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Field Measurements 5:3
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
Figure 5.1 Stationary Reference Electrode
Stationary reference electrodes containing both zinc and Ag-AgCl units are
used on offshore structures.
For oil heater-treaters, heat exchanger water boxes, and other vessels,
reference electrodes can be installed through the vessel wall at strategic
locations.
Similarly, embedded reference electrodes are installed in reinforced
concrete structures. Various types of electrodes are used for this purpose.
Typical Applications
Structure–to–Electrolyte Potential
Basis of Measurement
A structure-to-electrolyte potential commonly is referred to as a structure-
to-electrolyte or structure-to-soil potential. The definition of a structure-to-
electrolyte potential is:
“The potential difference between the metallic surface of the structure
and electrolyte that is measured with reference to an electrode in
contact with the electrolyte.”
A structure-to-soil potential is a parallel measurement. The external circuit
of this measurement is high, so a high-input resistance voltmeter is required
for accurate measurement.
Voltmeter Ranges
The most common DC voltage scales on meters and their usage are as
follows:
•
200 millivolts–Current shunt readings
•
2 Volts–Structure-to-electrolyte potentials
•
20 Volts–Structure-to-electrolyte potentials and rectifier voltage
output