Protection · Pipelines
Cathodic Protection
An electrical system that makes the buried pipe the cathode of a circuit so the steel does not corrode where the coating has gaps.
What it does
An impressed current system or galvanic anodes push current onto the pipe and work together with the coating. Crews check it with pipe to soil potential readings. In the US, 49 CFR 192 Appendix D lists at least minus 850 mV against a copper copper sulfate reference, with IR drop considered, or a 100 mV polarization shift; in Canada the requirements come from CSA Z662.
Basics
| Types | Impressed current or galvanic anodes |
| US criterion (49 CFR 192 App. D) | At least minus 850 mV vs Cu/CuSO4, IR drop considered |
| Alternative | 100 mV polarization shift |
| Canada | CSA Z662 |
Common failures
- Rectifier off or anode bed depleted, so the pipe loses protection without anyone noticing
Troubleshooting
- Symptom
- Pipe to soil readings less negative than the criterion
- Likely cause
- Rectifier off, coating damage or stray current
- What to check
- Check rectifier output, then survey the segment to find the coating holiday