What current does to a metal's potential: flowing across the surface, it drags the potential away from where the metal sits at rest. In cathodic protection, current drives the structure more negative, and the size of that shift, measured with IR drop removed, shows how well protection is working. Polarization builds over hours to weeks as surface films and local chemistry change, and decays slowly once current is interrupted, which is the basis of the 100 mV criterion.
Rectifier's only been on a week, give the polarization time to build before you call those readings low.
Also heard as
- cathodic polarization
- polarization shift
Related terms
100 mV polarization criterion
CP criterion met when a structure is polarized at least 100 mV more negative than its native potential.
Instant-off potential
Structure potential read in the split second after CP current is switched off, free of IR drop.
IR drop
Voltage error in a potential reading caused by current flowing through the soil between pipe and electrode.
Native potential
Potential of a buried or immersed structure before any cathodic protection current is applied.