Moser A.P., Folkman S. Buried Pipe Design
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Figure 6.51 Underground heat distribution test facility schematic.
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370 Chapter Six
Groundwater conditions: Class B—bad. The water table is expected
to be occasionally above the bottom of the system, and surface water
is expected to accumulate and remain for short periods (or not at all)
in the soil surrounding the system, or the water table is expected
never to be above the bottom of the system, but surface water is
expected to accumulate and remain for long periods in the soil sur-
rounding the system.
Soil corrosiveness: corrosive—all the soil resistivities.
Soil pH: Soil pH down to 4.5 for the hot pipe and 2.0 for the conden-
sate pipe. Both systems can be used in soil up to pH 12.
Figure 6.52 Cross-sectional view of the soil loading test cell.
Figure 6.53 Test layout for water damage, water infiltration, and joint leakage tests. This
schematic shows the test pipe layout including placement of the following: (1) couplings, (2) field
repair joint, (3) concrete anchor on elbow, (4) anchor of pipe protrusion to the test cell, (5) the fit-
ting where dyed water was inserted under pressure for the water damage test, (6) manhole ter-
minals (link seals), and (7) thermocouples for temperature measurement and control.
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Figure 6.54 Schematic of pressure controls.
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Steel and Ductile Iron Flexible Pipe Products 373
Figure 6.55 Test facility under construction. Foreground: soil load cell; center to rear:
water infiltration test cell.
Figure 6.56 Soil load cell used in structural damage test with test pipe in place and
return line connected. Note the hydraulic pump in the background and the hydraulic
controls.
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Soil stability: Both systems can be used in all soils where thrust
blocks are required, by direct bearing against undisturbed or satis-
factorily tamped soil; where friction block can be used; where unsta-
ble soil can be replaced by ballast of sufficient size and weight to
resist thrust; or where tie rods or piling can be used.
Operating temperature: Continuous operating temperatures of 200
to 450°F for hot pipe and 100 to 250°F condensate return piping.
Test procedures for the hot pipe. The purpose of the tests specified in
this section is to demonstrate that the hot pipe system meets the cri-
teria specified by the Federal Agency Pre-Qualification Procedures for
Underground Heat Distribution Systems. The following tests will be
performed:
1. Resistance to groundwater infiltration
a. Apparatus: Test box or tank 3 ft wide and 4 ft deep with a cover
that can be bolted in place to make the tank pressure tight up to
10 lb/in
2
gage. The foundation is capable of supporting 600/lb ft
2
.
The tank has a drain fill plug at its lowest point and a vent at its
highest point. Manhole terminals are centrally located on the
two end plates. This tank, its appurtences, and all other appara-
tus needed are shown in Figs. 6.51 to 6.54.
Figure 6.57 Soil load cell showing the insulation used on return piping.
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Two electric water heaters, 500 W each, a watthour meter, and a
circulation pump.
A 200 lb/in
2
gage water pressure pump and a 500 lb/in
2
gage
water pump.
A 0 to 500F thermometer input temperature recorder.
A temperature controller capable of handling the electric
heater load and controlling a temperature of 450F 3 percent.
Figure 6.58 System control center with the following fea-
tures: (1) temperature controller, (2) temperature fail-safe
circuits, (3) pressure controls, (4) pressure fail-safe circuits,
(5) dual control timer (concealed in photo), (6) flowmeter
readout, (7) power meter with digitized output for data sys-
tem, (8) associated warning lights for system operation.
Safety controls were necessary because the system was
operated at 500 lb/in
2
and 450°F. An electronically operated
pressure relief valve was controlled by the fail-safe circuits.
In addition, a manual pressure relief valve was incorpo-
rated into the system.
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A surge tank (1-gal capacity). The static pressure capacity must
be at least 500 lb/in
2
gage equipped with suitable pressure gage.
Thermocouples shall be mounted as shown on the drawing.
b. Procedure: A 4-in system consisting of 500 ft of test pipe with at
least three 13-ft sections, one 90 ell, one anchor at the ell, and
one short section with a field joint installed in the tank in a gravel
soil. (The field joint used in this test is the same joint that will be
used on the casing of a 20-ft length of pipe). Each joint is misaligned
with its mate by 1.5,with at least two of the misalignments in the
horizontal plane. The installation shall be made in strict accord
with installation guides except for these misalignments.
Figure 6.59 Looking down on the heating section located
between the two test cells. Note the following: (1) Tops of
two 5000-W immersion-type heaters (center right of photo).
A third heater is concealed from view. (2) Motor that runs
the circulation pump (center left of photo). (3) Insulation
applied to external piping to conserve energy.
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Figure 6.60 High-temperature pipe installed in the test cell. Note the following: (1) joints
misaligned by 1.5°, (2) thermocouple wire running along pipe, (3) fitting and hose for
water damage test.
Figure 6.61 Elbow with steel anchor plate before concrete thrust block was cast in corner.
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Figure 6.62 Test cell filled with soil.
Figure 6.63 Adjusting water pressure in cell to simulate a 20-ft head of groundwater
(9 lb/in
2
). Note the link seal around the pipe where it penetrates the tank.