Corrosion Performance of Damaged Thermally Sprayed Aluminium in Synthetic Seawater at Different Temperatures

This paper reports the corrosion performance of damaged thermally sprayed aluminium (TSA) in ASTM D1141 synthetic seawater at 5°C and ≈ 101.5°C (boiling seawater). This research is particularly relevant to subsea installations. Al was arc-sprayed on carbon steel and holidays exposing underlying steel amounting to 4-5% area of the samples were made. The corrosion potential of these samples when exposed to synthetic seawater was monitored. The corrosion potential initially became more electronegative, reached a minimum and then became less electronegative to give values of −970 mV and −840 mV at 5°C and ≈ 101.5°C, respectively after 1200 hours. The corrosion rate was calculated to be ≈ 5-10 μm/y after 1200 h of exposure at both temperatures. The exposed steel was covered by a scale which led to the reduction in corrosion rate. The scale had a two-layer structure, Mg-containing close to and Ca-rich away from the substrate, at 5°C and only brucite [Mg(OH)2] at ≈ 101.5°C.