Electrochemical corrosion measurements in viscous, low-conductivity organic media are limited by high cell impedance and parasitic artefacts. This work showcases a robust electrochemical protocol validated in a model bio-oil (MBO, 135 cP) and a more viscous pristine fast pyrolysis bio-oil (P-FPO, 7780 cP) to obtain reliable corrosion kinetic parameters. Established best practices, including open circuit potential (OCP) stabilization, low-amplitude perturbations, and electrochemical impedance spectroscopy (EIS) conductedwithin a charge-transfer-focused frequency window were implemented using a four-electrode cell. Experiments were performed in MBO under three aging systems: Same Solution–Same Electrode (SSSE), Same Solution–
Different Electrode (SSDE), and Different Solution–Different Electrode (DSDE). EIS analysis with a physically motivated equivalent circuit resolved the solution resistance (R_s), charge transfer resistance (R_ct), and EIS-derived polarization resistance (R_p(EIS)), thereby decoupling the contributions of interfacial film growth and bulk-solution aging to the measured resistances. Uncompensated linear polarization resistance (LPR) slopes initially overestimated R_p(LPR) due to the contribution of R_s; after ohmic drop (iR) correction using EIS-derived R_s, R_p(LPR) converged with R_p(EIS), enabling rapid yet quantitative corrosion screening. Cross-comparison between MBO and P-FPO systems confirms that a properly wired four-electrode configuration is essential for quantitative corrosion measurements in highly resistive, highly viscous, polymer-rich organic media, particularly when solution resistance is uncertain.

Hydrothermal liquefaction (HTL) products often contain substantial oxygen, which is conventionally associated with high total acid numbers (TAN), corrosion, and chemical instability. However, certain HTL bio-oils exhibit remarkable stability despite comparable or higher oxygen content relative to pyrolysis oils. Here, we investigate the role of oxygen accessibility, speciation, and molecular integration in governing the corrosion behavior and chemical stability of solid and highly viscous HTL products. Bulk elemental analysis reveals that oxygen content alone is a poor predictor of TAN and corrosivity. It is worth noting that thermogravimetry and chromatography analysis specifically demonstrate a scarcity of low-molecular-weight, volatile oxygenates in HTL products, indicating limited chemical accessibility. Further, solvent extraction experiments reveal that only a minor fraction of oxygenates is accessible, which rather limits their participation in corrosion reactions. These findings support a mechanistic framework in which oxygenated intermediates generated during HTL undergo condensation and structural embedding, suppressing the formation of reactive low-molecular-weight acids. Consequently, HTL products retain high oxygen content while exhibiting low TAN, negligible corrosion, and truly enhanced chemical stability. This study emphasizes that oxygen speciation and molecular integration, rather than total oxygen content, govern the stability of HTL bio-oils, providing a rationale for direct functionalization without extensive deoxygenation.

Carbon capture, utilization and storage (CCUS) is a critical technology for reducing atmospheric greenhouse gas emissions by capturing carbon dioxide (CO₂) emissions from industrial sources and transporting them for utilization or long-term geological storage. However, the captured CO₂ often contains reactive impurities that can accelerate corrosion in transport and storage infrastructure. In particular, water (H₂O) and nitrogen dioxide (NO₂) readily react to form nitric acid, creating highly aggressive corrosion conditions. While the CO₂ is often transported in the supercritical state, pressure reductions at end-use or storage sites can induce phase separation and water condensation. These locations create multi-phase conditions where acid formation and corrosion becomes a concern and emphasizes the need for proper material selection in these areas. This study investigates the initial corrosion behavior of five steels under simulated end-site conditions. Electrochemical corrosion testing in a 0.001 M HNO₃ (100 ppmv NO₂) solution continuously bubbled with CO₂ was performed on X80, 2Cr, 5Cr, P91, and 316L steels using open circuit potential, linear polarization resistance, and potentiodynamic polarization techniques. The chromium (Cr) content of the steels was found to highly influence corrosion resistance with increasing Cr content, reducing the resulting corrosion rate. Overall, X80 had the highest corrosion rate of 0.6 mm/yr, whereas 316L had the lowest corrosion rate of 0.005 mm/yr. Additionally, low Cr steels, particularly 2Cr, displayed unstable corrosion product formation in the linear polarization tests, indicating that small amounts of Cr may be insufficient for proper corrosion protection. The results show that higher-Cr-content steels are better suited for phase-transition regions along CCUS chains. Proper material selection at these critical locations is therefore essential to ensure long-term operational safety and reliability along the CCUS chain.

Duplex stainless steels (DSSs) are widely used in pressure-retaining components due to their high strength, toughness, and corrosion resistance arising from a balanced ferrite–austenite microstructure. However, exposure to inappropriate thermal conditions during fabrication or heat treatment can promote precipitation of intermetallic phases, particularly sigma (σ) phase, which severely degrades fracture toughness and corrosion performance. This study presents a detailed failure investigation of a DSS flange that fractured during hydrostatic pressure testing.

The failure investigation comprised visual examination, fractography, optical microscopy, scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), hardness mapping, ferrite content measurement, Charpy V-notch impact testing, and ASTM G48 corrosion testing. Material traceability records were reviewed to correlate metallurgical observations and property variations across different heat numbers supplied for identical service conditions.

Microstructural analysis revealed extensive sigma phase precipitation along ferrite–austenite interfaces in the failed flange, accompanied by chromium and molybdenum segregation consistent with intermetallic phase formation. Ferrite measurements indicated deviation from the recommended phase balance for DSS. Charpy impact testing showed a pronounced reduction in absorbed energy, confirming severe embrittlement, while ASTM G48 testing demonstrated localized corrosion attack associated with chromium-depleted regions. Fractographic examination revealed chevron patterns characteristic of rapid brittle fracture, with crack initiation associated with sigma-rich embrittled regions and unstable propagation during hydrostatic loading. Comparative assessment across multiple heat numbers demonstrated that these degradations were confined to a single material batch, whereas components from other heats exhibited acceptable microstructure, toughness, and corrosion resistance.

The combined evidence of intermetallic precipitation, microchemical segregation, mechanical embrittlement, corrosion susceptibility, and batch-specific occurrence indicates improper thermal exposure during heat treatment of the affected heat number as the root cause of failure. Sigma phase–induced embrittlement significantly reduced fracture toughness, causing brittle failure during hydrotesting. The findings highlight the critical importance of strict thermal process control, heat number traceability, and phase balance verification.

As a critical vulnerability in the piping systems of energy facilities, the structural integrity of copper–nickel (Cu-Ni) alloy welded joints under microbial environments has garnered significant attention. This study investigates the divergent corrosion behaviors of 90/10 Cu-Ni alloy welded joints induced by sulfate-reducing bacteria (SRB) through simulated experiments, comparing bulk immersion and thin liquid film (TLF) environments. The results demonstrate that under identical SRB inoculation concentrations, the localized corrosion of welded joints is significantly intensified in the TLF environment. Notably, the average depth of intergranular corrosion (IGC) trenches in TLF is approximately 50% greater than that observed in bulk immersion. This acceleration effect is primarily attributed to the restricted diffusion of metabolic products within the confined liquid phase space of the TLF. Mechanistic analysis reveals that despite the strictly anaerobic conditions, the limited volume of the TLF leads to the drastic enrichment of SRB cells and their metabolic sulfides (HS⁻) at the weld metal (WM) and heat-affected zone (HAZ), triggering severe localized MIC. Electrochemical Impedance Spectroscopy (EIS) further confirms that the sulfide-based corrosion product films formed under TLF exhibit higher porosity and lower charge transfer resistance, failing to provide effective passivity. This work elucidates the MIC evolution patterns under the specific service condition of anaerobic thin liquid films, offering a novel perspective for risk identification and integrity management of critical energy infrastructure components.

The co-occurrence of solid deposits and sulfate-reducing bacteria (SRB) poses significant risks of sudden localized failure for copper–nickel alloy infrastructure in complex marine settings. This study systematically investigates the synergistic corrosion mechanisms of B10 alloy beneath four representative deposits with distinct physicochemical properties: insulating silica sand (SiO₂), electroconductive magnetite (Fe₃O₄), semiconductive cuprous sulfide (Cu₂S), and adsorptive kaolin clay. Corrosion kinetics and complex interfacial electrochemical processes were monitored over long-term exposure using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and Tafel polarization. Furthermore, the severity of localized attack and denickelification was quantified via 3D laser confocal microscopy, SEM, and EDS analysis. The results demonstrate that the presence of deposits acts as a critical diffusion barrier, entrapping aggressive biogenic sulfides and triggering severe localized acidification and occluded cell effects at the metal/deposit interface. Crucially, conductive deposits such as Fe₃O₄ and Cu₂S were found to significantly accelerate cathodic depolarization by increasing the effective cathodic surface area and promoting robust galvanic coupling between the covered and bare metal regions. Meanwhile, kaolin clay exhibited a pronounced "synergistic protection" for SRB colonies by effectively adsorbing released Cu²⁺ ions, thereby mitigating their inherent biocidal effect and fostering robust biofilm development beneath the deposit layer. This research delineates how different deposit types modulate interfacial charge transfer, metabolic byproduct accumulation, and ion migration to accelerate the degradation of Cu-Ni alloys. These findings provide a comprehensive theoretical framework and practical data support for the durability assessment and corrosion mitigation of marine engineering materials under multispecies fouling conditions.

With the intensification of global warming, controlling CO₂ emissions has become a consensus within the international community. CCUS (Carbon Capture, Utilization, and Storage) technology is recognized as one of the critical pathways to achieve the dual carbon goals of 'carbon peaking and carbon neutrality'. Statistics indicate that coal-fired power plants in China contribute over 35% of the total CO₂ emissions. The amine-based CO₂ capture technology has been widely adopted due to its advantages of high absorption capacity and relatively low regeneration energy consumption. However, flue gas typically contains SO₂ in addition to CO₂. When SO₂ dissolves in amine solutions, it rapidly hydrolyzes to form HSO₃⁻ and SO₃²⁻. These sulfur-containing species exert a significant influence on the nucleation and growth processes of corrosion product films, triggering accelerated corrosion of carbon steel in equipment such as absorption towers and circulation pipelines. In this study, immersion experiments were conducted to investigate the influence of SO₂ on film evolution, as well as the organizational structure of the films at different stages. By employing techniques including weight loss testing, in situ electrochemistry, SEM,EDS, and XPS, this paper clarifies the structural characteristics, evolution, and corrosion behavior of corrosion products under SO₂-containing conditions, and elucidates the underlying mechanisms.

Introduction

Developing corrosion-resistant and conductive coating coatings is essential to promote the application of metal bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs). This report summarizes the research achievements of our group over the past decade, covering metal substrates, nitrides coatings, precious metal coatings, and specifically, oxide coatings and amorphous carbon/metal (a-C/Me) composite coatings.

Methods

To balance performance and costs, C/Ti, ML-C/Ti and ML-C/Cr coatings were designed via introducing transition layers and designing alternating multilayer structures.

Results

The multiple diffusion interfaces optimize the potential distribution to improved transpassivation potential (E_tp). In particular, the E_tp of ML-C/Ti coating was 1.6 V and offered full protection for BPs. However, the a-C layer and heterogeneous interfaces are prone to dissolution at high potentials. Significantly, to overcome the decline in conductivity induced by corrosion at high potentials, the developed oxide coatings firstly verified the effectiveness of “controllable oxidation”. The oxide coatings include ZrN_xO_y, TiN_xO_y and AO-C coatings, via oxygen plasma, heat treatment and in situ polarization, respectively. Band bending theory analysis reveals that the oxides with wider band gaps mitigated further oxidation during polarization. Notably, the AO-C layer effectively decreased the adsorption energy of corrosive ions. Combined with the electron tunneling effect through the nanoscale oxide layer, AO-C/Ti coating realized repelling corrosive ions while reserving electron conduction.

Conclusions

Since excessive oxides damage conductivity, determining the optimal content of O to achieve a balance performance is critical.

Pipe steels after long-term operation under the combined influence of anti-corrosion protection and mechanical stress may demonstrate property degradation, which leads to a deterioration in their service characteristics.

Comparative studies of stress-corrosion cracking of the parent metal of a main gas pipeline with a diameter of 1020 mm made of X60 steel after operation for 50 years, from an undamaged section and a section where a fracture site was detected, were conducted. Investigations were carried out in an NS4 solution under cathodic polarization. Spectrometry, optical metallography, mechanical testing, the slow-rate test method, and scanning electron microscopy methods were used.

The study’s results established that the mechanical properties of undamaged and damaged pipes are at the level of the values specified in the pipe certificates. The microstructure is typical for the steel manufactured in the XX century—ferritic–pearlitic with fine ferrite grains (20-25) microns in size. The share of the pearlite component was 50-60% and is approximately the same for both pipes.

The susceptibility to stress-corrosion cracking was estimated by the dimensionless coefficient K_S, which was calculated as the ratio of the relative narrowing of the specimens in air to the relative narrowing in the solution.

K_S for the metal of an undamaged pipe at the polarization potential range from -0.75 V to -1.05 V (relative to the saturated silver chloride electrode) in NS4 increases from 1.14 to 1.18. For specimens of damaged pipe, the maximum K_S value of 1.5 is observed at -0.75 V, and it decreases to 1.27 at -1.05 V. It was found that specimens of damaged pipe demonstrated higher maximum stress, lower relative elongation, and relative narrowing at the potential of -1.05 V than specimens from an undamaged pipe. Such patterns may be due to pipe deformation during the accident and the influence of local anodic dissolution.

Stress corrosion cracking (SCC) is a critical degradation process in structural materials exposed to service-relevant environments, yet the mechanisms governing early stages of crack development remain insufficiently understood. In this work, the early-stage SCC behavior of pipeline steels exposed to groundwater environments is investigated. Emphasis is placed on the initiation and evolution of surface cracks prior to the onset of steady-state crack growth. Experimental observations indicate that early-stage crack growth is not dominated by the random nucleation and coalescence of independent microcracks, but is instead strongly influenced by localized deformation and environmental interactions within the plastic zone ahead of existing surface cracks. Under load-controlled conditions, transient increases in the local strain rate may arise from material yielding behavior or the exhaustion of time-dependent deformation processes, promoting surface film rupture and localized dissolution. Consequently, new microcracks preferentially form near the surface and subsequently link with the main crack, leading to crack extension primarily along the surface direction while crack depth remains limited. This process progressively increases the stress intensity factor at the crack tip in the depth direction and facilitates the transition to rapid crack growth. These findings highlight the importance of early-stage deformation behavior and localized electrochemical activity in controlling SCC evolution and suggest that mitigating early crack growth may significantly extend the service life of structural materials operating under conditions conducive to SCC.