Coupling of water radiolysis and crack growth in sensitized stainless steels

The electrochemical potential from exchange reactions on an inert metal surface such as platinum is equivalent to the redox potential. Equivalents of oxidant (i.e., oxygen) reduced are equal to the equivalents of reductant (i.e., hydrogen) oxidized. Electrons flow through the metal. An equivalent ionic current completing the circuit, flows in the solution. Cations migrate in the opposite direction to anions. When a metal corrodes in a localized surface area or crack, the metal-solution potential at that location, as probed by a reference electrode, changes due to the metal dissolution. The amount of change in the mixed potential system depends on the magnitude of the previously controlling exchange reactions. It is usually significant and easily measured. Thus, the potential difference between the redox potential and the potential of the corroding metal gives at least an indication and perhaps a measure of corrosion. Calculations showed that an increasing conductivity in the external solution up to a concentration of about 10E-10 mol/cm3 (5.8 ppm) of NaCl sharply increased the crack growth rate. Stress intensity also increased the cracking rate but not so sharply