Corrosion kinetics of ductile iron in remineralized RO desalinated seawater

To understand the corrosion process better, corrosion kinetics of ductile iron coupons, which is a popular material for fabricating water distribution pipes, was investigated in a system using remineralized reverse osmosis membrane desalinated seawater under tropical conditions. Coupon corrosion rate and water quality were monitored during the test period up to 20 days. The corrosion rate decreased quickly during the first several days and slowly levelled off thereafter. Total hardness, total alkalinity and calcium concentration declined as the tests continued and approached to a stabilized value eventually. The passive behavior was observed because the rust layer formed during the test period has acted as a barrier of the corrosion process. Corroded products observed during the test included FeO(OH), Fe(OH)₃, FeO, CaO, CaO₂, CaCO₃, etc. The knowledge gained in this study could be useful in operation and asset management such as monitoring water quality and projecting pipeline life-span.