Influence of water velocity on marine immersion corrosion of mild steel

The rate of immersion corrosion is known to increase with water velocity. This has been demonstrated in laboratory conditions under short-term exposures. There are very few field data or longer-term exposure results. The present paper reports new field data for immersion corrosion under coastal tidal conditions with a peak velocity of similar to1.0 m/s. It was found that velocity increases the rate of corrosion nonlinearly, but not in the manner predicted by earlier investigations for mild steel. The reasons for this appear to be related to the degree of protection offered to the corroding surface by corrosion products and biofouling. Once sufficient protection is obtained, velocity appears to have little direct further effect.