Depolarization

Why This Term Matters

Depolarization is central to evaluating polarization-based criteria. If a structure shifts by a sufficient amount after CP current is removed, that shift may support a 100 mV polarization evaluation when the method is valid and permitted.

Depolarization is not just the difference between any two readings. The readings must represent valid test conditions on the same structure or test point.

Core Concept

Loss of polarization

When CP current is applied, the structure becomes polarized in the cathodic direction. When current is removed, that polarization begins to decay.

Time matters

Depolarization happens over time. The selected measurement interval affects the observed potential change.

Current source control

Significant CP current sources must be interrupted or disconnected for depolarization testing to be meaningful.

Use in criteria

Depolarization data may be used to evaluate polarization criteria where allowed by the applicable standard or project requirement.

Common Mistakes

1. Leaving current sources active during a depolarization test.
   Why it is wrong: Remaining CP current can prevent valid depolarization.
2. Comparing readings from different locations.
   Why it is wrong: The shift must represent the same structure condition or test point.
3. Assuming any 100 mV difference is valid polarization.
   Why it is wrong: The difference must be caused by CP and collected under a valid method.

Field Example

A tank-bottom reference cell has an instant-off potential of −780 mV_CSE. After CP current is interrupted and the structure depolarizes, the reading shifts to −660 mV_CSE. The measured depolarization is 120 mV.

That result may support a 100 mV polarization criterion only if the test method is valid and the applicable requirement permits it.

Related Pages

• Polarization
• 100 mV Polarization Criterion
• Polarization Change
• Instant-Off Potential
• 100 mV Polarization Criterion