Anode Cathodic Protection Research Articles

Development of Aluminium Base Anode for Cathodic Protection of Steel

Development of Aluminium Base Anode for Cathodic Protection of Steel

Synthesis of zinc from spent zinc-manganese-carbon batteries and its application as sacrificial anodes in cathodic protection

Synthesis of zinc from spent zinc-manganese-carbon batteries and its application as sacrificial anodes in cathodic protection

Evaluation of the electrical properties of carbon electrodes developed with bio-material additions as a sacrificial anode in cathodic protection

The use of zinc and magnesium sacrificial anodes for the protection of steel structures in cathodic protection techniques have been widely accepted but longevity and environmental friendliness of these materials in service still needs to be improved. Thus, the need to continually develop anodes that can potentially serve the same purpose and/or better performance. This work is a feasibility study on the production of carbon electrodes for possible application as sacrificial anodes for the cathodic protection of mild steel. The main aim of this investigation is to develop an electrode from carbon-based materials with a view to producing anodes that can potentially replace zinc and magnesium electrodes for cathodic protection of low-carbon steel. The electrodes were developed using mixture of coal, charcoal, mill scale, wood dust and coal tar (binder) that were heated and compressed in a metal die. The current passing through the electrodes was measured with the resistance, resistivity and conductivity determined, including the current densities (Iρ) which gives an indication of the electrochemical behavior of the electrodes. Morphology of the electrodes were examined by optical microscope (OM) and scanning electron microscope (SEM) to assess the influence of porosities of the electrodes produced. Based on these findings, it was generally observed that the conductivity increases from 5.23E-4 S/m to 5.87E-3 S/m for 150 µm and 600 µm particle sizes, respectively. Generally, resistivity increases with an increase in the amount of wood dust in the carbon anodes developed. The carbon electrode of 600 µm particle size with the composition of 67 wt% coal, 5 wt% charcoal, 10 wt% coal tar, 10 wt% mill scale and 8 wt% wood dust had the best current density that could offer corrosion protection for mild steel.

Modelling of 3D periodic cathodic protection problems in reinforced concrete structures with accelerated boundary element method

The steel used for concrete reinforcement exhibits either active or passive electrochemical behavior. As long as the concrete environment remains highly alkaline, the steel remains passive. However, carbonation and/or chloride contamination of concrete will cause steel to become active and corrode. In the latter case, a common strategy is the use of cathodic protection (CP) systems to lower the potential of the steel at a protective level. The numerical modelling of cathodically protected concrete buildings and infrastructures usually requires large-scale models due to their size and complex geometry. An efficient modelling approach is to consider any possible periodicity in these problems by applying periodic boundary conditions to a representative volume element of the structure. The boundary element method (BEM) is extensively used for solving CP problems. A BEM formulation is proposed for solving 3D periodic CP problems in this work. The computation cost is reduced by applying acceleration techniques based on adaptive cross approximation (ACA). As an engineering application, a sacrificial anode CP system of a reinforced concrete column is designed, illustrating the importance of detailed modelling in the design of such systems. To this end, the macrocell corrosion problem is initially solved, and a parametric study with respect to concrete conductivity is carried out.

Effective Use of Sacrificial Zinc Anode as a Suitable Repair Method for Severely Damaged RC Members Due to Chloride Attack

In many cases, the repair strategy by using sacrificial anodes for cathodic protection in real RC structures requires additional zinc anodes after several years due to the decreasing protective area. This experimental study evaluates the effectiveness of time lag application of sacrificial anode cathodic protection applied to RC beam specimens that deteriorated severely due to chloride attack. In the experiment, sacrificial anodes and cathodic protection (SACP) were applied to 41-year-old RC beam specimens exposed to natural marine environments in which the embedded steel bars were significantly corroded. The repair work was performed in three stages. Instant-off and rest potential tests of steel bars were conducted periodically to demonstrate the time-dependent depolarization value. In the first stage, a polymer-modified mortar as a patch repair material was cast to replace the concrete in the middle tensile part with small sacrificial anodes embedded in the mortar. After the protective current reaches an equilibrium state, the sacrificial anodes are disconnected from the steel bars for a year, defined as the second stage. During the one year in the second stage, the steel bar in the patch repair area remained passive, without any sign of corrosion. As for the third stage, additional sacrificial anodes were installed in the existing concrete part to protect the steel in it. From one year of observation after applying sacrificial anodes to old concrete parts, the time lag SACP application of both in patch and non-patch repair parts was clarified to be effective in stopping the corrosion of steel bar in both parts until 20–30 years based on the service life prediction. Doi: 10.28991/CEJ-2022-08-07-015 Full Text: PDF

Corrosion Behavior of Al Modified with Zn in Chloride Solution.

Aluminum-based alloys have been considered candidate materials for cathodic protection anodes. However, the Al-based alloys can form a layer of alumina, which is a drawback in a sacrificial anode. The anodes must exhibit uniform corrosion to achieve better performance. Aluminum can be alloyed with Zn to improve their performance. In this sense, in the present research, the electrochemical corrosion performance of Al-xZn alloys (x = 1.5, 3.5, and 5 at.% Zn) exposed to 3.5 wt.% NaCl for 24 h was evaluated. Polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to identify the electrochemical behavior. The microstructure of the samples before the corrosion assessment was characterized by means of X-ray diffraction analyses (XRD) and scanning electron microscopy (SEM). In addition, microstructures of the corroded surfaces were characterized using X-ray mappings via SEM. Polarization curves indicated that Zn additions changed the pseudo-passivation behavior from what pure Al exhibited in a uniform dissolution regime. Furthermore, the addition of Zn shifted the corrosion potential to the active side and increased the corrosion rate. This behavior was consistent with the proportional decrease in polarization resistance (Rp) and charge transfer resistance (Rct) in the EIS. The analysis of EIS was done using a mathematical model related to an adsorption electrochemical mechanism. The adsorption of chloride at the Al-Zn alloy surface formed aluminum chloride intermediates, which controlled the rate of the process. The rate constants of the reactions of a proposed chemical mechanism were evaluated.

A new strategy for cathodic protection of steel in fresh water using an aluminum electrode as an impressed current anode: a case study

Abstract In fresh water, aluminum cannot be used as a galvanic anode for the cathodic protection (CP) system because the accumulation of oxide films causes the electrochemical potential to change to an extremely noble potential (passivation). To work correctly, aluminum anodes often require chloride ions in the electrolyte. Because impressed current anodes are fairly inert, the anode component corrodes at an extremely low rate. The present case study focused on a novel strategy for employing aluminum anode as an impressed current anode for cathodic protection inside a fresh water storage tank made of X65 steel. According to the impressed current scenario, 0.6 A of current supply and 0.33 V of voltage were required to properly protect the X65 steel tank’s internal surface area of 421 m2. Prior to the implementation of cathodic protection, the potentials varied from −0.474 to −0.509 V (vs. Ag/AgCl). After 30 days, 60 days, and 90 days of cathodic protection, the potential values inside the protection zone showed a significant change (−0.800 and −1.150 V vs. Ag/AgCl). The results demonstrate that aluminum anodes with a considerable performance (current capacity) and a minimal consumption level can really be employed as impressed current anodes in fresh water applications.

A Rapid Test to Screen the Functionality of Galvanic Anodes for Cathodic Protection of Reinforced Concrete

Galvanic anodes are increasingly popular in the repair, rehabilitation, and maintenance of reinforced concrete structures suffering from chloride-induced corrosion for the added durability benefits. There is a consensus among engineers that demand will increase due to ageing infrastructure stock, climate change, and the option to reuse structures which is a logical solution to help reduce carbon emissions. New manufacturers will likely emerge to meet the needs of a growing market. However, there is no standard for galvanic anodes for use in concrete. In theory, products may come to market that fails to work as anodes, and hence corrosion may not be arrested, and repeated intervention could be required. This paper presents a methodology that has been developed for demonstrating anodes function as intended in a short-term test. Anodes were cast into concrete, and drive voltage, resistivity, and resultant current were measured when connected to an external cathode. The test setup was applied to several commercially available galvanic anodes. All anodes achieved a current output of 0.35 mA in this experimental setup. This could provide a rapid test to screen anodes new to the market. The analyses show inherent anode behaviour varied with different manufacturers, and there were also performance differences among replicate anodes. Such behavioural characteristics may affect the long-term performance of the anodes. These results provide new data on galvanic anodes and demonstrate the potential need for standardisation in the industry.

Influence of silicon on the corrosion behavior of Al–Zn–In sacrificial anode

Steel structures used in offshore sectors are often exposed to adverse weather conditions, and thus, require the application of efficient and safe corrosion protection techniques. The application of sacrificial anodes with aluminum alloys for cathodic protection is a viable anticorrosive protection alternative for long-term wet conditions owing to its low density, galvanic economy, better performance, availability, and recyclability. This study aims to evaluate the effect of different percentages of silicon in commercial Al–Zn–In alloys, used in aluminum sacrificial anodes, on the electrochemical properties of the alloys. The DNV-RP-B401 standard was used to analyze the electrochemical performance and manufacturing of commercial matrix alloys according to the prescribed chemical composition. They were characterized by optical emission spectrometry, electrochemical performance, electrochemical polarization assay, macrography, and scanning electron microscopy. The results revealed greater work efficiency and corrosion uniformity for aluminum cathodic protection anodes with the addition of 0.10% by weight of silicon, which resulted in disk shape precipitation and reduced grain size and smaller spacing between dendritic arms. Therefore, with this percentage of silicon, the anodes exhibit less automatic corrosion of the anode mass, that is, greater anticorrosive protection, smaller amounts of corrosion residues in the medium, less anode disposal with exhausted life, and greater application sustainability for the aluminum anode.

Development of Al-5%Zn-0.5%Sn-2.6%Mg Alloy as Sacrificial Anode for Cathodic Protection of Steel in 3 wt.% NaCl Solution

In this work, two aluminum alloys, Al-5Zn-0.5Sn and Al-5Zn-0.5Sn-2.6Mg, were prepared by melting in an induction furnace to be used as sacrificial anodes for cathodic protection of marine structures. The alloys are characterized by scanning electron microscopy mapping coupled to energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and X-ray diffraction. Afterwards, the corrosion behavior was studied in 3 wt.% NaCl solution through immersion tests, potentiodynamic polarization, electrochemical impedance spectroscopy and weight-loss measurements. Results display that active dissolution of Al-5%Zn-0.5%Sn-2.6%Mg alloy and its quasi-uniform corrosion is associated with the major precipitates MgZn2 and Mg2Sn particles formed during the melting process. Galvanic coupling measurements over 45 d were carried out on both alloys. The sacrificial cathodic protection of both anodes was successful but the couple efficiency was greater for Al-Zn-Sn-Mg owing to its more negative corrosion potential and uniform dissolution.

Does galvanic cathodic protection by aluminum anodes impact marine organisms?

BackgroundCathodic protection by sacrificial anodes composed of aluminum-zinc-indium alloys is often applied to protect offshore support structures of wind turbines from corrosion. Given the considerable growth of renewable energies and thus offshore wind farms in Germany over the last decade, increasing levels of aluminum, indium and zinc are released to the marine environment. Although these metals are ecotoxicologically well-studied, data regarding their impact on marine organisms, especially sediment-dwelling species, as well as possible ecotoxicological effects of galvanic anodes are scarce. To investigate possible ecotoxicological effects to the marine environment, the diatom Phaedactylum tricornutum, the bacterium Aliivibrio fischeri and the amphipod Corophium volutator were exposed to dissolved galvanic anodes and solutions of aluminum and zinc, respectively, in standardized laboratory tests using natural seawater. In addition to acute toxicological effects, the uptake of these elements by C. volutator was investigated.ResultsThe investigated anode material caused no acute toxicity to the tested bacteria and only weak but significant effects on algal growth. In case of the amphipods, the single elements Al and Zn showed significant effects only at the highest tested concentrations. Moreover, an accumulation of Al and In was observed in the crustacea species.ConclusionsOverall, the findings of this study indicated no direct environmental impact on the tested marine organisms by the use of galvanic anodes for cathodic protection. However, the accumulation of metals in, e.g., crustaceans might enhance their trophic transfer within the marine food web.

Effect of Zn/Mg ratio on cathodic protection of carbon steel using Al−Zn−Mg sacrificial anodes

Abstract Al−Zn−Mg alloys with different Zn/Mg mass ratios were evaluated as sacrificial anodes for cathodic protection of carbon steel in 3.5 wt.% NaCl solution. The anodes were fabricated from pure Al, Zn and Mg metals using casting technique. Optical microscopy, SEM−EDS, XRD and electrochemical techniques were used. The results indicated that with decreasing Zn/Mg mass ratio, the grain size of α(Al) and the particle size of the precipitates decreased while the volume fraction of the precipitates increased. The anode with Zn/Mg mass ratio >4.0 exhibited the lowest corrosion rate, while the anode with Zn/Mg mass ratio

Influence of impressed current cathodic protection systems on chemical characteristics of underground water.

Despite well-known corrosion inhibition behavior of cathodic protection (CP) system, this process might be a potential hazard to surrounding ecosystem resulted mostly from continuous electrical current which is applied to the adjacent environment and metallic anode dissolution as well. In this research, deepwater CP wells at different locations of Golestan province, Iran, were taken into consideration to evaluate the impact of these protective systems on underground waters from viewpoint of chemical and physicochemical characteristics resulted from anode dissolution. For this purpose, concentration of metallic constituents of the anode as well as the amount of pH, total dissolved solids (TDS), electrical conductivity (EC), and total hardness were determined. On the basis of obtained results, the concentration of Mn, Cr, and Fe in CP well located nearby an industrial district (i.e., 0.087, 0.475, and 8.5mg/L, respectively) was higher than both WHO and USEPA standards. This fact can be resulted from the position where the well was dug as well as the CP anode dissolution within the deep CP water wells. PRACTITIONER POINTS: The impact of impressed current cathodic protection (ICCP) system on chemical and physicochemical characteristics of underground water has been evaluated. Anode dissolution of ICCP systems influences the water characteristics nearby the anodes. Despite low dissolution rate of high silicon cast iron anodes, their long-term utilization might be harmful for adjacent ecosystem. The amount of heavy metals in underground waters was demonstrated to be influenced by the employment of ICCP system. Both anode dissolution and the geological properties of the Earth`s crust surrounding the wellbore might be responsible for significant increase of heavy metals concentration.

Cathodic protection design optimization of a buried vessel by FEM simulation

AbstractInstalling linear anode loops around a buried vessel is one of the latest cathodic protection anode arrangements for buried vessels. In this arrangement, besides the physical properties of the environment, for example, soil resistivity and oxygen content, the distance of anode loops to the vessel, number of anode loops, and distance between each loop are three main designing parameters. In the present study, the cathodic protection of a buried vessel (8‐m long; 2.5 m in diameter) with complete nonlinear polarization at the protected surface is studied with finite element method simulation. The analyzed variables are the number of anode loops from one to three, the anode‐to‐vessel distance from 0.2 to 0.6 m, the distance between loops from 0.2 to 1.6 m. Soil resistivity varies from 10 to 500 Ω·m, and oxygen limiting current density changes from 5 to 100 mA/m2. Increasing anode‐to‐vessel distances will reduce the potential differences, and the best condition is the maximum distance, 0.6 m. The optimum number of anode loops is two. Increasing soil resistivity will increase the potential difference, but in an optimum design, its effect is not significant.

Investigation on the electrochemical and mechanical performance of CFRP and steel-fiber composite bar used for impressed current cathodic protection anode

Impressed current cathodic protection (ICCP) has been proved to be an effective method to inhibite steel corrosion. Combined with ICCP technique, a new system has been proposed in this paper with carbon fiber reinforced polymer (CFRP) as dual-functional material: auxiliary anode and partial reinforcement simultaneously. The electrochemical and mechanical performances of CFRP in the new ICCP system were investigated experimentally with two kinds of reinforcement bar: CFRP bar and steel-fiber composite bar (SFCB). First, the accelerated anodic polarization test and electrochemical impedance spectroscopy (EIS) measurement were carried out for CFRP bar and SFCB to verify the electrochemical performances. Then, the mechanical performance and underlying degradation mechanism were identified for CFRP bar and SFCB based on the uniaxial tensile test and scanning electron microscopy (SEM). Finally, the service life of CFRP bar and SFCB has been evaluated to confirm the fesibility of the proposed system in practical engineering. Results showed that CFRP bar and SFCB possess excellent electrical conductivity and low electrical resistance as the anode in ICCP system. Compared with SFCB, CFRP bar is more promising as an anode material with a stronger polarization resistance capability, an acceptable degradation of the mechanical property and a longer service life. With a current density of 20 mA/m2, the service life was evaluated as 62 years for CFRP bar while 7 years for SFCB. To improve the application of SFCB in ICCP system effectively, some modifications are necessary, such as replacing the inner steel bar with stainless steel bar or adding a protective layer between the steel bar and fiber layer. Furthermore, the proposed system shows great potential for marine RC structures and the comprehensive study of this system will be carried out in future work.

Durability of impregnated carbon textiles in mortar as cathodic protection anodes

Current research focuses on the use of carbon (C) textiles as cathodic protection (CP) anodes. Carbon fibres are of particular interest due to their excellent mechanical properties. However, the influence of anodic polarisation on the durability of carbon anodes is still not sufficiently understood. In previous works, the durability of carbon anodes was examined by experimental investigations in saturated calcium hydroxide (Ca(OH)2) solution. In this work, various anodes (carbon textiles with different impregnations, as well as mixed-metal-oxide-coated titanium (Ti)) were investigated after embedding in mortar. The type of mortar as well as the environmental conditions were varied in order to represent diverse conditions. Potentiostatic polarisation was implemented for 8 months. Results of this work show that CP with impregnated carbon textiles is, at least under the investigated conditions, possible.

The research of the processes and properties of anodes for the cathodic protection of the thermally expanded graphite

Modern human activity requires the need for a reliable and high-quality infrastructure and equipment, which in use is a subject to environmental influences. Corrosion of metal products remains one of the most acute problems of our day. An effective way to protect metal products from corrosion is a cathodic protection. The paper presents the results of electrochemical studies to assess the possibility of using anodes of thermally expanded graphite for cathodic protection of metals. Thermally expanded graphite is produced from natural graphite by its interaction with strong oxidizing agents followed by heating. The result is a material that in its properties is a new modification of carbon. In this study, thermally expanded graphite was obtained from a fluorine-intercalated compound. The studied material is easy to mold in various types of pressure treatment, i.e. it is pressed and rolled at low pressures forming a porous framework, which is important when receiving electrodes. Polyethylene was introduced into the thermally expanded graphite powder to increase the electrode resistance. The process of co-pressing of the thermally expanded graphite with different contents of the polyethylene powder was previously investigated to select the composition of the composite material for conducting electrochemical tests. Investigations were carried out in a sodium chloride solution, as well as in a more aggressive environment – a potassium bromide solution. Conducted studies have shown the possibility of using the thermally expanded graphite-polyethylene composite material for the production of cathodic protection anodes.

Performance evaluation of zinc anodes for cathodic protection of mild steel corrosion in HCL

Abstract An assessment of performance of zinc anodes on the cathodic protection of mild steel in 0.5 M hydrochloric acid was made at both the room and elevated temperatures. The cathodic protection reactions process was evaluated by weight-loss method, corrosion rate calculation and potential measurement methods. The effectiveness of zinc sacrificial anodes were found to be cathodically protective on mild steel in the hydrochloric acid at both the room temperature (27 °C) and elevated temperature (60 °C). There was close correlation of the results obtained for the weight-loss method and potential measurement in the HCL environment.

Thin Film Coating of Mg-Intercalated Layered MnO2 to Suppress Chlorine Evolution at an IrO2 Anode in Cathodic Protection

Titanium-supported electrocatalysts composed of novel metal oxides have exclusively been utilized as anodes in the cathodic protection (CP) of steel structures. These types of anodes have a small overpotential toward the chlorine evolution reaction (CER) in impressed-current cathodic protection (ICCP) systems and vigorously evolve chlorine (Cl2) in electrolytes containing Cl−, such as seawater. Cl2 has a negative impact on the ecosystem because of its intrinsic toxicity and corrosivity. We present herein a thin film coating that can effectively suppress the CER without prevention of the oxygen evolution reaction (OER) at the underlying iridium oxide (IrO2) layer coated on a titanium substrate in 0.5 M NaCl solution. The thin film consists of buserite-type layered manganese dioxide (MnO2), the interlayer of which accommodates Mg2+ cations and two layers of H2O molecules, and is uniformly deposited via an electrochemical route and subsequent ion-exchange. The CER efficiency of the electrode modified with the Mg-buserite layer was as small as 11% at + 1.7 V vs. Ag/AgCl.

Application of CFRP as anode in cathodic protection for steel reinforced concrete – a review

Impressed current cathodic protection (ICCP) is an electrochemical method to prevent or stop corrosion of steel reinforcement in concrete structures. The use of this technique is limited although it has been proven to be effective. One of the reasons is the high cost of anode material, commonly titanium anode. Hence there is a need for alternative anode materials to lower the cost and at the same time to improve the performance of the ICCP system through design. This paper reviews carbon fiber reinforced polymer (CFRP) as an anode for ICCP systems in concrete and discusses the degradation mechanism and operating conditions of the anode. It also gives an overview of the performance of CFRP as an anode material, from laboratory experiments to field operation.