Natural Seawater Environment Research Articles

Evolution of Surface Integrity Characteristics and Mechanical Behavior of Diamond Burnished and Turned AISI 304 Steel Specimens After Prolonged Exposure to Natural Seawater

This article presents results on the evolution of surface integrity, microstructure, mechanical characteristics, fatigue strength, and wear behavior of AISI 304 steel specimens after prolonged exposure (up to 746 days) to a natural seawater environment, specifically near the port of Varna, Bulgaria. The samples, having different shapes and sizes according to the respective tests, were divided into two main groups based on the finishing process: fine turning (FT) and diamond burnishing (DB). Additionally, fatigue FT specimens were polished to meet the standard requirements. Some of the cylindrical samples from both groups were heat-treated to dissolve the car-bides. No significant improvement in the corrosion resistance of the heat-treated samples (FT and DB) was observed compared with untreated samples after 746 days of immersion in seawater. Overall, all types of DB specimens showed less mass loss (indicating a higher corrosion resistance), higher static and fatigue strength, greater plasticity, and greater wear resistance than the corresponding FT specimens. Notably, pitting corrosion was observed on all specimens, as well as trac-es of intergranular corrosion in some FT specimens. The hardening DB effects have a complex impact on corrosion activity. The increases in dislocation density and the surface and internal energy of the subsurface layers intensify the nucleation of corrosion centers in the surface layers; however, the refined fibrous structure and significant reduction in the roughness slow down the development of corrosion. Therefore, the implementation of DB as a smoothing process will re-duce the surface energy, and hence will lead to further increases in corrosion resistance.

Research on the Effect of Natural Seawater in Domesticating Bacillus pasteurii and Reinforcing Calcareous Sand

Microbial-Induced Calcium Carbonate Precipitation (MICP) is an environmentally friendly, efficient, and sustainable new soil reinforcement technology. For this study, Bacillus pasteurii were domesticated and cultured in a natural seawater environment with multiple gradients and used for coral reef calcareous sand reinforcement, comparing the mineral composition of the generated precipitates and the reinforcement strength under different domestication gradient conditions. The results revealed that, while the natural seawater environment inhibits the growth of Bacillus pasteurii, the gradient domestication method allows the bacteria to gradually adapt to the natural seawater environment. Notably, their shape becomes thin and long under the seawater environment. Furthermore, the MICP mineralisation reaction rate is faster in the natural seawater environment and, with an increase in the domestication gradient, the mineralisation reaction precipitates increased. At the same time, in the seawater environment, a small amount of mineral components were generated in addition to CaCO3, such as MgxCay(CO3)z, and the Mg2+ mineral content increased with an increase in the domestication gradient. When comparing the curing effect under different gradients in the natural seawater environment, it was found that the Bacillus pasteurii can effectively enhance the curing effect of the calcareous sand after multi-gradient domestication in the seawater environment, with the curing effect increasing with an increase in the domestication gradient. The results of this study provide new ideas for the application of MICP technology in seawater environments for the reinforcement of calcareous sand in the construction of South China Sea islands and reefs.

A simple antifouling coating selection exhibits notable benefits for industrial fishing vessels

Impacts of biofouling were evaluated in-real conditions as a decision support system for industrial purse seiners and trawlers operating in the Mediterranean and the Black Sea (GFCM) in a fishing season. Initially, face-to-face interviews determined the most commonly used antifouling coatings among fishermen, resulting in the selection of five self-polishing copolymer (SPC) coatings. These SPC coatings, along with an uncoated reference panel, were immersed in the Black Sea's natural seawater environment for periodic fouling accumulation observations (SPC immersion tests). Additionally, selected SPC coating patches were applied on a fishing vessel to compare performances of the SPC coatings under the same conditions after a year of operation (namely ship tests). These ship test results were then compared with the outcomes from the static immersion tests. Finally, case studies were employed with the data generated from the static immersion tests for three fishing vessels operating in two different locations equipped with either trawl or purse seine. In addition to SPC coatings, foul release (FR) coatings were tested to compare their performance. Results indicated that applying an SPC coating to an industrial fishing vessel can yield fuel savings of 6%–10.26%, while a basic antifouling coating choice can save up to 3.11% in total fuel consumption over a fishing season in the GFCM area. Regardless of fishing gear used (purse seiner or trawler) or location of fishing activities conducted (Mediterranean or Black Sea), antifouling coating selection decision can reduce fuel consumption by up to 146.1M litres, fuel costs by £112.5M, and CO2 emissions by 0.42M tonnes for the regional GFCM fleet. These numbers are extrapolated to global fleet, estimating that fuel consumption can be decreased by up to 660.37M litres, fuel costs by £508.48M, and CO2 emissions by 1.9M tonnes based on the antifouling selection.

The corrosion characteristic and mechanism of Mg-5Y-1.5Nd-xZn-0.5Zr (x = 0, 2, 4, 6 wt.%) alloys in marine atmospheric environment

The microstructure and precipitated phases of as-cast Mg-5Y-1.5Nd-xZn-0.5Zr (x = 0, 2, 4, 6 wt.%) alloys were investigated by optical microscopy, scanning electron microscopy, energy-dispersive spectrometry and X-ray Diffraction. The exposure corrosion experiment of these magnesium alloys was tested in South China Sea and KEXUE vessel atmospheric environment. The corrosion characteristic and mechanism of magnesium alloys of Mg-5Y-1.5Nd-xZn-0.5Zr (x = 0, 2, 4, 6 wt.%) alloys were analyzed by weight loss rate, corrosion depth, corrosion products and corrosion morphologies. The electrochemical corrosion tests were also measured in the natural seawater. The comprehensive results showed that Mg-5Y-1.5Nd-4Zn-0.5Zr magnesium alloy existed the best corrosion resistance whether in the marine atmospheric environment and natural seawater environment. That depended on the microstructure, type and distribution of precipitated phases in Mg-5Y-1.5Nd-4Zn-0.5Zr magnesium alloy. Sufficient quantity anodic precipitated phases in the microstructure of Mg-5Y-1.5Nd-4Zn-0.5Zr alloy played the key role in the corrosion resistance.

Phytoplankton community composition variation under natural and prolonged saline intrusion simulations

This study assessed phytoplankton community composition variation under two discrete salinity intrusion rate experiments. Experiment 1 simulated salinization under short-term, natural tidally induced rates of salinity change typical of the Mekong Delta, Vietnam (0–30‰ in 6 h), while Experiment 2 simulated salinization under a longer, more gradual rate of salinity change (0–30‰ at 5‰ increase per week). Phytoplankton community composition was, overall, more abundant following prolonged salinity change (Experiment 2) than rapid, tidally-induced salinity change (Experiment 1). Under both experimental conditions phytoplankton species number and density varied with changes in salinity, indicating a strong effect of salinity regardless of its rate of change. At the end of the salinity acclimation, Cyanobacteria, Chlorophyta, Euglenophyta and Bacillariophyta were all most abundant at a salinity of 5‰ after a short-term tidally simulated change in salinity, but with a longer, more gradual change in salinity, the abundance of different groups varied with salinity; With a longer, more gradual change in salinity, Chlorophyta was most abundant at 5–10‰ salinity, while Cyanobacteria, Euglenophyta and Bacillariophyta were all most abundant at a salinity of 5‰. The species composition in treatments of less than 10‰ had high similarity with the freshwater environment while treatments of 30‰ (Experiment 1) and 25‰ (Experiment 2) had high similarity with the natural seawater environment. This study demonstrates the utility of mesocosm experiments for understanding phytoplankton community composition variation in natural aquatic ecosystems under rapid and prolonged saline intrusion rates and predicting associated impacts on food webs in natural water bodies and aquaculture systems.

Highly promising recycled low-density polyethylene sheet adsorbents for uranium recovery from seawater

ABSTRACT Amidoximated absorbers based on recycled low-density polyethylene (LDPE) sheets (food packaging bags, breast milk storage bags and grocery bags) for uranium recovery from seawater were investigated. Simultaneous irradiation grafting by gamma ray was performed. A 40-µm thick LDPE sheet submerged in the acrylonitrile (AN): methacrylic acid (MAA) solution of 60: 40 v/v% with the optimal gamma ray dose of 40 kGy showed the highest cografting degree of 85.28% and the highest amidoxime group density of 4.38 mol/kg. The field study was performed along the coastal area of the Gulf of Thailand. After 56 days of soaking, the highest adsorption capacity reached 1.79 g-U/kg-adsorbent. The reusability study for up to 6 cycles revealed about 20% of the adsorption capacity remaining in the last cycle. The study demonstrated that recycled LDPE sheets can be utilized as a substrate to synthesize uranium absorbers. It showed an acceptable uranium loading with good reusability in natural seawater environment. This method of reusing discarded LDPE sheets also helps alleviate environmental issues of non-degradable plastic wastes.

Effect of sliding wear and electrochemical potential on tribocorrosion behaviour of AISI 316 stainless steel in seawater

Sliding tribocorrosion behaviours of AISI 316 stainless steel were investigated against alumina ball in natural seawater environment (SWE) under 5 N loads. OCP (open circuit potential), potentiostatic (−1 V and 0.3 V) and potentiodynamic measurements were enforced to understand the influence of the sliding wear and electrochemical potential on tribocorrosion behaviours of AISI 316 stainless steel in SWE. Tribocorrosion experiments were conducted with a ball-on-disk type reciprocating tribometer integrated with the three-electrode potentiostat. The wear track surfaces were examined by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and optical profilometry. Mechanical effects reduced corrosion potential under both OCP and potentiodynamic scans in tribocorrosion conditions. Ploughing effects on the wear track were evident at the OCP and −1 V potential because of the predominance of mechanical effects. Pits were determined to develop due to the formation of the galvanic couple between worn and unworn surfaces after the tribocorrosion test, which was conducted under 0.3 V potential. The reduction of the contact area because of the pits and the lubricating effect of the oxides on the surface caused the lowest coefficient of friction (COF) in the wear zone at 0.3 V potential. Besides, COF obtained under −1 V cathodic protection potential (0.35) was less than in OCP condition (0.37) since it only occurred by the wear effects. The study also revealed that material loss from the wear track increased from cathodic potential towards anodic potential.

Distinctiveness of Welding Joints Design Based on Mechanical and Corrosion Environmental Influence on Low Carbon Steel

Experimental investigations were carried out to study the effect of weld joint designs and post weld heat treatment (PWHT) on mechanical and corrosion properties of low carbon steel. Butt, bevel and half-lap joints were produced with a voltage of 20 V and current of 110 A with the use of 3.2 mm diameter electrode E6013. Full annealing was carried out on part of the welded samples in order to consider the possibility of post weld heat treatment for better performance. The mechanical properties (tensile, hardness, and impact toughness) were studied for both the as welded (AW) and PWHT samples as well as the corrosion performance in a natural sea water environment containing 3.5 wt.% NaCl using potentiodynamic polarization method. The microstructure of the AW and PWHT samples of the welded joints with the most promising mechanical and corrosion properties were then characterized by means of an optical microscopy. The results obtained reveals that the bevel joint followed by half lap joint and the butt joint of the as weld samples gave the best combination of the mechanical properties considered. On the other hand, the corrosion properties of the butt joint were superior to that of the bevel and half lap joint, respectively in the PWHT condition as compared to the AW samples. This implies that PWHT improves the corrosion resistance of the welded steel joints.

Friction and wear characterization of graphite/Polytetrafluoroethylene composites against stainless steel: A comparative investigation under different environments

The friction and wear characteristics of Polytetrafluoroethylene composites filled with 15 wt.% and 25 wt.% graphite were investigated against stainless steel under dry sliding and in aqueous environments. A pin on disc tribometer was employed for experimentation at room temperature. The friction performance of 15 wt.% Graphite/Polytetrafluoroethylene proved better than 25 wt.% Graphite/Polytetrafluoroethylene under all conditions, however the wear performance was better for 25 wt. % Graphite/Polytetrafluoroethylene. Moreover, the tribological behaviour of all the composites enhanced in natural sea water environment. An average COF (0.02) and wear rate (1.27 × 10-5mm3/Nm) were attained for 15 wt. % Graphite/Polytetrafluoroethylene in sea water; and an average COF (0.0293) and wear rate (5.2 × 10-6mm3/Nm) were obtained for 25 wt. % Graphite/Polytetrafluoroethylene in sea water. From SEM analysis it was revealed that the better tribological performance of graphite/Polytetrafluoroethylene in sea water is due to the formation of lubricious films on the surfaces in sea water.

Bioinspired superhydrophobic and oil-infused nanostructured surface for Cu corrosion inhibition: A comparison study

Inspired by the lotus leaf and pitcher plant, superhydrophobic surface (SHP) and oil-infused surface (OIS) have spurred wide interest in material protection field. However, which is the better choice for corrosion inhibition still remains to reveal. Herein, we report a scalable route to build superhydrophobicity and OIS onto representative Cu substrate. The as-prepared surfaces have been used for corrosion inhibition in natural seawater environment. For superhydrophobicity and OIS, the air and oil cushion anchored in Cu(OH)2 nano-needle matrix can both behave as the barrier to hurdle the diffusion of corrosive species in water phase. Using different electrochemical approaches including scanning Kelvin probe (SKP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization, the biomimic surfaces are confirmed to enable high corrosion inhibition to Cu. Compared with SHP, OIS shows a 10-fold increment in protection efficiency after being immersed in seawater for 768 h, demonstrating the high corrosion inhibition to protect Cu. The galvanic corrosion inhibition by SHP and OIS is further evaluated. Taking stainless steel 304 as the counter couple, OIS shows better corrosion inhibition to underneath Cu metal than superhydrophobic surface, demonstrating its promising application for galvanic corrosion protection.

Sulfate-Reducing Bacteria Impact on Copper Corrosion Behavior in Natural Seawater Environment

In this study, the electrochemical corrosion behavior of copper was investigated in seawater collected from four different marine zones of Agadir coastal. These zones are different by the degree of pollution in order to study the effect of this pollution on the copper corrosion, especially the microbial pollution by sulfate reducing-bacteria (SRB). So, to prove this relationship, the microbiological analyses researching the SRB are realized. In parallel, the electrochemical impedance measurement and atomic absorption analysis are established to compare the microbiological evolution cycles with the electrochemical behavior of copper during the immersion period. In the results, we found a good correlation between the growth cycle of marine sulfate-reducing bacteria and the copper corrosion rate by the sulfur and extracellular polymeric substances (EPS) produced as bacteria metabolites. Additionally, this corrosion rate depends on the immersed time: it is maximal after the first or second month depending on the marine zone.

Corrosion behavior of carbon steel in presence of sulfate-reducing bacteria in seawater environment

• Carbon steel was exposed to sulfidogenic bacteria seeded seawater in a flow loop. • Localized surface attacks followed inoculations with sulfidogenic bacteria. • Bacteria activity does not necessarily lead to significantly elevated corrosion. • Complex corrosion deposits structure. • Antimicrobial treatment temporarily suppressed bacterial activity. The influence of sulfate-reducing bacteria (SRB) on the corrosion behavior of carbon steel was studied in a laboratory test-loop, continuously fed with nutrient supplemented North Sea seawater. The main parts of the test-loop, represented by two separated flow cells, were fitted with steel specimens. The test-loop was operating anoxically for 2200 h and each flow cell was three times inoculated with Desulfovibrio alaskensis or Desulfovibrio desulfuricans species. Additionally, each flow cell was two times perturbed with antimicrobial treatments. Steel specimens exposed in flow cells exhibited comparable appearance and systems responding similarly to inoculations and antimicrobial treatments. The effect of the inoculations in both flow cells on the steel coupons electrochemical behavior was materialized as lower resistance to corrosion and higher surface activity or occurrence of localized pitting events. The localized surface attacks recognized in both flow cells after inoculations continued to progress with the time, although bacterial activity was temporarily suppressed by antimicrobial treatment. Post-exposure sample evaluations might suggest that, some particular steel surface areas have been subjected to a dramatic change in the corrosion mechanism from initial localized attack to general corrosion. The long-term exposure of the carbon steel specimens resulted in identifiable formation of biofilms and corrosion products. Corrosion deposits were characterized by a specific structure built of iron sulfides (FeS), sulfated green rust (GR(SO 4 2− )), magnetite (Fe 3 O 4 ), Fe(III) oxyhydroxides (FeOOH), chukanovite (Fe 2 (OH) 2 CO 3 ), carbonated green rust (GR(CO 3 2− )) and some calcareous deposits. Presented factual evidence reinforced the idea that sulfidogenic species in natural seawater environment may cause localized damage with a specific surface pattern; however, this does not necessarily lead towards significantly elevated corrosion rates.

“Quebracho” tannin derivative and boosters biocides for new antifouling formulations

The growth of fouling communities on ships’ hulls causes economic losses due to increased fuel consumption and to the deterioration of the metallic substrate by corrosion. Antifouling paints are formulated to avoid the settlement of these organisms and may contain biocides as active compounds. The objective of this research was to evaluate the antifouling performance of paints formulated with a “quebracho” tannin derivative (zinc “tannate”) and “boosters” (secondary biocides). The “boosters” used in this study were bismuth lactate, a zeolite exchanged with silver cations, and the same zeolite modified with silver chloride. Bioassays with “boosters” solutions were carried out employing Artemia persimilis. Soluble matrix antifouling paints were formulated and their action was assessed in a natural sea water environment. Results showed that the bismuth lactate resulted in a coating with almost triple service life of the antifouling paints with zinc “tannate.” Paints formulated with the silver composites behaved slightly better than the control paint.

Caesalpinia Spinosa Tannin Derivatives for Antifouling Formulations

AF coatings prevent the undesirable accumulation of a wide variety of marine organisms (biofouling) on ship hulls can lead to significant increased costs, principally by increased fuel consumption. The bioactive compounds (biocides) used in antifouling coatings, like tributyltin (TBT), are banned for their toxic action towards non-target marine organisms. As a consequence, the development of alternative AF coatings with new natural products as biocides inhibit is a key factor. In this approach, tara (Caesalpinia spinosa) tannin (TT) derivatives are being proposed as a promising solution.The aim of this research work was, primarily, to explore the possible application of a natural and abundant product, such as the TT, in the preparation of AF coatings. So, two TT derivatives were obtained at different temperatures (20¼C and 60¼C) as zinc “tannate” and characterized to be employed as bioactive compounds in AF coatings. Previous to the immersion in natural environments, the dissolution of TT from coatings in artificial sea water was studied. Antifouling paints with a soluble matrix were formulated and their action was assessed in natural sea water environment (Mar del Plata harbor)

Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: Electrochemical corrosion

AbstractTitanium tubes generally exhibit superior resistance against electrochemical corrosions amid seawater for their passive films TiO2. However, hydrogen‐assisted corrosion (HAC) is actually the Achilles' heel to titanium materials when the temperature exceeds near 70 °C. In this event, severe degradations like quick thinning and leakage were frequently detected on a large number of titanium tubes exposed to natural seawater environment within heat exchangers in a nuclear power plant, which caused serious safety problems. This paper is the Part I of totally two parts conducted for the whole failure analysis study, mainly focusing on electrochemical aspect of failure causes and their behaviors. By means of over ten kinds of characterization methods, the analysis results identified that the HAC induced by the interaction effects between galvanic corrosion and crevice corrosion led to local bulges of the inner walls of some titanium tubes, and then the bulges were quickly thinned and eventually ruptured under the eddy erosion from the seawater containing sediment particles. Finally, relevant mechanisms were addressed in detail and prevention methods were proposed as well.

A Mesocosm Study of the Changes in Marine Flagellate and Ciliate Communities in a Crude Oil Bioremediation Trial

Protozoan grazers play an important role in controlling the density of crude-oil degrading marine communities as has been evidenced in a number of microcosm experiments. However, small bioreactors contain a low initial titre of protozoa and the growth of hydrocarbon-depleting bacteria is accompanied by the fast depletion of mineral nutrients and oxygen, which makes microcosms rather unsuitable for simulating the sequence of events after the oil spill in natural seawater environment. In the present study, the population dynamics of marine protozoan community have been analysed in a 500 l mesocosm experiment involving bioaugmented oil booms that contained oil sorbents and slow-release fertilisers. A significant increase in numbers of marine flagellates and ciliates on biofilms of oil-degrading microbes was microscopically observed as early as 8 days after the start of the experiment, when protozoa exhibited a population density peak making up to 3,000 cells ml(-1). Further, the protozoan density varied throughout the experiment, but never dropped below 80 cells ml(-1). An 18S rRNA gene-based fingerprinting analysis revealed several changes within the eukaryotic community over the whole course of the experiment. Initial growth of flagellates and small ciliates was followed by a predominance of larger protozoa. According to microscopic observations and SSU rRNA molecular analyses, most predominant were the ciliates belonging to Euplotidae and Scuticociliatia. This is the first study to characterise the eukaryotic communities specifically in a large-scale oil bioremediation trial using both microscopy-based and several molecular techniques.

The Investigation on Optimum Corrosion Protection Potential of STS 316L in Seawater

Austenitic stainless steels have problem such as pitting, intergranular corrosion and stress corrosion cracking, which causes severe damage of structure in spite of high toughness and mechanical strength. To minimize these disadvantages in offshore structures demand of STS 316L which has small amount of C and has Mo is increasing. In this paper, the electrochemical experiments are executed to evaluate the durability at various protection potentials on stress corrosion cracking and hydrogen embrittlement of STS 316L in natural sea water environment. The polarization trend for STS 316L shows the effects of concentration polarization due to dissolved oxygen reduction reaction and activation polarization due to hydrogen gas generation. The turning point of two reactions in the polarization curve presented -0.92 V (vs. Ag/AgCl). The lowest current densities in the potentostatic test and non-correded surface condition of specimens by SEM analysis presented at potentials of 0 ~ -0.9 V and 0.4 ~ -0.9 V, respectively. Synthetically, the optimum corrosion protection range without stress corrosion cracking and hydrogen embrittlement is concluded with the potential range of -0.56 V ~ -0.92 V.

Antifouling Paints with Zinc “Tannate”

During the past decade, the necessity of new ecofriendly antifouling pigments was established. Among these new pigments, special attention should be paid to tannin and its derivatives. Tannins are synthesized by plants as part of their defense mechanism against the attack of pathogens. The objective of this work was to study the antifouling efficiency of paints containing zinc “tannate” in artificial seawater. The zinc “tannate” was precipitated at pH 4 and pH 8. Insoluble and soluble matrix antifouling paints, with different plasticizers, were formulated and tannins leached from the paints immersed in artificial seawater were determined by the Folin−Denis assay for polyphenols. The antifouling action of paints was assessed in a natural seawater environment. The results showed that the leaching rate of tannin from insoluble matrix paint decreases, reaching a constant value after 25 days of immersion. In the case of the soluble matrix paints, a lesser amount of tannin was leached, depending on the tannin and the plasticizer employed. The results in a natural sea environment are dependent on the matrix and the plasticizer employed.

Effect of Alternating Pressure of Seawater on Protective Properties of Organic Coating on Steel Substrate

In natural seawater environment, temperature and chlorine ion are important factors for organic coating degradation. The alternating pressure of seawater can also affect the lifetime in deep-sea environment and probably is conducive to synergistic effects with other ageing factors. The present work is to investigate the effect of alternating pressure of seawater on protective properties of epoxy organic coating on 907A steel substrate, and evaluates the organic coating degradation process after pressure tests at atmospheric pressure. EIS was used to study the degradation process of the organic coating in natural seawater. The results demonstrated that the impedance of coating under alternating pressure of seawater conditions decreased faster than that at atmospheric pressure. With the increase of alternating pressure cycles, the entire degradation process of organic coating was accelerated. It is concluded that alternating pressure of seawater has to be considered as an aggressive factor like temperature or chlorine ion.

Pitting corrosion studies of super austenitic stainless steels in natural sea water using dynamic electrochemical impedance spectroscopy

Potentiodynamic anodic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out on type 316L stainless steel (SS), alloys 33 and 24 in natural sea water environment in order to assess pitting corrosion resistance. The results revealed that the pitting corrosion resistance was higher in the case of alloys 33 and 24 than 316L SS; due to the higher contents of nitrogen, chromium and molybdenum. DEIS measurements were performed over a wide range of potentials covering the corrosion potential, passive region, breakdown region and dissolution region. It was shown that the impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure. The impedance spectra of various potential regions were also discussed. The Nyquist plots were fitted using non-linear least-square (NLSS) method for different potential regions.