In this paper, the stress corrosion cracking (SCC) behavior of Mg-alloys and the relevant failure mechanism were systematically summarized. Moreover, the effect of anodic dissolution, mechanical loading and hydrogen embrittlement on the SCC cracking modes was described. The measures for improving the SCC resistance of Mg-alloys were also introduced. Finally, the existing problems in the current study, the research emphasis and direction in the future are also pointed out.

Ti48Al5Nb alloy was electrochemically anodized in electrolyte of ethylene glycol with NH₄F to prepare anodic films containing fluorine and aluminum. The influence of anodization treatment on the oxidation behavior, the composition and structure of the oxide scale of the anodized Ti48Al5Nb alloy were then characterized. Results shown that a continuous and dense Al₂O₃ oxide scale will generate on the anodized Ti48Al5Nb alloy after high temperature oxidation. And this oxide scale has good adhesion with the substrate, therefore can efficiently prevent the inward diffusion of oxygen, resulting the enhanced high temperature oxidation resistance. After oxidation at 1000 ℃ for 100 h, the weight gain of the anodized Ti48Al5Nb alloy was dramatically decreased from 26.73 mg·cm^-2 for the bare Ti48Al5Nb alloy to 1.18 mg·cm^-2. Moreover, it is shown that anodization also changes the oxidation mechanism, leading to the disappearance of the Nb-enriched layer at the interface between the oxide scale and substrate. The enhanced high temperature oxidation of the anodized Ti48Al5Nb is derived from the halogen effect based on the fluorine compounds existed in the anodized film.

The corrosion performance of weld joints of nuclear grade stainless steel in high temperature and high pressure water was investigated by means of mass change measurement, scanning electron microscope (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that, in the initial stage before 340 h, the weld joints suffered from mass loss with a relative high rate, then the mass loss turned to decrease gradually, finally the weld joint exhibited a little mass gain when the test reached 1080 h and hereafter the mass gain kept at a stale level. The oxide scale formed on the weld joints consisted of FeOOH, FeCr₂O₄ and Fe₃O₄ primarily. In conclusion, the weld seam of 316LN stainless steel exhibited an equivalent resistance to uniform corrosion as the base metal.

In order to figure out the corrosion problem of water cooled-wall tubes caused by urea in a coal-fired power plant, the corrosion behavior of 15CrMo steel at high temperature were studied in urea containing media with an autoclave aiming to simulate the operation situation of the power plant. The urea decomposition process and the corrosion of the steel were simultaneously examined at 270 ℃ in solutions with varying urea concentrations of 70, 140, 280, 560 and 840 mg/L, respectively. Peculiarly, during the decomposition process of the medium with urea concentration of 280 mg/L, the yield liquid- and vapor-phase were extracted from the reaction chamber at different time intervals for characterization with TOC analyzer and infrared spectrometer. Besides, the corrosion of 15CrMo steel in the yield urea solution were assessed by weight loss measurement, electrochemical impedance spectroscopy and polarization curve measurement. The surface morphology of the tested steel was characterized by SEM, EDS and XRD. Results show that urea produced corrosive ions NH₂COO^- during decomposition, which caused the corrosion of water wall tubes. The corrosion rate of 15CrMo steel increased with the increasing urea concentration, and the maximum corrosion rate was 0.593 mm/a. The urea leaked into water cooled wall tubes may be ascribed to certain consequences of improper design of the denitrification system, therefore, to eliminate such engineering errors can effectively prevent the occurrence of urea induced corrosion for water-cooled wall tubes.

As one of the most corrosion resistant metallic material, Ti or its alloy may find a variety of applications in the marine industry. It is important to understand the passivation mechanism of Ti in seawater. In this paper, the activation process of a passivated pure titanium TA2 in artificial seawater was investigated by means of potentiostat polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The influence of seawater composition on the activation behavior was also studied. The result showed that the activation occurred around 1.6 V (SCE). Scanning electron microscope (SEM) and oxygen evolution monitoring indicated that obvious defects emerged on the surface of TA2 but no bubble was detected by applied potentials in the range of 1.4~1.6 V (SCE). According to Mott?Schottky analysis of the passivated and activated TA2 surface, the activation might be attributed to a transition of the semiconducting performance of the surface film on TA2.

The hydrogen-induced cracking behavior of a new-designed duplex stainless steel 2205 (including its two-subtypes A-DSS and B-DSS) used for marine structures in artificial seawater was investigated by means of slow strain rate test (SSRT), mechanical test and scanning electron microscope. While the hydrogen permeation behavior of A-DSS and B-DSS was studied by Devanathan-Stachurski's hydrogen permeation technique. The results showed that the hydrogen diffusion coefficients for A-DSS and B-DSS were 2.36×10^-10 and 2.31×10^-10 cm²/s, respectively. A-DSS and B-DSS exhibited the lowest susceptibilities to environment induced fracture when the applied cathodic potentials were -800 and -700 mV (SCE), respectively. Correspondingly, SEM observations of the fracture surface of the above two steels showed that cracks initiated in ferrite phase, and were arrested by austenite phase or interface boundaries of ferrite/austenite.

The relationship between the selective corrosion behavior and the microstructure of 022Cr25Ni7Mo4N duplex stainless steel was studied by means of electrochemical test, thermodynamic calculation, SEM, AES and XPS. The results show that the anodic polarization curve of test steel has obviously three stages, activation-passivation-transpassivation. In the conversion interval of activation to passivation, there exist two anode activation peak potentials, E_h=-236~-238 mV and E_l=-287~-294 mV, which may corresponds to the dissolution potential of γ-phase and α-phase respectively. 022Cr25Ni7 Mo4N steel has a higher E_l potential, a lower E_h potential and a smaller anode activation potential difference ΔE, which is related to the smaller difference of pitting resistance equivalent number (ΔPREN) between α-phase and γ-phase of the steel. The increase of Cr, Mo and N content can simultaneously increase the PREN value of α-phase and γ-phase of the test steel, and it can reach the balance of PREN between the two phases for the steel composed of 25.4%Cr, 4.8%Mo and 0.28%N (mass fraction). In such case, the Cr in the passive film is mainly as the chromia Cr₂O₃, and the transition zone width of the passivation film on α-phase is narrower than that on γ-phase.

The real sea water corrosion behavior of 304 stainless steel was studied at different depths such as 1200, 2000 and 3000 m below sea level in the South China Sea via a home-made series cage-like equipment, as well as SEM, EDS, EIS and XPS techniques. The results show that: the corrosion rate of 304 stainless steel in deep sea is relatively small. The corrosion rates for 0.5 a at depths of 1200, 2000, and 3000 m below sea level are 1.84, 2.07, and 3.11 μm/a, respectively, and the corrosion rate slightly increases with the depth. The influence degree of seawater environmental factors on the corrosion rate of 304 stainless steel decreases in a descending order as follows: pressure, oxygen content, electrical conductivity, temperature, pH. Crevice corrosion occurs locally on the surface of 304 stainless steel and the depth of the crevice corrosion increases with the increasing depth. The corrosion products for the tested 304 stainless steel consist mainly of Fe₃O₄ and NiO.

The effect of inhibitors on corrosion behavior of reinforced bar in coral aggregate seawater concrete (CASC) in artificial sea water was studied by means of linear polarization resistance method (LPR) and electrochemical impedance spectroscopy (EIS). Two inhibitors, calcium nitrite rust inhibitor (CN) and amino-alcohol rust inhibitor (AA) are concerned, while two ways are adopted for mixing inhibitor into the concrete, namely, the inhibitor was directly dissolved into the seawater (ordinary way) and absorbed onto the coral aggregate (pre-absorbed way). The results show that for CASC concretes without and with inhibitor added via ordinary way, E_corr, R_p and R_ct decreased with the extension of the exposure time, but for those with the pre-absorbed inhibitor, E_corr, R_p and R_ct has a grown trend when exposure for 90 d, demonstrating that the pre-absorbed inhibitor onto the aggregate would gradually and continuously be released into the concrete to increase its barrier effect to the migration of harmful Cl^-, therewith to alleviate the corrosion of the reinforced bar. Besides, the addition of CN or AA could enhance the corrosion resistance of the reinforcement bar, however the degradation rate of anticorrosion effectiveness of CN was higher than that of AA. Therefore, for marine engineering structures made of CASC on islands and reefs, it was suggested to adopt the pre-absorbed AA, which could prolong the time for the corrosion initiation of reinforced bar, reduce the corrosion rate and prolong the service life of the CASC structures.

The feasibility of several coating systems for offshore wind power generation system was assessed through adhesion measurement, neutral salt spray, wear resistance test, ultraviolet aging test, cyclic corrosion test and outdoor exposure test. Experimental results indicated that after cyclic corrosion and outdoor exposure test, two types of epoxy zinc-rich polyurethane coating systems S03 and S04 maintained adhesive strength of above 5 MPa. After neutral salt spray test for 2000 h, the rust- and blister-degree for the two zinc-rich primers P04 and P06 could be raked as grade 1 (S2), while the expand of the rust size is no more than 2.70 mm underneath the primer. Hence, the two primers have good resistance to salt spray and corrosion propagation. Five types of polyurethane coatings, including T01~T04 and T06, have excellent wear resistance of superior to 1.0 L/μm. The gloss reduction of four types of polyurethane coatings (T01~T04) did not exceed grade 1 during the course of uv-accelerated aging. However, there exists large variations in the protective performance for the same type of paint supplied by different manufacturers. It is concluded that the S04 coating system has better comprehensive protective performance, thus, which is suitable to the application in the sector of offshore wind power generation system.

Ni-Cr alloy coatings were prepared via a two-step process, namely Ni/Cr multilayered films of thickness modulation were firstly prepared by dual bath technique, which then subjected to alloying treatment at proper elevated temperature. The microstructure and chemical composition of Ni-Cr alloy coatings were characterized by means of SEM and EDS. The results show that with the decreasing period of modulation as well as the increasing heat-treatment temperature and time, the alloying process for Ni/Cr multilayered films could be expediently realized. After high temperature treatment, the chemical composition of the Ni-Cr alloy coatings is homogeneous on average, which is basically consistent with the theoretical value. Of which the surface morphology changes from the original nodular- or granular-like structure to block-like structure, while no thermal stress cracking is observed. Besides, their corrosion resistance was evaluated in comparison with nickel coating and chromium coating of the same thickness. It is found that the Ni-Cr alloy coatings have better corrosion resistance.

Extracellular polymeric substance (EPS) presents certain inhibitory effect on metal corrosion, which mainly composed of protein, polysaccharide. In the study here, Bovine serum albumin (BSA) and Dextran 40 were used to represent the protein and polysaccharide respectively, with which the carbon steel was coated by dip-coating method. Thereafter, the corrosion behavior of carbon steel without and with coatings of BSA and Dextrand 40 was studied via immersion test in an artificial corrosive solution of NaCl 58.5 mg/L+Na₂SO₄ 213 mg/L+NaHCO₃ 4.2 mg/L. The corrosion rate, surface morphology, corrosion products, and electrochemical behavior of the carbon steel, as well as the changes in functional groups of the BSA and Dextran 40 before and after dip-coating on carbon steel are mainly concerned in the study. Results shown that the corrosion products formed on the steel coated with BSA and Dextran 40 contained the amounts of Fe₃O₄ up to 113.6% and 145.5% of that on the plain steel, correspondingly, the corrosion rate decreased by 17.7%, 24.0%, respectively. The equivalent circuit of the plain steel is R(QR) and the dip-coating ones could be fitted with R(Q(R(QR))). Infrared spectroscopy revealed that, after dip-coating on the steel surface, the relevant peaks of the —C=O—, —COO— of protein, and the —C—OH, —CH₃, —CH₂—, —COO— of polysaccharide weakened or even disappeared, which indicated that after dip-coating a protective film may form on the surface of carbon steel. The fact implies that the functional groups of BSA and Dextran 40 may take part in the corrosion process, and play a key role on the formation of protective film.

AM60 and AM60Gd1.0 magnesium alloys were prepared by zone solidification purifying method. Microstructures and phase compositions of the alloys were analyzed. The corrosion resistance of the alloys in 0.9% (mass fraction) NaCl solution and simulated body fluid were examined by hydrogen evolution test and electrochemical test. Results show that AM60 alloy composed of α-Mg and β-Mg₁₇Al₁₂, while Al₂Gd was found for AM60Gd1.0. The corrosion rate of AM60Gd1.0 alloy was lower than that of AM60 alloy. The E_corr of AM60Gd1.0 alloy was much positive than that of AM60 alloy due to the addition of 1.0%Gd. The I_corr of AM60Gd1.0 alloy was smaller than that of AM60 alloy. In NaCl solution, the EIS curves of AM60 and AM60Gd1.0 alloy all composed of a capacitive loop and an inductive loop. In SBF, the EIS curves of the alloys composed of two capacitive loops. Being soaked in NaCl solution for the same period of time, the radius of the EIS curve of AM60Gd1.0 alloy was larger than that of AM60 alloy.

Air cooler is the key equipment in the process of hydrocracking. The corrosion of air cooler becomes a prominent problem in the safe and stable operation of equipment. In this paper, a numerical simulation model is established based on the analysis of the erosion corrosion of the air cooler tubes in a hydrocracking unit. The mixture model and the standard k-ε model of CFD simulation software is used to simulate the whole flow field of the tube box and tube bundle of the air cooler. The corrosion position of the air cooler is predicted by the turbulent kinetic energy distribution. The corrosion amount of erosion corrosion and electrochemical corrosion are predicted as well. According to the simulation, the maximum erosion amount is 4.76 mm/a, and it is concentrated at the inlet of the tube bundle of air cooler. The simulation results are consistent with the actual corrosion of the air cooler. Comparing with electrochemical corrosion, erosion corrosion is the main cause of corrosion of air cooler. The amount of erosion and corrosion of the tube bundle of air cooler has been greatly reduced after the retrofit of the air cooler structure, therewith, the safety and stability of the air cooler have been greatly improved.