Page 210 - Pipeline Rules of Thumb Handbook
P. 210
Corrosion/Coatings 197
Figure 2. Drainage current vs. distance for a coated finite line.
point, and how far will this current protect an infinitely long 500 micromhos/sqft. What is DE A /E T and what DI A is
pipeline? required? Assume that
DE A = 1.5 E T = 0.3
DE X = 0.3 From Figure 2 read
DE x = 50 E T = 58
.
.
DE A DE A
Refer to Figure 1 and read DE A = 1.74
.
.
L = 30,000ft DI A D ¥ 03 E T = 18 amp in.
.
.
.
D ¥ 03 DE x = 07 ( from Figure 1 ) DI A = 1.8 ¥ 3.5 = 6.3amp.
DI A
DI A = 0.7 ¥ 30 = 21amp. Estimate ground bed resistance for a rectifier
installation.
21amps will protect the line for 30,000ft in either direction
from the drain point. Example. A ground bed for a rectifier is to be installed
Estimate rectifier size for a finite line. Refer to Figure 2. in 1,000ohm-cm soil. Seven 3-in. ¥ 60-in. vertical graphite
A 31/2-in. OD line 20,000ft long is protected by insulat- anodes with backfill and a spacing of 10ft will be used. What
ing flanges at both ends and has a coating conductivity of is the resistance of the ground bed?
