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Microbiologically influenced corrosion of carbon steel was assessed in a laboratory environment simulating the deep geological repository of radioactive waste. A dense and diverse biofilm was formed on the surfaces of steel in biotic systems without concrete. Addition of nutrients favored biofilm formation and altered the bacterial community; most distinctly, the relative abundance of Alphaproteobacteria decreased, and Deltaproteobacteria or Betaproteobacteria became more abundant, when nutrients were available. Nutrient amendment also increased the corrosion rate and changed the composition and resistance of corrosion products (mostly FeS, Fe2O3, or Fe(OH)2). Presence of concrete inhibited the corrosion of steel and hindered the biofilm formation on steel. Only sparse biofilm consisting of known alkaliphilic bacteria was detected. In the presence of concrete, the corrosion rate was consistently radically decreased, as the properties of the surface deposits (mostly CaCO3) were different from those in the other systems. [ABSTRACT FROM AUTHOR]

A novel potassium zinc phosphate (PZP) pigment was synthesized in the presence of benzotriazole (BTA) as a fourth generation of zinc phosphate (ZP). The corrosion inhibition properties of PZP-BTA, compared to PZP and ZP, were investigated by electrochemical techniques in the extract solutions. The chemical composition of the carbon steel surface immersed in different extract solutions was studied by scanning electron microscopy with energy dispersive spectroscopy. The corrosion protective performance of the epoxy coatings reinforced with 10 wt% PZP-BTA and PZP was studied by salt spray test. Results showed superior performance of PZP-BTA in comparison to its former generation, i.e., PZP. [ABSTRACT FROM AUTHOR]

The internal corrosion of pipeline steel in the presence of hydrogen sulfide (H2S) represents a significant problem in the oil and gas industry. Its prediction and control pose a challenge for the corrosion engineers. In previously published research by the same authors, an electrochemical model of H2S corrosion was developed in both pure H2S and H2S/CO2 aqueous systems. An additional electrochemical cathodic reaction, direct H2S reduction, was uncovered based upon the carbon steel corrosion experimental results. However, in the carbon steel corrosion experiments, the Tafel's region of cathodic reactions experienced interference by the anodic iron dissolution reaction, making the electrochemical kinetics of cathodic reactions unclear. In the present study, experimentation was conducted to better resolve the direct reduction of H2S while minimizing the effect of the anodic reaction by using a passive stainless steel working electrode. The electrochemical kinetics parameters for H2S reduction (i.e., Tafel slope, exchange current density, and reaction order with H2S concentration) were determined. Moreover, the electrochemical kinetics parameters for H+ reduction were also revisited. [ABSTRACT FROM AUTHOR]

The influence of zinc content on the mechanisms of corrosion protection of zinc-rich epoxy primers containing carbon nanotubes (CNT-ZRPs) on carbon steel under exposure to simulated concrete pore solutions was investigated. The barrier and cathodic protection control mechanisms were characterized by electrochemical techniques, such as open-circuit potential and electrochemical impedance spectroscopy, accelerated tests in a salt spray chamber, and high-resolution techniques, such as scanning electron microscopy coupled with energy dispersive x-ray spectroscopy and x-ray diffraction. Based on the zinc content, three mechanisms of corrosion protection were identified. The CNT-ZRP with 60 wt% Zn exhibited good barrier protection during the entire immersion period as a result of the highly cross-linked character of the epoxy binder. In contrast, the CNT-ZRP with 70 wt% Zn afforded short-term sacrificial protection to the metallic substrate, followed by intermediate barrier protection. Furthermore, it was found that the presence of CNTs in the coating system with 70 wt% Zn enhanced the electrical contact between the zinc particles and the carbon steel surface, which is required to guarantee an efficient galvanic protection process. In addition, CNTs increased the barrier properties of the coating, suggesting that CNTs blocked micropores and defects in the material hindering the diffusion of the electrolyte throughout the coating. Finally, an extended galvanic protection was provided for the CNT-ZRP with 80 wt% Zn. Insoluble zinc corrosion products were found inside the material and at the coating surface, as a result of the galvanic protection process and a self corrosion process of the zinc particles. The influence of chloride concentration on the corrosion degradation mechanisms of these coating systems was also investigated. It was found that concrete pore environments with low chloride concentration promoted the passivation of the carbon steel surface and the formation of solid zinc corrosion products. In contrast, the simulated concrete pore solution with high chloride concentration induced the breakdown of the passive layer, blister formation, and dissolution of zinc corrosion products previously formed during the sacrificial protection process or the self-corrosion process. [ABSTRACT FROM AUTHOR]

The morphological structures displayed by iron oxides present a very wide range of shapes and sizes, reflecting to a large extent the growth environment where the iron has been exposed. However, the structure of the rust phases formed on carbon steel in atmospheric exposure includes many imperfections, and real component structures appear to diverge from the ideal crystallographic structure of typical iron oxides. Rigorous information on the morphology of the rust phases formed in atmospheric exposure is very scarce, and there are even fewer studies of analytical information on the chemical compounds corresponding to these rust morphologies. The aim of this paper is to advance this field using scanning electron microscopy (SEM)/micro-Raman spectroscopy to perform a more direct and rigorous characterization of the main rust phases. The equipment used consists of a fully integrated confocal Raman microscopy module, which includes an optical video microscope and a high-resolution XY stage on top of the SEM main stage. Correlation between the SEM images and Raman images is achieved by overlaying the video and SEM images of the sample itself. The study consists of a micro-Raman characterization of the morphologies most commonly observed for the main rust phases: lepidocrocite (γ-FeOOH), goethite (α-FeOOH), akaganeite (β-FeOOH), and magnetite (Fe3O4). [ABSTRACT FROM AUTHOR]

The effect of polyacrylic acid on the corrosion behavior of carbon steel and magnetite was investigated in alkaline aqueous solutions at 25°C using potentiodynamic polarization and zero resistance ammetry. The corrosion current density of carbon steel was increased by the addition of 100 ppm polyacrylic acid, whereas that of magnetite was decreased. Carbon steel acted as the anode of the galvanic couple between carbon steel and magnetite, regardless of the presence of polyacrylic acid. In this couple, the galvanic corrosion current density of carbon steel decreased by the addition of 100 ppm polyacrylic acid. [ABSTRACT FROM AUTHOR]

Buried carbon steel pipe are provided with corrosion prevention systems, namely an insulating coating and a cathodic protection system which reduces (or halts) corrosion rate as a result of soil corrosiveness. The presence of alternating current (AC) interference may cause serious corrosion damages on metallic structures corresponding to coating defects, even if the -0.850 VCSE protection criterion is matched. Nowadays, the AC corrosion mechanism, as well as the protection criteria in the presence of AC, is still controversial and debated. In this paper, a two-step AC corrosion mechanism of carbon steel under cathodic protection condition is proposed: (1) AC causes the electromechanical breakdown of the passive film formed on carbon steel under overprotection condition, and (2) after passive film breakdown, high-pH chemical corrosion takes place. In order to investigate AC effects on passive condition (Step 1), experimental tests have been performed on stainless steels in neutral solution, as a result of its passive behavior: AC has harmful effects on passive condition, reducing anodic overpotential, and causing film breakdown over a critical AC interference level. The electromechanical oxide breakdown mechanism resulting from high alternating electric fields (of the order of 106 V/cm) within the passive film is proposed. Electrostriction stresses are a possible explanation. After film breakdown, corrosion can occur if the pH inside the crack is close to 14; this strong alkalization can be reached in overprotection condition (high cathodic current density) and in the presence of AC. [ABSTRACT FROM AUTHOR]

The objective of the present study is to evaluate the corrosion properties of pipeline steels in CO2/H2S/H2O mixtures with different amounts of water (undersaturated and saturated) related to a natural gas transportation pipeline. Corrosion behavior of carbon steel, 1Cr steel, and 3Cr steel was evaluated using an autoclave with different combinations of CO2 partial pressure and temperature (8 MPa/25°C and 12 MPa/80°C) with 200 ppm H2S. The corrosion rate of samples was determined by weight-loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed using surface analytical techniques (scanning electron microscopy and energy dispersive x-ray spectroscopy). Results showed that the corrosion rate of materials in supercritical and liquid phase CO2 saturated with water was very low (<0.01 mm/y). However, adding 200 ppm of H2S to the supercritical and liquid CO2 system caused mild corrosion (<0.5 mm/y). Reducing water content to 100 ppm in the supercritical and liquid CO2 systems with 200 ppm of H2S reduced the corrosion rate to less than 0.01 mm/y. [ABSTRACT FROM AUTHOR]

The stress corrosion cracking (SCC) of carbon steel in nitratecontaining environments has been known for a long time and has become important in managing the integrity of aging underground radioactive waste storage tanks. This paper describes the latest research on the effect of environmental chemistry on localized corrosion and SCC of steel in nitratecontaining solutions, especially as it relates to radioactive waste storage systems. Nitrate is known to be an aggressive species for the localized corrosion and SCC of carbon steel while nitrite, hydroxide, and carbonate are inhibitive species. The role of nitrate and nitrite in localized corrosion and cracking appear to be related to their effects on active dissolution and passivity, rather than on corrosion potential. The long-term corrosion potential is influenced mostly by the pH. [ABSTRACT FROM AUTHOR]

Over the past decade, the knowledge related to predicting internal pipeline corrosion for sweet and particularly sour environments has dramatically improved. Advancement in understanding of the corrosion mechanisms related to H2S corrosion environments enabled the development of an integrated electrochemical model for CO2/H2S uniform corrosion, including the effect of H2S on the protective corrosion product formation on mild steel. The latest model of uniform CO2/H2S corrosion of carbon steel accounts for the key processes underlying of corrosion: chemical reactions in the bulk solution, electrochemical reactions at the steel surface, the mass transport between the bulk solution to the steel surface, and the corrosion product formation and growth (iron carbonate and iron sulfide). The model is able to predict the corrosion rate, as well as the surface water chemistry, as related to all of the key species involved. The model has been successfully calibrated against experimental data in conditions where corrosion product layers do not form and in environments where they do, and compared to other similar models. [ABSTRACT FROM AUTHOR]

A galvanostatic method was used to accelerate pre-corrosion of three low-alloyed carbon steels. The resulting surface morphology, cathodic reaction rates and corrosion rates, and the cathodic reaction mechanism are discussed. The method is suited to accelerate pre-corrosion; however, significant self-corrosion must be taken into account. Surface roughening and increasing amounts of uncovered cementite, associated with increasing metal loss, increases cathodic reaction rates. The cathodic reaction is under mixed chemical and diffusional control in the pH range of these experiments (pH?2CO3 is regarded as an additional source of H+. Although the dissociation of H2CO3 is restricted by the slow hydration of CO2, its presence enhances the corrosion rates. [ABSTRACT FROM AUTHOR]

A systematic study examining the pitting corrosion behavior of X65 carbon steel (UNS K03014) in CO2-saturated 10 wt% NaCl brine is presented. This paper examines the impact of changes in a key environmental parameter (temperature) on the pitting corrosion processes of carbon steel. Pit propagation studies were conducted in static conditions at different operational temperatures. The evolution of corrosion products on carbon steel was followed over 168 h of immersion and their characteristics were related to initiation and growth of pits on the steel surface. The developed corrosion products were studied through the use of x-ray diffraction and scanning electron microscopy. The extent of pitting was evaluated through the implementation of surface interferometry to study discrete pit geometry, namely, the size and depth, while the general corrosion rate was evaluated using linear polarization resistance measurements. The results indicate that pitting corrosion dominates the general thickness loss of the material in conditions where the morphology of the corrosion product layer was predominantly cementite (Fe3C) and/or a form of iron carbonate (FeCO3) often referred to in literature as "amorphous" FeCO3.At 30°C and 50°C, pit propagation continued unhindered despite the growth of an amorphous FeCO3 layer. However, at 80°C, results suggest that a "self-healing" effect involving the precipitation of substantial levels of nano-scale polycrystalline FeCO3 is capable of hindering the growth of active pits in the conditions evaluated. The results also reflect that in instances where high general corrosion rates of the steel surface were observed, the growth rate of pits were heavily underestimated by profilometry measurements (which recorded pit depths relative to the corroded surface). The concept of "relative" pitting and "absolute" pitting rates/depths are consequently introduced and the discrepancies between both interpretations are discussed. [ABSTRACT FROM AUTHOR]

Jacketing or a weather barrier is usually installed in insulated piping systems and pressure vessels to prevent water ingress and protect the insulation. In the event of water penetration and accumulation resulting from poor design and/or aging of the jacketing, drain holes are proposed to accelerate the water dry-out process. This study investigated the influence of jacketing and drain holes on corrosion under insulation of carbon steel. In an enclosed system without the drain holes, where the water dry-out process is reduced, the underlying steel remains exposed to the corrosive environment for a longer period of time. Severe pitting corrosion was observed, which could be a result of limited oxygen diffusion into the insulation creating differential aeration environments favorable for pitting corrosion. The presence of drain holes promoted the water dry-out rate and oxygen diffusion into the insulation. As a result, the average corrosion rate increased in short-term exposure tests, but over a longer term the average corrosion rate, as well as the pitting rate, decreased. [ABSTRACT FROM AUTHOR]

Empirical correlations that enable fast estimation of maximum and average pit depths and pitted area percentage from the standard 3D surface parameters obtainable with infinite focus microscopy were established in this study. Carbon steel coupons pitted by the sulfate-reducing bacterium Desulfovibrio vulgaris were used as the specimens. The maximum and average pit depths and the pitted area percentage were first deter- mined from laborious measurements of individually manually identified pits on the specimens and then used as the basis for developing the correlations. A four-phase diagram, with average pit depth as the y-axis and pitted area percentage as the x-axis, was proposed as an effective visual tool to categorize the varying pitting and risk patterns. The study results afford more effective, quantitative characterization of pitting corrosion. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement behavior in terms of hydrogen-induced surface blistering and hydrogen-induced internal cracking of the friction stir welded high carbon steel plates was evaluated by the cathodic hydrogen charging method. The welding processes were performed at different revolutionary pitches of 0.83, 0.5, and 0.25 mm/rev and therefore, the stir zones of the welds had various microstructures accordingly. After hydrogen charging for 4 hours, the base metal showed large quantities of irreversible dome-shaped blisters on the sample surface. On the contrary, the blisters were hardly observed in the stir zone regardless of the welding parameters and only a small number of microcracks were formed. Compared with the base metal, the stir zones produced at 0.83 mm/rev and 0.5 mm/rev had less ductility reduction after hydrogen charging for the same time. It revealed that the stir zones showed higher resistance to hydrogen embrittlement than the base metal. However, the specimen welded at 0.25 mm/rev showed premature failure after hydrogen charging as a result of the formation of cracks in the twin martensite structure beneath the specimen surface. [ABSTRACT FROM AUTHOR]

The corrosion inhibition of 2-mercaptobenzimidazole on A 106 carbon steel and its stability in a post-combustion CO2 capture system with application of 5 M monoethanolamine aqueous solutions has been evaluated by linear polarization resistance, electrochemical impedance spectroscopy, immersion corrosion testing, scanning electron microscopy/energy dispersive spectroscopy, x-ray diffraction, and liquid chromatography-mass spectroscopy. Although no notable layer of protective corrosion product was found on the A 106 surface at 80°C and atmospheric pressure for >180 h, corrosion was inhibited, and its polarization resistance increased nearly an order of magnitude when 2-mercaptobenzimidazole was added. However, degradation of 2-mercaptobenzimidazole, associated with the formation of an FeS layer with cracks, occurred at 108°C and 4.13x105 Pa. [ABSTRACT FROM AUTHOR]

In this work, the general and localized corrosion behavior of X65 carbon steel in water-saturated supercritical CO2 conditions containing O2 and SO2 at 35°C and 80 bar is evaluated. The results indicate that crystalline FeCO3 formed in the presence of water and CO2; however, the combined introduction of small concentrations of O2 and SO2 (as low as 20 ppm and 2 ppm, respectively) changed its crystal morphology. Increasing the concentration of SO2 to 50 ppm and 100 ppm, while maintaining O2 content at 20 ppm, results in the formation of FeSO3 ⋅ 3 H2O. General corrosion rates increased significantly from 0.1 mm/y to 0.7 mm/y as a result of the increase in SO2 content from 0 ppm to 100 ppm based on 48 h experiments, while localized corrosion rates rose from 0.9 mm/y to 1.7 mm/y. Additional tests involving solution replenishment over 48 h indicated that the higher corrosion rates observed in the presence of SO2 did not present the worst case scenario corrosion rates and highlight the importance of having a system where the process fluid is continuously replenished. The corrosion product morphology and chemistry were identified through a combination of scanning electron microscopy (SEM). energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), and surface profilometry measurements. [ABSTRACT FROM AUTHOR]

Kinetics of passivity and chloride-induced depassivation of iron exposed to simulated concrete pore solutions were studied using electrochemical quartz crystal nanobalance (EQCN), electrochemical impedance spectroscopy (EIS], and open circuit potential (OCP) monitoring. Passivation followed a two-stage logarithmic film formation process: protective film mostly formed within the first 10 min to 20 min of exposure to the passivating solutions as indicated by a sharp mass increase accompanied by impedance and phase angle data showing trends toward passivation. After this initial passivation period, mass continued to increase, albeit at a significantly slower rate. Electrochemical indicators during this period remained relatively constant and stable, suggesting that the iron remained passive. The mass increase during the post-passivation period was indicative of the formation of additional oxides, while relative stability of the OCP, impedance and phase angle measurements suggested that these oxides were likely more porous, and therefore, less protective than those that had formed during the first 10 min to 20 min. Chloride addition initially caused mass gain while all electrochemical indicators indicated stable passivity, suggesting an induction period before the first signs of pitting. Mass increase during this period supports the predictions of depassivation models that hypothesize the adsorption and ingress of chlorides though the outer layers of oxides. [ABSTRACT FROM AUTHOR]

The present work discusses the influence of specimen dimensions and boundary conditions on the deviation towards 2D diffusion during hydrogen permeation measurements on thick carbon steel plates. It was mathematically found and experimentally confirmed that hydrogen losses through lateral diffusion could significantly affect the validity of laboratory measurements on thick plates, since the common ID simplification of diffusion equations is no longer valid. Based on a finite element analysis, two options are proposed to minimize the effects of side diffusion on permeation measurements. The first option, which encompasses ISO 17081 criteria, recommends optimum radii for hydrogen charging and extraction surfaces and is valid for a wide range of specimen thicknesses. The second option relies on modification of boundary conditions and consists of applying a hydrogen-diffusion barrier on the specimen side edges. This second option was experimentally tested and validated by means of an oxide layer deposited using a heat treatment. The present paper will describe in detail the mathematical modeling and experimental approaches and the basis for our recommendation. [ABSTRACT FROM AUTHOR]

Innovative top-of-the-line corrosion (TLC) inhibition techniques are being investigated as an alternative to batch treatment. A novel idea consists of injecting the corrosion inhibitor within a foam matrix. Previously, a "proof of concept" validation of the novel TLC mitigation method was successfully conducted in a small-scale laboratory setup. The findings in this paper present the next step in the study before field trial: validation of the method and characterization of the foam properties in realistic, large-scale flowing systems. The foam containing the inhibitor was injected into the flow loop, forming a dense plug, which was pushed forward by the gas. The foam-generation method carried considerable importance for foam stability, as well as inhibition persistency. Foam created under stagnant conditions retarded the corrosion rate up to 97%, however the inhibition effect was not persistent. When the foam containing 20,000 ppmv of corrosion inhibitor, TOFA/DETA imidazoline, was created in flowing conditions, the corrosion inhibition efficiency was calculated to be higher than 90%, and the inhibition effect lasted up to 50 h. The novel TLC mitigation method showed promising results in a large-scale flow loop, and applications in oil and gas field environments should be considered. [ABSTRACT FROM AUTHOR]

The present study has been conducted to investigate the electrochemistry of mild steel corrosion in a mixed hydrogen sulfide/carbon dioxide (H2S/CO2) aqueous environment, and develop an electrochemical model to simulate the experimental results. The experiments were designed to determine the effect of H2S on C02 corrosion for short-term exposures of a few hours before any interference from iron sulfide corrosion product layers happened. Tests were conducted at different H2S concentrations, ranging from 0 to 10% in the gas phase at 1 bar total pressure at pH 4 and pH 5. Mechanisms related to H2S/C02 corrosion have been examined by using different techniques such as linear polarization resistance (LPR) using the scan rate 0.125 mV/s), potentiodynamic sweeps (scan rate 1 mV/s), and comparison of experimental results with electro-chemical model predictions. Results indicate that the presence of H2S could affect both cathodic reactions and the anodic reaction. An electrochemical model was developed for a mixed H2S/C02 system, which was calibrated with new experimental results and compared to data found in the open literature. The model predictions fit experimental data well for short exposures (measured in hours) but overestimate the experimental results for longer term exposures (measured by days and weeks) due to the formation of an iron sulfide corrosion product layer, which is not accounted for in the present model. [ABSTRACT FROM AUTHOR]

The corrosion behavior of carbon steel UNS K02600 in 50 wt% methyldiethanolamine solutions was investigated in the background of the carbon dioxide (CO2) capture process in fossil fuel-fired power plants for the purpose of carbon capture and storage. A series of experiments was conducted under regenerator conditions (120°C) with different combinations of CO2 loading (0.3 mol/mol and 0.05 mol/mol), O2, and heat-stable salts (including sulfate, formate, and N,N-bis[2-hydroxyethyl] glycine). The corrosion behavior of carbon steel was investigated using electrochemical techniques (open circuit potential, linear polarization resistance, and potentiodynamic polarization), surface analytical techniques (scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction), and weight-loss methods. The results showed that the corrosion rate of carbon steel initially decreased and then stabilized with time in CO2-loaded methyldiethanolamine solution due to the formation of an iron carbonate (FeCO3) layer, with the exception of methyldiethanolamine/CO2/O2/heat-stable salts, which exhibited a low CO2 loading (0.05 mol/mol). It was found that the presence of HSS significantly accelerated the corrosion process at low CO2 loading, whereas the effect of oxygen on the corrosion rate was not significant at low CO2 loading. The formation mechanism of the FeCO3 layer, which is a key issue in the control of corrosion in these environments, was discussed. [ABSTRACT FROM AUTHOR]

Corrosion inhibitors are commonly used to mitigate corrosion in oil and gas pipelines, and the choice of inhibitor for a particular oilfield depends on the conditions of the field (oil chemistry, water chemistry, temperature, etc.). To find the optimum formulation for each field condition, extensive laboratory tests are carried out, which include corrosion inhibitor performance, foaming, and emulsification, to name a few. However, corrosion inhibitors can have the additional advantage of altering the wettability of the steel surface from hydrophilic (water wet) to hydrophobic (oil wet) by forming a hydrophobic adsorption layer on the steel surface. In the current work, the ability of chemicals to alter the wettability of the steel is investigated by measuring the static contact angle in a goniometer, as well as the dynamic wetting with a small scale flow apparatus, called a doughnut cell, especially designed for this purpose. The doughnut cell makes it possible to measure the water and oil wetting of a steel surface using flush-mounted conductivity pins that detect whether water (conductive fluid) or oil (nonconductive fluid) are covering the surface. The two generic compounds tested here, a quaternary ammonium chloride and a fatty amine, lowered the corrosion rate, altered the surface wetting from hydrophilic (mostly water wet) to hydrophobic (mostly oil wet), and lowered the oil-water interfacial tension, facilitating water entrainment in the oil. A doughnut cell was used to map out how an inhibitor can increase the oil-wetting regime for a given water cut. It is a practical tool that can be used to help optimize the inhibitor dosage and maximize its value. It can also be used in new field development, where enhanced oil wetting could be factored into the corrosion allowance calculation. [ABSTRACT FROM AUTHOR]