What is Pitting Corrosion

The severity of the environment is very largely dependent upon two factors - the chloride (Cl-may continue to grow, and if they do can lead to perforation, while the majority of the steel surface may still be totally unaffected.rrosion is usually described in terms of what % Cl- (or ppm Cl-)) and °C it can resist. It should be noted that the most common grade of stainless steel, Type 304, may be considered susceptible to pitting corrosion in sea water (2% or 20,000 ppm chloride) above about 10°C, and even in low chloride content water may be susceptible at only slightly elevated temperatures. A safe chloride level for warm ambient temperatures to prevent Pitting Corrosion is generally about 150ppm (150mg/l). Grade 316 is more resistant to Pitting and is commonly used in ambient sea water, but can be attacked in crevices or if the temperature increases even slightly.

The velocity of the liquid is also significant; a stagnant solution is more likely to result in pitting corrosion and crevice attack, particularly if there are particles to settle out of the liquid.