Aqueous CO2 corrosion of mild steel is one of the major problems in the oil and gas industry. While current understanding primarily focuses on cathodic reaction mechanisms, less attention has been given to the impact of aqueous CO2 on the anodic iron dissolution reaction. In contrast, the mechanism of iron dissolution in strongly acidic environments has been thoroughly investigated. Among the reaction mechanisms found in the open literature, a multipath mechanism was identified that could explain the iron dissolution in strong acidic sulfate solution; both in terms of steady-state polarization sweeps and impedance data at various pH values and current densities. However, the role of aqueous CO2 in solutions containing chlorides on the mechanism of iron dissolution remained an open question. The present study used electrochemical impedance spectroscopy (EIS) as the main technique, to study the mechanism of iron dissolution in strong acid chloride solution with and without the presence of CO2. Results showed that the presence of chloride ions (0.5 M) decreased the rate of iron dissolution by competing with hydroxide ions to adsorb on the metal surface, forming chloride-containing intermediate species that participate in the iron dissolution reaction. The resulting decrease in the availability of hydroxide intermediates, which are more effective at enhancing the reaction rate compared to chloride-containing intermediates, leads to an overall decrease in the rate of iron dissolution. While the presence of CO2 increases anodic current density, EIS investigation revealed that neither aqueous CO2 nor other carbonic species directly react on the bare metal surface to form adsorbed intermediates involved in the anodic reaction. EIS investigation suggested that aqueous CO2 may induce changes in the chemical composition of adsorbed species, rate constants, and surface coverage, thereby altering the kinetics of the underlying reactions.

Internal corrosion is a problem for steel pipelines transporting natural gas or CO2 containing water and partial pressures of H2S higher than 0.3 kPa (0.05 psi). This work aims to mitigate internal corrosion in steel pipelines transporting natural gas containing H2S using cold spray coatings. Two types of the cold spray binary metallic coatings (zinc chromium [ZnCr]. zinc niobium [ZnNb]) were studied using electrochemical techniques: potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy. The corrosion resistance of cold spray coatings (ZnCr, ZnNb) was evaluated in an environment containing 4 bar CO2 pressure, simulating the partial pressures found in gas transmission lines over a solution of 3.5 wt% NaCl heated to 40°C. A concentration of 0.003 M Na2S2O3·5H2O, corresponding to H2S partial pressures around 0.079 bar (1.146 psi), was used to simulate sour conditions. Postcorrosion surface characterization was performed using a scanning electron microscope (SEM) equipped with an energy-dispersive x-ray spectroscope (EDS) and x-ray diffraction analysis. The data showed that the presence of 0.003 M Na2S2O3·5H2O shifted the corrosion potential to more anodic values and decreased the corrosion current density. Both coatings showed similar behavior after 1 h of exposure in the CO2/H2S environment, indicating that similar electrochemical reactions were occurring on ZnNb and ZnCr. SEM images and EDS surface analyses for specimens showed a significant change in the surface chemical composition of carbon steel coated with ZnNb and ZnCr after 24 h of immersion. In the presence of thiosulfate (under sour conditions), the formation of corrosion product layers (ZnCO3 and ZnS) on top of ZnNb and ZnCr coatings increased their corrosion resistance, which helped to reduce their corrosion by a factor of 2. Under a sweet environment, the corrosion rates for steel coated with cold spray coatings after 14 d of exposure are lower than that for galvanized steel by a factor of 5 due to the ZnCO3 layer formed on top of the coatings. The ZnCO3 layer formed on the steel surface acts as a physical barrier against corrosion by blocking the diffusion of corrosive species to the surface. No localized attack was observed. ZnCr Cold spray coating with defect showed promising corrosion protection against CO2 corrosion (sweet corrosion) after 14 d of exposure to a CO2 environment. The scratch on the coating simulated damage created in service, and it was deep enough to expose the substrate material (steel). The formation of zinc oxide (ZnO) and zinc carbonate (ZnCO3) on the scratch confirmed the cathodic protection of the steel by ZnCr and ZnNb coatings.

This study simulates the behavior of 2205 duplex stainless steel (DSS) in an actual service environment under hydrogen charging/releasing cycles. Electrochemical and immersion experiments are conducted to compare the pitting susceptibility and corrosion behavior of 2205 DSS under single hydrogen charging and several hydrogen charging/releasing cycles. The results reveal that under single hydrogen charging, pits preferentially initiate and propagate within the austenite phase; this finding is consistent with the results of previous studies. However, under cyclic hydrogen charging/releasing cycles, pits initiate at the phase boundary and propagate along it. Moreover, a hydrogen microprint technique is used to characterize the hydrogen enrichment sites in 2205 DSS. The results demonstrate that pits preferentially initiate at the same hydrogen enrichment sites. The study creates a schematic of hydrogen redistribution and hypothesizes that under actual service conditions, the phase boundary, rather than the austenite phase, is the primary site for pitting corrosion because of its transformation into a hydrogen enrichment site from a hydrogen trap.

In the oil and gas industry, produced water with a high dissolved salt content is a common byproduct of hydrocarbon extraction from conventional and unconventional wells. Other than salts, corrosive gases such as CO2 are abundant in the production stream, which dissolve and acidify the solution, posing a risk of internal pipeline corrosion. To mitigate this issue, injection of corrosion inhibitors has emerged as a cost-effective approach. In various aggressive conditions, heterocyclic molecules that contain nitrogen atoms have proven to be highly effective corrosion inhibitors for many alloys. In this study, tetrahydropyrimidinium (THP-C14) inhibition efficiencies were investigated at temperatures of 25°C, 55°C, and 80°C using electrochemical methods, including linear polarization resistance and potentiodynamic sweeps. Corrosion inhibition data were then correlated with THP-C14 concentration, using the five adsorption isotherms: Langmuir, Temkin, Frumkin, Flory-Huggins, and Dhar-Flory-Huggins models. These isotherms utilize different assumptions to establish the correlation between coverage and inhibitor concentration. The suitability of these five isotherm models for describing the corrosion inhibition behavior of THP-C14 was examined. In addition, the thermodynamic parameters (Kad, ΔadGo) of adsorption for THP-C14 at 25°C, 55°C, and 80°C were calculated and compared using the aforementioned adsorption isotherm models. Finally, a mechanism was proposed for the adsorption behavior of the THP-C14 corrosion inhibitor model compound. Chloride ions were important for inhibitor adsorption.

Filiform corrosion (FFC) is one of the possible failure mechanisms of organic-coated steel. Beyond cathodic delamination, FFC causes paint detachment and the dramatic loss of the protective properties given by the applied paint. As both failure mechanisms occur during in-field exposure (depending on the environment), when assessing the performance of the protective paint by lab scale tests, we must be aware of the failure mechanism we induce with different accelerated aging cabinets. In this study, we investigate the effect of the prohesion test on the initiation and propagation of FFC. We highlight the concurrent development of FFC and cathodic blistering, which includes the change between the cathodic and anodic delamination front, during an accelerated aging procedure that cycles between saturated humidity and dry stages. The role of the presence of aggressive contaminants (Cl− and ) is discussed. According to our findings, cyclic aging tests seem to better stick to the failure mechanism occurring during in-field exposure, particularly due to the wet/dry cycles.

Protection against atmospheric corrosion of steel infrastructure and its components requires assessment and prediction of corrosion rates using quantitative and reliable modeling of the environmental parameters that impact the corrosion process. This has become even more critical in the context of climate change. This study demonstrates the feasibility of using ISO dose-response functions (DRFs) to classify atmospheric corrosiveness in Canada to improve the current qualitative approach to the corrosion design of carbon steel infrastructure, especially bridges. The DRF predictions for first-year corrosion rates were first validated using a set of historical field data collected from different locations across Canada. Further examination has revealed a dramatic change in atmospheric corrosiveness at many locations in Canada since the last systematic effort in field data collection in the 1950s to 1960s. It is believed that this was caused by a significant drop in in sulfur dioxide levels in the atmosphere. A projection of future corrosiveness in various Canadian cities with differing climates was also presented by considering the projected impacts of climate change on the temperature and relative humidity. This study has shown a promising precursor for the development of a corrosiveness map in Canada to better guide the corrosion design and protection of steel infrastructure. Furthermore, this study has demonstrated an acute need to understand the current chloride deposition conditions of steel bridges, including the increased local exposure of roadways to corrosiveness by the use of de-icing salts.

Chlorination is widely used in seawater systems to avoid fouling and associated microbial-induced corrosion. Free chlorine is a strong oxidizing agent that prevents biofilm formation on immersed surfaces when used above a certain content. However, the presence of residual chlorine associated with the relatively high chloride content in seawater significantly increases the risk of localized corrosion for most stainless steels. In the present study, a module initially developed to quantify the formation of electroactive biofilms on stainless steels has been used to assess the corrosiveness of chlorinated seawater. Both the electrochemical potential and the cathodic current were measured on super-duplex stainless steel as a function of residual chlorine levels and seawater temperatures. In parallel, long-term localized corrosion tests have been performed in simulated environments to assess the environmental limits for the safe use of high-grade stainless steels in chlorinated seawater. It includes crevice corrosion exposure tests using adapted ISO 18070:2015 crevice formers and internal tube pitting corrosion exposure tests in model tube heat exchangers simulating heat flux from 35°C to 170°C. The synergetic effect of residual chlorine content and temperature on the risk of localized corrosion has been quantified. Corrosion resistance properties are correlated to the electrochemical monitoring data, and the environmental limits of selected base materials stainless steels have been established for duplex stainless steel UNS S32205, super-duplex stainless steel UNS S32750, hyper-duplex stainless steels UNS S32707 and UNS S33207, and the high-grade austenitic stainless steel UNS S31266.

This study aimed to enhance the corrosion resistance of an Al-Mn-Zr alloy containing Fe impurities by using heat-treatment processes. Three processes were implemented to distribute intermetallic particles uniformly, promote Al6(Mn, Fe) and Al3Zr particle formation, and eliminate Fe and Zr segregation. Increasing the amount of Al6(Mn, Fe) reduced the galvanic effect between the Al matrix and Al3Fe particles, leading to improved localized corrosion resistance. Al3Zr promoted smaller grain size by preventing recrystallization. Microstructure analysis confirmed the inhibitory effect on grain growth and the promotion of Al6(Mn, Fe) and Al3Zr particle formation. The effect of grain size on galvanic corrosion was evaluated through corrosion simulation. Furthermore, the improved localized corrosion resistance was evaluated through electrochemical and immersion tests. Consequently, the designed heat-treatment process significantly improved the localized corrosion resistance of the Al-Mn-Zr alloy with Fe impurities. These results demonstrate the effectiveness of the used heat-treatment processes in improving the corrosion resistance of the alloy.

Erosion-corrosion behavior of high-speed steel (HSS) and titanium aluminum nitride (TiAlN) coating were investigated under different flow conditions in simulated seawater. On the front side (facing toward the direction of water flow), there was a negligible failure of the TiAlN coating, but clear marks of erosion-corrosion on the HSS. Notwithstanding, unexpected failure features were identified on the back side (back against the direction of water flow) on both specimens because the high-velocity water flow was localized at the edge and the center was high in turbulence. For the HSS, there was dominant corrosion in the center and dominant erosion at the edge. For the TiAlN/HSS coating, the dense and layered structure retards the propagation of surface cracks as the major failure into the bulk and instead promotes layer-by-layer spallation. Additionally, visible “flow marks” were observed on both specimens and can be explained by the flow-accelerated-corrosion.

This paper investigates the initiation and propagation of localized corrosion on cold-sprayed (CS) aluminum alloy 2024 and 7075 deposits. CS deposits on AA2024-T351 and AA7075-T651 substrates were produced with commercially available AA2024 and AA7075 powders using helium as carrier gas. Electrochemical and immersion tests in 0.6 M NaCl and ASTM G110 test were used to evaluate the corrosion properties of CS AA2024 and AA7075 deposits. For analysis, optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction were utilized before and after the experiment. The results indicated that the initiation and propagation of localized corrosion highly depend on microstructural characteristics, such as the distribution and chemical composition of intermetallic networks with the matrix and propagated along these networks and prior particle boundaries, where an ultrafine grain structure is present. Accelerated localized corrosion tests generated deep penetration as well as a large area of defects owing to the coalescence of fissures.