The main cause of the global warming is considered to be the increase in CO2 emission due to the developed economic activity of mankind. Nowadays, strict reduction of CO2 emission to the atmosphere is required to keep the rise in temperature less than 2.0℃ after the industrial revolution. One potential technology is CCS （Carbon dioxide Capture and Storage） consisting of four processes, ①Separation and recovery of CO2 from raw gases, ②Transportation of dense phase CO2 to an injection site, ③Injection of super critical CO2 into deep subsurface reservoirs, and ④Confirmation of the safe storage of the injected CO2. However, CO2 is an acid gas and it becomes highly corrosive when it exists with liquid water, contaminants, and the variation of temperature and pressure. The corrosive conditions of the four processes are technically reviewed in relation to the corrosion behavior of steels.
A large-scale CCS demonstration project is currently being undertaken by the Japanese government in the Tomakomai area, Hokkaido prefecture, Japan. The project is scheduled to run for the period JFY 2012 - 2020 to demonstrate the viability of CCS system from CO2 capture through to injection and storage. 100,000 tonnes per year or more of CO2 derived from an industrial source will be injected and stored in saline aquifers under the seabed in the offshore area of the Tomakomai Port. Commissioning of the ground facilities has continued, after completion of construction in October 2015. CO2 injection will be stared in April 2016.
It is important to study the CO2 corrosion behavior in CCS operation which applies the CO2 injection. In Oil and Gas exploration and production environments, reservoirs may contain acid gases such as CO2, and the corrosion environments would become harsh for OCTG and linepipe. In this paper, the research work on CO2 corrosion and its countermeasure is reviewed. CO2 corrosion can be characterized by its relatively high corrosion rate and localized corrosion (ringworm corrosion). It is also recognized that the corrosion behavior depends on the environmental factors such as partial pressure of CO2 and temperature, and also the effect of flow velocity is remarkable. The addition of Cr as an alloying element is effective to mitigate the CO2 corrosion, therefore, stainless steels such as Super 13Cr have been widely applied, as OCTG and linpipe.
Coal-fired power plants emit large amounts of CO2, which constitutes one of the largest causes of global warming. Reducing carbon emission from coal-fired power plants is crucial for preventing global warming while stably supplying power. Toward this end, this article features an initiative aimed at achieving CO2 capture technology based on an oxyfuel system, and a post-combustion capture technology based on a chemical absorption method.
The experiment for developing ant nest corrosion was conducted by using two kinds of copper tubes; a phosphorous deoxidized copper (PDC) tube containing 0.028% P and an oxygen-free copper (OFC) tube without P. Ant nest corrosion occurred on both PDC and OFC tubes after the exposure to an atmosphere derived from 100, 1000 and 10000ppm formic and acetic acid solutions. The propagation rate of ant nest corrosion occurred on the PDC tube was faster than that on the OFC tube, whereas the weight loss of the OFC tube after the exposure test was higher than that of the PDC tube. In the immersion test of PDC and OFC tubes in 100 and 1000ppm formic and acetic acid solution, ant nest corrosion occurred on copper tubes except for the OFC in acetic acid solution. Since the ant nest corrosion is developed on the OFC tube containing none of P, phosphorous in copper is not necessarily required for the formation of ant nest corrosion.
The distribution of electric potential and current density was numerically analyzed by the finite element method with 8 noses iso-parametric elements during crevice corrosion process of SUS304 at E=399mV in the artificial seawater. The crevice corrosion propagation mechanism before and after arrival of the corrosion tip to the edge of crevice was proposed by the results of this numerical analysis. The main results were as follows: (1)Before the corrosion tip reached to the edge of crevice, the electric potential of the passive area decreased linearly from the edge of crevice to the corrosion tip due to the IR drop even though under the constant potential condition. (2) The electric potential dropped greatly and the current density increased discontinuously at the corrosion tip. (3) The current density in the corroded area decreased from the corrosion tip to the initiation site of corrosion. (4) The current density of the corrosion tip at the edge side was predominantly larger than that at the crevice center side. For this reason, the migration speed of the corrosion tip at the edge side was accelerated as compered with that at the crevice center side. It was considered that the pH in front of the corrosion tip at the crevice edge side remarkably dropped because of the much dissolved metallic ions.(5) When the corrosion tip reached to the crevice edge, the electric potential and current density of the tip increased furthermore. However, the metallic ions diffused to outside the crevice and water came into the crevice from the outside. The movement of the corrosion tip to the outside of crevice stopped by this mitigation of corrosive solution.