20031015Application.pdf

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Avista Utilities~ast Mission P.O. Box 3727
Spokane, Washington 99220-3727
Telephone [phone]
Toll Free 800-727-9170
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IDAHO PUBLIC
IPUC Commission Secretary UTILITIES COMMISSION
472 W. Washington
O. Box 83720
Boise, ill 83720-0074
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Utilities
Washington Water Power DivisionOctober 10, 2003
Re: Waiver for above ground plastic pipe in steel casing
DOT ~ 192.321 (a)11 Vit... (;-03-(/
Dear IPUC:
A vista Corporation is requesting a waiver for an above ground 6-inch PE pipe in steel casing.
The pipe is scheduled to be installed in the November 2003 timeframe across the South Fork
Palouse River on the US Highway 95 Bridge in Moscow, Latah County, Idaho. The design of
the pipe and casing system is as follows:
The MAOP of this gas line is 60 PSIG.
The lO-inch steel casing will terminate below ground level on both sides of the bridge.
The casing will be suspended from a new 67-foot length concrete bridge (Idaho
Transportation Department Project No. BR-41l0(147)).
A boot-type end seal will be used at both ends of the casing to positively seal between the
casing and gas carrier pipe.
Casing vent pipes will be installed to prevent the possible buildup of pressure and to detect
leakage of gasses.
Casing insulators (thinsulators) will be installed and spaced at a minimum of 5 feet to provide
positive separation between the casing and carrier pipe.
Casing pipe is housed under the open-girder bridge and consequently will be shielded from
the effects of direct sunlight.
The computed design pressure for PE pipe (SDR 11.5) at 120 degrees F is 61 PSIG; the
highest recorded temperature for the area is 109 degrees F. Gas pressure within the pipe on
the bridge will therefore not exceed system MAOP due to ambient temperature.
The maximum thermal contraction of the PE pipe is calculated to be 13.0 inches. Since the
ends of the pipe are "fixed" by the burying of the facility at the ends of the bridge, this
contraction will be exhibited as internal stresses. The internal stress is calculated to be 737
psi which is less than the 1000 psi HDB rating of the PE pipe.
If you have any questions, please contact my Project Engineer, Randy K. Bareither at (509) 495-
8716.
CC:Ron Law, Executive Administrator, IPUC
A division of Avista Corp-