Field term for a casing, the larger steel sleeve around a carrier pipe at road and rail crossings, that has lost its isolation from the carrier through failed spacers, crushed end seals or debris. The casing then soaks up CP current meant for the pipeline and shields the carrier inside, so potentials near the crossing read low. Techs spot it when casing and pipe potentials match, and confirm it with current and resistance tests.
Casing and pipe both read -910 at the highway, it's a shorted casing, schedule a clear or a fill.
Also heard as
- casing short
- metallic short
Related terms
Low
CP tech shorthand for a potential that is not negative enough to meet the protection criterion.
Test station
Above-ground post or box with wires bonded to a buried structure, used to take CP readings.
Insulating joint
Fitting that electrically isolates one pipe section from another so CP current stays where it belongs.
Pipe-to-soil potential
Voltage between a buried pipe and a reference electrode on the soil surface, the basic CP measurement.