Abstract
Magnesium is widely used as anode material for the potable water tanks in the offshore structures due to its excellent corrosion protection performance. However, Mg anodes installed in the PWT sometimes corrode with an abnormally high corrosion rate, leading to pH increase and H2 accumulation in the tanks. In this study, we investigated the influences of PW treatment chemicals (NaClO, CaCl2 and NaHCO3) on the corrosion behavior of Mg anode to ascertain the cause of excessive corrosion.
Corrosion of Mg is facilitated with increase in the concentration of NaClO, CaCl2 and NaHCO3. Because OH- and H2 are generated as products of Mg corrosion reaction, the higher corrosion rate results in the higher change of solution pH and hydrogen evolution rate. Thus, solution pH and hydrogen evolution rate increases with concentration of NaClO, CaCl2 and NaHCO3. Especially, concentration of CaCl2 and NaHCO3 has significant effects on the corrosion rate of Mg compared to NaClO concentration. The results suggest that overdosing of the treatment chemicals can cause the abnormal degradation of Mg anodes, leading to pH increase and H2 accumulation in the PWTs. To prevent the degradation of Mg anode, chemical injection rate should be controlled within the normal injection range.