AC Interference Troubleshooting
Use observations to choose the next check
This diagnostic does not convert a symptom into an automatic diagnosis. Use the observation to identify a plausible mechanism or risk layer, then collect the evidence needed to confirm it.
Unexpectedly high AC pipe-to-earth voltage
Possible interpretation: significant AC exposure is present.
Check next: source, coupling mode, power-system loading, geometry, time variation, and localized current-density evidence.
Do not conclude: voltage alone does not quantify AC-corrosion risk or establish personnel safety.
High AC current density with acceptable DC CP potential
Possible interpretation: conventional DC CP compliance does not eliminate AC-corrosion risk.
Check next: coupon/area representativeness, DC current density, CP condition, local resistance/resistivity context, and time weighting.
AC voltage tracks transmission-line loading
Possible interpretation: the correlation is strong evidence consistent with inductive coupling.
Limit: other coupling modes or conditions may coexist.
Mitigation lowers voltage but current-density criterion remains exceeded
Possible interpretation: voltage reduction has not demonstrated corrosion control.
Check next: local resistance/current paths, CP condition, coupon setup, and the quantities the mitigation was intended to control.
Mitigation device changes CP behavior
Possible interpretation: the device or ground path is interacting with DC CP/isolation.
Check next: electrical function, isolation behavior, CP condition, and post-mitigation verification. Do not label the device failed from this observation alone.
Corrosion variables appear acceptable but touch voltage is unsafe
Next action: the personnel/electrical-safety layer controls. A corrosion result is not personnel-safety clearance. Apply the applicable SP0177/electrical-safety process.
Low AC voltage but significant localized AC current density
Possible interpretation: localized current density can remain important under low local resistance conditions.
Check next: localized current evidence, area basis, resistance/resistivity context, and representative time behavior. Do not infer corrosion control from voltage alone.
Could this be normal CP attenuation?
If the observation is primarily a spatial decay/distribution pattern without external AC source evidence, use Current Distribution & Attenuation. Normal CP attenuation is not AC interference.