Polarization Effects in Galvanic Corrosion

Galvanic corrosion In couples of AISI 304 stainless steel (SS), Ferralium(1) Alloy 255, Hastelloy(1) Alloys B-2 and G-3, grade 2 titanium, and graphite was examined in boiling 10% sulfuric and ambient-temperature hydrochloric acids. The galvanic corrosion rates were determined by measurement of the galvanic current using (1) a zero resistance ammeter technique and (2) weight loss measurements. Prediction of galvanic corrosion was attempted by determining the potentiodynamic polarization curves of the individual alloys and combining these with an iterative numerical solution for the zero potential difference between the alloys. In some cases, a reasonably good correlation was obtained between the predicted and measured galvanic corrosion rates. No correlation was found between the measured open circuit potentials (OCPs) (galvanic series) and galvanic corrosion rates. The effect of changing the area ratios was also examined.