Seawater Medium Research Articles

Grain structure orientational change in Ti6Al4V alloys induced by sea water quenching and novel stress relief annealing process

We report on the microstructures and properties of Ti6Al4V alloys, which were achieved upon quenching in sea water medium with potential high cooling rate. The Ti6Al4V alloys were quenched at 1000 and 1100 °C, respectively. Moreover, the effect of post-quenching annealing performed at 900 °C was analyzed. As a result, the quenched alloy experienced surface thermal stress, due to rapid cooling and thermal shock, due to exposure to high temperature annealing. The alloy quenched at 1000 °C developed equiaxed grain structure after annealing, while the 1100 °C-quenched alloy generated irregular shaped lamellae structures. TEM analysis for the 1000 °C-quenched samples revealed the α′-martensite decomposed into the equilibrium α + β phases. Moreover, the 1100 °C-quenched Ti6Al4V alloy revealed an α′-acicular martensitic structure.

Corrosive engineering assistedin situconstruction of an Fe–Ni-based compound for industrial overall water-splitting under large-current density in alkaline freshwater and seawater media

The synthesized flower-like Fe–Ni–O–N presents excellent electrocatalytic performance for OER. The assembled electrolyzer shows remarkable catalytic performance and stability in alkaline freshwater, seawater and industrial conditions (60 °C, 6 M KOH).

Evaluation of The Biochemical Contents in Guillard f/2 and Walne Growth Medium to Fulfill the Animal-Free Aspects of Microalgal Bioprocessing

Marine microalgae with their diverse biomolecule contents could be used as potential sources of food, cosmetics, and pharmaceutical ingredients. In accordance with regulations in some countries and to competitively engage huge numbers of consumers, microalgae-based products should be properly manufactured using non-animal-derived materials. As a cultivable microorganism using a scalable bioreactor technique, consideration of the origin of the material used in the upstream process of marine microalgae was inevitable. Currently, the material origin of chemical contents within common artificial microalgal seawater medium had not been evaluated. This article evaluated Guillard f/2 and Walne medium as common artificial microalgal nutrients used in marine microalgal bioprocess-related activities. The risk assessment results showed that the largest portion of Guillard f/2 and Walne media were inorganic salts considered as low, while the remaining biochemical contents of vitamins were categorized as high risk due to their relatively complex chemical synthesis and enzymatic stages during the manufacturing process. As a suggestion, several plant-based bioproducts were proposed as alternative sources to substitute related biochemical actions to fulfill non-animal-origin aspects in the initial stages of the bioprocessing of marine microalgal-based products.

Chemical speciation models based upon the Pitzer activity coefficient equations, including the propagation of uncertainties. III. Seawater from the freezing point to 45 °C, including acid-base equilibria

A quantitative understanding of pH, acid-base equilibria, and chemical speciation in natural waters including seawater is needed in applications ranging from global change to environmental and water quality management. In a previous study (Humphreys et al., 2022) we implemented a model of solutions containing the ions of artificial seawater, based upon the use of the Pitzer equations for the calculation of activity coefficients and including, for the first time, the propagation of uncertainties. This was extended (Clegg et al., 2022) to include the Tris buffer solutions that are used to calibrate the seawater total pH scale. Here we apply the same methods to develop a model of solutions containing the ions of standard reference seawater, based upon studies by Millero and co-workers. We compare the predictions of the model to literature data for: the dissociation of dissolved CO2 and bicarbonate ion; boric acid dissociation; saturation with respect to calcite, the ion product of water, and osmotic coefficients of seawater. Estimates of the uncertainty contributions of all thermodynamic equilibrium constants and Pitzer parameters to the variance of the calculated quantity are used to determine which elements of the model need improvement, with the aim of agreeing with properties noted above to within their experimental uncertainty. Further studies are recommended. Comparisons made with several datasets for carbonate system dissociation in seawater suggest which are the most reliable, and identify low salinity waters (S < 10) as a region for which dissociation constants of bicarbonate are not yet accurately known. At present, the model is likely to be most useful for the direct calculation of equilibria in natural waters of arbitrary composition, or for adjusting dissociation constants known for seawater media to values for natural waters in which the relative compositions of the major ions are different.

From lab to application: Cultivating limnetic microalgae in seawater coupled with wastewater for biodiesel production on a pilot scale

The technology of cultivating salt-tolerant limnetic microalgae in seawater reduces the freshwater demand and costs of biodiesel production. However, all current trials still occur on the bench scale, and efforts for pilot-scale operation are urgently needed. This study firstly optimised the diameter of the photobioreactors (PBRs) to 0.2 m, as the single module to produce lipid-rich Golenkinia sp. SDEC-16 because of the better algal growth and light attenuation in the PBRs, and then established a 1000 L algal cultivation system. In a medium of seawater supplemented with monosodium glutamate wastewater at a ratio of 1:1000 (S-MSGW), the biomass productivity was 0.26 g/L/d, which was approaching the 0.30 g/L/d obtained in BG11, and the lipid productivity (98.99 mg/L/d) was doubled in comparison to growth in BG11. C16-C18 accounted for more than 98% of the total fatty acid in S-MSGW, and the biodiesel properties also met the biodiesel standards. The input cost of the biodiesel in this pilot-scale system was estimated to be 2.2 $/kg. When considering the carbon reduction and diversified application of the biomass, Golenkinia sp. would annually capture 186.77 kg/m3 PBR of CO2, and yield an output-to-input ratio (OIR) of 3.4 in S-MSGW, higher than the 2.8 in BG11.

Preparation of Ni-Cu composite coatings with excellent tribological property and corrosion resistance by doping OH-BN(h)-PA-Zn-DCD hybrid

In this study, a novel Ni-Cu/OH-BN(h)-PA-Zn-DCD composite coatings with excellent wear resistance and corrosion resistance was developed, which may be used in the field of seawater corrosion. By the self-assembling of phytic acid, Zn2+ and dicyandiamide to grow PA-Zn-DCD structure onto the surface of hydroxylated BN(h) nanosheets, obtained a hybrid denoted as OH-BN(h)-PA-Zn-DCD, which was doped into Ni-Cu coating by pulse electrodeposition. The results show that OH-BN(h) and OH-BN(h)-PA-Zn-DCD hybrids affect the surface morphology, roughness, microcrystals size and thickness of the composite coatings. Simultaneously, compared with NC coating and NC/HB-1.5 coating, NC/BP-1.5 coating has the highest microhardness (559.26 Hv), the lowest friction coefficient (0.172), and the best corrosion resistance (icorr is 3.551 × 10−8 A·cm−2, Rct is 1.098 × 106 Ω·cm2). In addition, the EIS results of the immersed specimens showed that the NC/BP-1.5 composite coating still has good protective ability after soaking for 15 days in simulated seawater medium (Rct is 7.434 × 106 Ω·cm2).

Fe-Incorporated Ni/MoO2 Hollow Heterostructure Nanorod Arrays for High-Efficiency Overall Water Splitting in Alkaline and Seawater Media.

Developing high-efficiency and cost-effective bifunctional catalysts for water electrolysis is fascinating but still remains challenging. Thus, diverse strategies have been utilized to boost the activity toward oxygen/hydrogen evolution reactions (OER/HER) for water splitting. Among them, composition and structure engineering as an effective strategy has received extensive attention. Here, by means of a self-sacrificing template strategy and simultaneous regulation of the composition and structure, Fe-incorporated Ni/MoO2 heterostructural (NiFe/Fe-MoO2 ) hollow nanorod arrays are designed and constructed. Benefiting from abundant catalytic active sites, high intrinsic activity, and fast reaction kinetics, NiFe/Fe-MoO2 exhibits superior OER (η20 = 213 and 219mV) and Pt-like HER activity (η10 = 34 and 38mV), respectively, in 1m KOH and alkaline seawater media. This results in attractive prospects in alkaline water and seawater electrolysis with only voltages of 1.48 and 1.51V, and 1.69 and 1.73V to achieve current densities of 10 and 100mA cm-2 , respectively, superior to the Pt/C and RuO2 pair as a benchmark. Undoubtedly, this work provides a beneficial approach to the design and construction of noble-metal-free bifunctional catalysts toward efficient hydrogen production from alkaline water and seawater electrolysis.

Fatty acid profile of Spirulina sp cultivated in Bangka Seawater

Microalgae can be used as a good biodiesel raw material because there are quite a lot of oil microalgae, one of which is Spirulina sp. Cultivation Process of Spirulina sp. using seawater media produces more optimal biomass than freshwater media. This study used Bangka Seawater as a growth medium for Spirulina sp., and identification fatty acid of Spirulina extract by GC-MS methode. cell growth of Spirulina sp. on media Bangka seawater using Walne fertilizer can experience an exponential phase until the 9th day due to the addition of Walne fertilizer. Culture with 1 ml of Walne fertilizer had the best growth. The use of Bangka sea water without fertilizer can also grow Spirulina sp with a peak on day 5. The total fatty acid in the hexane extract of Spirulina in this study was 69.60% with similarity indeks above 70%. As many as 33.78% are Saturated Fatty Acids (SFA) such as docosanoic acid, hexadecanoic acid, octadecanoic acid, and hexanedioic acid. While 35.82% are Unsaturated Fatty Acids (UFA). The profile of fatty acid from Bangka seawater media showed that the largest fatty acids contained in Spirulina sp. is palmitic acid (hexadecanoic acid) with presentage 25.21%.

Carbon content, carbon fixation yield and dissolved organic carbon release from diverse marine nitrifiers.

Nitrifying microorganisms, including ammonia-oxidizing archaea, ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria, are the most abundant chemoautotrophs in the ocean and play an important role in the global carbon cycle by fixing dissolved inorganic carbon (DIC) into biomass. The release of organic compounds by these microbes is not well quantified, but may represent an as-yet unaccounted source of dissolved organic carbon (DOC) available to marine food webs. Here, we provide measurements of cellular carbon and nitrogen quotas, DIC fixation yields and DOC release of 10 phylogenetically diverse marine nitrifiers. All investigated strains released DOC during growth, representing on average 5-15% of the fixed DIC. Changes in substrate concentration and temperature did not affect the proportion of fixed DIC released as DOC, but release rates varied between closely related species. Our results also indicate previous studies may have underestimated DIC fixation yields of marine nitrite oxidizers due to partial decoupling of nitrite oxidation from CO2 fixation, and due to lower observed yields in artificial compared to natural seawater medium. The results of this study provide critical values for biogeochemical models of the global carbon cycle, and help to further constrain the implications of nitrification-fueled chemoautotrophy for marine food-web functioning and the biological sequestration of carbon in the ocean.

Analysis of special technical problems of wireless charging at UUV docking stations and a new underwater electromagnetic coupler

In order to solve the problem of insufficient range of autonomous underwater vehicles, underwater docking stations deployed on the seabed can wirelessly charge autonomous underwater vehicles through recyclers. Compared with traditional wireless charging of electric vehicles, wireless charging based on underwater docking stations has many special technical problems that need to be further understood and deciphered. This paper introduces the basic functions of the docking system and the docking process, and then focuses on the following three aspects of wireless charging at docking stations: firstly, the design of the coupler to suit the underwater vehicle and the complex marine environment, the coupler mechanism should match the shape and structure of the underwater vehicle, and the coupler should have a high resistance to deflection; secondly, the influence of the seawater medium on the wireless charging system. The impact of seawater medium on the wireless charging system is analysed, and the equivalent circuit model considering seawater eddy currents and the equivalent circuit model considering cross-connecting capacitance effects are established respectively; thirdly, the design of communication-independent wireless charging system. The existing eddy current loss calculation methods are analysed for the key technical problem of eddy current loss in seawater. A new type of electromagnetic coupler is proposed, the structural characteristics of the coupler are introduced and the simulation results show that the new coupler has a strong anti-deflection capability.

CuAl layered double hydroxide as a highly efficient electrocatalyst for the electrolysis of water into hydrogen and oxygen fuels

The production of green H2 through water electrolysis processes has become a prominent technology to deal with energy and environmental crisis worldwide. The total energy consumption of electrolysis processes can be reduced by the development of low-cost electrocatalysts. In this paper, we report first time the synthesis of a highly efficient 2D CuAl LDH electrocatalyst to produce the green H2. The electrocatalyst was characterized with the help of various analytical instruments such as FT-IR, XRD, BET, TGA, ICP-OES, and XPS. The morphological characterization was done by SEM and TEM. The electrochemical characterization such as CV, LSV, Tafel plot, and EIS was done in acidic, basic, seawater, and alkaline seawater medium. It was found that CuAl LDH electrocatalyst exhibits a good current density of 100 mA/cm2 at a potential of 1.178 V in acidic medium and 10 mA/cm2 at 1.114V in seawater medium. It was investigated that the CuAl LDH behaves as a bifunctional electrocatalyst and exhibits excellent HER and OER activity in an acidic medium. The effect of temperature on the efficiency of the electrocatalyst under the above electrolyte mediums was also studied. The electrochemical data suggests that the CuAl LDH electrocatalyst can be utilized in an alkaline/PEM electrolyzer to produce the green H2 at an industrial scale with optimum cost.

Structural and Electronic Modulation of Iron-Based Bimetallic Metal-Organic Framework Bifunctional Electrocatalysts for Efficient Overall Water Splitting in Alkaline and Seawater Environment.

Metal-organic frameworks (MOFs) are considered potential electrocatalysts for efficient water splitting. However, the structure-activity relationship of most MOFs is not systematically analyzed for electrocatalysis for anodes and cathodes. In this paper, we provide a strategy to modulate the electronic microstructure of iron-based bimetallic MOFs (MFe-BDC (M: Mg, Zn, Cd)) grown on the nickel foam (NF) as bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The optimal bimetallic CdFe-BDC via modulating appropriate metal cations of IIA and IIB possesses excellent OER and HER performance with the lowest overpotentials of 290 mV at 100 mA cm-2 and 148 mV at 10 mA cm-2, respectively. The overall water splitting performance of the as-prepared CdFe-BDC requires 1.68 V to achieve a current density of 10 mA cm-2 in the real seawater media, and it exhibits the competitive H2 and O2 production rates of 6.4 and 3.1 μL s-1, respectively, in ambient alkaline conditions, suggesting its potential practical applications. Density functional theory (DFT) calculations demonstrate the relationship between microstructure and electrocatalytic performance of bimetallic MFe-BDC. This work emphasizes the significance of tailoring the electronic microstructure of bimetallic MOFs for efficient overall water splitting in alkaline and seawater environment.

Impact of 17-β estradiol on growth and metabolism of marine diatom Thalassiosira weissflogii

• Cultivation of T.weissflogii on synthetically designed media of seawater and estradiol. • Biomass productivity and cell number declined with increase of E2 concentration in samples. • Enhanced production of protein and carbohydrate content mainly in samples T4 and T5. • The level of oxidative stress induced was assessed through MDA and other enzymatic reactions. The inefficiency of existing effluent treatment systems to eliminate pharmaceutical chemicals like endocrine disrupting estrogenic compounds from contaminated waters has raised global environmental and ecological concerns. Diatoms are unicellular, eukaryotic phytoplankton that inhabits ubiquitously and possess adaptive plasticity which enables them to withstand rapid environmental fluctuations. Thus, diatoms can be employed as indicators organisms and bioremediation agents of even trace amounts of Pharmaceutical Contaminants (PCs) like the estrogenic compounds. In this study, the influence of simulated wastewater containing pharmaceutical effluent 17-β Estradiol (E2) on the growth, cellular metabolites and oxidative stress response of the diatom, Thalassiosira weissflogii was assessed. Though an increasing concentration of the chemical displayed a negative correlation with growth, number of cells and biomass productivity; the photosynthetic profile of the diatom showed varied responses with significant enhancement in chlorophyll a and carotenoid content. The test concentrations T1 and T3 showed elevated carbohydrate and protein levels (0.82 ± 0.003 g L -1 and 2.04 ± 0.020 g L -1 ) establishing that E2 stress can be optimised to enhance primary metabolite secretion in diatoms, thereby valorizing its potential as suitable aqua feed. Besides this, an elevation in the antioxidative response against the reactive oxygen species generated was also distinctly recorded with respect to the increased release of catalase (152.70 ± 0.05–265.52 ± 0.06 k mg -1 ) and ascorbate peroxidases (0.959 ± 0.008–1.92 ± 0.021 U mg -1 ) as well as a conspicuous increment in the lipid peroxidation and hydrogen peroxide content was also there. Thus, this novel strategy of employing diatom for multitude of biorefinery aspects besides reacclimating contaminated water reveals the perspective application of this approach. .

A Vision-Based Underwater Formation Control System Design and Implementation on Small Underwater Spherical Robots

The ocean is a significant strategic resource, and the insufficient development and use of the ocean, as well as the increase in attention to the ocean, have led to the development of underwater robot technology. The need for in-depth marine exploration and the limitations of one underwater robot has sparked research on the underwater multi-robot system. In the underwater environment, weak communication is caused by the shielding effect of the seawater medium, which makes multi-robot systems difficult to form. Hence, we combine the robot’s vision system with the leader-follower structure to form a vision-based underwater formation method, in which the visual solution serves as the control system’s feedback. By using three small underwater robot platforms, the proposed method is proved to be effective and practicable through underwater formation experiments. Furthermore, the coordination period and error of the control system are analyzed.

Cultivation of previously uncultured microorganisms with a continuous-flow down-flow hanging sponge (DHS) bioreactor, using a syntrophic archaeon culture obtained from deep marine sediment as a case study.

In microbiology, cultivation is a central approach for uncovering novel physiology, ecology, and evolution of microorganisms, but conventional methods have left many microorganisms found in nature uncultured. To overcome the limitations of traditional methods and culture indigenous microorganisms, we applied a two-stage approach: enrichment/activation of indigenous organisms by using a continuous-flow down-flow hanging sponge bioreactor and subsequent selective batch cultivation. Here, we provide a protocol for this bioreactor-mediated technique using activation of deep marine sediment microorganisms and downstream isolation of a syntrophic co-culture containing an archaeon closely related to the eukaryote ancestor (Candidatus Promethearchaeum syntrophicum strain MK-D1) as an example. Both stages can easily be tailored to target other environments and organisms by modifying the inoculum, feed solution/gases, attachment material and/or cultivation media. We anaerobically incubate polyurethane sponges inoculated with deep-sea methane seep sediment in a reactor at 10 °C and feed anaerobic artificial seawater medium and methane. Once phylogenetically diverse and metabolically active microorganisms are adapted to synthetic conditions in the reactor, we transition to growing community samples in glass tubes with the above medium, simple substrates and selective compounds (e.g., antibiotics). To accommodate for the slow growth anticipated for target organisms, primary cultures can be incubated for ≥6-12 months and analyzed for community composition even when no cell turbidity is observed. One casamino acid- and antibiotic-amended culture prepared in this way led to the enrichment of uncultured archaea. Through successive transfer in vitro combined with molecular growth monitoring, we successfully obtained the target archaeon with its partner methanogen as a pure syntrophic co-culture.

Toward developing more sustainable marine biorefineries: A novel ‘sea-thermal’ process for biofuels production from microalgae

This work explores the ‘sea-thermal’ treatment of the aquatic protein-rich microalga Chlorella Vulgaris to produce energy-dense biofuels and value-added, nitrogen-rich liquid products. The impact of the processing conditions (temperature, 200–300 °C; time, 20–180 min) and reaction medium (seawater/(deionized water + seawater) ratio, 0–100 wt%) on the yields and properties of these products has been addressed using a two-level, three-factor (23) Box-Wilson Central Composite, Face Centered (CCF, α: ±1) design. These processing parameters ruled the distribution of the overall reaction products, including gas (1–5 %), biocrude (17–57 %), aqueous product (32–47 %) and hydrochar (3–45 %), and the fuel and chemical properties of these fractions. The calorific values of the hydrochar and biocrude ranged from 2 to 25 MJ/kg and 23 to 32 MJ/kg, respectively. Using low temperatures and/or short reaction times favored biocrude formation, while higher temperatures and/or more prolonged processing times boosted the repolymerization of the biocrude to hydrochar. These transformations depended on the reaction medium, with seawater exerting different influences based on the reaction medium salinity. Diluted seawater promoted the dissolution and depolymerization of polysaccharides and proteins in the alga by disrupting the H-bonding networks within these macromolecules, while enriched seawater media favored the deoxygenation and repolymerization of the biocrude. These variations highlighted the bespoke nature of this ‘sea-thermal’ process to furnish liquid and solid biofuels and/or biochemicals. Process optimization based on the formulae developed from the ANOVA of the experimental data showed that 55–60 wt% of the alga could be converted either to energy-dense (30 MJ/kg) biofuels (36 wt% biocrude, with hydrocarbons and fatty acids/esters in high amount, and 20 wt% hydrochar) at 200 °C for 180 min using enriched seawater (64 wt% seawater) as a solvent or to value-added liquids (a nitrogen-rich (88 %) biocrude, including abundant fatty amides and N-heterocycles) at 237 °C for 169 min in seawater. These results lay the first stone toward developing more sustainable marine biorefineries using marine-based solvents to valorize marine feedstocks.

A novel high-entropy alloy with an exceptional combination of soft magnetic properties and corrosion resistance

The lack of corrosion resistance limits the application of most conventional soft magnetic materials (SMMs) in a corrosive environment, especially in seawater. Hence, enhancing the corrosion resistance of SMMs is critically important. However, a severe contradiction exists between magnetic properties and corrosion resistance as the main anticorrosion element Cr has strong anti-ferromagnetism that deteriorates the magnetism of alloys. This study aimed to report a novel single body-centered cubic high-entropy alloy (HEA) (Fe2.25Co1.25Cr)94Al6 with an optimal combination of soft magnetic properties, corrosion resistance, and mechanical properties. The saturation magnetization of the HEA was as high as 141.88 emu g−1 and the coercivity was only 2.9 Oe, which were superior to most of the reported magnetic HEAs and conventional alloys. The corrosion resistance of the HEA was better than that of the 304 stainless steel, all of soft magnetic HEAs, and most of the reported HEAs in simulated seawater medium. In addition, the novel HEA exhibited excellent mechanical properties with a yield strength of 1100 MPa, a compressive fracture strain of more than 33%, and an outstanding Vickers hardness value of 469 HV. Thus, this novel (Fe2.25Co1.25Cr)94Al6 HEA is a promising SMM for marine environment applications.

Competitive Coordination-Pairing between Ru Clusters and Single-Atoms for Efficient Hydrogen Evolution Reaction in Alkaline Seawater.

The coordination environment of Ru centers determines their catalytic performance, however, much less attention is focused on cluster-induced charge transfer in a Ru single-atom system. Herein, by density functional theory (DFT) calculations, a competitive coordination-pairing between Ru clusters (RuRu bond) and single-atoms (RuO bond) is revealed leading to the charge redistribution between Ru and O atoms in ZnFe2 O4 units which share more free electrons to participate in the hydrogen desorption process, optimizing the proton adsorption and hydrogen desorption. Thus, a clicking confinement strategy for building a competitive coordination-pairing between Ru clusters and single-atoms anchored on ZnFe2 Ox nanosheets over carbon via RuO ligand (Ru1, n -ZnFe2 Ox -C) is proposed. Benefiting from the optimized coordination effect and the electronic synergy between Ru clusters and single-atoms, such a catalyst demonstrates the excellent activity and excellent stability in alkaline and seawater media, which has exceptional hydrogen evolution reactionactivity with overpotentials as low as 10.1 and 15.9mV to reach the current density of 10mA cm-2 in alkaline and seawater media, respectively, higher than that of commercial Pt/C catalysts as a benchmark. Furthermore, it owns remarkably outstanding mass activity, approximately 2 and 8 times higher than that of Pt catalysts in alkaline and seawater media, respectively.

Agar content of estuarine seaweed Gracilaria using different cultivation methods

Red algae Gracilaria is one of the most cultivated seaweeds and a major source of agar in the world. Gracilaria demonstrates easy propagation, high growth rates, and tolerance to a broad range of salinities. Agar usage is related to thermo-reversible gels formation at low concentrations in water with wide applications in food, pharmaceutical, medical, engineering, agricultural and other fields. In this work, we analyzed and compared agar content of the estuarine seaweed Gracilaria sp. grown in two distinct cultivation methods: (1) inshore tank cultivation technique and (2) indoor cultivation technique using different mediums (seawater and brackish water) to get a better understanding about the best medium for large scale sustainable cultivation in the future; wild Gracilaria sp. samples were used as control. Inshore tank cultivation exhibited the highest agar extraction yield (20.67±0.27%) when compared with the control (16.67±2.72%); indoor cultivation using brackish water medium (13.8 ± 1.5%) and seawater medium (11.64±2.38%) revealed lower values than the control, but still promising for large scale cultivation and agar exploitation.

Study on hysteretic performance of welded T-joints circular tube on platform considering seawater corrosion

In this study, the macroscopic hysteretic mechanical behaviour of welded circular tube T-joints corroded by seawater was evaluated through hysteretic mechanical performance tests. Full immersion accelerated electrochemical corrosion tests with a proportioned seawater medium were conducted on steel specimens obtained from tube joints. The generalised degradation rule of the mechanical performance of the material with the development of corrosion was obtained via a monotonic tensile test of steel specimens. The hysteresis test of corroded joints revealed that corrosion and cyclic loading have degradation effects on joint strength, stiffness, bearing capacity, and energy dissipation. At a low number of cycles, the effect of corrosion is generally greater than that of cyclic loading. A hysteretic skeleton model that can determine the ultimate load of the corroded joint was established based on the load–displacement curve. Moreover, the hysteretic rules that describe the degradation characteristics of the loading and unloading stiffness were established. Finally, the hysteresis model of corrosion joints was proposed. The model was validated using experimental results, and we demonstrated that it can accurately reflect the effect of the degree of corrosion and loading process on the hysteretic characteristics of joints.