Pipeline Cathodic Protection Attenuation (Morgan) Calculator

Determine the electrical attenuation constant (α), pipe-to-soil potential profile along the line, and maximum permissible spacing between CP drain points.

Pipeline Electrical Parameters

Pipeline Outside Dia D (mm): 24-inch pipeline

Steel Wall Thickness t (mm):

Coating Resistance r_c (Ω·m²): Good coating: 10,000 - 100,000 Ω·m²

Steel Resistivity ρ_s (Ω·m):

Drain Point Potential E_0 (V vs CSE): Max overprotection limit: -1.20 V

Min Protection Criterion E_crit (V): NACE SP0169: -0.85 V vs Cu/CuSO4

Attenuation & Drainage Reach

Max Protection Reach L_max:

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Attenuation Constant (α):

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Longitudinal Resistance (R_L):

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Leakage Resistance (R_leak):

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CP Drainage Station Spacing:

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Frequently Asked Questions

What is cathodic protection attenuation in long pipelines?

As cathodic protection current travels down a pipeline, internal electrical resistance of the steel pipe causes an IR voltage drop, steadily degrading the pipe-to-soil potential with distance from the drainage point.

What is the attenuation constant α?

Derived from telecommunication transmission line theory by J.H. Morgan, α = √(RL / Rleak) measures how rapidly potential decays with distance. High pipe steel conductance and high coating resistance minimize α, extending protection reach.

Why is there a maximum limit on drainage point potential (-1.20 V)?

Applying overly negative potentials (> -1.20 V vs Cu/CuSO4) causes excessive cathodic hydrogen evolution, which blisters protective coatings (cathodic disbondment) and causes hydrogen embrittlement cracking in high-strength steels.