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impressed current
The current supplied by a rectifier or other direct-current source (specifically excluding a sacrificial anode) to a protected structure in order to attain the necessary protection potential.

instantaneous-off potential
The structure/electrolyte potential measured immediately after the synchronous interruption of all sources of applied cathodic protection current.

Joints:

isolating joint
A joint or coupling between two lengths of pipe, inserted in order to provide electrical discontinuity between them.

insulated flange
A flange joint between adjacent lengths of pipe in which the nuts and bolts are electrically insulated from one or both of the flanges and the jointing gasket is non-conducting, so that there is an electrical discontinuity in the pipeline at that point.

interaction test
A test to determine the severity of corrosion interaction between two buried or immersed structures.

ion
An atom, or group of atoms, carrying a positive or negative electrical charge.