A metal sample of known area, usually matching the pipe steel, buried near the structure and connected to it through a test station so it receives CP the way a holiday would. Disconnecting the coupon gives an IR-free instant-off potential without switching every current source, and coupon current shows how much protection a bare spot gets. A paired native coupon, left unconnected, gives the free-corrosion baseline.
Rectifiers on this corridor can't be interrupted, so read the CP coupon off at each station instead.
Also heard as
- cathodic protection coupon
- probe coupon
Do not mix it up with
- Corrosion coupon: A CP coupon is wired to the pipe to measure protection potential; a weight-loss coupon is weighed after exposure to measure corrosion rate.
Related terms
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.
Test station
Above-ground post or box with wires bonded to a buried structure, used to take CP readings.
Corrosion coupon
Weighed metal strip exposed inside a system for a set time, then reweighed to calculate corrosion rate.