S

standard hydrogen electrode
A reference electrode consisting of an electro-positive metal, such as platinum, in an electrolyte containing hydrogen ions at unit activity and saturated gas at 1 atm.

sensing electrode
A permanently- installed reference electrode used to measure the structure / electrolyte potential and to provide a reference signal to control the protection current of an automatic impressed current system.

saponification
The chemical process of forming a soap; more particularly a deterioration by softening of paint films caused by the action of aqueous alkali on fatty-acid constituents of the film.

stray current
Current flowing in the soil or water environment of a structure and arising mainly from cathodic protection, electric power or traction installations, and which can pass from the environment into the structure and vice versa.

NOTE: Stray alternating current is not considered in depth in this standard (see 3.8.5).

Structures:

protected structure
A structure to which cathodic protection is applied.

unprotected structure
A structure to which cathodic protection is not applied.

primary structure
A buried or immersed structure cathodically protected by a system that may constitute a source of corrosion interaction with another (secondary) structure.

secondary structure
A buried or immersed structure that may be subject to corrosion interaction arising from the cathodic protection of another (the primary) structure.

structure/electrolyte potential
The difference in potential between a structure and a specified reference electrode in contact with the electrolyte at a point sufficiently close to (but without actually touching) the structure to avoid error due to the voltage drop associated with any current flowing in the electrolyte.

NOTE: Similar terms such as metal/ electrolyte potential, pipe/electrolyte potential, pipe/soil (water) potentials etc., as applicable in the particular context are also used.

sulphate-reducing bacteria
A group of bacteria found in most soils and natural waters, but active only in conditions of near neutrality and freedom from oxygen, which reduce sulphates in their environment with the production of sulphides.