Accelerated degradation of carbon steel in seawater for the purpose of passive demolition of marine structures

This work investigates electrochemical methods for accelerating the corrosion of plain carbon steel in seawater with the intention of informing efforts to passively demolish steel marine structures. The study examined both galvanic (dissimilar metal) and oxidizing chemical (non-galvanic) approaches to increasing the corrosion rate of plain carbon steel in seawater. Grade 2 titanium and 316 stainless steel were investigated as candidate alloys for accelerating the corrosion of plain carbon steel locally via galvanic effects. Zero-resistance ammetry was employed to measure the galvanic current over a range of practical cathode-to-anode area ratios. The stainless steel – plain carbon steel and titanium - plain carbon steel couples were found to increase the corrosion rate of plain carbon steel (over baseline) by 4.8× and 13× respectively. Polarization measurements were used to investigate the effect of oxidizing chemicals in Substitute Ocean [Sea] Water on the corrosion rate of plain carbon steel, in the absence of a galvanic couple. Oxalic acid and citric acid solutions were studied with and without the addition of ferric chloride, FeCl 3 . The oxalic acid solution produced plain carbon steel corrosion rates 26.1 and 10.8 mpy, with and without ferric chloride, respectively. Given the results of this work, future development of degradation-enhancing apparatus should focus on titanium – plain carbon steel galvanic couples with high cathode-to-anode area ratios and time-released oxalic acid + ferric chloride (non-galvanic) environments. • Titanium – plain carbon steel galvanic couple produced a carbon steel corrosion rate 13× larger than the baseline (free) corrosion rate in substitute ocean [sea] water • oxalic acid + ferric chloride in a substitute ocean [sea] water base, produced a corrosion rate of 26 mpy in plain carbon steel • galvanic couples (titanium-plain carbon steel) and oxidizing (oxalic acid + ferric chloride) show potential for the passive demotion (toppling) of steel marine structures on a 3–5 year time frame in support of decommissioning operations.