The research progress on CO₂ corrosion product scales of carbon steels was reviewed. The structure, chemical composition, growth process, electrochemical properties and mechanical properties of the corrosion product scales were mainly introduced. The development trend and emphasis of the research on the CO₂ corrosion product scales of carbon steel in the future are prospected.

The stress corrosion cracking behavior of two oil casing steels TP110TS and P110 in a simulated solution in the annulus space of CO₂ injection wells was comparatively studied by U-bend specimen immersion test and electrochemical test. The results show that TP110TS steel and P110 steel have certain degree of stress corrosion sensitivity in the solution (large amount of CO₂ and micro H₂S), and the stress corrosion mechanism is the synergistic mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). In the CO₂-H₂S environment, the concentration of imidazoline corrosion inhibitor has different effect on the stress corrosion of oil casing steels TP110TS and P110. Adding sufficient corrosion inhibitor has a good inhibitory effect on the stress corrosion behavior of P110 steel. However, when the added amount is insufficient, the corrosion inhibitor increases the stress corrosion tendency of P110 steel. The stress corrosion sensitivity of TP110TS steel decreases with the increase of corrosion inhibitor concentration. It follows that TP110TS is more suitable for the CO₂-H₂S environment where corrosion inhibitors are added.

The corrosion behavior of 20# steel in CO₂ saturated mixture liquor of alkanolamine solution with ionic liquid ([Bmim]BF₄) was studied by means of weight loss measurement, electrochemical impedance spectroscopy (EIS) and SEM equipped with EDS. The results showed that monoethanolamine (MEA) was easy to degrade with CO₂, and the formed degradation products would lead to severe corrosion of 20# steel in experimental conditions. When the [Bmim]BF₄ was added, the corrosion of 20# steel was inhibited and hence its uniform corrosion rate was reduced. Besides, due to the existence of BF₄^- in [Bmim]BF₄, the range of passivation zone is narrowed, which is an important cause for pitting corrosion of 20# steel.

The work aims to evaluate the risk of corrosion and stress corrosion cracking (SCC) of L80 tubing steel during long-term service in Jilin Oilfield. The surface morphology and corrosion products of L80 tubing steel replaced from Jilin Oilfield were analyzed by SEM and laser confocal microscope. Besides, the electrochemical means and slow strain rate tensile tests were used to evaluate the electrochemical behavior and SCC risk of L80 tubing steel in a simulated oil well production fluid. Results indicated that, after serving for several years, the degree of corrosion on the outer wall of L80 tubing steel was mild and dominated by uniform corrosion accompanied with few corrosion products. In the contrast, the inner wall of the L80 tubing steel was badly corroded with a scale of dense corrosion products, beneath which there existed certain localized corrosion, deep pits, as well as microcracks. The indoor tests indicated that the increase in water content, CO₂ and H₂S accelerated the electrochemical corrosion process, thereby promoting the corrosion in the oilfield produced water, while these factors affected little on the SCC sensitivity. In sum, L80 steel displayed good resistance to SCC in the simulated oilfield produced water environment, implying very low risk of SCC for L80 steel as casing materials for oil well.

The stress corrosion cracking (SCC) behavior of X80 pipeline steel and its weld joint in a simulated liquor of soil at Lunnan area of Xinjiang was studied by means of slow strain rate tensile tests (SSRT), SEM observation and potentiodynamic polarization tests. The results showed that both the X80 pipeline steel and its weld joint have obvious SCC susceptibilities, and the mode of fracture cracking propagation is transgranular cracking (TGSCC) under different applied potentials, and the SCC susceptibility of the weld seam is higher than that of the base metal under the same applied potential. SCC susceptibility and mechanism would vary with the applied potential. At -500 mV, the SCC of both X80 steel and its weld joint may be ascribed to the synergistic action of the anodic dissolution (AD) at crack tip and the rupture of passivation film. The SCC susceptibility of X80 pipeline steel increased markedly for potentials below -800 mV (-850, -1000 and -1500 mV) due to a strong hydrogen embrittlement (HE) effect on SCC process and hydrogen induced cracking promoted by cathodic hydrogen evolution reaction.

316 stainless steel pate was paired face by face with four plates of different materials respectively, i.e. 316SS, tetrafluoroethylene, rubber and plastic, and then the crevice corrosion behavior of the 316SS for the above four pairs was assessed via immersion test in FeCl₃ solution, while the relevant electrochemical performance was examined in an artificial seawater. After corrosion test, the samples were examined by laser confocal microscopy. Results show that among others, the pair 316SS/316SS presented the widest corrosion area with the most shallow depth, indicating that the corrosion pits tended to spread preferentially sideways. When the corrosion pits reach a certain depth, the lateral migration of corrosive solution got easier. The corrosion morphology of the pair 316SS/rubber showed the minimum width with the maximum depth, suggesting the longitudinal development of the corrosion pit, which is related to the stress applied on the rubber. In that case, the corrosive medium is closely attached to the steel surface, hence hard to migrate laterally into the gab, thereby the corrosion expanded vertically in depth. Furthermore, the relevant mechanisum of crevice corrosion for different type of pairings was analyzed through electrochemical measurements.

The effect of alternating electric field on the corrosion behavior of A6082-T6 Al-alloy in an artificial atmospheric environment, namely, an electrolyte film on the surface of Al-alloy is studied by means of electrochemical impedance spectroscopy, open circuit potential and cathodic polarization curve measurements, as well as scanning electron microscopy. The results show that, with the decreasing of thickness of electrolyte film, the corrosion rate of A6082-T6 Al-alloy was accelerated. Meanwhile, the applied AC electric field could clearly alter the morphology of localized corrosion type of A6082-T6 Al-alloy, namely transformed from pitting corrosion with a large number of pits to serious exfoliation corrosion.

The corrosion behavior of an as-extruded Mg-6Zn-1.2Y-0.8Nd alloy before and after solid solution (T4) treatment was assessed comparatively in Hank's solution by means of hydrogen evolution examination, electrochemical tests and corrosion morphologies characterization. The results showed that after being solution treated at 475 ℃ for 4 h, the corrosion resistance of the alloy was improved. In addition, when the pre-soaking time was less than 24 h, the corrosion resistance of the alloy before and after T4 treatment all increased with the pre-soaking time. However, when the pre-soaking time was 48 h, the corrosion resistance of the differently treated alloys was reduced. The hydrogen evolution data showed that the hydrogen evolution rate of the T4 alloy was 0.75 times as high as that of the as-extruded ones. As the corrosion morphology of different treated alloys was compared, it can be seen that the corrosion attack on the surface of as-extruded alloy was much severe with deeper corrosion pits.

Metallic materials exposed to fire scenes are usually subjected to high temperature oxidation, of which the atmosphere composition and temperature have been considered as vital parameters. In this study, the high temperature oxidation behavior of 1Cr11Ni2W2MoV stainless steel in air and simulated kerosene-combustion atmosphere at 600, 700 and 800 ℃ were studied by means of visual analysis and micro-structural observation of the formed oxide scale. The results show that the 1Cr11Ni2W2MoV possessed good oxidation resistance and the scales primarily remained continuous and well adherent to the substrate in air. Whilst, the presence of kerosene combustion products apparently increased the consumption of Cr element, reduced the adhesion of oxide scale and hence decreased the oxidation resistance of the steel. Additionally, the combustion products of kerosene resulted in the formation of nodular oxides in the formed scale. Therefore, the combustion of kerosene in fire scene could increase the oxidation rate of 1Cr11Ni2W2MoV, which are expected to offer complementary insight into reconstruction of fire scene.

In order to improve the thermal stability and adhesion strength of PSO (polysiloxane)-PBSZ (polyborosilicate)-TiB₂ modified PSNB (polysilborazane) (labeled as PPPT), PSNB was modified by Al₂O₃-PSO-PBSZ-TiB₂ (denoted as PPPTA), and it was used for joining SiC ceramic discs. The microstructure and phase composition of the modified adhesive were analyzed by SEM and XRD. The effect of pyrolysis temperature and addition amount of nano-Al₂O₃ on the microstructure and adhesion strength for the bonding pair of SiBCN ceramics were investigated. The strengthening and toughening mechanism of nano-Al₂O₃ to the bonding SiBCN ceramics was revealed. After curing in air at 120 ℃ for 2 h and then pyrolysis in air at 1000 ℃ for 2 h, the room temperature adhesion strength of PPPT and PPPTA is up to 11.23 and 15.91 MPa, respectively, and more importantly, the high temperature (in air at 800 ℃) shear strength reaches 10.4 and 12.1 MPa, respectively. The analysis shows that nano-Al₂O₃ can effectively suppress the volume shrinkage of the adhesive layer and inhibit the volatilization of the glass phase at high temperature, thereby significantly improving the adhesion strength.

Resin-filled recrystallized silicon carbide (EP/RSiC) composites with good corrosion resistance were prepared by using E44 epoxy resin as the filling material. The corrosion behavior of EP/RSiC composites in 2 mol/L H₂SO₄ solution and 4 mol/L NaOH solution at room temperature was studied by means of weight loss measurement, potentiodynamic polarization curves measurement, electrochemical impedance spectroscopy as well as corrosion morphology characterization. The results demonstrated that the EP/RSiC composites had a dense structure, low corrosion current density and high free-corrosion potential, and good corrosion resistance. Electrochemical tests suggested that the corrosion of EP/RSiC composites was caused by the active dissolution of silicon carbide. Therefore, EP/RSiC composites were more susceptible to corrosion by alkaline solutions, and their corrosion behavior was controlled by charge transfer. The corrosion rate decreased as the amount of epoxy resin filler increased, among others, the EP/RSiC with 15% (volume fraction) epoxy resin had the best corrosion resistance, namely its corrosion rate was 152 mg/(dm²·d) in 2 mol/L H₂SO₄ solution, while 310 mg/(dm²·d) in 4 mol/L NaOH solution respectively. Which demonstrates that the EP/RSiC with 15% epoxy resin exhibits a corrosion protection efficiency about 90.5% regarding to the plain RSiC without the addition of epoxy resin.

The Cl^- permeation resistance of polyvinyl alcohol fiber reinforced concrete under cyclic tests of drying in air and wetting in chloride salt solution by means of nuclear magnetic resonance (NMR) technique and microscopic scanning electron microscopy (SEM). The distribution of pores and chloride salts in concretes with different among of 18 mm long polyvinyl alcohol (PVA) fibers were assessed. The results show that under the same number of dry-wet cycle, the Cl^- permeation resistance for the concretes increases first and then decreases with the increase of fiber content. The concrete with 1.2 kg/m³ polyvinyl alcohol fiber has a maximum Cl^- penetration depth of 4.1 mm, and the peak value of free chloride ion content is 0.17%, which is 29.3% and 32% lower than that of the reference concrete, respectively, but when the fiber content exceeds 1.2 kg/m³, the Cl^- permeation resistance of the concrete degraded, namely its maximum intrusion depth rose to 5.2 mm with Cl^- penetration resistance of only 10.3% above that of the plain concrete. With the increase number of the dry-wet cycle, the peak value of the free Cl^- content of the fiber-filled concretes filled with the same among of PVA was continuously shifted to the right side, correspondingly, the maximum intrusion depth and free Cl^- content increased significantly. It follows that the fiber content and the number of dry-wet cycle have significant effect on the Cl^- penetration resistance of PVA fiber concrete.