Polarization & Potential Shift — Before vs After CP (Diagram #003)
A before/after visual showing native vs polarized pipe-to-soil potentials (vs CSE) and how cathodic polarization reduces anodic metal loss.
What this visual explains
This diagram shows polarization as a shift in measured pipe-to-soil potential when CP is applied. The “before” condition represents native/free-corrosion potential, and the “after” condition represents a polarized surface (more cathodic behavior).
Diagram
How to read it
- Native potential: free-corrosion condition (no applied CP current).
- Polarized potential: surface condition after CP drives cathodic reactions.
- Reference electrode: measurement is always “structure vs reference,” not an absolute voltage.
- Shift direction: CP drives the potential more negative (typical convention for steel vs CSE).
Field interpretation
- Polarization is what reduces anodic metal loss on the protected structure.
- Interpretation depends on measurement quality (electrode placement, contact, stability).
- ON readings can be influenced by IR drop; OFF readings better approximate polarized potential.
Common mistakes
- Treating any more-negative ON reading as “proof of polarization” without considering IR drop.
- Mixing reference electrodes (CSE vs Ag/AgCl vs SCE) without converting reference values.
- Forgetting sign conventions when describing “more positive/more negative” in the field.
CP 3 relevance
CP 3 problems frequently combine polarization with measurement effects (IR drop, placement error, interference). This visual establishes what “polarization” means before the ON/OFF and interference visuals.