TM 5-811-7
(7) Insulating joints must be provided on both steam and condensate lines at the first flange connection
inside all buildings.
(8) All conduit must be metal-bonded together in each manhole.
(9) All conduit will be precoated at the factory and will not have been holiday-checked.
(10) Single-phase electrical power is available at 120/240 volts a.c. from the administration building.
b. Computations.
(1) Find the conduit's total outside area. Because the gage of the metal from which the conduit is made
ranges between 14 and 16, the pipe's outside diameter is considered the same as the inside diameter.
(a) Steam conduit area must be calculated (table D-1).
Table D-1. Dimensions for finding steam conduit area: heat distribution system
Conduit area
Conduit
Conduit size
Conduit length
(sq ft/
area
(in.)
(ft)
(lin ft)
(sq ft)
14
1700
3.67
6239
12
1125
3.14
3533
10
1525
2.62
3996
Total area of steam conduit
13,768
U.S. Air Force
(b) Condensate return conduit area must be calculated (table D-2).
Table D-2. Dimensions for finding condensate return conduit area: heat distribution system
Conduit area
Conduit
Conduit size
Conduit length
(sq ft/
area
(in.)
(ft)
(lin ft)
(sq ft)
8
1700
2.09
3553
6
2650
1.57
4161
Total area of condensate return conduit
7713
Total outside area of all conduit
21481
U.S. Air Force.
(2) Find the area of bare pipe to be cathodically protected based on 80 percent coating efficiency:
A=21,481 x 0.2
A = 4296 sq ft.
(3) Find the maximum protective current required based on 4 milliamperes per square foot of bare
metal:
I = 4296 x 4
I = 17,184 mA or 17.2 A.
(4) Compute the maximum weight of anode material needed for 15 years' life.
(a) Graphite anodes are used.
(b) Average deterioration rate for graphite is 2.0 pounds per ampere-year.
D-5
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