Steel In Natural Seawater Research Articles

Cathodic protection of structures in seawater using solar panels

It is well known that the cathodic protection of structures in seawater is accompanied by the formation of calcareous deposits on them. In current study, we consider the physicochemical modelling of the formation of the deposit composition against cathode current density in seawater. The reliability of the model representations is confirmed by direct experiments. The work also studied the protective properties of the deposits with a different composition for low-alloy steels in natural sea water. It has been shown that the deposits of pure Mg(OH)2and the deposits of CaCO3+ Mg(OH)2had better protective ability against corrosion than the deposits of pure CaCO3. However, the deposits of Mg(OH)2dissolved faster than the deposits of CaCO3and CaCO3+ Mg(OH)2. Theoretical concepts and experiments on the laws governing the formation of the deposits and their protective properties are in complete agreement with each other. This allows to use the obtained patterns in the cathodic protection of structures in sea water using solar panels, forming standard deviations with predetermined protective properties in the daytime.

Corrosion Crack Nucleation Mechanism in the Welded Structures of X65 Steel in Natural Seawater

The nucleation mechanism of corrosion cracks in welded structures in natural seawater has been revealed through investigation on the corrosion behavior of X65‐welded structures in natural seawater. The evolution laws of surface corrosion morphology, residual stress, and areas of welded structures with the most serious corrosion damage were analyzed by microstructure observation, corrosion morphology observation, residual stress detection, and magnetic field detection. The results show that the main factors of determining surface corrosion morphology evolution law of welded structures are microstructures of the weld joint, heat‐affected zone (HAZ), and the fusion line. Due to the difference of corrosion rates between the weld joint, HAZ, and the coarse Widmänstatten structure in fusion line, the fusion line of welded structures receives the most serious damage while being corroded. Meanwhile, mutual reinforcement of residual stress and corrosion damage on the surface of welded structures further accelerate the nucleation of corrosion cracks. Under the influences of microstructure, residual stress, and corrosion, corrosion cracks that are parallel to weld joints generate first in the fusion line of welded structures. Therefore, it makes welded structures the source of marine steel structures’ corrosion failure.

Investigation on the effect of nano-ceria on the epoxy coatings for corrosion protection of mild steel in natural seawater

PurposeThis paper aims to investigate the effect of introducing nano-ceria (CeO2) particles to the epoxy coatings on mild steel in natural seawater.Design/methodology/approachThe epoxy–ceria nanoparticles were coated with mild steel using a wire-wound draw-down bar method. The effects of ceria nanoparticles on the corrosion resistance of epoxy-coated samples were analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS).FindingsLocalized measurements such as oxygen consumption and iron dissolution were observed using SECM in natural seawater in the epoxy-coated sample. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating was measured from EIS measurements after wet and dry cyclic corrosion test. Scanning electron microscope (SEM)/energy dispersive X-ray spectroscope (EDX) analysis showed that complex oxides of nano-ceria were enriched in corrosion products at a scratched area of the coated mild steel after corrosion testing. Focused ion beam-transmission electron microscope (FIB-TEM) analysis confirmed the presence of the nanoscale oxide layers of ceria in the rust of the steel.Research limitations/implicationsThe tip current at −0.70 V for the epoxy–CeO2-coated sample decreased rapidly because of cathodic reduction of the dissolved oxygen. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating were measured from EIS measurements after wet and dry cyclic corrosion test.Practical implicationsThe presence of complex oxide layers of nano-ceria layers protects the coated steel from rusting.Social implicationsThe use of this nano-ceria for corrosion protection is environment-friendly.Originality/valueThe results of this study indicated the significant effect of nano-ceria particles on the protective performance and corrosion resistance of the epoxy coating on mild steel. The dissolution of Fe2+ was lower in the epoxy–ceria nanoparticle-coated mild steel than that of the epoxy-coated mild steel resulting in a lower anodic current of steel. The increase in film resistance and the charge transfer resistance showed that the nano-ceria particles and the formation of complex oxides provide better barrier protection to the coating metal surfaces.

Study of poly(3,4-ethylendioxythiphene) as a coating for mitigation of biocorrosion of AISI 304 stainless steel in natural seawater

In this work the poly(3,4-ethylenedioxythiophene) (PEDOT) was evaluated to mitigate biocorrosion of conventional stainless steel (SS), grade AISI 304, under exposure to natural seawater. PEDOT was obtained electrochemically onto the steel and coated coupons were immersed in flow-through exposure rig fed with fresh seawater. Corrosion performance of the coupons SS and SS/PEDOT was characterised using electrochemical analysis of open circuit potentials and polarization curves measured on samples retrieved after 7, 35 and 210 days of exposure. For the same retrieval times, the evolution of the biofilm was inspected by scanning electron microscopy (SEM), and microbiological analysis by denaturing gradient gel electrophoresis (DGGE) and fluorescence microscopy. Results indicate that PEDOT delays the growth of the biofilm on the modified steel surface by at least 35 days, producing a less variable bacterial community over time as compared to the uncoated steel surface. In addition, PEDOT retains electrochemical stability throughout the exposure, which is mainly attributed to the intrinsic properties of the conducting polymer.

Electrochemical Investigation into the Effect of Nano-Titania on the Protective Properties of Epoxy Coatings on Mild Steel in Natural Seawater

The effect of introducing nano tinania TiO particles to the epoxy coatings on mild steel in natural seawater was analyzed using Scanning Electrochemical Microscopy SECM and Electrochemical Impedance Spectroscopy EIS Line profile and topographic image analysis were measured by applying V and V as the tip potential for the cathodic and anodic reactions respectively The tip current at V for the epoxy coated sample with TiO nanoparticles decreased rapidly due to cathodic reduction of dissolved oxygen The EIS measurements were conducted in natural seawater after wet and dry cyclic corrosion test The EIS measured the film resistance Rf and charge transfer resistance Rct values which were increased by the addition of TiO nanoparticles in the epoxy coating SEM EDX and FIB TEM analysis showed that complex oxides of titania were enriched in corrosion products at the scratched area of the coated steel and confirmed the presence of the nanoscale oxide layers of titania in the rust of the steel The formation of complex oxides of titania had a beneficial effect on the corrosion resistance of coated steel

Electrochemical Investigation into the Effect of Nano-Titania on the Protective Properties of Epoxy Coatings on Mild Steel in Natural Seawater

Electrochemical Investigation into the Effect of Nano-Titania on the Protective Properties of Epoxy Coatings on Mild Steel in Natural Seawater

The influence of Desulfovibrio sp. and Pseudoalteromonas sp. on the corrosion of Q235 carbon steel in natural seawater

Corrosion behavior of Q235 carbon steel is investigated in sterilized air-saturated natural seawater inoculated with mono-, and di-cultures of Desulfovibrio sp. (D. sp.) and Pseudoalteromonas sp. (P. sp.). The electrochemical and weight loss results demonstrate that the corrosion rate increases in the order: P. sp.˂D. sp.+P. sp.˂D. sp.≈abiotic blank. Mechanisms for the corrosion inhibition of P. sp. and the difference in the function of D. sp. in D. sp. and D. sp.+P. sp. containing media are discussed on the analysis of surface morphology, biofilm development, environmental parameters, and bacterium number.

自然海水中におけるSUS304の長期動的すきま腐食観察

自然海水中におけるSUS304の長期動的すきま腐食観察

Quantitative determination by SRET measurements of pit dissolution rate of AISI 304 stainless steel in natural sea water

Pit dissolution rate on samples of an AISI 304 stainless steel (SS) in natural sea water was assessed using a scanning reference electrode technique (SRET) and compared with chronoamperometric measurements. Corrosion pits generated in AISI 304 SS samples under potentiostatic control at room temperature and smooth surface presented an empirical exponential growth rate law. The quantity of dissolved metal per pit as a function of polarisation time determined using SRET and chronoamperometric measurements presented acceptable agreement. Considering the capabilities and limitations of scanning techniques, this study presents an approach of the pit growth rate determination from SRET measurements demonstrating the possibility to perform real time quantitative determination of localised dissolution rate.

Influence of strain Bacillus cereus bacterium on corrosion behaviour of carbon steel in natural sea water

This paper examines the corrosion behaviours of carbon steel immersed in sterile natural sea water with and without strain Bacillus cereus. Electrochemical studies, including Tafel plots and electrochemical impedance spectroscopy (EIS) were performed to evaluate the variation of the corrosion behaviour of carbon steel in medium containing B. cereus as compared to the sterile control samples. The results of Tafel plot measurements showed significant reduction in the corrosion rate in the presence of bacterial biofilm produced by strain B. cereus. The EIS data showed that the charge transfer resistance is greater in a medium containing B. cereus and increases with immersion time.

Corrosion potential and cathodic reduction efficiency of stainless steel in natural seawater

Stainless steels are widely used for different applications in seawater in the oil and gas and desalination industries. It is well known that the corrosion potential of stainless steel shifts to the noble direction (ennoblement) when exposed to natural seawater. The other significant effect of the biofilm on metallic surfaces is a dramatic increase of the cathodic reduction efficiency (e.g. cathodic reduction of dissolved oxygen), promoting the corrosion reactions and increasing the rate of corrosion propagation. Although, this has been widely studied in natural seawater at temperature ranging from 15 to 40 °C, very little is known on the effect of temperature (in a wider temperature range), dissolved oxygen content and chlorination level on the corrosion potential and the cathodic reduction efficiency of stainless steel in natural seawater. In this paper, corrosion potential and cathodic reduction efficiency of stainless steel are reported as a function of temperature (e.g. from 5 to 70 °C), dissolved oxygen content (e.g. from 20 ppb to saturation) and chlorination level (from 0 to 0.5 ppm). The results are discussed in terms of risk for crevice corrosion and bi‐metallic corrosion when coupling to other materials. In addition results from exposure in tropical sea are presented and compared to that of temperate seawater heated at the same temperature.

Sunlight-enhanced calcareous deposition on cathodic stainless steel in natural seawater

In replicate series of experiments in natural seawater, one in full darkness and the other in a 1:1 diurnal cycle with as little as ∼5% of natural solar illumination, sunlight promoted calcareous deposition on cathodic stainless steel surfaces. As exemplified by scanning electron microscopy, the deposit that formed under the natural diurnal cycle, in the presence of photosynthetic biofilms, was composed of finer calcareous crystals that provided more compact and more uniform surface coverage than the one formed in the dark. The light-enhanced deposit also possessed better scale properties, as suggested by X-ray analysis and electrochemical measurements. Sunlight enhancement of calcareous deposition looked all the more conspicuous when day and night regimes were examined independently. These results not only bear important implications for cathodic protection in marine waters, but also provide an intriguing analogy to coral reef calcification.

Corrosion Characteristics of 16Mn and Q235B Steel in Natural Seawater

In order to study the corrosion characteristics of 16Mn and Q235B steel in natural seawater, the indoor contrast corrosion experiments are carried out in seawater by electrochemical method. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) techniques are employed to investigate the corrosion electrochemical behavior of 16Mn and Q235B steel, which are acquired by electrochemical workstation. The results of polarization curves and EIS reveal the respective corrosion rules of 16Mn and Q235B steel in natural seawater. At last, the different influence of rust layer on the corrosion process of 16Mn and Q235B steel is analyzed contrastively.

Corrosion pit growth on austenitic stainless steels in chloride containing solution: a quantitative approach

PurposeThe purpose of this paper is to quantitatively assess the pit growth rate on AISI 304L and AISI 316 austenitic stainless steels in natural seawater and 3.5 wt.% NaCl solutions through electrochemical measurements during the potentiostatic growth of pits.Design/methodology/approachA quantitative characterisation was carried out based on chronoamperometric measurements. The volume of dissolved metal per pit was calculated from the charge registered and Faraday's law, considering both, hemispherical and semi‐elliptical pit shapes and the density of the steels. Empirical growth laws for maximum pit depth as a function of polarisation time were obtained and compared with pits volumetric profile obtained from optical microscopy analysis and mechanical removal of material on both steels.FindingsElectrochemical‐based calculations of localised metal dissolution per pit present acceptable fit with the real volume of dissolved metal on hemispherical pits.Originality/valueThe paper presents the quantitative relationship of the corrosion pit growth rate of stainless steels in chloride containing solution determined by chronoamperometry (electrochemical technique) through the Faraday law's, with the mechanical removal of material (pit profile) through the density of metal.

Influence of Pseudomonas on corrosion and mechanical properties of carbon steel in sea water

In order to separate the effects of a specific microbial species (Pseudomonas) in sea water on carbon steel, a comparative study of the corrosion and mechanical properties of AISI 1045 carbon steel in natural sea water, sterile sea water and Pseudomonas inoculated sea water was carried out using tensile testing, mass loss experiments and microscopy. The results of mass loss showed that the corrosion rate of the specimens in the single Pseudomonas system was faster than that in sterile sea water but slower than in natural sea water. Microscopy revealed that a loose corrosion product layer formed on the surface of carbon steel, and micropitting corrosion occurred underneath the corrosion product. Energy dispersive X-ray analysis of this deposit indicated that iron and oxygen were the main components, and a large amount of carbon, which most likely originated from the bacteria and its exopolymer, could also be detected. The tensile strength of carbon steel was reduced by the action of Pseudomonas, but hydrogen embrittlement was not found.

Cathodic protection of carbon steel in natural seawater: Effect of sunlight radiation

Abstract Cathodic protection of metals in seawater is known to be influenced by chemical–physical parameters affecting cathodic processes (oxygen discharge, hydrogen evolution and calcareous deposit precipitation). In shallow seawater, these parameters are influenced by sunlight photoperiod and photosynthetic activity. The results presented here represent the first step in studies dedicated to cathodic protection in shallow photic seawater. This paper reports on carbon steel protected at −850 mV vs . Ag/AgCl (oxygen limiting current regime) in the presence of sunlight radiation but in the absence of biological and photosynthetic activity, the role of which deserves future research. Comparison of results obtained by exposing electrochemical cells to daylight cycles in both biologically inactivated natural seawater and in NaCl 3.5 wt.% solutions showed that sunlight affects current densities and that calcareous deposit interfere with light-currents effects. Sunlight radiation and induced heating of the solution have been separated, highlighting results not otherwise obvious: (1) observed current waves concomitant with sunlight radiation depend fundamentally on solar radiation, (2) solar radiation can determine current enhancements from early to late phases of aragonite crystal growth, (3) a three-day-old CaCO 3 layer reduces but does not eliminate the amplitude of the current waves. Theoretical calculations for oxygen limiting currents and additional field tests showed that sunlight, rather than bulk solution heating, is the main cause of daily current enhancements. This was confirmed by polarizations performed at −850 and −1000 mV vs . Ag/AgCl (constant bulk temperature), during which the electrode was irradiated with artificial lighting. This test also confirmed O 2 discharge to be the cathodic process involved. A mechanism of radiation conversion to heat in the oxygen diffusion layer region is proposed.

Interactions between steels and sulphide-producing bacteria—Corrosion of carbon steels and low-alloy steels in natural seawater

Metallic infrastructure immersed in natural seawater is exposed to important corrosion phenomena, which are sometimes characterised by microorganism influenced corrosion. The presence of sulphide-producing bacteria is generally associated with catastrophic cases of material degradation. In this work, commercial steel grades (carbon steels and low-alloy steels) are immersed for approximately 1 year in two types of natural seawater, which contain different concentrations of sulphide-producing bacteria. Gravimetric, microbiological, and electrochemical measurements and corrosion product analyses indicate that in seawater the observed corrosion phenomenon is composed of two different phases. The first phase is characterized by decreased corrosion kinetics correlated with a higher concentration of sessile sulphide-producing bacteria and the formation of sulphur-containing chemical species. The second phase is marked by an increased rate of corrosion. This multidisciplinary study demonstrates the complexity of the interactions between steels and bacteria. The presence of alloying elements in the steel composition affects the rate of corrosion and growth patterns of sessile sulphide-producing bacteria. At the same time, the presence of sulphide-producing bacteria affects in the process of steel corrosion in natural seawater.

Ennoblement of stainless steel in natural seawater – A new explanation

AbstractThe ennoblement of corrosion potential (Ecorr) of passive metal immersed in seawater was investigated with electrochemical technology and epifluorescence microscopy. The in situ observation showed that the bacteria number increased on the metal surface according to an exponential law which was in the same way with the ennoblement of Ecorr. At the same time, the anodic polarization current of high‐Mo stainless steel decreased in the initial days. According to the mix‐potential theory and the characteristics of polarization curves of high‐Mo steel in natural seawater, the ennoblement of corrosion potential may be induced by the decrease of the passive current density.

Measurements of the Localized Dissolution Rate During Potentiostatic Generation of Corrosion Pits in Austenitic Stainless Steel in Natural Seawater

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Electrochemical studies on the alternating current corrosion of mild steel under cathodic protection condition in marine environments

Alternating current (AC) corrosion of mild steel in marine environments under cathodic protection (CP) condition was studied. Electrochemical studies at the two protection potentials namely −780 and −1100 mV versus SCE were examined by different techniques. DC polarization study was carried out for mild steel in natural seawater and 18.5 g/L NaCl solution to evolve corrosion current density. The corrosion rate determination, pH of the end experimental solution and surface morphology of the mild steel specimens under the influence of different AC current densities were studied. The amount of leaching of iron into the solution was estimated using inductively coupled plasma spectrometry. All these techniques revealed that AC influences the corrosion of mild steel in the presence of marine environments even though CP was given. Surface micrographs revealed that spreading of red rust products noticed on the mild steel surface. At −780 mV CP, red rusts are visually seen when the AC source was above 10 A/m 2 in both the media but red rusts are appeared after 20 A/m 2 in the case of −1100 mV CP. Weight loss measurements coupled with surface examination and solution analysis is a effective tool to characterize and quantify the AC corrosion of mild steel in marine environments.