{"id":10181,"date":"2021-10-21T11:33:27","date_gmt":"2021-10-21T08:03:27","guid":{"rendered":"https:\/\/n-icc.com\/what-is-cathodic-protection\/"},"modified":"2021-10-22T22:14:30","modified_gmt":"2021-10-22T18:44:30","slug":"what-is-cathodic-protection","status":"publish","type":"post","link":"https:\/\/n-icc.com\/en\/what-is-cathodic-protection\/","title":{"rendered":"What is cathodic protection"},"content":{"rendered":"

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To better understand what cathodic protection<\/strong> is; We must know that this method is one of the most effective methods of corrosion control. In this way, industrial structures, pipes and equipment installed underground or underwater are protected.<\/p>\n

Only corrosion attacks that are accompanied by electrochemical reactions and changes in material valence can be controlled by cathodic protection.<\/p>\n

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What is the basis of cathodic protection<\/h2>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\n\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\n\t\t\t\t\t
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Cathodic protection<\/strong> systems are based on the application of cathodic current and the reduction of potential and corrosion current of parts that are subject to corrosion attacks.<\/p>\n

What are the two main methods for cathodic protection<\/strong>:<\/p>\n

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  1. Sacrificial anode method<\/li>\n
  2. Impressed cathodic current protection (ICCP)<\/li>\n<\/ol>\n

    In order to better understand the concepts of potential and corrosion current, we need to know Mixed Potential Theory.<\/p>\n

    The mixed potential theory was introduced by Wagner. This theory was proposed in 1938 and is based on two important hypotheses:<\/p>\n

    1. Each electrochemical reaction is a set of at least two or more oxidation and reduction reactions.<\/p>\n

    2. The sum of the charges exchanged in an electrochemical reaction is zero. In other words, the sum of the oxidizing current is equal to the sum of the decreasing current (the principle of charge survival).<\/p>\n

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    Based on this theory, flow-density diagrams (i<\/em> E-log or Evans) have been drawn, which are known as the basic principles of cathodic protection<\/strong>.<\/p>\n

    Although this theory is very practical, it is not error free. The coupon method is considered as the safest method to determine the corrosion rate.<\/p>\n

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    Now, in the article “What is cathodic protection”, the subject of “corrosion coupons<\/strong>” is mentioned, we will provide a brief explanation about it. You can read the full article “<\/span>Corrosion Coupons<\/a>“<\/span><\/span> on Naftan Payesh website.<\/p>\n

    Corrosion coupons:<\/h5>\n

    Corrosion coupons<\/strong> are a very simple and effective tool that provides a small estimate of the rate of corrosion that occurs within a particular operating system. Coupons also provide an objective signal of the type of corrosion that may occur in the monitored system.<\/span><\/p>\n

    This method involves placing a sample of material (coupon) in a process environment for a certain period of time, then sampling it for analysis. The basic measure of corrosion coupons is weight loss. Weight loss during the period of exposure to the environment is expressed as the rate of corrosion.<\/p>\n

    Corrosion coupons are also known as corrosion monitoring coupons.<\/p>\n

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    What is the meaning of Mixed Theory in cathodic protection<\/h3>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\n\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\n\t\t\t\t\t
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    Here we examine what the concept of mixed potential in cathodic protection<\/strong> is. The figure below shows an image of a piece of zinc (Zn) immersed in hydrochloric acid (HCl).<\/p>\n

    According to Wagner’s theory, for the reaction of dissolution of zinc in hydrochloric acid, two halves of anodic and cathodic reactions can be considered:<\/p>\n

    Half anodic reaction of zinc oxidation<\/p>\n

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    Half cathodic hydrogen reduction reaction<\/p>\n

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    These two half-reactions are occurring simultaneously on the metal surface. Each half reaction has its own potential and current density.<\/p>\n

    It is important to note that these half-reactions cannot be present separately and at the same time on the zinc surface (Zn). So they have to adapt their potential to what is called the corr<\/sub> E<\/em> potential.<\/strong><\/p>\n

    In fact, what we know as corr<\/sub>E<\/em> is the combination of the potentials of the two halves of anodic and cathodic reactions, and this is the concept of mixed potential.<\/p>\n

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    Cathodic protection: What is corrosion<\/span><\/a><\/h5>\n

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    What are Evans or Evans Diagrams in Cathodic Protection<\/h3>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\n\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\n\t\t\t\t\t
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    The vertical axis of these diagrams shows the potential for a standard electrode reference and the horizontal axis the logarithm of the current density.<\/p>\n

    Drawing Evans diagrams requires equilibrium potential (0<\/sub>E<\/em>) and exchange current (0<\/sub>i<\/em>) and straight anode and cathode lines.<\/p>\n

    It should be noted that an electrochemical corrosion<\/strong> system can be characterized by kinetic parameters. Such as TOEFL slope (c<\/sub>\u03b2a<\/sub>, \u03b2), exchange current density (0<\/sub>i<\/em>) and limit current density (li<\/sub><\/em>).<\/p>\n

    But E<\/em>0<\/sub> is a thermodynamic parameter and is obtained for each reaction from the EMF series in the equilibrium state of the substance with its ion solution.<\/p>\n

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    What is cathodic protection; The equation does not exist<\/h3>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\n\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\n\t\t\t\t\t
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    The electrode potential (Ecorr<\/sub><\/em>) and the current density (icorr<\/sub><\/em>) are obtained from the point where the lines of hydrogen reduction (H +<\/sup> \/ H2<\/sub>) and oxidation of zinc (Zn+2<\/sup> \/ Zn) intersect.<\/p>\n

    Exchange current density (0<\/sub>i<\/em>) and open circuit potential (OCP<\/sub>E<\/em>) are required to plot graphs.<\/p>\n

    This type of flow potential-density diagram can be drawn for all solids that have one or more oxidizing agents in contact with the solution. The calculations needed to draw the lines can be done using electrochemical equations.<\/p>\n

    Like the Nernst equation<\/strong> and the reactions written on the anode and cathode lines:<\/p>\n

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    What is corrosion flow and corrosion potential in cathodic protection<\/strong>:<\/p>\n

    Corrosion current and corrosion potential are obtained from the intersection of the anodic and cathode lines of these diagrams. If we have several oxidizing or reducing factors, due to the principle of equality of oxidation and reduction currents, the flow and corrosion potential can be calculated.<\/p>\n

    If an oxidizing component such as ferric ion is added to the solution, the corrosion potential can be calculated on the Evans diagram. This is done with the help of the principle of equality of oxidation and reduction current.<\/p>\n

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    Conclusions from Wagner's theory<\/h4>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\n\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\n\t\t[vc_column_text woodmart_inline=”no” text_larger=”no”]<\/p>\n

    In the following; Our conclusion from Wagner’s theory in the article “What is cathodic protection<\/strong>“:<\/p>\n

    What can be deduced from Wagner’s theory of mixed potential is summarized as follows:<\/p>\n