The structure and mechanical properties of CO₂ corrosion scale formed on X65 pipeline steel in simulated CO₂ corrosion environment in oil field under various flow rates were investigated. XRD and EDS analysis indicate that at static condition, the composition of the scale is (Fe,Ca,Mg)CO₃, while the scale changes to (Fe,Ca)CO₃ at dynamic conditions. The increment in flow rate increased the thickness of the scale remarkably, but had little influence on the hardness and Young's modulus of the scale. The fracture toughness of the scale exhibited the lowest value at the flow rate of 0.5 m/s, whereas the adhesion strength increased with increasing the flow rate.

Stochastic analysis was applied to the investigation of the influence of the presence of the magnetic field on the pitting mechanism of pure magnesium, in which pitting corrosion was simulated as the combination of two physical processes: pit initiation and pit growth. The result revealed that the magnetic field could strongly affect the ions in the electrolyte by the magnetohydrodynamics (MHD) phenomena. For the pit initiation process, the mechanism of pit initiation was changed by the presence of magnetic field from the parallel birth and death stochastic model (B1) to the parallel birth stochastic model (A3). The pit generation rate $\lambda$ was increased while the repassivation rate μ  was decreased, which indicated that magnetic field accelerated the pit initiation process of pure magnesium. For the pit growth process, the stable pit growth mechanism was not changed, but the ability of repassivation of pit corrosion was decreased resulting in a great probability for the stable pit corrosion to grow up with a higher growth rate and finally develop into larger pit cavity.

Cast austenitic stainless steels reinforced by modified SiC nano-powders have been prepared with pour over process under industrial conditions, and the effect of modified SiC nano-powders on the pitting corrosion resistance of the austenitic stainless steel was characterized by pitting chemistry immersion and pitting electrochemistry tests, metallographic analysis, SEM and energy dispersive analysis. The results showed that, compared with the samples without SiC nano-powders, the reinforced stainless steel was characterized with finer microstructure, and less ferrite precipitation owing to composition segregational the pitting corrosion velocity had decreased by 16% and the electric potential increased by three times respectively when the content of nano-SiC rose to 0.1 mass%. Furthermore, the results of energy dispersive analysis of samples with the scanning electron microscopy revealed that the Cr segregation in the reinforced austenitic stainless steels reduced, and the Cr depletion in such zones sensitive to pitting corrosion as grain boundaries has been improved.

The effect of hydrostatic pressure on pitting behavior of Fe-20Cr alloy in 3.5% NaCl solution was investigated by means of potentiodynamic polarization and potentiostatic technology. For the polarization curve measurement, the specimens were kept for 1 h in the NaCl solution at various hydrostatic pressures and then scanned in 0.333 mV/s, 3 mV/s, and 5 mV/s scan rate respectively. For the induction time measurement, the specimen was pretreated in Na₂SO₄ solution at a constant potential, -0.22 V, for 500 s. After pretreatment, the specimen was kept in the NaCl solution at various hydrostatic pressures, and a potentiostatic technique\linebreak(-0.22 V) was used to measure the anodic current trace. Experiment data was analyzed based on statistical and stochastic approaches. With the increasing of hydrostatic pressure, the pit corrosion resistance of Fe-20Cr alloy was deteriorated, which was distinguished by the decrease of E_crit and the increase of passive current density.The results also showed that there were obvious effects on processes of pit initiation and pit growth of Fe-20Cr alloy: (1) the pit generation rate was evidently increased compared with that under lower hydrostatic pressure resulting from the metastable pits'  frequent initiation and increased tendency to stable pits. However, it seemed that pit generation mechanism showed no hydrostatic pressure dependence. (2) the probability of pit growth increased with the increasing of hydrostatic pressure, which implied that the metastable pit on Fe-20Cr alloy exhibited higher probability to become larger pit cavity during the same time interval than that under lower hydrostatic pressure.

A newly experimental method is proposed for determination of the critical pitting temperature (CPT) of metals. The current noise of steel coupon is measured during the continuous heating process in ASTM standard solution. CPT is determined based on assessment of the maximal transition point in the item of standard deviation of current noise. The CPT values of eight steels commonly used in oil industry are measured by this quick and easy method.

Time of wetness (TOW) of Q235 steel covered by thin liquid layer of 1 mmol/L NaCl，10 mmol/L Na₂SO₄ and Na₂CO₃ is measured by taking consideration of three control factors, i.e. temperature (Temp), relative humility (RH) and time of immersion (TOI), as well as corrosion deposits. The standardization procedure from data mining is adopted and applied to all parameters before a linear model is introduced to correlate the TOW and its control factors. Effect and pattern of the control factors as well as corrosion deposits on TOW is studied. The result shows that the pattern of temperature and RH on TOW is greatly changed due to the involvement of Cl^-, SO₄^2- and CO₃^2-  ions compared with that without these contaminants. Depending on the chemical/physical properties of the contaminants and the composition and distribution of corrosion deposits, the contribution of temperature and RH terms to TOW could be reversed or enhanced or weakened. Specifically, the TOW behavior can be clustered into two sections with the threshold values of 24 ℃ and RH 70%~80% which is determined approximately and conclusively. In each section, the contribution of temperature and RH to TOW is changed at different levels. At the end, the synergic effect of temperature and relative humidity on TOW is found and discussed in detail including the cause of this effect and possible dependence on the contaminating ions and corrosion deposits.

High energy micro-arc alloying process was successfully used to prepare compact microcrystalline Fe₃Al coating with a metallurgical bonding between the coating and the substrate alloy, when keeping all the parameters such as power, frequency, and time proper. Moreover, the preparation process is accompanied with a minimal thermal distortion or microstructural changes of the substrate. Air oxidation experiments at 900 ℃\linebreak and 1000 ℃ indicated that the Fe₃Al coating exhibited better oxidation resistance than the cast Fe₃Al, forming continuous and compact Al-rich scales with good adhesion. This may be due to the fact that the microcrystallization of Fe₃Al enhances short-circuit diffusion paths and reduces the critical Al content for the formation of a continuous Al₂O₃ scale.

The roles of zinc phosphate on the corrosion of the scratched coating were studied by electrochemical impedance spectroscopy(EIS), electrochemical noise measurements(EN) and scanning electrochemical microscopy(SECM). The experimental results of EN and EIS revealed that zinc phosphate had inhibition effect on the corrosion of the scratched epoxy coatings. The SECM results implied that the scratched surface of zinc phosphate coating was healed by an insulated film indeed. The mechanism of zinc phosphate on the corrosion of the scratched coating was analyzed based on the combined stochastic theory and shot noise theory using the Weibull distribution and Gumbel distribution function. It showed that the corrosion generation rate and the corrosion growth probability of the metal under the coatings were decreased with the addition of zinc phosphate.

Atmospheric corrosion behavior of LY12 was investigated in five typical atmospheres in China over 20 years. Mass loss and loss in mechanical properties were measured; Appearance, cross-section photomicrograph and corrosion products were observed and analyzed by optical microscope and XRD. The results show that in hot and humid atmosphere of Wanning and Qionghai exfoliation corrosion occurred on LY12 after 6 and 10 years, respectively, and almost lost its mechanical properties after 20 years exposure. While in Beijing atmosphere, LY12 still performed excellent mechanical properties after 20 years exposure. The mass loss data were higher in Jiangjin and Qingdao due to higher average RH and SO₂ or Cl^- contamination of the atmosphere, and lowest in Beijing atmosphere because of lower average RH. Before exfoliation corrosion occurred, the mass loss data with exposure time obeyed well with power function C=KTⁿ. The main exfoliation corrosion products are γ-Al(OH)₃ and α-Al₂O₃．3H₂O.

The inhibition effect of red tetrazolium on the corrosion of cold rolled steel (CRS) in 1.0 mol/L~10.0 mol/L  H₃PO₄ solution has been studied by mass loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the CRS surface conditions. The results show that neutral red tetrazolium is a moderate inhibitor for CRS. Inhibition efficiency increases with the inhibitor concentration, while decreases with increasing the temperature. The adsorption of red tetrazolium on the CRS surface follows the Freundlich adsorption isotherm equation. The experimental data have been treated with adsorption thermodynamic and corrosion kinetic equations. Three adsorption thermodynamic parameters (adsorption free energy ΔG⁰, adsorption heat Δ H⁰, adsorption entropy Δ S⁰) and two kinetic parameters (corrosion ratek, kinetic reaction constant B) are also calculated. The inhibitive mechanism is discussed in detail according to the parameters. The results show that the adsorption process is a spontaneous and exothermic process accompanied by a decrease in entropy. The corrosion of cold rolled steel in  H₃PO₄ support the kinetic equation proposed by Mathur and Vasudevan. The rate constant k and kinetic reaction constant B decreased after adding red tetrazolium. Polarization curves show that red tetrazolium is a mixed-type inhibitor, and its inhibition on CRS is caused by geometric blocking effect. AFM results show that the introduction of red tetrazolium into  H₃PO₄ solution results in decreasing the surface roughness.

The corrosion behaviors of X70 steels in Xinjiang Ku'erle saline soil (moisture content 1.04%) during the initial corrosion period (0~7 days) were studied by electrochemical noise (EN). The characteristics of the EN time records and their related corrosion information were identified by analysis of the EN fluctuations, statistical parameters including standard deviation of potential and current (σ_E, σ _I) and noise resistance (R_n), as well as Q-type clustering, which was further proved by corrosion morphology and electrochemical impedance spectroscopy (EIS) results. The results show that cluster analysis could be used to treat the EN signals to identify different corrosion states. Based on the hierarchical agglomerative cluster using σ_E and σ  _I as variables, three different states for the local  corrosion in the studied system could be classified clearly, including instable germination state, quick development state and stable development state.

Part of the reinforced concrete sample was put into 3.5% NaCl solution, a titanium bar was deposited in concrete as reference electrode. the potential and current between reinforcing bars (rebars) and titanium was tested separately, the microcell current of samples was calculated by polarization resistence R_p. The results showed that the current of rebars placed in solution decreases with increase of depth, the current of rebars placed above solution reduces with  the height of sample position. This indicates that  in solution the rebar corrosion has a close relationship with the concentration of oxygen, the rebar corrosion has a close relationship with the humidity of the concrete above the solution.

The rust layer formed on the surface of Q235 steel subjected to a high temperature and high humidity marine atmosphere in Xisha Islands was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe micro analyzer (EPMA) and Raman Spectrum (RS). The results showed that corrosion behavior of Q235 steel was more severe in Xisha atmosphere than in other marine environments. The surface morphology was observed by SEM and the distributions of elements were analyzed by EPMA. There were many cracks and holes in the rust layer. Cl^- can penetrate into the rust-metal interface along the cracks and holes in the Q235 steel rust film. Outer rust of Q235 steel was mainly composed of β-FeOOH, Υ-FeOOH and a little α-FeOOH. Much iron oxide, such as Fe₃O₄, Υ-Fe₂O₃ were found in the inner of rust layer. These iron oxides could be deoxidized from FeOOH, and this can accelerate oxidation of substrate steel.

An in-field measurement system for detecting the atmospheric corrosion of aluminum alloy was built based on electrochemical noise technology. A special probe, the apparatus and software were developed for performing electrochemical noise measurement with zero resistance ammetry （ZRA） mode. Experiments were carried out in the air condition in laboratory and then in natural atmosphere outdoors. The results showed that the atmospheric corroding process could be effectively detected or monitored by analysis of the electrochemical potential and current noise and the changing of noise resistance.

Composite coating was prepared by adherence of the epoxy Al-rich coating on sintered Zn-Al coating, in order to improve the anticorrosion performance of Zn-Al coating in seawater. The adhesion of sintered Zn-Al coating and composite coating were tested by cross cut test. The two different coatings were observed by scanning electron microscope (SEM). The anticorrosion performances of the two different coatings were studied by means of immersion test in seawater and neutral salt spray test. The corrosion electrochemical behaviors of the two different coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that the composite coating is more compact than the Zn-Al coating. It exhibits better waterproof performance than the Zn-Al coating. The epoxy Al-rich coating could effectively prevent corrosive species attacking. The composite coating exhibits obviously better anticorrosion performance than the Zn-Al coating. A typical Warburg impedance character appears at the beginning of corrosion process of the composite coating；Al flakes of the epoxy coating dissolve and exert sacrificial anode effects with the penetration of erosive species. The organic top coating improves the application of Zn-Al coating in seawater.

Corrosion behavior of carbon steel and stainless steel in white oil withm naphthenic acid were studied under high temperature by mass loss method and surface analysis. Naphthenic acid corrosion (NAC) rates were directly related to experimental temperature and total acid number (TAN). The activation energy was calculated and the process kinetics could be represented by Arrhenius-type equation. The relationship between the isothermal line in liquid phase and that in vapor phase at different TAN values had a significant distinction with the change of temperature. The relationship between corrosion rate and square root of TAN is linear. The corrosion rate decreased sharply with the increase of exposure time from 1.5 h to 12 h, and then remained comparative steady state after 12 h. The findings have important implications for assessing the corrosivity of crude oils with high TAN value from various resources.

A newly synthesized triazole compound, 3-(4-fluoro-phenyl)-1- {4-([1,2,4]triazol-1-ylmethoxy)-phenyl}-propenone（FTPP）, was investigated as corrosion inhibitor of mild steel in 1mol/L HCl solution using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. Then the surface morphology was studied by scanning electron microscopy (SEM). Generally, inhibition efficiency of the investigated compound was found to depend on the concentration of the inhibitor. The results showed that FTPP has excellent inhibiting effect and its inhibition efficiency（IE%）up to 91.4% at a concentration of 1 mmol/L. Potentiodynamic polarization curves of mild steel in 1 mol/L HCl solution clearly revealed that both cathodic and anodic processes of corrosion were suppressed. Thus, FTPP is inhibitor of mixed-type. The inhibition efficiencies obtained from weight loss measurement and electrochemical tests were in good agreement. Thermodynamic parameters such as adsorption heat (ΔH⁰ads), adsorption entropy (ΔS⁰_ads) and adsorption free energy (Δ G⁰_ads) were obtained and discussed from experimental data of the temperature studies of the inhibition process at four temperatures ranging from 298 K to 318 K. The adsorption processes are exothermic reaction and belong to chemisorption and physisorption. The Langmuir isotherm model is followed.

Influences of temperature on CO₂ corrosion behavior of P110 steel were investigated in stimulated oil and gas field environments. The corrosion scales were analyzed by using SEM，EDS and XRD. Simultaneously, the corrosion rate was measured by the weight loss method. The results showed that the corrosion rate of P110 steel increased first and decreased subsequently with the increase of temperature at static state, and the maximal corrosion rate was presented at 100 ℃. Corrosion rate increased first and deceased subsequently with increasing temperature at 5 m/s too, the maximal corrosion rate was presented at 60 ℃ and the corrosion rate under dynamic and static state were equivalent approximately at 160 ℃. The effect about flow rate operated on corrosion rate was not obvious when temperature was more than 140 ℃, and there were lesser change of the corrosion rate with further increasing temperature. After analyzing, a conclusion can be drawn that temperature affected corrosion rates in that it changed the surface morphologies, constructions, compositions, corrosion scale factor, scale density of the material and so on.

The oleic acid imidazoline and acrylic acid imidazoline were synthesized and their structures were characterized by IR spectrum. Their inhibition behaviors for aluminium foil in 2.0 mol/L HCl solution were studied by polarization curves and electrochemical impedance methods. The influences of specific capacitance of the two imidazolines on aluminium foil for electrolytic capacitors during DC etching were investigated by capacitance measuring instrument and SEM. The results show that the two compounds were both cathodic corrosion inhibitors for aluminium foil in 2.0 mol/L HCl solution. The inhibition efficiency of acrylic acid imidazoline was better than oleic acid imidazoline. Of the etched aluminum foil, weight loss decreased, tunnel density increased and well distributed, specific capacitance increased by 25% when inhibitors added in 2.0 mol/L HCl solution.

The relationship between the pitting depth（D_σ）of LY12CZ in 3%NaCl aqueous solution and applied stress（σ） and corrosion time（t） was calculated，and the results showed that the correlation was accorded with the formula D_σ=AΧC₀ exp(bσ)tⁿ=A' tⁿ , the formula indicated that the relationship between pitting depth and applied stress was accorded with exponential function D_σ =D ₀ exp(bσ)t ⁿ under the same corrosion time and power function  D_σ=A' tⁿ under the same applied stress. Experiment results under various applied stress prove that correctness of the formula above, the experimental results showed that pitting data of LY12CZ accords with the same power function D_σ=A' tⁿ  no matter what  applied stress existed or not, the influence of applied stress was showed in the coefficient of A, the relationship between A'(coefficient A under stress) and σ was D_σ=AΧexp(bσ). so the pitting data of aluminum alloys in natural environment could be extended to the natural environment corrosion under applied stress through amendment to the coefficient A.