Corrosion Resistance of Super Duplex Stainless Steel for CCS Usage under Supercritical CO₂ Conditions with Impurity Gas

In carbon capture and storage (CCS), the CO₂ emitted from various industries containing impurities is captured and injected to underground in dense or supercritical phase through a tubing. In order to evaluate corrosion resistance of the tubing materials in supercritical CO₂ environment with impurity, corrosion tests were performed in the conditions of CO₂, containing 5 wt% NaCl with O₂ or SO₂ at total pressure of 130 bar and temperature of 100 °C. The corrosion rates of UNS S41426 (13Cr super martensitic stainless steel) were higher than 1 mm/y in the solution saturated CO₂ with 2% O₂, as well as with 0.02% SO₂. On the other hand, UNS82551 (25Cr duplex stainless steel) and UNS S39274 (25Cr super duplex stainless steel) showed the corrosion rates of 0.1 mm/year or less and no pitting corrosion when the impurity gas concentration was 0.02% SO₂. UNS S39274 showed the same results even in the condition with 4% O₂ or 0.50% SO₂.The authors conducted the analysis by X-ray photoelectron spectroscopy and confirmed that Cr concentrated in the passivation film of S39274 after the corrosion test. Therefore, it is considered that UNS S39274 would be a suitable material even in the supercritical CO₂ environment contaminated with impurities (O₂ or SO₂).

Carbon capture, utilization and storage (CCUS) is one of the key technologies to achieve the net-zero emission. One of the CCUS method is CO₂ injection to depleted oil and gas wells or aquifers and storage (CCS). The CO₂ emitted from fossil fuel-based powers and industrial plants are captured and transported to the injection point by ships or pipe line. Following that, the dense phase or supercritical phase CO₂ will be injected to depleted oil and gas wells or aquifers through oil country tubular goods, for examples, seamless pipe.

Since the transported CO₂ is dehydrated, there are little risk of corrosion to pipe line materials. On the other hand, it is necessary to consider the risk of corrosion when it comes to injection pipes, because formation water is present in depleted oil and gas wells or aquifers and there is a possibility of flow back. In addition that the captured CO₂ from various industries includes impurities, for instance O₂, SO_x, and NO_x, which are reported that they accelerate general corrosion of steels^1,2,3).