AC Mitigation for Pipelines and CP Systems
AC mitigation reduces hazardous or damaging AC effects while preserving the intended DC behavior of the cathodic protection system.
Mitigation Goals
AC mitigation may be designed for personnel safety, coating protection during faults, AC corrosion control, equipment protection, or a combination of those objectives. The design goal must be defined before selecting hardware.
Common Mitigation Elements
| Element | Purpose |
|---|---|
| Gradient control mat | Reduces touch-and-step voltage around aboveground appurtenances. |
| Gradient control wire or zinc ribbon | Provides distributed grounding along affected pipeline sections. |
| Decoupling device | Passes AC or fault current while blocking or limiting DC current so CP is not shorted. |
| Surge protection | Protects insulating joints, equipment, and CP components from lightning or fault transients. |
| Grounding cell or sacrificial grounding | Provides AC grounding and may also participate in corrosion-control strategy depending on configuration. |
Design Cautions
- Grounding that reduces AC voltage can also drain CP current if not decoupled correctly.
- Mitigation equipment must be rated for steady-state, fault, and lightning conditions.
- AC voltage reduction alone does not automatically prove AC corrosion risk has been eliminated.
- Isolation devices may need surge protection where AC or lightning exposure exists.
- Post-installation testing is needed to confirm both AC mitigation and CP performance.