Pipeline CP Potential Attenuation

Longitudinal and leakage resistance, the attenuation constant.

Run the calculator

Example

You enter

Pipe outside diameter (in) 12.75
Wall thickness (in) 0.25
Steel resistivity (ohm-in) 0.000007087
Coating resistance (ohm-sq ft) 100000
Drain point potential shift (V) 1
Distance of interest (miles) 10
Degraded coating resistance (ohm-sq ft) 10000

You get

Steel area (sq in) 9.81748
Leakage (ohm/ft) 29958.6
Characteristic resistance at the drain 0.5094 ohms
Shift remaining at the distance 0.407 V at 10 miles -- 41% survives
Where the shift has halved 7.7 miles
With the degraded coating 0.0584727
Degraded half shift (mi) 2.44135
Attenuation rise factor 3.16228

Details, formula, and sources

Longitudinal and leakage resistance, the attenuation constant, and the shift surviving at a distance along a coated line. A tenfold coating degradation raises attenuation only by its square root, yet the reach still collapses by that factor. The far-end test stations show it; the rectifier does not.

R_L = steel resistivity / steel area; R_G = coating resistance / surface per foot; alpha = sqrt(R_L / R_G); R_k = sqrt(R_L x R_G); shift at x = drain shift x e^(-alpha x).

The infinite-line attenuation relations. The pipeline's own close interval survey governs.

Public transmission-line analogue relations.

Estimate. AHJ and licensed professional govern.

Field names used by the API: pipe_od_in, wall_thickness_in, steel_resistivity_ohm_in, coating_resistance_ohm_sqft, drain_shift_v, distance_mi, degraded_coating_resistance_ohm_sqft, steel_area_sqin, leakage_ohm_ft, characteristic_resistance_ohm, shift_at_distance_v, half_shift_mi, degraded_shift_at_distance_v, degraded_half_shift_mi, attenuation_rise_factor

Line infinite and uniformly coated; a finite line or a holiday changes itspec-v1765 scope
Steel resistivity entered; about 7.1 x 10^-6 ohm-in for line pipematerials data