Determination of suitable corrosion inhibitor formulation for a potable water supply

The inhibition effects of sodium silicate and polyphosphate on corrosion of carbon steel in a potable water supply have been studied using weight loss, electrochemical impedance and Tafel polarization measurements. In the water supply under test there were sufficient calcium ions, (220 ppm), to form the normal polyphosphates salts, which is a requisite for good protection. It was concluded that the inhibition efficiency of polyphosphate was higher than that of silicate. The synergistic inhibition effects of polyphosphate on the inhibition of silicate were studied. The results illustrated that silicates and polyphosphates can be useful as corrosion inhibitors for reducing the corrosion of carbon steel in potable water supply distribution systems. The optimal concentration for silicate alone was determined to be 11 ppm and for polyphosphate alone was 8 ppm. The optimum ratio of concentration for sodium silicate to sodium polyphosphate was 4 : 3.