Corrosion of carbon steel and the passivating properties of corrosion films formed under high-PT geothermal conditions

Abstract

Corrosion is a major obstacle to a safe implementation of geotechnical applications. Using a novel approach that includes vertical scanning interferometry (VSI) and electrochemical impedance spectroscopy (EIS) we discuss timedependent carbon steel corrosion and film formation at geothermally relevant temperatures (80-160°C) in CO2saturated mildly acidic Na-Cl brine. Iron dissolution kinetics follows a logarithmic rate at 80 and 160°C and a linear rate at 120°C. At 80°C, high initial corrosion rates (first 24 hours) generate H2 at a minimum rate of 12 µmol h-1 cm-2 and lead to the formation of a continuous ~100 µm thick porous corrosion film. It exhibits a duplex structure with a crystalline outer FeCO3 layer and an inner layer composed of a skeletal network of Fe3C impregnated with FeCO3. Being an electrical conductor we hypothesize the Fe3C to strongly enhance corrosion rates by providing additional cathodic sites. Pseudo-passivity due to an anodic film-forming reaction (presumably Fe-oxide) was observed at 120 and 160°C, soon followed by the initiation of pitting at 120°C. Steady-state corrosion rates at 160°C are at least one order of magnitude lower than for 120°C. Our experimental approach demonstrated potential for general applicability in studying corrosion-related phenomena.

Kinetic and thermodynamic analysis of high-temperature CO2 corrosion of carbon steel in simulated geothermal NaCl fluids

“…1b. Low R p values in the initial stage of the experiments suggest that corrosion is catalytically enhanced and instantaneous corrosion rates of up to 30 cm y −1 are observed [12]. Similar results have been found by Farelas et al [13] and have been attributed to the selective dissolution of the ferrite component within the steel microstructure.…”

“…It is the main driver that accelerates all the processes involved: electrochemical, chemical, and transport [11]. Another important factor is time and instantaneous corrosion rates have been found to vary over orders of magnitude between initial (Fe 3 C-catalyzed) and steady-state corrosion rates [12,13]. This wealth of influencing and often time-variant factors makes a comprehensive assessment of material stabilities technically impossible.…”

“…Dissolved or gaseous CO 2 is ubiquitous in geothermal fluids. CO 2 corrosion ("sweet corrosion"), mainly in the context of hydrocarbon exploration and transportation, has been discussed extensively by many authors [2,[11][12][13][14][15][16][17]. CO 2 can have a corrosion-enhancing or corrosioninhibiting impact on the corrosion rate.…”

Laboratory tests simulating corrosion in geothermal power plants: influence of service conditions

“…Moreover, this result is in agreement with previous studies testing the same kind of fluid and metal (Vallejo Vitaller et al 2019), in which the averaged corrosion rate over 120 h at 100 °C (308 µm/year) was higher than at 200 °C (52 µm/ year). Other studies have also evidenced lower corrosion rates toward higher temperatures (> 120 °C) (Mundhenk et al 2019). In phase 3, the corrosion rate gradually decreased down to approximately 50-70 µm/year.…”

A Robust Superhydrophobic/Conductive Composite Coating with Excellent Anticorrosive Performance

“…The common anti‐corrosion methods have cathodic protection, anodic protection, passivation, coatings, etc [7–10] . The coating and passivation are the most common anti‐corrosion methods [11–14] . However, the passivation often relates to carcinogenic chromates and the traditional coatings are powerless against pitting corrosion [15–17] …”