Search Results (286)

With the large-scale deployment of high-voltage direct current (HVDC) transmission projects, monopolar ground return operation has increasingly intensified stray current interference risks to adjacent buried metallic pipelines. This study investigates a high-pressure natural gas pipeline project in Guangdong Province by integrating field monitoring, soil resistivity measurements, polarization characterization, and numerical simulations to elucidate the potential distribution characteristics and corrosion evolution mechanisms under stray current influence. The results indicate that under an extreme operating condition of 1980 A, the pipe-to-soil potential shift ranges from −71 V to 69.9 V, significantly exceeding the safety threshold, while the maximum corrosion rate reaches 0.34 mm/y. Based on this, a combined protection system consisting of zinc ribbon drainage, deep-well drainage, and forced current drainage is further proposed. The selected mitigation scheme reduces the maximum corrosion rate to 0.0017 mm/y, demonstrating excellent mitigation performance. The results can provide theoretical and engineering references for the design, protection, and operation of long-distance pipelines in HVDC interference environments. Full article

Compared with traditional Al–Si die-cast alloys, which have good formability and low cost but poor brazeability and inadequate corrosion resistance, high-pressure die-cast (HPDC) Al–RE alloys exhibit superior comprehensive properties. To satisfy the demand for lightweight, high-performance materials in automotive thermal management, a controlled-atmosphere brazing (CAB) furnace was employed in this work to investigate the effect of the complete brazing cycle on the microstructure, mechanical properties, and corrosion resistance of the HPDC Al–RE alloy. In the as-cast state, the eutectic Al₁₁(La,Ce)₃ phase presents a lamellar structure. After the simulated brazing process, this phase transforms into dispersed near-spherical particles. Such microstructural evolution directly determines the mechanical and corrosion behaviors of the alloy. The yield strength and ultimate tensile strength decrease, while the elongation increases substantially owing to the alleviation of stress concentration. The corrosion resistance of the alloy depends on the service environment. After 960 h of neutral salt spray (NSS) testing, the alloy showed excellent corrosion resistance with only slight corrosion. Nevertheless, severe localized pitting corrosion (maximum pit depth: 0.932 mm) was observed after 480 h of sea water acidified accelerated test (SWAAT) exposure. This pitting phenomenon is directly associated with spheroidized Al₁₁(La,Ce)₃ particles. In acidic chloride-containing media, these intermetallic particles undergo preferential anodic dissolution relative to the α-Al matrix, resulting in micro-galvanic corrosion. In conclusion, after simulated brazing treatment, the ductility of the Al–RE alloy is remarkably improved at the cost of a moderate reduction in strength. The Al–RE alloy possesses good corrosion resistance in neutral saline environments. However, severe localized corrosion tends to occur in acidic environments due to the high electrochemical activity of spheroidized intermetallic phases. Full article

The 100 mV depolarization value cathodic protection (CP) criterion is widely used to protect the steel bars in atmospherically exposed concrete structures. The CP on the steel in concrete creates a secondary effect by increasing OH^- ions and decreasing Cl^- ions near the surface of the steel, against steel corrosion. In this phenomenon, there is a possibility that the CP criteria of 100 mV could be decreased due to the environmental changes caused by these secondary effects. In this study, the effects of different depolarization values of 25, 50, and 100 mV for the protection of steel bars in concrete specimens with different chloride ion concentrations were experimentally evaluated, and their effects on the corrosion rate of steel were investigated. The concrete had a water-to-cement ratio of 0.55 and a sand-to-total-aggregate ratio of 49%, and chloride was admixed as NaCl to give Cl⁻ contents of 2, 5 and 10 kg/m³, equivalent to 0.58%, 1.45%, and 2.90% by mass of cement. The steel bars were pre-corroded by an impressed current of 1.33 A/m² and were then protected for 250 days at 20 ± 2 °C and 60% relative humidity, the protection current being adjusted to hold average depolarization values of 21–37 mV, 57–63 mV, and 117–121 mV. After 250 days, the corrosion rate under CP was 0.18–0.95 mA/m², a reduction of 60–77% relative to the unprotected specimens, and raising the target depolarization from 25 mV to 100 mV improved that reduction by only 6–11 percentage points. The measured reduction factor of 2.5–4.3 is far below the factor of 50 predicted by the Tafel relationship for a 100 mV activation polarization, which is attributed to the partly passive state of the steel and to the non-activation components of the 24 h potential decay. Within the exposure conditions tested, a depolarization criterion below 100 mV therefore protected the steel as effectively as the conventional 100 mV criterion while requiring a markedly lower protection current density. Full article

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 (CR_12h). CR_12h 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. Full article

A novel orthophosphate compound, BaNb_0.5In_0.5(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. Full article

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. Full article

In this study, the inhibition efficiency (IE) of symmetrical bis(imino)pyridines (BIPs) used in corrosion protection for zinc and iron was investigated in 0.5 M NaCl (pH 3 and pH 7) and an acidic (1 M HCl) medium using linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Three derivatives, BIP-9, BIP-14 and BIP-16, exhibited the most relevant inhibition performance and acted as mixed-type corrosion inhibitors. In a neutral medium, BIP-16 exhibited the highest IE calculated from EIS, reaching 74.8% on iron and 61.2% on zinc. In 1 M HCl, the highest IE inhibition efficiency was obtained for BIP-9 on iron (93.7%), while BIP-16 and BIP-14 reached 78.8% and 75.1%, respectively. The IE increased with concentration up to an optimum value, while time- and temperature-dependent studies indicated partial loss of protection for individual inhibitor systems and improved long-term protection for the Ce(III) acetate + BIP-16 system, particularly on iron. The highest IE was observed at 25 °C, likely due to inhibitor desorption at higher temperatures. Ce(III) acetate also showed the highest IE for iron in 0.5 M NaCl at pH 3. Adsorption of inhibitors followed the Langmuir model, and calculated parameters indicated spontaneous adsorption with dominant physisorption. DFT calculations supported a medium-dependent inhibition mechanism. Environmental hazard assessment identified BIP-16 as the least hazardous compound with promising eco-friendly potential. Full article

Laser powder bed fusion (LPBF) produces microstructural anisotropy that influences hydrogen transport and passive film stability, yet the mechanistic relationship between build orientation, passive film chemistry, and corrosion behavior remains insufficiently understood. This study investigates how LPBF build orientation governs hydrogen-assisted passive film degradation by correlating electrochemical behavior with passive film chemistry. Additively manufactured 316L stainless steel specimens were fabricated in two build orientations, horizontal (0°) and vertical (90°), and subjected to electrochemical hydrogen charging for durations ranging from 2 to 36 h. Corrosion behavior was evaluated using open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and potentiodynamic polarization (PDP), while X-ray photoelectron spectroscopy (XPS) was employed to characterize hydrogen-induced changes in passive film chemistry. The electrochemical response showed that hydrogen charging progressively reduced the corrosion resistance of both build orientations. However, the degradation exhibited a non-monotonic dependence on charging duration, with intermediate charging durations suggesting transient repassivation before renewed deterioration during prolonged hydrogen exposure. EIS analysis revealed a substantial decrease in the fitted total resistance (R_total = R_ct + R_po), from 1.44 to 0.27 kΩ cm² for the 0° specimens and from 4.23 to 0.55 kΩ cm² for the 90° specimens. Potentiodynamic polarization showed that prolonged hydrogen charging increased the corrosion current density from 20.99 to 98.91 μA cm⁻² for the 0° specimens and from 0.79 to 46.86 μA cm⁻² for the 90° specimens. XPS analysis revealed progressive depletion of protective oxide species (Fe₂O₃, Cr₂O₃, Mo oxides, and lattice oxygen) together with enrichment of hydroxide-rich species, resulting in a lower O²⁻/OH⁻ ratio and transformation of the passive film into a more porous and less protective surface layer. These chemical changes were more pronounced in the 90° build orientation and were consistent with the greater reduction in passive film stability observed from the electrochemical measurements. The combined electrochemical and XPS analyses establish that LPBF build orientation governs hydrogen-assisted corrosion through its influence on microstructural anisotropy, hydrogen transport, passive film chemistry, and the resulting electrochemical response, providing mechanistic insight into the corrosion behavior of additively manufactured 316L stainless steel in hydrogen-containing environments. Full article

External corrosion of buried ferrous water mains remains the dominant driver of structural failure in aging water distribution networks, yet the mechanisms linking soil physical and chemical heterogeneity to corrosion kinetics and product phase evolution have not previously been synthesized into a unified critical framework. This review evaluates three partially competing accounts of electrochemical degradation—anodic dissolution coupled to oxygen reduction within porous rust layers, redox cycling of iron oxide phases driven by seasonal soil moisture fluctuations, and microbially influenced corrosion (MIC) mediated by direct extracellular electron transfer (EMIC) and chemical metabolite pathways (M-MIC)—and assesses the weight of evidence for each. We demonstrate that corrosion products retain electrochemical activity long after formation, functioning as dynamic redox mediators that continue the reactions responsible for their own growth: the reduction of lepidocrocite under anoxic conditions regenerates Fe²⁺ ions that sustain anodic dissolution and catalyze oxygen reduction, while repeated soil moisture cycles drive the irreversible transformation of γ-FeOOH to Fe₃O₄, which fundamentally alters the conductivity and cathodic capacity of the rust layer. The widely cited universal critical-moisture threshold of 65% water-holding capacity (WHC) is evaluated and found to be a single-point approximation contradicted by texture-resolved experimental data that show the critical degree of saturation ranges from S_r ≈ 0.5 in sand to S_r ≈ 0.8 in clay. Modern machine learning analyses of field corrosion databases confirm that chloride content, pH, pipe-to-soil potential, and water content are the four highest-ranked predictors of maximum pit depth, consistent with the mechanistic framework developed here. The classical cathodic depolarization model of SRB-driven corrosion is evaluated against EMIC evidence and found insufficient: measured pure-culture SRB corrosion current densities range from 14 to 135 µA cm⁻², not the milliampere-level values reported in some earlier reviews. An explicit research agenda is proposed to address the five most consequential unresolved mechanistic questions. Full article

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. Full article

Metal guitar strings are essential components whose acoustic performance and durability are compromised by surface degradation, mainly corrosion. This phenomenon directly affects their mechanical properties, limiting their useful life. This study investigated the corrosion behavior and associated mechanical degradation of commercial acoustic guitar strings under accelerated saline exposure. Electrochemical testing, accelerated ageing and frequency sweep testing were combined to assess the evolution of corrosion resistance and apparent dynamic stiffness. The results demonstrate a progressive and substantial loss of stiffness and corrosion resistance in the exposed guitar strings. This study contributes to the understanding and prediction of corrosion-induced degradation in metallic acoustic components. Full article

The article investigates the role of carbon nanomaterials (CNMs), surface-oxidized carbon nanotubes (CNTs) and few-layer graphene fragments (FGFs), as well as FGFs hetero-doped with N and P atoms, as anticorrosive additives in industrial paints based on polyvinyl chloride. All CNMs were characterized by thermogravimetry, transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray photoelectron spectroscopy. Corrosion resistance was determined using electrochemical tests and impedance spectroscopy. The surface and internal 3D structure of steel and coated steel were visualized using laser confocal microscopy and computed tomography. Coatings containing polyvinyl chloride with 0.05 wt% oxidized CNTs or FGFs show the highest electrochemical resistance and the best anticorrosive properties. The corrosion rate for coatings containing CNMs decreases by an average of 5–7 times compared to uncoated steel. It is shown that the improvement in anticorrosive characteristics is determined by the texture parameters and the composition of CNMs. The pores in CNMs act as a reservoir for the electrolyte and increase the corrosion rate. Oxygen-containing surface groups prevent corrosion by increasing the resistance of the materials. Full article

Hydrogen–steel interactions remain a critical concern for the safe deployment of hydrogen–natural gas mixtures in pipeline infrastructures. Thermally grown iron oxides may be a good barrier to hydrogen ingress into the crystalline lattice of pipeline steels, but their actual effectiveness depends strongly on their composition and stability under service conditions. Several experimental approaches have been proposed to investigate the correlation between thermally grown oxides and hydrogen permeation. Among these, electrochemical permeation testing offers a more complex but safer methodology compared to pressurized hydrogen gas tests. However, when the oxide is directly exposed to the charging side (cathodic charging conditions), permeation behaviour often appears comparable to that of bare steel, and rapid oxide degradation occurs. This study introduces an alternative permeation testing configuration that enables direct assessment of thin thermally grown oxides while preserving their structural integrity. By deliberately placing the oxide on the anodic detection side, mechanical removal during hydrogen evolution is suppressed, allowing the intrinsic resistance of the oxide to hydrogen transport to be evaluated. Carbon steel samples were thermally oxidized at 250 °C for controlled exposure times, and the resulting oxide scales were characterized by Raman spectroscopy, revealing variations in hematite and magnetite fractions. Hydrogen permeation was evaluated using a Devanathan–Stachurski cell by positioning the oxidized surface either on the cathodic charging side or on the anodic detection side. Under these conditions, significant variations in apparent steady-state permeation current density were observed as a function of oxidation time and oxide composition. Full article

Pitting corrosion is particularly dangerous due to its localised nature, which can render materials unusable and cause catastrophic failures. It is important to characterise the material in regard to pitting corrosion resistance in order to improve material selection according to the conditions of the exposed environment. Electrochemical tests were carried out to assess pitting corrosion in austenitic stainless steel EN 1.4301. This study identifies the optimal experimental conditions to ensure reliability and reproducibility in electrochemical tests. The results demonstrate the influence of these parameters in evaluating the resistance of stainless steels to pitting corrosion. To ensure the reproducibility of the breakdown potential (Eb), deaeration was standardised using an N₂ flow rate of 0.6–0.8 L/min for 20 min. Furthermore, mechanical agitation at 280 rpm was established as a necessary condition to homogenise the electrolyte and effectively renew the metal/solution interface. Finally, the water flow rate was set at a critical value of 7 mL/h, statistically identified as the most decisive parameter (p < 0.05). This optimisation mitigates crevice corrosion, ensuring that damage nucleation occurs exclusively via a pitting mechanism. Full article

In this work, an experimental evaluation was performed using four analytical methods applied to electrochemical noise (EN) signals to estimate the corrosion rate ($C_r$) 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 $C_r$. 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 $0.0366 \mathrm{mm}/\mathrm{year}$ in reverse-osmosis water (MEM) to $0.2022 \mathrm{mm}/\mathrm{year}$ in 3.5% NaCl (MEM). For ST, the corresponding values ranged from $0.0652 \mathrm{mm}/\mathrm{year}$ to $0.3504 \mathrm{mm}/\mathrm{year}$ 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. Full article