Principle of Cathodic Protection in Self-Bunded Tanks

Cathodic protection (CP) is an electrochemical technique used to prevent corrosion in self-bunded tanks, particularly those made of steel. Since these tanks store hazardous liquids (fuels, chemicals, etc.), corrosion resistance is critical for structural integrity and environmental safety.

How Cathodic Protection Works

1. Electrochemical Basis

   • Corrosion occurs when metal (e.g., steel) oxidizes in the presence of an electrolyte (e.g., soil, water).

   • CP forces the tank to become the cathode in an electrochemical cell, halting oxidation.

2. Two Main CP Methods

   • Galvanic (Sacrificial Anode) System

     • Uses more reactive metals (magnesium, zinc, or aluminum anodes) connected to the tank.

     • These anodes corrode instead of the tank, "sacrificing" themselves over time.

     • Ideal for smaller tanks or low-conductivity environments.

   • Impressed Current System

     • Uses rectifiers to apply a direct current (DC) to the tank, making it cathodic.

     • Inert anodes (e.g., titanium-coated) are buried nearby to complete the circuit.

     • Used for large tanks or high-corrosion-risk areas (e.g., coastal zones).

3. Key Components

   • Reference Electrodes – Monitor protection levels (typically -0.85V vs. Cu/CuSO₄).

   • Insulating Flanges – Prevent stray current interference.

   • Test Stations – Allow periodic voltage/current measurements.

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