Impurities such as pipeline corrosion products and dissolved oxygen etc. in the secondary circuit of pressurized water reactor (PWR) can enter the steam generator through the water supply system and deposit at different positions, resulting in the decrease of heat transfer capacity and the instability of thermal and hydraulic system. The water chemistry control in secondary circuit of PWR is of great significance for a safe operation of system equipment and core components. The purpose of this work is to summarize the application of pH control agents at home and abroad, and the research progress in the compatibility between employed alkalizing agents and structural materials. Firstly, the development process in alkalizing agent for PWR secondary circuit and its application at home and abroad are detailed. Secondly, the factors influencing the compatibility between the employed alkalizing agents and structural materials are discussed from three aspects: structural materials, hydrochemistry and the physicochemical properties of alkalizing agents. Finally, the working mechanism of alkalizing agent in adjusting pH is discussed, especially the mechanism of interactions between amine molecules and the oxide scales formed on the surface of structural materials.

It is well known that the widely distributed microorganisms can induce corrosion of metallic materials, i.e., microbiologically influenced corrosion (MIC), which is also an important form of corrosion. However, it is found that extracellular polymeric substances (EPS), as metabolites of microorganisms, play an important role in the corrosion process. In this work, the characteristics of metabolites of typical corrosive microorganisms such as bacteria, fungi, and microalgae, as well as their possible influence on the corrosion of metallic materials are systematically summarized. And then, the structure and functions of EPS, the primary metabolites of microorganisms, are mainly analyzed. The possible functions of EPS are discussed. Finally, the acceleration or inhibition effects of EPS on the corrosion of metallic materials and the relevant mechanisms were analyzed too. This work aims to provide reference for the subsequent research on the corrosion of metallic materials caused by EPS and corresponding protective countermeasures as well.

Although the relevant performance indicators of various artillery equipment have been significantly improved in recent years, the development of artillery is still limited by the service life of gun barrel. Nowadays, improving the firepower and extending the service life of artillery have become a hotspot for researchers. Therefore, more strict requirements are put forward on the ablation- and wear-resistance of the gun barrel, which has been the focus of the study on the longevity of the gun barrel. It is an effective method to improve the performance and to prolong the service life of the gun barrel by changing the material and the structure of the gun barrel. The development and recent advances in coating modification of gun barrel bore are summarized in this paper, and the performance requirements and modification related problems of the gun barrel bore are pointed out. The research progress and properties of Cr coating, Ta coating and new ceramic coatings are introduced emphatically. Then, advantages and disadvantages of various coatings are comparatively analyzed so that to provide reference for further research on life extension technology for gun barrel. Besides, the significant improvement the resistance to ablation, oxidation and wear of coatings prepared by electroplating and magnetron sputtering are introduced emphatically. The comprehensive analysis shows that the Cr coating and Ta coating prepared by electroplating and magnetron sputtering respectively have good resistance to ablation, oxidation and wear, which are the current and future research hotspots. Meanwhile, the new ceramic materials also show their advantages, namely, they present properties similar to the previous two coatings. It is also the development direction of surface modification of gun barrel bore in the future.

The pitting growth behavior of super 13Cr stainless steel in high-temperature and high-pressured CO₂ containing artificial formation waters was comparatively assessed via immersion corrosion test and finit element simulation, focusing on the effect of corrosion time, temperature and partial pressure of CO₂ on pitting corrosion. The results show that the pitting depth of super 13Cr stainless steel after high-temperature and high-pressure corrosion tests is consistent with that of finite element simulation, and the average pitting depth increases with the increase of immersion time, temperature and CO₂ partial pressure. The finite element simulation shows that the interior of the pit is acidified due to cationic hydrolysis, and the pH value decreases with the decrease of temperature and the increase of CO₂ partial pressure. In addition, Fe²⁺ concentration inside the pit increases with the increase of corrosion time and temperature while the partial pressure of CO₂ has little effect.

The corrosion inhibition behavior of 4-mercaptopyridine (4MP), sodium dodecyl sulfate (SDS), and compound inhibitor 4MP-SDS for aluminum in 3.5%NaCl solution was comparatively investigated via experimental test and digital simulation. The results show that the presence of corrosion inhibitor could effectively reduce the free-corrosion current density. Moreover, the increase dosage of corrosion inhibitor has a positive effect on the enhancing desorption potential of corrosion inhibitor. The corrosion inhibition efficiency of the three inhibitors may be ranked as 4MP + SDS > SDS > 4MP. The mass loss test results show good agreement with the electrochemical test results. After the injection of compound inhibitor, a corrosion inhibitor film can form on the metal surface. Thus, the resistance to the diffusion and migration of corrosive ions increased and the corrosion rate of Al slowed down, correspondingly, the Al surface maintains a good metallic luster and shows the characteristics of a uniform corrosion pattern. In addition, the anti-corrosion mechanism of the compound inhibitor 4MP + SDS was revealed by molecular dynamics (MD) simulation. The compound inhibitor 4MP + SDS showed greater ability to slow down the build-up of interfacial water layers, increase the surface coverage, and the bonding effect is more stable, compared with the presence of a single 4MP or SDS, demonstrating the strong adsorption of the compound inhibitor on Al, while the best anti-corrosion performance.

Al-coating is considered to be an ideal protective coating for steels. Multi-arc ion plating Al-coating is of significance for improving steel corrosion resistance, because multi-arc ion plating has advantages, such as non-toxicity, non-pollution, low-energy consumption, and easy operation etc. In this paper, multi-arc ion plated Al-coatings on 45# carbon steel were prepared by setting different bias parameters (0, -50, -100, -200, -300 V). Their surface and cross-section morphologies were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The protective properties of the coatings prepared by different bias parameters were studied by electrochemical means, such as open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS), electrochemical polarization (EI) measurement and neutral salt spray test. The results showed that the number of pores and roughness of the Al-coatings decrease first then increase with the increasing bias voltages. Correspondingly, their OCPs, charge transfer resistances and free-corrosion current densities were stable between -0.72~-0.77 V, (1.50~2.98) × 10⁴ Ω·cm², and (1.18~5.49) × 10^-6 A·cm^-2, respectively. It is worthy noted that the corrosion resistance of the Al-coatings was obviously better than that of the bare 45# carbon steel. Being subjected to neutral salt spray test for 336 h, the Al-coatings still exhibit protective performance to certain extent because of cathodic protection mechanism, especially the Al-coating prepared by -200 V had excellent protective properties. In conclusion, the Al-coating, which was prepared by the following process parameters i.e., target current 55 A, Ar gas pressure 1.0 Pa, and bias voltage -200 V, is compact with better adhesive to the substrate thus exhibits the best protective performance.

To deliever mixed natural gas and hydrogen with the existed natural gas pipelines is an important way to achieve efficient hydrogen transportation. However, corrosion defects present on these aged pipelines will affect the diffusion and enrichment of hydrogen atoms, potentially causing hydrogen embrittlement in the pipeline steel and further leading to the pipeline failure. In addition, corrosion defects on pipelines often exist in the form of adjacent double corrosion defects and even multiple corrosion defect groups. The interaction between adjacent defects can complicate the hydrogen diffusion and enrichment behavior, and ultimately affect the hydrogen induced failure behavior of the pipeline. In order to study the distribution of hydrogen concentration on pipelines containing double corrosion defects, a finite element model coupled with stress field and diffusion field was developed. The influence mechanism of corrosion defect length, defect spacing and applied tensile strain on hydrogen diffusion and enrichment behavior in steel was investigated in terms of the stress coupling behavior between the two corrosion defects. The results showed that the existence of corrosion defects caused the accumulation of hydrogen atoms in steel, and the value and location of the maximum hydrogen concentration in accumulation area changed with tensile strain, defect length and defect spacing. However, when the distance between the two defects is large enough, they will not have a superposition effect on the hydrogen diffusion and enrichment, and thus they can be regarded as two independent defects. This study provides a theoretical reference for the safety assessment of hydrogen damage in hydrogen transmission pipelines with double corrosion defects.

The effect of sulfate-reducing bacteria (SRB) strain Desulfovibrio bizertensis SY-1, which isolated from rust scales on steels formed in the South China Sea, on the corrosion behavior of X70 pipeline steel was investigated at different polarized potentials of -0.85 and -1.05 V vs. SCE. The results showed that neither of the planktonic cell growth or the attached cells could not be effectively inhibited at the -0.85 V vs. SCE cathodal polarization potential. The Raman analysis showed that the corrosion product of mackinawite and goethite were both detected by this applied polarization potential. Under the applied polarization potential of -1.05 V vs. SCE, the growth and metabolic process of planktonic D. bizertensis SY-1 cells could be effectively inhibited, and the corrosion products were mainly magnetite. The mass loss data also showed that the mass loss of coupons at the polarization potential of -1.05 V vs. SCE was basically the same as that in the sterile condition, and the maximum pitting depth at this potential was reduced by 75% compared with those in non-polarized condition. The results provide a reference for the selection of cathodic protection potential and the study on the interaction between microorganisms and polarization potential in the environment containing D. bizertensis SY-1.

The use of doped hydrogen or pure hydrogen as fuel poses a severe test to the key structural components of gas turbines, especially the resistance of materials to steam oxidation. The high-temperature steam oxidation behavior of 4 typical high temperature alloys, namely DD5, K447A, GH3230 and GH3536 for gas turbine in a mixed flow of air with 10% steam at 1000^oC was studied by means of mass change measurement and thermodynamic theoretical calculation. It follows that the GH3230 and K447A alloys showed an oxidation mass gain and followed a parabolic law, while the alloys DD5 and GH3536 showed oxidation mass loss on the contrary. The oxidation products formed on K447A and GH3230 alloy were mainly layered Cr₂O₃ and Al₂O₃ scales. The spallation of Al₂O₃ oxide scales occurred on the surface of DD5 alloy, while oxide volatilization was found on GH3536 alloy. In sum, the steam oxidation resistance of the four alloys may be ranked as following: K447 > GH3230 > DD5 > GH3536.

An electrochemical sensor for monitoring atmospheric corrosion of metallic materials was constructed. Two metallic materials with different corrosion potentials, i.e. low alloy steel and copper conductive paint, were chosen to form the two electrodes of the sensor based on the principle of galvanic corrosion. The two electrodes are separated by a thin silicone insulating film, and thus an electrochemical corrosion system may be established by the two electrodes while which was covered by a thin liquid film came from the atmosphere, correspondingly, galvanic corrosion current is generated. This galvanic current is monitored to reflect the corrosion state of the material in the environment. A new type of electrochemical sensor was used to study the influence of factors such as insulation film thickness, liquid film thickness, temperature, relative humidity, and cathode to anode area ratio on the galvanic current with the assistance of an electrochemical workstation and a high-precision electronic balance. It is confirmed that the new electrochemical sensor has high sensitivity and can be used for monitoring the atmospheric corrosion process under thin liquid film.

TiO₂ nanotube arrays are decorated with CdS and Bi₂S₃ by an ultrasonic-assisted successive ionic layer adsorption and reaction (SILAR) method aiming to enhance thephotoelectric conversion ability of TiO₂ and correspondingly the photogenerated cathodic protection performance for 304 stainless steel. The morphology, structural, element type and valence state of the TiO₂ nanocomposites are characterized by SEM, XRD and XPS, the photoelectrochemical performance of nanocomposites is studied systematically under irradiation of a simulated sunlight. The results indicate that the TiO₂ nanocomposites decorated with proper amount of CdS and Bi₂S₃ by an optimal procedure exhibit the best performance, namely, the band gap is reduced to 2.4 eV, the light absorption range extends to the visible region, and the recombination rate of charge photogenerated carriers is greatly reduced. The electrochemical test results show that Bi₂S₃/CdS/TiO₂ nanocomposites have the lowest charge transfer resistance and the fastest electron transfer rate, and the photocurrent density is enhanced to 850 μA·cm^-2 under the condition of turning on light, which is 11.8% higher than that of CdS/TiO₂ nanocomposites and 3.4 times that of TiO₂ nanotube arrays. After coupling the nanocomposite with 304 stainless steel, the potential can be reduced to -0.99 V under simulated sunlight, which is about 70 mV lower than that with the undecorated TiO₂ nanocomposites, and it can further enhance the photogenerated cathodic protection effect on 304 stainless steel.

Superamphiphobic surface films were successfully prepared on AZ31B Mg-alloy via etching with HNO₃ solution and afterwards modifying with PFDTES (1H, 1H, 2H,2H-perfluorodecyltriethoxysilane). The superamphiphobic surface film were characterized by means of scanning electron microscope (SEM), X-ray diffractometry (XRD), X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectrometer (XPS). The static contact angle (CA) was measured by optical contact angle meter to estimate their wettability, The electrochemical performance was evaluated in 3.5%NaCl aqueous solution by electrochemical work-station to estimate their corrosion resistance. Results show that the non-uniform distribution of chemical composition of the Mg-alloy leads to different dissolution rates and degrees of the alloy surface during the etching process, resulting in different morphology on surface. The special microstructure formed on the etched alloy surface, combined with the modification of low surface energy materials (PFDTES), enables the formation of a film with excellent liquid repellency on Mg-alloy. The contact angles (CAs) of water and ethylene glycol on the modified Mg-alloy surface were 159.3° and 155.2° respectively. In contrast to the bare Mg-alloy, the free corrosion potential of the superamphiphobic film covered Mg-alloy shifted positively by 297 mV, and the corrosion current density decreases by more than 3 orders of magnitude, the charge transfer resistance increases by more than 2 orders of magnitude, in other word, the anti-corrosion performance of the AZ31B Mg-alloy was well improved by the surface modification. Even after soaking in 3.5%NaCl solution for 72 h, the Mg-alloy with superamphiphobic film still maintains good corrosion resistance.

At present, TiO₂, as a low-cost and non-polluting N-type semiconductor material, has been applied to photogenerated cathodic protection technology due to its excellent photoelectric conversion performance. In comparison with the ordinary nanotube arrays, the highly ordered lotus root-like TiO₂ nanotube arrays (TNTAs) present much larger specific surface area and more effective photoreaction sites, which is conductive to enhancing the photoelectrochemical properties of TiO₂ nanotube arrays. In this paper, lotus root-like TiO₂ nanotube arrays were prepared by a two-step anodization process in NH₄F-(NH₄)₂SO₄ composite electrolyte. The effect of different anodization voltages on the performance of TiO₂ nanotube photoanodes was studied. The structure, morphology and separation rate of photogenerated carriers of TNTAs prepared by different appllied anodic oxidation voltages were studied by XRD, SEM and photoluminescence spectra (PL). At the same time, under the irradiation of a simulated sunlight, the photoelectrochemical performance was evaluated by the photocurrent density measurement, and the cathodic protection effect of the photoanode on 304 stainless steel was evaluated by measurements of open circuit potential and Tafel polarization potential, as well as by fitting EIS curves. The results show that when the anodic oxidation voltage is 25 V, TNTAs have clear lotus root-like shape, high regularity, high photogenerated carrier separation rate and high photogenerated current density. Accordingly, the prepared TNTAs present lower open circuit potential, while better cathodic protection effect for 304 stainless steel substrates.

The performance-based study on anticorrosive pigment is of significance to the development of new pigment for anticorrosive coatings. Zinc phosphate and zinc phytate were prepared from phosphoric acid, phytic acid and zinc chloride. Then the two pigments were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetry analysis (TG) and infrared spectroscopy (FT-IR). The solubility of zinc phosphate and zinc phytate in aqueous solution was analyzed by titration test. The corrosion characteristics of Q235 carbon steel in extracting solutions of zinc phosphate and zinc phytate were examined respectively by Tafel polarization method, electrochemical impedance spectroscopy (EIS) and immersion test. The results showed that the zinc phosphate presents micron-sheet like structure of non-uniform size with thickness in the range of 0.5-1 μm, and the zinc phytate was agglomeration particle with a particle size of 2-5 μm. While after extracting for 2 h, the content of zinc phytate was basically saturated, and it showed that zinc phytate had excellent inhibition effect, which could slow down the corrosion of Q235 steel with inhibition efficiency up to about 90%.

A silica sol coating for corrosion protection of reinforce bars in concrete structures was prepared via mechanical blending and ultrasonic dispersion with water glass as the film precursor and calcium aluminate as filler. Then the effect of different amounts of calcium aluminate addition on the protective performance of the coating was studied. The structural morphology and ion exchange ability of calcium aluminate and its hydrates, as well as the structural morphology and protective performance of the coating were characterized by XRD, FT-IR, SEM, ion chromatograph analysis and electrochemical measurement. The results indicate that calcium aluminate can be hydrated to form LDH during the coating preparation, thus due to their anion exchange function, LDHs can absorb corrosive chloride ions from corrosive media, meanwhile, the layered structure of LDHs may be benefit to alleviate the internal stress generated during the coating curing process, in turn, eliminate the cracking in the coating and improve effectively the barrier performance of the coating, while slow down the infiltration rate of chloride ions and other corrosive ions reaching the surface of the steel bar, eventually enhance the protective performance of the silica sol coating against the steel bar corrosion.

A silica sol coating for the surface of steel bars was prepared via mechanical blending and ultrasonic dispersion with water glass as the film precursor and α-Titanium hydrogen phosphate (α-TiP) as fillers, since the α-TiP is a cationic layered compound with excellent ion exchange performance. The structural morphology and ion exchange ability of α-TiP, as well as the structural morphology and corrosion resistance of the coating were assessed by means of XRD, FT-IR, SEM, ion chromatography, and electrochemical measurement respectively. The results indicate that with ion exchange function the α-TiP can absorb free sodium ions within the water glass, and the prepared silica sol coating contains flakes of α-TiP filler can effectively improve the barrier performance of the coating, thereby enhance the protective performance of the silica sol coating against steel corrosion, whilst the coating has the best protective performance when the addition amount of α-TiP is 0.4 g.

In order to acquire the critical chloride ion concentration for the break-down of passivation film in the initial carbonization environment of concrete. According to the basic principle of electrochemical reaction, the anodic polarization characteristics of rebar steel HRB400 in a simulated initial carbonized concrete solution were studied by means of open-circuit potential- and anode polarization curve-measurement. Results showed that there was a linear relationship between the breakdown potential and the chloride ion concentration in logarithmic plots, and the rationality of passivation potential and tranpassivation potential as the key parameters of the breakdown potential was analyzed. Based on this, the upper limit [Cl^-]_u and lower limit [Cl^-]_l of critical chloride ion concentration for rebar steel HRB400 are obtained. Accordingly, the relationship between pH value and chloride concentration of pitting corrosion sensitivity of the rebar steel was drawn. The service status of rebar steel HRB400 in the pH range of 12.5-11.0 is evaluated, and the expressions of the upper limit [Cl^-]_u and lower limit [Cl^-]_l of the critical chloride ion concentration and pH value are given.

Cold rolling and reverse phase transformation are the main methods to enhance the yield strength of austenitic stainless steel. Therefore, the effect of deformation strengthening and grain refinement strengthening on the microstructure and corrosion behavior of Fe-18Cr-8Ni austenitic stainless steel was characterized by SEM, TEM, EBSD, electrochemical workstation and other technical characterization means. The results show that the deformation strengthening and the inverse phase transformation induced grain refinement strengthening could enhance the pitting resistance of austenitic stainless steel in 3.5%NaCl solution, grain refinement led to an increase in grain boundary density, which promote the diffusion rate of Cr at grain boundaries, thereby improving the stability and compactness of the passivation film. After sensitization treatment, deformation strengthening and inverse phase transformation induced grain refinement strengthening could enhance the intergranular corrosion resistance of austenitic stainless steel. The appearance of Cr-depletion zone around chromium carbide precipitates will deteriorate the intergranular corrosion resistance of the steel, while the rapid diffusion of Cr in ultrafine grain/fine grain structure will promoted the rapid healing of the passivation film on the Cr-depletion zone, thus the intergranular corrosion resistance of the steel may be improved.

Various corrosion characteristics such as rust spots and cracks will appear on the surface of metal plates after corrosion. Their corrosion degree can be determined by corrosion characteristics. At present, the corrosion degree of metal plates is mainly judged by manual visual inspection. But it has many non-ignorable shortcomings such as low consistency and low efficiency etc. In this paper, the RGB values of image pixels of corroded metal sheets were collected and then clustered by means of K-means++ clustering algorithm, afterwards the relevant corroded- and uncorroded-regions were separated. Whether corrosion occurred or not was judged in each cluster area by means of image structural similarity index SSIM. The results show that setting the number of clustering centers ‘k’ to 5 can effectively delineate each clustering area based on the image color distribution. Compared to peak signal-to-noise ratio and mean square error, the structural similarity index SSIM is strongly correlated with the occurrence of erosion. Setting the SSIM index threshold at 0.95 can effectively judge whether erosion occurred in each cluster area. Compared to manually dividing corrosion areas based on pixel color, our method had a higher identification efficiency and an accuracy of not less than 90%. This research can be applied to automate the evaluation of the corrosion degree of metal sheets after environmental testing.

To address the issue of low content of accelerant residues at the fire site due to combustion, volatilization and site contamination, which leads to difficulties in identification. In this study, n-heptane was used to simulate the fire site environment of gasoline as an accelerant. To perform the experiments, a pipette was adopted to monitor and generate a specific number of n-heptane drops onto the surface of a pure iron plate just beneath, the n-heptane was then ignited, after the combustion was completed the iron plate was soon cooling down to room temperature at the site. The microscopic morphology and phase composition of the corrosion products, as well as the distribution of surface particles were characterized by means of scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) etc. The results showed that: Upon combustion of n-heptane, granular amorphous carbon is observed on the surface of pure iron as a result of high-temperature cracking reaction. The amount of deposited carbon is closely linked to the surface temperature of pure iron and n-heptane content at the site, and tends to accumulate at defects and nearby grain boundaries of the pure iron plate. The combustion of n-heptane creates a local oxidizing atmosphere at the accelerant interface, resulting in numerous defects on the surface of pure iron. This, in turn, promotes the flaking of the surface oxide scale. The insights gained in this study can help to identify the presence of accelerant at the fire scene.

An oil-soluble Mannich base corrosion inhibitor (OMB) was synthesized from formaldehyde, dodecylamine and acetone, and which then was characterized by Fourier transform infrared spectroscopy (FT-IR). The corrosion inhibition effect of OMB and barium petroleum sulfonate (T701) on copper in 25# transformer oil was comparatively assessed by means of salt spray test, scanning electron microscopy (SEM) and atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). According to the quantum chemical calculation (Gaussian 09), molecular dynamics simulation (M-S) and Langmuir isothermal adsorption equation, the corrosion inhibition mechanism of OMB on copper was further discussed. The results show that OMB is a corrosion inhibitor with excellent corrosion inhibition effect on copper in salt spray test. The adsorption behavior of OMB on copper surface is spontaneous adsorption, which accords with mixed adsorption law and is mainly chemical adsorption, and the OMB moleculars are adsorbed parallel to the surface of copper.

Several sulfoaluminate cement-ordinary Portland cement-based repair materials (CSA-OPC) were prepared, then their corrosion resistance in artificial seawaters containing NaCl, NaCl+Na₂SO₄, NaCl + Na₂SO₄ + MgCl₂ respectively were assessed via dry-wet cycle test, X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The study focuses on the evolution of mass, compressive strength, bond strength and Cl^- content of the CSA-OPC with the variation of OPC content and corrosion process. The results show that in the test conditions with solutions of NaCl, NaCl + Na₂SO₄, NaCl + Na₂SO₄ + MgCl₂, an appropriate amount of OPC incorporation can significantly improve the corrosion resistance of CSA in artificial seawaters. When the content of OPC is 20%-30%, the mass change, compressive strength, bond strength and Cl^- combination ability of CSA-OPC are the best. The Cl^- infiltrated into the CSA-OPC materials are trapped through the formation of Friedel's salt, while the SO₄^2- may inhibit the combination of Cl^-, and Mg²⁺ may reduce the combination rate of Cl^- by consuming more OH^-.

To clarify the influence of magnetic fields on the corrosion behavior of oil pipelines of L360 steel in service, the corrosion behavior of L360 pipeline steel and its welded joints in 3.5%NaCl solution by applied magnetic field of various intensities was studied via electrochemical tests and corrosion morphology characterization. The results indicate that as the magnetic field intensity increases, the charge transfer resistance of L360 pipeline steel and its welded joints initially increases and then decreases, while the corrosion current density initially decreases and then increases. Corrosion is inhibited by a lower intensity magnetic field (60 mT), while it is accelerated by a higher intensity magnetic field (120 mT). Moreover, by the same applied magnetic field intensity, the corrosion rate of the welded joints is higher than that of the base metal. It is proposed that the existed gradient magnetic field force may be favor the adsorption of metal ions at the electrode interface, resulting in the formation of a corrosion product film that hinders the corrosion process. Under the influence of a high-intensity magnetic field, the Lorentz force can disrupt the corrosion product film, accelerating ion diffusion and subsequently accelerating the corrosion of the steel.

The initial corrosion behavior of 3Cr alloy steel in urea assisted heavy oil steam huff and puff environments was studied by means of mass loss measurement, macroscopic morphology observation, SEM, EDS, XRD and XPS. The results show that the initial corrosion of 3Cr alloy steel in urea assisted heavy oil steam huff and puff environment is a synergistic corrosion of CO₂ (acid gas) and NH₃ (alkaline gas) in high temperature steam, showing uniform corrosion characteristics. The corrosion products are mainly FeCO₃. When the concentration of urea solution is in the range between 10% and 20%, with the increase of the concentration of urea solution, the amount and compactness of corrosion products all increase. When the concentration of urea solution higher than 30%, the adhesion of the corrosion product scale to the steel substrate becomes weaker with the increase of the concentration of urea solution, as a result, obvious spallation of the formed scales may emerge. If there not crude oil exists in the wellbore environment of the urea assisted steam huff and puff production well, the average corrosion rate of 3Cr alloy steel is higher than the oilfield corrosion control index 0.076 mm/a when the concentration of urea solution is greater than 10%, so that this operating condition is not recommended. In the presence of crude oil, the corrosion rate of 3Cr alloy steel is greater than 0.076 mm/a for 30% urea solution, apparently which cannot meet the requirements of wellbore corrosion control in production wells, therefore, this operating condition is not recommended too. Anyhow, the average corrosion rate of 3Cr alloy steel with crude oil is lower than that without crude oil. The incorporation of crude oil has certain corrosion inhibition effect due to the geometric covering effect. Therefore, it is suggested that the concentration of urea solution should not exceed 10% when designing the site operation scheme.

In fact, the variation of water content within an organic coating will affect its corrosion protection performance. Thus, the penetration of water in an epoxy coating would be studied via distribution of relaxation time (DRT) technique and finite element simulation method in terms of the perspective of micro electrochemistry in this article. Results show that the water penetration process of the epoxy coating may be differentiated into three stages: initial stage, saturation stage and failure stage. In the three stages, the different content of water and corrosive medium inside the coating can seriously affect the variation of capacitance of the coating. This paper provides a new comprehensive analysis method for the mechanism study of organic protective coatings.

Pure zinc bars with different deformation degree were prepared by hot rolling. The effect of deformation degree on the microstructure and corrosion properties of pure zinc in a leaching solution of soil at Tianjin were studied by electrochemical test, immersion accelerating corrosion test and metallographic characterization. The results showed that the cast pure zinc had a coarse microstructure with a large number of fine sub-grains and casting twins. The primary grains of zinc were obviously refined, while the sub-grains were merged and grown with the increase of plastic deformation degree. The cast twins were significantly reduced as the deformation degree increased. The pitting potential and passivation interval of pure zinc in the soil leaching solution increased with the increase of deformation degree. While the corrosion current density and passivation current density decreased as the deformation degree increased. The resistance of passive film and the charge transfer resistance of corrosion process of zinc obviously increased after plastic deformation treatment. The continuously improved metallographic homogeneity of pure zinc, which resulted from the increased plastic deformation degree could enhance the corrosion resistance of pure zinc in the soil leaching solution.

A mill scale may form on the steel surface during hot rolling process, which exhibits a certain degree of anti-corrosion effect. When a large number of steel bars are used in a construction project, most of them may be naturally exposed to atmosphere for a long time, and thus the mill scale will turn into a loose and porous yellow-brown rust scale due to atmospheric corrosion. In order to understand the nature of the passivation behavior of pre-corroded steel rebars with mill scale during the concrete curing process, the electrochemical behavior of HRB400 rebars with mill scale before (bare bar) and after being atmospherically pre-corroded for 3 months (pre-corroded bar) was comparatively assessed in simulated concrete pore solution by means of open-circuit potential measurement, electrochemical impedance spectroscopy, dynamic potential polarization curve, Mott-Schottky curve and XPS. The results show that the type of rebars can be completely passivated in the simulated concrete pore solution, whilst their surface all reached stability within 5 d. But the passivation effect and corrosion resistance of pre-corroded rebars are slightly worse than those of the bare rebars. The changes in surface composition of the two kind rebars before and after passivation are mainly due to the significant decrease in Fe(II) oxides, while significant increase in Fe(III) oxides and hydroxyl oxides, and the excellent passivation effect and corrosion resistance of the bare rebars compared with the pre-corroded rebars are due to the lower Fe(II) oxide content and higher Fe(III) compound content after passivation.

The direct current voltage gradient method (DCVG) is an indirect measurement method used to evaluate defects in anti-corrosion coatings of pipeline. The implementation of DCVG detection has certain requirements for the DC test current and the setting of interrupters, but these technical details are often ignored in actual on-site work. %IR is a parameter used in the DCVG method to evaluate the severity of pipeline coating damage. There are many misconceptions in the calculation and application of this parameter in the pipeline industry, such as the incorrect selection of the test current and on-off period, and lack of consideration of factors such as soil resistivity and burial depth of the pipe. This article has conducted research and discussion on the testing current requirements of DCVG and the principle and calculation method of %IR, clarified the signal strength requirements for conducting DCVG inspection, analyzed the factors that affect the %IR value, and pointed out that it's uncertain to evaluate the size and severity of coating defects using %IR.