Severe localized corrosion in crude unit overhead systems is a critical integrity concern, particularly under transient wetting conditions. This study combines high-frequency online ultrasonic (UT) monitoring with a simplified dew-point temperature margin (ΔT) to evaluate short-term changes in corrosion severity during operation. Wall-thickness data obtained at 12 h intervals were used to derive long-term thinning trends and a short-interval corrosion rate indicator (CR12h). CR12h increased as ΔT decreased, indicating that reduced dew-point margin was associated with increased corrosion severity. Although ΔT is not an exact thermodynamic dew-point prediction, it served as a practical operational proxy for transient wet-corrosion propensity. The evaluation supported partial replacement of the affected column-top region with Alloy C-276 cladding. Follow-up inspection after four years showed approximately 0.1 mm of pitting, corresponding to about 0.025 mm/y, which was approximately one order of magnitude lower than the previous Type 405 stainless-steel cladding. These results demonstrate a practical approach for linking continuous corrosion-monitoring data with operational indicators and material-selection decisions in crude unit overhead systems. The study further illustrates how monitoring-derived insights can be translated into repair planning and subsequently validated through long-term field performance following material upgrade.
This paper investigates the stress corrosion cracking (SCC) behavior under constant loading conditions and the early-stage grain-scale deformation mechanisms of a friction-stir-welded (FSW) joint of 7A52 aluminum alloy. The results show that when a constant load equivalent to 1.0 times the yield strength (439.43 MPa) of the base metal is applied, the joint fractures after 72 days of immersion in a 3.5 wt% NaCl solution, with the fracture located in the heat-affected zone on the advancing side (AS-HAZ). The fracture surface exhibits a mixed-mode morphology characterized by both brittle and ductile features. Observations suggest that cracks mainly initiate at the bottom of corrosion pits, at grain boundaries, and at the interfaces between precipitates (such as Mg-Si-rich, Al-Fe-rich, or Al-(FeMn)-rich) and the Al matrix. It is suggested that the initiation mechanisms are closely related to galvanic corrosion, interfacial weakening, and mechanical property mismatch. In situ tensile and EBSD results indicate that the AS-HAZ is the first region to undergo deformation. As the load increases from 400 N to 1500 N, the degree of strain localization intensifies, with high-strain regions preferentially concentrated at grain boundaries. Grain boundary damage is likely a key mechanism responsible for the initial failure on the advancing side of the FSW joint. Further in situ SEM observations reveal that during the early stage of tensile deformation, as the load increases from 300 N to 455 N, the grain surface in the AS-HAZ evolves from a flat morphology to a typical orange peel appearance. Meanwhile, grain boundaries change from clearly visible to blurred, slip traces increase, and multiple slip systems are activated within the grains. The continuous pile-up of dislocations at grain boundaries leads to a sharp increase in local stress concentration, ultimately inducing grain boundary instability and crack nucleation.
A novel orthophosphate compound, BaNb0.5In0.5(PO4)2 (FA31), was investigated as a corrosion inhibitor for mild steel in 1.0 M HCl using electrochemical techniques, adsorption studies, and surface characterization. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements demonstrated that the inhibition efficiency increased with inhibitor concentration, reaching a maximum value of 94.8% at the optimal concentration. The charge-transfer resistance (Rct) increased significantly from that of the uninhibited solution to 427.2 Ω·cm2 in the presence of FA31, indicating the formation of a protective interfacial layer that effectively suppressed the corrosion process. The adsorption of FA31 on the mild steel surface followed the Langmuir adsorption isotherm, while the calculated standard Gibbs free energy of adsorption (ΔG°ads) indicated that the inhibition process was predominantly governed by physisorption. SEM/EDS analyses further confirmed the formation of a compact and homogeneous protective film on the steel surface. The combined electrochemical and surface analyses demonstrate that FA31 is an effective and environmentally promising corrosion inhibitor for mild steel in acidic media.
This study evaluated the influence of scan rate (4.23 mm/s [S10] and 6.35 mm/s [S15]) on the localized corrosion and tribocorrosion behavior of a laser engineered net shaping (LENS)-produced stainless steel 316L (SS316L) in a phosphate-buffered saline (PBS) solution. Electrochemical impedance spectroscopy (EIS) was performed by applying an AC signal from 105 to 10-2 Hz and cyclic potentiodynamic polarization (CPP) was performed by sweeping from -150 mV to +1.5 V (vs. open circuit potential) and back to characterize passivation and pitting susceptibility. Potentiostatic tribocorrosion tests were conducted using a reciprocating tribometer integrated with a potentiostat to probe material response in passive and cathodic regimes. S15 exhibited manufacturing-related defects that served as preferential pit initiation sites, with pits in both S10 and S15 showing evidence of cell-interior dissolution. Electrochemical results indicated that the charge transfer resistance was reduced by 66% for S15 and that the repassivation potential decreased by 35% compared to S10. Under tribocorrosion, material degradation was dominated by mechanical wear for both samples. However, sliding significantly accelerated electrochemical dissolution in S15, with the corrosion rate affected by wear (Vc-w) increasing by 46.8%. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of wear scars revealed plastic deformation, abrasive grooves, and bio-tribofilm formation composed primarily of phosphates. Micro-pits associated with processing defects were observed exclusively in S15. Overall, lower scan rate processing (S10) produced a more defect-resistant microstructure with improved resistance to localized corrosion and tribocorrosion in PBS.
Highlights What are the main findings? Establishing the new criteria for 3LPE coating of underground steel pipelines, including re-definition of defect severity classification, and stricter minimum performance thresholds for oil/gas and water pipelines. First systematic QA framework for post-installation/backfilling assessment of polymer coatings. Introduction of quantitative criteria for average specific electrical resistance of polymer coatings. Direct correlation between coating defects, dielectric degradation, and cathodic protection (CP) current demand. Introduction of a physically based new parameter: specific coating defect ratio (Ae). Integration of complementary NDT methods into a unified polymer coating QA protocol. What are the implications of the main findings? Enhanced coating reliability and service life through early post-installation QA, enabling detection of installation-induced defects and control of corrosion protection performance from initial service stages. Optimized inspection strategy through integration of DT (Drainage Test) and DCVG (Direct Current Voltage Gradient) results into a unified polymer coating QA protocol, enabling efficient staged diagnostics and reducing unnecessary excavations. Defect-controlled integrity management linking defect density (Ae), electrical resistance, and CP current, enabling predictive maintenance focused on localized damage rather than bulk polymer degradation. Transition from qualitative to quantitative QA through resistance-based criteria and defect metrics, enabling standards revision aligned with the dielectric performance of modern 3LPE coatings.Highlights What are the main findings? Establishing the new criteria for 3LPE coating of underground steel pipelines, including re-definition of defect severity classification, and stricter minimum performance thresholds for oil/gas and water pipelines. First systematic QA framework for post-installation/backfilling assessment of polymer coatings. Introduction of quantitative criteria for average specific electrical resistance of polymer coatings. Direct correlation between coating defects, dielectric degradation, and cathodic protection (CP) current demand. Introduction of a physically based new parameter: specific coating defect ratio (Ae). Integration of complementary NDT methods into a unified polymer coating QA protocol. What are the implications of the main findings? Enhanced coating reliability and service life through early post-installation QA, enabling detection of installation-induced defects and control of corrosion protection performance from initial service stages. Optimized inspection strategy through integration of DT (Drainage Test) and DCVG (Direct Current Voltage Gradient) results into a unified polymer coating QA protocol, enabling efficient staged diagnostics and reducing unnecessary excavations. Defect-controlled integrity management linking defect density (Ae), electrical resistance, and CP current, enabling predictive maintenance focused on localized damage rather than bulk polymer degradation. Transition from qualitative to quantitative QA through resistance-based criteria and defect metrics, enabling standards revision aligned with the dielectric performance of modern 3LPE coatings. Abstract The article deals with non-destructive methodologies for assessing and preventing corrosion of polymer-coated underground pipelines, advanced corrosion-barrier coating systems based on extruded three-layer high-density polyethylene (3LPE), corrosion control strategies for buried oil, gas, and water transmission infrastructures, and mechanisms and engineering approaches for corrosion prevention and mitigation. The quality assurance of newly polymer-coated underground pipelines, following construction (installation and backfilling), is vital for evaluating the polymer coating quality state and the efficiency of passive anti-corrosion protection, aimed at reducing corrosion risks and prolonging the pipeline's service life. The evaluation relies on the coating average specific electrical resistance and the presence of coating defects (number, total area, and distribution) of inspected pipeline sections. In this study, based on extensive real data obtained from testing of newly installed underground water and oil/gas pipeline networks (60 projects with a total pipeline length of 260 km) with various technical characteristics, Drainage Test and DCVG (Direct Current Voltage Gradient) complementary non-destructive indirect methods have been investigated to determine the quality level and identify the location and severity of defects in polyolefin (polyethylene) coatings. The novel concepts and criteria were defined: the quantitative criteria for average specific electrical resistance are established; in addition, a new parameter related to the specific coating defects ratio is introduced, which has been shown to correlate with the criteria for the average specific electrical resistance of the polymer coating and consumed electrical current; finally, following DCVG measurements of the 3LPE coating system, a novel degree of relative defect sizes (%IR) for repairs has been suggested. The innovative and comprehensive approach can support the efforts of regulatory quality assurance, design, maintenance, safety, and research communities to ensure the long-term integrity and sustainability of underground polymer-coated steel pipelines.
Tribocorrosion is one of the main degradation mechanisms affecting metallic components exposed simultaneously to mechanical wear and electrochemical corrosion. In this work, the influence of the Nb/Ti ratio on the tribocorrosion behavior of Fe-Cr-Mo-Nb-Ti multicomponent alloys produced by vacuum arc melting was investigated. The alloys were designed through systematic variations in the relative contents of niobium and titanium to assess their effect on electrochemical stability, wear resistance, and surface degradation. Electrochemical behavior was evaluated by potentiodynamic polarization in a 3.5 wt.% NaCl solution, while tribological and tribocorrosion tests were conducted using a ball-on-disk configuration under controlled conditions. Post-test surface analysis was performed using stereomicroscopy combined with digital image processing, enabling three-dimensional topographical reconstruction of the wear tracks and extraction of quantitative parameters including groove depth, pile-up height, wear track width, and surface roughness. The results demonstrate that the Nb/Ti ratio significantly influences both electrochemical and tribological responses. The alloy with the highest Nb/Ti ratio exhibited the best overall performance, showing the lowest corrosion current density (5.37 & times; 10-8 A/cm2) under static conditions and the lowest wear rate (1.32 mm3/mm2 & centerdot;year), together with the least severe surface degradation, characterized by a groove depth of approximately 7.8 & micro;m and minimal pile-up formation. A progressive deterioration in performance was observed as the Nb/Ti ratio decreased, with the lowest-ratio compositions presenting higher wear severity and surface instability. The AISI 316L reference material exhibited intermediate performance across all evaluated parameters. Overall, increasing the Nb/Ti ratio enhances passive film stability, reduces plastic deformation, and mitigates material removal under tribocorrosion conditions. The incorporation of three-dimensional surface analysis provides a more robust evaluation of wear mechanisms, supporting the design of multicomponent alloys with improved resistance to combined mechanical and electrochemical degradation in aggressive environments.
Models are described for calculating the crack initiation times for Alloy 600 and Type 304 SS in PWR and BWR primary coolant circuits, respectively. In PWRs, initiation is defined in terms of the grain boundary oxidation concept of Scott and Le Calvar, whereas in BWRs, cracks are envisioned to nucleate from corrosion pits. In contrast, in BWRs, we envision cracks to nucleate from corrosion pits, with the difference in the two systems being primarily due to electrochemical factors. Thus, in BWR primary coolant and the absence of hydrogen water chemistry (HWC), the oxidizing conditions due to the radiolytic production of H2O2 cause the ECP to be significantly more positive than the critical pitting potential. Accordingly, the nucleation and growth of pits due to passivity breakdown and the establishment of differential aeration between the pit nucleus’s internal and external environments, which results in growth of pits to the critical size necessary to satisfy the Kondo criteria for transition of a pit into a crack, is judged to be a realistic scenario. Contrariwise, in PWR primary coolant, the ECP is so negative [≈−1.0 Vshe] due to the large amount of pressurizing H2 present in the circuit [20–60 cm3(STP)/kg H2O] that the nucleation and growth of pits is not possible. However, Totsuka and Smialowska found that MA Alloy 600 suffers hydrogen-induced cracking (HIC) at an ECP < −0.85 Vshe, demonstrating that, in service with a high hydrogen concentration, brittle fractures will occur. The initiation sites were not identified. The crack initiation models for Alloy 600 in PWRs and Type 304 SS in BWRs reproduce the effects of the following independent variables: applied stress, temperature, cold work, grain boundary segregations, water chemistry, pH, and electrochemical potential. The origins of the observed scatter in experimentally measured crack initiation times are discussed, and the challenges of developing a more general crack initiation model (GCIM) are identified. From a mathematical viewpoint, the most significant challenge arises from the nested distributions involving the many parameters and expressions within the GCIM that are either distributed because of an imprecise definition or because some experimentally determined input parameters are experimentally scattered. Additionally, the evolution of semi-elliptical surface cracks resulting from the electrochemical crack length (ECL) being shorter than the classical mechanical crack length (MCL) must be incorporated if the GCIM is to find utility in the water-cooled nuclear power industry where semi-elliptical surface cracks are normally observed.
This study investigates the effect of sintering temperature on the hot-corrosion behavior of Ti-6Al-4V alloy in a molten salt environment. Samples were sintered at 800 degrees C, 900 degrees C, 1000 degrees C and 1100 degrees C, then exposed to the Na2SO4-25%NaCl for 300 h at 650 degrees C. The corrosion kinetics were evaluated by measuring the mass change in the specimens, and the results were correlated with their corresponding corrosion rates. The results show that the sintering temperature drives corrosion kinetics by influencing the sample density and grain size. The sample sintered at 900 degrees C shows a low corrosion rate due to its refined microstructure. This refined microstructure provides a high grain boundary density, which serves as a diffusion path and enables the formation of a dense, protective Al2O3-TiO2 layer, as confirmed by XPS. In contrast, the sample sintered at 800 degrees C exhibits high porosity, resulting in an initial weight loss due to molten-salt penetration and evaporation of volatile metal chlorides. The samples sintered at 1000 degrees C and 1100 degrees C exhibit coarsened grains, leading to a thicker, brittle oxide layer and severe delamination, which in turn result in high corrosion rates. The results show that optimizing the sintering temperature to around 900 degrees C would enhance hot-corrosion resistance in salt-contaminated environments.
In this work, an experimental evaluation was performed using four analytical methods applied to electrochemical noise (EN) signals to estimate the corrosion rate (Cr) of reinforced concrete structures. A dataset comprising 10,166 synchronized EN files acquired over approximately 220 days was analyzed. The EN signals were obtained from various natural aqueous media, including seawater and river water, as well as from two laboratory reference media (3.5% NaCl solution and reverse-osmosis water). The Statistical Method (SM), the Fast Fourier Transform (FFT), the Maximum Entropy Method (MEM), and the Stockwell Transform (ST) were used to calculate Cr. The resulting corrosion rates were evaluated using a two-way analysis of variance (ANOVA) with full interaction, followed by Tukey HSD post hoc comparisons. Significant effects were found for both the analytical methods and the exposure media (p<0.001). Among the methods evaluated, MEM showed the greatest statistical stability and robustness, while ST showed the greatest tolerance to noise and the non-stationary characteristics of the EN signals. Estimated corrosion rates ranged from 0.0366 mm/year in reverse-osmosis water (MEM) to 0.2022 mm/year in 3.5% NaCl (MEM). For ST, the corresponding values ranged from 0.0652 mm/year to 0.3504 mm/year in the same media. These results demonstrate that both the analytical method and the corrosive medium significantly influence EN-based corrosion rate estimates and highlight the potential of MEM and ST for long-term corrosion monitoring of reinforced concrete.
This study analyses the behaviour of brass CB773S with extra-low-lead content in relation to corrosion and the corrosion-cavitation phenomenon. Electrochemical corrosion tests, both potentiodynamic and potentiostatic, as well as corrosion-cavitation tests, were conducted. Various potentials were applied to brass, alongside cavitation generated by an ultrasonic bath. Artificial seawater and artificial brackish water were used as electrolytes. Surface damage was evaluated using a stereo microscope and scanning electron microscopy. The results indicate that the interfaces between alpha and beta phases of brass serve as preferential sites for the nucleation and collapse of vapour bubbles under cavitation conditions, leading to a deep pitting, especially in artificial brackish water under this synergy. Susceptibility to a selective corrosion of the Zn-rich phase was observed, highly dependent on the test solution, as well as on the applied potential during the tests. The corrosion-cavitation synergistic damage was strongly dependent on the electrochemical parameters, particularly the applied potential, which plays a key role under cathodic protection conditions. In general, it can be concluded that low-lead brass behaviour is governed by a complex interaction between applied potential, electrolyte chemistry, microstructure, and mechanical effect. These findings provide valuable insights into brass's performance under service conditions where corrosion and cavitation may appear simultaneously in marine environments.
This study proposes a new deep learning-based approach for detecting pitting corrosion on stainless-steel sheet pile surfaces in drainage channels. Conventional ultrasonic thickness measurement methods cannot detect microscopic pitting corrosion that occurs before measurable thickness reduction. The research develops an automated detection system using visible images captured with smartphone cameras and U-net semantic segmentation. Two stainless steel grades (SUS410 and SUS430) were exposed for 5 years to a brackish water environment and analyzed. The deep learning approach achieved F1-scores of 0.831 (SUS410) and 0.808 (SUS430), outperforming binary thresholding methods (F1-scores: 0.407 and 0.329, respectively). Data augmentation improved performance by 1-3 percentage points. The method enabled non-destructive, quantitative assessment of early-stage corrosion using readily available equipment, providing a practical tool for infrastructure maintenance and long-term durability evaluation.
Mild steel remains one of the most widely used structural materials in mechanical and industrial engineering due to its favorable mechanical performance and low cost. However, its high susceptibility to corrosion continues to cause significant operational and economic losses across engineering systems. This study presents a unified analytical framework for analyzing corrosion-related molecular and nanostructured systems using reverse degree-based topological descriptors, namely, the Reverse M-polynomial and Reverse NM-polynomial. The framework is demonstrated in two complementary stages relevant to corrosion engineering. First, an exploratory structure-property correlation analysis based on Quantitative Structure-Property Relationship (QSPR) principles is conducted for furan-based organic inhibitors reported in the literature, examining the relationship between reverse degree-based descriptors and inhibition efficiency on mild steel surfaces. The analysis reveals a strong statistical correlation within the analyzed dataset (r = 0.958), indicating the sensitivity of selected reverse topological descriptors to molecular structural variations. The statistical significance of the correlations was evaluated using p-values and F-statistics, confirming the reliability of the observed associations within the analyzed dataset. However, owing to the limited dataset size, no claims of external predictivity are made. Second, the framework is extended to advanced protective materials through the analytical formulation of reverse descriptors for nanoporous graphene nanoribbons containing 14-annulene pores, focusing exclusively on structural and topological characterization. These graphene structures are considered as potential physical barrier materials; however, in this study, the analysis is limited to structural descriptor characterization without modeling corrosion performance. This work provides analytical results for reverse degree-based descriptors of such graphene architectures. Overall, the findings establish a versatile analytical framework that supports exploratory structure-property investigations of organic inhibitors and provides descriptor-based structural benchmarks for graphene nanostructures, offering theoretical insights relevant to corrosion mitigation research.
Concentrated Solar Power (CSP) tower systems require receiver materials capable of operating above 1000 degrees C to meet the efficiency targets of third-generation technologies (25-30%). Hybrid solutions, combining ceramic coatings with metallic substrates, offer promising thermomechanical stability under severe thermal cycling. This study investigates the high-temperature behavior of silicon carbide (SiC) coatings deposited on Fe-C-Al-Mo alloys under concentrated solar flux. Substrates were pre-oxidized to form a continuous 1-2 mu m alpha-Al2O3 interlayer, serving as a chemical and mechanical buffer. SiC coatings (10-24 mu m thick) were deposited via High-Temperature Chemical Vapor Deposition (HT-CVD). Characterization using XRD, SEM, EDS, and optical spectrophotometry identified cubic 3C-SiC with a globular microstructure and high compressive residual stresses (-2000 to -2400 MPa), inducing microcracking. Stress relaxation was achieved by increasing coating thickness or post-deposition annealing. Controlled oxidation formed a thin silica layer, enhancing solar absorptivity to over 90%. Accelerated thermal cycling (up to similar to 900 kW/m(2), 1050-1200 degrees C) revealed that coating stability depends on SiC thickness, residual stress evolution, alpha-Al2O3 interlayer thickness, and cycling severity. Optimizing these parameters is essential for ensuring the long-term durability of hybrid CSP receivers.
For the corrosion behavior of three extruded Mg alloys (WE43, Mg10Gd, ZX10), the corrosion morphology and the resulting local stress distribution are correlated with the residual strength using & micro;CT, Digital Image Correlation and tensile tests. Samples are corroded in HBSS at 37 degrees C for various exposure times to increase the extent of corrosion. They are then examined by using the gravimetric method to determine the corrosion rate. Corroded tensile samples are subjected to & micro;CT analysis before and after tensile testing. The crack formation originating from pitting corrosion is discussed on the basis of the stress distribution around local corrosion-its extent is clearly influenced on the morphology. & micro;CT analyses reveals that fractures occur in different ways, either at the smallest cross section, at isolated deep pitting sites, or in other critical areas with critical pitting quantity or size. Mg10Gd has a slightly higher strength compared to WE43 and ZX10. ZX10 maintains superior residual strength over time. Pitting corrosion is mainly observed in Mg10Gd and WE43, with different degrees of residual strength. This study allows for a better understanding and prediction of critical areas of non-uniform corroded Mg alloys and provides information on the bearable stress concentration.
This study investigates the corrosion behaviour of a WC-6Co cemented carbide (94 wt% WC, 6 wt% Co) in acidic (pH 2) and alkaline (pH 13) electrolytes used for industrial PVD coating removal. The removal of the coating was not investigated, since no coatings were applied or analysed in this study. The objective was exclusively to simulate the corrosion response of the exposed substrate after the coating had been removed during electrochemical stripping. Potentiodynamic polarisation measurements were performed from OCP -0.2 V to +3 V at a scan rate of 1 mV.s(-1), followed by surface characterisation using SEM/EDS and laser profilometry to identify corrosion mechanisms and quantify material degradation. In an acidic solution, corrosion was dominated by cobalt dissolution, followed by the formation of a W-O-rich corrosion-product layer, as indicated by increased tungsten and oxygen contents in SEM/EDS analyses. The layer became increasingly porous and mechanically unstable at higher potentials. Progressive thickening of the corrosion-product layer and subsequent breakdown resulted in significant material loss, including surface abrasion up to similar to 8 mu m. In alkaline electrolytes, SEM/EDS analyses revealed a Co-O-rich surface layer, suggesting cobalt-containing hydroxide/oxide corrosion products. These results suggest that surface-layer formation on WC-Co does not necessarily provide reliable corrosion protection, as stability and morphology strongly depend on pH. These findings provide valuable guidance for the use of cemented carbides in electrochemical stripping processes for PVD coating removal.
The use of alternative water sources in construction, especially in regions with limited freshwater availability, makes the influence of mixing water composition on the durability of cement mortars a critical issue, particularly under aggressive conditions such as ammonium exposure (XA3). A clear difference in material behavior was observed before and after exposure to an aggressive aqueous environment, highlighting the importance of durability assessment under realistic service conditions. Cement mortar specimens prepared with tap water, distilled water, and modified waters containing Cl-, Ca2+, SO42-, and PO43- ions were tested. The experimental program included flexural and compressive strength, water absorption, and residual properties after exposure to an NH4Cl solution. Statistical analysis was performed using one-way ANOVA, correlation analysis, a heatmap, and PCA. Compressive strength varied within a narrow range (33.85-47.24 MPa), while flexural strength showed larger differences (5.21-10.40 MPa). After exposure, residual flexural strength decreased to 1.16-5.87 MPa and compressive strength to 23.92-37.68 MPa. The most severe degradation was observed for sulfate- and chloride-modified waters. Correlation analysis revealed weak dependence between flexural and compressive strength. ANOVA confirmed a significant influence of water composition (p < 0.05), with the strongest effect observed for residual compressive strength (eta(2) = 0.81). The results demonstrate that mixing water composition is a key factor controlling durability in an XA3 environment. Compressive strength alone is not a reliable durability indicator. Durability is governed primarily by transport properties and microstructure. A multi-parameter approach is required for an accurate durability assessment.
Microbially induced corrosion is a common problem in the petroleum industry. In this study, weight loss and surface analysis of grade 20 carbon steel corrosion witness samples were used to evaluate biocorrosion in produced fluids from different wells (Romashkino oilfield, Republic of Tatarstan, Russia). The structure of the resulting microbial communities in the systems with high corrosion indicators was elucidated. The addition of acetate/lactate, yeast extract, and sulfate was found to promote the growth of individual microorganisms in the designed systems and to increase the corrosion rate in several samples (to an average of 0.12 mm year-1). The results of 16S rRNA gene sequence analysis showed that water from different wells from the Romashkino oilfield had distinct microbial compositions. The main genera in the analyzed waters were Oleidesulfovibrio, Halanaerobium, Proteiniphilum, Acetobacterium, Fusibacter, and Methanocrinis, but their relative abundances depended on the water itself and the type of stimulation. Acetogenic bacteria of the genera Fusibacter, Proteiniphilum, Acetobacterium, and acetoclastic methanogenic archaea Methanocrinis became dominant in the microbial community structure in the acetate-enriched systems in water from one of the studied wells. Electron donors, generated by various bacteria and artificially introduced ones, facilitated active dissimilatory sulfate reduction by Oleidesulfovibrio, Desulfotignum, Desulfocurvus, and Pseudodesulfovibrio in water from another production well. The obtained results are important for identifying the causes of premature failures of oilfield equipment, particularly in areas where microbial enhanced oil recovery is used.
This study quantitatively analyzed rust-streak formation under controlled droplet supply and its relationship with the rust-removed surface profile of the substrate. A NaCl aqueous solution was dropped at a constant flow rate onto SPCC steel plates inclined at 70 degrees to observe the temporal development of the rust streak. Surface line profiles before and after the removal of red rust were measured, and profile changes were quantified relative to the initial surface. Rust layer height hrustx and rust-removed surface profile zr & lowast;x were determined, and their distributions and integrated values were compared. The rust width reached approximately 2.5-3.0 mm, comparable to the droplet diameter under the present conditions. Downstream, rust layer height increased with the extension of test duration, whereas the integrated profile of the rust-removed surface remained relatively small. Rust layer height and rust-removed surface profile were not directly related at each observation position L. These results suggest that rust streak formation within the tested parameter window involves not only locally formed rust but also rust carried from upstream by liquid flow, and indicate that visible rust morphology alone cannot adequately represent substrate-side profile changes under these specific conditions.
Aluminum-lithium (Al-Li) alloys are widely used in aerospace applications because of their high strength-to-weight ratio and reduced density. However, their corrosion behavior can be significantly affected by thermomechanical processing and exposure to chloride-containing environments. In the present study, the corrosion behavior of AA8090-T3 Al-Li alloy was investigated in 3.5 wt.% NaCl solution under simulated marine conditions. The specimens were extracted from a plate and subsequently subjected to annealing and rolling treatments using a specially designed wedge-shaped geometry to generate a continuous strain gradient, enabling the evaluation of deformation-dependent corrosion behavior across different deformation zones. The corrosion behavior was evaluated using potentiodynamic polarization, immersion testing, and surface characterization techniques. The results revealed significant variations in corrosion behavior with thermomechanical condition and deformation zone. The T3 temper-rolled specimen exhibited superior corrosion resistance compared to the annealed and rolled conditions. The lowest corrosion rate of 0.003 mpy was observed for the highly deformed T3 temper-rolled condition, whereas annealed specimens showed higher corrosion susceptibility associated with localized corrosion attack and precipitate-related galvanic activity. Surface characterization confirmed the formation of aluminum hydroxide- and copper oxide-based corrosion products. The study demonstrates the effectiveness of the wedge-shaped rolling methodology for evaluating zone-dependent corrosion behavior in thermomechanically processed AA8090 alloy.
The efficiency of cathodic protection in the tidal zone, in particular in its highest part, remains questionable. To address this problem, experimental vertical structures were designed and set in a commercial seaport. Each structure was composed of 10 cm × 10 cm carbon steel coupons and 50 cm × 10 cm carbon steel strips to obtain a 5.1 m long continuous structure extending all along the tidal zone. Cathodic protection of the structures was carried out with an Al-Zn-In galvanic anode permanently immersed in seawater. The mineral layers formed on the coupons after 32 and 52 months were analyzed by XRD and µ-Raman spectroscopy. The evolution of the mineral layer from the low water zone to the splash zone was due to (i) the decreasing efficiency of the cathodic protection and (ii) the changes in corrosion processes, from those typical of a permanent immersion to those typical of atmospheric corrosion. In particular, brucite Mg(OH)2 was found up to the high tide zone and, in agreement with the estimated degradation of the coupons, its formation was an indicator of the altitude at which the cathodic protection remained efficient.
