This study investigates the mechanism of formation of calcareous deposits on cathodically protected BS EN 10027-1 S355 J2G4 steel in boiling synthetic seawater. Steel specimens were arc sprayed with commercially pure aluminum (99.5%) and a ≈4% holiday was drilled into the coating to expose the underlying steel. The specimens were then immersed in boiling (101±1°C) ASTM D1141 seawater solution for approx. 5000 hours. The potential was monitored and the linear polarization resistance (LPR) method was used to obtain the corrosion rate. After completion of the test, the pH of the solution was measured and the specimens were analyzed, first by XRD and then by SEM. After test, the solution pH was found to be 6.29 at 20°C and the holiday region was covered with a deposit with no visible rust. A thin film was observed in cross-section which seemed to be divided into layers when viewed at a higher magnification. Energy dispersive x-ray spectroscopy (EDX) showed the presence of Mg, with no Ca being detected. XRD confirmed the presence of brucite [Mg(OH)2] in the calcareous deposit.

Subject
Holidays, Steel surfaces, Water, Precipitation (solids), Corrosion rate, Aluminum, Solubility, Seawater, Scale formation, Steel, Deposit corrosion, Calcareous deposits, Samples
Keywords:
TSA, calcareous deposit, aluminum, seawater, thermal spray coating
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2016
Association for Materials Protection and Performance (AMPP)
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