Search Results (441)

This study investigates the mechanical degradation of HRB400 corroded reinforcing steel induced by corrosion and introduces a tailored constitutive model to capture the influence of mass loss ratios. A series of tensile tests were conducted following chloride-driven wet–dry cycles combined with a simulated marine corrosion environment, enabling the quantification of the relationship between mass loss ratios and mechanical performance. A degradation equation based on mass loss ratios was derived and benchmarked against both experimental data and the existing Hooputra’s Ductile Damage (HDD) model. The proposed equation achieved approximately 80% accuracy in predicting strength reduction across varying corrosion levels. A finite element model incorporating the HDD framework was developed to simulate tensile failure, successfully capturing key degradation characteristics, including reduced yield strength, diminished ductility, and a shortened yield plateau. Unlike other models, it maintained high predictive accuracy even under severe corrosion. These findings demonstrate the model’s potential for structural analysis and reinforcement design in corrosion-prone environments. Full article

The increasing demand for lightweight, high-performance materials in marine and offshore engineering has driven the development of hybrid solutions combining metals and composites. This study investigates the stress corrosion cracking (SCC) and tribocorrosion behaviour of a novel hybrid wire consisting of a superaustenitic stainless steel (6Mo) outer shell and a carbon fibre-reinforced polymer (CFRP) core. Microstructural analysis, residual stress measurement, and corrosion testing were performed to assess the integrity of the welded structure under harsh conditions. The results revealed that residual stresses and interdendritic segregation in the weld zone significantly contribute to SCC susceptibility, while the 6Mo steel showed improved corrosion resistance over 316L under tribocorrosion conditions but was more sensitive to the sliding frequency. These findings provide critical insights into the degradation mechanisms of metal composite hybrid wires and support the future design of corrosion-resistant components for offshore and structural applications. Full article

In Arctic regions, ship structures face low temperatures, overloads, thickness effects, and fluctuating stress ratios, which significantly influence the fatigue crack growth (FCG) behavior of marine steels. This study investigates the FCG behaviors of DH36 steel by a series of experiments under the combined effects of low temperatures, overload ratios R_ol, specimen thickness B, and stress ratios R. Experiment results show that the yield strength, ultimate tensile strength, and elastic modulus of DH36 steel exhibit negative correlations with temperature varying within the Arctic temperature range. A reduction in fatigue crack growth rate (FCGR) is observed under the combined effects of low temperature and overload, and the magnitude of decrease shows a positive correlation with R_ol. Notably, low temperatures weaken the FCG retardation effect induced by overload, and this attenuation becomes more pronounced as temperature decreases. Under low temperatures, while maintaining constant peak load, increasing R significantly reduces both initial and terminal stress intensity factor ranges ΔK₀ and ΔK_e, resulting in diminished effective crack driving force and thereby substantially extending FCG life. Although increased B enhances FCGR at low temperatures, thinner plates demonstrate shorter FCG life due to their higher ΔK₀ values. Full article

Marine engineering thick plates are essential structural materials for large vessels and offshore platforms, and optimizing their manufacturing processes is critical for advancing marine equipment. This study examined the microstructural and property variations in 120 mm-thick S460 plates fabricated by thermo-mechanical controlled processing (TMCP). A finite element model was developed to simulate the cooling phase, enabling the prediction of the internal cooling path in the thick plate. An optimized cooling scheme was proposed, which was validated against the model and implemented. The following key results were obtained: (1) Under the initial cooling parameters (initial temperature: 715 °C, duration: 130 s), the 60 mm depth toughness was severely compromised, as evidenced by a low −40 °C impact energy of 59 J, significantly lower than values observed at the10 mm and 30 mm depth positions. Microstructural analysis revealed that the 60 mm depth region was dominated by ferritic bainite and pearlite, with a pearlite content of 8.7%. Numerical simulations further indicated a 60 mm depth cooling rate of 1.10 °C/s under these conditions. (2) Model predictions confirmed the original 60 mm depth cooling rate of 1.10 °C/s. The optimized process increased the initial cooling temperature to 725 °C and extended the cooling time to 160 s, achieving an enhanced 60 mm depth cooling rate of 1.36 °C/s. (3) The optimized process remarkably improved the 60 mm depth impact energy to 144 J, achieving near-complete elimination of pearlite, increased granular bainite content, refined M-A constituent size, and enhanced density of high-angle grain boundaries. This study demonstrates that enhancing internal temperature gradients and prolonging cooling durations can effectively inhibit microstructural degradation in 60 mm depth regions of thick plates, providing both theoretical foundations and practical methodologies for optimizing TMCP processes of extra-thick steel plates. Full article

This study presents a novel approach to fabricating magnetic sponge-like composites by melting various types of steel onto three-dimensional (3D) carbonized spongin scaffolds under extreme biomimetic conditions. Spongin, a renewable marine biopolymer with high thermal stability, was carbonized at 1200 °C to form a turbostratic graphite matrix capable of withstanding the high-temperature steel melting process (1450–1600 °C). The interaction between molten steel vapors and the carbonized scaffolds resulted in the formation of nanostructured iron oxide (primarily hematite) coatings, which impart magnetic properties to the resulting composites. Detailed characterization using SEM-EDX, HRTEM, FT-IR, and XRD confirmed the homogeneous distribution of iron oxides on and within the carbonized fibrous matrix. Electrochemical measurements further demonstrated the electrocatalytic potential of the composite, particularly the sample modified with stainless steel 316L—for the hydrogen evolution reaction (HER), offering promising perspectives for green hydrogen production. This work highlights the potential of extreme biomimetics to create functional, scalable, and sustainable materials for applications in catalysis, environmental remediation, and energy technologies. Full article

Marine steel structures face severe corrosion risks due to harsh environmental conditions, posing significant logistical, economic, and safety challenges for inspection and maintenance. Traditional corrosion assessment methods are costly, labor-intensive, and potentially hazardous. This study evaluated the capabilities of visible-to-near-infrared hyperspectral imaging (HSI) for automating corrosion detection and severity classification in steel samples subjected to accelerated corrosion conditions simulating marine exposure. Marine steel coupons were partially coated to simulate protective paint and immersed in natural brackish water from the Panama Canal, creating varying corrosion levels. Hyperspectral images were acquired in controlled illumination conditions, calibrated radiometrically, and reduced in dimensionality via principal component analysis (PCA). Four machine learning models, including k-nearest neighbors, support vector machine, random forest, and multilayer perceptron, were tested for classifying corrosion severity. The multilayer perceptron achieved the highest accuracy at 96.18%, clearly distinguishing among five defined corrosion stages. These findings demonstrate that hyperspectral imaging, coupled with machine learning techniques, provides a viable, accurate, non-destructive methodology for assessing marine steel corrosion, potentially reducing costs, improving safety, and streamlining maintenance procedures. Full article

Over the years, artificial reefs with diverse forms and functions have become increasingly important in maritime engineering and ecosystem restoration plans, with socio-economic and ecological impacts on marine ecosystems. However, due to the increasing complexity of designs and durability requirements, the current structural design approaches lack adequate documentation and standardization. This work addresses this challenge by detailing an engineering-driven approach for the structural design of artificial reef structures made of reinforced concrete or composite steel and concrete. This study establishes the premises for the structural design, followed by the quantification of actions based on standards and recommendations for marine structures. Hydrodynamic and numerical models were utilized to assess the effects of these actions on the structure. A cross-section organic design was then implemented, followed by a parametric study exploring various structural and material combinations for optimization. This study validates the developed design methodology combining hydrodynamic actions and strength analysis for complex modular artificial reef structures of 3 to 15 m size, specifically tailored for open waters. The results confirm the applicability and reliability of the developed design methodology, demonstrating its potential for guiding future numerical and experimental studies on modular artificial reef structures in open waters. Full article

This study investigated the corrosion behavior and mechanism of offshore platform steel in a simulated marine atmospheric environment using electrochemical analysis, phase analysis, and rust layer characterization. The findings demonstrate that the addition of trace amounts of the rare earth element Ce significantly enhances the steel’s corrosion resistance in the marine environment and effectively reduces the corrosion rate. The addition of Ce promotes the enrichment of Cr in the inner rust layer and forms a dense protective rust layer, thereby preventing the rust layer from falling off, as well as hindering the penetration of oxygen ions. Phase analysis and electrochemical studies further confirmed that the addition of rare earth Ce optimized the structure of the rust layer, improved the matrix protection effect, and enhanced the corrosion resistance of the steel. The crystal structure of the rust layer and the stability between the matrix were simulated by first principles. The results show that the addition of rare earth enhances the bonding force and compactness of the steel matrix and the rust layer, thereby improving corrosion resistance. Full article

Offshore wind turbines serve as critical infrastructure components in marine renewable energy systems, enabling sustainable energy extraction within offshore engineering frameworks. Monopile foundations for offshore wind turbines in deep-water environments are subjected to strong nonlinear wave actions. This study introduces a novel composite monopile foundation specifically designed for deep-sea applications, with its fully nonlinear hydrodynamic performance systematically investigated using potential flow theory. The novel hybrid monopile incorporates a concrete-filled double-skin steel tubular (CFDST) configuration to reduce pile diameter at water level. In the numerical model, the higher-order boundary element method (HOBEM) is implemented to resolve boundary value problems at each temporal iteration. Following numerical validation, nonlinear wave loading and run-up characteristics for the CFDST hybrid structure are quantified, while the limitations of Morison’s equation for large-scale structures under strongly nonlinear wave conditions are concurrently assessed. Results indicate that CFDST implementation effectively attenuates both nonlinear hydrodynamic forces and wave run-up amplitudes, enabling safer and more economical design approaches for deep-water offshore wind turbine foundations. Full article

In the present work, chemical and ion beam surface treatments were performed in order to modify the electrochemical behavior of industrial austenitic–martensitic steel VNS-5 in 3.5 wt. % NaCl. Immersion for 140 h in a solution containing 0.05 M potassium dichromate and 10% phosphoric acid promotes formation of chromium hydroxides in the outer surface layer. By means of a new type of ion source, based on a high-current pulsed magnetron discharge with injection of electrons from vacuum arc plasma, ion implantation with Ar⁺ and Cr⁺ ions of the VNS-5 steel was performed. It has been found that the ion implantation leads to formation of an Fe- and Cr-bearing oxide layer with advanced passivation ability. Moreover, the ion beam-treated steel exhibits a lower corrosion rate (by ~7.8 times) and higher charge transfer resistance in comparison with an initial (mechanically polished) substrate. Comprehensive electrochemical and XPS analysis has shown that a Cr₂O₃-rich oxide film is able to provide an improved corrosion performance of the steel, while the chromium hydroxides may increase the specific conductivity of the surface layer. A scheme of a charge transfer between the microgalvanic elements was proposed. Full article

Steel pipes, while essential for modern infrastructure due to their high strength and load-bearing capacity, are prone to corrosion in the marine environment, leading to material degradation, compromised structural integrity, and elevated safety risks and economic losses. In this study, distributed fiber-optic sensors were deployed on steel pipe surfaces to monitor corrosion in the splash zone (a region particularly vulnerable to cyclic wet–dry conditions). The sensors were engineered to withstand aggressive marine exposure. Strain variations induced by expansive corrosion products were detected via the fiber-optic array and used to calculate localized mass loss. Color-coded corrosion severity maps were generated to visualize the non-uniform corrosion distribution. Experimental results demonstrate that sensor-derived mass loss values align with 3D laser scanning measurements, validating the operational efficacy of distributed fiber-optic sensing for marine corrosion monitoring. This approach provides quantitative insights into the field applicability of optical sensing in structural health monitoring. Full article

Steel fiber-reinforced polymer (FRP) composite bars (SFCBs) combine the ductility of steel reinforcement with the corrosion resistance and high strength of FRP, providing stable secondary stiffness that enhances the seismic resistance and safety of seawater sea–sand concrete structures. However, the seismic performance of SFCB-reinforced seawater sea–sand concrete beam–column joints remains underexplored. This study presents pseudo-static tests on SFCB-reinforced beam–column joints with varying column SFCB longitudinal reinforcement fiber volume ratios (64%, 75%, and 84%), beam reinforcement fiber volume ratios (60.9%, 75%, and 86%), and axial compression ratios (0.1 and 0.2). The results indicate that increasing the axial compression ratio enhances nodal shear capacity and bond strength, limits slip, and reduces crack propagation, but also accelerates bearing capacity degradation. Higher column reinforcement fiber volumes improve crack distribution and ductility, while beam reinforcement volume significantly affects energy dissipation and crack distribution, with moderate volumes (e.g., 75%) yielding optimal seismic performance. These findings provide insights for the seismic design of SFCB-composite-reinforced concrete structures in marine environments. Full article

This study focuses on the nameplate of Vila D. Bosco, a modern building in Macau from the time of Portuguese rule, and looks at the types of metal materials and surface coatings used, as well as how they corrode due to the tropical marine climate affecting the building’s metal parts. The study uses different techniques, such as X-ray fluorescence spectroscopy (XRF), scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and cross-sectional microscopic analysis, to carefully look at the metal, corrosion products, and coating of the nameplate. The results show that (1) the nameplate matrix is a resulfurized steel with a high sulfur content (Fe up to 97.3% and S up to 1.98%), and the sulfur element is evenly distributed inside, which is one of the internal factors that induce corrosion. (2) Rust is composed of polycrystalline iron oxides such as goethite (α-FeOOH), hematite (α-Fe₂O₃), and magnetite (Fe₃O₄) and has typical characteristics of atmospheric oxidation. (3) The white and yellow-green coatings on the nameplate are oil-modified alkyd resin paints, and the color pigments are TiO₂, PbCrO₄, etc. The surface layer of the letters is protected by a polyvinyl alcohol layer. The paint application process leads to differences in the thickness of the paint in different regions, which directly affects the anti-rust performance. The study reveals the deterioration mechanism of resulfurized steel components in a subtropical polluted environment and puts forward repair suggestions that consider both material compatibility and reversibility, providing a reference for the protection practice of modern and contemporary architectural metal heritage in Macau and even in similar geographical environments. Full article

Steel fiber-reinforced concrete structures designed for marine environments can become compromised by the ingress of water and ions. Water and ion transport through the pores between steel fibers and concrete gels significantly affects the durability of such structures, but the mechanisms of this transport are not sufficiently understood. Reported here is a molecular dynamics-based investigation of the transport of water, NaCl, Na₂SO₄, and mixed solutions of NaCl and Na₂SO₄ through γ–FeOOH/CSH pores. The effect of pore width on the capillary transport of NaCl + Na₂SO₄ solutions was also investigated and reported. It is shown that the depth of water penetration in NaCl solution increases parabolically with time. It is further shown that the CSH surface forms bonds with different ions to form Na–O_CSH, Cl–Ca_CSH, and S–Ca_CSH compounds, which results in reduced rates of solution transport. The mixed NaCl + Na₂SO₄ solution was found to have the lowest transport rate. A reduction in pore width was found to reduce the transport rate of water molecules and diminish the transport of ions. In pores smaller than 2.5 nm in width, the immobilized ions aggregate into clusters, occupying pore inlets and blocking more ions from entering the channels. Compared with the matrix on both sides, solutions are transported significantly faster along the CSH side than along the γ–FeOOH side, indicating that the addition of steel fibers can effectively slow down the transport of water molecules and ions in concrete. These data on the difference in the transport of solutions along the two sides of the matrix may provide molecular-level insights to support studies on the durability of concrete materials. Full article

In this study, a non-stationary electrochemical model was verified to be equally applicable to X70 pipeline steel under polarization potential in a marine environment, and the mechanism of stress corrosion cracking (SCC) was revealed. A quick SCC evaluation model for X70 pipeline steel in a marine environment was established. The model only requires electrochemical tests and a small number of slow strain rate tests to obtain the stress corrosion susceptibility distribution of pipeline steel across the whole potential range. The model is applicable to the marine environment and is characterized by its easy operation and accurate results. Full article