Use of thermally sprayed aluminium (TSA) coatings to protect offshore structures in submerged and splash zones

Abstract

In this work, the behaviour of arc-sprayed aluminium (1050) coatings was investigated under full artificial seawater immersion and compared with simulated splash zone conditions under droplets of artificial seawater exposed to controlled conditions. To gain a better insight into the mechanism of corrosion of thermally sprayed coatings, tests were also performed on solid 1050 aluminium. Effectiveness of TSA coatings was evaluated using electrochemical techniques and corrosion products were examined by SEM/EDX and Raman spectroscopy.Sulphur containing corrosion products, such as felsobanyaite, were found on the coating as well as on the solid metal. This highlights the importance of using seawater, and not NaCl solutions, as a corrosive medium simulating marine environment. Moreover, it was observed that cathodic and anodic regions on thermally sprayed coatings were not easily distinguishable, whereas on solid metal, cathodic areas were located in the spreading region, where carbonate corrosion product (dawsonite) was detected. Full immersion studies revealed the need for pre-exposing samples before electrochemical testing, to predict long-term behaviour of the coating in marine service.

Sacrificial Thermally Sprayed Aluminium Coatings for Marine Environments: A Review

“…Moreover, electrochemical measurements revealed more noble potential of the sample that was exposed to artificial seawater than to the solutions containing only a combination of the following salts: MgCl 2 , CaCl 2 , and NaHCO 3 .The reason for this could be due to the presence of SO4 2− ions in artificial seawater. Those ions were detected in Al corrosion products by Syrek-Gerstenkorn et al on TSA coatings after immersion in artificial seawater for 32 days [34]. Other researchers who studied the effect of SO4 2− on the corrosion of aluminium in NaCl solution observed that the addition of those ions inhibited the initiation of pitting corrosion, but it enhances the growth of pre-existing pits [81].…”

Effects of thermal spray aluminium coating on SSC and HIC resistance of high strength steel in a sour environment

“…6b), OCP and CR showed some important changes up to 48 h, which according to López-Ortega et al [35] might be a consequence of solution penetration through the non-homogeneous topography of TSA coatings. Moreover, Syrek-Gerstenkorn et al [42] also explained this effect based on the dissolution of oxide layers and penetration of the electrolyte into the coating. In this work, the LSV evaluation of CC samples indicated a typical region associated with passive films.…”

Application of metallization coatings for protection of submersible electric motors of pumping equipment from influence of complicating factors in oil wells

“…Кроме того, в отличие от органических покрытий, алюминиевые обеспечивают защиту не только при целостной системе, но и в случаях, когда стальная подложка подвергается частичному повреждению. Будучи более активным элементом в гальваническом ряду по отношению к стали, покрытие на основе алюминия, разрушаясь, обеспечивает защиту, работая как равномерно распределенный анод [29]. Алюминиевые покрытия наносились методами электродуговой металлизации [29] или холодного напыления [30,31] и характеризовались равномерной однородной структурой с низкой пористостью и достаточно высокой износостойкостью по сравнению с металлом подложки.…”