This paper systematically summarizes the formation and evolution of the iron oxidizing bacteria (IOB) related biofilm and the relevant mechanism, and then introduces the metabolic process of IOB and the corrosion process induced by IOB with emphasis on the role in the corrosion process of their metabolite of extracellular polymeric substance (EPS). The paper also reviews the research progress of synergic corrosion induced by typical aerobic IOB and anaerobic sulfate reducting bacteria (SRB). In addition, the paper further summarizes corrosion prevention methods applied in oilfields and the corresponding research progress, which may provide reference for the corrosion control for oilfield.

Corrosion under-deposits is briefly introduced, and then the application status of electrochemical testing technologies in this field is highlighted. Meanwhile, the future prospect related with the development and application of electrochemical testing technologies is put forward. At present, linear polarization, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN), and the wire beam electrode (WBE) technology are the optimal choice in the study of under-deposit corrosion. To make up for the inadequacy of using a single electrochemical testing technology, the combination of two or more electrochemical testing technologies will become the main stream in this field.

Effect of external electric field on the inhibition efficiency of cyclohexylamine carbonate (CHC) for carbon steel N80 beneath adsorbed thin electrolyte layers (ATEL) was investigated by means of electrochemical measurement, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results illustrated that CHC mainly suppresses the anodic corrosion reaction and has strong inhibition effect on the carbon steel corrosion. When an electric field vertical to the steel was applied, the inhibition efficiency of CHC decreased greatly and the adsorption of CHC on the carbon steel surface decreased significantly, so that the surface morphology varied quite obviously after corrosion test.The relevant quantum chemical parameters related to the corrosion inhibition efficiency of CHC were calculated by materials studio software. The acquired parameters such as dipole moment (μ), E_HOMO, E_LUMO and ?E all implied that the reactivity and adsorption ability of CHC were reduced significantly after applying external electric field, which affects the inhibition efficiency of CHC.

Effect of crude oil on the inhibition behavior of imidazoline inhibitor were illustrated by dynamic mass loss method, electrochemical test, contact angle measurement, scanning electron microscopy etc. The oilfield produced water was simulated in the presence of CO₂ under pressure of 2.5 MPa at 80 ℃, then in the above corrosive medium the corrosion inhibition performance of imidazoline corrosion inhibitor for N80 steel was assessed. The results showed that the open circuit potential and charge transfer resistance of the carbon steel increased when adding crude oil into the corrosive medium which contained imidazoline corrosion inhibitor. It is also found that the wettability of carbon steel surface against water was reduced obviously and the coverage of the inhibitor film became more complete, whilst the inhibition efficiency increased greatly after introducing crude oil into the oilfield produced water.

Influence of the content of coupling reagent KH-550 on the morphology, phase constituent and corrosion resistance in 3.5%NaCl solution of micro-arc oxidation (MAO) coatings, prepared on Mg-alloy AZ31B by a constant voltage mode in an electrolyte of Na₂SiO₃-KOH-NaF, was investigated by scanning electron microscopy, X-ray diffractometer and electrochemical methods. Results showed that the size of micro pores and the roughness of the MAO coatings are increased firstly and then decreased with the increasing amount of KH-550 in a concentration range of 0~20 mL/L, but its thickness and corrosion resistance show a converse result. However, the phase constituents of the MAO coatings are not changed. The preliminary analysis suggested that KH-550 hinders the ionic migration on certain weak areas, where silanol was adsorbed and/or reacted with, and thereby the arc discharge was modulated during MAO process. Therefore, KH-550 improves the growing efficiency of MAO coating, homogenizes the size and distribution of micro pores, and enhances the corrosion protection ability of the MAO coating on Mg-alloy.

Pipeline steel has been widely used in modern industry such as the transportation of natural gas and oil. However, its service life is mainly affected by the corrosion because of its hydrophilic and oleophilic properties. In this study, the surface of X80 pipeline steel was converted to be of super-hydrophobicity and oleophobicity by acid etching and fluoride modification. The steel was first etched by a mixed acid solution to roughen its surface, and then modified with a kind of low surface energy material, 1H, 1H, 2H, 2H-Perfluorodecyltriethoxysilane. The fluoride modification can reduce the surface energy, which is an essential step to prepare the amphiphobic surface. The influence of acid etching and modification on the morphology and the wetting behavior of the modified surface was characterized and the corrosion behavior of the amphiphobic surface was studied by potentiodynamic scanning. The result showed that the modified amphiphobic surface exhibits excellent both of hydrophobicity and oleophobicity, for substances such as water, glycerin and ethylene glycol, as well as hexadecane. After 4 h etching and fluoride modification, the contact angles of the modified steel with deionized water, glycerin, ethylene glycol and hexadecane were 161°, 156°, 151.5° and 146° respectively. The modified surface can enhance the corrosion resistance of the pipeline steel and such amphiphobic surface can be easily repaired.

TiAlN coatings were deposited on high-speed steel substrate by filtered arc ion plating technic. Effect of nitrogen partial pressure on phase structure, chemical composition, mechanical properties, deposition rate, surface roughness, adhesion and tribological properties of TiAlN coatings is studied. The results reveal that there is a strong influence of nitrogen partial pressure on coating structure and properties. By varying the nitrogen partial pressure, the maximum hardness of 34 GPa is achieved for the TiAlN coating with a strong (111) preferred orientation. The deposition rate and surface roughness of the coatings decrease gradually with increasing the nitrogen partial pressure. Due to the improved surface quality by eliminating the most of macro-particles, all the TiAlN coatings show relatively low coefficient of friction, which varies in the range of 0.15~0.33. The coatings also possess good wear resistance, showing the lowest wear rate of 8.8×10^-7 mm³/(Nm).

The degradation behavior of a modified epoxy resin coating was comparatively studied in sea water at atmospheric pressure and in a simulated deep-sea environment with high hydrostatic pressure of 6 MPa by means of electrochemical impedance spectroscopy (EIS), 3D optical microscope and scanning electron microscope (SEM). The results showed that the resistance of the coating decreased to 10⁵ Ωcm² after 30 d immersion under high hydrostatic pressure, while that decreased to 10⁸ Ωcm² at atmospheric pressure. The deep-sea environment can induce the enlargement of the active area and shorten the water-saturation process of coatings, therewith, the corrosion rate of the substrate was instantly accelerated. SEM showed that the hydrostatic pressure can deteriorate the attachment of pigments with the epoxy and weaken the adhesion between the epoxy coatings and the metal substrate. In this case, the active area of corrosion was enlarged, whilst the degradation of coatings and the corrosion of the steel substrate simultaneously occurred.

Epoxy coatings with different mass fraction of carbon nanotube (CNT) is prepared with epoxy as matrix, amine silane as curing agent, fumed silica as disperse dispersant, and carbodiimide as modifying agent. The effect of CNT amount on properties of epoxy coating is overall evaluated by means of pull-off adhesion test, ball-on-disk ear test, electrochemical impedance spectroscopy (EIS) and filiform corrosion test. The results show that, the adhesion strength, abrasion resistance and corrosion resistance are improved remarkable for the epoxy coating with 2% (mass fraction) of CNT in comparison to that without CNT addition. All the above mentioned properties are further improved for the epoxy coating with 5% and 7% of CNT. Furthermore, when the epoxy coating with the addition of CNT is up to 10%, of which the adhesion strength and abrasion resistance decreased, while the corrosion resistance and conductivity reach the optimum.

Atmospheric corrosion monitor (ACM), zero resistance amperemeter (ZRA) and electrochemical impedance spectroscopy (EIS) were applied to detect deeply the real-time galvanic corrosion of the couple of 2024 Al-alloy and 316L stainless steel beneath a thin electrolyte film. The galvanic corrosion process could be divided into three phases: initial phase, acceleration phase and deceleration phase. The smaller the insulative space between the two different materials is, the shorter the initial and acceleration phases are.

Effect of Cr on the corrosion resistance of Q420 steels with different Cr content (2%, 5% and 9% mass fraction) in atmosphere with high salinity was investigated by means of weight loss test, XRD and SEM. The results show that corrosion resistance of Cr modified Q420 steels is higher than that of simple Q420 steel. Among others the Q420 steel with 9%Cr shows the lowest corrosion rate and the highest corrosion resistance. The curve of corrosion rate versus time of the simple Q420 steel kept stable within a high level. While the corrosion rate of Cr modified steels increases in the initial stage and then increases, which indicates that the rust scale became compact and stable in the later stage. It was revealed that Cr can promote the formation of α-FeOOH, which is a stable phase and makes the rust scale much compact and stable so that to act as an effective barrier for the transfer process of the corrosive species.

The atmospheric corrosion behavior of anodized pure Al 1060 as well as Al-alloys 2A12 and 7A04 exposed for 24 months in atmosphere with pollutants at Jiangjin region was investigated by mass loss method, scanning electron microscope (SEM), energy dispersive X-ray detector (EDS) and X-ray diffractometer (XRD). The results show that the relation of mass loss versus time (h) accords with power function law as C=At ⁿ. In other words, the corrosion product is increasing with testing time. The order of corrosion severity of the tested materials can be ranked as the following order 2A12 alloy>7A04 alloy>1060. The corrosion products show agglomerate structure composited of Al₂O₃,Al(OH)₃ and aluminum sulfate hydrate. After removing the surface corrosion products, clear difference in the damage manner and the quantity of corrosion pits can be observed for the three anodic oxidation films. The corrosion mechanism may be ascribed to the dissolution of alumina in certain acidic medium.

The pitting corrosion behavior of 7020 aluminum alloy in 3.5%(mass fraction) NaCl solution was investigated by immersion test and cyclic polarization curve, while the corrosion morphology of the alloy was characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The results show that the curve of maximum depth of corrosion pits versus time exhibits ''S''-like shape. α-AlFeSiMn phase may act as a local cathode, thereby de-alloying occurred around particles of α-AlFeSiMn phase, i.e. Al matrix nearby the particles of α-AlFeSiMn phase was dissolved due to its anode nature, while Mn-and Cr-containing precipitates in the matrix may fall off along with the dissolved Al. Pitting susceptibility reduces in the later stage of corrosion due to that the formed corrosion products may act as a protective barrier for the alloy to some extent.

Three groups of the same 7050 Al-alloy plates were all aged firstly at 121 ℃ for 6 h and then aged subsequently at 163 ℃ for 0, 12 and 24 h respectively. The corrosion performance of the aging treated alloy plates was characterized by means of mass loss measurement, potentiodynamic polarization curve measurement and corrosion cracking propagation measurement, as well as optical microscope (OM). The results show that the corrosion type of the aged alloy plates changed from localized corrosion to general corrosion gradually with increasing ageing time and the corrosion rate decreased constantly. Meanwhile, the manner of corrosion cracking propagation for the aged alloys transformed from intergranular to transgranular gradually with the increasing ageing time. This makes the rate of corrosion cracking propagation become lower continuously. The corrosion current density for the different aged alloy plates were assessed by potentiodynamic polarization technique, which may be ranked as the following order: peak-aged state >under-aged state > over-aged state.

The intergranular corrosion behavior of friction-stir welding (FSW) joint for 20 mm thick plate of 7075 Al-alloy was investigated in solution of 57 g NaCl+1000 mL H₂O+10 mL H₂O₂ corresponding to the national standard GBT7998-2005. The microstructure of welded joint, the composition and distribution of the second phase, corrosion depth and corrosion morphology of different zones of the weld joint were characterized by optical microscope and scanning electron microscope. The results show that the corrosion severity of the center zones of the weld joint is the lightest. The corrosion severity of the thermal mechanical affected zone (TMAZ) is between that of the center zones and heat affected zone (HAZ). Downward along the thickness direction of the weld joint, the corrosion severity of the nugget zone (NZ) gradually increased, while that of the TMAZ increased first and then decreased, and that of the HAZ gradually decreased. The difference in the size and the distribution of the second phase and in the grains size of the weld joint along the thickness direction may be the main factor which caused the different corrosion severity for different zones along the thickness direction of the weld joint.

The corrosion behavior of L245 steel in simulated oilfield produced water was investigated by means of weight loss measurement, polarization curve measurement, electrochemical impedance spectra (EIS) and SEM. The results showed that the corrosion reaction of L245 steel is more intensive at higher temperature. When the temperature of the solution is elevated from 30 ℃ to 90 ℃, the corrosion current density of L245 steel in the solution with saturated CO₂ increases from 66.1 μAcm^-2 to 177 μAcm^-2 while the charge transfer resistance of L245 steel decreased from 5155 Ωcm² to 1182 Ωcm². The above results indicated that the corrosivity of oilfield produced water increased with the increasing temperature within the range of 30~90 ℃, localized corrosion of the steel occurred at 60 ℃, then the localized corrosion would be intensified when the temperature is elevated to 90 ℃.