Morphology Of Corrosion Products Research Articles

Accelerated corrosion tests of a contact pair austenitic stainless steel – titanium alloy

The results of accelerated corrosion tests of a pair of austenitic stainless steel — titanium alloy under conditions of elevated temperatures and high concentrations of corrosive agents are presented, conditions for the developing the mechanism of local corrosion being the same. The proposed approach included provoking the appearance of microstress concentrators by three-point loading of test samples with subsequent forced development of local types of corrosion through simultaneous exposure to an increased concentration of corrosive agents and temperatures at a fixed exposure in an autoclave. The results of modeling the corrosion process in a titanium alloy being in contact with stainless steel are assessed proceeding from the data obtained from metallographic studies of the state of surface layers of the metal and the morphology of corrosion products on prepared sections of the surface of templates cut from the samples under study. We considred a pair of steel 08Kh18N10T — titanium alloy VT-5. It is shown that the contact of samples under conditions of accelerated corrosion tests does not lead to a significant development of local types of corrosion of the titanium alloy. On the contrary, analysis of the state of the surface layers of the samples of stainless steel revealed the presence of deep corrosion pits, triggering the intergranular corrosion. In this case, corrosion of austenitic steel, both in the presence and in the absence of contact with titanium, proceeded in three stages: the initiation and fusion of pitting; formation of knife corrosion ulcers; propagation of intergranular cracks into the depth of steel. The proposed methodology of corrosion testing can be used to predict the possible nature of the development of metal corrosion under operating conditions that form local zones of static stresses in structural materials, and for prompt response to extend the design life of the equipment at thermal and nuclear power facilities.

Studying the formation of nodules in a Ni-Fe-Cr based superalloy used in fireside corrosion under the impact of creep stress

Creep rupture tests on a Ni-Fe-Cr based superalloy were conducted in a custom-built rig at 750 °C under simulated fireside corrosion environment. The impact of creep stress on corrosion was investigated by controlling load level (without loading, loads of 120–195 MPa). The phase composition, microstructure, and morphology of surface corrosion products and corrosion-affected area were studied. The mechanism responsible for the production of surface nodules and the observed uniform oxide scale during fireside corrosion are discussed. Results show that the presence of creep stress promotes the development of surface nodules and increases the corrosion-affected area.

Insights into the role of H2O2 on corrosion behavior of NiCu low alloy steel in simulated Beishan groundwater

Steel containers used for geological disposal of high-level radioactive waste will be gradually thinned or even perforated due to corrosion, which will lead to radiolysis of nuclides when they contact with infiltrated groundwater and produce H2O2. This work focused on investigating the influence of H2O2 concentration (0%, 0.001%, 0.01%, 0.1% and 1% by volume) on the corrosion behavior of NiCu low alloy steel as the candidate material for containers was comparatively studied by combining corrosion weight loss test, corrosion product analysis, morphology characterization, thermodynamic analysis and electrochemical measurements. As [H2O2] = 0.001%, H2O2 inhibited the formation of γ-FeOOH and enhanced the compactness of rust layer, which effectively blocked the migration of aggressive ions and slowed down the cathodic reduction reaction of rust, thus improving the corrosion resistance of NiCu steel. With the increase of [H2O2] (0.01%→1%), the cathodic process of NiCu steel corrosion was promoted by the increase of dissolved oxygen involved in cathodic depolarization. Meanwhile, the relative content of Fe3O4 in the rust increased, while Fe6(OH)12SO4 and Fe6(OH)12CO3 decreased obviously, which led to the loose and porous rust layer, thus accelerating the corrosion of NiCu steel.

Corrosion failure analysis and solutions of aluminum alloy gas path plate used in sanding device of high-speed train

During the maintenance of a high-speed train, it was frequently found that the anodized aluminum alloy gas path plates in the sanding device had different degrees of corrosion. In this paper, SEM, EDS, XRD and LAD-EDTEST spectrometer were used to analyze the macro and micro morphology, elements and phases of corrosion product, element compositions of the matrix and assembly problem of the gas path plates. The mechanism of delamination spalling corrosion caused by local pitting corrosion of anodized aluminum alloy gas path plate was described. In addition, the properties of the coatings produced by different surface treatment methods and different substrate materials were compared. The test results indicate that the corrosion protection level of the micro-arc oxide coating is higher than that of the anodic oxide coating, which is mainly composed of γ-Al2O3 and contains a certain amount of α-Al2O3. Compared with 2A12-T4 aluminum alloy, the micro arc oxidation (MAO) coating of 6082-T6 aluminum alloy has lower porosity, higher hardness, higher corrosion potential, lower corrosion current, and better corrosion resistance, and 6082-T6 aluminum alloy is more suitable for use as the gas plate material. Meanwhile, it is proposed that the MAO coating with 35 μm can obviously improve the corrosion resistance of the gas path plate.

Atmospheric corrosion of carbon steel: Results of one-year exposure in an andean tropical atmosphere in Colombia

In this study was examined the response of carbon steel to atmospheric corrosion after one-year exposure in Valle de Aburrá, a subregion located in northwestern Colombia. The study involved the assessment of material mass loss and corrosion rate, the characterization of atmospheric aggressiveness, and the analysis of the morphology and composition of corrosion products in five different sites. Climatological and meteorological factors were assessed by testing for chloride content, sulfur dioxide levels, and time of wetness (TOW). The analysis of corrosion products was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Based on corrosion rates, two sites exhibited a more aggressive environment, with a corrosivity category of C3, while the remaining sites were categorized as C2. The study confirmed the presence of lepidocrocite and goethite phases on the surface of carbon steel at all test sites. Data analysis revealed that both the TOW and the industrial activity significantly influence the corrosion of this metal.

Characteristics of corrosion products of steel bars in modified magnesium oxysulfide cement containing chloride salts

The effects of chlorides on the corrosion of steel bars within a matrix comprising modified magnesium oxysulfide (MMOS) cementitious materials was investigated. The phase composition, morphology and distribution of steel corrosion products (SCPs) were studied. There was basically no corrosion of the steel bars in the MMOS cement without chlorides. A high chloride content and a high water/cement (w/c) ratio in the MMOS matrix had adverse effects on the steel bar corrosion. The primary SCPs in the MMOS mixes were iron oxyhydroxides (FeOOH) and ferric oxide (Fe2O3), while ferrous oxide (FeO) was only observed at low w/c ratios, indicating a lower degree of oxidation. The presence of di-iron nonacarbonyl (Fe2(CO)9) at high w/c ratios suggested a higher degree of oxidation. At lower w/c ratios, rust products readily diffused. Conversely, at higher w/c ratios, these products accumulated close to the steel bars, resulting in a compact structure.

An Investigation into the Factors and Mechanisms Underlying Corrosion Failure of B10 Copper Tubes in Shipboard Pipelines

The present study investigated the corrosion behavior and mechanism of B10 copper tubes used for shipboard pipelines through various analytical techniques, including macroscopic inspection, chemical analysis, electrochemical impedance, corrosion product morphology, and physical phase and electron microscopic observation. The research findings revealed that the surface corrosion product film on the B10 copper tube in seawater mainly consists of Cu2O. Furthermore, the corrosion behavior under actual working conditions was attributed to crevice corrosion, non-electric coupling corrosion, and the corrosion mechanism was found to be the result of the combined effect of oxygen concentration difference cell and occlusion cell autocatalytic effect. These observations provide valuable insights into the corrosion performance of B10 copper tubes in seawater, which could potentially aid in improving their durability and reliability in marine applications.

Nano-emulsification method as a strategy for oil soluble corrosion inhibitor transform to water soluble

Corrosion inhibitor is one of the most economical and effective approaches to protecting metal pipes in the oil and gas industries. However, a great amount of corrosion inhibitors such as imidazoline, are difficult to distribute fast due to their poor solubility or dispersibility in water, which results in inhomogeneous concentration distribution and ineffectiveness. In this study, nano-emulsification technique was developed to improve the dispersity of mercaptoacetic acid-modified oleic imidazoline (MOI) in corrosive water. The formulation of nanoemulsion is optimized with the phase inversion temperature (PIT) and droplet diameter. The prepared nanoemulsion which the hydrophilic lipophilic balance value (HLB) was 11.5 and the loading of corrosion inhibitor was 20 wt% exhibited remarkable water dispersion performance and its mean particle size was less than 100 nm. Moreover, its dispersion performance in water was significantly better than that of the paraffin oil system, and was similar in the ethanol system. The inhibition performances and mechanisms of nanoemulsion for L245 carbon steel in the H2S/CO2 containing 5.0 wt% NaCl solution were investigated with weight loss measurements and electrochemical tests. In terms of inhibition efficiency, the corrosion inhibitor encapsulated in nanoemulsion was exceeding 90%, which was comparable to the system employing ethanol and liquid paraffin as solvents. Further experimental results indicated that the nanoemulsion system was more consistent with the Freundlich adsorption model, unlike the other two systems which followed the Langmuir adsorption model. The morphology and composition of corrosion products were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The SEM and XPS results demonstrated that the nanoemulsion system did not change the material type of corrosion products, but had a visible influence on their morphology. In addition, the inhibition mechanism was also revealed by theoretical calculations. These findings suggest that nano-emulsification technique has the potential to improve the solubility or dispersibility of oil soluble corrosion inhibitor, thereby expanding its application fields.

Experimental exploration of metallic chloride salt corrosion of stainless steel sheets

In recent years, biomass generation in China has been steadily increasing. The high-temperature corrosion of the heating surface of biomass boilers is mainly caused by HCl and alkali metal chlorides in the sediment, which seriously affects the efficiency and safety and the degree of economic utilization of biomass energy. In this paper, the corrosion products were characterized by total-immersion experiments under constant temperature on different thicknesses of 304 stainless steel in various concentrations and types of alkali metal chloride salts. Through thermal microscopy scanning and XRD experiments, the composition, characteristics, and microscopic morphology of corrosion products on stainless steel flakes are determined to find out the corrosion mechanism of stainless steel flakes in solution alkali metal chloride salts. The results show that in a water bath at 80 °C, alkali metal chlorides weaken the corrosion resistance of the stainless-steel sheet by destroying the integrity of its reticular structure, thus promoting the chemical reaction between the iron contained in the stainless steel and other elements to generate various types of corrosion products rich in iron. Meanwhile, among various alkali metal chloride salts, the catalytic effect of saturated CaCl2 on the corrosion of 0.1 mm and 0.01 mm stainless steel sheets at 80 °C is the most significant.

Effects of cathodic protection potential on microbiologically induced corrosion behavior of X70 steel in a near-neutral pH solution

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion x-ray spectrometer (EDS), and an x-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was −775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was −875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits. When CP potential was −1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.

The promotion effect of aluminium ion on hydrogen entry into steel during atmospheric corrosion

The effect of Al3+ on the hydrogen permeation behaviour of steel during cyclic corrosion was investigated under AlCl3 droplets with varying Al3+ concentrations. The permeated hydrogen during the corrosion process was measured by electrochemical techniques. The observation of corrosion morphology and analysis of corrosion products were performed in the corrosion tests. It was found that Al3+ presented a significant effect on corrosion morphology and hydrogen entry into steel. The amount of permeated hydrogen through steel increased with increasing Al3+ concentrations. The precipitation of Al species under salt droplets, the localized acidification under rust layers, and the hygroscopic property of AlCl3 were considered contributing factors enhancing the hydrogen evolution and absorption into steel during wet-dry cyclic corrosion.

Study on corrosion resistance mechanism of Cr-containing steel in simulated oilfield produced fluid

In view of the CO2 corrosion environment of oil and gas fields, the corrosion behavior of 5Cr, 9Cr and 13Cr steels was studied by high temperature and high pressure weight loss test and electrochemical test with J55 material as comparison. Scanning electron microscopy (SEM) analysed the morphology of corrosion products. The corrosion resistance mechanism of Cr-containing steel was analyzed from the perspective of structural stability by first-principles. The results show that the uniform corrosion rate of Cr-containing alloy steel is lower than that of J55 steel, and the CO2 corrosion resistance of the material increases with the increase of Cr content. With the increase of temperature, the self-corrosion current density of different Cr-containing steels gradually increases, the pitting potential of 9Cr and 13Cr gradually decreases, and the pitting resistance decreases. The electrochemical corrosion kinetic resistance of Cr-containing steel increases under long-term immersion corrosion. Molecular dynamics and first-principles calculations show that the corrosion product preferentially formed by Fe is FeCO3, and the corrosion product preferentially formed by Cr is Cr(OH)3. On the surface of the iron matrix, Cr(OH)3 is more easily adsorbed on the surface of the iron matrix, thereby protecting the matrix from corrosion resistance.

Localized Corrosion Mechanism of Q125 Casing Steel in Residual Acid Solution during Oil Reservoir Acidizing

This paper aims to investigate the localized corrosion mechanism of Q125 casing steel in residual acid solution with Mannich base type inhibitors during oil reservoir acidizing process. The corrosion behavior of Q125 casing steel in fresh acid (20% HCl) and residual acid solution (pH 1.0 and pH 3.0 HCl) with and without 3-(4-chlorophenylimino)-1-(piperidine-1-ylmethyl) indolin-2-one (Mannich base type, Mb) inhibitor was studied by electrochemical test, weight loss, and surface analysis. The morphology and composition of corrosion products were analyzed by SEM/EDS and XPS; the local corrosion rate of casing steel with or without inhibitor was obtained by 3D profilometry. It was determined that the inhibitor had higher inhibition efficiency in fresh acid conditions than in residual acid conditions. Under the condition of residual acid, the decrease in inhibitor molecular coverage on the substrate surface promotes the occurrence of local corrosion. Pitting corrosion was detected in the residual acid solution containing Mannich base inhibitor, which may be related to the fact that FeCO3 hinders the adsorption of inhibitor molecules on the substrate surface.

Corrosion performance and possible mechanism of aluminium nitride-molybdenum gradient material in a simulated liquid metal battery environment

After being fabricated successfully by spark plasma sintering technology, corrosion performance of aluminum nitride-molybdenum gradient material was investigated using X-ray diffraction, scanning electron microscope, XPS techniques, etc. in a simulated liquid metal battery environment with LiF–LiBr–LiCl eutectic salt as electrolyte. The research results indicated that low temperature corrosion at 550 °C occurs mainly in pure aluminum nitride region with the corrosion products grown on the grain boundaries including alumina, nitrogen-lithium, aluminum-lithium intermediate phase or their complex compounds. Moreover, the formed corrosion product morphology is influenced significantly by aluminum nitride distribution. As the gradient compositions developed towards the pure molybdenum zone, the product morphologies tended to evolve in a sequence of sphere, flake and octahedron. At temperatures higher than 600 °C, alumina tends to be dissolved in molten salt vapor and molybdenum starts to be corroded simultaneously resulting in a substitute of the formed lithium aluminum molybdenum oxide phases for alumina in the final corrosion products. Mass change study on the samples suggested both the holding time and temperature have significant influences on the corrosion behavior of aluminum nitride-molybdenum gradient material. At temperatures higher than 700 °C, sudden change in sample mass accompanied by interface cracking would happen within the holding time of 100 h. Therefore, under long-term isothermal conditions, the serviced temperature of aluminum nitride-molybdenum functional gradient materials is suggested to be lower than 600 °C.

Role of Al and Mg alloying elements on corrosion behavior of zinc alloy‐coated steel substrates in 0.1 M NaCl solution

AbstractThe corrosion behavior and corrosion products of three zinc alloy‐coated steel substrates with different Al and Mg contents such as hot‐dip galvanized steel (HDG), Zn–Al‐coated steel (ZA), and Zn–Al–Mg‐coated steel (ZM) substrates were investigated during 168 h of immersion in 0.1 M NaCl solution. The characteristics and morphology of corrosion products on all the substrates formed during exposure to electrolyte solution were observed by X‐ray diffraction, X‐ray photoelectron spectroscopy, and scanning electron microscopy/energy‐dispersive X‐ray spectroscopy. Their electrochemical behavior was investigated by open‐circuit potential, polarization curves, and electrochemical impedance spectroscopy. The addition of Al and Mg alloying elements affected the corrosion mechanism as well as the anticorrosion properties. The main crystalline corrosion products on the HDG surface were simonkolleite and zincite, while the ZnAl hydrotalcite was identified as the main corrosion product on ZA and ZM surfaces. The corrosion resistance of ZA and ZM substrates was improved compared to the HDG substrate due to the enhanced adhesion of the corrosion product layer.

Analysis of Failure Causes of Grounding Flat Steel for 110kV Transmission Tower

The corrosion causes of the grounded flat steel of a 110kV transmission tower were experimentally analyzed by means of macro testing, microstructure inspection, chemical composition analysis, corrosion product morphology and energy spectrum, galvanized layer thickness test, soil physical and chemical property analysis and other test methods. The results show that the improper selection of anti-corrosion process of grounded flat steel and the service environment of alkaline and high salt are the main reasons for its corrosion fracture. It is proposed that the power grid equipment should not use the grounding flat steel of cold galvanizing process, and the inspection of the grounding flat steel of the transmission tower in the Irrigation areas along the Yellow River should be strengthened.

Protection of galvanized steel using benzotriazole as a corrosion inhibitor in simulated concrete pore solution and alkali-activated fly ash solution

In this study, the natural passivation ability and chloride-induced subsequent increased levels of corrosion behaviour of galvanized steel in simulated concrete pore (SCP) solution and alkali-activated fly ash (AAFA) solution, with and without benzotriazole (BTA), were evaluated using corrosion potential (Ecorr), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP). In addition, scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS) were used to observe the morphologies of passive layers and corrosion products of galvanized steel. It was highlighted that the hydrogen evolution could be prevented by AAFA solution to some extent, thus providing a new insight on the inhibition of hydrogen evolution for galvanized steel in concrete. Moreover, due to the formation of a complex protective film, galvanized steel in AAFA solution exhibited significantly higher corrosion resistance to chloride attack than that exposed to SCP solution, which could be further enhanced by the addition of BTA.

Atmospheric corrosion of silver, copper and nickel exposed to hydrogen sulphide: a multi-analytical investigation approach

The effect of two concentrations of H2S (0.5 and 2.5 ppm), in controlled laboratory conditions (20 °C, 75%RH), on the atmospheric corrosion of pure Ag, Cu and Ni was investigated in this study. The corrosion product morphology and composition were analysed through a multi-technique approach including SEM/EDX, Raman spectroscopy, XPS and XRD. Different corrosion products were identified depending on the type of characterisations providing a better overview of the effect of H2S on the atmospheric corrosion of pure Ag, Cu and Ni. Possible mechanisms involved in the formation of these corrosion products are also discussed in this work.

Effect of hydrostatic pressure on galvanic corrosion of low-alloy steel in simulated deep-sea environments

ABSTRACT In order to study the effect of high hydrostatic pressure on the corrosion of low-alloy steels in deep-sea environments. The electrochemical corrosion behavior of single-metal system and triple-metal coupled system of 907A steel, 921A steel and 1# steel under different hydrostatic pressures were studied by electrochemical, weight loss and morphology observation methods. The results show that the high hydrostatic pressure promotes the corrosion of low-alloy steel by changing the composition and morphology of corrosion products. In addition, there was also severe galvanic corrosion between the couples with a low potential difference (< 60 mV),907A steel was used as the anode of the three-metal coupled system, and 921A steel and 1# steel as the cathode. The galvanic coupling effect accelerates the pitting corrosion of 907A steel as an anode metal. When using multi-metal couplers with low potential differences, they should be protected by both coating protection and cathodic protection.

Corrosion mechanism of X65 steel exposed to H2S/CO2 brine and H2S/CO2 vapor corrosion environments

Wet gas gathering and transportation in natural gas production has good economic benefits, but it also brings many risks. Due to the synergistic effect of corrosive gas and multi-phase flow in the wet gas pipeline, there are two corrosive environments, which leads to frequent accidents of pipeline corrosion failure. In this paper, the corrosion experiments of X65 steel in two environments (H2S/CO2 vapor; H2S/CO2-dissolved brine) were completed by a high-temperature and high-pressure reactor. Combined with SEM, EDS and XRD instruments, the morphology, elements and compounds of corrosion products were analyzed. The corrosion impact of temperature, flow rate, CO2 and H2S in both environments was determined. Finally, corrosion mechanism in two corrosion environments were established. When CO2 and H2S coexisted, both in two corrosive environments, the two gases were involved in the corrosion of X65 steel, and the corrosion products formed were FeCO3 and FeS in the liquid phase. The difference was that the corrosion product film in the gas phase was denser than that in the liquid phase and the corrosion rate in the gas phase was smaller than that in the liquid. There was a large amount of Cl− and high shear force brought by the flowing, the corrosion product film fell off and formed local corrosion. In the gas phase, due to the H2S and CO2 higher concentration, a dense corrosion product film rapidly formed in the droplets. In the two environments, the order of corrosion factors is PH2S ≫PCO2 Velocity > Temperature. But in the gas phase environment, H2S dominates in the gas phase more than in the liquid phase because it is more soluble in droplets.