Corrosion behavior of 60Si2MnA spring steel in mixed salt environments

The corrosion behavior of a high manganese steel in simulated marine splash zone environment was studied by dry-wet cyclic corrosion experiment and electrochemical experiment. Corrosion kinetics, composition, surface morphology, cross-section morphology, element distribution, valence state, polarization curve and electrochemical impedance spectroscopy were analyzed with the aim of characterizing the characteristics of corrosion product films. The results show that in chloride-containing environment, in the initial corrosion products, Mn oxides with porous structure lead to higher corrosion rate. As corrosion extends, the formation of alloy element oxides in corrosion products changes the corrosion properties of rust layers at different stages. Mo oxides form a stable passivation film, which reduces the influence of chloride ion on corrosion. Ni oxides in the inner rust layer facilitate the transformation of goethite, and Cr oxides in the outer rust layer increase the densification of the rust layer. The stability and compactness of Fe3O4, α-FeOOH and FeCr2O4 in the later corrosion products inhibit the corrosion action of manganese iron oxides and slow down the corrosion rate. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.

This paper analyzed the corrosion behavior and corrosion performance of ER8 wheel steel through a full immersion test. The average corrosion rate of the ER8 wheel specimen in 2.0% NaCl solution shows a gradual increase over the whole corrosion cycle. Although the corrosion rate showed fluctuations at 3.5% and 5.0% concentration before 576 h, the corrosion rate also showed a steady increase after 576 h. The corrosion rates of specimens at different concentrations after 2160 h were over 0.12 mm/year. With increasing immersion times or concentrations of NaCl solution, the coverage area of the corrosion products dominated by iron oxides gradually increased, and the corrosion products on the surface became denser. The corrosion products were primarily γ-FeOOH, α-FeOOH and Fe3O4. As the density of the surface corrosion products increased, cracks and holes appeared on the surface of the rust layers, which made the rust layer unable to protect the substrate from further corrosion. After removing the corrosion products, pitting corrosion appeared on the surface of the substrate. The radius of the capacitive reactance arc gradually decreased with the increasing immersion time. The impedance modulus in the low-frequency region decreases and then increases with increasing NaCl solution concentration, which is the highest in 3.5% NaCl solution. Icorr increased with an increasing Cl− concentration, which was similar to the mechanism of catalytic electrolysis due to Cl−. The specimens with rust layers have worse corrosion resistance when the immersion time is extended. The corrosion product did not protect the substrate but accelerated the corrosion process.

The influence of surface roughness on the static corrosion behavior of J55 carbon steel in CO2-containing geothermal water environment was investigated with respect to average corrosion rate, morphology, chemical composition, corrosion depth, and the cross section of corrosion products. The influence of surface roughness on the CO2 corrosion of J55 carbon steel was then proposed based on the understanding of corrosion at 65 °C. The results show that the static corrosion rate of J55 carbon steel in CO2-containing geothermal water increases with increasing surface roughness. The surface roughness of J55 carbon steel increases 5.3-fold and the CO2 corrosion rate increases by 1.4-fold under different exposure times. The static corrosion rate of J55 carbon steel in CO2-containing geothermal water changes with exposure time. The corrosion rate of J55 carbon steel decreases with the increase in exposure time, and there is little change in the corrosion rate after immersion for 2 days. At the initial stage of corrosion, the corrosion rate of J55 carbon steel was mainly affected by surface roughness. The greater the roughness, the greater the corrosion driving force and the corrosion reaction surface area and therefore the greater the corrosion rate of J55 carbon steel. After immersion for 2 days, a continuous corrosion product layer was formed on the surface of J55 carbon steel and the corrosion rate was mainly affected by the corrosion product layer. The corrosion products of J55 carbon steel are not altered by surface roughness in a CO2-containing geothermal water environment. The corrosion products of J55 carbon steel are FeCO3 and a minute amount of CaCO3.

The corrosion behavior of low-C medium-Mn steel in simulated marine immersion and splash zone environment was studied by static immersion corrosion experiment and wet-dry cyclic corrosion experiment, respectively. Corrosion rate, corrosion products, surface morphology, cross-sectional morphology, elemental distribution, potentiodynamic polarization curves and electrochemical impedance spectra were used to elucidate the corrosion behavior of low-C medium-Mn steel. The results show that corrosion rate in immersion zone is much less than that in splash zone owing to its relatively mild environment. Manganese compounds are detected in the corrosion products and only appeared in splash zone environment, which can deteriorate the protective effect of rust layer. With the extension of exposure time, corrosion products are gradually transformed into dense and thick corrosion rust from the loose and porous one in these two environments. But in splash zone environment, alloying elements of Mn appear significant enrichment in the rust layer, which decrease the corrosion resistance of the steel.

The annual direct cost of corrosion on bridge structures is over $8.3 billion. Much of this cost is due to broadly applied corrosion mitigation and prevention methods for steel components. On-going efforts by many state and local agencies focus on reducing maintenance costs through improved corrosion detection and prevention methods. In our research, we focus on linking corrosion mechanisms to corrosion predictions for materials commonly used for steel beams on bridges. Plain carbon steel remains a common material for bridge construction despite its poor corrosion performance. Porous and fragile corrosion products such as Hematite (α-Fe2O3), Goethite (α-FeOOH), Akagneite (β-FeOOH), and dense and highly adhesive Lepidocrocite (γ -FeOOH) form. Due to the porous corrosion layer, a high concentration of chlorine ions are trapped, further accelerating corrosion. To prevent rapid corrosion, typical protection measures on bridge steels in Connecticut include the application of a three-layer paint system containing primer, intermediate urethane coat, and an epoxy topcoat. Breakdown of the coating can result in pitting corrosion below the paint layers, which is difficult to detect visually. Periodic removal and replacement of paint is essential to long-term maintenance. In fact, the paint layer protection is typically designed to last 15-20 years, and removal and recoating costs range from $5-$20 per square foot, creating a high driving force to identify lower cost options for maintenance. Weathering steel is a potentially lower-cost alternative. A primary benefit of weathering steel (WS) over plain carbon steel is its ability to form dense, protective, and highly adhesive Lepidocrocite (γ-FeOOH) layer on the surface. With continued exposure, corrosion resistance of WS increases. Although the corrosion behavior of plain carbon steel and WS have been heavily researched, prediction of the corrosion performance of these steels coupled in coated and uncoated bridge applications remains difficult. In this study, we conducted a series of accelerated corrosion tests and evaluated the electrochemical corrosion behavior of A36 plain carbon steel and A588 weathering steel to predict corrosion rates. Accelerated corrosion testing of both bare and scratched painted A36 and A588 steel coupons of 50 x 30 x 5 mm was conducted through 200 cycles of wet/dry immersion at room temperature in 3.5% NaCl and simulated seawater (ASTM D1141). Bare steel samples were polished with 800 grit SiC paper and cleaned with ethanol and distilled water. Painted samples were polished with 240 grit SiC paper and cleaned with ethanol and distilled water prior to coating with zinc primer Carbozinc® 11 HS, epoxy coating Carboguard® 893, and polyurethane top-coat Carbothane® 133 LV. After the coating, the samples are scratched with diamond wafering blade on an IsoMetTM saw. Samples were photographed using a Nikon D5000 DSLR camera and weighed using microscale (FisherScientific XA-200DS) after every 20 cycles. A36 and A588 coupons were characterized by Potentiodynamic polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) testing using a Bio-Logic VSP-300 potentiodynamic tester. Sample surfaces were polished with 800 grit SiC paper and cleaned with ethanol and distilled water for PDP testing to establish baseline corrosion rates prior to oxide formation. EIS testing was applied to coupons in the original (clean surface) and corroded surface state to characterize the electrical nature of the corrosion layers formed on the surface. In addition, all corroded sample surfaces were analyzed using XRD (Rigaku SmartLab) and GIXRD, and microstructural features were examined using optical and electron microscopies. All bare surface samples demonstrated continuous weight gain during wet/dry cycling. Scratched samples gained weight at a slower rate. Both corrosion potential (Ecorr) and corrosion current (i corr) of the A36 samples was found to be higher than that of A588, and the corrosion rate of A36 is calculated at nearly 2,600 mmpy compared to 570 mmpy for A588. The EIS results indicate that A36 surface layers have a slightly higher electrical resistance than A588 surface layers, but the capacitance of A588 corrosion products is higher than for A36. Overall, the corrosion resistance of A588 is better than the corrosion resistance of the A36, as expected. The results from electrochemical testing correspond to the Scanning Electron Microscopy (SEM). The cross-sectional microstructural analysis of sample revealed A588 contains denser and thicker corrosion layer, and A36 corrosion products are highly porous and detached from the substrate. Furthermore, severe pitting was observed on the A36 surfaces, and mostly uniform corrosion was observed on the A588 surfaces. The pitting observed scratched samples for both A36 and A588 was similar and not severe.

The corrosion behavior and mechanism of Q235 steel during a two-year exposure to the subtropical marine atmospheric environment on an offshore platform in the East China Sea were investigated in this study. Methods including corrosion weight loss measurement, macro/micro-morphological observation (using a digital camera, SEM, and 3D-CLSM), composition analysis (XRD and XPS), and electrochemical tests (EIS and Tafel polarization curves) were employed to systematically examine corrosion kinetics, rust layer evolution, and electrochemical performance. The results indicated that the corrosion rate of Q235 steel initially increased and subsequently decreased with prolonged exposure, with the atmospheric corrosivity reaching CX level as defined (according to the ISO 9223 standard). The corrosion products transitioned from an early-stage rust layer predominantly consisting of γ-FeOOH to a later-stage layer primarily composed of α-FeOOH and Fe3O4. XPS analyses revealed that both the α*/γ* ratio and the Fe(II)/Fe(III) ratio increased over time, demonstrating a progressive improvement in the protective properties of the rust layer. The polarization resistance of the rust layer gradually rose, while the corrosion current density declined significantly, further confirming the enhanced stability and protective performance of the rust layer following long-term exposure. Chloride ions accumulated at defects within the rust layer, inducing local acidification, which played a key role in promoting the initiation and propagation of pitting corrosion. This study elucidated the corrosion behavior and mechanism of Q235 steel in the marine atmospheric environment of the East China Sea. Despite the increase in exposure time from 6 to 24 months, during which the electrochemical stability of the rust layer enhanced over time, it failed to prevent the initiation and propagation of severe localized corrosion-an issue of critical importance for load-bearing structures. The findings provide important theoretical and data support for service-life assessment and corrosion protection design of offshore photovoltaic steel structures.

Low carbon steel was exposed at two sites in Mauritius, namely Port Louis and Belle Mare. The site at Port Louis is basically an industrial marine one whereas the one at Belle Mare is a purely marine site. Though the corrosion loss trend at both sites follow the power law, the corrosion loss at Port Louis was found to be higher than that at Belle Mare. This study has been performed to investigate the surface characteristics of the rust layers of the samples exposed at the two sites, through Raman spectroscopy and SEM, so as to get a better insight into the mechanism of the atmospheric corrosion process. For Port Louis, it was observed that there was not much change in the corrosion products in the rust layer over the 3 years period. The structure was less compact than that at Belle Mare with the presence of lepidocrocite and akaganeite as commonly observed corrosion products. The corrosion rate at Port Louis is, therefore, expected to follow the same trend over the long term. For Belle Mare, the corrosion products changed significantly after 3 years of exposure. Though lepidocrocite and akaganeite were observed on the surface after 0.2 years of exposure, magnetite was the most probable corrosion product in the more compact rust layer after 3 years of exposure. This compactness of the rust layer is expected to have reduced the corrosion rate as compared to that of Port Louis. Significant changes in the corrosion rate at Belle Mare are, therefore, expected over the medium and the long term.

The effect of hydrostatic pressure (HP) on the corrosion behavior of low alloy steel in 3.5% NaCl was studied in a pressure vessel using gravimetric, electrochemical and imaging techniques. The results indicate that HP influences the corrosion behavior of steel to different extents all through the immersion period: in the initial immersion (first 5 days), the corrosion rate at 35 atm is obviously higher than that at 1 atm; which is followed by a period of no obvious difference between the two pressures; and after 15 days, the corrosion rate at 35 atm is only slightly higher than that at 1 atm. Generally, it stimulates the corrosion process, especially during the initial immersion. Further study reveals that the increased corrosion rate at high HP during the initial immersion could be related to the enhanced Cl− adsorption. After the formation of integrated rust layer, HP affects the chemical and physical properties of rust layer. Consequently, it is more conducive for the transport of Cl− at high HP, which further gives rise to the accelerated corrosion. This study aims to be conducive to the fundamental understanding of the corrosion behavior of steel in deep ocean environments.

PurposeSome power plants in China that adopt reverse osmosis (RO) product water as their fresh water source face serious metal corrosion of their water distribution system. The corrosion process of carbon steel in RO product water is still not clear and there is no suitable anti‐corrosion method for the power plant to employ. The purpose of this paper is to study the corrosion behavior of carbon steel in RO product water, determine the factors leading to the high corrosion rate of carbon steel, and then suggest appropriate anti‐corrosion measures.Design/methodology/approachBy measuring polarization curves and AC impedance values of the corrosion system and analyzing corrosion products using scanning electron microscopy (SEM), infrared spectroscopy (IR) and X‐ray diffraction (XRD), the corrosion behavior of Q235A carbon steel in the RO product water derived from seawater was studied.FindingsThe experimental results showed that the corrosion process of carbon steel in RO product water is controlled by the diffusion process of oxygen, and the corrosion products contain γ‐FeOOH, Fe3O4 and small amounts of α‐FeOOH. Although rust formed had a double layer structure, the outer rust layer, which contained γ‐FeOOH and a little α‐FeOOH, was thin. The inner rust layer, containing Fe3O4, was the main component of the rust layer. Due to the weak acidity of RO product water, γ‐FeOOH can be transformed to Fe3O4 very quickly and Fe3O4 will accumulate on the metal surface. Because of the electrical conductivity and fractured surface of the Fe3O4 layer, the corrosion product layer cannot inhibit the corrosion process by hindering the diffusion process of oxygen, and hence the corrosion rate of carbon steel is always high.Originality/valueThe paper describes the first systematic research to be carried out on the corrosion behavior of carbon steel in RO product water. It was found that the generation and accumulation of Fe3O4 on the metal surface was the primary reason leading to the high corrosion rate of carbon steel, and anti‐corrosion measures can be chosen following the following rules: deoxygenation, raising of the pH of the solution, or addition of corrosion inhibitors to the solution.

The effects of hydrogen sulfide (H2S) on the corrosion of high strength carbon steel have been studied due to their relevance to the oil and natural gas industries. Since H2S behaves as an acid in aqueous solutions, the presence of dissolved H2S results in a decrease in pH through dissociation into H+(aq) and HS-(aq) ions. It is known that the effects of sulfide on iron oxidation dependent on the solution pH. For example, at very low pH the metal surface is free of corrosion products and resulting in high rates of active corrosion. In a pH region from 3 to 5, the addition of H2S can result in an initial increase in corrosion rate that decreases over time as a protective iron sulfide layer forms and passivates the metal. Our goal was address the corrosion processes on high strength carbon steel due to H2S at high pH values. In-situ electrochemical corrosion measurements were performed for high strength low alloy steel in 5 %wt. NaCl solution at 85 °C. The solution pH was tested from 7 and 12 to simulate conditions that may be present for drill pipes operating in deep-well environments. Exposure for each sample was at least 60 hours to allow for the observation of steady-state behavior. It was found that the calculated corrosion rate dramatically increased from around 3 mm y-1 or less to over 10 mm y-1 as the solution pH fell below 9, which is an event that could occur if pH control is temporarily lost during gas or oil extraction operations.The change in corrosion rate corresponded to an observed change in the electrochemical impedance spectroscopy (EIS) behavior, with a shift from two well-defined time constants at more alkaline conditions to what appeared to be a single low-frequency time constant at more neutral pH. Varying the rate of stirring in the test vessel did not appear to change the corrosion behavior across the pH range tested, suggesting that the corrosion process was not diffusion limited.The results were correlated to previous work that found the mechanical failure mechanism to shift from stress corrosion cracking at alkaline conditions to hydrogen induced cracking over a similar pH range. This would suggest that changing the pH alters the nature of the corrosion process, possibly by changing the mechanism or the nature of the corrosion product film. Thermodynamic modeling has been performed to investigate the stable corrosion products and aqueous species at each condition. Pourbaix diagrams suggest that corrosion products shift from iron sulfides to iron oxides as the solution pH is increased.

To investigate the corrosion behavior and mechanisms of X70 steel in sands, polarization curves (PCs) and electrochemical impedance spectroscopy (EIS) were carried out using an electrochemical test set-up. X70 steel represents a common and standard API designation for pipelines with 70 ksi or 485 MPa strength. For acceleration of the process at different charging times, a direct current (DC) with 6 V voltage was applied. The results show that DC accelerates the corrosion process of X70 steel in sands and that the corrosion rate increases with charging time of the DC. Corrosion potential changes the process of positive-negative-positive charging with increasing process time, indicating that pore water, oxygen substances and corrosion ions of sands all affect the corrosion reaction. Based on the experimental results from the equivalent circuit of EIS, the corrosion process can be divided into the following three phases: developing and formatting of corrosion product film, pitting corrosion, and progressing pitting period. The low-frequency inductive slope on the EIS graph appears during the period of corrosion pitting as resulting from the corrosion product film. The film slows down the corrosion process and reduces the corrosion rate temporarily. With the increasing charging time, the corrosion product film may be damaged and the corrosion rate will thus increase significantly. The testing results of energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) indicate iron hydroxides as the original corrosion products. With increasing charging time, the original corrosion products may be oxidized to form stable and protective film products such as Fe2O3 and Fe3O4. Lastly, during the pitting progressing period, oxidized film products will be damaged and the corrosion rate increases with increasing charging time.

Effect of different UV intensity on corrosion behavior of carbon steel exposed to simulated Nansha atmospheric environment

PurposeThe purpose of this paper is to explore the long‐term corrosion behavior of carbon steel in 3% NaCl solution and evaluate the effect of rust layer on the corrosion process.Design/methodology/approachThe corrosion behavior of rusted carbon steel in 3% NaCl solution was studied by means of infrared spectroscopy (IR) and electrochemical impedance spectroscopy (EIS).FindingsThe results indicated that the corrosion of carbon steel was affected by chloride ion in initial immersion and then controlled by the rust layer. The rust layer consisted of a thin outer layer (γ‐FeOOH layer) and a thick inner layer (Fe3O4 layer). The outer rust layer facilitated the cathodic process via reduction of γ‐FeOOH, while the inner rust layer provided a large cathode area and oxygen could be reduced on its surface. As a result, the corrosion rate of carbon steel was determined by the limiting diffusion rate of oxygen and stabilized at a high value.Originality/valueThe corrosion model of rusted carbon steel in 3% NaCl solution was established. It is probable that the iron rust in all slightly acidic water with low alkalinity can promote the corrosion process via reduction of γ‐FeOOH. Anti‐corrosion measures for iron in this type of solutions should be aimed to reduce the promoting effect of rust layer on the metal corrosion. The NaCl solution prepared from tap water is more suitable for the substitution of artificial water than that prepared from deionized water.

Corrosion behavior of steel under wet and dry cycles containing Cr 3+ ion

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed (C1 steel), and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.