AC Interference Assessment
Purpose
Characterize AC exposure and collect the evidence needed for the applicable personnel-safety, AC-corrosion, fault/lightning, or mitigation-verification question without treating one quantity as a substitute for another.
1. Define the assessment objective
State whether the task is steady-state personnel safety, AC-corrosion risk, fault/lightning evaluation, initial exposure survey, detailed coupon/probe assessment, or post-mitigation verification.
2. Establish prerequisites and boundaries
Identify the structure, nearby AC power system/corridor, accessible points, existing CP/isolation/decoupling/grounding systems, known coating defects or coupons/probes, and the applicable controlling authority. Electrical-safety work beyond this bounded corrosion-reference method requires the applicable qualified safety procedure.
3. Record AC exposure
Measure and document AC voltage at defined locations with exact location, date, and time. Where obtainable, correlate readings with power-system loading. Do not interpret voltage alone as the corrosion result.
4. Collect corrosion-assessment quantities where applicable
Collect the authorized coupon/probe evidence needed to determine AC current density and DC current density, together with CP condition and local resistance/resistivity context. State coupon/probe area and representativeness limits.
5. Preserve quantity identity
Report AC voltage in volts rms where applicable; AC current in A or mA; AC current density in A/m² or controlled converted units; DC current density separately; soil resistivity in Ω·m or controlled conversion; and potential measurements with reference-electrode identity and measurement state.
6. Use representative time evidence
When the criterion or risk question is time-dependent, use representative-period or datalogged evidence sufficient to capture the relevant variation under the controlling method. Do not substitute one spot reading.
7. Apply criteria by purpose
Apply personnel-safety thresholds only to personnel-safety questions. Apply SP21424 corrosion-rate/current-density criteria only within their scope and measurement basis.
For §6.2, preserve the two branches exactly: JAC ≤ 30 A/m² when JDC > 1 A/m²; JAC ≤ 100 A/m² when JDC < 1 A/m². At exactly JDC = 1 A/m², the supplied wording assigns neither branch; do not invent an equality rule.
8. Verify mitigation
After mitigation, repeat the measurements tied to the original objective. Verify the intended AC exposure/current-density effect as applicable and confirm that DC CP/isolation behavior remains acceptable.
9. Document limitations
Record missing load data, coupon representativeness limitations, unavailable time history, uncertain defect area, uncontrolled conditions, or any other limitation that prevents a complete conclusion.