Prototype experiments of the low voltage mineral deposition technology as eco-friendly solution for improving the sustainability of offshore platforms at the end of their production life

Several oil and gas offshore platforms are approaching the end of their production life, thus requiring sounding sustainable management solutions. This study aimed to improve the current knowledge on the low voltage mineral deposition technology as an eco-friendly strategy to protect offshore platforms from corrosion and to create suitable substrates for the colonization and growth of sessile marine organisms, thus minimizing environmental impact due to metal release, supporting biodiversity and increasing ecological sustainability. To do so, experimental prototype structures were installed in the Ligurian Sea (NW Mediterranean Sea) with the aim to simulate the sub-merged parts of offshore platforms and to analyze over time (up to ca. 6 months), elemental and chemical composition, growth rates and corrosion protection ability of the minerals deposited on steel substrates, through the alkalization induced by cathodic polarization of the metal. The influence of operational (applied current density) and natural environmental parameters on the deposition process was investigated. Results of this experiment revealed that in general the mineral deposits were mainly composed by aragonite (CaCO₃) and brucite (Mg(OH)₂) and, more specifically, the amount of the latter prevails a little bit on the amount of the former. This result is most likely related to high cathodic polarization current densities reached during the experimentation. Despite brucite is expected to worsen the physical–mechanical​ characteristics of the mineral deposits, the overall deposits were able to protect to a certain extent the electrified steel material from corrosion. After about 6 months of induced mineral deposition, the layer over the steel reached the maximum thickness of about 2.4 mm, following a non-linear trend as a function of time, whereas the deposition rates ranged from 20.0 to 50.3 μm d⁻¹, in relation with the applied current densities. At the same time, a positive relationship of the deposit grow rates with seawater temperature has been observed. Overall, the outcomes reported in this study provide new elements for the application of low voltage mineral deposition technology in temperate seas and pave the way for defining the best operating conditions to protect steel structures from corrosion and support biodiversity, thus contributing to the sustainability of the natural capital.