Cathodic Protection In Seawater Research Articles

Investigation of corrosion behavior, tensile and cyclic fracture mechanism of EH36 steel welded joints

This work systematically revealed the static-dynamic corrosion failure behavior of EH36 joints under air, simulated seawater and cathodic protection in seawater. The result indicated that the seawater environment affected tensile performance slightly but acted a critical role in the fatigue behavior. Specifically, the corrosion pit and cyclic stress would respectively induce high-stress concentration and corrosion current density, significantly decreasing the fatigue strength of joints. The application of cathodic protection on joints in seawater would decrease the tensile behavior, but would continuously provide electrons for the surface and crack tip to prevent corrosion damage, improving fatigue performance of EH36 joints.

Electrochemical calcareous deposition in seawater. A review

Pollution and climate change issues are calling for advanced techniques of pollutant sequestration to decrease toxicity, of coral and costal remediation, and of carbon sequestration to decrease atmospheric CO2 levels. For that, calcareous deposition appears as an overlooked, but potentially efficient technique. The calcareous deposit is a well-known precipitation by-product of cathodic protection in seawater. The deposit is made of a mixture of CaCO3 and Mg(OH)2. A calcareous deposit is formed electrochemically when a metal connected to an electrical power source is immersed in seawater. So far, electrochemical calcareous deposition has seldomly found applications, except for speedup of coral growth, prevention of shore erosion, reinforcement of artificial marine structures and remediation of polluted seawater. Here, we review the principles and mechanisms of electrochemical calcareous deposition. The growth, composition and mechanical properties of calcareous deposits are controlled by several factors such as 1) the impact of electrochemical parameters on the Ca/Mg ratio. For instance, CaCO3 formation is favoured at low cathodic potentials and low currents, whereas Mg(OH)2 precipitates preferentially at high cathodic potentials and high applied current; 2) the nature of the metallic electrode: although lime could be deposited onto any metallic surface at a fixed potential, electrochemical reactions and deposit composition are controlled by the metal nature. Moreover, the state of the electrode surface, e.g. with the presence of oxides or biofilms, modifies the kinetics of deposit formation; and 3) electrolyte composition, pH, temperature and stirring. For instance, in seawater, Ca2+ and Mg2+ concentrations control the allotropic variety of CaCO3 formed, e.g. Mg2+ inhibits the formation of calcite and vaterite. Hydrodynamic conditions near the electrode also influence the deposit composition since conditions regulate the mass transport at the electrode–solution interface. Below 10 °C, aragonite is not formed and the deposit stays thin. In the first stage of the deposit formation, an Mg-based compound is formed, followed by the growth of a Ca-based compound with time.

Effect of the Seawater Flow Velocity on the Protectiveness of Calcareous Deposits by Electrochemical Methods

The influence of flow velocity on the protectiveness of calcareous deposits which formed by cathodic protection in seawater was studied. The deposition process and the protectiveness of calcareous deposits were investigated by electrochemical impedance spectrum (EIS) and linear polarization resistance technique (LPR). The EIS results showed that the capacitive loops sizes decreased with increasing flow velocities, indicating that calcareous deposits formed at higher flow velocities provided poorer protectiveness. An exponential decrease of protectiveness with increasing flow velocities was observed, which was quantified by LPR. The results of SEM and XRD showed that aragonite of calcium carbonate deposited at lower flow velocities but magnesium hydroxide deposited at higher velocities.

Electric Field Calculation of Pipe with Cathodic Protection in Seawater by BEM

To investigate the corrosion state of subsea pipeline under cathodic protection, the surface potential distribution of the pipeline has to be measured exactly, but it’s very difficult to measure directly in actually. On base of boundary element methods (BEM), a 2D model about pipe’s cathodic protection under sea water was established, and then software to calculate the electric field distribution on pipe surface in even media (seawater) was developed by way of Matlab. The developed software was verified through an experiment in lab. The result shows that numerical calculation based on BEM by Matlab is feasible for cathodic protection electric field of pipe in marine environment.

해수 중 CO2기체의 유입에 의한 환경 친화적인 전착 코팅막의 형성과 그 내식특성

The peculiar feature of cathodic protection in seawater has the capability to form mineral calcareous deposits such as magnesium and calcium on metal surfaces. It is assumed that <TEX>$OH^-$</TEX> ions are generated close to the metal surface as a result of cathodic protection and generated <TEX>$OH^-$</TEX> ions increases the pH of the metal/seawater interface outlined as the following formulae. (1) <TEX>$O_2+2H_2O+4e{\rightarrow}4OH^-$</TEX>, or (2) <TEX>$2H_2O+2e{\rightarrow}H_2+2OH^-$</TEX>. And high pH causes precipitation of <TEX>$Mg(OH)_2$</TEX> and <TEX>$CaCO_3$</TEX> in accordance with the following formulae. (1) <TEX>$Mg^{2+}+2OH^-{\rightarrow}Mg(OH)_2$</TEX>, (2) <TEX>$Ca^{2+}+CO{_3}^{2-}{\rightarrow}CaCO_3$</TEX>. The focus of this study was to increase the amount of <TEX>$CO{_3}^{2-}$</TEX> with the injection of <TEX>$CO_2$</TEX> gas to the solution for accelerating process of the following formulae. (1) <TEX>$H_2O+CO_2{\rightarrow}H_2CO_3$</TEX>, (2) <TEX>$HCO^{3-}{\rightarrow}{H^+}+CO{_3}^{2-}$</TEX>. Electrodeposit films were formed by an electro-deposition technique on steel substrates in solutions of both natural seawater and natural seawater dissolved <TEX>$CO_2$</TEX> gas with different current densities, over different time periods. The contents of films were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD). The adhesion and corrosion resistance of the coating films were evaluated by anodic polarization. From an experimental result, only <TEX>$CaCO_3$</TEX> were found in solution where injected <TEX>$CO_2$</TEX> gas regardless of current density. In case of injecting the <TEX>$CO_2$</TEX> gas, weight gain of electrodeposits films hugely increased and it had appropriate physical properties.

Characterization of steel surface under cathodic protection in seawater

Purpose – The purpose of this paper is to characterize the surface of steel under cathodic protection while submerged in seawater, to understand the mechanism that controls the operation of the protection system.

Electrochemical formation and transformation of corrosion products on carbon steel under cathodic protection in seawater

Carbon steel coupons were permanently exposed to seawater in the low water zone of two French harbors for 5years before to be subjected to cathodic protection (potential about −0.95V vs. Ag/AgCl/seawater) for 1year. The application of cathodic polarization to the previously unprotected coupons induced the transformation of GR(SO42-) into GR(CO32-). Other coupons were permanently protected by cathodic protection during the 6years immersion. A thin film of green rust and mackinawite was observed on the steel surface. This film was covered by a thicker layer of calcareous deposits.

Finite Element Modeling for Cathodic Protection of Pipelines under Simulating Thermocline Environment in Deep Water Using a Dynamic Boundary Condition

A finite element model (FEM) was established to calculate the cathodic protection (CP) potential distribution on pipelines, under the environment of the thermocline structure in deep water. Supplemental boundary conditions were applied on the interfaces of two different mediums in the thermocline model. To solve the problem of time-dependent polarization curves due to calcareous deposits formed on the steel surface during CP in seawater, a dynamic boundary condition based on Ohm's law was proposed, instead of polarization curves or the Butler-Volmer equation. A good agreement was obtained between the calculated and experimental potential distributions, which proved that the model was practical and feasible. The anode placement studies revealed that the anode could supply a more efficient protection when it was placed at the thermocline zone rather than the surface zone or the deep water zone.

Electrochemical characteristics of stainless steel using impressed current cathodic protection in seawater

Stainless steels such as STS 304, 316 and 630 are frequently used as shaft materials in small fiber reinforced polymer (FRP) fishing boats. If the shaft material is exposed to a severely corrosive environment such as seawater, it should be protected using appropriate methods. The impressed current cathodic protection was used to inhibit corrosion in shaft materials. In anodic polarization, passivity was remarkably more evident in STS 316 stainless steel than in STS 304 and STS 630. The pitting potentials of STS 304, 316, and 630 stainless steels were 0.30, 0.323, and 0.260 V, respectively. The concentration polarization due to oxygen reduction and activation polarization due to hydrogen generation were evident in the cathodic polarization trends of all three stainless steeds. STS 316 had the lowest current densities in all potential ranges, and STS 630 had the highest. Tafel analysis showed that STS 316 was the most noble in the three. In addition, the corrosion current density was the lowest for STS 316.

Hydrogen uptake by structural steels at cathodic protection in sea water inoculated with sulfate reducing bacteria

AbstractThe effect of sulfate reducing bacteria (SRB) on the hydrogen permeation rate through ferrite‐pearlite and sorbite steels of quite similar chemical composition was studied using a specially designed facility. Tests were carried out in synthetic sea water, sterile or inoculated with bacteria, at potentials corresponding to cathodic protection (− 800 mV to − 1400 mVNCE). Cathodic polarization within the studied potential range did not stop the metabolism of SRB. Presence of SRB was found to increase the hydrogen permeation rate, to form S2− ions, to increase the polarization current, to modify the impedance spectrum and to change the appearance of cathodic deposits in comparison with sterile conditions. The promoting effect of SRB on the hydrogen uptake was concluded to be the result of the increase in polarization current due to the formation of the less protective layer of cathodic deposits on the steel surface, the presence of S2− ions and the possible decrease in pH. Despite the similar tendencies, the effect of SRB on hydrogen uptake was more pronounced in the case of sorbite steel. The bacteria action can cause hydrogen deterioration of steel at potentials, recognized as safe ones at cathodic protection.

Comportamiento de ánodos de sacrificio en la protección de aluminio NV-5083 en agua de mar, bahía de Valparaíso

The behavior of aluminum and zinc alloys were evaluated and compared as sacrifice anodes in cathodic protection of aluminum NV-5083 hulls in seawater in Valparaiso bay. Samples of the aluminum alloy used to manufacture boat hulls and Al-Zn-In, Al-Zn-Sn, and Zn anodes were made. Electrochemical behavior was evaluated by means of polarization curves and corrosion potential as function of time. In parallel, galvanized pairs (boat hull-sacriice anode), were designed and immersed in the electrolyte for 16 days, determining the weight loss and evolution of the open circuit potential for each material. The results show that the aluminum based anodes provide the NV-5083 aluminum hull cathodic protection in seawater. However, they do not exceed the economical horizon and useful life of zinc anodes, because the aluminum based anodes present higher corrosion for the protection of a similar exposed area of aluminum.

EIS characterization of thick flawed organic coatings aged under cathodic protection in seawater

Electrochemical impedance spectroscopy (EIS) was used to monitor, up to 20 months, the degradation kinetics of four thick organic coatings under cathodic protection in seawater. EIS experiments were realized onto a flawless zone, which surrounds an artificial hole of the coating using the Luo's cell or a removable cell. EIS spectra were analyzed first with classic equivalent circuits and then with an approach involving the dipolar relaxation of polymer layer. These two models were unable to explain the experimental data, especially for a long immersion experiments. Taking into account the presence of vacuoles, namely pre-existing air pockets that will be then filled by electrolyte, modified equivalent circuits were used and a good representation of experimental data was obtained. The parameters extracted allowed the coating degradation to be followed. It was found that a solvent-free coating exhibited the best compatibility with cathodic protection.

Localized Corrosion Probability in Stainless Steels After Cathodic Protection in Seawater

Abstract Growth of calcareous deposits on stainless steels (SS) exposed to seawater under cathodic protection (CP) conditions was examined. CP was performed by galvanic coupling with iron, zinc, or...

Evaluation of hydrogen assisted cracking resistance of high strength Jack-up steels

The use of high strength steels is very attractive for the fabrication of the legs of Jack-Up platforms, however, there are still some concerns on the possibility of hydrogen assisted cracking resulting from cathodic protection. An experimental programme was performed to assess the hydrogen assisted cracking sensitivity of a high strength steel in conditions of cathodic protection. Hydrogen activity resulting from cathodic protection has been evaluated from electrochemical hydrogen permeation test results and from hydrogen analysis on exposed samples. It is shown that cathodic protection in sea water results in low hydrogen activity. Comparative slow strain rate tests performed on high strength steel and on lower strength materials show that, for a given test condition, comparative behaviour is observed. Fracture mechanic tests indicate that high K ISCC values are obtained under cathodic protection. Finally, tests performed on weld structures confirm that high strength steels are suitable for use under cathodic protection. An increase of the protection potential (from −1050m V/ECS to −850m V/ECS) can still improve the behaviour.

Fatigue-Strength Distribution of a Cathodic-Protection Steel and Stainless Steels in Seawater.

The influence of a corrosive environment on fatigue-strength distribution was studied for a slightly notched specimen (stress concentration factor α=1.03) and a sharply notched specimen (α=4.60) of S35C carbon steel. Fatigue strength is markedly lower and the standard deviation is also lower for S35C steel in synthetic seawater than those in laboratory air, because many cracks initiate on the specimen surface. Cathodic protection restores the fatigue strength and increases the standard deviation to those obtained in laboratory air. Since many cracks initiate in the sharply notched specimen in laboratory air, the standard deviation of the fatigue strength is lowered to one-third that of slightly notched specimen. Cathodic protection in seawater reduces the number of cracks and increases the standard deviation to a value twice as large as in the air. The influence was also studied for three kinds of stainless steels with slight notch (SUS304, SUS316 and SUS403). Among stainless steels, low-corrosion-resistance SUS403 in seawater exhibits a large decrease in fatigue strength compared with that in air. However, the standard deviation is not lowered by the kind of stainless steel, because the number of cracks is extremely low compared with the carbon steel. The dispersion of the fatigue life has a good correlation with that of the fatigue strength in terms of standard deviation. Therefore, the standard deviation is a significant parameter for the corrosion fatigue. The standard deviation of the fatigue strength has a good correlation with the number of cracks which led to the final fracture.

Technical note: Effect of metal temperature on current density requirements for cathodic protection of bare steel in sea water: laboratory study

The production. of oil and gas from deeper seas and deeper wells means that crude oil is now to befound at higher temperatures than previously experienced. It is expected that oil from wells with bottom hole temperatures of up to 300°C will be produced in thefuture. To model the effect of elevated external skin temperature on the effectiveness of the cathodic protection of an uncoated steel riser, three sea water cells were used, each of which consisted of a fabrication comprised of a simulated riser housing a cartridge heater, a sacrificial anode, and measuring instrumentation. After a preliminary aging period under cathodic protection at low temperature to allow a calcareous deposit to form on the substrate, the heaters were switched on and the specimens were subjected to temperatures in the range 40–90°C, and the applied current density to achieve a suitable level of cathodic protection was recorded. The results, which are discussed in the context of previous studies, show that there is no simple and reliable relationship between the operating temperature of a surface and the required current density for cathodic protection in sea water. Further work needs to be undertaken to produce a more reliable model for the determination of necessary cathodic protection densities.

Statistical behaviour of fatigue crack growth for HY-80 steel plate and its weldments under cathodic protection in seawater and in air: Matthews, J. R., Betancourt, T. and Robicheau, M.Eng. Fract. Mech. 1989 34, (4), 785–802

An investigation of boundary sliding in the superplastic Pb-62% Sn eutectic alloy shows that the contribution from sliding is high in the superplastic region II (ϵgbsϵt − 50–60%, where ϵgbs is the strain due to sliding and ϵl is the total strain), but there is a decrease in the magnitude of sliding in the less superplastic regions I and III (ϵgbsϵl − 20%). A series of detailed measurements of boundary offset and type of interface indicates that the three boundaries in Pb-62% Sn exhibit very significant differences in sliding behavior: the largest sliding offsets occur at the Sn-Sn intercrystalline boundaries, smaller offsets are recorded at the Pb-Sn interphase boundaries and there is little or no sliding at Pb-Pb intercrystalline boundaries. No theory of superplasticity is available which satisfactorily accounts for either the decrease in ϵgbsϵl in region I or the variation in average sliding offset at the three types of boundary. The results are consistent with earlier reports, from cavitation studies, that the various interfaces in a microduplex alloy exhibit different susceptibilities to cavity formation.Une étude du glissement aux joints dans l'eutectique Pb-62% Sn montre que la contribution du glissement est importante dans la région superplastique II (ϵgiϵl − 50–60%, où ϵgj est la déformation due au glissement et ϵl est la déformation totale), mais qu'elle diminue dans les régions moins superplastiques I et III (ϵgbsϵl − 20%). Des mesures précises du décalage aux joints et du type d'interface ont montré que les trois types de joints dans Pb-62% Sn se comportaient très différemment, en ce qui concerne le glissement: le plus grand décalage par glissement se produisait aux joints de grains Sn-Sn des décalages plus faibles s'observaient aux joints interphases Pb-Sn, et il n'y avait que peu ou pas de glissement aux joints de grains Pb-Pb. On ne connait pas de théorie de la superplasticité qui rende compte de la diminution de ϵgjiϵl, dans la région I ou de la variation du décalage moyen par glissement aux trois types de joints. Nos résultats sont en accord avec des travaux antérieurs concernant la cavitation. selon lesquels les divers interfaces d'un alliage diphasé à grains fins sont plus ou moins favorables à la formation de cavités.Eine Untersuchung des Korngrenzgleitens in der superplastischen eutektischen Legierung Pb-62% Sn zeigt, daβ der Beitrag durch Gleiten im superplastischen Bereich II (ϵgbsϵl − 50–60%. mit ϵgbs, die durch Gleiten aufgebrachte Dehnung und e, Gesamtdehnung) hoch ist. Es besteht aber ein Abfall in der Dehnung durch Gleiten in den weniger superplastischen Bereichen I und III (ϵgbsϵl − 20%). Aus einer Serie genauer Messungen der Korngrenzverschiebungen und der Grenzflächentypen folgt, daβ die drei in Pb-62% Sn vorhandenen Korngrenzen sich sehr unterschiedlich beim Gleiten verhalten: die gröβten Verschiebungen durch Gleiten finden an den interkristallinen Grenzen Sn-Sn statt, kleinere Verschiebungen werden an den Pb-Sn -Grenzflächen festgestellt und an den interkristallinen Grenzflächen Pb-Pb wird wenig oder keine Gleitung gefunden. Es gibt keine Theorie der Superplastizität, die zufriedenstellend entweder den Abfall von ϵgbsϵl im Bereich I oder die Unterschiede in der mittleren Gleitverschiebung an den drei Korngrenztypen beschreibt. Die Ergebnisse sind verträglich mit frÜheren Untersuchungen von Kavitation, nach denen die verschiedenen Grenzflächen in einer Mikroduplex-Legierung verschiedene Neigung zur Hohlraumbildung aufweisen.

Statistical behaviour of fatigue crack growth for HY-80 steel plate and its weldments under cathodic protection in seawater and in air

This paper deals with fatigue crack growth data for various weldments of HY-80 steel plate in seawater and a statistical method for using this data in life predictions and deviations from mean life estimates. Typical results of crack growth behaviour with crack length and examples of the effect of averaging increment on variability of crack growth data are given. The standard deviation for incremental crack growth rates are determined. Use of the data in the calculation of confidence limits in life cycle determination are discussed. The A and N data, from which crack growth data were obtained, were generated on HY-80 base plate and HY-80 weld containing compact tension specimens. They were fatigue-tested either in air at 23°C or in seawater at 23°C. Specimens tested in seawater were also galvanically protected with zinc electrodes. Fatigue loading was at constant ΔK and R = 0.1 or 0.5. Frequency of loading was 0.3 Hz.

The Cathodic Protection of Metallic Structures In Marine Environments★

Abstract Theoretical and practical considerations involved in using cathodic protection in sea water are covered, including anode location, polarization, economics and other factors. Specific cases of cathodic protection application are mentioned, including drydocks and ships. Means of checking the effectiveness of cathodic protection are reviewed. The importance of supervision by competent personnel is mentioned, as is automatic control of potentials. Other topics discussed include use of compartmented cells, effect of cathodic protection current on marine growth and problems involved in making cathodic protection automatic. 5.2.1