Abstract
AbstractThermally sprayed coatings are often used to mitigate corrosion of offshore structures. They act as a physical barrier to the aggressive marine environment and as a sacrificial distributed anode for low carbon steel. In such environments, the severity of material degradation depends on many factors. The effect of temperature, exposure time or the presence of micro‐organisms are the focus of many studies, for example, however, the effect of the different ions present in seawater remains largely unexplored. The chemical composition of the water changes considerably depending on the location; industrial, glacial, estuarine, and so forth. In addition, when thermal spray aluminum (TSA) protects steel in seawater, calcareous matter precipitates as a result of the cathodic polarization and subsequent localized increase in pH. Therefore, understanding how ions such as magnesium (II), calcium (II), or carbonates alter the coating properties in the marine environment is important. This paper reports the experimental work carried out with TSA‐coated steel samples with defects to simulate mechanical damage or erosion of the coating. The combination of electrochemical tests and surface characterization provided evidence of the efficiency of the calcareous bilayer that forms on top of steel reducing the TSA degradation.
Highlights
Low carbon steel is commonly used as a structural material for marine applications, despite its relatively poor corrosion resistance
After 90 days of exposure, corrosion deposits were formed both on top of the Thermal spray aluminum (TSA) coating and the holiday region
The work carried out shows that TSA is able to protect steel in various environments even in presence of defects
Summary
Low carbon steel is commonly used as a structural material for marine applications, despite its relatively poor corrosion resistance. Due to the high chloride levels present in marine environments, coupled with erosion and microbial effects, extensive material loss occurs in offshore platforms, pipelines, and ships. To mitigate the corrosion of steel in seawater, cathodic protection is used in the form of impressed current, sacrificial anodes and sacrificial coatings.[1]. Thermal spray aluminum (TSA) has been used for decades to prevent steel corrosion in subsea conditions, acting both as a physical barrier and as a sacrificial, anodic coating. TSA has been reported to provide protection for over 25 years, offering low maintenance and good performance at a low cost in places where inspection is not easy to perform.[2] It is well known that offshore corrosion depends on several parameters, such as dissolved oxygen content, the presence of microbial species, type and concentration of dissolved solids, and temperature among others.
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