When joining dissimilar metals in pipelines, proper electrical insulation must be ensured to prevent galvanic corrosion

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When connecting dissimilar metals in pipelines, it is essential to ensure proper electrical insulation to prevent galvanic corrosion. Example: A pipeline system in a certain factory required the use of low-carbon steel pipes in combination with copper pipes. To prevent galvanic corrosion during design, a ceramic joint was added between the carbon steel pipe and the copper pipe. However, during installation, the pipes are fixed to the wall made of metal plates using metal brackets. A few years later, the steel pipes suffered extensive leaks due to galvanic corrosion. Analysis: In the electrochemical corrosion cell formed by the coupling of carbon steel and copper in this case, the carbon steel acts as the anode, while the copper tube serves as the cathode. However, for the two metal components to form a corrosion cell in an electrolyte solution, they must also have electrical contact, that is, a closed circuit through which electric current can flow. In the metal part, the electrons generated by the anodic metal oxidation reaction can flow smoothly through the cathodic metal to be consumed in the reduction reaction of the depolarizer. In the solution phase, ions can migrate smoothly. Therefore, for galvanic corrosion, an effective protection method is to insert an insulating material between the two metals to separate them and break the electrical circuit. Measure: Insert insulating materials such as plastic or rubber gaskets, sleeves, etc., between the dissimilar metal components. When it is not possible to use insulating gaskets or sleeves, an insulating coating (or putty) can be applied to the joint surfaces of dissimilar metal components in order to increase the resistance of the electrical circuit, thereby reducing the intensity of the galvanic corrosion current.