What Affects The Rate Of Corrosion

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Most corrosion is an electrochemical reaction. Anything that affects the speed of the chemical reaction will in turn affect the amount of current flow, which will affect the rate of corrosion. The rate of corrosion is directly proportional to the amount of current in the electrochemical corrosion cell. If the current can be measured accurately, then an exact calculation of the metal loss can be made.

2.2.1 ELECTRICAL EFFECTS ON THE RATE OF CORROSION

Any issue that have an effect on the quantity of current flowing in a circuit can affect the speed of the electrochemical reaction (corrosion). Ohm’s law applies to those electrical circuits. The law states that the direct current flowing in a circuit is directly proportional to the potential
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The electrolyte resistivity may be a property of the electrolyte. The definition of an electrolyte is a material that may permit ions to migrate, and also the resistivity of the electrolyte is the rate at which it permits ions to migrate at a given potential. Current is reciprocally proportional to resistivity (V/R=I) and thus, in an electrochemical cell. If the resistivity is doubled, and all different factors stay constant, the quantity of corrosion is cut in 0.5.
3) Contact Resistance
The contact resistance of the anode to electrolyte and of the cathode to electrolyte is a component of the overall corrosion cell resistivity—the lower the contact resistance, the greater the corrosion current. As the contact resistance increases, the corrosion cell current will decrease. The decrease will be in relation to the sum of the total resistance of the circuit. That is, the resistance of the electrolyte plus the contact resistance.
4) Coating of the Structure
Coating of the structure usually raises the contact resistance of the anode and therefore the cathode since most coatings have a high dielectric (non-conductive)
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A more active metal is anodic to a more metallic element. Metal at an elevated temperature becomes anodic to identical metal at a lower temperature. Generally, as temperature will increase, corrosion increases. However, this relies on the availability of oxygen. Since elevated temperature makes a metal more active, it will become anodic for rest of the metal. So an electrochemical corrosion cell might cause fast corrosion on metals that are at elevated temperatures.
2) pH of the Electrolyte
The ph of the electrolyte in an electrochemical corrosion cell affects the speed of the corrosion by speeding up or slowing down the chemical reactions at the anode and/or the cathode. The ph of an electrolyte is basically the concentration of hydrogen ions. A ph. below 4 can increase the corrosion rate of mild steel. At a ph of 3 the corrosion rate can increase tremendously. Metals having the potential to react to an acid or a base, known as amphoteric metals, in addition show an increase in the corrosion rate in alkali environments. Aluminum and lead are some examples of amphoteric

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