NATIONAL BUREAU OF STANDARDS REPORT

5631

SIMULATED FIELD TESTS OF DURANT INSULATED PIPE

by

Selden D. Cole

and

Paul R. Achenbach

Report to

Office of the Chief of Engineers

Department of the Army

Washington, D. C.

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUKEAU OF STANDARDS

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The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, J90I, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

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Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003-20-4881 October 30, 1957 5631

SIMULATED FIELD TESTS OF DURANT INSULATED PIPE

by

Selden D. Cole

and

Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Office of the Chief of Engineers

Department of the Army

Washington^.. D. . C, .

IMPORTANT NOTICE

NATIONAL BUREAU OF 5 intended for use within th

tc additional evaluation am

listing of this Report, eithe the Office of the Director, I however, by the Governmer

to reproduce additional coj:

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

formally published it is subjected

g, reproduction, or open-literature

ission is obtained in writing from Such permission is not needed,

ly prepared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

. . . M
. nm.c-
SIMULATED FIELD TESTS OF DURANT INSULATED PIPE

by

Selden D. Cole and Paul R. Achenbach

ABSTRACT

Simulated field tests were made of several specimens of Durant Insulated Pipe primarily to study

the effect of operating an underground steam system of this type when the unibestos insulation

became wetted during installation or at a later

time. The unibestos was deliberately wetted for

these tests. Some specimens were buried in a

trench, others were tested above ground, and the

metal jackets were removed from some specimens to

simulate the conditions that would exist after

the sheet metal had rusted away.

Investigation was also made of the effect of

pouring the asphalt in the field at other than

the recommended asphalt temperature and in low

ambient temperatures such as occur during winter

weather.

The results showed that steam would be formed in

the wet unibestos insulation when steam at a temperature above 212 F was admitted to the pipe and

that enough pressure could be built up in the

insulation to rupture the asphalt covering. The

asphalt reached temperatures up to 216 F around

the wet insulation and softened enough to settle

to the sides and bottom of the pipe to a noticeable

degree when buried in a trench and it slipped off

the unibestos entirely when it was not restrained

by the surrounding earth or the metal jacket.

Continued heating of the pipe with steam at a temperature of 375 F dried the unibestos covering to

a distance of 3/^- inch to one inch from the pipe

in two weeks time. There was evidence that a

steady state moisture distribution in the unibestos was approached during this time with dry

insulation near the pipe and free water in

evidence at the inner surface of the asphalt

jacket. Asphalt poured at temperatures ranging

from 350 F to 500 F and in ambient temperatures

down to 12 F appeared to produce a jacket free of

voids, fissures, or lines of cleavage. Measurements of heat loss from the specimens were not

made during these tests.
,• .

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Introduction

At the request of the Office of the Chief of Engineers,

Department of the Army, tests were made on several specimens

of Durant Insulated Pipe to study the temperature gradients

in the insulation as received, to study the effects of wetting

the molded pipe insulation, and to evaluate the effect of

applying the asphalt in the field during severe winter weather.

The specimens were buried in earth for a part of the tests,

but no measurements were made of the heat loss through the pipe

insulation.

Description of Test Specimens

Durant Insulated Pipe is manufactured by Durant International Corporation, Williamstown, N. J. The prefabricated

specimens submitted for the tests consisted of 20- foot lengths

of four-inch diameter black steel pipe encased in a two-inch

thickness of molded Unibestos insulation, a one-inch layer of

asphalt waterproofing and a sheet metal casing of 26-gage

galvanized steel. Load-bearing spacers rings, one-inch in

radial depth, were placed around the molded insulation to support the pipe in the sheet metal jacket. The one-inch annular

space between insulation and jacket was filled by pouring highmelting-point asphalt at a temperature of 450 F through holes

in the jacket spaced 15 in. apart. The insulation spaces of

these specimens were sealed at the ends by steel plates welded

to the pipe and to the jacket. Pipe sections prefabricated for

field installation do not have these welded end plates, but had

the ends of the insulation on each section covered with a

waterproof fabric. This fabric is removed after adjacent

lengths of pipe are welded together in the field and sections

of molded insulation and waterproofing are applied to complete

the joint. The welded steel end plates are used only in manholes and in buildings.

One of the three test specimens was submitted without the

asphalt waterproofing between the molded insulation and the

sheet metal jacket. A quantity of asphalt was furnished so

information could be obtained on the effect of pouring the

material when heated to different temperatures and in different

ambient temperatures.

Test Equipment and Procedure

Each of the three specimens was fitted with a steam supply connection and a condensate drain. Steel plates, l/2-inch

thick, were welded over the ends of the four-inch pipe. A

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plece of 3/^-inch pipe, 18 inches long., had been welded into

the plate at the inlet end with nine inches projecting on each

side. The inner end of the 3/^-inch pipe was capped and enough

1/4-inch holes were drilled into the sides of the pipe to provide an aggregate area equal to the area of the 3/4-inch pipe.

This arrangement caused the steam to be sprayed against the

inner walls of the four-inch pipe at its inlet end. At the

outlet end, a l/2-inch pipe nipple was welded into the bottom

of the four-inch pipe and connected to a high pressure buckettype steam trap.

Steam was generated in a thermostatically controlled

boiler of ten-gallon capacity and 11- KW electric energy input.

A float, located in a vertical by-pass line at the side of the

boiler, actuated "a solenoid valve to admit cold water to the

boiler as required to maintain a constant water level. Adequate pressure was maintained on the cold water supply by

means of a turbine type pump.

Thermocouples of 26-gage copper-constantan wire were used

with a Rubicon portable precision potentiometer to indicate

temperatures. The steam temperature was observed in the supply

pipe and in the condensate outlet. Stations for temperature

observation on the pipe covering were located (l) at the center

of the pipe, on the top and bottom, (2) approximately four feet

from each end of the specimen missing the spacer ring, and

( 3 ) on the spacer ring adjacent to the station at the inlet end

of the pipe. Two thermocouples were used at each station, one

on the outer surface of the Unibestos and the other on the

outer surface of the asphalt. The stations of temperature

measurement are indicated on the diagram at the top of Fig. 1.

The asphalt used to complete the unfinished specimen was

heated in a metal container equipped with a built-in immersion

electric heater. When the asphalt reached the desired temperature for a particular pouring, it was ladled into a two-gallon

sprinkling can, from which the spray nozzle had been removed,

and immediately poured into one of the pour holes in the metal

jacket. This procedure was repeated with quantities of asphalt

heated to 350 F, 400 F, 450 F, and 500 F using a different pour

hole with each temperature. The first round of pourings filled

one half the void circumferentially, the second round of

pourings nearly filled the void, and the third round completed

the asphalt jacket. One half the length of the specimen was

poured with the specimen in equilibrium with an ambient temperature of 70 F; the other half was poured after the specimen

had been cooled to 12 F.

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Several two-inch cubes of asphalt were poured from one of

the several batches to be used later for studying the softening

point of the material. A chromatographic analysis of the

asphalt was made in accordance with the method described in

NBS Research Paper 2577 to determine its composition.

The first specimen was buried in a trench 18 inches deep

and covered with six inches of dirt after first removing the

sheet metal jacket. The pipe was heated with steam at a temperature of 375 F for a week with one or more observations of

the temperatures on the pipe covering being taken each day.

The results are plotted in Pig. 1.

At the conclusion of the first test made with the insulation in the condition received from the factory, the specimen

was removed from the trench and the unibestos was saturated

with water through two holes, one at each end, cut in the

asphalt covering. The holes were sealed with hot asphalt

after wetting the insulation and the specimen was buried in

the trench again. The pipe was heated with steam at an average

temperature of 375 P for two weeks. The temperatures observed

during this test are plotted in Pig. 2.

The unibestos of the second specimen was wetted like the

first after removing the sheet metal jacket and was supported

above ground by a pipe support at either end while it was

heated for 11 days with steam at a temperature of 373 °P.

The welded caps were removed from the ends of the insulated jacket on the third specimen and the unibestos was

saturated by immersing the specimen in a trench full of water

for two days. The excess water was drained from the unibestos

before heating and the specimen was supported above ground

during the heating period of 15 days.

Results and Discussion

First specimen with dry Insulation

The highest temperature observed on the surface of the

unibestos was 138 P and the highest temperature observed on

the surface of the asphalt was 95 F during the seven days of

heating. Pig. 1 shows that the unibestos surface reached its

maximum temperature in a little over 24 hours whereas the temperature of the asphalt surface was still rising slowly after

seven days. The latter condition may have resulted because the

temperature gradient in the earth over the pipe had not become

stable or because the outdoor temperature was rising.

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The jacket was removed from this specimen to simulate conditions that would exist in use after the jacket was rusted

away. The asphalt showed a slight tendency toward plastic

flow when the specimen pipe was heated in the earth without the

metal covering. The plastic deformation was a little more pronounced near the metal caps at the ends and at the spacer rings

First specimen with wetted Insulation

The unibestos insulation absorbed a maximum of 10 to 12 lb

of water per running foot. About two-thirds of the original

quantity of water introduced into the insulation was evaporated

during two weeks of heating the pipe with steam at a temperature of 373 F. Inspection showed that approximately the inner

half of the unibestos covering had been dried, and there were

pockets of free water on the inside surface of the asphalt

covering. There was evidence that the moisture distribution in

the unibestos had approached a steady state during the twoweek test. Fig. 2 shows the temperatures observed at various

stations during this test. The stations of temperature

observation were the same as those shown on the diagram in

Fig o 1.

The temperatures on the inner and outer surfaces of the

asphalt reached 212 F and 216 F at two stations during the

first three hours after admitting steam to the pipe as shown

in Fig. 2, After two weeks operation temperatures as high as

151 F were observed on the outer surface of the asphalt and

temperatures up to 198 F were observed at the interface between

the unibestos and the asphalt. Inspection showed that the

steam generated in the unibestos had ruptured the asphalt

covering in several places. Fig. 3 shows the temperatures

observed at stations 2 and 3 during the first seven hours of

the test on an expanded time scale. This figure indicates

that steam penetrated the asphalt covering at thermocouple No.

3

Fig. 4 shows specimen No. 1 after removal from the trench

and after inspection.

Apparently water was continuously evaporated at the 212 F

isotherm in the insulation, but the vapor condensed to water

again in the cooler regions farther from the pipe. Since the

total pressure inside the asphalt covering did not exceed

atmospheric pressure, additional water vapor could be lost

from specimen only by diffusion through the fissures in the

asphalt covering. This would be a very slow process. The

asphalt became quite soft and there was plaptic flow of the

asphalt away from the top side especially near the metal caps.

In some sections the asphalt had flowed to the sides of the

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pipe and in others the asphalt thickness was greater on the

bottom than on either the top or sides at the conclusion of the

test. Presumably this plastic flow would not occur as long as

the metal pipe covering was intact. The metal casing was

removed before burying the specimen: for the purposes of these

tests

.

Second specimen with wetted insulation

The second specimen was tested above ground with the metal

jacket removed to observe what might happen if movement of the

asphalt were not restrained by the surrounding earth.

With steam at temperatures increasing from 275 F to 345 F

during an eight-hour period, the asphalt covering softened and

fell off the pipe leaving a thin asphalt film on the unibestos

and leaving the surface of the spacer rings bare. After ten

days heating with steam at a temperature of 373 F the unibestos

was dried from the pipe surface outward for about one half its

total thickness. The remainder was quite wet to the touch.

Third specimen with wetted insulation

The third specimen was tested above ground. The metal

jacket was left on this specimen but the end caps had been

removed to expose the ends of the unibestos insulation.

With the ends of the unibestos insulation open to the

atmosphere about one third of the unibestos adjacent to the

steam pipe was dried in 15 days with steam in the pipe at a

temperature of 373 F. The outer two-thirds of the unibestos

was wet. Steam was emitted from the open ends of the unibestos

during the early part of the drying period, but none was visible

at the end. A column of water vapor was ejected from the unibestos when the asphalt was ruptured for inspection at the end

of the test. The asphalt showed no deformation except conformation to the sheet metal enclosure.

The asphalt jacket poured at the National Bureau of

Standards using asphalt at different temperatures ranging from

350 F to 500 F and under winter and summer ambient conditions

was continuous in appearance and contained no voids, fissures,

or lines of cleavage.

Pig. 5 shows the effect of heating small cubes of the

asphalt, like the sample in the upper left of the figure, at

various temperatures for selected periods of time. The asphalt

slumped some in two hours at a temperature of 200 F and it

flowed outward to a smooth flat mass in 35 minutes at a temperature of 248 F.
'

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The chromatographic analysis of the asphalt used on

Durant Insulated pipe showed the following percentages:

The composition and physical characteristics of this blown

petroleum asphalt is typical of this class of bitumens in the

220 to 240 F softening point range. Blown petroleum asphalts,

when subjected to heat, will show an Increase in asphaltenes

due to changes occurring mainly in the dark oils and asphaltic

resins rather than to volatile losses. The lower the ratio of

asphaltenes (black solids) to the petrolenes (combination of

water white oils, dark oils, and asphaltic resins) the lower

will be the softening point and the more easily fusible will be

the bitumen.

Conclusions

Knowledge of the insulating characteristics of dry unibestos insulation indicates that Durant Insulated Pipe would

not have excessive heat loes as long as the insulation were dry

throughout its entire thickness, even though no measurements of

heat loss were made during these tests.

These tests show that unibestos will absorb large quantities of water. When the insulation is thoroughly wetted and

steam at a temperature above 212 P exists in the pipe, steam

will be formed in the insulation near the pipe and will probably rupture the asphalt jacket to relieve the pressure unless

some means are available for the escape of steam. After initially wetting the unibestos, about half the thickness of the

unibestos insulation dried out in a two-week period when steam

at a temperature of 375 F was supplied to the pipe. It is

doubtful that the outer layers of the unibestos would dry out

during the useful life of the system once it became wet in an

actual installation.

The metal cover will contain the asphalt as long as it is

intact, but prolonged corrosion might eliminate this support

permitting some plastic flow of the asphalt, especially if the

insulation were wet.

Asphaltenes

Water White Oils

Dark Oils

Asphaltic Resins

Chloroform Desorbed

42.8

24.6

23.9

8 .

6

0.5

Total 100.4

Softening Point

Penetration at 77 F

235 °F

13
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The integrity of the asphalt jacket does not appear to be

adversely affected by using asphalt temperatures in the range

from 350 F to 500 P or by ambient temperatures down to 12 P

during the pouring operation.

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INSULATION

TEMPERATURE,

AVERAGE

STEAM

TEMPERATURE

,°F



INSULATION

TEMPERATURE

AVERAGE

STEAM

TEMPERATURES

HOURS

I

CONTROL 179.6 °F

60 MINUTES

200.0 °F

120 MINUTES

226.4 °F

40 MINUTES

I

248.0 °F

35 MINUTES

DURANT ASPHALT SPECIMENS

Fig. 5

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is ^jggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out spe- cialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the

inside front cover of this report.

WASHINGTON, 1). C. Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation.

Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology

and Lubrication. Engine Fuels.

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Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories, Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Analogue Systems. Application Engineering.

• Office of Basic Instrumentation • Office of Weights and Measures

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular

Propagation Services. Sun-Earth Relationships.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radio

Systems Application Engineering.

Radio Standards. Radio Frequencies. Microwave Frequencies. High Frequency Electrical

Standards. Radio Broadcast Service. High Frequency Impedance Standards. Calibration

Center. Microwave Physics. Microwave Circuit Standards.
NBS