Answer:
The primary method to verify a cathodic protection (CP) system is providing adequate corrosion protection is measuring the DC pipe-to-earth or DC structure-to-electrolyte potential with respect to a stable reference electrode such as a Cu:CuSO4, Zinc, or Ag:AgCl (for sea water applications). This is a measurement that requires training and experience specifically in CP to perform properly because it is unlike most measurements taken by facility personnel. Key differences are:
1. The potential is DC not AC like power electricity.
2. The magnitude is less than a volt; not 115 VAC and higher like power electricity.
3. The current that provides the corrosion protection flows through the soil or water and not the insulated cables of regular electrical power or signals.
4. The volt meter common is connected to an electrochemical half cell in contact with the electrolyte, not the electrical ground.
5. The voltage on the meter will include error due to current in the electrolyte that CP experts are trained to measure and account for in the analysis.
NACE International (www.nace.org) provides a directory of people trained, qualified and certified to test CP system.
To ensure the CP system is operating, it is easy to measure and record the current flow on the cable connection between the structure and anode. This is fairly easy to measure an can be performed by facility maintenance personnel.
Mawhinney - Corrpro