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CP Survey Analysis Calculator

NACE SP0207 & SP0169 Pipe-to-Soil Potential Analysis

CP Survey Analysis Calculator (NACE SP0207)
Analyze cathodic protection survey data for buried pipelines. Enter pipe-to-soil potential readings from close-interval surveys (CIS), specify soil conditions and coating type, and evaluate protection adequacy against NACE SP0169 criteria. Includes IR drop correction, coating condition assessment, and remediation recommendations.

Pipe-to-Soil Potential Readings

pts

mV Cu/CuSO4 (negative values, e.g., -920, -850, -780)

If provided, used for IR-free potential and IR drop calculation.

Protection Criteria

mV

Typical bare steel: -500 to -600 mV Cu/CuSO4

mV

More negative than -1200 mV risks coating disbondment and hydrogen embrittlement.

Soil & Coating

ohm-cm
years

Pipeline Parameters

in
ft

Understanding CP Surveys

CP Criteria
The -850 mV Cu/CuSO4 criterion (NACE SP0169) is the most common standard for adequate cathodic protection of buried steel. IR-free (instant-off) potentials must meet this threshold.
IR Drop Correction:
ON potentials include voltage drop through soil resistance. Instant-OFF readings (taken within 0.1-1s of current interruption) remove this IR error for accurate assessment.
Assessment Levels: Adequate (≤ -850 mV OFF) | Marginal (-800 to -850 mV) | Inadequate (> -800 mV) | Overprotected (< -1200 mV)

📚 Learn the Theory

Understand cathodic protection principles, survey techniques, IR drop correction methods, and NACE criteria interpretation

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CP Criteria

V_ps ≤ -850 mV (Cu/CuSO4)
V_ps = Pipe-to-soil potential (IR-free)
-850 mV = NACE SP0169 primary criterion
IR Drop = V_on − V_off
100 mV shift = Alternative: V_off − V_native ≥ 100 mV

Standards & References

  • NACE SP0207
    Performing Close-Interval Potential Surveys and DC Surface Potential Gradient Surveys on Buried or Submerged Metallic Pipelines
  • NACE SP0169
    Control of External Corrosion on Underground or Submerged Metallic Piping Systems
  • 49 CFR 192.463
    External corrosion control: Cathodic protection
  • NACE TM0497
    Measurement Techniques Related to Criteria for Cathodic Protection

Engineering Notes

  • IR-Free: Always use instant-OFF potentials for compliance assessment per 49 CFR 192
  • Overprotection: Potentials more negative than -1200 mV can cause coating disbondment and hydrogen damage
  • Soil resistivity: Low resistivity (<2000 ohm-cm) indicates aggressive soil requiring more CP current
  • CIS spacing: NACE SP0207 recommends 2.5-5 ft intervals for adequate resolution

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