Pipeline CP Potential Attenuation
Longitudinal and leakage resistance, the attenuation constant.
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
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeLongitudinal 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.
Formula or tableR_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).
Source and editionThe infinite-line attenuation relations. The pipeline's own close interval survey governs.
Free accessPublic transmission-line analogue relations.
What governsEstimate. AHJ and licensed professional govern.
API field namespipe_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