Simulated Marine Environment Research Articles

Initiation Mechanism of Localized Corrosion Induced by Al2O3-MnS Composite Inclusion in Low-Alloy Structural Steel

The present work systematically investigated the initiation mechanism of localized corrosion induced by Al2O3-MnS composite inclusion in E690 steel under a simulated marine environment. The results showed that a micro-gap exists between the Al2O3-MnS inclusion and the matrix, and electron backscattered diffraction (EBSD) analysis revealed significant lattice dislocation zones around the Al2O3-MnS composite inclusion. The presence of the micro-gap and the lattice dislocation both promoted the localized corrosion initiation. The Volta potential of Al2O3 detected by scanning Kelvin probe force microscopy (SKPFM) was approximately 149.33 mV higher than that of the steel matrix, and the Volta potential of MnS was 10 mV lower than that of the steel matrix. The current-sensing atomic force microscopy (CSAFM) results showed that the Al2O3 was not conductive, while the MnS had good conductive properties. Therefore, it was not possible for a galvanic couple to be formed between Al2O3 and the adjacent steel matrix. A galvanic couple effect between the MnS and the adjacent steel matrix was directly demonstrated for the first time. The MnS acted as the anode phase for preferential dissolution in the corrosion process. The in situ immersion experiments and the Pourbaix diagram results confirmed that the dissolution of MnS was an electrochemical reaction process and the dissolution of Al2O3 was a chemical reaction.

A comparative study of mechanical and chemical durability of non-wetting superhydrophobic and lubricant-infused surfaces

Fabrication of bioinspired non-wetting superhydrophobic surfaces (SHS) and lubricant-infused surfaces (LIS) has been studied extensively on a variety of materials. In contrast, durability of the surfaces exposed to harsh mechanical and chemical environments has been the subject of little attention. This study considers the mechanical and chemical durability of SHS and LIS copper surfaces fabricated via facile electrodeposition and chemical etching methods. The as-fabricated surfaces demonstrate excellent non-wetting characteristics with water contact angle of 160° and sliding angle below 5°. The surfaces are subject to mechanical wear through scratch test and water jet impingement at 15 psi and 20 psi as well as accelerated corrosion following the ASTM-E407 standard. The performance of the electrodeposited and etched non-wetting surfaces is systematically assessed in terms of contact and sliding angles and corrosion rate in a simulated marine environment. All surfaces are shown to be robust to mechanical wear after scratch test, with excellent stability of contact and sliding angles, and up to two orders of magnitude reduced corrosion rate compared to bare copper surface. SHS retained steadfast non-wetting characteristics under high-pressure water jet tests compared to the other surfaces while LIS, regardless of texturing method, showed one to two orders of magnitude reduced corrosion rate compared to bare copper surface throughout water jet impingement and chemical durability tests. The study presents for the first time a systematic comparison of durability of SHS and LIS through a common set of fabrication and testing protocol and helps identify appropriate non-wetting surfaces and fabrication methods based on the use environment.

Corrosion behavior of 1Cr18Ni9Ti–1Cr11Ni2W2MoV galvanic couples in a simulated marine environment

The corrosion behavior of 1Cr18Ni9Ti–1Cr11Ni2W2MoV galvanic couples with different surface treatments (including chemically passivated, Cd-plated, Cu-plated, and damaged Cu-plated) was studied in a simulated marine environment. Scanning electron microscopy was used to analyze the micro-corrosion morphology and structure of the samples. Polarization curves, galvanic currents, and rates of corrosion of the samples were each measured and determined. The results showed that galvanic corrosion was much more serious on the galvanic couples than monomer corrosion. With increasing corrosion sensitivity under acidic conditions, the specimens were more prone to corrosion. Under neutral and acidic conditions, the average galvanic current densities of the damaged Cu-plated sample were five and eight times those of the Cu-plated sample, respectively, indicating that the integrity of the surface plating improved the corrosion resistance of the samples effectively. In neutral environments, the chemically passivated sample had the highest self-corrosion potential, the lowest corrosion rate, and the best corrosion resistance, while the Cd-plated sample showed the opposite behavior. The corrosion mechanism of the damaged Cu-plated and Cd-plated samples was related to the combined effects of galvanic corrosion and crevice corrosion. As the potential difference between the Cu-plated and the chemically passivated samples was less than 50 mV, the corrosion was relatively weak.

Long-Term Performance of Seawater Sea-sand Concrete (SSC) Columns Wrapped with CFRP Strips Under Simulated Marine Environment

This article presents a durability study of carbon fiber-reinforced polymer (CFRP) partially wrapped seawater sea-sand concrete (SSC) columns exposed to natural seawater to explore the effect of exposure duration on the long-term performance of the specimens. Thirty-two cylinders were wrapped with CFRP jackets and exposed to different times of wet-dry cycles (up to 360 days) in an outdoor simulated marine environment. Test results indicate that exposure has no obvious influence on the failure process and ultimate strains of specimens, but the compressive strengths of confined columns (fcc) increase with the increment of exposure time, especially for the partially confined concrete specimens. Moreover, due to the significant variation of unconfined concrete strength fco*), the retentions of fcc and fcc/fco * exhibit an opposite trend. Therefore, the increase of fco* should be considered when using the parameter of the confined-to-unconfined ratio of strength to evaluate the long-term performance of the specimens.

Preparation of Superhydrophobic Coating on 5083 Aluminum Alloy for Corrosion Protection in Simulated Marine Environment Containing SRB

Preparation of Superhydrophobic Coating on 5083 Aluminum Alloy for Corrosion Protection in Simulated Marine Environment Containing SRB

Focusing on the relationship between the precipitated phases and the pitting corrosion of ZL101A aluminum alloy

The pitting corrosion behavior of ZL101A aluminum alloy in simulated marine environment was investigated for guiding the composition design. The Volta potential of the precipitated phases was mainly characterized via the in situ SKPFM technique. The obtained results indicated that the precipitated phases of ZL101A were composed of Al–Si phase, Si–Mg–Fe phase and Si-rich/Al-poor phase, accelerating the formation of corrosion pits during immersion test. Both Al–Si phase and Si–Mg–Fe phase accelerated the corrosion process through the self-dissolution and the galvanic effect, respectively, which can be contributed to the high corrosion sensitivity of the two phases. Si-rich/Al-poor phase presented high corrosion resistance, which should be related to the deficiency of impure elements such as Mg and Fe.

Event-triggered robust adaptive control for path following of the URS in presence of the marine practice

This note investigates an event-triggered robust adaptive control for path following of the unmanned robot sailboat (URS) by employing the proportional integral sliding mode manifold and the robust neural damping technique in presence of marine practice. The dominant assignment of this note can be summarized into three points: (1) The double-layer virtual guidance is developed to generate the reference signal for three navigation conditions (i.e., the upwind sailing, the downwind sailing and the crosswind sailing). That can enhance the navigating automatism of the URS while the tacking and the gybing. (2) The system uncertainties are approximated by the radial basis function neural networks (RBF-NNs). To further simplify the controller form, the robust neural damping technique has been introduced to evade the updated information of the neural weights. Furthermore, the input saturation of the closed-loop control system is tackled by constructing the auxiliary variable in the control design. (3) The communication burden in the channel from the controller to the actuator can be reduced for merits of the event-triggered rule. Besides, the system chattering, caused by the marine disturbances has also been reduced through the proportional integral sliding mode manifold and gain-related adaptive law. The tracking errors of the closed-loop control system will converge to a compact set, and all the signals satisfy the semi-global uniformly ultimately bounded (SGUUB) stability. Finally, the effectiveness and the robustness of the proposed algorithm have been demonstrated via the numerical simulations under the simulated marine environment.

Durability assessment and behavior under axial load of circular GFRP-RC piles conditioned in severe simulated marine environment

This study concerns the feasibility of using innovative glass fiber-reinforced polymer (GFRP) bars, spirals, and hoops in constructing sustainable marine reinforced concrete structures. The experimental investigation aimed at assessing the durability and structural performance of GFRP-reinforced concrete (RC) circular piles exposed to two simulated marine environments in the laboratory. A total of 15 GFRP-RC circular piles measuring 304 mm in diameter and 1000 mm in height were longitudinally reinforced with GFRP bars and transversely with GFRP spirals or hoops. Five specimens were fabricated as references (unconditioned). The remaining 10 specimens were continuously immersed in simulated marine environments (conditioned) for 12 months: five were kept in seawater at room temperature (22 °C), while the other five were stored in a large chamber that produced hot waves at high temperature (60 °C). After conditioning, all the specimens were tested under axial compression loads. Two structural variables were considered: the transverse reinforcement configuration (spirals versus hoops) and the confinement level (spiral spacing). The durability assessment included microstructure examinations (i.e., differential scanning calorimetry (DSC) and scanning electron microscopy (SEM)) were performed on GFRP bars and spirals taken from the conditioned piles. Furthermore, the bond between concrete and bars or spirals was checked by optical microscopy (OM). The microanalysis observations indicate no visible damage in the contact surface between concrete and GFRP bars or individual fibers and the resin matrix. The compressive test results pointed out that the GFRP-RC piles subjected to severe marine environments experienced 19% enhancement in their axial capacities compared to their reference counterparts. The GFRP spirals and hoops performed well in severe marine environments. The nominal axial capacities of the columns were predicted with the available design equations and are presented and discussed herein.

The influence of Ni on the microstructure and corrosion resistance of high-strength low alloy steel in the Cl-containing environment

PurposeThis paper aims to search the optimum content of Ni on the microstructure, phase and electrochemical behavior of high-strength low alloy (HSLA) steel in the 3.5 wt.% NaCl solution.Design/methodology/approachThe microstructure and corrosion resistance of Ni-containing HSLA steel in the simulated marine environment was studied by optical microscopy, scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques.FindingsThe sample containing 3.55 wt.% of nickel exhibited a finer grain size of 10 μm and a lower icorr of 2.169 µA cm−2. The XRD patterns showed that the Fe-Cr-Ni solid solution, FeC and Cr3C2 were observed in samples when Ni was added. Besides, the 3.55 wt.% of nickel addition enhanced the charge transfer resistance of the low alloy steel which suggested the sample possessed excellent inhibition of electrochemical reaction and corrosion resistance. The XPS spectrum suggested that nickel was beneficial to improve the corrosion resistance of steel by forming protective oxides, and the ratio of Fe2+/Fe3+ in protective oxides was increased.Practical implicationsFinding the comprehensive performance of HSLA steel which can be applied to unmanned surface vehicles in marine operations.Originality/valueThis study has a guiding significance for optimizing the composition of HSLA steel in a Cl- containing environment.

Investigation on the SCC behavior of ZL101A aluminum alloy in simulated marine environments

Stress corrosion cracking (SCC) behavior of ZL101A aluminum alloy in solution and thin electrolyte layer (TEL) with different pH was investigated in detail. The results indicated that the precipitated phases of ZL101A were composed of α-Al/Si eutectic crystal phase and Si–Mg–Fe precipitated phase, which accelerated the formation of corrosion pits. ZL101A presented the highest SCC susceptibility in pH = 4 solution compared with pH = 7 and 10 solutions, which was mainly attributed to the enhanced synergistic effect of anodic dissolution, stress and hydrogen embrittlement. The basically similar SCC susceptibilities in TEL environments were mainly controlled by the anodic dissolution, which was attributed to the high diffusion rate of O2 in the thin electrolyte film.

Corrosion behavior of aluminium alloys 2024 and 7075 under simulated marine environment

Corrosion behavior of aluminium alloys 2024 and 7075 under simulated marine environment

A comparative study on the corrosion behavior of CoCrNi medium-entropy alloy and 316L stainless steel in simulated marine environment

This paper investigates the difference in the corrosion resistance and passive property of CoCrNi medium-entropy alloy and 316 L stainless steel in a simulated marine environment by using electrochemical measurements, immersion test and surface analysis technology. The results reveal that CoCrNi MEA has more superior anti-corrosion resistance than that of 316 L. The difference in the corrosion resistance is related to the microstructure and surface passive film. Due to the presence of oxide inclusion, micro-galvanic corrosion is formed between the oxide inclusion and CoCrNi matrix, which promotes the anodic dissolution of CoCrNi MEA and induces the formation of pits. The matrix as the anode mainly undergoes the selective dissolution of Co element, while the selective dissolution of Co and Ni elements is occurred in the cathodic oxide inclusion.

Not Only Diamonds Are Forever: Degradation of Plastic Films in a Simulated Marine Environment

In recent years, biodegradable polymers have been hailed as one of the potential solutions to the plastic pollution problem, due to their ability to fully degrade rather than break down in smaller pieces over time. However, complete degradation of biodegradable polymers is often achievable only under strictly controlled conditions (i.e. increased temperature and pressure), which are not found in the natural environment – particularly in aquatic and marine habitats. This study aims to compare the degradation performance of plastic films made of two different biodegradable polymers – polylactic acid (PLA) and polyhydroxyalkanoates (PHA) – to that of low-density polyethylene (LDPE) films, in a simulated marine environment. Plastic films of the three chosen polymers, of equal dimensions, were exposed to natural sunlight within a novel setup - which simulated the sea surface - for six months. Films were chosen as they are among the most frequently reported type of plastic litter in coastal environments worldwide, and because of the increasing adoption on the market of biodegradable films for packaging. Results showed that, after six months, no consistent degradation could be observed on any of the films–not even the biodegradable ones. Between PLA and PHA films, the latter weathered slightly more than the former, but not at a significant level. Interestingly, differences were reported among the different polymer films in terms of type and extent of biofouling, brittleness, surface charge and surface microstructural changes. Overall, this work suggests that biodegradable plastic behaves rather similarly to traditional plastic in the marine environment over a half-year span. Albeit further experiments on even longer timescales are needed, this study provides evidence that, unless properly disposed of in an industrial composter facility, biodegradable plastic may only contribute to the very problem it was intended to solve.

Long-term flexural behavior of concrete beams with hybrid FRP and steel reinforcements in simulated marine environment

In this study, the long-term flexural behavior of beams reinforced by basalt fiber-reinforced polymer (BFRP) and steel in a simulated marine environment was investigated. Nine beams were designed based on the principle of equal-rigidity, and they were reinforced with steel rebars, BFRP bars and grids. Four-point flexural experiments were carried out after accelerated corrosion treatment for 0, 3 and 6 months respectively. The experimental results indicated that the flexural capacity, stiffness after yielding and crack control of the beams with hybrid reinforcements were effectively improved compared to the reinforced concrete (RC) beams. Compared with the beams without soak, the flexural behavior of the RC beams decreased after 6 months, on the contrary, the beams reinforced with steel and BFRP bars did not show any degradation. For steel bars-BFRP bars and grids hybrid reinforced beams, the additional grids led to a more outstanding flexural behavior before steel yielding compared to the RC beam, however, a sustained decline in flexural behavior was observed after steel yielding owing to the thinner cover and higher sustained loads in the simulated ocean environment. The secondary stiffness and ductility of the hybrid reinforced concrete beams changed slightly after conditioning. Further, the hybrid reinforced concrete beams exhibited narrower crack width compared to RC beams during the entire experimental period.

Hot corrosion-creep interaction in IN718 under simulated marine environment: Introducing strain-associated-time (SAT) plots for comprehensive understanding

Creep-rupture behaviour of IN718 with deposit of 87.5 wt.%Na2SO4+5 wt.%NaCl+7.5 wt.%NaVO3 (3SM) in the stress range of 550–850 MPa at 650 °C is investigated. 3SM shortens the creep-rupture time by ≈70–90 %. Comprehensive microstructural analysis suggests that oxygen-induced-dynamic- embrittlement, sulphidation followed by oxidation, and vanadic-hot corrosion operate during creep. Creep-hot corrosion interaction influence on rupture strain is explained by introducing strain-associated-time (SAT) and Δtε plots, for the first time. These plots accompanied by detailed microstructural examination demonstrate that deleterious influence of 3SM increases with decreasing stress. Further, SAT plots and EPMA analysis confirm that oxygen-induced-dynamic-embrittlement commences from ∼9% strain under 3SM at 550 MPa.

Impact of seasonal variations on Nannochloropsis oculata phototrophic productivity in an outdoor pilot scale raceway

This study investigated the impact of seasonal variations on the productivity of Nannochloropsis oculata culture, cultivated in an outdoor pilot scale open pond raceway over 16 months. The 2.5 m3 pilot (i.e. water depth of 20 cm) was operated under phototrophic conditions in a simulated marine environment at 50 g.L−1 of salinity. Results revealed that culture growth rates, doubling times and productivity were highly impacted by weather conditions with a good reproducibility of seasonal features. During summer, growth rate (i.e. 0.15 d−1) was higher than in winter (i.e. +300%) and in spring-autumn (i.e. +40%). Average areal productivities were higher during summertime (i.e. 13.2 t.ha−1.y−1 or 3.61 g.m−2.d−1) compared to those of winter (i.e. +264%) and autumn-spring conditions (i.e. +90%). Monthly correlation analysis revealed also a significant correlation between productivity and weather conditions (i.e. higher than 0.85), especially during culture periods not affected by microbial contamination, while daily correlation analysis showed that microalgae have a relative long-time spread response (i.e. about 10 days) to change in weather conditions. Therefore, the monthly approach appeared more suitable for considering weather effects over microalgae culture.

Permeation Characteristics and Surface Accumulation of Chloride in Different Zones of Concrete along Altitude in Marine Environments

The accumulation characteristics of surface chloride in concrete in different zones are different in the marine environment. A series of laboratory experiments were conducted to investigate the surface chloride and permeation characteristics of concrete in a simulated marine environment. The experimental results indicated that the surface chloride and chloride profiles of concrete in different zones of marine environment decreased in the following order: tidal zone > splash zone > submerged zone > atmospheric zone. The width of the ascent zone of Cl− concentration at tidal and splash zones was far less than that of the influential depth of moisture transport (IDMT), and the range of convection zone was dependent on the IDMT. Cl− at splash and tidal zones penetrated into concrete as a bulk liquid by non-saturated permeation driven by a humidity gradient. The change of chloride profiles in concrete along the altitudinal gradient was consistent with that of the cyclic water absorption amount (CWAA). The transport rate of chloride was the highest at the highest point of the tide.

Correlation between hyperfine structure of inclusion and localized corrosion mechanism of DSS2101 with Ce microalloying in simulated marine environment

The discrepancies in inclusion characteristics and localized corrosion behaviour and mechanism induced by inclusions in DSS2101 are contrastively investigated. We found that the two types of inclusions consisted of (Al, Mn, Cr)–O–S and (Ce, Al, Mn)–O–S. Numerous twins and denser entangled dislocations were distributed near the (Al, Mn, Cr)–O–S/matrix. The distorted and normal BCC phase exhibited the {1‾10}N∥{1‾12}D orientation relationship, whereas severe lattice expansion existed along the {01‾2} and {1‾20} crystallographic directions, presumably resulting in the priority initiation of pitting. Besides, the (Al, Mn, Cr)–O, (Al, Mn)–O core and CeAlO3 shell had especially poor electrical conductivity, making formation of the galvanic couple difficult. However, the deformed matrix served as an anode relative to the normal matrix (as a cathode), facilitating pitting rate of Ce-free steel. In contrast, the electrochemical reaction of MnS (as an anode) and the chemical reaction of the CeAlO3 shell protected the adjacent matrix (as a cathode) from erosion by self-dissolution in Ce-modified steel. The synergistic effect of the differential aeration cell (DAC) and occluded corrosion cavity (OCC) was supposed to deteriorate the microcrevice corrosion and galvanic corrosion.

Effect of Acinetobacter Sp. on Corrosion Behavior of 10MnNiCrCu Steel in Simulated Marine Environment

Effect of Acinetobacter Sp. on Corrosion Behavior of 10MnNiCrCu Steel in Simulated Marine Environment

Effect of Beam Oscillation Patterns on the Electrochemical Corrosion Behavior of Electron Beam Welded Ti-5Al-2.5Sn Alloy in Simulated Marine Environment

Ti-5Al-2.5Sn alloy plates of 1.6 mm thickness were EB welded using four weld patterns (rectangular, elliptical, concentric circles and arrow). The fusion zone of all the patterns with variable amount had α´ martensite and acicular α with prior β at grain boundaries which resultantly affected the corrosion resistance. Several electrochemical techniques indicated that the elliptical pattern showed better passivation and film stability as compared to other patterns. The arrow pattern experienced more pitting due to the higher proportion of α´ martensite in its FZ. The EIS data indicated that the elliptical pattern had a stable uniform layer formation on the surface with low passivation resistance. In case of BM, uniform passivation layer of oxides was formed, without any sensitization.