Splash Zone Research Articles

Submerged and completely open solid–liquid triboelectric nanogenerator for water wave energy harvesting

AbstractTriboelectric nanogenerator (TENG) is an emerging wave energy harvesting technology with excellent potential. However, due to issues with sealing, anchoring, and difficult deployment over large areas, TENG still cannot achieve large‐scale wave energy capture. Here, a submerged and completely open solid–liquid TENG (SOSL‐TENG) is developed for ocean wave energy harvesting. The SOSL‐TENG is adapted to various water environments. Due to its simple structure, it is easy to deploy into various marine engineering facilities in service. Importantly, this not only solves the problem of difficult construction of TENG networks at present, but also effectively utilizes high‐quality wave energy resources. The working mechanism and output performance of the SOSL‐TENG are systematically investigated. With optimal triggering conditions, the transferred charge (Qtr) and short‐circuit current (Isc) of SOSL‐TENG are 2.58 μC and 85.9 μA, respectively. The wave tank experiment is taken for fully demonstrating the superiority of the SOSL‐TENG network in large‐scale collection and conversion of wave energy. Due to the excellent output performance, TENG can harvest wave energy to provide power for various commercial electronic devices such as LED beads, hygrothermograph, and warning lights. Importantly, the SOSL‐TENG networks realizes self‐powered for electrochemical systems, which provides a direction for energy cleanliness in industrial systems. This work provides a prospective strategy for large‐scale deployment of TENG applications, especially for harvesting wave energy in spray splash zones or at the surface of the water.image

Coupling dynamic characteristics of installation vessel - Multi buckets jacket foundation lowering system

Precise control of the splash zone lowering process of the multi-bucket jacket foundation for an offshore wind turbine can save time during the entire construction period, thereby reducing construction and installation costs. This paper focuses on the “installation vessel - multi buckets jacket foundation” coupled dynamic system during the lowering process of the multi-bucket jacket foundation. Taking the three-bucket jacket foundation (TBJF) and the four-bucket jacket foundation (FBJF) as the research objects, four different sling layout types were proposed. The influence of the slings layout types on the motion response of the installation vessel and foundation and the slings' tension in this system were comparatively studied through numerical simulation. Research shows that through the lowering of Type 1 conditions, that is, each chord corresponds to a vertical sling and is directly connected to the crane's lifting point, the motion performance of the foundation and installation vessel can be reduced, ensuring the smooth progress of the lowering process of the structure. Under the same conditions, the FBJF has greater motion response due to the large wave force bearing area and large water plane area. Under different conditions, the DAF value and failure factor of the slings of the two structures during the lowering process all meet the specification requirements.

Constructing ZSM-5 loaded with 2-mercaptobenzimidazole on glass fiber for enhancing the anti-corrosion and erosion resistance properties of epoxy coating

Glass fiber reinforced polymer coatings (GFRPC) are used to protect steel structures in harsh Marine environments due to high mechanical strength and chemical stability. The composite coating not only suffers from impact damage by seawater and sediment but also experiences corrosion damage in the splash zone. However, the GF has weak interfacial adhesion with polymer resins due to the chemical inertia and smooth surface, which limits the service lifespan of GFPRC. Hence, ZSM-5 zeolites were in situ prepared on the surface of glass fibers by hydrothermal synthesis, and 2-mercaptobenzimidazole (MBI) was further adsorbed to obtain difunctional hybrid glass fibers (ZGFM) to enhance the interfacial adhesion strength of glass fiber/resin and also the erosion resistance and anti-corrosion ability of composite coatings. Compared to GF/EP, the interfacial shear strength of ZGFM/EP was increased by 104.39 %. After immersion under an alternating hydrostatic pressure of 20 MPa for 12 days, the impedance value of the ZGFM/EP composite coating remained at 6.40 × 109 Ω•cm2, demonstrating outstanding deep-sea anti-corrosion performance. Following the erosion test, the ZGFM/EP exhibited a reduction in mass loss and volume loss by 10.65 % and 12.55 %, respectively, in comparison to the pure EP coating. The excellent interfacial strength between ZGFM and EP ensured effective stress transfer, which prevented crack propagation, thus enhancing the mechanical properties and erosion resistance of the composite coating. Meanwhile, electrochemical experiment proves glass fiber with MBI loaded obviously inhibited the corrosion reaction.

Surface Modification of Composite Coating for Marine Application: A Short Review

Corrosion is one of the phenomena that affects the deterioration of materials in offshore applications. Marine corrosion is particularly aggressive, due to the high salt content and low electrical resistivity of seawater. Corrosion cannot be stopped completely, but the reaction can be slowed down. Applying coating is an effective and widely used method to protect metal surfaces from corrosion. Coatings act as a barrier between the metal and its environment, preventing or slowing down the corrosive processes. Pursuant to ISO 12944, the most commonly used generics for coating systems in marine service are alkyd, acrylic, ethyl silicate, epoxy, vinyl ester, polyurethane, polyaspartic, and polysiloxane. The latest innovations in marine coatings still use a layer-by-layer coating method (e.g. primer coats, intermediate coats, and top coats) depending on thickness. Marine structures exposed to the atmospheric zones are usually coated with one or two coats of epoxy. A slightly more costly system of one coat of zinc-rich primer, one coat of epoxy, and one coat of aliphatic polyurethane may provide better performance. Coating systems for the atmospheric zones are frequently used in the intertidal and splash zones. Immersion zones of marine structures are commonly coated with one or two coats of 100% solid epoxy or three coats of solvent-borne epoxy. A single polymer as a generic coating have limitations. Adding fillers is a common method to improve the properties of polymers to become a composite. In marine coatings, fillers are still limited to glass flakes and powder. Poor dispersion and agglomeration might reduce the effectiveness of fillers in the matrix, which decreases the adhesion properties. The fillers must be surface modification before the application. This review provides a comprehensive and critical review of the current research status of composite coatings that serve as candidates to be used in marine coating.

Robotic Technology Enables Automated Nondestructive Weld Inspection in Subsea Zone

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215588, “Automated Nondestructive Weld Inspection in Splash/Subsea Zone,” by Karsten Husby, Magnus Bjerkeng, and Jens T. Thieleman, SINTEF, et al. The paper has not been peer reviewed. _ Jacket structures all over the world are now reaching the limit of their estimated service life, but new discoveries and improved production methods require lifetime extension of the assets. The complete paper presents an automated underwater robot and a nondestructive testing (NDT) eddy-current probe for alternating-current field-measurement analysis of jacket main welds. This robot makes integrity testing, which often is required for lifetime extensions, possible. Introduction Jacket lifetime calculations are based on long service intervals. Some welded braces in the splash zone often are considered unserviceable because of the hostile environment. Thus, divers or remotely operated vehicles cannot be used under normal weather conditions and wave heights. Structural integrity is ensured with long service intervals, often long enough for the lifetime of the jacket. However, multiple jacket platforms are approaching their certified lifespan limit. The question, then, is whether they should be decommissioned, reused, or have their lifespan extended. New discoveries and improved production methods make extended operation desirable for certain fields. For other platforms, repurposing for offshore wind, aquaculture, or geothermal energy may be a cost-effective alternative. Regardless, before any action can be taken, the integrity of the jackets must be tested. There is, therefore, a growing need for subsea condition monitoring of aging offshore jacket steel platforms. To speed up operations and to handle complicated health, safety, and environment (HSE) issues in the splash zone, robots can be used. A robot for NDT inspection in the hostile splash zone is pictured in Fig. 1. The robot clamps itself to the circular braces and is equipped with 3D vision camera, kinematics algorithms, and an NDT probe. Integrity Testing Under Rough Conditions Testing for integrity of critical infrastructure often is performed by different NDT methods. In this study, eddy-current testing was chosen as the preferred method because it is fast and can penetrate layers of marine growth on the surface. The normal procedure is to use lightweight hand-held equipment. The splash zone, however, is often inaccessible under modern HSE standards. In this project, an automated NDT robot helped conduct efficient NDT testing for longer periods in challenging conditions. This robot offloads the NDT operator and makes testing more efficient.

Corrosion evolution and quantitative corrosion monitoring of Q355 steel for offshore wind turbines in multiple marine corrosion zones

Offshore wind turbines operating in harsh marine environments are at risk of corrosion. Thickness loss and perforation caused by corrosion can lead to component failure or structure collapse. An environmental test setup was constructed to simulate various marine corrosion zones. Several experimental studies were conducted on Q355 steel, commonly used in offshore wind turbines. The mass loss and electrochemical properties of the steel specimens were analyzed, including electrochemical impedance spectra and polarization curves. The results indicate that corrosion remains stable in the immersion and tidal zones, whereas corrosion in the splash zone is the most severe, with a corrosion rate as high as 0.70 mm/a. A significant macroscopic corrosion cell effect was observed on the vertical steel strip, accelerating corrosion in the splash zone and at the low tide line. The corrosion product compositions and corrosion morphology of each corrosion zone were characterized and analyzed. Furthermore, a corrosion monitoring sensor based on electromechanical impedance was proposed. A prediction model for the mass loss rate of vertical steel strips was developed based on the conductance peak frequency. This study elucidates the corrosion evolution of wind turbine structural steel and proposes a comprehensive steel corrosion monitoring solution.

Analysis of service life and reliability of C50CASC structures in the splash zone of the South China Sea

This paper presents the results of a reliability analysis of the service life of hydraulic structures made of C50 coral aggregate seawater concrete (CASC) in the splash zone of the South China Sea. The analysis was conducted using the ChaDuraLife V1.0 software, which is based on reliability theory and modified chloride diffusion theory. Several parameters such as the surface free chloride concentration (Cs), chloride binding capacity (R), free chloride diffusion coefficient (Df), apparent chloride diffusion coefficient (Da), and time-dependent index (m) were considered in this analysis. The (1-m) boundary condition is adopted in this study. The effect of concrete cover thickness on the service life of CASC structures was discussed. The influence of rebar types and external protective measures on the service life was also investigated. Durability recommendations for C50CASC hydraulic structures in the splash zone were proposed. The minimum concrete cover thickness needed to achieve the service life of 30a to 100a was determined to provide theoretical support for the application of CASC in island and reef engineering. The results found that the best technical measures for extending the service life were the application of 2205 duplex stainless steel bars and silane protective coating on the surface of concrete structures. A concrete cover thickness of 6–7 cm could achieve the service life of 50a, while a thickness of 8.5–10 cm, could achieve the service life of 100a.

Polarization-Accelerated Seawater Splash Simulation for Rapid Evaluation of Protection Performance of an Epoxy Coating on Carbon Steel.

The application of organic coatings is the most cost-effective and common method for metallic equipment toward corrosion, whose anti-corrosion property needs to be improved and evaluated in a short time. To rapidly and rationally assess the anti-corrosion property of organic coatings in the ocean splash zone, a new accelerated test was proposed. In the study, the corrosion protection property of the coating samples was measured by an improved AC-DC-AC test in a simulated seawater of 3.5 wt.% NaCl solution, a simulated ocean splash zone test and a new accelerated test combining the above two tests. The results showed that the corrosion rate of the coating samples was high in the improved AC-DC-AC test, which lost its anti-corrosion property after 24 cycles equal to 96 h. The main rapid failure reason was that the time of the water and corrosive media arriving at the carbon steel substrate under the alternating cathodic and anodic polarization with symmetrical positive and negative electric charges was shortened. The entire impedance of the coating samples was improved by about 1.6 times more than that in the initial early time in the simulated ocean splash zone test, which was caused by the damage effect from the salt spraying, drying, humidifying, salt immersion, high temperature and UVA irradiation being weaker than the enhancement effect from the post-curing process by the UVA irradiation. In the new accelerated test, the samples lost their corrosion resistance after 12 cycles equal to 288 h with the fastest failure rate. On account of the coupling process of the salt spraying, drying, humidifying, salt immersion, high temperature combined with the cathodic and anodic polarization and the UVA irradiation, the penetration and transmission rate of water and corrosive media in the coating were further accelerated, the corrosion rate on the carbon steel substrate was reinforced even larger and the destruction of the top polymer molecules was more serious. The new accelerated test showed the strongest damage-acceleration effect than that in the other two tests.

Corrosion resistance behavior of enhanced passivation Cr-modified rebars and their service life prediction based on Monte Carlo simulation

This work investigates enhanced passivation and corrosion resistance of various Cr-modified rebars compared to carbon rebar. It also evaluates their service life through time-varying probability analysis based on Monte Carlo simulation, combined with the parameters obtained from sampling and testing reinforced concrete mortar samples exposed to various marine conditions over 5 years. The results show that the free energy required for oxide thickening of rebar decreases from 20.12 kJ/mol to 9.25 kJ/mol as the Cr content increases from 5 % to 11 % (wt.), which facilitates the developed Cr-modified rebars rapidly form a passive film, exhibiting a chloride threshold level 6–14 times higher than that of carbon rebar. In the harshest marine splash zone, sea sand concrete with Cr11 rebar ensures a theoretical 50-year service life, contrasting sharply with the much shorter lifespan estimated at 5–6 years for carbon rebar. The corrosion rate of Cr-modified rebars was notably lower than that of the carbon rebar, and the Cr oxides/hydroxides facilitate the transformation of FeO(OH) with larger volume expansion to Fe3O4 with smaller volume expansion, reducing from 130 μm in HRB to 70 μm in the case of the thinnest Cr11 rebar. The thin and dense rust layer of the developed rebars is advantageous in blocking Cl- and guarantees a smaller volume expansion of structure even if the rebars are corroded. This study underscores the suitability of Cr-modified rebars for sea sand concrete structures and sheds new light on rebar-reinforced concrete structure developments toward eco-efficient and sustainable infrastructures.

Evaluation of corrosion potential in near-shore piles and analysis through RSM modelling

Corrosion is a significant problem in marine environments that ultimately leads to structural failure and economic losses. The assessment of the conditions of concrete piles is an essential part of corrosion prevention measures in marine environments. This research investigated the corrosion potential of concrete marine piles using a half-cell potentiometer. Following this, the observed potential values are subjected to RSM modeling. Approximately ten piles were chosen in Chennai Fishing Harbor, and the corrosion potential values along the depth of the piles in three different zones, namely, the atmospheric, splash and submerged zones, were measured at three-month intervals. Based on the visual inspection, the piles were damaged, and minor cracks developed on the surfaces of the concrete due to the dynamic impact of wave action, specifically in the splash zone. From the results obtained in the field for the chosen piles in the fishing harbor, the corrosion potential values are in the range of −361.45 mV to −527.57 mV in the atmospheric zone, − 520.67 mV to −784.85 mV in the splash zone and– 401.23 mV to—631.28 mV in the submerged zone. RSM was noted to be the most accurate predictor with the highest R2 and least errors. The RSM model captured the variability of the data according to the R2 threshold (R2 > 0.9855). The splash zones have higher corrosion potentials and are more prone to corrosion than the other zones.

Geopolymer composites for marine application: Structural properties and durability

In marine environments, traditional ordinary Portland cement (OPC) and reinforced concrete structures are prone to corrosion, reducing their durability and service life dramatically. Geopolymers, with exceptional corrosion resistance, have great value and application potential in marine engineering. This paper presents a comprehensive overview of the research advances on geopolymer cements and concretes in marine environments in terms of mechanical properties, durability, and structural properties. The research so far has demonstrated that geopolymers exhibit superior mechanical properties and durability due to their denser interface and lower porosity compared to OPC. However, geopolymers have significant brittleness defects, and their performance in marine environments, especially in splash and tidal zones with alternating wet and dry conditions, is severely affected. This is due to the influence of chloride ions, divalent cations, pH, and sulfate in seawater, which promote or inhibit the formation and transformation of reaction products and microstructures, thereby affecting their mechanical properties and stability. Nevertheless, the use of composite technologies such as modified precursors, fibers, and nanomaterials has a positive effect on enhancing their structural properties and durability. This provides guidance and solutions for the application of high-durability, low-carbon emission, and more sustainable building materials in maritime engineering.

Integrating physics-based simulations with gaussian processes for enhanced safety assessment of offshore installations

Installing large floating objects during offshore operations is a challenging and failure-prone task, especially when passing through the splash zone due to extreme lifting loads on the wire and the payload. For a safe operation, it is essential to predict the peak loads on the installation system and create an early decision-making scenario for the installation vessel before starting the real operation on site. To this end, the extreme loads that can lead to unsatisfactory performance of the system must be evaluated accurately; however, the operation involves a great deal of uncertainty and physics complexity that can lead to unreliable decision-making. It is also challenging to perform numerical calculations to support ongoing marine operations, as it usually takes hours to evaluate different environmental load cases. Thus, it is essential to create an efficient prediction method associated with the environment and the corresponding response levels. In this study, a model is proposed that integrates physics-based simulations with Gaussian Processes, for estimating peak loads in lifting wires. The model offers the advantage of addressing shorter simulation times while still maintaining accuracy in predicting extreme response levels and quantifying the loads uncertainty during the operation. Bayesian Inference is used to incorporate the uncertainty, estimating hyper-parameters and predict the peak loads for various marine environmental conditions. A real case study is considered to demonstrate the application of the proposed model. The results show good agreement with the simulations obtained from time-domain dynamic analysis. The current study provide insights for both onboard and pre-planned decision-making on installation conditions, thereby enhancing predictive accuracy and improving safety in complex marine lifting operations.

Asymmetric deterioration of reinforced concrete marine piles subjected to nonuniformly localized corrosion: Experimental study

Reinforced concrete (RC) marine piles usually suffer from local stiffness deterioration caused by chloride attack in splash and tidal zones. Moreover, pre-existing concrete cracks and defects at the steel–concrete interface usually lead to nonuniformly localized corrosion, which has seldomly been discussed. In this study, the effects of nonuniformly localized corrosion on the lateral behaviours of piles were experimentally studied. The localized electrochemical chloride erosion (LECE) technique was employed, and the corrosion level was represented by the number of corroded steel bars and the length of the corroded sections. Results show that the nonuniform localized corrosion caused asymmetric force–displacement hysteresis curves and changed the failure mode of pile structure under cyclic loading. The highly contrast mechanical responses suggest the importance of the loading directions in assessing the mechanical behaviours of corroded piles. Skeleton curves, stiffness degradation and energy dissipation capacity were further analysed to investigate the bearing capacity of corroded piles. These findings can benefit the comprehensive understandings and assessment of the asymmetric stiffness deterioration of corroded marine RC piles.

Constructing PANI@CF hybrids enhanced epoxy coatings with integrated functionalities of interfacial enhancement, erosion wear resistance and anti-corrosion

Factors such as sediment erosion and diffusion of corrosive ions in the splash zone result in a serious decrease in the protective performance of organic coatings. Carbon fiber (CF) reinforced polymer coatings have attracted much attention due to the impressive high mechanical strength and reliable chemical stability, but their protection period for steel structures is usually limited by the surface inertness and poor interfacial compatibility of the original CF. Herein, we created a composite coating with excellent erosion and wear resistance and corrosion resistance through simple self-polymerization of polyaniline on carbon fibers. The PANI layer not only helped to improve the interfacial compatibility between fibers/resin, but also exerted its corrosion inhibition effect. The interfacial shear strength (IFSS) value of the modified PANI4@CF monofilament and resin (60.63 MPa) was 46.73 % larger than that of the unmodified CF monofilament. In the simulated splash zone, PANI4@CF5/EP composite coating showed the best erosion resistance and corrosion resistance, and the mass loss and volume loss after erosion test were reduced by 53.39 % and 50.10 %, respectively, compared with pure epoxy coating. The local electrochemical impedance spectroscopy (LEIS) value of PANI4@CF5/EP coating with artificial defect was one order of magnitude higher than the epoxy coating after 48 h immersion. Finally, the environmental conditions of the splash zone were simulated to evaluate the anti-corrosion performance and erosion resistance of the CF reinforced composite coatings, and the protective mechanism was discussed in depth, which has great significance to the development of protective coatings for the splash zone under extreme marine environments.

Investigation of a Cathodic Protection Configuration for the Steel Casing Pipes in Reinforced Concrete Bridge in the Niger Delta

This paper details the Design of a Cathodic Protection System on the steel casing pipes of the 60m reinforced concrete bridge project in the Niger Delta, Nigeria. Galvanic anode cathodic protection system was provided for the submerged steel support piles on the newly reinforced concrete bridge to ensure adequate corrosion protection of the structures. A total of fifty-six (56) Aluminum Anodes (32 kg) were used. Two of the Aluminum anodes were installed on each of the twenty-eight (28) steel casing piles. The anode installation was achieved by means of clamping at the predetermined water depth of 37.2 m with purpose made carbon steel clamps. The bonding of the anode to the pile structure to make electrical contact was achieved through welding of the pre-installed anode steel core extension bar against the steel pile at the water splash zone area of the river. A pre- and post-installation test and survey activities were conducted on each of the steel piles to ascertain the integrity of the installation and degree of corrosion protection of the steel casing piles. The field test and measurement results indicated mean values of open circuit potential of 0.600 Volts and polarized corrosion potential of 0.850 Volts. The recorded corrosion potential for the installed cathodic protection system confirmed adequate corrosion protection for ten (10) years from anode life for the steel casing supports of the 60 m reinforced concrete bridge.

Predicting corrosion for life estimation of ocean and coastal steel infrastructure

AbstractPhysical infrastructure in coastal and offshore locations often is constructed from mild and low alloy steels. These are prone to marine corrosion even with the application of protective coatings and cathodic protection. Particularly for high‐value assets such as energy facilities (wind farms, oil and gas production and subsea pipelines), the prediction of their safe and economic life is of much interest. Herein, a review is given of the modern development of models for the prediction of long‐term marine corrosion of steel exposed to various marine environments. These include immersion, tidal, splash and atmospheric zones and contact with sands and soils. The effects of temperature and water pollution are especially important, as is the ability of the steels or irons to form protective corrosion products. Comments are made also about other alloys such as copper‐nickels and aluminium. All show that corrosion, including pitting corrosion, develops with increased exposure time in a bimodal manner. The reasons for such behaviour are considered, together with the practical implications, important for containment structures such as pipelines, tanks and floating offshore energy platforms.

A Corrosion- and Repair-Based Reliability Framework for Offshore Platforms

Offshore platforms are important infrastructures that often face severe environmental conditions, such as corrosion, throughout their lifetime. This can continuously decrease their structural robustness. Despite the availability of many anti-corrosion strategies, there is still a need for a sound management scheme that can systematically address the lifetime operation of offshore platforms under corrosion. To address this, the work here proposes a corrosion- and repair-based reliability framework for the lifetime operation of offshore platforms. A fixed offshore platform is designed based on current design codes for severe environmental conditions in a given return period, and the effect of corrosion on the structure’s serviceability is modeled. The results show that the extent of the corrosion depth and damage in different years highly affects the ability of a repair to restore a damaged element to its original design strength. The results also show that the residual reliability of the structural members under the splash zone becomes almost zero after the first 10 years of the operation period, implying that these members require quick repair strategies. This study establishes a management program for fixed offshore platforms subjected to long-term corrosion by performing reliability analyses on the components of the platforms and evaluating the maintenance of the components in the splash zone. In the absence of commonly accepted contemporary industry practice standards, this study proposes a corrosion growth model based on API-RP-2A, DNV, and NORSOK standards that can effectively evaluate code-based structural designs. The framework developed here can help offshore platform owners in their decision-making process for corrosion-based safety analysis.

Cementitious composites in aquatic environments, evaluation of fracture and mechanical behavior in long-term submerging in fresh and saltwater, and simulated splash zone conditions

Aquatic environments can be severely harsh, so structures need suitable materials to endure them. Among the materials promising for aquatic environments are cementitious composites; however, their ability to withstand degrading environments should be evaluated. This study aims to evaluate cementitious composite's mechanical and fracture behavior with seven mix designs in three aquatic environments submerged in fresh and saltwater and exposed to a simulated offshore tidal-splash regime. Environmental exposure durations were chosen as 28, 90, and 365 days. Cementitious composites were developed with glass, PVA, and PP fibers. The results show materials with different behaviors, from fully brittle (without fiber) to strain-hardening (made of PVA and PP fibers). In the simulated splash zone environment, up to 25% strength degradation is seen in the most severe conditions. Among the parameters, fracture indexes are reduced more severely. The failure patterns were investigated, some SEM photos were presented, and some statistical evaluations (including trends and correlations) were presented.

Reaction mechanisms and diagnostic mineralogy of intertidal steel corrosion: An X-ray photoelectron spectroscopy study

The products of intertidal and super tidal (splash zone) corrosion on steel piles have been characterised at 3 UK sites with contrasting environmental conditions in order to determine corrosion reaction mechanism and if a common mechanism for accelerated low water corrosion occurs across sites. Intertidal corrosion samples at Shoreham and Newhaven ports show an internal composition of iron mono- and bi-sulphide, with intermediate sulphur oxidation state compounds, and an outer surface dominated by iron oxides and oxyhydroxides with a component of iron sulphates. The FTIR spectra are characteristic of sulphate green rust. In contrast, samples from Southend have all sulphur species below detection levels and are dominated by iron oxides and oxyhydroxides. Carbon binding energy spectra are consistent with the development of biofilms at all sites except for a splash zone sample at Southend. The results demonstrate a common mechanism for ALWC at Newhaven and Shoreham, involving the action of sulphate-reducing bacteria generating iron sulphides on the steel surface. These are subsequently oxidised to produce sulphate green rust, which may in turn oxidise to produce lepidocrocite. At Southend differences in environment are inferred to restrict the activity of sulphate reducing bacteria, resulting in direct oxidation of steel to generate iron oxyhydroxide gels, which subsequently recrystallise, dehydrate and oxidise to goethite, magnetite and ultimately hematite in both splash zone and intertidal samples. The multi-technique approach used here characterises the full range of corrosion products.

Corrosion behavior and microstructure analysis of butt welds of Q690 high strength steel in simulated marine environment

Steel components that have served in the marine environment for extended periods often face challenges in preventing surface damage caused by corrosion protection measures. These challenges can ultimately diminish the expected service life of structures. To investigate the corrosion behavior and time-varying effects in butt welds of Q690 high strength steel in the ocean splash zone, a macroscopic morphology analysis was conducted using various corrosion times involving indoor saltwater immersion and hot-humid cycling accelerated corrosion. Quantitative analysis of corrosion pits' size and distribution range was performed in both the weld zone (WZ) and heat-affected zone (HAZ) to establish a relationship between roughness parameters and corrosion time. Experimental results were compared with corrosion parameters of regular steel. The findings reveal a gradual reduction in metallic luster with increasing corrosion time on specimen surfaces. Moreover, a greater accumulation of corrosion products is observed in the butt weld region, leading to progressive corrosion damage. High strength steel (HSS) exhibits superior corrosion resistance compared to ordinary steel. However, the corrosion damage of HSS weld joints gradually approaches that of ordinary steel in the later stage of corrosion. Microscopic scanning indicates that the accumulated corrosion layer effectively impedes the penetration of corrosive media into the matrix's interior, while the surface microstructure transitions from pitting to corrosion pits. These research findings significantly contribute to assessing the performance and analyzing the reliability of high strength steel in marine environments.