A range of impurities may exist in supercritical CO₂ stream of transmission pipelines for carbon capture and storage (CCS) process, which are the potential corrosive factors to induce operational risks of the supercritical CO₂ transmission pipeline. The impurities induced inner side corrosion of supercritical CO₂ pipelines may become the bottleneck restricting the development and application of CCS. This paper reviews the recent research progress on the corrosion behavior of pipelines for supercritical CO₂ transmission. The potential corrosion risks and the impact factors on corrosion are analyzed. The influence of impurities on the phase behavior, water chemistry characteristics, corrosion scales and the corrosion mechanism of transmission pipelines is also discussed. The shortcomings in the present investigations and the key scientific problems for further research are also pointed out.

The corrosion behavior of X65 MS pipeline steel in 5%NaCl solutions with different concentrations of H₂S and pH values, and the morphology, composition and phase constituent of the corrosion product scales were investigated by means of mass-loss method, electrochemical impedance spectroscope, field emission scanning electron microscopy (FE-SEM) and X-ray diffractometer (XRD). The results showed that, in the solutions with the same pH value, the average corrosion rate of X65 MS pipeline steel increased with the increasing H₂S concentration. When the ratio [H₂S]/[H₃O⁺]<10^1.5, the average corrosion rate of the steel decreased with the increasing pH, on the contrast, which was independent to both of pH value and H₂S concentration if the ratio [H₂S]/[H₃O⁺]>10^1.5. Besides, the formed corrosion product scales on X65 MS pipeline steel were mainly composed of amorphous ferrous sulfide, iron sulfide and mackinawite, the amount of each phase varied with the pH value and H₂S concentration of the solutions. It is noted that all the corrosion product scales exhibited relatively poor protectiveness.

The inner- and outer-surface corrosion behavior of X65 pipeline steel used in Shengli Chengdao oilfield was studied in this paper. The inner surface corrosion behavior of X65 pipeline steel in oil-water mixtures with different flow rate and oil content was examined by means of mass loss method and electrochemical technique. The corrosion resistance of the outer surface of X65 pipeline steel in soil extracts was also examined by means of polarization curves and electrochemical impedance spectroscopy (EIS). The phase constituents and surface morphology of corrosion products were characterized by using X-ray diffraction techniques (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that the corrosion rate of X65 steel increased with the increasing flow rate of oil-water mixture, which could reach the maximum value when the oil content was 0.5% (mass fraction). The corrosion current density of X65 steel increased with immersion time in soil extracts. A loose corrosion product film formed on the steel surface, which can accelerate the cathodic depolarization reaction.

The inhibition effect of Brönsted acid ionic liquids (BAIL) 1-methyl-3-(4-sulfonic acid) butyl imidazolium hydrogen sulfate ([(CH₂)₄SO₃HMIm][HSO₄]) on the corrosion of Q235 steel in 0.5 mol/L HCl solution was investigated by electrochemical measurements. The results showed that the BAIL could suppress the corrosion process of Q235 steel in HCl solution at 25 ℃ through adsorption. The inhibition efficiency increased with the increasing concentration of BAIL in the range 0~14 mmol/L, but decreased with the increasing concentration of BAIL in the range 14~16 mmol/L. The best inhibition efficiency was 80.7% for the solution with 14 mmol/L BAIL. The potentiodynamic polarization curves revealed that the BAIL could act as a mixed-type inhibitor. SEM observation of Q235 surface showed that the adsorption of inhibitor molecules on Q235 surface could form a film of BAIL, and which could prevent both the hydrogen evolution and iron dissolution. This inhibition mechanism was proved further by the results of XPS analysis.

Corrosion inhibition of 2-undecyl-N-carboxymethyl-N-hydroxyethyl imidazoline (UHCI) on carbon steel in an artificial water, which simulated the water produced by seawater reverse osmosis (RO) process, was investigated by mass loss test, electrochemical methods, and X-ray photoelectron spectroscopy (XPS). Results show that UHCI could inhibit the corrosion of carbon steel, and the inhibition efficiency increases with the increasing concentration of UHCI. The UHCI acts as an anodic type inhibitor responsible for reducing the anodic current density. XPS results suggest that UHCI was adsorbed on the mild steel surface, which can effectively protect carbon steel from corrosion in the artificial water. Quantum chemical calculation results reveal that carboxymethyl and the ring of UHCI play the important role when UHCI adsorbed on carbon steel surface, which leads to the enhancement in the corrosion resistance of carbon steel and thereby a reduction in the corrosion rate.

The inhibition performance of two compounds of benzimidazole N-mannich base namely PAB and PPB for N80 steel in HCl solution was investigated by means of weight loss test, potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that both PAB and PPB were mixed-type inhibitor, and were adsorbed on the surface of mild steel spontaneously; whilst PPB has higher inhibition efficiency than that of PAB, which accorded well with theoretical prediction. Furthermore,the adsorption of both PAB and PPB follows Langmuir isotherm law.

The microstructure characteristics, exfoliation corrosion behavior of 7050-T7451Al- alloy plates were examined by optical microscopy, scanning electron microscopy and Image Pro Plus. The effect of the distribution of grain boundary precipitates, the fraction of recrystallized grains and the length-width ratio of grains on the exfoliation corrosion behavior was investigated. The results indicate that the microstructures of the 7050-T7451 plates fabricated by different processes are composed of recrystallized grains and non-recrystallized grains with precipitates distributed discontinuously along grain boundaries; but which varied corresponding to the relevant fabrication processes. The average length-width ratio of grains plays an important role in the exfoliation corrosion process of the plate, while the influence of the discontinuity of precipitates distribution and the fraction of recrystallized grains is weak. When the precipitates distribute discontinuously along grain boundaries and the average length-width ratio of grains is less than 5, the EXCO resistance of 7050-T7451 plate can reach EA degree or better.

The microstructure and corrosion performance in 3.5%NaCl solution of an Al-Zn-Si-RE containing water-borne coating were investigated by means of SEM with EDS as well as potentiodynamic polarization curves and electrochemical EIS. The results indicate that Al-Zn-Si-RE coating shows a typical lamellar structure, which significantly increases the length of diffusion path for corrosive species; and an excellent coating uniformity in micro scale, which may be beneficial to its protectiveness. The corrosion process of Al-Zn-Si-RE coating can be divided into four stages during immersion in 3.5%NaCl solution: I) the active corrosion of Al-Zn-Si-RE flakes on the surface layer; II) the coverage of Al-Zn-Si-RE flakes by the corrosion product layer thereby decreasing their dissolution; III) the temporary sacrificial anode protection of the coating for the steel substrate when the electrolyte reached the interface coating/substrate; IV) the barrier protection caused by corrosion products. Therefore, the protection mechanism of the coating is physical barrier combined with a weak sacrificial anode protection.

Epoxy resin coatings reinforced with different amount of carbon fiber of varied length were prepared, and which then were covered with a top coating of insulation. The antibacterial performance of the above coatings, especially for flavobacterium was examined by high voltages of 11 and 15 kV respectively. It was observed that the sterilizing efficiency of epoxy resin coatings without carbon fiber were 90.82% and 93.18% by voltage 11 and 15 kV respectively. For the coating with 0.01%(mass fraction) of carbon fiber, the sterilizing efficiency increases slightly with the increasing fiber length by voltage 11 kV. The epoxy resin coatings with carbon fiber of 7 mm in length achieved a sterilizing efficiency up to 99.82%. While the epoxy resin coatings containing 0.03% carbon fiber of 3 mm in length exhibits the highest sterilizing efficiency 99.73% by voltage of 11 kV; whilst the sterilizing efficiency of the epoxy resin coatings increased with the increasing voltage. Therefore, the conductive epoxy resin coating may provide a new prospect for environment-friendly and energy-saving technique of fouling prevention in the relevant industrial processes, which adopt pulse electric field technology.

The 8-hydroxyquinoline (8Q), as a sustained-release corrosion inhibitor was deposited onto nano-particles of mesoporous-silica to prepare 8-hydroxyquinoline-silica (8Q-SiO₂) powder. Then the powder was used as pigment to modify epoxy resin to prepare 8Q-SiO₂-epoxy resin coating. The prepared 8Q-SiO₂ was characterized by means of infrared spectrum and ultraviolet absorption spectrum. The corrosion performance of the 8Q-SiO₂-epoxy resin coating was examined by salt spray test and electrochemical impedance measurement. The results revealed that the 8Q can enhance the corrosion resistance of epoxy coating, and among others the epoxy coating with 5% (mass fraction) 8Q-SiO₂ exhibits the highest corrosion resistance, which may be ascribed to that the 8Q may slowly release from the mesoscopic channels within SiO₂ into the epoxy coating and then arrive at the interface coating/substrate to provide corrosion inhibition for the substrate.

Epoxy varnish coatings with different amount of sulfosalicylic acid were prepared on galvanized steel. The adhesion and corrosion performance of the coatings were characterized by means of pull-off adhesion tester and electrochemical impedance spectroscopy (EIS) respectively. While the effect of sulfosalicylic acid on the corrosion resistance of the coatings was also studied in 3.5%NaCl solution. The results show that with the increasing amount of sulfosalicylic acid, the adhesive strength of the coatings increases firstly, and then decreases. Among others, the coating with 3% (mass fraction) sulfosalicylic acid exhibits the highest adhesive strength, modules at low frequency and pore resistance during the immersion process only except for the initial stage; as well as the highest charge transfer resistance. These results show that the epoxy varnish coatings containing 3% sulfosalicylic acid has the best adhesion and corrosion resistance.

Corrosion resistance and corrosion sensitivity to chloride containing environment of 20MnSiCrV steel and 20MnSiV steel was comparatively investigated by salt-spray corrosion test with 3.5%NaCl solution, as well as electrochemical impedance spectroscopy and polarization curve measurements in chloride containing alkaline solutions. The formed corrrosion product scales were characterized by SEM, EPMA and XRD. The results show that the corrosion resistance to Cl^- of 20MnSiCrV steel was 1.5 times over that of 20MnSiV steel. The average corrosion rate and depth of corrosion pits of 20MnSiCrV steel were 58% and 74% of those of 20MnSiV steel, respectively. The major components of corrosion products of the two steels were Fe₃O₄, α-FeOOH and γ-FeOOH. Corrosion scale of 20MnSiCrV steel can be differentiated into an inner layer and an outer layer. The inner layer is enriched in Cr and Si, thereby beneficial to the corrosion resistance of the steel.

The electrochemical characteristics of rebar in a polymer-modified mortar (PMM) and a common mortar (CM) were comparatively studied by means of electrochemical impedance spectroscopy (EIS), linear polarization (LP) and open circuit potential measurements. The result showed
that the formation rate of passive film on the rebar steel in PMM was slower than that in CM. After the passive film was completely formed, the impedance of the rebar steel in PMM was larger than that in CM. The effect of polymer modification on the resistance to chloride ion penetration of polymer-modified concret (PMC) was evaluated by rapid chloride diffusion coefficient method (RCM)and which on the mechanical property of PMC was also examined. It showed that the addition of polymer can clearly enhanced the resistance to chloride ion penetration and also the mechanical property of the modified concrete.

The corrosion rate of steels in marine splash zone is high, and it is generally considered to be due to the environmental characteristics of this zone. One of the important distinctions between the marine splash zone and the normal atmospheric zone is the wetting condition of steel surfaces. However even in the same splash zone, the corrosion rate of one spot is different to that of the other ones on the surface of one steel pile, thereby on which a corrosion rate peak should exist at a specific spot. In order to reveal the nature of the difference in corrosion rate at different positions of a steel pile, the variations of the wetting condition of steel specimens with tidal movement was monitored, while the specimens located at different positions along a vertical line passing the tide zone. It follows that the wetting degree of the steel specimen in the splash zone is closely related with its location and the tidal movement, and which substantially follows an overall trend that the wetting degree increases with the rising tide level and decrease with the lowering tide level; the wetting degree of the steel specimen increases with the increase of exposure time. But for a specific moment, a certain relationship dose not exist for the wetting degree with the tide movement and the location of steel specimen. Even though by the time of the low tide level the steel specimen located in splash zone is still in a wet condition due to the effect of the high air humidity and flying seawater foam, which correlates also to the high moisture absorption characteristics of corrosion products scale on the carbon steel. The extreme corrosion rate of the steel in splash zone corresponds to a specific wetting degree. Furthermore, on the area below the extreme point, thin water film on the surface of steel specimens can often be observed by naked eyes, which is consistent with the relationship between corrosion rate and thickness of liquid film on the metal surface.