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CCS technology - Carbon Dioxide Capture and Storage, has been recognized as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost effectiveness currently hinder the future of CCS. Recent studies have shown that even at a very low concentration of impurities (less than 100 ppmV of SO2, NO2, O2 and H2O) the droplet formation and condensation of sulfuric and nitric acids in dense phase CO2 are possible and observable [1-3].To reveal the mechanism of droplet corrosion in dense CO2 at high pressure and low temperature, further studies on factors that affect wettability and resulting corrosion behaviors of transport pipeline steels are needed.
In this work, carbon steel 1.8977 (L485MB), CrMo-alloyed steel 1.7225 (42CrMo4), martensitic steel 1.4313, and superaustenite steel 1.4562 (alloy 31) were investigated. The wettability was determined by contact angle measurement of sessile drop in CO2 atmosphere, at different pressure and temperature. The corrosion behavior of steels was investigated with standard exposure tests, followed by mass loss determination, surface characterization by scanning electron microscope (SEM) and chemical analysis by Energy Dispersive X-Ray Analysis (EDX). Exposure tests with and without the synthetic CO2 saturated water droplets were performed at both low temperature (278 K) and higher temperatures (288 K and 313 K) at high pressure where CO2 is supercritical or in dense phase. The investigated flue gases were SO2 (70-220 ppmV) and O2 (6700 ppmV) and water (50-200 ppmV). To reveal the effects of surface morphology, carbon steel coupons with different surface roughness were prepared to expose to CO2 stream containing oxidizing/reducing impurities to observe the condensation and the corrosion process that followed.
This work examined the droplet corrosion of CO2 pipeline steels caused by impurities in CO2 supercritical/dense phase at 278 K, simulating the underground transport condition. The wetting properties of carbon steels (X52 and X70) as well as martensitic steel UNS S41500, and superaustenite UNS N08031 were studied by contact angle measurement, revealing reactive wetting behavior of carbon steels. Exposure tests with CO2 saturated water droplet on steel surface showed that the impurities (220 ppmv SO2 and 6700 ppmv O2) diffused into the droplet and then reacted with metal coupons in supercritical/dense phase condition, forming the corrosion product instantly during pumping process. Due to the active wetting behavior, the carbon steels suffered from heavily attack, while negligible corrosion product was observed in cases of martensitic steel UNS S41500 and superaustenite UNS 08031 coupons. Condensation experiments that were carried out on fresh polished coupons in CO2 with 1200 ppmv H2O showed that the formation and aggregation of droplet is dependent on the presence of impurities. Without SO2 and O2, the same concentration of H2O did not cause observable corrosion process after a week of exposure. With 220 ppmv SO2 and 6700 ppmv O2 even low water concentration (5-30 ppmv) still resulted in heterogeneous nucleation and subsequent growth of droplets, leading to corrosive process on carbon steel surface albeit to a lesser extent.
In this work, the focus was set on the corrosion process of condensate as drops on the surface of carbon steels (X52, X70), martensitic steel UNS S41500, and superaustenite UNS 08031 in CO2 atmosphere with impurities at 278 K (to simulate the transportation condition in a buried pipeline). Exposure tests were performed at both normal pressure and high pressure where CO2 is supercritical or in dense phase. The drop, 1 ‑ 10 µL in volume, was prepared by dropping CO2 saturated ultra-pure water onto the surface of steel coupons in a one-liter-autoclave. The CO2 gas stream, simulating the oxyfuel flue gas with varying concentration of impurities (SO2 and O2), was then pumped into the autoclave to observe the condensation and corrosion impacts of impurities. Comparable exposure tests were carried out with the same gas mixture and the same volume of water as vapor to observe the drop formation and the corrosion process that follows. The wettability and stability of drops on the surface of steel coupons in CO2 supercritical/dense phase environment was evaluated additionally by contact angle measurement.
Impact of acid condensation on wetting and corrosion behavior of CO2 transport-pipeline steel
(2018)
Es ist allgemein akzeptiert, das Korrosion in CO2-Transport-Pipelines vernach¬lässigbar ist, solange der Wassergehalt des CO2-Stroms deutlich unter der maximal löslichen Menge liegt. Bisher gibt es keinen allgemeinen Konsens darüber, welcher maximale Wassergehalt in zu transportierendem CO2 zugelassen werden sollte. Bei einem Druck von 100 bar und im Temperaturbereich von 277 K bis 298 K beträgt die Löslichkeit von Wasser in CO2 ca. 1.900 bis 3.200 ppmv, aber die Korrosionsrate von Stählen steigt schon ab einem Wassergehalt von 500 ppmv deutlich an. Bei Anwesenheit von Begleitstoffen wie SO2, NO2 und O2, können sich HNO3, H2SO3 und H2SO4 bilden. Menge und Zusammensetzung von kondensierter Säure sind von der Gaszusammensetzung abhängig, und der Korrosionsmechanismus und die Korrosionsform sind vom Kondensationsverhalten abhängig.
In this work, the focus was set on the corrosion process of condensate as drops on the surface of carbon steels (X52, X70), martensitic steel UNS S41500, and superaustenite UNS 08031 in CO2 atmosphere with impurities at 278 K (to simulate the transportation condition in a buried pipeline). Exposure tests were performed at both normal pressure and high pressure where CO2 is supercritical or in dense phase. The drop, 1 ‑ 10 µL in volume, was prepared by dropping CO2 saturated ultra-pure water onto the surface of steel coupons in a one-liter-autoclave. The CO2 gas stream, simulating the oxyfuel flue gas with varying concentration of impurities (SO2 and O2), was then pumped into the autoclave to observe the condensation and corrosion impacts of impurities. Comparable exposure tests were carried out with the same gas mixture and the same volume of water as vapor to observe the drop formation and the corrosion process that follows. The wettability and stability of drops on the surface of steel coupons in CO2 supercritical/dense phase environment was evaluated additionally by contact angle measurement.