PART C - PIPELINE CONSTRUCTION
The aluminum pipe used in the IPDS is highly
susceptible to heat. Changes in temperature cause the pipe to expand and
to contract. This tendency requires pipeline installation to follow
certain rules exactly. The pipeline must be installed as straight and
level as possible. Any desired turns or changes in direction must be
made using elbows, vertical as well as horizontal directions. Anchors
are used to direct expansion and contraction of the pipeline into
expansion and contraction devices. Aluminum pipe is subject to thermal
expansion that can overstress couplings and cause breaks in the pipeline.
Since the pipeline will be installed above ground, the pipe will move as
it expands and contracts with temperature variation. In some geographical
locations where the pipeline may be used, the temperature can vary by as
much as 100 degrees Fahrenheit in 24 hours, which can cause an expansion
of up to 20 inches for 50 sections of pipe. Expansion can cause the
pipeline to fail at a coupling if side pressure deflects the joint more
than 4 degrees. This expansion must be controlled and directed to spots
specifically designed to move with pipeline expansion and contraction.
Controlling expansion and contraction.
To control this expected
expansion/contraction movement, the pipeline must be equipped with
anchors and expansion devices. The anchor fixes the pipeline to the
ground and directs any expansion towards the expansion device. The flex
in the couplings at the elbows allow these devices to move without
breaking the integrity of the pipeline. In a desert environment, where
the temperature change can be anywhere from 50 to 100 degrees Fahrenheit,
there must be a maximum of 50 sections of pipe between
expansion/contraction devices, with an anchor in between. In a more
temperate environment with an expected temperature change of less than 50
degrees Fahrenheit, the distance between expansion/contraction devices
can be extended up to 100 sections of pipe. There still must be an anchor
between devices. The pipeline must be laid in an anchor - expansion
device - anchor sequence with the anchor just outside of each pump
station starting the sequence. Expansion loops on hills should be no more
than 15 sections of pipe hanging downhill from an anchor.
There are two types of expansion devices used with the IPDS. The "U"
shaped loop and the "Z" shaped offset. Both devices provide required
pipeline flexibility and are considered equal from that standpoint. The
"Z" shaped offset should be used if sufficient cleared trace (width 30
ft.) is available. If the trace is not available, the "U" shaped loop
should be installed. A cleared area of about 30 ft. by 30 ft. is required
for each "U" loop.
"U" shaped loop, will normally be constructed with one pipeline length
(19 ft.) on a side and may use 45 or 90 degree elbows or a combination
thereof. As elbows are limited, 90 degree elbows should be used
whenever possible. The deflection at the loop can be as much as 20
inches from the cold to the hot position.
"Z" shaped offset will normally be offset one 19-foot pipe length. To
allow for proper expansion, the "Z" should be constructed only with 45
degree elbows unless two 19-foot lengths of pipe are used in the