Localized Corrosion Of Steel Research Articles

Electrochemical tomography as a nondestructive technique to study localized corrosion of metals

We present an approach, termed electrochemical tomography (ECT), for the in-situ study of corrosion phenomena in general, and for the quantification of the instantaneous rate of localized corrosion in particular. Traditional electrochemical techniques have limited accuracy in determining the corrosion rate when applied to localized corrosion, especially for metals embedded in opaque, porous media. One major limitation is the generally unknown anodic surface area. ECT overcomes these limitations by combining a numerical forward model, describing the electrical potential field in the porous medium, with electrochemical measurements taken at the surface, and using a stochastic inverse method to determine the corrosion rate, and the location and size of the anodic site. Additionally, ECT yields insight into parameters such as the exchange current densities, and it enables the quantification of the uncertainty of the obtained solution. We illustrate the application of ECT for the example of localized corrosion of steel in concrete.

Proteins identified through predictive metagenomics as potential biomarkers for the detection of microbiologically influenced corrosion.

The unpredictability of microbial growth and subsequent localized corrosion of steel can cause significant cost for the oil and gas industry, due to production downtime, repair, and replacement. Despite a long tradition of academic research and industrial experience, microbial corrosion is not yet fully understood and thus not effectively controlled. In particular, biomarkers suitable for diagnosing microbial corrosion which abstain from the detection of the classic signatures of sulfate-reducing bacteria are urgently required. In this study, a natural microbial community was enriched anaerobically with carbon steel coupons and in the presence of a variety of physical and chemical conditions. With the characterization of the microbiome and of its functional properties inferred through predictive metagenomics, a series of proteins were identified as biomarkers in the water phase that could be correlated directly to corrosion. This study provides an opportunity for the further development of a protein-based biomarker approach for effective and reliable microbial corrosion detection and monitoring in the field.

Identification of steel corrosion in alkaline sulfate solution by electrochemical noise

AbstractResearch on the effects of sulfate ions on steel corrosion has been conducted in response to the observations of premature localized corrosion of steel strands in cementitious grouts in posttensioned bridge construction. Electrochemical noise (EN) was shown to be an effective technique to assess the development of localized corrosion of steel in the alkaline sulfate solution. General statistics of the EN potential and current time signatures revealed the negative effect of elevated sulfate concentrations and the development of pitting events. Spectral analysis indicated an increase in the characteristic charge and decrease in characteristic frequency with sulfate ion concentration, whereas an increase in the overall corrosion rate was observed, indicating the development of pitting corrosion. Pitting events could be sustained in solutions above 10 g Na2SO4/L H2O and more extensive localized corrosion developed above 20 g Na2SO4/L H2O.

Distinct beneficial effect of Sn on the corrosion resistance of Cr–Mo low alloy steel

In this work, the beneficial effect of Sn addition on the corrosion resistance mechanism of Cr–Mo low alloy steel was studied. Results demonstrated that Sn improves the corrosion resistance of the steel matrix mainly by influencing the microstructural transformation. Sn addition and the synergistic effect of Sn, Cr, and Mo promote the formation of α-FeOOH, SnO2, SnO, Cr(OH)3, and molybdates, lead to the improved protection and stability of the rust layer. This synergistic effect also endows the inner rust layer with cation selectivity, preventing the further penetration of Cl− and inhibiting the localized corrosion of steel.

Galvanic Corrosion Due to a Heterogeneous Sulfate Reducing Bacteria Biofilm

In this work, the galvanic corrosion behavior of sulfate reducing Desulfotomaculum nigrificans biofilm-covered and uncovered carbon steel was investigated using various electrochemical measurements. The results showed that the bare specimen in the abiotic solution functions as the anode; whereas the biofilm-covered specimen in the SRB-containing solution functions as the cathode after two electrodes being coupled. The anodic reaction of specimen in the biotic solution containing SRB was inhibited; whereas the cathodic reaction was considerably promoted after coupling. Hence, localized corrosion of specimen in the abiotic solution was observed due to the galvanic corrosion effect. SRB could still accelerate steel corrosion even after coupling, but the results indicate that the contribution of SRB to steel corrosion decreased. The localized corrosion of steel in the SRB-containing environments not only involved the SRB biofilm, but also a galvanic corrosion effect. The flow of electrons from the anodic dissolution of Fe in the abiotic solution to the SRB cells of cathodic area decreased the acceptance capacity of electrons by SRB from steel beneath biofilm. As a result, the steel corrosion beneath SRB biofilm decreased after coupling.

Thin Benzotriazole Films for Inhibition of Carbon Steel Corrosion in Neutral Electrolytes

This article investigates the modification of a carbon steel surface by benzotriazole (BTA), and the structure and properties of the formed layers. Adsorption was studied by surface analytical methods such as X-ray photoelectron spectroscopy (XPS) and reflecting infrared microscopy (FTIR). It has been established that a polymer-like film containing iron-azole complexes that are 2 nm thick and strongly bonded to the metal is formed on the surface as a result of the azole interacting with a steel surface. This film is capable to inhibit uniform and localized corrosion of steel in neutral aqueous electrolytes containing chloride ions. It is shown that the iron-azole layer located at the interface acts as a promotor of adhesion, increasing the interaction of polymeric coatings with the steel surface. Taking into account these properties, the steel pretreatments can be used for improving the anticorrosion properties of polymeric coatings applied for the protection of steel constructions.

Impedance study on calcium nitrite as a penetrating corrosion inhibitor for steel in concrete

Penetrating corrosion inhibitors are thought to be able to penetrate through the capillary structure of concrete to reinforcing steel and to reduce the already initiated corrosion of steel. In this work the ability of calcium nitrite to inhibit the chloride induced corrosion of steel was studied. The test protocol was adjusted to simulate the performance of penetrating corrosion inhibitors in concrete structures. Steel samples were first prepassivated in saturated solution of Ca(OH) 2 and then exposed to the same solution with 1% NaCl addition, simulating pore liquid in chloride contaminated concrete. After the initiation of steel corrosion, the first dose of calcium nitrite was added, and then its concentration was gradually increased and the inhibition effect was related to the molar ratio of chloride to nitrite ions [Cl −]/[NO 2 −]. Different rates of the increase in the inhibitor concentration were applied. Electrochemical impedance spectroscopy was used to follow the behaviour of steel at different stages of the corrosion process. The evolution of acquired spectra reflected the initiation of localized corrosion of steel and then the gradual inhibition with increasing concentration of the inhibitor. It was found, that calcium nitrite is able to inhibit the initiated corrosion (pitting) of steel and the optimum inhibitor efficiency was observed for the [Cl −]/[NO 2 −] ratio below 1. The inhibition efficiency was larger, when this value of the [Cl −]/[NO 2 −] ratio was reached in early stages of the corrosion development. Calcium nitrite can be effective as a penetrating corrosion inhibitor for steel in concrete, if it will be present in the sufficient concentration at the steel surface in early stages of the corrosion development.

Localized EIS characterization of corrosion of steel at coating defect under cathodic protection

Localized electrochemical impedance spectroscopy (LEIS) technique was used to investigate localized corrosion of steel at defect of coating and, furthermore, to determine the effects of cathodic protection (CP) on local electrochemical environment and the resultant corrosion reaction at the base of coating defect. The results demonstrated that corrosion of steel is dependent on CP potential and the defect geometry. For coated steel containing defect under appropriate CP potentials, cathodic reaction is dominated by reduction of oxygen. Mass-transfer of oxygen through solution layer and the defect with a narrow, deep geometry (the depth/width ratio is about 5.5) is the rate-limiting step for the corrosion process of steel. Even at a very negative potential, e.g., −1200 mV (SCE), the measured impedance spectroscopy is still associated with the diffusion-controlled charge-transfer reaction of steel at the base of defect. It is attributed to the fact that the applied CP is partially shielded by the defect with a narrow, deep geometry. With the negative increase of cathodic potential, charge-transfer resistance and the local impedance of electrode increase. It is attributed to the elevation of local alkalinity at the base of defect when the coated steel is under CP. This conclusion is subject to the condition that a significant cathodic disbonding of coating has not occurred. Furthermore, with the increase of test time, the charge-transfer resistance increases, which is attributed to the enhancement of the alkaline environment at the base of defect under CP with time.

Application of steel thin film electrical resistance sensor for in situ corrosion monitoring

The corrosion sensor should have high sensitivity enough to measure the corrosion rate in mild corrosive environments and the ability to detect the corrosion mechanism. Therefore, our goal is to develop and apply a steel thin film electrical resistance (TFER) sensor based on the measurement of changes in electrical resistance of the sensing elements in order to follow the corrosion of steel in a wide range of environments. The sensor with a thickness of 600 nm is fabricated by DC magnetron sputter deposition of steel on an Al 2O 3 substrate, followed by silk screen printing to improve the sensitivity of the sensor, especially to measure the corrosion rate in low corrosive environments such as anoxic corrosion in neutral solutions, steel protected by protective measures like a corrosion inhibitor or cathodic protection, and atmospheric corrosion. The sensor also has multiple-line sensing elements to detect the localized corrosion of steel. The TFER sensor is laboratory and field tested. All the studies demonstrate that the newly developed TFER sensor can be a promising and reliable tool for corrosion monitoring of steel exposed to various environments.

Scanning electrochemical microscopy measurement of ferrous ion fluxes during localized corrosion of steel

Local fluxes of ferrous ions at low carbon steel surfaces coated with tin and an epoxy-phenolic resin on tinplate samples, and at chrome steel (tin-free steel) have been monitored by oxidation of Fe 2+ ions at the tip of a Pt scanning electrochemical microscope (SECM). The samples were immersed in 10 mM H 2SO 4 in order to avoid Fe(OH) 3 precipitation. The SECM was employed in the collection mode at constant height (≈10–15 μm) on an x– y plane above the sample, monitoring the tip current as a function of tip location.

Effects of some ions on ion-selectivity of ferrous sulfide film

The ion-selectivity of ferrous sulfide film formed on a cellulose sheet was determined by measuring the film potentials in neutral chloride solution. The results show that ferrous sulfide film is a bipolar film consisting of an inner cation-selective layer and an outer anion-selective layer. This kind of film structure can accelerate the localized corrosion of steel. The influence of some anions, cations and imidazoline corrosion inhibitor on ion-selectivity of the film was also investigated. The ion-selectivity of the film is altered from bipolar to anion-selective with the adsorption of Ca2+, Mg2+ and Ba2+ ions, or to cation-selective with the adsorption of MoO42-, PO 43-and imidazoline inhibitor. Potentiodynamic polarization, AC impedance technology, and the weight-loss method were used to understand the relationship between the ion-selectivity and corrosion behaviors of steel in sulfide-containing solution.