Effect of Oxygen, Chlorides, and Calcium Ion on Corrosion Inhibition of Iron by Polyphosphates

Abstract

Data are presented showing that sodium polyphosphates are effective corrosion inhibitors for steel, provided the dissolved oxygen concentration is above a critical minimum. Presence of calcium ion appreciably improves inhibition under all conditions. In solutions containing less than the critical amount of oxygen (1 ml/l), 60 ppm sodium polyphosphate accelerates corrosion. This is also true when 60 ppm Ca++ is added to the polyphosphate solution, although the critical oxygen concentration is now about 0.15 ml/l.