1. Definition of Cathodic Protection Cathodic protection (Cathodic Protection) is a technique used to control corrosion of metallic surfaces by making such metal surfaces as catheodes of these cathodic protection Volta cells is a commonly used method for Protects metal structures from corrosion. This cathodic protection system is usually used to protect steel, pipeline, tank, stake, vessel, offshore platform and oil-wells (sheath) on land. A side effect of improper use is the onset of hydrogen molecules that can be absorbed into the metal thereby causing hydrogen embrittlement. Cathodic protection is an effective way of preventing stress corrosion cracking (cracking due to corrosion). Cathodic protection mechanism basically cathodic protection is electrochemical corrosion control wherein the oxide reaction in galvanized cells is centered in the anode area and suppresses the corrosion process on the cathode area in the same cell. Thus, this technology is actually a combined form of electrochemical elements, electrical and knowledge of materials. Electrochemical elements cover the fundamentals of the process of occurrence of corrosion reactions, while the electrical elements cover the basic concept of protected object behaviour and its environment if the electric current is flowing. To get an overview of the basic concepts of corrosion processes and the Cathodic protection application theoretically ( be seen in Figure 2.) Figure 2. (a) The corrosion process mechanism between two metals dipped in an electrolyte and (b) the basic concept of the cathodic protection system of the victim In Figure 2 (a) indicates that two pieces of iron and zinc are separated and are dipped in an electrolyte. Both metals will be corroded and both of the corrosion (oxidation) reactions are balanced with the same reduction reaction, which in both cases occurs the release of hydrogen gas. The incident will be different if the two metals are connected to each other electrically as shown in Figure 2 (b). Here the corrosion reaction is centered on the zinc electrode (anode) and almost all the reduction reactions are centered on the iron electrode (cathode). The reaction of zinc in Figure 2 (b) will be faster than the series (a). At the same time, corrosion in iron will cease. In other words, zinc has been sacrificed to protect iron. In the application in the field, the protected structure will dius. Image 3. Principe of catodic protection In the image it appears that the current flows to the pipeline in the area where previously as an anode. The Cathodic protection system should be greater than the ongoing corrosion-cell driving voltage. For cathodic protection system to work, there must be a current flowing from the groundbed. During current flow to the ground, the groundbed material will be the subject of corrosion. Because groundbed is used to remove the current, it is better to use a material that is lower consumption than the cheek itself. Or thermodynamically, the potential of a protected pipe/structure is made into immune that is at-850 mV (CSE3). 2. Type of Cathodic Protection a. Sacrificial Anode This system is also known as galvanic anode, where the way of work and current source is derived only from the anode galvanized reaction itself. The basic principle of the victim's anode system is simply by creating a galvanic electrochemical cell where two different metals are connected electrically and planted in natural electrolytes (soil or water). In such different metal cells, the higher metals in the Electromitive-EMF series series (more active) will be anodic against the less active and consumed metals during electrochemical reactions. Less active metals receive cathodic protection on its surface due to the presence of current flow through the electrolyte of an anodic metal. Images of cathodic protection system with the victim anode can be seen in figure 4 b. Impressed Current Unlike the victim's anode system, the current source of the comparable current system comes from outside, usually derived from DC and air-conditioning which is equipped with current rectifier (rectifier), where the negative pole is connected to the protected structure and the positive pole Connected to anode. The current flows from the anode through the electrolyte to the surface of the structure, then flows along the structure and return to the rectifier through the electrical conductor. Because the structure receives current from the electrolyte, the structure becomes protected. The rectifier current output is set to drain enough current so as to prevent the corrosion current which will leave the anode area on the protected structure. With the current output from this anode then the anode is consumed. Therefore, it is recommended to use a material that is lower consumption than magnesium, zinc and aluminum commonly used for the system, generally used a combination of special material combination. Gambar 5. The typical impressed current cathodic protection system A comparable current system is used to protect a large structure or that requires a greater flow of protection and is deemed less economical when using anode. This system can be used to protect the structure of both the uncoated, the poor coating conditions as well as the condition of the good, the advantages of the power system is to be designed for applications with a high degree of flexibility Because it has a wide range of current output capacity. It means that the current needs can be adjusted either manually or automatically by changing the output voltage according to the needs. Another advantage of this system, with just installing the system in one of the places can protect the structure is quite large. The downside of this system is that it requires more care than the victim's system so that the operational costs will increase. This system also has a dependence on the reliability of energy suppliers (rectifier) so that damage to this system will be fatal to the performance of protection system. Disadvantages of other comparable current systems are likely to be more expensive because of the more equipment and materials used. In addition, there may be a problem with the effect of current interference against the surrounding structures. 3. The Nature of Cathodic Protection System When a metal is exposed to a certain environmental condition, the metal will behave like one of the properties of the following three metal properties. a. Immunities In this first property the metal will be invulnerable or totally unaffected by environmental conditions, metals that can describe this property are commonly referred to as precious metals, such as gold, silver and platinum. The combination of the environment and the metals mentioned above will produce an immune property for the metal. There will be no chemical reaction process on the metal or corrosion process will not occur on the metal, if the metal is weighed before being put into a certain environmental conditions then weighed again after some time then the weight of the metal is not reduced at all. This nature of resistance occurs because the type of metal is very thermodynamically stable in certain environmental conditions so that the corrosion process cannot occur spontaneously. b. Active or Reactive In this second property the metal will be very easy to react with the environment or in other words the metal is very easily corroded when the metal is submerged in a certain liquid environment for example, and if examined further it can be seen that the metal is dissolved in water and transforms into ions dissolved and further more these dissolved ions will transform into corrosion products that are not protective of metals. Corrosion process on this metal will continue because the corrosion products that are formed are not able to prevent the corrosion process from going further. The reactive character of this metal can be described by the loss of most of the weight of the metal after being exposed to certain environmental conditions, if we weigh the weight of the metal before and after the metal reacts with its environment. c. Passivity In this third property, we will find that the corrosion process actually occurs the same as in the reactive nature but in a certain phase we will find that the metal will be passive to its environment. In other words the metal is corroded so that the metal dissolves in water and turns into dissolved ions but furthermore the dissolved ions will turn into a film layer of very thin corrosion products, which will actually protect the metal from further corrosion processes. This corrosion product film layer is also called a passive film layer (protective passive layer), where this layer will reduce the rate of metal corrosion at low levels even at very low levels if the film layer can be formed properly. Whether or not a passive film survives the corrosion process is very dependent on the integrity of the passive film. And vice versa if the film layer is damaged then the metal can undergo a process of corrosion or return to the reactive phase. Some examples of metals that have passive properties are iron, chrome, titanium, nickel and some alloys consisting of the basic metals mentioned above such as stainless steel or carbon steel. 4. Use Of Cathodic Protection In Corrosion Systems Many methods are used to reduce the rate of corrosion, among which the easiest application is coating (coating), cathodic protection, the addition of inhibitors and others. Cathodic protection is widely used to protect steel structures that are in the soil and the seawater environment, and is used little under certain conditions. This cathodic protection system is usually used to protect steel, pipelines, tanks, piles, ships, offshore platforms and casing (casing) of oil wells on land. The application of cathodic protection is often combined with coatings. The aim is to protect the steel when the coating is damaged. The side effect of improper use is the emergence of hydrogen molecules that can be absorbed into the metal causing hydrogen embrittlement (hydrogen trembling). The principle of cathodic protection is by connecting the external anode with the structure to be protected and by passing a DC electric current, and making the entire area of the protected structure become cathodic and uncorroved. In general: reduce the rate of corrosion by making metals as cathodes through the impressed current method or by connecting metals with sacrificial anodes. 5. Making corrosion protection using a cathodic system a. Steel coating with paint to help it more durable against the oxidation from the surrounding environtment. b. Sacrificial anode : Before determining the suitable anode, the resistivity of the soil to be installed with the pipe must be measured first. After measuring the resistivity, next step is to calculate the current for the installed pipe and choosing the suitable anode material for the soil resistivity. Wipe clean the surface of the pipe and anode from the impurity. Then, coat the pipe with paint to increase it’s resistant to the anode, so that it can last longer. Then, dig the space for the anode near the pipe which is called “Groundbed”, then connect the pipe, and the anode to the coil wire so that it can transfer electricity, with the pipe as the cathode. Then, the protected pipes and the anode are buried and tested with the appropriate current. c. Impressed Current Cathodic Protection (ICCP) / Arus Tanding : Almost the same as the sacrificial anode method. The difference is, direct current is used. Usually the positive pole will be connected to the anode, while the negative pole is connected to the protected metal. The anode used is usually also inert or semi consumable. 6. Differences in The Cathodic Protection System a. Sacrificial anode The principle of this sacrificial anode method is to protect the metal by sacrificing more reactive metals, where the process mechanism is the same as the galvanic corrosion process, namely the transfer of electrons from more reactive (potentially more negative) metals to protected (potentially more positive) metals corrosive electrolyte with a connecting conductor. Where the anode meterials that can be used in the sacrificial anode method are metals which have a more negative or reactive potential than the steel potential, for example aluminum alloys, zinc and magnesium. b. Impressed current The principle of this impressed current anode method is to protect the metal by flowing direct electrical current obtained from an external source, usually from a current rectifier (transformer rectifier), where the negative pole is connected to the protected metal and the positive pole is connected to the anode. Where the anode meterial that can be used in the impressed current method is a conductive metal and has inert or semi consumable properties, platinum-titanium, Ferro silicon, carbon steel, ferro silicon crhom, PA-Ag, graphite. 7. Conclusion Cathodic protection (Cathodic Protection) is a technique used to control corrosion of metallic surfaces by making such metal surfaces as catheodes of these cathodic protection Volta cells is a commonly used method for Protects metal structures from corrosion. There are two types of cathodic protection systems namely sacrificial anode and impressed current. REFERENCES Davis, J. R. 2000. Corrosion: Understanding the Basics. USA:ASM International Fahmi, Rizki; Jufriadi, dan Fakhriza. “Kajian Proteksi Katodik (Cathodic Protection) pada Jaringan Pipa Transfer RWI (River Water Intake) di PT. 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