Peculiar corrosion behavior of type 316L ss in simulated cooling water at various pH values

The effect of pH on the corrosion behavior of Type 316L stainless steel (SS) (UNS S31603) in simulated cooling water was studied using corrosion potential and potentiodynamic polarization techniques. The fundamental result is that corrosion is very effectively controlled within a relatively narrow range of neutral to near-neutral pH values with increased corrosion rates outside that range in either direction. The negative (active) open circuit potential at pH values lower and higher than neutral (6 ≥ pH ≥ 8) was due to dissolution of the passive film by a hydrogen reduction reaction and oxidation of hydroxyl ions by oxygen evolution in the presence of chloride ions. It was also found that the corrosion potential was relatively positive (noble) when the concentration of hydrogen and hydroxyl ions was balanced (pH = 7), which depicted excellent corrosion protection of SS.