Inhibition of stress corrosion cracking in water-cooled nuclear reactors by dielectric coatings

Theory predicts that the electrochemical corrosion potential (ECP) and the rate of propagation of intergranular cracks in sensitized Type 304SS in high temperature aqueous solution should be displaced in the negative direction and reduced, respectively, by inhibiting the redox reactions (e.g., O-2 reduction) that occur on the external surface. This prediction has been experimentally demonstrated by measuring ECP and crack growth rate (CGR) data for sensitized Type 304 SS in oxygenated, high temperature (288 degrees C) dilute sulfate solutions using C(T) specimens that had been coated with compact ZrO2 films. The role of the film is to reduce the exchange current density for the redox reaction (O-2 reduction), thereby limiting the ability of the external surface to consume the current exiting the crack.