DC Stray Current
Current through paths other than the intended circuit, including transit systems, welding, HVDC systems, and interference from nearby CP systems.
Cathodic Protection Interference
Interference is one of the main reasons CP data can change unexpectedly. It can create corrosion risk, false readings, safety hazards, and current-distribution problems that are not obvious from ordinary test-station checks.
Types of Interference
AC Interference
AC influence caused by capacitive, inductive, or conductive coupling with nearby AC power systems.
Telluric Current
Geomagnetically induced current that can create time-varying potential and current changes on long pipelines.
AC Mitigation
Grounding, decoupling, gradient control, isolation protection, and other methods used to reduce AC voltage and risk.
Interference Testing
Technical practice guide covering stray current, foreign structures, bonds, and interference interpretation.
Why Interference Matters
Interference can make a structure appear protected at one moment and unprotected at another. It can also produce current discharge at localized areas, create unsafe touch potentials, damage isolation devices, or mask the true CP condition.
The practical rule is simple: when readings fluctuate, reverse, or disagree with system behavior, do not force the data into a normal CP interpretation. First determine whether another current source is influencing the structure.
Signs That Interference May Be Present
- Rapidly fluctuating structure-to-electrolyte potentials.
- Potential swings that correlate with transit operation, welding activity, rectifier cycling, or geomagnetic activity.
- Current flow reversal through bonds or test stations.
- Localized corrosion at crossings, near foreign structures, or near current-discharge areas.
- AC voltage at aboveground appurtenances or test leads.
- Different readings depending on time of day, season, load, or power-line condition.