Search Results (167)

Corrosion fatigue damage significantly affects the long-term service of marine platforms such as propellers. Fatigue testing of pre-corrosion specimens is essential for understanding damage mechanisms and accurately predicting fatigue life. However, traditional seawater-based tests are time-consuming and yield inconsistent results, making them unsuitable for rapid evaluation of newly developed equipment. This study proposes an accelerated corrosion testing method for ZCuAl₈Mn₁₃Fe₃Ni₂ nickel–aluminum bronze, simulating the marine full immersion zone by increasing temperature, adding H₂O₂, reducing the solution pH, and preparing the special solution. Coupled with the fatigue test of pre-corrosion specimens, the corrosion damage characteristics and their influence on fatigue performance were analyzed. A numerical simulation method was developed to predict the fatigue life of pre-corrosion specimens, showing an average error of 13.82%. The S–N curves under different pre-corrosion cycles were also established. The research results show that using the test solution of 0.6 mol/L NaCl + 0.1 mol/L H₃PO₄-NaH₂PO₄ buffer solution + 1.0 mol/L H₂O₂ + 0.1 mL/500 mL concentrated hydrochloric acid for corrosion acceleration testing shows good corrosion acceleration. Moreover, the test methods ensure accuracy and reliability of the fatigue behavior evaluation of pre-corrosion specimens of the structure under actual service environments, offering a robust foundation for the material selection, corrosion resistance evaluation, and fatigue life prediction of marine structural components. Full article

Antifouling coatings are integral to the maritime economy. The efficacy of the applied painting system is closely correlated with susceptibility to fouling and the adhesion strength of contaminants. A fouled hull might result in an elevated fuel consumption and journey expenses. Biofouling on ship hulls also has detrimental environmental consequences due to the release of biocides during maritime travel. Therefore, it is imperative to develop eco-friendly antifouling paints that inhibit the robust adhesion of marine organisms. This study aimed to assess a biocide-free antifouling coating formulated with polymers intended to diminish molecular adhesion interactions between marine species’ adhesives and the coating. The evaluation included laboratory corrosion experiments in artificial seawater and the immersion of samples in a marine environment in Attica, Greece, for varying durations. The research indicates that an antifouling coating applied to naval steel in an artificial seawater solution improves corrosion resistance by more than 60%. The conductive polymer covering, comprising polyaniline and graphene oxide, diminishes corrosion current values, lowers the corrosion rate, and enhances corrosion potentials. The impedance parameters exhibit analogous behavior, with the coating preventing water absorption and displaying corrosion resistance. The coating serves as a low-permeability barrier, exhibiting exceptional durability for naval steel over time, with an operational performance up to 98%. Full article

Prefabricated unidirectional carbon fiber reinforced polymer (CFRP) composite strips are extensively used as a means of infrastructure rehabilitation through adhesive bonding to the external surface of structural concrete elements. Most data to date are from laboratory tests ranging from a few months to 1–2 years providing an insufficient dataset for prediction of long-term durability. This investigation focuses on the assessment of the response of three different prefabricated CFRP systems exposed to water, seawater, and alkaline solutions for 5 years of immersion in deionized water conducted at three temperatures of 23, 37.8 and 60 °C, all well below the glass transition temperature levels. Overall response is characterized through tensile and short beam shear (SBS) testing at periodic intervals. It is noted that while the three systems are similar, with the dominant mechanisms of deterioration being related to matrix plasticization followed by fiber–matrix debonding with levels of matrix and interface deterioration being accelerated at elevated temperatures, their baseline characteristics and distributions are different emphasizing the need for greater standardization. While tensile modulus does not degrade appreciably over the 5-year period of exposure with final levels of deterioration being between 7.3 and 11.9%, both tensile strength and SBS strength degrade substantially with increasing levels based on temperature and time of immersion. Levels of tensile strength retention can be as low as 61.8–66.6% when immersed in deionized water at 60 °C, those for SBS strength can be 38.4–48.7% at the same immersion condition for the three FRP systems. Differences due to solution type are wider in the short-term and start approaching asymptotic levels within FRP systems at longer periods of exposure. The very high levels of deterioration in SBS strength indicate the breakdown of the materials at the fiber–matrix bond and interfacial levels. It is shown that the level of deterioration exceeds that presumed through design thresholds set by specific codes/standards and that new safety factors are warranted in addition to expanding the set of characteristics studied to include SBS or similar interface-level tests. Alkali solutions are also shown to have the highest deteriorative effects with deionized water having the least. Simple equations are developed to enable extrapolation of test data to predict long term durability and to develop design thresholds based on expectations of service life with an environmental factor of between 0.56 and 0.69 for a 50-year expected service life. Full article

Hydrogel sensors show unique advantages in underwater detection, ocean monitoring, and human–computer interaction because of their excellent flexibility, biocompatibility, high sensitivity, and environmental adaptability. However, due to the water environment, hydrogels will dissolve to a certain extent, resulting in insufficient mechanical strength, poor long-term stability, and signal interference. In this paper, a double-network structure was constructed by polyvinyl alcohol (PVA) and poly([2-(methacryloyloxy) ethyl]7 dimethyl-(3-sulfopropyl) ammonium hydroxide) (PSBMA). The resultant PVA/PSBMA-PA hydrogel demonstrated notable swelling resistance, a property attributable to the incorporation of non-covalent interactions (electrostatic interactions and hydrogen bonding) through the addition of phytic acid (PA). The hydrogel exhibited high stretchability (maximum tensile strength up to 304 kPa), high conductivity (5.8 mS/cm), and anti-swelling (only 1.8% swelling occurred after 14 days of immersion in artificial seawater). Assembled as a sensor, it exhibited high strain sensitivity (0.77), a low detection limit (1%), and stable electrical properties after multiple tensile cycles. The utilization of PVA/PSBMA-PA hydrogel as a wearable sensor shows promise for detecting human joint movements, including those of the fingers, wrists, elbows, and knees. Due to the excellent resistance to swelling, the PVA/PSBMA-PA-based sensors are also suitable for underwater applications, enabling the detection of underwater mannequin motion. This study proposes an uncomplicated and pragmatic methodology for producing hydrogel sensors suitable for use within subaquatic environments, thereby concomitantly broadening the scope of applications for wearable electronic devices. Full article

This study provides a systematic comparison of three types of phosphate coatings, applied by identical immersion phosphating processes and tested under two different environmental conditions representative of real industrial scenarios. The focus of this study is the investigation of the corrosion behaviour of zinc, magnesium, and manganese phosphate coatings on reinforcing steel in two different corrosion environments: river water and seawater. The phosphate coatings were obtained via the immersion phosphating technique. Various techniques, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), potentiodynamic polarization curve (PDP) testing, and electrochemical impedance spectroscopy (EIS), were used to evaluate the morphology and corrosion resistance of the coatings. The overall corrosion protection performance of the coatings followed the order of Zn phosphate > Mn phosphate > Mg phosphate. The results indicate that the samples with the Zn-phosphated coating showing the highest improvement. This coating showed no major morphological changes and achieved significantly reduced corrosion rates—0.258 µm/year in river water and 3.060 µm/year in seawater—compared to the typical corrosion rate of uncoated steel, which is about 45 µm/year. These findings emphasize the effectiveness of Zn phosphate coatings in mitigating corrosion in both river water and marine conditions. Full article

This study involved covering naval steel samples with a biocide-free, innovative antifouling coating, which were subsequently immersed in either artificial seawater or a Greek maritime environment for durations ranging from 1 to 50 weeks. The objective was to assess the efficacy of the coating as an anticorrosion and antifouling barrier on the steel samples. Non-coated samples were analyzed alongside the coated samples for comparative purposes. The findings indicate that a reduction in coating thickness during static immersion in laboratory settings leads to the removal of precipitated corrosion products, exposing a fresh layer of “pristine” coating. This layer decreases the corrosion rate by almost 90% throughout extended immersion durations. The efficacy of the coating is validated through trials conducted in natural maritime environments, demonstrating an operational performance of 99% for the coated samples after 50 weeks of continuous exposure to seawater. In fact, the coated samples showed only soft fouling, in contrast to the uncoated samples which were characterized by a strong presence of hard fouling within a short period of time after immersion. Full article

The corrosion behavior of Inconel 718 alloy, developed through two different methods—forging (S1) and additive manufacturing (S2)—was evaluated in a seawater environment, and the results were compared with those of Inconel 825 alloy (S3). The corrosion performance of the alloys was examined according to ISO 8044/2024, using open circuit potential (OCP), potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS), in natural seawater at 25 °C over an extended immersion period. After 5000 h of immersion, the corrosion rate (R_corr) estimated from anodic polarization tests was found to be lower for the wrought Inconel 718 alloy (1.21 µm y⁻¹) compared to the wrought 825 alloy (4.1 µm y⁻¹) and to the SLM Inconel 718 alloy (35.1 µm y⁻¹), indicating high corrosion resistance for wrought Inconel 718. A morphological analysis of the alloy’s surface conducted using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed a continuous, compact film with localized salt deposits on wrought Inconel 718 and Incoloy 825. In contrast, SLM Inconel 718 exhibited a porous, inhomogeneous film, leading to reduced protective capabilities and lower corrosion resistance. The results demonstrate that wrought Inconel 718 exhibits excellent corrosion resistance in seawater, making it a promising alloy for marine applications. Full article

Wave gliders’ power system shafts face complex conditions. To enhance their operational stability, it is crucial to study PTFE, a polymer material that could replace traditional metals. This study added carbon fiber (CF), titanium carbide (Ti-C), and both to a PTFE matrix. The impact of seawater immersion on water absorption and the mechanical properties was examined, as well as friction and wear characteristics under constant amplitude cyclic (CAC) loading and seawater lubrication. The results indicated that while Ti-C boosts PTFE matrix hardness, its poor binding with the PTFE matrix leads to high water absorption in Ti-C/PTFE (PTFE-3), causing a significant decrease in the mechanical properties post-immersion and poor friction and wear performance. In contrast, CFs and the PTFE matrix have good interfacial bonding and greatly improve the resistance of the PTFE matrix to cyclic loading and seawater immersion. Therefore, CF/PTFE (PTFE-2) shows good mechanical and tribological properties. Moreover, incorporating a certain amount of CFs into Ti-C enhances its adhesion to the PTFE matrix, reducing the occurrence three-body wear and allowing Ti-C to fully utilize its high hardness. Thus, the combination of Ti-C and CFs markedly improves PTFE’s mechanical and tribological properties under cyclic loading and in seawater. Full article

This study utilized tetramethylammonium hydroxide (TMAH) as a substitute for traditional catalysts and successfully incorporated platinum octaethylporphyrin (PtOEP) into SiO₂ nanoparticles (PtOEP@SiO₂) via the Stöber method. Methyl silicone resin was employed as the matrix material, and a drop-coating technique was applied to fabricate thin films of PtOEP@SiO₂ particles for dissolved oxygen (DO) sensing in seawater. By optimizing the concentrations of TMAH and PtOEP, a highly sensitive oxygen-sensing film with a quenching ratio (I₀/I₁₀₀) of 28 was ultimately developed, with a wide linear detection range (0~20 mg/L, R² = 0.994). Stability tests revealed no significant performance degradation during five oxygen–nitrogen cycle tests. After 30 days of immersion in East China Sea seawater, the quenching ratio decreased by only 6%, confirming its long-term stability and excellent resistance to ion interference. This research provides a novel strategy for developing highly reliable in situ marine DO sensors. Full article

Mineral admixtures exhibit significant enhancement effects on the seawater corrosion resistance of sulfoaluminate cement (SAC). This study systematically investigates the influence mechanisms of fly ash (FA), silica fume (SF), and slag powder (SP) on the physicochemical properties of SAC-based materials. Experimental results demonstrate that FA effectively enhances the fluidity of fresh SAC paste while mitigating drying shrinkage. Under standard curing conditions, the compressive strength of SAC mortar decreases with increasing FA content, reaching optimal performance at a 5% replacement level. However, in seawater immersion environments, FA undergoes chemical activation induced by seawater ions, leading to a positive correlation between mortar strength and FA content, with the 10% replacement ratio demonstrating maximum efficacy. SF addition reduces workability but significantly suppresses shrinkage deformation. While exhibiting detrimental effects on flexural strength under standard curing (optimal dosage: 7.5%), a 5.0% SF content manifests superior seawater resistance in marine environments. SP incorporation minimally impacts mortar rheology but exacerbates shrinkage behavior, showing limited improvement in both standard-cured compressive strength and seawater corrosion resistance. Orthogonal experimental analysis reveals that SF exerts the most pronounced influence on SAC mortar fluidity. Both standard curing and seawater immersion conditions indicate FA as the dominant factor affecting mechanical strength parameters. The optimal composite formulation, determined through orthogonal combination testing, achieves peak compressive strength with 5% FA, 5% SF, and 5% SP synergistic incorporation. Full article

The ongoing development of maritime powers has driven markedly growing requirements for novel naval and civilian vessel categories in recent years. The import temperature of gas turbines is rising, and the issue of corrosion can no longer be ignored, creating an urgent need to develop coatings with high-temperature resistance, corrosion resistance, and good toughness. This study utilized plasma spraying technology to prepare composite AT13 ceramic coatings with 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% GO/Cu (GO:Cu = 1:10) content. It systematically investigated the effects of GO/Cu doping on the porosity, Vickers hardness, fracture toughness, thermal shock resistance, and corrosion resistance of the AT13 coatings while exploring the corrosion behavior of the composite coatings. The experimental results indicate that doping with GO/Cu can effectively fill the pores of the coatings, leading to an overall improvement in coating performance. The coating with 10 wt.% doping (G2) exhibited the best comprehensive performance, with a 72% reduction in porosity compared to the original coating, a 23.2% increase in Vickers hardness, a 31.4% enhancement in fracture toughness, and an 83% decrease in corrosion rate. It also demonstrated the best thermal shock resistance, maintaining a relatively intact surface after 31 days of immersion in artificial seawater, with only a few pitting and cracking defects observed in the areas of corrosion. Full article

To address the protective demands of marine engineering equipment in complex corrosive environments, this study proposes an environmentally friendly composite coating based on carboxylated graphene oxide (CGO)-modified water-based epoxy organosilicon resin. By incorporating varying mass fractions (0.05–0.25%) of CGO into the resin matrix via mechanical blending, the microstructure, corrosion resistance, and long-term corrosion kinetics of the coatings were systematically investigated. The results demonstrate that the coating with 0.15 wt.% CGO (designated as KCG15) exhibited optimal comprehensive performance: its corrosion current density (I_corr = 4.37 × 10⁻⁸ A/cm²) was two orders of magnitude lower than that of the pure resin coating, while its low-frequency impedance modulus (∣Z∣_0.1Hz = 4.99 × 10⁶ Ω⋅cm²) is significantly enhanced, accompanied by improved surface compactness. The coating achieved a 97% inhibition rate against sulfate-reducing bacteria (SRB) through synergistic physical disruption and electrostatic repulsion mechanisms. Long-term corrosion kinetics analysis via 60-day seawater immersion identified three degradation phases—permeation (0–1 day), blockage (1–4 days), and failure (7–60 days)—with structural evolution from microcrack networks to foam-like blistering ultimately reducing by 97.8%. Furthermore, a 180-day atmospheric exposure test confirms the superior weatherability and adhesion of the KCG15 coating, with only minor discoloration observed due to its hydrophobic surface. This work provides theoretical and technical foundations for developing marine anti-corrosion coatings that synergize environmental sustainability with long-term protective performance. Full article

The global demand for liquefied natural gas (LNG) has led to a significant increase in the number of LNG carriers (LNGCs), consequently elevating the risk of operational accidents. Unlike conventional vessels, LNGCs present a high risk of fire and explosion and involve extensive repair times and costs due to the complex structure of the cargo containment system (CCS). This study investigates the effects of seawater exposure on the uni-axial compressive properties of plywood used in LNGC CCS structures, with the goal of establishing material strength criteria that could reduce repair requirements. The analysis focuses on the NO96 CCS, which incorporates the highest volume of plywood among existing designs. In this configuration, compressive strength is a critical design parameter. Therefore, the mechanical response of plywood was evaluated under both room temperature and cryogenic conditions (−163 °C), simulating the LNG operating environment. The results demonstrate that plywood exhibited increased compressive strength after three hours of seawater and saltwater immersion, although the rate of improvement diminished with extended exposure. In contrast, specimens immersed in distilled water showed a consistent reduction in compressive strength. Furthermore, cryogenic temperatures significantly enhanced the compressive strength compared to ambient conditions. This study establishes a methodology for assessing the mechanical performance of plywood under marine and cryogenic conditions, contributing to its reliable application in LNG carrier structures. Full article

The corrosion behavior was investigated for three Al-Mg aluminum alloys (i.e., 5052, 5083 and 5182 aluminum alloys) with different alloying contents in 3.5 wt.% NaCl solution at 35 °C by means of potentiodynamic polarization, electrochemical impedance spectroscopy, immersion test, X-ray photoelectron spectroscopy and microscopy techniques. All alloys spontaneously passivate in the test solution, but the pitting corrosion takes place at the intermetallic phases during the long-term immersion test. The comparative analyses indicate that more Mg and less Cr in aluminum alloys result in increases in the passive current density and the pit depth and decreases in the polarization resistance, the pitting potential and the ratio of Al₂O₃/Al(OH)₃ in the product film. However, the differences in the pitting potentials of the three aluminum alloys are smaller than approximately 22 mV. Their pit depth values are less than 110 μm after 120 days of immersion. The three aluminum alloys have relatively high corrosion resistance in the simulated seawater solution. Full article

This research aims to evaluate the effectiveness of protective coatings in preventing the corrosion of steel in the marine environment. Electrochemical tests were performed on S355JR steel immersed in natural seawater (Black Sea, Port Constanta) over a period of 22 weeks, using electrochemical techniques such as the evolution of the open circuit potential (OCP) and linear polarization resistance to calculate R_p and the corrosion rate (V_corr). The investigated steel surfaces included (a) S355JR steel blasted with Al₂O₃, (b) S355JR steel blasted and coated with epoxy primer enriched with zinc, (c) S355JR steel blasted and coated with epoxy primer and polyurethane paint, and (d) S355JR steel blasted and subsequently coated with epoxy primer and then polyurethane paint to which kreutzonit particles had been added. The proportion of kreutzonit particles added to the polyurethane paint was 2 wt% of the total mass of the paint. Subsequently, the samples were subjected to morphological analyses and cross-sectional analysis by scanning electron microscopy (SEM), topographical characterization (roughness and microhardness), and structural assessments (FTIR and XRD), as well as an analysis of hydrophobicity (contact angle). The results of this study revealed significant differences in corrosion behavior between the different surfaces and coatings tested. Electrochemical analysis revealed that the coating with epoxy primer and polyurethane paint to which kreutzonit particles had been added provided the best corrosion protection in the marine environment during immersion. Full article