Impact of pH level and magnesium addition on corrosion of re-mineralized seawater reverse osmosis membrane (SWRO) product water on pipeline materials

Remineralization of desalinated seawater has been widely applied to reduce pipeline corrosion problems and to achieve drinking water standards. This study investigated the effects of pH and magnesium addition on corrosion of pipeline materials in stagnant remineralized desalinated seawater under tropical conditions. Three pipeline materials, ductile iron, cement-lined ductile iron and cast iron were examined. The pH of the remineralized reverse osmosis (RO) desalinated seawater ranged from 7.0 to 8.4. Weight loss method was used. The pH variations showed little effect on the corrosion product composition and final water quality for the three pipeline materials. The overall findings suggested that the impact of pH level from pH 7.0 to pH 8.4 on corrosion rates of iron coupon materials was unpronounced. Addition of magnesium changed the morphology and microstructure of CaCO3 precipitant, reduced the amount of the precipitant and maintained a high alkalinity and hardness concentration in the re-mineralized RO permeate. For cement-lined ductile iron coupons, an intense protection was found in water with magnesium addition under pH 7.0 condition.