The dramatic development of oil, electric power and transportation industries deteriorated alternating current (AC) interference of the pipelines. As a consequence, not only the corrosion of pipelines would be enhanced, but also the cathodic protection (CP) systems be affected significantly. The traditional CP criterion (-850 mV(vs CSE)) was ineffective and a new CP criterion was in needed. The researches about effects of AC interference on CP parameters, such as CP potential，CP current density, sacrificial anode potential, sacrificial anode consumption rate and sacrificial anode efficiency, were reviewed in this article. At the same time, the latest researches on CP criterions and AC corrosion mechanisms were introduced. Finally, the key problems were indicated and the development trend of this research field was predicted.

The corrosion behavior and stress corrosion cracking (SCC) of 35CrMo steel were examined respectively by means of electrochemical measurements and slow strain rate tensile test in an artificial solution with various concentration of H₂S, which aimed to simulate the drilling well environments at oil field. It is shown that 35CrMo steel exhibits a susceptibility to SCC in hydrogen sulfide solutions with pH=5. The susceptibility increases by decreasing the concentration of H₂S. When the concentration of H₂S reached 200 mg/L, the corrosion electrochemical process of 35CrMo steel can be promoted, whilst the steel exhibits obvious susceptibility to SCC. The SCC of 35CrMo steel is mainly induced by hydrogen embrittlement (HE) process associated with anodic dissolution (AD) in hydrogen sulfide solutions with pH=5.

Microbiologically influenced corrosion of 316L stainless steel (316LSS) by iron-reducing bacteria (IRB) Shewanella algae was investigated by means of open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS) and cyclic anodic polarization curves, and scanning electron microscopy and energy dispersive X-ray spectroscopy for characterization of corrosion products. The results showed that after immersion in the IRB containing solution the free corrosion potential of 316LSS shifted negatively; the polarization resistance of 316LSS increased firstly, and then decreased; the presence of IRB reduced the hysteresis loop area of the cyclic anodic polarization curves and also the characteristic potential range of 316LSS, which indicated that IRB inhibited the initiation and propagation of pitting corrosion of 316LSS. The presence of IRB might be beneficial to the formation of biofilms on the surface of 316LSS exposed to in the solution, and therewith the chemical composition and property of the 316LSS surface might be changed by biofilms and metabolites, whilst which resulted in a stronger corrosion inhibition to the 316LSS immersed in the IRB containing solution.

A rust layer was formed on X80 pipeline steel in Yingtan acid soil simulated solution for 30 d, and the micrographs and element compositions of this rust layer were investigated by using SEM, EDS, and XRD. The electrochemical corrosion behavior of the X80 steel with short-term rust layer was investigated by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results showed that, as compared with the X80 steel, the X80 steel with the rust layer possessed more negative free corrosion potential and larger free corrosion current density. This is because that short-term rust layer was composed of Fe₃O₄ and β-FeOOH, had a great number of microcracks and microvoids, which provided the sites for adsorbing of Cl^- in the simulated solution. Moreover, these defects also increased the effective reaction areas for corrosion reactions. β-FeOOH could not prevent aggressive ions from inward penetration, and was reduced in the cathodic sites. These factors resulted in increasing of the corrosion rate of X80 steel with pre-formed rust layer in acid soil simulated solution.

The corrosion behavior of four steels used in making crude oil distillation unit in high temperature crude oil fractions was studied in an autoclave to simulate the corrosive environment in atmospheric and vacuum distillation unit. The mass loss of the samples was measured and then the corrosion morphology was characterized by scanning electron microscopy. The result showed that the higher acid value, sulfur content and salt content of the crude oil resulted in much serious corrosiveness on 20 steel and the corrosiveness of the substances could be ranked as the desalted crude oil > the second atmospheric side-cut fraction > the first atmospheric side-cut fraction. Alloying elements Cr, Ni and Mo could help to improve the corrosion resistance of steels，and the corrosion resistance of the test steels could be ranked as 316 stainless steel > 304 stainless steel > 1Cr5Mo > 20 steel. The overall corrosion rate usually increased with increasing temperature, however, which could reach extreme value in certain range of temperature.

A kind of 1-tetradecylphosphonic acid (TDPA) SAMs was formed on 430 stainless steel by the immersion method. The adsorption behavior and pitting corrosion inhibition performance were investigated by FT-IR spectrum, electrokinetic potential scanning, contact angle measurement and X-ray photoelectron spectroscopy (XPS) observations. The results showed that after modification by TDPA molecules, the stainless steel surface changed from hydrophilicity to hydrophobicity, and the highest pitting potential was obtained after 6 h self-assembling. The oxidation could enhanced corrosion inhibition of 430SS，and the TDPA SAMs also could form on the oxidized 430SS.

Stress corrosion cracking (SCC) of X80 pipeline steel after electrochemically hydrogen-charging in an artificial solution simulated the waters contained in sour soil at Yingtan district in south China was studied by means of potentiodynamic polarization curves, slow strain rate tests (SSRT) and SEM observation. The results show that X80 pipeline steel has high SCC susceptibility in the solution after hydrogen-charging and the failure mode is transgranular cracking. Moreover, the SCC susceptibility and relative plasticity losses increased with increasing electrochemical charging time, the tensile fracture surfaces exhibited a change from ductile dimple fracture to cleavage fracture. In addition, permeation of hydrogen promoted the formation of pits，and therewith pits and nonmetallic inclusions in the steel were found to play an important role for the initiation of SCC cracks.

The corrosion behaviors of galvanized steel for power transmission tower with local breakage of zinc coating were investigated by using EIS and open circuit potential (OCP) measurements in NaCl and NaHSO₃ polluted atmosphere. The results showed that the OCP of the electrode shifted to positive direction gradually as the broken area and exposure time increased. With the increase of broken area of zinc coating, the corrosion rate of galvanized steel increased gradually and more and more close to that of Fe.

Due to the combustion chamber usually provide flam with a non-uniform temperature field, therefore, a lateral temperature gradient should exist on the surface of nozzle guide-vanes for a gas turbine. In the present article, the structure evolution of thermal barrier coatings on nozzle guide-vanes was examined under the action of the above mentioned lateral temperature gradient by means of a home madeinfrared thermal shock testing system combined with impedance spectroscopy measurement. Meanwhile, the failure analysis of thermal barrier coatings being subjected to thermo-mechanical loading was also studied using finite element analysis. It's found that with constrain at both ends of a tube, cracks are apt to initiate at the edge of a heated area.

In order to reveal the evolution of corrosion damage of the anti-corrosion coating for steel box girder, and predict its corrosion life, in-door accelerated tests was carried out for samples Q345C steel, which were coated firstly with an arc spraying aluminum layer and then a top sealing paint. Corrosion morphology image of paints was collected through flat-scanner. Characteristic parameters of corrosion morphology image were extracted through image processing technology to monitor the corrosion process so that to predict corrosion life and evaluate corrosion grade of the coating. The results show that image processing technology could realize a quantitative analysis of blistering area of the paint, and provide a new method for evaluting the corrosion grade as well as revealing the evolution process of corrosion damage. The coating losts efficacy with 5% blistering area of the top paint after 598 h indoor-accelerated corrosion test.

The stress corrosion crack (SCC) initiation of Alloy 690TT was studied by using scratch technique in oxygenated water at 325 ℃. The SEM results show that intergranular stress corrosion cracks were initiated at the bottom of the scratch groove，and the relevant mechanism was discussed. Mechanical cracks which were produced during slow strain rate tensile stage and tips ofthem highly approached to or were along grain boundaries，could be the precursor for stress corrosion crack initiation and growth in the following constant loading stage. Therefore，Alloy 690TT is susceptible to stress corrosion cracking in high temperature oxygenated water.

Al-B₄C composite is a candidate material of neutron absorption for spent nuclear fuel storage racks. The corrosion behavior of Al-B₄C composite with different surface pre-treatments was examined by immersion test in solutions simulated the pressure water reactor (PWR) and boiling water reactor (BWR) spent nuclear fuel storage environments. Then the surface morphology of the corroded samples was observed by SEM, the elemental distribution and the phase constituent of corrosion products were characterized by EDS and XRD respectively. The results showed that the composite was corroded due to the preferential corrosion of Al and trace elements such as Mg and Fe. After immersion in PWR spent nuclear fuel storage solution, four different corrosion morphologies on the polished sample could be differentiated showing a poor corrosion resistance, which might be related with the Fe distribution in the composite. However, after immersion in BWR storage solution an Al(OH)₃ film formed on the polished sample surface indicating a good corrosion resistance. The pre-anodized samples exhibited mass gain after immersion test in the two storage solutions of PWR and BWR respectively, indicating the best corrosion resistance, which may be due to that the pores of the anodized film was sealed by the formed corrosion products in the solutions.

In order to improve the corrosion resistance of chromium-free Zn/Al coating, three different nanoparticles, eg. SiO₂, TiO₂ and ZnO were added in the coating respectively to form nanocomposite coatings. Corrosion properties of the nanocomposite coatings were examined through salt water immersion method and electrochemical method. Furthermore, the microstructure and corrosion products of the coatings were analyzed by means of SEM and EDS. The experimental results showed that the nanoparticles dispersed in the coating in the form of flake structure which formed a more effective physical shield, extending the path of the corrosive medium to substrate. Furthermore, the fine grain strengthening was dominant to make the coating a good shielding property when nanoparticle was added. Tafel curves indicated that the nanocomposite coating with SiO₂ possessed the best cathodic protection among three nanocomposite coatings, and the corrosion resistance of three nanocomposie coatings was better than that of the chromium-free Zn/Al coating.

Multi-walled carbon nonotubes (MWCNTs) /AZ31 composites were fabricated by joining preform of MWCNTs during melting. The corrosion behaviors of the composites were studied by electrochemical corrosion experiments in 3.5% (mass fraction) NaCl solution. The surface morphologies of the composites before and after corrosion were observed and analysised by SEM. The results showed that additions of MWCNTs improved anticorrosive performances of AZ31 Mg-based alloy, the corrosion current density (I_corr) decreased from 5.279 to 2.994 μA/cm².

A composite coating was prepared by means of micro-arc oxidation (MAO) and sol-gel technique on a magnesium alloy, the coating consisted of a micro-arc oxidation (MAO) sub-layer and sol-gel top-layer. The corrosion resistance of the composite coating was examined by cyclic heat-NaCl solution spray/dry test, while the free corrosion potential of the coated alloy was measured in Na₂Cl solution. Then the surface topography and adhesion of the composite coating were characterized by SEM with EDS, and cross cut test respectively. The results show that white spots appeared on the coating surface due to cyclic corrosion test and the number of spots increased with time. The adhesion of composite coatings is good. The coating exhibits a free corrosion potential about -1.43 V, and a rather good adhesion to the substrate. It is observed that there exist many micro-cracks and holes on the coating surface, however the number and size of which reduced with the increase of cyclic corrosion time; and a few corrosion pits can be observed until 720 h corrosion test. It follows that the applied sol-gel permeated into and then sealed the cracks and holes on the coating, thus enhanced the protectiveness of the later.