Identification and formation of green rust 2 as an atmospheric corrosion product of carbon steel in marine atmospheres

Green rust 2 (GR2(SO^2?₄ )) was detected amongst the products formed on a carbon steel rod exposed to atmospheric corrosion using X‐ray diffraction (XRD). The presence of green rust 2 has been related to sulphate reducing bacteria (SRB) in the sea spray. These were detected using test catch rods made out of inert material and posterior lab identification using Starkey culture. Likewise, after the exposure of said rods to sea environmental conditions, SRBs have been isolated from among the carbon steel corrosion products. The evolution of GR2(SO^2?₄ ) from GR1(SO^2?₄ ) was ruled out due to the tendency of this compund to produce GR2(SO^2?₄ ) in the presence of sulphate ions, as is the case here. Likewise, the evolution from GR1(Cl^?) has also been ruled out since in such case as this compound should be formed (it has not been detected in any of the 39 stations studied), the enormous affinity of the GRs with divalent anions (such as is the case with SO^2?₄ ) as opposed to the monovalent ions (such as is the case of the Cl^?) makes GR1(Cl^?) transform into GR2 (SO^2?₄ ).     

The effect of cathodic polarization on the corrosion behavior of X65 steel in seawater containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) are one of the main reasons for the accelerated corrosion of steel. Cathodic polarization has been reported as an effective and economic method against marine corrosion, including microbiologically induced corrosion. However, the interaction between cathodic polarization and microbial activity has not been well defined. In this study, a fluorine-doped tin oxide electrode is used to study the effect of cathodic current on SRB cells. Fluorescence microscopy results clearly show that the attachment degree of SRB is dependent on the electric quantity and current intensity. The large electric quantity and high cathodic current (400 mA/m² × 30 h) can effectively inhibit bacterial attachment and subsequent biofilm formation. Furthermore, the effect of cathodic potential on the corrosion behavior of X65 steel in the presence of SRB is systematically investigated. Results show that the impressed charges, the increase of pH, and the formation of calcareous deposits on the electrode surface at the cathodic potential of −1,050 mV/SCE inhibit the attachment of SRB. In turn, the presence of SRB also interferes with the electrochemical reactions that occur during the polarization process, thus increasing the cathodic current. The interaction between SRB-induced corrosion and the process of preventing corrosion by various cathodic potentials is discussed.     

Effect of Co and W on the corrosion behaviour of 1% Cr steel in flowing synthetic seawater

The aqueous corrosion characteristics of 1% Cr‐steel alloyed with small amounts of Co and W in synthetic seawater was studied by using immersion weight‐loss tests, electrochemical corrosion tests (potentiodynamic tests and electrochemical impedance spectroscopy (EIS) measurements) and analytical techniques. 1% Cr steels containing Co or W from 0.2 to 0.4 wt.% showed higher corrosion resistance than the 1% Cr steel in the immersion and potentiodynamic tests. EIS measurements showed that the Nyquist plot presented one time constant. Furthermore, the Co‐ and W‐bearing steels present higher R_p values than the 1% Cr steel through all the test period. The better corrosion resistance of the Co‐and W‐bearing steels is attributed to the protectiveness of the surface layer. The corrosion products were examined using electron probe microanalysis (EPMA) and X‐ray photoelectron spectroscopy (XPS). The results of EPMA indicated that Cr was concentrated in the inner region of the rust layer, while Co and W were distributed all over the rust layer. XPS results showed that Co existed as a trivalent oxide in the rust layer and W in the rust appeared in the form of a WO₄ compound. These compounds act as a factor for corrosion resistance in aqueous solutions.     

Atmospheric corrosion of carbon steel under field exposure in the southern part of Vietnam

The corrosion behavior of carbon steel with and without shelter at four test sites (four cities) in the south of Vietnam was investigated in terms of the environmental factors such as average relative humidity, rainfall, sulphur dioxide and chloride depositions, and various exposure periods. The mass losses of the specimens with shelter at four test sites were related to SO₂ concentration at each site. Without shelter, the mass loss at HoChiMinh was lower than that with shelter, whereas those of the other sites were higher without shelter than with shelter. Although the corrosion behavior at HoChiMinh was difficult to explain based on the environmental factors, it was estimated from a protective corrosion products caused by a synergistic effect among SO₂ concentration, rain and sunlight.     

The effect of CeCl3 inhibitor on the localized corrosion of stainless steel in chloride solutions

Stainless steels have been used extensively in many sectors such as medical and household appliances as well as construction. This has been primarily due to their high resistance to corrosion attacks, reasonable cost, and excellent mechanical properties. However, when placed in corrosive media stainless steel is susceptible to localized corrosion attacks, especially when placed in chloride solutions. The paper explores the issue of corrosion liability of austenitic (AISI 316) and duplex (UNS S32205) stainless steels in et aconditions of seawater environment as well as under the influence of an inhibitor in the same environmental conditions. The behavior of stainless steels was examined via electrochemical testing relying on DC and AC techniques, optical metallographic analysis, scanning electron microscopy, and X‐ray diffraction analysis. Duplex stainless steel showed better resistance to localized corrosion but a higher tendency toward general corrosion in all examined solutions. Cerium chloride in a chloride solution showed inhibiting properties for both the AISI 316 and the UNS S32205.     

Determination of adhesion between corrosion product film and carbon steel by a scratch test

A scratch test is used to measure the adhesion between corrosion product film (CPF) and carbon steel in deionized water under different pH and temperatures. The fuzzy feature model is modified to minimize errors between calculation and scanning electron microscopy (SEM) results. Findings illustrate that the maximum error decreases to 11%. The adhesion between CPF and substrate increases with rising temperature and pH of deionized water. The Poisson's ratio and Young's modulus of CPF are in the ranges [0.34 and 0.45] and [0.08 and 0.11 GPa], respectively, as temperature and pH change.     

Atmospheric corrosion of hot and cold rolled carbon steel under field exposure in Saudi Arabia

Carbon steel (hot and cold rolled) specimens have been exposed to the action of different atmospheres at 20 test sites distributed in Saudi Arabia and was investigated in terms of environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (Cl⁻ and SO₂). Applying the standard ISO 9223 norm aggressiveness of the atmospheres corresponding to 0the different test sites has been determined. Calculations of corrosion rates were made via loss of weight and characterization of the corrosion products formed on samples has been carried out by means of X-ray diffraction (XRD). The major constituent of the rust formed in marine and marine-industrial environment is goethite (α-FeOOH). These samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe₂O₃). In the case of urban and rural samples goethite is the major constituent of corrosion layers. The rust formed under the urban environment also contains large amounts of ferrihydrite and in a lesser proportion, of goethite and maghemite.     

Outdoor atmospheric corrosion of carbon steel and weathering steel exposed to the tropical-coastal climate of Thailand

This study focuses on atmospheric corrosion of carbon steel and weathering steel exposed at two different locations with dissimilar meteorological parameters and airborne pollutants in Thailand. The samples are subjected to an outdoor atmosphere for up to 36 months at Rayong, close to the Gulf of Thailand, and Phangnga, near the Andaman Sea. Thickness loss (µm), corrosion rate (µm/year) together with corrosion product morphology and composition are systematically analyzed using X-ray diffraction and a scanning electron microscope. Corrosion resistance of the tested steels exposed at both locations is discussed based on the above-mentioned parameters and calculated corrosion kinetics. The results indicate that the total time of wetness, amount of rainfall and chloride deposition rate play an important role in corrosion behavior of the tested steels. Alloying elements, copper, chromium and nickel, are shown to improve corrosion resistance of the samples when exposed at the location with a higher chloride concentration.     

Effect of initial CaCO3 saturation levels on the CO2 corrosion of 1Cr carbon steel

This paper presents the investigation on the effect of calcium on the corrosion behavior of 1Cr carbon steel under various levels of initial CaCO₃ saturation () of the bulk solutions. All the experiments were performed at 80°C in 1 wt% aqueous NaCl solution saturated with CO₂. Four initial levels were investigated, namely 0, 0.6, 2, and 10. The corrosion process was followed using linear polarization resistance, potentiodynamic sweeps, and electrochemical impedance spectroscopy. The surface morphology of the corrosion products was analyzed with scanning electron microscopy and structural information using X-ray powder diffraction. Precipitation of a substitutional solid solution of Fe_xCa_yCO₃ (x + y = 1) was found on the steel surface. The growth of this layer was delayed by Ca²⁺ ions in the solution, but its protectiveness was not affected and was comparable with the pure FeCO₃ corrosion product. No signs of localized corrosion were detected on the material.     

General corrosion of carbon steel in a synthetic concrete pore solution

In this study, we reviewed our recent work on the general corrosion of carbon steel (P355QL2) overpack material for the isolation of high-level nuclear waste in Belgium's supercontainer concept. By using electrochemical impedance spectroscopy and by optimizing the mixed potential model, which incorporates quantum mechanical tunneling of charge carriers across the barrier layer to describe the kinetics of the partial cathodic process, we evaluated all parameters in the model as a function of independent variables such as voltage, temperature, and pH. By delineating the partial anodic and cathodic processes, we found that the corrosion rate (CR) is independent of voltage over the voltage range from 0.2 to −1.0 V_SHE, which is predicted to be experienced in the repository. Furthermore, the CR is found to increase strongly with decreasing pH and increasing temperature.     

Corrosion behavior of SRB Desulfobulbus propionicus isolated from an Indian petroleum refinery on mild steel

In this study, Desulfobulbus propionicus (D. propionicus), a sulfate reducing bacterium (SRB) was isolated and identified in cooling towers by molecular biologic techniques. This bacterial species has been reported for the first time in the cooling towers of an Indian petroleum refinery. Corrosion behaviors were analyzed by electrochemical and weight loss methods. The high corrosion rate and the enhancement of anodic current in increased chloride environment was noticed in the presence of D. propionicus indicating that this SRB species enhances the pitting corrosion of mild steel. Propionate metabolism in H₂S production is discussed as a new pathway of corrosion enhancement.     

Oxidation of tungstate‐containing green rust (Cl–) in aqueous solution

The influence of tungstate on the oxidation of green rust [GR(Cl^–)], which contains both Fe(II) and Fe(III), was investigated by synthesizing suspensions of GR(Cl^–) containing tungstate and oxidizing them via injection of N₂ gas containing O₂. XRD and TEM analyses were used for characterizing the solid particles formed during synthesis and oxidation. The results showed that the formation of fine α‐FeOOH was enhanced by the addition of tungstate to the GR(Cl^–) suspensions, while GR(Cl^–) without tungstate was transformed primarily into γ‐FeOOH. The pH, oxidation‐reduction potential (ORP), and dissolved oxygen (DO) values of the aqueous solution were measured during oxidation of GR(Cl^–) with and without tungstate. The results showed that whereas the pH value of the solution was decreased and the ORP value was increased monotonically by oxidation of GR(Cl^–), the pH and ORP values during oxidation the GR(Cl^–) suspension containing tungstate revealed characteristic changes with time. XAS was also used for characterizing the chemical state and local structure of tungstate in the oxidized particles. The results indicated that the local structure of WO was essentially retained in the particles precipitated from GR(Cl^–) suspensions.     

Corrosion of low alloy steel in stagnant artificial or stirred natural seawater: The role of Al and Cr

Carbon steel and low alloy (containing Al and Cr) steel coupons were immersed for 6–7 months in stagnant artificial seawater or in natural marine site. The corrosion processes were studied via the combination of electrochemical techniques and the analysis of corrosion product layers by µ‐Raman spectroscopy and X‐ray diffraction. In natural seawater, the low alloy steel showed better resistance to corrosion and the best results were obtained when the mill scale was removed from the steel surface. This shows that improved corrosion resistance is due to a protective layer that forms spontaneously in the environment. In stagnant artificial seawater, the behavior of low alloy steel coupons (without mill scale) was compared with that of carbon steel coupons. The polarization resistance of the carbon steel coupons remained approximately constant over time. The corrosion product layer proved to be mainly composed of magnetite, an electronic conductor that does not hinder oxygen reduction. In contrast, the polarization resistance of the low alloy steel coupons increased with time, as the growing corrosion product layer, enriched with insulating FeOOH compounds, hindered oxygen diffusion.     

Corrosion resistance and corrosion behavior of high-copper-bearing steel in marine environments

Thus far, research on the corrosion resistance of copper-containing steel has been limited to Cu content of less than 1%, and the corrosion resistance of antibacterial Cu-containing steel with Cu content above 3% has not been reported. In this study, 0Cu3 carbon steel (CS), 0Cr15Cu3 stainless steel (SS), and Q345 CS were investigated. The corrosion resistance and corrosive behavior of high-copper (high-Cu)-bearing steel in a marine environment were examined by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, electrochemical impedance spectroscopy, and potentiodynamic polarization. Coupon test results showed that the Cu in the 0Cr15Cu3 SS and 0Cu3 CS can promote the formation of stable α-FeOOH from γ-FeOOH in the outer rust layers, and make the rust layers more thick and dense. In the electrochemical experiment, the impedance loop diameters and R_ct values of the 0Cr15Cu3 SS and 0Cu3 CS were higher than those of Q345, while the I_corr was less than that of Q345, which indicates that the anticorrosion property of these two types of high-Cu-bearing steel was higher than that of Q345. The aim of this study was to define the properties of corrosion resistance and corrosive behavior in high-Cu-bearing steels to promote their application in marine engineering.     

Atmospheric corrosion of carbon steel at marine sites in Saudi Arabia

Atmospheric corrosion tests, according to ASTM G50‐76, have been carried out in Saudi Arabia, at eight marine sites representing different environmental conditions. Environmental factors such as average temperature, average relative humidity, and deposition rates of atmospheric pollutants (Cl^? and SO₂) was investigated. X‐ray diffraction has been used to determine the composition of the corrosion products. Corrosion rates have been determined for each sample at each of the exposure sites via loss of weight. The obtained data were used for the classification of atmospheric aggressivity, according to ISO 9223. The results obeyed well with the empirical kinetics equation of the form C = Ktⁿ, where K and C are the corrosion losses in mg/cm² after 1 and t years of the exposure respectively, and n is constant. Based on n values, the corrosion mechanism of carbon steel is predicted. The major constituent of the rust formed in marine environment is goethite (α‐FeOOH). Samples also show the presence of a large proportion of lepidocrocite (γ‐FeOOH) and small amounts of ferrihydrite and maghemite (α‐Fe₂0₃).     

Studies on waterline corrosion processes and corrosion product characteristics of carbon steel in 3.5 wt% NaCl solution

The waterline corrosion behaviors of carbon steel partially immersed in a 3.5 wt% NaCl solution were investigated using the wire beam electrode technique, and the effects of corrosion products on the processes of waterline corrosion were analyzed. The results demonstrated that the initial stage and development stage of waterline corrosion were mainly controlled by the concentration and diffusion of dissolved oxygen, respectively, and the deceleration stage of waterline corrosion was mainly affected by corrosion products. The main component of the yellow corrosion products was γ-FeOOH, and γ-FeOOH that exhibited a high reduction reactivity could be involved in the cathodic reaction. The black corrosion products were mainly composed of Fe₃O₄ with strong thermodynamic stability and the processes of dissolved oxygen diffusion and ion transports were obviously affected due to the continuous accumulation of Fe₃O₄ on the surface of the electrodes. Polarity reversals were observed on the single electrodes below the waterline, but the reasons for the phenomena were different from each other.