Reference Electrode

The reference electrode is the 'ruler' for measuring the potential of the protected structure (pipeline, tank, vessel, bridge, etc.) in a cathodic protection system. The most common types are copper/copper sulfate (CSE), silver/silver chloride and high-purity zinc; as the electrode itself is nearly non-polarized in the measuring circuit, the reading reflects the true potential of the protected structure and is the direct basis for judging protection effectiveness (e.g. off-potential ≤ -0.85 V vs CSE in soil).

In typical soil, a buried steel pipeline with an off-potential <= -0.85 V vs CSE is considered to have achieved effective cathodic protection; in seawater, -0.80 V vs Ag/AgCl or +0.25 V vs Zn is commonly used as the criterion.

Copper / Saturated Copper Sulfate

• Electrode potential+0.318 V (vs SHE, 25 °C)
• Common formPortable, long-term buried type (ceramic porous plug)
• Applicable mediumSoil, fresh water, concrete
• Typical useBuried pipeline/tank potential measurement, protection criterion baseline
• Temperature coefficient≈ -0.9 mV/°C
• AdvantagesStable, cheap and durable; long-term buried type needs no maintenance for years
• DisadvantagesNot suitable for long-term seawater immersion; ceramic plug clogs easily, solution must stay saturated

Silver / Silver Chloride

• Electrode potential+0.197 V (saturated KCl, vs SHE, 25 °C)
• Common formSolid-state, seawater type, portable
• Applicable mediumSeawater, salt lakes, concrete
• Typical useShips, offshore platforms, reinforced concrete monitoring
• Temperature coefficient≈ -0.6 mV/°C (small)
• AdvantagesRobust against impact, can be used directly in seawater; small temperature coefficient
• DisadvantagesSensitive to organic/oil contamination; KCl solution or solid structure must be kept intact

Zinc Reference Electrode

• Electrode potential≈ -0.79 V (vs SHE, seawater)
• Common formSolid metal block, built-in polarization probe
• Applicable mediumSeawater, fresh water (as polarization probe)
• Typical useHull, offshore structure embedded monitoring
• Temperature coefficientSmall, varies with medium
• AdvantagesNo electrolyte needed, maintenance-free, robust, suitable for long-term embedding
• DisadvantagesLower accuracy; potential affected by alloy purity and medium

Selection Guide