Thermally sprayed coatings for corrosion protection of offshore structures operating in submerged and splash zone conditions

摘要

Corrosion protection of structures operating in seawater is usually provided by cathodic protection (CP) by sacrificial anodes, often in conjunction with protective organic coatings. However, these methods have some limitations. Organic coatings, when used without CP, can provide protection to steel only when intact and anodes not only significantly increase the overall mass of the structure, but also have to be replaced periodically. An alternative corrosion mitigation method is the application of thermally sprayed metallic coatings, such as Al, Zn and ZnAI, which work as a barrier to corrosive environments when intact, and as an evenly distributed sacrificial anode when damaged. In this work, the behavior of arc-sprayed ZnAI- and Al-coatings was investigated under two conditions - (i) full immersion in artificial seawater (ASTM D1141), and (ⅱ) under droplets of artificial seawater. The first to simulate the immersed zone and the second to simulate above-surface splash zone conditions. The effectiveness of the coatings was evaluated using electrochemical techniques (OCP monitoring, dynamic polarization and LPR). Raman spectroscopy and SEM/EDX were employed to analyze corrosion products.