USACERL TR 97/10

foam varied considerably depending upon the system’s pipe diameter and soil
conductivity.

From these results it can be seen that the calcium silicate thickness needs to be
increased in order to lower the maximum temperature experienced by the polyure-
thane insulation to a value well within its specified operating limits. Because the
manufacturer did not specify a temperature limit for this insulation (TPS Inc. 1989),
this study uses a conservative value of 200 °F as the maximum long-term
continuous-use temperature for polyurethane insulation. Additional calculations
are included for when it is assumed that the limiting temperature is 250 °F.

Error Analysis

For this estimation it was assumed that some effects were negligible and could be
ignored without seriously affecting the results. The first assumption was that the
carrier pipe inner wall convective heat-transfer coefficient is negligible. The thermal
conductivity of steel is 300 Btu in/hr ft’ 2 °F and the inner wall convective coeffi-
cient is approximately 1400 Btwhr ft’ 2 °F (Research Associates 1991). As a result
the net effect of including this aspect would be a minor temperature decrease—not
more than approximately 2 °F for all cases examined.

Another factor not considered is the contact resistance associated with the material
interfaces. Without more detailed information characterizing the interfaces that
include polyurethane foam insulation, reliably accounting for this factor would be
difficult. If a contact resistance factor were included, the result would be to impede
heat transfer and raise the temperature profile.

A final source of potential error involves the assumption that the heat transfer
through soil may be modelled as a hollow cylinder of diameters of 2 ft and 6 ft, with
a constant outside temperature of 60 °F. Given that soil temperature often exceeds
this value, the assumption leads to a slight overestimation of the heat loss, lowering
the temperature profile.


39

*(g = Ayanonpuos j1os) 4. oge 12 edid “ul g “p'g eunBig

[u!] snipey
ve 6L vl 69 v9 6s vs ey vy ee
09
p—t
—*
Hebb + ObL
og)

2
a
[y.) eamyesedwe,

“yg oinqesedwiey---- ~~ 09%
“yg eunjesedwe, ———
ole
= 4p. ose
los Buseo aUeYOINA|Og Is 1D adi

USACERL TR 97/10



USACERL TR 97/10

Appendix B: Temperature Distribution
Profiles for Different Carrier Pipe
Diameters, Soil Conductivities, and
Temperatures



USACERL TR 97/10

“(OL = AAnonpuos

S) 4. OSE Ie adid ‘ul 9 “G*g aunBiy

do Gv) 14
TMT QO} = Auanonpuog jos lun empey
$9 09 ss os cp oF se ve
~ 09
ol
09}
olz
09%
“Uz sunyesedwa | ———
“yg oinjesodwia| - - - - - - ole
Ho0SE
= te 098
OS eueyjoinh|odg us 18D adiq

[y.] eanyesoduoy,



USACERL TR 97/10

11

¢ the temperature of the inner wall of the carrier pipe was assumed to be equal
to the temperature of the carrier fluid
¢ the temperature of the outer radius of the soil was assumed to be 60 °F.

Calculations were performed for representative system configurations for each of the
six different carrier pipe diameters. The burial depth, carrier fluid temperature, and
soil conductivity were varied to represent the range of conditions that the piping
would typically experience while in service. One should note that the thermal con-
ductivity for calcium silicate varies with temperature. Because the temperature of
the calcium silicate varies significantly between its inner and outer radii, the value
of the thermal conductivity of calcium silicate was chosen at a temperature conser-
vatively below each of the carrier fluid temperatures. The thermal conductivity
value for 300 °F was used for the case of 350 °F fluid temperature, while the value
for 350 °F was used for the 450 °F fluid temperature. The configuration for the
representative system, based on the manufacturer’s system design brochure, was as
follows:

Scope

Carrier fluid temperature

Burial depth

Soil thermal conductivity

Pipe thermal conductivity

Calcium silicate thermal conductivity
Calcium silicate thermal conductivity
Polyurethane thermal conductivity
Casing thermal conductivity

Soil surface temperature

350 & 450 °F

2 & 6 feet

5, 10, & 15 BTU in/hr ft*2 °F

300 BTU in/hr ft*2 °F

0.44 BTU in/hr ft*2 °F for 350 °F fluid
0.46 BTU in/hr ft*2 °F for 450 °F fluid
0.1415 BTU in/hr ft*2 °F

1.3 BTU in/hr ft*2 °F

60 °F :

This report documents a theoretical analysis of piping configurations and operating
conditions. The reader may find it useful to compare these findings with a field
study underway at the U.S. Army Cold Regions Engineering Laboratory (USA-
CRREL), Hanover, NH. (Results of the USACRREL field study are expected by the
end of Fiscal Year 1996.)

This analysis applies only to the piping, and does not address the temperature
profile within the expansion joints. This study was not intended to consider all
possible extremes of conditions that a complete design analysis would typically
include. A more detailed treatment of the soil and surface effects is beyond the scope
of this study.


USACERL TR 97/10

72
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279
10/96


USACERL TR 97/10

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Fed =
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09€

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USACERL TR 97/10

“(gi = Ayanonpuos Hos) 4, ose 12 edid ‘ul OL “ZL°@ eunBig

to Gv 4Y
TIM Sj = Auanonpuo:

se

[ut] snipey
os gL oz

so

09

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lug einyeiodwiej- - - - - «
luz ounpesodue

|p

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52



USACERL TR 97/10

*(g = Ayanonpuod |10s) 4, OSp 38 adid ‘ul OL “ez"q eunBiy

to @v 44 2
UM G = Aunnonpuog jog [ui] smipey
6 06 se 08 62 oz s9 v9 ss vs
09
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evel oot

2g 2
8 =
a a
[4.] eampesodwiay

2
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“yg eumesoduiey- - =~ - -
“yz eameseduie ose
oly
~= >< a sr
10S Buiseg aueyjainsjodg

. adid

58



USACERL TR 97/10

“(OL = Awanonpuod j1os) 4, ost ye adid ‘ul 9 “Zz"g aunBig

do Bu 44
TM OI = Auanonpuog jlo [ul] snipey
s9 o9 ss os sy ov se oe
09
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09t

eg 2
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[4.] eanyesodwie,

°
5

Wz eimeseduie | 09e
“yg eumesodwia) ------
Oly
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~ > — at 097
los Buse aueYJesNA|Od ls eo adig

62



USACERL TR 97/10

“($1 = Awanonpuoo jos) 4. OSE 12 edid ‘ul 9 “Sig eunBi4

to Gv) UY
OM GS} = Auanonpuod j10g [ui] snipey
s9 09 ss os sv ov se of
— + 09
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408 | “SS

“} ont
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8
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Ac0SE
~—= — p> ~<a pg — pe 098
!0S aueyjasnA|Od Ils 120 edid

50



USACERL TR 97/10

21

Table 8. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 5 BTU in/hr ft*2 °F and carrier temperature = 450 °F.

Current Thickness of

Required Thickness of

Nom. Pipe Dia. | Burial Depth Calcium Silicate Calcium Silicate Percent Difference

[in.] [ft] fin.] [in]

2 1.00 1.72 72%

$ 6 1.00 1.81 81%

2 1.00 1.76 76%

‘ \ 6 1.00 1.86 - 86%

| 2 1.50 I 2.16 44%

6 | 6 1.50 | 2.30 53%

2 1.75 | 2.86 63%

° 6 1.75 3.03 73%

2 2.50 _ 2.86 14%

_ 6 2.50 3.06 22%

2 : 2.50 2.89 15%

” 6 2.50 3.11 24%

Table 9. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 10 BTU in/hr ft*2 °F and carrier temperature = 450 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
fin] [ft] [in.] [in]
2 1.00 1.66 66%
3 = |.
6 1.00 1.70 70%
2 1.00 1.69 69%
4 —
6 1.00 1.74 74%
2 1.50 | 2.08 39%
6 |
6 1.50 i 2.15 43%
7
2 1.75 | 2.78 59%
8 , _
6 1.75 | 2.86 63%
2 2.50 2.78 11%
10 7 OO
6 2.50 2.87 15%
2 2.50 | 2.80 12%
12 T
6 250 | 2.91 16%



USACERL TR 97/10

40

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€ We adid ‘ul QL “s'q eunBi4

fo G14
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s6 06 s8

[ul] snipey
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71

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gol

$6

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06 se oe SL oz s9 o9

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SUBUOINA|Og

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USACERL TR 97/10



REPORT DOCUMENTATION PAGE Gua Ne c7oe-o188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,
gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this
collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson
Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave Blank) | 2. REPORT DATE 3, REPORT TYPE AND DATES COVERED
October 1996 Final

4, TITLE AND SUBTITLE 5. FUNDING NUMBERS
Thermal Evaluation of Piping Components Used in a Commercial Underground Heat JNS
Distribution System

6. AUTHOR(S)
Charles P. Marsh and Matthew W. Streibich

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
U.S. Army Construction Engineering Research Laboratories (USACERL) REPORT NUMBER
P.O. Box 9005 TR 97/10
Champaign, IL 61826-9005

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING / MONITORING
Headquarters, U.S. Army Corps of Engineers AGENCY REPORT NUMBER:
ATTN: CEMP-ET
20 Massachusetts Ave. NW
Washington, DC 20314-1000

11. SUPPLEMENTARY NOTES
Copies are available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.

12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited.

13. ABSTRACT (Maximum 200 words)
Super Temp-Tite heat distribution piping is the only product of its design type approved by the Federal Agency Committee
for Underground Heat Distribution Systems. This system employs a water-spread-limiting (WSL) design to restrict any
leakage to a single segment of piping. WSL systems are intended to withstand continuous carrier medium temperatures of
up to 450 °F. On the basis of approval by the Federal Agency Committee for use at Class B, C, and D sites, the Super
Temp-Tite WSL design is currently approved for the same applications by the Army Corps of Engineers. Recently the
system manufacturer asked the Federal Agency Committee to approve use of its system at Class A sites—those with the
harshest conditions. The U.S. Army Construction Engineering Research Laboratories (USACERL) was tasked to conduct
mathematical modeling and simulations to help determine whether Super Temp-Tite meets the technical specifications for
Class A applications.

It is concluded that the polyurethane foam insulation in this WSL design would be exposed to temperatures well exceeding
conservative design values, both in Class A applications and for operating temperatures below 350 °F. Consequently, the
system as now designed is not recommended for approval by the Federal Agency Committee.

14, SUBJECT TERMS, 15. NUMBER OF PAGES.
underground heat distribution systems 74
evaluation 16. PRICE CODE
simulation models

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION. 19. SECURITY CLASSIFICATION 20. LIMITATION OF

OF REPORT OF THIS PAGE OF ABSTRACT ABSTRACT
Unclassified Unclassified Unclassified SAR
NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANS! Std 239-18
298-102


32

USACERL TR 97/10

(5). Lock Block-The lock block which holds the bronze
coupling in the casing consists of a composite of pearlite
mixed with high temperature epoxy. The only description of
this material is shown on page 11, para. 2.5 which indi-
cates a "k" factor of 1.0 at 300 °F. Casing Temperatures
at the coupling should be computed based on this "k"
factor. Recent field inspections have shown very severe
corrosion of the bronze coupling at its interface with the
epoxy material. A chemical analysis of the epoxy together
with an indication of its stability at temperatures up to
450 °F. should be provided in order to establish compati-
bility with the bronze coupling.

(6). Silicon Lubricant—It is apparent from thee italicized
warning contained on page 41, that the type of lubricant is
of some significance in the construction and possibly the
operation of the system. Physical and chemical character-
istics of the material should therefore be provided.

b. Condensate Line Conduits. The two condensate line

conduits "Sch 80 Heat-Tite" and "RTRP Vee-Tite" are similar
in design and construction except for the heat carrying
piping. As indicated in their nomenclature, schedule 80
steel pipe is provided for "Sch 80 Heat-Tite" conduit and
reinforced plastic pipe is used in the "RTRP Vee-Tite"
system. Conduits are provided in 20 foot sections and
utilize polyurethane insulation with a PVC jacket. These
materials are in accord with Corps of Engineers guide
specifications CEGS -02698 "Prefabricated Underground
Heating/Cooling Distribution System" and are therefore
considered satisfactory for this application.

(1). Coupling Dimensions—Dimensions for ductile iron and
RTRP couplings are not provided as was done for Super Temp-
Tite on page 24.

(2). Carrier Sealing Ring—On page 13, sealing rings are
specified to be molded, heat resistant EPDM. On page 47,
these rings are designated as "Heat-Tite R.T." and "HTHR"
in paragraphs 8.5.1 and 8.5.2. Clarification is required.

(3). Steel Pipe Spigot Ends-For Super Temp-Tite, spigot
ends are required to be metallized with nickel alloy then
machined back to the required 0.D. with a maximum rms of 32


18 USACERL TR 97/10

3 Calcium Silicate Thickness Requirements

Analysis

To calculate the minimum thickness of the calcium silicate required to limit the
maximum temperature of the polyurethane to either 250 °F or 200 °F, the same
system of equations for each case in Chapter 2 was used, but the thickness of the
calcium silicate and polyurethane foam were also variables. The calculations were
executed in such a way as to keep the diameter of the conduit constant. Therefore,
as the thickness of the calcium silicate increased, the thickness of the polyurethane
foam decreased by the same amount. Consequently, another constraint had to be
applied to solve for the minimum thickness: the temperature at the calcium silicate/
polyurethane foam interface, r, must equal either 250 °F or 200 °F.

Tete) = 250°F (Eq 7)

T(t.) = 200°F [Eq 8]

From this system of equations, the minimum thickness of the calcium silicate was
calculated numerically.

Results

Tables 5-10 show the results of the thickness calculations for the 250 °F case
compared to present system design. It can be seen that calcium silicate thickness
needs to be increased for the smaller pipe diameters with a 350 °F carrier fluid
temperature (independent of soil conductivity). The two largest diameters have an
adequate thickness of calcium silicate for this case. For carrier fluid temperatures
of 450 °F, the thickness of the calcium silicate needs to be increased, independent
of soil conductivity, by a minimum of 10 percent to a maximum of over 80 percent.

Tables 11-16 show the results of the thickness calculations for the 200 °F case
compared to the present system design. It can be seen that the thickness of the


24

USACERL TR 97/10

Table 14. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 5 BTU in/hr ft42 °F and carrier temperature = 450 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
[in.] [ft] [in] in]

2 1.00 1.98 98%
5 6 1.00 2.08 108%

2 1.00 2.01 |
‘ 6 1.00 2.12 1 12%
2 1.50 2.45 63%
5 6 1.50 2.61 74%
2 1.75 3.24 85%
5 6 1.75 3.44 96%
2 2.50 3.23 29%

| ° 6 2.50 _ 3.46 38% _|
2 2.50 3.24 30%
” 6 2.50 3.50 40%

Table 15. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 10 BTU in/hr ft*2 °F and carrier temperature = 450 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
[in.] [ft] [in.] [in.]

2 1.00 1.90 90%
3

6 1.00 1.95 95%

2 1.00 1.93 93%
4 -

6 1.00 1.98 98%

2 1.50 2.36 57%
6

6 1.50 2.44 63%

2 1.75 3.14 79%
8

6 1.75 3.24 85%

2 2.50 3.13 25%
10 ~

6 2.50 3.24 30%

2 2.50 3.15 26%
12

6 2.50 3.27 31%



20 USACERL TR 97/10

Table 6. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 10 BTU in/hr ft*2 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate | Percent Difference
[in] [ft] [in.] [in.]
2 1.00 i 1.24 24%
3
1.00 | 1.27 27%
2 1.00 1.28 28%
4 _ —_|
6 1.00 1.31 31%
2 1.50 1.59 6%
6 -
6 1.50 1.63 9% _
2 1.75 2.11 20%
8 i]
6 1,75 | 2.17 24%
2 2.50 2.13 -15%
10
6 2.50 i 2.21 -12%
2 | 2.50 2.16 -14%
12
6 2.50 2.25 -10%

Table 7. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 15 BTU in/hr ft*2 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of | Percent Difference
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate
[in.] [ft] fin] [in]

2 1.00 1.22 22%
3

6 1.00 1.24 24%

2 1.00 1.26 26%
4 ¢

6 1.00 1.28 28%

2 1.50 | 1.57 4%
6 _|

6 1.50 1.60 6%

2 1.75 2.09 19%
8

6 1.75 2.13 22%

2 2.50 2.11 -16%
10 -

6 2.50 2.16 -14%

2 2.50 2.14 -15%
12 i ~

6 2.50 2.20 -12%



USACERL TR 97/10

(page 12). For the steel condensate pipe, the spigot ends
are sand blasted to white metal and zinc coated (para.
4.1.1, page 14). The method of application of the zinc
should be described and an indication that the finish is
adequate to provide a tight seal is required.

(4). Silicone Caulking—End of para. 9.8, page 52 permits
the use of silicon caulking in lieu of EPDM end seal.
Method of application, physical, and aging characteristics
for this material should be provided.

General Recommendations

a. Testing Requirements. An in-depth field inspection
survey of TPS systems is currently being done by the Cold
Regions Research and Engineering Laboratory. The results
of that survey should verify or dispel concerns regarding
the suitability of the materials furnished such as, conduit
end seals, pipe sealing rings, conduit casing, polyurethane
foam, and epoxy. Any new aging tests proposed by the
manufacturer should be reviewed in detail by the government
to insure that procedures and resulting data will be
acceptable. Actual testing should not be done by the
material manufacturer but should be performed by an
approved independent testing laboratory. All test data
should be directly available to the government for review
and analysis.

b. Maintenance and Repair. The repair sections for
the TPS conduits are very difficult to follow and are
somewhat confusing. Foe example, the dimensions shown on
the diagram on page 64 appear to be for 10 foot pipe
sections rather than for the standard 20 foot lengths.
Also, repairs include the use of epoxy adhesive and
compression couplings for which no descriptive details are
provided. Recommend that this entire section be rewritten
and augmented with clarifying sketches at each step of the
repair procedure.



USACERL TR 97/10

15

The general solution of Eq 1 for each n-region (Incropera 1990), assuming constant
thermal conductivity within those regions, is

T,(N = C, in) +C, [Eq 2]

In the system under study, there were five different material regions (see Figure 2).
In order to specify the situation completely it is necessary to determine the values
of ten constants. To do this, at least ten boundary conditions must be considered.
The boundary conditions used here assume that (1) temperatures are equal at the
inner and outer radii of all surfaces, (2) carrier medium and soil temperatures over
the entire system are constant, discounting insignificant localized gradients, (3)
there is no contact resistance at the various material interfaces, and (4) heat energy
is neither created or destroyed during steady-state flow. These boundary conditions
are expressed as follows:

T,(r,) = 350 or 450°F [Eq 3]

TM) = Tres Fad n=14 [Eq 4]

n=1-4 [Eq 5]

T(t.) = 60°F [Eq 6]

Results

From the stated equations and boundary conditions, the general temperature
profiles for the piping system were found. A spreadsheet was used to calculate and
plot the temperature profiles for the different carrier pipe diameters, soil conductivi-
ties, burial depths, and carrier pipe fluid temperatures (see Appendix B).



USACERL TR 97/10

“(OL = AAnonpuod 10S) 4, OSp 38 edid “ul ¢ “Gz'q eunBi4

to vy AY
UME OQ} = Aanonpuog jig

sy

ov ge

ful] snipey
oe

se

x4

gt

“yg esmesedwe |
“We eunresedwie |

a <_+t

dol SE

Fousl

Hos

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Ws 1eD

adid

OlL

ogt

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a

092

[4.] eunyesodwias

ole

O9€

Oly

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60



USACERL TR 97/10

Tables
1 Thickness of insulation and casing for Super Temp-Tite design ........ 14

2 Maximum temperature experienced by polyurethane insulation for
350 °F and 450 °F carrier medium temperatures (k,oi = 5 BTU in/hr

3 Maximum temperature experienced by polyurethane insulation for
350 °F and 450 °F carrier medium temperatures (k,,, = 10 BTU in/hr

4 Maximum temperature experienced by polyurethane insulation for
350 °F and 450 °F carrier medium temperatures (k,,, = 15 BTU in/hr
[Ca op CC) 16

5 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 5 BTU in/hr ft*2 °F and carrier
temperature = 350 °F 0... 2. cece ee eee eee eee e eens 19

6 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 10 BTU in/hr ft*2 °F and
carrier temperature = 350 °F «1.2... eee eee eee eee eee eens 20

7 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 15 BTU in/hr ft*2 °F and
carrier temperature = 350 °F «6.6.1 eee eee eee eee eee eens 20

8 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 5 BTU in/hr ft*2 °F and carrier
temperature = 450 °F 6.2... cee eee e eet 21

9 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 10 BTU in/hr ft*2 °F and
carrier temperature = 450 °F ow... eee eee eee tee eee eee 21

10 Change in calcium silicate thickness to achieve 250 °F at polyure-
thane interface with soil conductivity = 15 BTU in/hr ft*2 °F and
carrier temperature = 450 °F oo... 1 cece eee eee eens 22

1 Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 5 BTU in/hr ft*2 °F and carrier
temperature = 350 °F 1... . eee cee ee ce eee reenter nees 22


30

USACERL TR 97/10

which they would be subjected under normal system opera-
tion. Also, aging tests were of very short duration and,
even though significant degradation was evident, no attempt
was made to extrapolate the data to estimate anticipated
useful life. The brochure inadequacies primarily concern
the materials, design, and construction of the conduit
system and are independent of external site conditions.

Specific Comments

a. Super Temp-Tite Conduit. (for steam and hot water
up to 450 °F.). The conduit consists of 20 foot sections

composed of steel heat carrying pipe, a layer of calcium
silicate insulation, a layer of polyurethane foam, and a
fiberglass casing. The casing ends contain an annulus
sealing ring extending from the pipe to the casing and made
of ethylene propylene diene monomer (EPDM). The sections
are joined with a bronze coupling into which the steel
carrier pipes are free to slide with the aid of a silicone
lubricant. Sealing each pipe in the coupling are two O-
rings. One O-ring is of a high temperature rubber compound
(HTRC) having a circular cross-section while the other
consists of a Teflon® encased stainless steel spring with
a "C" cross section. Binding the bronze coupling to the
casing is a lock block composed of pearlite mixed with high
temperature epoxy.

(1). Polyurethane Insulation—There are two specifications
for polyurethane foam; one described in a letter from Cook
dated 28 September, 1979 and the other contained in para.
2.4.1 on page 10 under "Hardware". It is not known which
is being provided at this time. In neither case is there
a temperature limitation indicated. Some preliminary
computations using the insulation thicknesses shown on page
28 indicate that in many instances temperatures well above
300 degree F may be reached at the interface of the calcium
silicate and polyurethane. At these temperatures the
polyurethane will be destroyed resulting in loss of
efficiency and exposing the casing to possible damage. The
manufacturer should include in the brochure the upper
limitation of the polyurethane being used and steady state
calculations showing that this limitation will not be
exceeded under varying pipe temperature and soil conductiv-
ity conditions.


67

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do @vis 44
TIT Gy} = Alanonpuog jos [ul] snipe
os sy ov se of sz 0z
09
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09€
“yz asmjesoduse | AolSE
Oly
o0SP
~at wept >! pe (097
0S Buiseg eueyjeins|od lls 2D adid

USACERL TR 97/10



69

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Pn
TIME Sy} = Ayanonpuog los [ul] snipey
ve 6L ve 69 v9 6s vs ey vy 6
09
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4
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“yz aunyesode | ——— ow
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~t <-> tt i a oor
Buiseg aueyyeins|od ls 12O edi

USACERL TR 97/10



USACERL TR 97/10

“($1 = Auanonpuos j10s) 4, OS 18 edid ul oO} “seg eunBi4
1

do Sv} 4

UM S|}. = Ayanonpuog jlo [uy] snipey,

sé

gL OL g9 o9 gs

os

fg oumesoduiaj---- ~~
luz eumesodue |

pet a

los

Buiseg, aueYjaInA|Odg leo

4.0Sb

adig

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8
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70



¢ no estimation of temperature profile around the coupling joints where a 1-2 in.
air space is present

¢ lack of detail on various manufacturing and installation procedures

* confusing or incomplete description of maintenance and repair procedures.

Recommendations

Based on the results of this analysis, it is recommended that the Super Temp-Tite
heat distribution system, as currently designed and specified for carrier tempera-
tures up to 450 °F, not be approved for use at Class A sites. It is further recom-
mended that the Federal Agency Committee reevaluate its previous approval for

USACERL TR 97/10 27
using the system at Class B, C, and D sites.



USACERL TR 97/10

Contents

Units of Weight and Measure ......... cece cece eee ee eee eee eee enee
Equation Symbols and Variables

2 Temperature Distribution .......... 0... cece cece eee ee tenet eee eee 13
Piping Specifications .. 2.0.0... e ccc ccc tet e ete eee eens 13
Analysis .-

Results . .
Error Analysis... . 00. ccc e eee cece ete eee tenet e eet e ete n ene eens 17

3 Calcium Silicate Thickness Requirements ............... 0. ccc eee eee ee nee 18
Analysis .

Results ..
Error Analysis 2.0.2... cece ccc cece ce eee een eee e nee 19

4 Conclusions and Recommendations ................ 06sec cece eee eens 26
CONCIUSIONS .. 6... ce ete tent e eee tenet e eee 26
Recommendations ........ 606s cece cece eee ence eee n nent een ene 27

References ....... 2... cece cnet n teen teen e tenet ee ee nes 28

Appendix A: Independent Engineering Evaluation of TPS Inc. Heat Distribution System
Design Brochure ........ 0... cece cece cece ete eet nee e eee eee 29

Appendix B: Temperature Distribution Profiles for Different Carrier Pipe Diameters, Soil
Conductivities, and Temperatures .......... 0... e cece eee eee 35

Distribution


2 USACERL TR 97/10

Foreword

This study was conducted for Headquarters, U.S. Army Corps of Engineers under
Reimbursable Work Unit JN5, “Investigation of Fiber-Reinforced Plastic Condensate
Return Carrier Piping.” The technical monitor was Dale Otterness, CEMP-ET.

The work was performed by the Materials Science and Technology Division (FL-M)
of the Facilities Technology Laboratory (FL), U.S. Army Construction Engineering
Research Laboratories (USACERL). A portion of this work was performed under
contract to USACERL by NMD & Associates, 2001 Paul Springs Parkway,
Alexandria, VA 22308. Dr. Iker R. Adiguzel is Acting Chief, CECER-FL-M, and
Donald F. Fournier is Acting Operations Chief, CECER-FL. The USACERL
technical editor was Gordon L. Cohen, Technical Information Team.

COL James T. Scott is Commander of USACERL, and Dr. Michael J. O’Connor is
Director.


16

USACERL TR 97/10

Using the insulation thickness values in Table 1, it was found that the temperatures
at the calcium silicate/polyurethane foam interface were about 265 °F to 350 °F for
carrier fluid temperatures of 350 °F and 450 °F, respectively. These temperatures
are in excess of the long-term, continuous-use temperature for polyurethane foam
insulation. As shown in Tables 2-4, the maximum temperature of the polyurethane

Table 2. Maximum temperature experienced by polyurethane insulation for 350 °F and 450 °F
carrier medium temperatures (k,,, = 5 BTU in/hr ft* 2 °F).

Carrier Pipe Diameter T,(supply) = 350 °F T,(supply) = 450 °F
3 281 360 |
4 285 366
6 268 344
8 267 342
10 240 306
12 243 310

Table 3. Maximum temperature experienced by polyurethane insulation for 350 °F and 450 °F
carrier medium temperatures (k,,, = 10 BTU in/hr ft* 2 °F).

Carrier Pipe Diameter

T,(supply) = 350 °F

T,(supply) = 450 °F

3 276 354
4 280 359
6 261 334
8 261 334
10 229 291
12 232 295

Table 4. Maximum temperature experienced by polyurethane insulation for 350 °F and 450 °F
carrier medium temperatures (k,,, = 15 BTU in/hr ft* 2 °F).

Carrier Pipe Diameter

T,(supply) = 350 °F

T,(supply) = 450 °F

3 274 351
|

4 278 357

6 258 331

8 258 331

10 225 286

12 227 289



USACERL TR 97/10

B.17

B.18

B.19

B.20

B.21

B.22

B.23

B.24

B.25

B.26

B.27

B.28

B.29

B.30

B.31

B.32

B.33

B.34

B.35

B.36

10 in. pipe at 350 °F (soil conductivity =15) ................ eee eee 52
12 in. pipe at 350 °F (soil conductivity =15) ................. eee eee 53

3 in. pipe at 450 °F (soil conductivity = 5)

4 in. pipe at 450 °F (soil conductivity =5) .......... 0. cee eee eee eee 55
6 in. pipe at 450 °F (soil conductivity =5) .......... eee e eee ee eee ee 56
8 in. pipe at 450 °F (soil conductivity =5) ............. eee eee eee 57
10 in. pipe at 450 °F (soil conductivity =5) ..................0 2 eee 58
12 in. pipe at 450 °F (soil conductivity =5) ......... 0. cece eee eee 59
3 in. pipe at 450 °F (soil conductivity =10) ............... eee eee ee 60
4 in. pipe at 450 °F (soil conductivity =10) ........ ccc e eee eee eee 61
6 in. pipe at 450 °F (soil conductivity =10) ................ ee eee eee 62
8 in. pipe at 450 °F (soil conductivity = 10) ............ eee e eee eee 63
10 in. pipe at 450 °F (soil conductivity = 10) .................0.0088 64
12 in. pipe at 450 °F (soil conductivity =10) ............ cc cece eee ee 65
3 in. pipe at 450 °F (soil conductivity = 15) ............... cece eee 66
4 in. pipe at 450 °F (soil conductivity =15) ......... ccc eee 67
6 in. pipe at 450 °F (soil conductivity = 15) ........ 0. cece eee ee eee 68
8 in. pipe at 450 °F (soil conductivity = 15) ............. eee eee eee 69
10 in. pipe at 450 °F (soil conductivity = 15) ........... ee eee eee eee 70

12 in. pipe at 450 °F (soil conductivity = 15) .................. eee 71



22 USACERL TR 97/10

Table 10. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 15 BTU in/hr ft*2 °F and carrier temperature = 450 °F.

| | Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth | Calcium Silicate Calcium Silicate Percent Difference
fin] { [ft] [in.] fin}
2 1.00 1.64 64%
3
6 1.00 | 1.66 66%
2 1.00 1.67 67%
4 -
6 1.00 1.70 70%
2 1.50 2.06 37%
6 - -
| 6 1.50 2.10 40%
2 1.75 2.75 57%
8 t
6 1.75 2.80 60%
2 2.50 2.75 | 10%
10 ~ ~
6 2.50 | 2.81 12%
2 2.50 2.77 1%
12 - ~
6 2.50 2.84 I 14%

Table 11. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 5 BTU in/hr ft*2 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate | Calcium Silicate Percent Difference
[in.] [ft] [in.] | [in.] |

2 1.00 1.71 71%
3 -

6 1.00 1.79 79%

2 1.00 1.75 75%
4 = - me

6 1.00 1.85 85%

2 1.50 2.15 43%
6

| 6 1.50 2.28 52%

2 1.75 2.84 62%
8 -

6 1.75 3.01 72%

2 2.50 2.84 | 13%
10

6 2.50 3.04 21%

2 2.50 2.86 14%
12

6 2.50 3.09 23%



US Army Corps

of Engineers

Construction Engineering
Research Laboratories

USACERL Technical Report 97/10

October 1996

Thermal Evaluation of Piping Components
Used in a Commercial
Underground Heat Distribution System

by
Charles P. Marsh and Matthew W. Streibich

Super Temp-Tite heat distribution piping is the only
product of its design type approved by the Federal
Agency Committee for Underground Heat
Distribution Systems. This system employs a
water-spread-limiting (WSL) design to restrict any
leakage to a single segment of piping. WSL systems
are intended to withstand continuous carrier medium
temperatures of up to 450 °F. On the basis of
approval by the Federal Agency Committee for use
at Class B, C, and D sites, the Super Temp-Tite WSL
design is currently approved for the same
applications by the Army Corps of Engineers.
Recently the system manufacturer asked the Federal
Agency Committee to approve use of its system at
Class A sites—those with the harshest conditions.
The U.S. Army Construction Engineering Research
Laboratories (USACERL) was tasked to conduct
mathematical modeling and simulations to help
determine whether Super Temp-Tite meets the
technical specifications for Class A applications.

It is concluded that the polyurethane foam insulation
in this WSL design would be exposed to
temperatures well exceeding conservative design
values, both in Class A applications and for operating
temperatures below 350 °F. Consequently, the
system as now designed is not recommended for
approval by the Federal Agency Committee.

Approved for public release; distribution is unlimited.

Carrier Fluid
Carrier Pipe

Calcium Silicate}

s9gei2a0 082



USACERL TR 97/10

46

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do Sv 14

gs os

=

TMA O} = Alagonpuog os ful] snipey
$6 gL oz s9 09
na
hug aunqesedua |» - = = =~
yz eammeredwe |
~« lg _plne =
los Buisep aueyjesnhiog 1s leo

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OF

O9b

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a

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a

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[y.] eamesedwie,



USACERL TR 97/10

1

Introduction

Background

Super Temp-Tite heat distribution piping’ is the only product of its design type
approved by the Federal Agency Committee for Underground Heat Distribution
Systems. This commercial piping system employs a water-spread-limiting (WSL)
design that is intended to restrict any leakage to a single segment of piping
(Phetteplace and Carbee 1992).

The Super Temp-Tite system comprises a steel carrier pipe encased in a layer of
calcium silicate insulation; the calcium silicate is sheathed with a layer of poly-
urethane foam insulation, and the entire system is clad with a reinforced thermoset-
ting resin plastic casing (as shown in the cross-sectional view in Chapter 2,
Figure 1). These expansion joints are designed to take up thermal expansion by
allowing the piping to expand into brass couplings without the use of right-angle
bends or thermal-expansion loops. Mounted to each end of the 20-ft carrier pipe sec-
tions are a Teflon®-coated stainless steel sealing ring and an EPDM (ethylene propy-
lene diene monomer) cleaning ring, both of which fit inside the brass coupling. Each
coupling is held in place by a “lock block” consisting of a mixture of pearlite and
epoxy resin.

WSL piping systems are designed for direct-buried use, and are intended to with-
stand continuous carrier medium operating temperatures of up to 450 °F. Full in-
formation on system design, installation, and field repair can be found in the manu-
facturer’s system brochure (TPS Inc. 1989). The system design brochure specifies
the various insulation thicknesses associated with nominal carrier pipe diameters
of 3, 4, 6, 8, 10, and 12 in. (see Chapter 2, Table 1).

On the basis of approval by the Federal Agency Committee for use at Class B, C, and
D sites, the Super Temp-Tite WSL design is currently approved for the same appli-
cations by Corps of Engineers Guide Specification (CEGS) 02695, Preapproved
Underground Heat Distribution Systems. Recently the system manufacturer asked
the Federal Agency Committee to approve use of the Super Temp-Tite system at

* Super Temp-Tite is a trademark of Thermal Pipe Systems, Inc., 505 New Churchmans Rd., New Castle, DE 19720.



USACERL TR 97/10

12

13

15

Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 10 BTU in/hr ft*2 °F and
carrier temperature = 350 °F 0.2... eee eee eee eee nee 23

Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 15 BTU in/hr ft*2 °F and
carrier temperature = 350 °F ow... oe cece cece eee eee eee 23

Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 5 BTU in/hr ft*2 °F and carrier
temperature = 450 °F 0.0... eee eee nee 24

Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 10 BTU in/hr ft*2 °F and
carrier temperature = 450 °F

Change in calcium silicate thickness to achieve 200 °F at polyure-
thane interface with soil conductivity = 15 BTU in/hr ft*2 °F and
carrier temperature = 450 °F .. 0... kee eee ee eee eter eee 25


59

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fo Gv 1Y
UII G = Auanonpuog jog, [ui} snipey
SOL oor s6 06 s8 08 SL OL s9 09
09
q on
ees
2681 091
oz
3
3
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é
3
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“yz eumesedwe)
olv
09h
ob
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los BuiseQ, aueyyeinijog ls 12D adig

USACERL TR 97/10



USACERL TR 97/10

42

“(01 = Auanonpuod jos) 4, ose 1 edid “ul ¢ *2°q eunBiy

do vs JY

ULM OF = Auanonpuog jos {u] enipey
ov se o€ sz 0% st

09
ol
091
o1z
092

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“yz aimjeseduie | ore

o0SE
ove
pq —_p <a —_ > <a a <—_
ers} Buisep eueyjeinsjog ls reo adid

[4.] eanyesodwie)



USACERL TR 97/10

Appendix A: Independent Engineering
Evaluation of TPS Inc. Heat Distribution
System Design Brochure

[Editor’s note: this appendix contains the full text of an independent engineering
evaluation of the Super Temp-Tite system by NMD & Associates, Alexandria, VA.]

Purpose

The purpose of this review is to consider the viability for
preapproval acceptance of the described heat distribution
systems within CEGS 02695 for use on class A sites. The
brochure reviewed is that dated February, 1995 and titled
"Super Temp-Tite - Underground Prefabricated Heat Distribu-
tion Systems". The brochure describes a conduit system for
high temperature water and steam lines ("Super Temp-Tite")
and two condensate return line conduit ("Sch 80 Heat-Tite"
and "RTRP Vee-Tite"). Comments are based in an expected
reliable and energy efficient life of 25 years. A class A
site is the most severe of four site classifications and is
designated when the water table is either frequently or
occasionally above the bottom of the system and when
surface water is expected to accumulate and remain for long
periods in the soil surrounding the system. Super Temp-
Tite conduit is presented as suitable for system tempera-
tures up to 450 °F. while condensate return conduits are
limited to a temperature of 250 °F.

General Conclusion

The content of the brochure does not provide sufficient
data to show acceptability for use of this product in Class
A sites. The lack of relative data should also preclude
the use of the product in less severe B, C, D sites.

The major problem involves the failure to indicate the
physical properties of materials at the temperatures to



47

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do @v UY
WA Qf = Auanonpuog 110s [uy] snipey
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09

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USACERL TR 97/10



28 USACERL TR 97/10

References

Incropera, Frank P., and David P. DeWitt, Fundamentals of Heat and Mass Transfer, 3d ed. (John
Wiley and Sons, New York, 1990).

Phetteplace, Gary, and David Carbee, Survey of Field Experience with Thermal Pipe Systems Super
Temp-Tite, Technical Report IR1113 (U.S. Army Cold Regions Research and Engineering
Laboratory, September 1992).

Research Associates, Evaluation of Heat Losses from Army UHDS Systems, contractor report for U.S.
Army Construction Engineering Research Laboratories (November 1991.)

Thermal Pipe Systems, Inc: Super Temp-Tite Underground Prefabricated Heat Distribution Systems,
system design brochure (Thermal Pipe Systems [TPS], Inc., Media, PA, May 1989).


USACERL TR 97/10

“($1 = Ayanonpuod 10s) 4. OSp 38 edid “ul € “Le"g eunBl4

do Sv AU

UA SG} = Aanonpuod |10s [ul] sripey
ov se oe sz o¢ oh
09
Ob
Og!

J
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3
8
&

[4.] eanyesedwiay

2
o

“yg eumesodwaj------
49 1 t00SE

“yg eunqeiedwioy ——— dole ose
ov
0S
ogy
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IS Buse aueyjauns|og

ie) adig



4 USACERL TR 97/10
List of Figures and Tables
Figures,
1 Super Temp-Tite piping configuration ......... 6.6 e cece ee eee eee 13
2 Model for analysis 20.6... cece cece ere cent teen tees 14
B.1 3 in. pipe at 350 °F (soil conductivity =5) ....... 0... eee ee eee eee 36
B.2 4 in. pipe at 350 °F (soil conductivity = 5) 1.1.60... eee eee eee eee 37
B.3 6 in. pipe at 350 °F (soil conductivity =5) 1.0.0... 6s ese e eee eee 38
B.4 8 in. pipe at 350 °F (soil conductivity = 5) ...........- se seen eee eee 39
B.5 10 in. pipe at 350 °F (soil conductivity =5) 1.01.26... cece eee eee 40
B.6b 12 in. pipe at 350 °F (soil conductivity =5) 1.02.6... 6. cece eee eee ee 41
B.7 3 in. pipe at 350 °F (soil conductivity = 10) ......-.-. sss eee eee e eee 42
B8 4 in. pipe at 350 °F (soil conductivity = 10) ......... 6. eee eee ences 43
B.9 6 in. pipe at 350 °F (soil conductivity = 10) 1.0.6.0... eee e eee eee 44
B.10 8 in. pipe at 350 °F (soil conductivity = 10) ........ esc e eee eee eee 45
B.11 10 in. pipe at 350 °F (soil conductivity = 10) .......-.--.e esses eee 46
B.12 12 in. pipe at 350 °F (soil conductivity =10) ...-..... see ee sere eens 47
B13 3 in. pipe at 350 °F (soil conductivity = 15) ........ 6. see eee eee eee 48
B14 4in. pipe at 350 °F (soil conductivity = 15) .......... sees sees ee eee 49
B.15 6 in. pipe at 350 °F (soil conductivity = 15) ....... 2... e eee eee eee 50
B.16 8 in. pipe at 350 °F (soil conductivity = 15) ........- 6s see eee ee eee 51


USACERL TR 97/10 19

calcium silicate needs to be increased, independent of soil conductivity, by a
minimum of 9 percent for carrier fluid temperatures of 350 °F to a maximum of over
100 percent to handle some cases where carrier fluid temperatures are 450 °F.

Error Analysis
The same errors that applied to the calculations in Chapter 2 apply to this calcula-

tion.

Table 5. Change in calcium silicate thickness to achieve 250 °F at polyurethane interface with soil
conductivity = 5 BTU in/hr ft*2 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
[in] [ft] [in.] {in.] —
2 1.00 1.28 28%
3 _ — _
6 1.00 1.34 34%
2 1.00 1.33 33%
4
6 1.00 1.40 40%
2 1.50 1.65 10%
6 -
6 1.50 1.74 16%
2 1.75 2.17 24%
8 - t
| 6 1.75 2.30 31%
2 2.50 2.20 | 12%
10
6 2.50 2.34 | 7%
| 2 2.50 2.23 “11%
12 ~
6 2.50 2.39 { 5%



57

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do Sv AY
OTM G = Atayonpuog |10g, [ul] snipew
v8 62 vl 69 v9 6s vs 6y vy 6e
og
tt
weneees) Ol
Ho6 bE
o9t
ozs
3
3
+ 09% 8
2
3
oe
"yg omjeieduiej- ~~ + ~~
“yg eumesedwie ose
ow
~= <> ogy
los Buiseg aueU;aINA|Og us reo edid

USACERL TR 97/10



USACERL TR 97/10

“(01 = Ayanonpuod 10s) 4. OSp 32 adid ‘ul OF “6z"a eaNBiy

do vj 14
TAIT Ol = Aagonpuog os [ui] snipey

s6 06 ss os gL OL $9 09 gs os

09

Ob

og}

e
AQ

09g

Ore

{4.] eanyesodwiey

[hig emesodwe)------
| uz eunreseduie 1

~ <p saan!
[10S Buisep aueyaunh|og Ws 2D



37

USACERL TR 97/10

*(¢ = Ayanonpuod j1os) 4, ose 12 edid “uy » “2"q aunBi4

do Bvis 44
UG G = Alanonpuog jlo (ul) snipey
os sv ov se o€ sz oz

09

4oS01 ou
ost
2
3
3
g
oz 8
€
o
a

“yg eunyesedwe | | 092

“yz einjesodwie |.
= ae ee!
los Bulseg aueyyeinsjod ils 120 adid



USACERL TR 97/10

*(g = Ayanonpuos j10s) 4, ose 1e edid “ul 9 “E°q aunBiy

do Gv JU
TIME = Aianonpuog j!og

[ul] snipew
s9 09 ss os sy ov se o€

09

ObF

2
3

2
a
[4.] eanyesadwiey

092
“yz eunjesedwua |
"yg ounyeiodwa)------ ore
4006
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Mets} Buisep aueYeinAjog lis le. adid

38


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do Bvib 44
TPM GI = Aintonpuog jog [ul] snipey
FOL ooF s6 06 $8 08 SL OZ s9 o9
09
4
HobS

Ol

094
a
3
3
8
ow &
&
3
a

‘ug eunyesedue | 092

[uz eunjesedwa | |
oe
~ — oe

los Buyseg eueYyeiNA|Od

ro adiq

USACERL TR 97/10



USACERL TR 97/10

25

Table 16. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 15 BTU in/hr ft*2 °F and carrier temperature = 450 °F.

Current Thickness of

Required Thickness of

Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
[in] | [ft] [in] [in.]

2 1.00 1.87 87%
3 —

6 1.00 1.91 91%

2 1.00 1.90 90%
4

6 1.00 1.94 94%

2 1.50 2.33 55%
6

6 1.50 2.38 59%

2 1.75 3.11 78%
8

6 1.75 3.18 82%

2 2.50 3.10 24%
10 fr ~

6 2.50 3.17 27%

2 2.50 3.11 24%
12

6 2.50 3.20 28%



USACERL TR 97/10

“(g = Ayanonpuos j10s) 4, OS 38 edid ‘ul g “12"g anBiy

do Bvij 1Y
UPA g = Awmnonpuoo los

[ul] snipey
Ex) 09 gs os sy ov ge OE

09

Ob

ogt

g °e
a a
[4.] eanyesodwiay

°
o

Ose

"yg eimeseduio |

“yg eumesodwa|--- = - - ow

ogy

Buiseg aURYoINA|Og

56



65

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do Zvi Y
I Ol = Aunnonpuod jiog [ul] snipey
SOL oor s6 06 $8 08 gL OL s9 09
s0e8 09
ol
oot
oz
092
ore
yg einqesodwie| --- ~~ = oe
uz eunyeseduio |
oly
HOSP.
~=t —¢_p et : 09b
ess} Buse aueUyyen|od Is 12D

adig

[4.] eanyesedwie,

USACERL TR 97/10



i. General Comments. (Indicate what you think should be changed to make this report and future reports
of this type more responsive to your needs, more usable, improve readability, etc.)

5. If you would like to be contacted by the personnel who prepared this report to raise specific questions or
discuss the topic, please fill in the following information.

Name:

Telephone Number:

Organization Address:

6. Please mail the completed form to:

Department of the Army

CONSTRUCTION ENGINEERING RESEARCH LABORATORIES
ATTN: CECER-TR-I

P.O. Box 9005

Champaign, IL 61826-9005


45

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ao ev 4
TIMI OQ} = Aumonpuog og {ul] snypey
ve eZ ve 69 v9 6s vs 6P ve 6e
09
a:
4.58
ott
o9t
ole
“yg omjesedwe]------ 082
“Uz eanyesedua | -
ole
~= <> ose
0S Buse aueyjainsjog adid

[4] eamesodwioy,

USACERL TR 97/10



*(01 = Aanonpuos j1os) 4. ose 38 adid ‘ul y “g"g eunBiy

WM Oh = Aianonpuog jos

“yg aunyesodwa
“yz eamesodue |.

j086

os

aUeYeINA|Og

oe Ex4 Kd
og
Ob
oot
my
3
3
ol &
z
é
a
A822 098
ole
HoOSE
—_~< pag 098
us leo adid

USACERL TR 97/10



USACERL TR 97/10

“(G1 = Awanonpuod j10s) 4. OSp ye adid “ul 9 “ge"g eunBig

do Gv 1Y
UME GS}. = Amonpuog jos [ut] snipey
s9 o9 gs os sy ov ge OF
og
7 OL
og
ole

2
&
[4.] aanjesadwiey

AolZe ore
09€
“yz einereduie
“yg oinyesodwia} - ~~ - - -
‘yg eumessduio ol
4.0S7
~ ><! gp 097
auRyyens|od us leD adid

68



12

USACERL TR 97/10

Units of Weight and Measure

U.S. standard units of weight and measure are used in this report. A table of
conversion factors for standard international (SI) units is presented below.

Sl conversion factors

Tin.
1ft
1Ib
1gal
1 psi
°F

25.4mm
0.305 m
0.453 kg
3.76L

6.89 kPa

(°C x 1.8) +32

w

Equation Symbols and Variables

The symbols and variables used in this report are defined in the table below.

Definition of mathematical symbols and variables.

Symbol Definition
Cc Arbitrary constant
k Thermal conductivity [BTU-in/hr-ft*2-°F]
k, Thermal conductivity of n" material region [BTU-ir/hr-ft*2-°F]
T Temperature [°F]
T, Temperature in n® material region [°F]
r Radius [in.]
ia Outer radius of n" material region [in.]



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do Bi U
trmg G = Aianonpuog jiog

[ul] snipey
os sb or se oc 52 oz
09
Ou
AolZb
091

°
a

e
&
[y.] eaunyesodwe,

oe
“yg eumesedwio | - = = = = =
“yz eunjesodwie) ove
ol
Jo0SP
~ — —i—pe= 097

10S Buse SUBYIOINA|Od

did

USACERL TR 97/10



61

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do Sv 4
OME O} = Atanonpuog jos [ui] snipey

os sy ov se oe sz -

2
Q

3
8
&

[4.] esnpesadwiey,

°
oS

"yg omeieduej-- ~~~ =

“ye ainjyesedwa | Ac9SE

o9e

Oly

0S
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Hos Buse aUeYIaINA|Og Sze) adi

USACERL TR 97/10



14 USACERL TR 97/10

Polyurethane

Calcium silicate

Figure 2. Model for analysis.

Analysis

For the case of an n-region hollow cylinder with given surface temperatures at the
inner and outer radii, the appropriate form of the heat equation within each of the
n material regions may be expressed as

taf ke] =0 (Eq 1]
Table 1. Thickness of insulation and casing for Super Temp-Tite design.
Pipe Size Calcium Silicate Thickness Polyurethane Thickness | Casing Thickness
[in] fin.] [in.] lin.]
3 1.00 1.27 0.1900
4 1.00 1.27 0.1900 |
6 1.50 ; 1.27 0.1875 __|
8 2.00 1.73 _ 0.2500
10 _ 2.50 1.18 0.1950
12 2.50 1.18 0.1950



USER EVALUATION OF REPORT

REFERENCE: USACERL Technical Report 97/10, Thermal Evaluation of Piping Components Used in a
Commercial Underground Heat Distribution System

Please take a few minutes to answer the questions below, tear out this sheet, and return it to USACERL. As
user of this report, your customer comments will provide USACERL with information essential for improving
future reports.

1. Does this report satisfy a need? (Comment on purpose, related project, or other area of interest for which
report will be used.)

2. How, specifically, is the report being used? (Information source, design data or procedure, management
procedure, source of ideas, etc.)

3. Has the information in this report led to any quantitative savings as far as manhours/contract dollars
saved, operating costs avoided, efficiencies achieved, etc.? Ifso, please elaborate.

4. What is your evaluation of this report in the following areas?

a. Presentation:

b. Completeness:

c, Easy to Understand:

d. Easy to Implement:

e. Adequate Reference Material:

f. Relates to Area of Interest:

g. Did the report meet your expectations?

h. Does the report raise unanswered questions?



USACERL TR 97/10

*(g = Ayanonpuos j1os) 4. ose ve edid “uy ¢ “1g eunBiy

do Sv AU
Ur = Aanonpuod los:

{ui} snipe

se oe Ex

Kd

st

a= el el

los Buise9

“yg aunyesadwa |
“yg eamesadwe j.

aueyjainsjog

us 1leD

09€

edi

+ 09

Ou

2
2

2
jo) eimeiodwie,

36.


USACERL TR 97/10 23

Table 12. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 10 BTU in/hr ft42 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate Percent Difference
{in.] [ft] [in.] [in.]

| 2 1.00 1.64 64%
3 6 1.00 1.68 68%
2 | 1.00 1.68 68%

4 6 1.00 1.73 73% _|
2 1.50 2.07 - __ 38%
6 _ 6 fo 1.50 2.13 42%
2 1.75 2.75 57%
8 6 | 1.75 2.84 62%
2 2.50 2.76 __ 10%
10 6 2.50 2.85 __ 14%
2 2.50 2.78 11%
12 6 2.50 2.89 15%

Table 13. Change in calcium silicate thickness to achieve 200 °F at polyurethane interface with soil
conductivity = 15 BTU in/hr ft*2 °F and carrier temperature = 350 °F.

Current Thickness of | Required Thickness of | Percent Difference
Nom. Pipe Dia. Burial Depth Calcium Silicate Calcium Silicate
[in] [ft] [in] | [in.]

2 1.00 1.62 62%
3

6 1.00 1.65 65%

2 1.00 1.66 66%
4

6 1.00 1.69 69%

2 1.50 2.04 36%
6

6 1.50 2.08 39%

2 1.75 2.73 56%
8 ~ —

6 1.75 2.78 59%

2 2.50 2.73 9%
10

6 2.50 2.79 11%

2 2.50 2.75 10%
12

6 2.50 2.82 13%



The contents of this report are not to be used for advertising, publication
or promotional purposes. Citation of trade names does not constitute ar.
official endorsement or approval of the use of such commercial products.
The findings of this report are not to be construed as an official

Department of the Army position, unless so designated by other authorized
documents.

DESTROY THIS REPORT WHEN IT IS NO LONGER NEEDED

DO NOT RETURN IT TO THE ORIGINATOR


USACERL TR 97/10

“(gt = Ayanonpuoo j108) 4. ose ye edid “uy € “E1"g ouNB}t

do Gv 4U

{ui] srupey
IME Gf =Ayanonpuog ios} oy se oe s@ rd sh
09
sold

ol
09}
oz

“yg einyeieduie| - = - = - 40612 092

“yz einyesedwe sovle
oe

Jo0SE
o9¢
—" pa >< >
[10S Buiseg aueYLeINA\Og us reo edid

[4.] eamesedwes



USACERL TR 97/10

31

(2).  Annulus Rings—The EPDM annulus rings at the ends of
the conduit sections are intended to limit the spread of
leaks between adjoining units. It is important then that
a tight seal be maintained at the heat carrying pipe at the
casing. Para. 2.3 on page 10 under "Hardware" indicates
very significant changes in physical characteristics when
the material is subjected to aging for only 240 hours at
300 °F. Changes of around 60 percent in tensile strength,
elongation at rupture, and urometer hardness suggest rapid
deterioration of the material. Since the ring will be in
direct contact with the heat carrying pipe, test should be
performed at 450 °F. for an extended period and the contact
surface carefully checked to see whether a seal can be
maintained.

(3). Conduit and Coupling Casing—The casing is a rein-
forced thermosetting resin plastic (RTRP) using a polyester
isothalic resin. The only data regarding physical proper-
ties is contained in para. 2.6, page 11 where tensile and
compressive strengths are shown at 75 and 200 °F. These
indicate a radical decrease strength at higher tempera-
tures. The manufacturer should provide steady state
calculations to establish casing temperatures at maximum
operating temperatures and variable soil conditions. Based
on coupling dimensions shown in the table in para. 1.11.1
on page 24 under "Hardware", there will be a 1 to 2 inch
annular air space on each side of the coupling where the
casing will be exposed directly to heat transfer from the
hot piping. Casing temperatures at those points should
also be established. Since casing failures have often been
found on systems using RTRP casings after a few years of
operation, it is important that acceptable aging test data
be provided for this element of the system.

(4). Secondary Joint Sealing Ring—Letters from Seals
Eastern, Inc. indicate that two HTRC formulations were
available for this system element. One was suitable for
operation at 300 °F. and the other at 400 °F. Para. 2.1 on
page 9 under "Hardware" does not state which is being
provide and what other material is available for tempera-
tures exceeding 400 °F. These matters should be clarified
and acceptable aging tests should be provided to insure
proper long term operation.



cil

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fo @v 44
UM G = Aianonpuod |10S, [ul] snipey
SOL oor s6 06 se 08 SL oz s9 09
09
Ho68
oll
09h
a
3
3
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09
“Ug aunjesedwia| - - -
We eunyeseduie | |
ole
= <> ose
los Buisep aueyaink|og lls 12 adig

USACERL TR 97/10



26 USACERL TR 97/10

4 Conclusions and Recommendations

Conclusions

Based on this analysis, it is concluded that the temperature experienced by the
polyurethane foam insulation for this WSL design will be well above a conservative
continuous use maximum operating temperature. This conclusion applies both to
the upper limit of carrier medium temperature allowed in Class A uses (450 °F) and
a typical operating temperature of 350 °F, which corresponds to a saturated steam
pressure of 120 psig. The conclusion also holds for a range of temperatures below
350 °F. The calculations presented here strongly indicate that shortly after being
put into service, the polyurethane insulation closest to the carrier pipe will be
exposed to excessive temperatures, which in turn will cause it to degrade. Over time
this degradation will adversely affect the insulating effectiveness of the polyure-
thane foam and will cause heat losses in excess of design values. Ongoing excess
heat loss will adversely affect the total life cycle cost of any heat distribution system.
The amount of extra calcium silicate insulation needed in order to limit the maxi-
mum polyurethane foam temperature to 250 °F and 200 °F has been calculated, and
is found to be significant. For the carrier temperatures examined, anywhere from
an additional 4 percent to 112 percent calcium silicate is needed. Alternatively, the
permissible upper limit on operating temperature could be reduced to lower the
amount of heat to which the polyurethane foam insulation may be exposed.

It should be noted that only the steady-state temperature profile some distance
away from the expansion joints of this piping design fell within the scope of this
analysis. Furthermore, a number of questions raised in the independent analysis
of the system brochure (Appendix A) apparently could require a more complete
examination, with an emphasis on materials temperature limitations and long-term
reliability. The major concerns raised are as follows:

¢ — lack of quantitative data on the physical properties of various materials at
elevated temperatures and over time (e.g., polyurethane foam insulation,
EPDM and HTRC sealing rings, silicone lubricant, RTRP with polyester iso-
thalic resin casing, and the composite lock block)

¢ — lack of chemical compatibility testing of the lock block composite material
where in direct contact with the bronze coupling at elevated temperatures


10 USACERL TR 97/10

Class A sites as defined in CEGS 02695. Class A sites present the most severe
conditions, with water tables expected periodically to rise above the bottom of the
system, and surface water expected to accumulate and remain for long periods of
time in the soil surrounding the system.

The Federal Agency Committee tasked the U.S. Army Construction Engineering
Research Laboratories (USACERL) to conduct mathematical modeling and simula-
tions to help determine whether Super Temp-Tite meets the technical specifications
for use at Class A sites.

Objectives
The objectives of this study were to:

* provide a preliminary engineering analysis pertaining to the suitability of the
Super Temp-Tite system for use at Class A sites

* accurately model the radial temperature profile of the Super Temp-Tite system
in characteristic service conditions for six stock carrier pipe diameters

¢ provide a recommendation to the Federal Agency Committee regarding the
approval of the subject system for Class A applications.

Approach

A preliminary evaluation of the WSL system design brochure for use on Class A
sites (TPS Inc. 1989) was conducted by an independent contractor (see Appendix A).

The theoretical analysis models the radial steady-state temperature profile and
employs design parameters stated in the company brochure for the various nominal
carrier pipe diameters. This analysis applies only to the piping between the
couplings. No attempt was made to estimate the temperature profile within the

couplings.

This WSL system was modeled as a one dimensional steady-state heat conduction
problem. The following assumptions were made:

¢ the soil was assumed to be a large homogeneous cylinder surrounding the
piping system with a radius equal to the burial depth (see Chapter 2, Figure 2)

¢ each of the different materials was assumed to have a constant thermal
conductivity and a negligible contact resistance at their interfaces


63

“(OL = Auanonpuod j1os) 4, OS 1 edid ‘ul g “gz"g eunBi4

NG QO} = Aunonpuog jog [ul] snypey
v8 6L vl 69 v9 6s vs ey vy ee
09
ca
4ov6 ol
o9t
o1z
092
ore
“yg oumesodwa|------
“yz esmeseduie | o9e
ol
pe ¢ p= ogy
10S, Buiseg euReyjainsjog ls 1k adig

[4] eanyesedwiey

USACERL TR 97/10



49

*(¢1 = Aanonpuos j10s) 4, ose 1e edid “ul p “pia eunBi4

fo vy 24
TIME G} = Ayanonpucg los) lun snpey
oS sv ov ce oe e ne
09
408L

ol
ot
2
3
3
2
ow 8
=
@
09 4

old
“yg einyezedwie| - - - - delle
“yz aunyesedwe | A822
ore
<> HoOSE
~« a a — at — pep 098
los Bulseg aueyjeinh|od WS 12D adiq

USACERL TR 97/10



51

“(G1 = Ayanonpuod jos) 4, ose 1e edid ‘ug “g1'@ eunBiy

do Gv 4U

ME S|. = Ayanonpuoo los

[-ug aimesedwe

yz aumeroduie

6s vs ev vy ee
09
Ob
091
ry
3
3
ow
cy
a
092
ole
|4.0s€
-_———
pana + 098
Is IRD add

eueyjainh|od

USACERL TR 97/10



USACERL TR 97/10

13

2 Temperature Distribution

Piping Specifications

Figure 1 is an illustration (not to scale) of the basic Super Temp-Tite piping con-
figuration. Figure 2 presents an illustration of the system as modeled in this
analysis, including indications of the radii expressed in the equations that follow.

Table 1 lists the thicknesses of pipe insulation and casing for six different pipe
diameters, as specified in the TPS Inc. system brochure (1989). These illustrations
and specifications also apply to the analysis in Chapter 3.

Carrier Fluid

Carrier Pipe
| Calcium Silicate

Polyurethane
Casing

Figure 1. Super Temp-Tite piping configuration.

| |
lig