Research on the Corrosion of J55 Steel Due to Oxygen-Reducing Air Flooding in Low-Permeability Reservoirs

Oxygen-reducing air flooding is a low-permeability reservoir recovery technology with safety and low-cost advantages.However,in the process of air injection and drive,carbon in the air is oxidized through the crude oil reservoir to generate CO_(2),and this can cause serious corrosion in the recovery well.In this study,experiments on the corrosion of J55 tubular steel in a fluid environment with coexisting O_(2)and CO_(2)in an autoclave are presented.In particular,a weight loss method and a 3D morphometer were used to determine the average and the local corrosion rate.The corrosion surface morphology and composition were also measured by means of scanning electron microscopy(SEM)and an X-ray diffractometer(XRD).The corrosion pattern and morphological characteristics of J55 steel were analyzed in the O2/CO_(2)environment for different degrees of oxygen-reduction.As made evident by the experimental results,the corrosion products were mainly ferrous carbonate and iron oxide.In general,air injection increases the degree of oxygen reduction,from oxygen corrosion characteristics to CO_(2)corrosion-based characteristics.As a result,the corrosion product film becomes denser,and the corrosion rate is lower.

Kinetics and corrosion products of aqueous nitrate reduction by iron powder without reaction conditions control

Although considerable research has been conducted on nitrate reduction by zero-valent iron powder （Fe^0）, these studies were mostly operated under anaerobic conditions with invariable pH that was unsuitable for practical application. Without reaction conditions （dissolved oxygen or reaction pH） control, this work aimed at subjecting the kinetics of denitrification by microscale Fe^0 （160-200 mesh） to analysis the factors affecting the denitrification of nitrate and the composition of iron reductive products coating upon the iron surface. Results of the kinetics study have indicated that a higher initial concentration of nitrate would yield a greater reaction rate constant. The reduction rate of nitrate increased with increasing Fe^0 dosage. The reaction can be described as a pseudo-first order reaction with respect to nitrate concentration or Fe^0 dosage. Experimental results also suggested that nitrate reduction by microscale Fe^0 without reaction condition control primarily was an acid-driven surface-mediated process, and the reaction order was 0.65 with respect to hydrogen ion concentration. The analyses of X-ray diffractometry and X-ray photoelectron spectroscopy indicated that a black coating, consisted of Fe2O3, Fe3O4 and FeO（OH）, was formed on the surface of iron grains as an iron corrosion product when the system initial pH was lower than 5. The proportion of FeO（OH） increased as reaction time went on, whereas the proportion of Fe3O4 decreased.

Effects of alternating magnetic field on the corrosion rate and corrosion products of copper

The effects of alternating magnetic field on the corrosion morphologies, corrosion rate, and corrosion products of copper in 3.5% NaCl solution, sea water, and magnetized sea water were investigated using electrochemical test, scanning electron microscopy/energy dispersive analysis system of X-ray （SEM/EDAX）, and X-ray diffraction （XRD）. The results show that the corrosion rate of copper in magnetized sea water is minimal. Moreover, the surface of the specimen in magnetized sea water is uniform and compact as compared with those in 3.5% NaCl solution and sea water. The corrosion products of copper in magnetized sea water are mainly Cu2O and CuCl2. However, the corrosion products in sea water are CuCl, Cu2Cl（OH）3, and FeCl3-6H2O. The electrochemical corrosion mechanisms of copper in the three media were also discussed.

Deterioration Mechanism of Sulfate Attack on Concrete under Freeze-thaw Cycles

The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.

A Calculation Model for Corrosion Cracking in RC Structures

A novel calculation model is proposed aiming at the problem of concrete cover cracking induced by reinforcement corrosion. In this article, the relationship between the corrosion depth of the bar and the thickness of the rust layer is established. By deducing the radial displacement expression of concrete, the formula for corrosion depth and corrosion pressure before cracking is proposed. The crack depth of cover in accordance with the maximum corrosion pressure is deduced; furthermore, the corrosion depth and corrosion pressure at the cracking time are obtained. Finally, the theoretical model is validated by several experiments, and the calculated values agree well with the experiment results.

Identification of Iron Oxides Qualitatively/Quantitatively Formed during the High Temperature Oxidation of Superalloys in Air and Steam Environments

Mossbauer spectroscopy has been used to study the morphology of iron oxides formed during the oxidation of superalloys, such as SS-304L （1.4306S）, Incoloy-800H, Incoloy-825, UBHA-25L, Sanicro-28 and Inconel-690, at 1200℃ exposed in air and steam environments for 400 h. The basic aim was to identify and compare the iron oxides qualitatively and quantitatively, formed during the oxidation of these alloys in two environments. The behaviour of alloy UBHA-25L in high temperature oxidation in both environments indicates that it has good oxidation resistance especially in steam, whereas Sanicro-28 has excellent corrosion resistance in steam environment. In air oxidation of Inconel-690 no iron oxide, with established Mossbauer parameters, was detected.

Wear Resistance of CO_2 Corrosion Product Scale Formed at High Temperature

To investigate the correlation between structure characteristics and wear resistance of CO2 corrosion product scales at high temperature and high pressure, an autoclave was used to prepare CO2 corrosion product scales on N80 steel in carbon dioxide corrosion environment. The correlation between wear resistance of the scales and many other factors, such as temperature, pressure, morphology, structure, velocity of fluid medium, sand grain size, and so on, was comparatively analyzed by a self assembled wear device, and the scale morphologies before or after being worn were observed by scanning electron microscope （SEM）. And then the surface grain size and thickness of scale were measured. The results showed that the cross-section of the corrosion scale was of a double-layer structure, the outer layer of which was composed of regular crystals, whereas the inner layer was a thin scale of fine grains. The outer grain size and thickness of scale varied with temperature, and the initial wear loss was consistent with the surface grain size; at the same time, the total wear loss corresponded to the thickness of scale. Compared to wear resist- ance in different depths of the scale, it was found that the structure of scale was a double-layer structure in cross-section, and the wear resistance of inner layer was better than that of the outer layer; the closer the scale to the matrix, the greater was the wear resistance of scale; and the larger the size or the higher the rotary speed of solid grain in multiphase flowing medium, the more was the wear loss of scale.

A homogenous microstructural Mg-based matrix model for orthopedic application with generating uniform and smooth corrosion product layer in Ringer’s solution:Study on biodegradable behavior of Mg-Zn alloys prepared by powder metallurgy as a case

For high corrosion resistance and extensively modified biodegradable Mg-based alloys and composites for bone implants,a new Mgbased matrix model prepared by powder metallurgy is discussed and developed.In this research,Mg-5 wt.%Zn alloys were selected as a case.And they were impacted by hot extrusion and aging treatments to construct microstructure with different characteristics.Their selfforming corrosion product layer in Ringer’s solution,biodegradable behavior and corrosion mechanism were minutely investigated by in vitro degradation,electrochemical corrosion and cytocompatibility.The results demonstrated the extruded Mg-5 wt.%Zn alloy aged for 96 h showed high corrosion resistance,good biocompatibility for L929 and excellent ability of maintaining sample integrity during the immersion.Significantly,the alloy showed fine-grain microstructure and uniform distributed hundred nano-sized second phases,which promoted the formation of the uniform and smooth corrosion product layer at the beginning of immersion.The corrosion product layer was more stable in chloride containing aqueous solution and could be directly formed and repaired quickly,which effectively protected the matrix from further corrosion.In addition,an ideal model of Mg-based matrix for bone tissue engineering was tried to presume and propose by discussing the causal relationship between microstructure and bio-corrosion process.

Multi-physics analysis of the galvanic corrosion of Mg-steel couple under the influence of time-dependent anisotropic deposition film

The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species,thereby affecting the electro-chemical behavior and the evolution of galvanic corrosion.The limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism,which can be complemented by numerical simulation.A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition layer.By utilizing the multi-physics field coupled technique,various coupled physical-chemical processes underlying the corrosion behavior are built into the model,including chemical reactions,ionic mass transfer in the bulk solution and the deposition layer,interfacial reaction,deposition of corrosion products as well as the morphological transitions caused by metal dissolution and deposition.In particular,the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion evolves.The predicted corrosion morphology by this model is better than the previous models.The coupled relationship between the electrochemical behavior(e.g.,electrode reaction kinetics,current density,surface potential)and the physical processes(e.g.,ionic transport,geometric evolution of metal surface and film interface)is revealed.The results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated,leading to more significant inhibition of mass transfer in the inner layer than the outer layer.The anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the electrolyte.The current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion process.The competition between the transport process and the electrochemical reaction determines the spatial-temporal evolution of the ion concentration.

Effect of Cl^-Concentration on the Corrosion Behavior of 16Mn Steel in Saturated H2S/CO2 Solution

The corrosion behavior of 16Mn steel was studied in saturated H2S or H2S/CO2 solutions containing different Cl^-concentrations at 80℃.The microstructure and chemical composition of the corrosion products were investigated through scanning electron microscopy,energy-dispersive X-ray spectroscopy,EPMA,and X-ray diffraction.Results showed that the corrosion rate decreased with increasing Cl^-concentration in saturated H2S or H2S/CO2 solution at pH 4.Conversely,the corrosion rate increased with increasing Cl^-concentration in saturated H2S solution at pH 6.The relative H^＋concentration decreased because of the increase of Cl^-concentration at pH 4,and Cl^-acted as a catalyst in the corrosive medium at pH 6 because the net H^＋concentration decreased obviously compared with the condition at pH4.Cl^-promoted the formation of Fe-deficient iron sulfide at pH 4,and the opposite effect was observed in the nearly neutral solution.The corrosion rate increased firstly with increasing Cl^-concentration and then decreased in the saturated H2S/CO2solution at pH 6.The corrosion products were mainly composed of two kinds of iron sulfide.Sulfide FeS（1-x） was a kind of tetragonal crystal,whereas the other was the hexagonal/monoclinic iron sulfide Fe（1-x）S.The corrosion film that was mainly composed of FeS（1-x） did not confer a protective effect on the base metal.The atomic ratio of Fe/S was more than 1 for FeS（1-x）.The appearance of sulfide FeS（1-x） resembled a square block or small,needlelike,flocculent particles.The atomic ratio of Fe/S was less than 1 for Fe（1-x）S,and the corrosion film mainly composed of Fe（1-x）S conferred some protective property on the base metal.The sulfide FeS（1-x） exhibited a long claviform morphology with a hexagonal or quadrilateral cross-sectional shape.

INFLUENCE OF THE MICROSTRUCTURE OF Cu-Ni ALLOY ON ITS CORROSION RESISTANCE

The microstructures of two kinds of Cu-Ni alloys were observed by TEM.The results show that one of the alloys is a homogeneous solid solution.The other contains discontinuous precipitates at some grain boundaries,and the precipitate is a phase rich in Fe-Ni.By monitoring the corrosion potential(E_(con))in artifical seawater and exposure to natural seawater for a long time,it is found that the E_(con)of the former alloy steadily decreases,while the E_(con)of the latter decreases a little and fluctuates,and the corrosion rate of the former is clearly lower than that of the latter.Aanalyses of SEM and EDX show that the corrosion product film of the former is thin,uniform,compact and rich in nickel,and the film of the latter is thick,loose and covered with numerous deposits.Additionally serious intergranular corrosion occurs in the underlying substrate of the latter.The author proposes that the intergraular corrosion results from preferential dissolution of discontinuous precipitates at grain boundaries.In addition,the protective characteristics of corrosion product films are related not only to the enrichment of nickel but also to their compactness.

Atmospheric corrosion behavior of Nb-and Sb-added weathering steels exposed to the South China Sea

The atmospheric corrosion behavior of new-type weathering steels(WSs)was comparatively studied,and the effects of Nb and Sb during corrosion were clarified in detail through field exposure and characterization.The results showed that the addition of Nb and Sb played positive roles in corrosion resistance,but there was a clear difference between these two elements.Nb addition slightly improved the rust property of conventional WS but could not inhibit the electrochemical process.In contrast,Sb addition significantly improved the corrosion resistance from the aspects of electrochemistry and rust layer.Compared with only 0.06wt%Nb,the combination of 0.05wt%Sb and 0.06wt%Nb could better optimize the rust structure,accelerate the formation of a high proportion of dense and protectiveα-FeOOH,repel the invasion of Cl^(−),and retard the localized acidification at the bottom of the pit.

Wear Resistances of CO_2 Corrosion Product Films in the Presence of Sand Particles

Wear resistances of CO2 corrosion product films formed on P110 carbon steel at different CO2 partial pressures were investigated in water sand two-phase flow by weight loss method, and the microstructures and compositions of corrosion product films were analyzed by scanning electron microscope(SEM) and X-ray diffraction(XRD), respectively. The results showed that the wear rate of CO2 corrosion product films increased until a maximum and then decreased with the increasing of the film-forming pressure, and the maximum occurred at 2 MPa. However, the maximal corrosion rate and the loose and porous CO2 corrosion product films were obtained at 4 MPa. And the wear rate decreased and then went to be flat with increasing test time. Furthermore, the microstructures and compositions of corrosion product films and the impact and wear of sand particles played an important role on wear resistances. In addition, the wear rate and corrosion rate were fitted by cubic polynomial, respectively, which were well in accordance with the measured results.

Protective Characteristics and Formation Mechanism of the Corrosion Product Films of B30 Tubes Exposed to Seawater

The corrosion product films of two kinds of B30 tubes(similar to CDA 715)exposed to seawat- er for various periods of time were investigated by SEM,AES and XPS.The results show that the pro- tective corrosion product film is thin,uniform and adherent.FeOOH is found to be present in the film surface,which confirms the hypothesis that iron hydroxide segregates at the surface of the film.The FeOOH promotes Ni enrichment in the corrosion layer by preventing Ni from running off.The corro- sion product film with no protectiveness is of lay- ered structure,loose and bad adherence.The for- mer film is formed through direct oxidation and the latter by precipitation and redeposition from dis- solved species.

Parametric study of thermo-hydro-mechanical response of claystone with consideration of steel corrosion

In this paper,the thermo-hydro-mechanical(THM)response of claystone is studied via a series of parametric studies,considering the evolution of mechanical properties and deformation behavior of corroded steel.The numerical simulations are performed by using a coupled THM finite element code and two different constitutive models:a visco-elastoplastic model for geological formation and a von Mises type model for steel liner.The mechanical properties and deformation behavior of corroded steel are described in a conceptual model.Finally,a disposal tunnel supported by a steel liner is studied and a series of parametric studies is defined to demonstrate the corrosion effects of steel liner on the THM response of the claystone.The comparison of different numerical calculations exhibits that the volumetric expansion related to corrosion products has an important impact on the stress and displacement fields in the claystone surrounding the disposal tunnel.However,the evolutions of temperature and liquid pressure in the claystone are essentially controlled by its THM properties and independent of the steel corrosion.

Anticorrosion performance of the coating/metal system by electrochemical impedance spectra

In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.

Studying Cu Alloy Corrosion Products in Cooling Liquid

The effect of cooling liquid used for heat exchangers on the Cu alloy corrosion products has been examined using potential-time measurements under applied current condition (anodizing), potentiodynamic polarization, X-ray diffraction (XRD) and infrared spectroscopy (IR) The corrosion products formed on the Cu alloy surface during anodizing, are Cu2O, Cu2(OH)3Cl, and Cu2S. NaCl is detected in the corrosion products. The film formation depends on the applied current and the shift of potential to nobler direction indicates its formation progress.

Effect of Zn on mechanical and corrosion properties of Mg-Sc-Zn alloys

The effect of different Zn concentrations(0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)on the microstructure,cor-rosion property,and mechanical property of Mg-0.3Sc-x Zn(x=0 wt.%,1 wt.%,3 wt.%,and 6 wt.%)alloys was investigated.Here,MSZ1 alloy exhibits the highest corrosion resistance(0.194 mm/y)and appropriate mechanical properties with an ultimate tensile strength of 228 MPa and elongation of 19%.The superior corrosion resistance of Mg-0.3Sc-1Zn alloys is attributed to the homogeneous volta-potential distribution and the dense corrosion product film.With the increase in zinc content,the strength and plasticity of Mg-0.3Sc-x Zn alloys(x=0 wt.%,1 wt.%,3 wt.%,6 wt.%)improved to some extent.The precipitated ScZn phase plays the role of the second phase strengthening,which enables MSZ6 to obtain the maximum tensile strength.However,the ScZn phase with low volta potential intensifies the galvanic corrosion,re-sulting in the decline of the corrosion performance.

Effects of Aerobic and Anoxic Conditions on the Corrosion Behavior of NiCu Low Alloy Steel in the Simulated Groundwater Solutions

The present work focused on investigating the corrosion behavior of NiCu low alloy steel in 0.05 M NaHCO_(3) solutions with different Cl−concentrations under the aerobic–anoxic condition.The results showed that NiCu steel tended to be pseudo-passivated in the solutions of 0.05 M NaHCO_(3) and 0.05 M NaHCO_(3)+0.01 M NaCl exposed to air.The cathodic process transformed from oxygen reduction to the common reduction of oxygen andα-FeOOH,while the anodic process was the iron dissolution.As Cl^(−)increased to 0.1 M,the steel tended to be activity dissolution.Due to the blocking effect of rust layer on the oxygen,the cathodic process transformed to the reduction ofα-FeOOH.After the solutions were deoxidized,the cathodic process was controlled by only rust reduction.Meanwhile,both the cathodic process and anodic process of NiCu steel corrosion were significantly inhibited.During the whole aerobic–anoxic immersion,the corrosion rate of NiCu steel increased with Cl^(−)concentration.It was not only related to the promotion of Cl^(−)on the anodic dissolution of steel,but also related to the cathodic reduction of moreα-FeOOH generated,which could accelerate the cathodic process.