HYDROGEN PERMEATION MEASUREMENT ON LACQUER COATED MILD-STEEL UNDER CATHODIC POLARIZATION IN SODIUM-CHLORIDE SOLUTION

Hydrogen permeation measurements have been carried out on chlorinated rubber and VMCH Coated mild steel at -1200mV and -1500mV (S.C.E.), using a modified Devanathan cell. Hydrogen permeation current was found to correlate with the rate of delamination of the coating around a defect, thus relating the delamination to the formation of hydroxyl ions in the hydrogen evolution reaction. However, access of sodium ions to the coating/substrate interface is also important for delamination to occur, and a high hydrogen permeation current is possible without the same highly localised delamination underneath a defect-free coating. The high ionic resistance of a coating is able to prevent full cathodic protection at -1200mV (S.C.E.).