Electrochemical effects on carbon steel in circulating cooling water systems: Scaling, corrosion and chemicals synergies

In cooling water systems balancing anti-scaling and simultaneous anti-corrosion effect on carbon steel needs to be addressed in applying electrochemical treatment procedure. This study investigated the impact of dosing corrosion inhibitors into electrochemical treatment process to achieve an optimized effect. An electrochemical unit equipped with Ti/RuO2 anode and Ti cathode was used in a simulated cooling water system. Initial results show that embedding a sole electrochemical system did reduce the scale deposition rate on the steel to about 20 %, and simultaneously change the crystalline form to a more readily removable aragonite-type, but promote an increase of corrosion rate to 65 % due to accelerated conversion of Fe2+ to Fe3+ on the surface of carbon steel. Three typical agents were selected to mitigate such adverse effect. It was shown that adding imidazoline and Na2MoO4 could effectively mitigate the corrosive effects, but dosing HEDP had surprisingly led to an opposite consequence. The best performance achieved by dosing Na2MoO4 was demonstrated due to the formation of surface film impedance on carbon steel which reduced its self-corrosion current density. Due to the electrochemical phosphorus recovery function, the phosphorus-containing corrosion inhibitor HEDP is deposited on the cathode plate. This deposition results in inadequate film formation on the surface of carbon steel, ultimately leading to an increase in the corrosion rate of carbon steel. The outcomes suggest that a combination of suitable corrosion inhibitor with electrochemical treatment procedure could be a new strategy in the application of such processes for simultaneous controlling scaling and corrosion.