Impressed Current Cathodic Protection (ICCP)

Impressed Current Cathodic Protection (ICCP): A brief overview Corrosion is a costly and pervasive problem for metal structures exposed to water, soil, or concrete. Impressed Current Cathodic Protection (ICCP) is a preventive technique that uses an external power source to deliver a protective electrical current, turning the metal surface into a cathode and greatly reducing or stopping corrosion. How ICCP works - In ICCP, the protected structure (for example, a pipeline, offshore platform, or a steel tank) is connected to the negative side of a direct current power supply. - Anodes are placed in the surrounding electrolyte (soil, seawater, or concrete pores) and connected to the positive side of the supply. - The external power source forces current from the anodes through the electrolyte toward the structure. This makes the structure more cathodic (negative) relative to the environment, suppressing anodic metal loss and effectively reducing corrosion. - To ensure the correct level of protection, the structure’s potential is monitored against an independent reference electrode data point, and the current is adjusted accordingly. Key components of an ICCP system - Power source (rectifier): Converts AC to controlled DC current and voltage to drive the system. - Anodes: Selected for longevity and compatibility with the environment. Common types include MMO-coated titanium, graphite, and mixed-metal-oxide or proprietary coatings. - Protected structure: The metal or concrete reinforcement that is intended to stay cathodic and protected. - Reference electrodes: Portable or fixed reference sensors (such as Cu/CuSO4 or Ag/AgCl) used to measure the structure’s potential and verify adequate protection. - Monitoring and control: Instrumentation for potential surveys, current output, and data logging. Regular surveys ensure the structure remains in the protective range. Where ICCP is typically used - Offshore and onshore pipelines and risers. - Marine structures: piers, jetties, seawater intakes, and hulls. - Storage tanks and process equipment in contact with corrosive environments. - Reinforced concrete elements where embedded steel reinforcement benefits from cathodic protection. Protective criteria and design considerations - The goal is to maintain the protected structure at a potential that suppresses active corrosion. This is often expressed as a target potential relative to a reference electrode (for example, a copper/copper sulfate reference). Typical targets are in the range of about -0.85 V to -1.0 V (relative to Cu/CuSO4) depending on the environment (soil vs. seawater) and material. - Design factors include electrolyte conductivity, coating condition on the structure, temperature, the geometry of the protected asset, anode type and spacing, and the required monitoring plan. - Overprotection can cause hydrogen embrittlement in some steels or coating disbondment; underprotection leaves the metal susceptible to corrosion. Careful control and regular monitoring are essential. Advantages and limitations - Advantages: Effective for large or complex structures, works in environments where sacrificial anodes would be insufficient, provides uniform protection across irregular geometries, and allows real-time monitoring and adjustment. - Limitations: Requires a reliable power source and ongoing maintenance; initial setup can be costly; salts or stray currents can complicate protection; anode lifespan and replacement are ongoing considerations. Maintenance and monitoring - Regular potential surveys to verify protective levels. - Monitoring rectifier performance, anode current, and any drift in readings. - Inspecting wiring, connections, grounding, and reference electrodes. - Periodic inspection of anodes for consumption and replacement as needed. A practical summary ICCP is a robust and scalable corrosion protection method ideal for large or difficult-to-coat metal structures in aggressive environments. By applying an external DC current, it keeps the structure at a protected potential, reducing corrosion rates and extending service life. Successful ICCP requires careful design, proper installation, and ongoing monitoring to ensure the protective criteria are met and maintained over time.