Cathodic protection (CP) is a corrosion-control method that forces a structure (like a pipeline or tank) to behave as a cathode of an electrochemical cell so it does not dissolve as an anode.
What CP is doing (conceptually)
- Corrosion is an electrochemical process that requires anodic metal dissolution.
- CP supplies electrons to the structure and shifts its potential in the negative direction.
- This reduces or stops the anodic dissolution rate on the protected surface.
Two main methods
1) Galvanic (sacrificial anode) CP
- Attach a more active metal (e.g., Zn, Mg, Al) that becomes the anode and corrodes instead.
- Simple, self-powered, limited driving voltage.
2) Impressed current CP (ICCP)
- Use a DC power source (rectifier) and inert anodes to drive protective current.
- Higher output capability; requires monitoring and power.
How to think about “protection”
CP is not “making corrosion impossible.” It is controlling the electrochemical conditions so the structure is no longer the place where metal dissolution occurs.