Corrosion-Induced Performance Degradation of Phosphorus-Containing Scale Inhibitors at Carbon Steel–Water Interface

Phosphorus-containing scale inhibitors have been widely used to mitigate CaCO3 scaling on the surface of metal device. In this work, the antiscale performances of two typical additives, sodium salts of hexametaphosphate (SHMP) and ethylenediaminetetramethylene phosphonate (EDTMPS), were evaluated on carbon steel through comparing scaling behavior under self-corrosion and cathodic polarization conditions, respectively. Results reveal that anodically released Fe2+ ions exert important influences on their antiscale behavior at carbon steel-water interface. During cathodic polarization processes, fewer or no Fe2+ ions are produced at the interface, and the two inhibitors effectively retard scale formation by their chelating role. However, once electrochemical corrosion occurs, more Fe2+ ions released from anode tend to diffuse toward cathodic regions, strongly interfering in their antiscale performances by preferentially replacing interfacial chelated Ca2+ ions. Then, these liberated Ca2+ ions are forced to react with cathodically formed CO3 ions, resulting in the scaling of CaCO3 at carbon steel-water interface.