How can you evaluate CP effectiveness on buried or submerged structures?

• A. Visual inspection only
• B. Thermal imaging
• C. Potential surveys with a reference electrode and monitoring CP current output and coating condition against standards
• D. X-ray scanning

Answer: (C)

Measuring how well a cathodic protection (CP) system is working on buried or submerged structures requires a real, in-situ assessment of protective conditions. The best way to do this is to combine three pieces of information: the structure’s electrical potential relative to a reference electrode, the actual current being supplied by the CP system, and the coating’s condition compared to accepted standards.

First, perform potential surveys using a reference electrode placed in contact with the soil or water near the structure. This tells you whether the structure is polarized to a protective level—what potential it is sitting at relative to the reference. If the potential is sufficiently negative, the metal is considered protected against corrosion in that environment. Second, monitor the CP current output from the rectifier and anodes. Adequate current is needed to maintain that protective potential, especially as environmental conditions change or as coatings age or are damaged. Third, evaluate the coating condition and the presence of any holidays or disbondment, and compare these findings to standard criteria. Damaged coating can create pathways that bypass CP or alter current distribution, so understanding coating integrity is essential to interpreting potential and current data.

Together, these elements provide a practical, comprehensive picture of CP effectiveness for buried or submerged structures. Visual inspection alone isn’t feasible for these cases, thermal imaging has limited ability to confirm protection along the entire structure, and X-ray scanning isn’t practical for large underground or underwater assets.