Abstract
The corrosion module of COMSOL Multiphysics 5.6® software was employed to simulate the influence of the corrosion products and calcareous deposits on the damage tolerance of a Thermally Sprayed Aluminium coating (TSA) in a simulated marine immersion environment. The capacity of TSA to polarise the steel was evaluated by modelling 5%, 50%, and 90% of the sample uncoated’s area (i.e., substrate exposed). Additionally, the consumption of the sacrificial coating was simulated by Arbitrary Lagrangian-Eulerian (ALE) for the geometry of the experimental system. The parameters used in the model were obtained from polarisation curves and Electrochemical Impedance Spectroscopy (EIS) available in the literature. The results are in good agreement with measurements of Open Circuit Potential (OCP) and Corrosion Rate (CR) from experiments reported in previous studies. The model predicted the sacrificial protection offered by TSA as a function of the exposed steel surfaces, indicating the ability of TSA coating to polarise steel even with up to 90% damage. Furthermore, a 90–70% reduction in the corrosion rate of TSA was calculated with the simultaneous influence of corrosion products and deposits formed after 20 days of exposure to artificial seawater at room temperature.
Highlights
In offshore steel structures, galvanic anodes in conjunction with dielectric barrier coatings are often used for corrosion control
The ability of Thermally Sprayed Aluminium coating (TSA) coating to polarise exposed steel by varying surfaces of damage; The formation of calcareous deposits block the diffusion of dissolved O2 to steel; The precipitation of corrosion products fill the porous of the coating, reducing the corrosion of aluminium; The model replicates the behaviour of corrosion products and calcareous deposits assuming a film resistance on each electrode surface
The model proposed in this work simulated the damage tolerance of the TSA coating by varying the surface of the exposed substrate, including the simultaneous effect of aluminium corrosion products and deposits through a time-dependent model
Summary
Galvanic anodes in conjunction with dielectric barrier coatings are often used for corrosion control. The complexity of installing cathodic protection system offshore add costs and risks. An unexpected failure of protective paint can lead to severe corrosion. The onset of pitting corrosion can act as fatigue crack initiation sites exacerbating the situation, in offshore wind turbines [1]. Cathodic protection systems maintenance and coating repairs are expensive and sometimes unfeasible. It is estimated that offshore coating repairs cost 50–100 times greater than onshore installations [1,2]. A reliable corrosion mitigation system requiring little or no maintenance is desirable
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