During previous instruction you were given an understanding of the flow of
fluids in pipelines. We discussed equations that can be used to determine
how fast the fluids flow and what effects the flow has on pressure. The
purpose of this instruction is to teach you how to obtain information from
other methods that are much easier. Although the information obtained may
not be as accurate, it is suitable for Army pipelines.
PART A - FRICTION LOSS
Friction Loss Graph
: The friction loss graph is an expedient method
obtaining friction loss per mile of pipe in military pipelines. Although the
results are not exact, it is close enough and is a much faster way than
using the Darcy Weisbach equation. The basic graph (Figure 2-1) contains
the following information. Barrels per hour top horizontal line. Gallons
per minute bottom horizontal line. Friction loss per mile of pipe left
vertical line. The other lines on the graph represent pipe diameter in
inches and velocity of the fuel in feet per second. The graph has been
8 x 10 minus 6 ft per sec and absolute roughness of 0.00015. For this
reason you must use a correction factor for fuels other than MOGAS and at
temperatures other than 60, F.
Using Figure 2-1, given a flow rate of 700 gallons per minute and a pipe
diameter of 8.415 inches: enter the graph at the lower right hand corner
and move to the left to 700 gallons per minute. Move up the graph until you
locate the pipe diameter (8.415). Read to the left and read 33 feet. This
means that for every mile of pipe you will lose 33 feet of head. If the
pipeline was 10 miles long you would lose 330 feet of head.
PART B CORRECTION FACTOR
Correction Factor. To determine the friction head loss for fuels other than
MOGAS at 60, F, it becomes necessary to correct the value obtained from
Figure 2-1. Table 2-1 contains correction factors for all military fuels at
temperatures ranging from -20 F to 80, F.
At temperatures other than these, interpolation must be used. These
factors can be used for any flow rate and for API pipe or light weight steel
tubing having the same nominal diameter as that shown in the tables.
If we use the same flow rate and the same pipe diameter (700 GPM and
8.415), we know that our head loss is 33 feet per mile. If we were pumping
DF2 at a temperature of 80, F, we must use the correction factor.
Using Table 2-1, locate DF2 at 80, F and read the correction factor 1.17.
Multiply 33 feet by 1.17 which equals 38.61 feet or 39 feet. You now have
the friction loss per mile of pipe for DF2 flowing at 700 GPM through an
8.415 diameter pipeline.
Once computed, the head loss due to friction for one mile of pipe has a
special name; hydraulic gradient (hg). Since hg is a constant ratio of two
linear dimensions: head loss in feet over pipe distance in miles; it can be
expressed graphically as the slope of a straight line.