, whereas cathodic control only exists near the mouth of the crack.