What Reference Electrodes are Mostly Used in Cathodic Protection System?

What Reference Electrodes are Mostly Used in Cathodic Protection System?

Reference electrodes are used to measure the polarization potential of cathodic protected structures. They shall be kept in contact with the same electrolyte (soil or water) surrounding the structures, and the voltage that rises between the structure and the lead cable of the electrode, measured with a high-impedance voltmeter, gives an indication of the effectiveness of Cathodic Protection.
Depending on the electrolyte where the reference electrode will be used, and the particular operational condition, different chemistry are available including Cu/CuSO4 (for soil and freshwater), Ag/AgCl (seawater), Zinc (Seawater) reference electrode.

Copper-Copper Sulfate Reference Electrode (Cu/CuSo4)
Copper sulfate reference electrodes (CSE) are the most commonly used reference electrode for measuring potentials of underground structures and also for those exposed to freshwater. CSE is not suitable for use in off-shore environments or in a chloride electrolyte as the chloride ions migrate through the porous plug and contaminate the CSE.
The portable type CSE is composed of a copper rod, saturated solution of copper sulfate, and a non-conducting cylinder with a porous plug at the bottom as shown in the above picture.
AFIC can supply a wide range of CSE that is intended to use in soil applications and are made for portable use or for permanent installations i.e., suitable to use along the pipeline route or under the above-grade storage tanks, etc.

Silver chloride electrode
Silver-silver chloride (Ag-AgCl) reference electrodes are most commonly used for testing cathodic protection corrosion control systems in seawater environments. The Ag-AgCl electrode is also used in concrete structures. There are two types of Ag-AgCl reference electrodes; in one type the silver electrode is exposed to seawater and in the other, the electrode is immersed in a potassium chloride (KCl) solution contained in a cylinder with a porous plug.

Zinc Reference Electrode
Zinc is commonly used for onshore and offshore corrosion potential measurement. Zinc reference electrodes are not stable in carbonates or at high temperatures. For underground use, the zinc electrode is packaged in a cotton bag containing the same backfill as used around zinc anodes. In off-shore zinc electrodes used bare.