/

NATIONAL BUREAU OF STANDARDS REPORT

4231

A STUDY OF GILSULATE AS UNDERGROUND

FIFE INSULATION

^7

Selden D. Cole

Faul R. Achenbach

Frank J. Fowlitch

to

Office of The Chief of Engineers

Department of the Army

Washington, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL DUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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of the divisions and sections engaged in technical work. In general, each section is engaged in

specialized 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

of the back cover of this report.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

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Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
I^ATSOi^AL BUREAU OF STANDARDS REPORT

ms P8I®JECT NBS REPORT

1003-20-4881 July 20, 1955 4231

A STUDY OF GILSUIATE AS UNDERGROUND

PIPE INSULATION

i:>y

Selden D. Cole

Paul R. Achenbach

Frank J. Powlitch

Heating and Air Conditioning Section

Building Technology Division

to

Office of The Chief of Engineers

Department of the Army

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprin

unless permission Is obt 25,D,C. Suchpermist

cally prepared If that

Approved for public release by the ®'*' '* p'"®*’"’'*®'*

Director of the National Institute of

* **’’

haa been epeclfi- Standards and Technology (NIST)

, on October 9, 2015.

A STUDY OF GILSUI.ATE AS UNDERGROUND PIPE INSULATION

'by

Selden Do Cole^ Paul R. Achenbach;, and Frank Jo

ABSTRACT

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

laboratory and simulated field tests were made of Type B

Gilsulate as a proposed insulation for underground steam

lines. Gilsulate consists of specially selected;, sized^ and

blended particles of gilsonite;, a natural mineral found in

Utah. Gilsulate is asphaltic in nature and changes in

physical appearance and chemical composition when heated.

It was foxmd tha.t rapid heating sintered the particles at

a temperature of about 225 °F and consolidated it into a voidless material at a temperature of about 3^0 °F to 370 °F.

Slower heating or dampening of the raw Gilsulate before heating inhibited consolidation but permitted sintering to take

place. Gilsulate swells and increases in volume on heating

and cracks during repeated heating and cooling. Because of

this cracking a Gilsulate envelope around a steam pipe

permits penetration of water un.der conditions of high water

table. The thermal conductivity of raw granular Gilsulate

was found to be about 0.64 Btu/hr (sq ft)(°F/ln) at a mean

temperature of 130°F. A sintered and consolidated envelope

on a steam pipe operating at a temperature of 350 °F had an average thermal conductivity of about 1.33 Btu/hr (sq ft)

( °F/in) when surrounded by dry earth and only slightly

higher in damp earth because it is non-hygroscopic . The

test results indicate that Gilsulate might be an economical

and useful insulation for underground steam lines in dry

climates although conditions for corrosion might develop

temporarily/ even in arid regions during periods of heavy

rainfall because of its demonstrated tendency to crack

under repeated heating and cooling.

1. INTRODUCTION

In response to the request of the Office of The Chief of

Engineers, Department of the Army, an investigation was made of

the mineral Gilsonite as an insulating material for underground

steam pipes operating at a pressure of 125 psig corresponding to

a saturation temperature of 350 F.

Gilsonite is produced under the trade name of Gilsulate

by the Anierican Gilsonite Company of .Salt Lake City, Utah, for

insulating hot umderground pipes and protecting them against

- 2-

corrosion, Gilsulate consists of specially selected, sized, and

blended particles of gilsonites ranging in diameter from dust to

3/16 in. and resembles asphalt in its appearance but differs from

asphalt in its composition and characteristics

.

Gilsulate is produced in three grades for complete coverage

of three temperature ranges

.

Grade Temperature range

Type A 220 F to 310 F

Type B 300 F to 385 F

Type C 385 F to 520 F

A typical Gilsulate installation consists of a pipe,

supported in a dry trench or form, covered with a minimum thickness of four inches of the material, packed under and around the

pipe, and tamped on the top surface to eliminate voids.

If the installation is below the ground water table or is

made during inclement weather, the granular Gilsulate should be

heated by passing steam through the pipe before covering with a

minimum six-inch back fill in order to consolidate and sinter

the material. For type B material consolidation and sintering

is accomplished by passing steam through the pipe for 4 hours at

385 F, or 8 hours at 350 F, or 38 hours at 3OO F and then allowing

the pipe to cool down normally. The structure thus formed around

the pipe consists of three layers wi,th different characteristics

(1) the consolidated zone nearest the pipe, (2) the semi-consolidated or sintered zone outside of it, and (3) the unconsolidated

or granular zone . The consolidated part loses all trace of the

individual particles from which it formed and resembles a hard.
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black, glossy, glass after it cools. The semi-consolidated or

sintered material consists of the individual particles adhering

together rigidly. The unconsolidated part shows no change visible

to the eye from the original material as first used. It is the

consolidated core and the semi -consolidated zone of the structure

which are reported by the manufacturer to be watertight and to

afford protection against corrosion.

To obtain both basic and practical information on Gilsulate

when dry or wet, laboratory tests and full scale trench performance

tests were conducted for determining physical characteristics,

chemical properties, and performance under simulated use conditions.

The laboratory phase consisted of (l) heating dry or wet

Gilsulate surrounding a hot pipe, (2) comparing the effect when

the material was gradually oven-heated to progressively higher

temperatures with that resulting from a rapid heating at one

temperature, ( 3 ) determining the chemical properties chromatographically, (it-) determining the thermal conductivity by the hot plate

method.

The full scale tests consisted of passing steam at 350 F

through a i|--in. pipe insulated with Gilsulate when embedded (l) in

dry dirt, (2) in moist dirt with the water table 1 foot below the

pipe, ( 3 ) with the water table level with the pipe, and (4) with

water covering the insulating conduit. A second pipe was buried

in the ground and insulated (l) with dry Gilsulate, (2) with

dampened Gilsulate. The second installation was subjected to

alternate heating and cooling, with the trench being wetted at

each phase change.

2. DESCRIPTION OF EQUIPMENT

Part of the laboratory apparatus used to simulate the use of

Gilsulate as a pipe insulation consisted of two cement asbestos

boxes with a pipe running lengthwise through the center of each.

One box was 9 ^ 9 x 24 in. constructed so that either end

or any side could be removed independently. A 1-in. diameter

galvanized pipe extended through the center of the box and had

electric resistance wire wound on one end for a heater. Energy

input to this heater was controlled with a thin-walled thermo1 static switch located at the hot end. In use, the temperature of

the pipe decreased with distance from the hot end so that successive

transverse sections of the surrounding insulation were thus subjected

to different pipe temperatures in one test, the duration of which

may be several days or weeks . Thermocouples were peened into the

surface of the pipe, and were spaced every two inches from the hot

end for the first fourteen inches and every three inches for the

remainder of the specimen.

The second cement-asbestos box was 9 x 9 x 36 in. in size

containing a 1-in. diameter pipe centered lengthwise in it which

was heated internally and thermostatically controlled, so that the

surrounding insulation was uniformly heated. Thermocouples were

peened into the surface of the pipe.

The thermal conductivity of unconsolidated Type B Gilsulate

was measured in an 8-in. guarded hot plate apparatus conforming

with the requirements of Fed. Spec. LLL-F-321b and of A.S.T.M.

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C177-^5.

Tventy-one aluminum boats, each 2 x 2 x 4 in. were prepared,

and random filled with Gilsulate. These filled boats were placed in

an electrically heated oven for exposure to various levels of

temperature for selected lengths of time.

An analysis was made on four samples of Gilsulate in

accordance with the method described in N.B.S, RP 2577, "A

Chromatographic Method for the Fractionation of Asphalt Into

Distinctive Groups of Components".

The full scale trench test was conducted in a watertight

box 4 X 4 X 12 ft in size. Along the longitudinal center line

and pitched l/4 in. to the foot a l4 ft long 4 in. IPS test pipe

was suspended (See Fig. 1). The inside of the 4-in. pipe was

divided into three sections: two internal half moon baffles in

the bottom and two half moon baffles in the top, one slightly

downstream and one upstream of the lower ones isolated a 4 ft

measuring section at the middle. Separate internal condensate

drain lines were brought out from each section and connected to

high pressure steam traps. The condensate from the measuring

section could be directed through a sight glass bj/passing the

steam trap. In each case, the condensate from the traps, or

sight glass, was passed through a water-cooled heat exchanger

to reduce the temperature to near room temperature so it could be

collected and weighed in open vessels without appreciable loss by

evaporation.

An electrically heated steam boiler of potential capacity
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SCHEMATIC

DIAGRAM

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UNDERGROUND

PIPE

INSULATION

TEST

APPARATUS

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ranging from I .5 to I3 KW (5000 to 45,000 Btu/hr) produced steam

at the necessary pressure. The water level of the boiler was maintained by a float control opening a solenoid valve in a line from

a supply tank held at a higher pressure than that of the boiler. A

check valve in the supply line before the tank and one in the

line after the solenoid valve prevented loss of pressure in the

system from back feed.

Steam was delivered from the boiler through a 3A tn. pipe

extending about 1 ft into the upper end of the 4 in. pipe. The

1 ft extension was capped off at the end and a series of lA in.

holes drilled in its side walls whose aggregate area equalled

1.5 times the area of the open end of the 3 A in. pipe. This

produced a spray of steam on the side walls at the inlet end

instead of a Jet down the longitudinal center of the pipe.

The box was filled with oven-dried dirt^ a typical Chester

loam, to approximately mid-height. At this point a wooden form

was placed about the pipe to make a 12-1/2 in. square conduit

when filled with Gilsulate. After filling the form with Gilsulate,

dirt was added to the sides, the form removed and the remainder

of the box filled with dry dirt. Both materials were tamped with

a 1/4 in. thick 8 x 8 in. iron tamper as they were added.

Five thermocouples were peened into the top of the pipe at

positions 23 in. apart starting at the center and extending in both

directions. A thermocouple was fastened to the pipe at its entrance

to and its exit from the box. In addition, thermocouples were
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loca.ted in the Gilsulate and dirt vith 11 in each of three strings

in a plane perpendicular to the steam pipe, at its center. The

thermocouples in the three strings, extending downward ^laterally

and in an upward direction from the pipe, respectively, were

spaced 1 on the pipe, the next l/2 inch from the pipe, 4 at 1 in.

intervals, 3 at 2 in. intervals, and 2 at 4 in. intervals (See Fig. l)

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Temperature stations were also located on the steam traps and on

the boiler. All thermocouples were of 2^ gage copper-constantan

wire and were used with a Rubicon portable precision potentiometer

to indicate temperatures

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In order that the water table in the box might be adjusted,

six 1/2 in. diameter pipes were equally spaced along each side of

the box extending vertically from the top to the bottom. A 12 in.

length of 2 in. pipe was fastened to the top of each l/2 in. pipe

for ease in introducing water. Before the dirt was added to the box,

a 100 ft length of l/2 in. rope was placed on the bottom of the box

to provide distributing channels for the water introduced through

these vertical pipes. Two 1 in. diameter vertical pipes placed

diagonally from each other 1 ft from the side and 1 ft from either

end of the box served as wells for measuring the actual water level

(see Fig. l)

.

The 4 X 4 X 12 ft box and its necessary auxiliary parts were

set up in a specially erected building, 12 ft wide, 24 ft long

and about 10 ft high, constructed of prefabricated insulated panels.

An air chiller was placed at one end of the inside of the building

with capacity enough to freeze the contents of the box, if desired.
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The air chiller was used to hold a steady temperature in the

building when a test was in progress. The building was supplied

with a 100 ampere, 3 phase, 208 volt electric service and a l/2 in.

water line with 70 lb pressure.

The outdoor apparatus consisted of a trench about 13 in. wide,

l8 in. deep and 22 ft long. A 20 ft piece of 4 in. pipe was

supported at each end raising it 4 in. above the bottom of the trench.

Both ends of the pipe were sealed off with l/4 in. iron plates. In

one end a 3 A pipe l8 in. long was inserted through the plate

and welded to it with about 12 in. projecting into the inside of

the pipe and 6 in, on the outside. The 12 in, projection was

drilled with lA in. holes and the end was capped off to make a

side delivery steam nozzle. At the other end of the 4 in. pipe,

a short l/2 in. nipple was welded to what would be the bottom of

the pipe, and the hole drilled through the side wall of the 4 in.

pipe. A steam trap was connected to the l/2 in. nipple using

about 3 of copper tubing.

The 3 A in. pipe was tied into the steam boiler. A thermocouple was inserted in a well in the steam line at the inlet end

of the pipe and in the condensate line at the outlet end of the

pipe . A thermocouple was fastened to the pipe about 3 ff from the

inlet end and 3 ff from the outlet end.

The trench was filled with Gilsulate until there was a

minimum of 4 in. covering the top of the pipe. The trench was

then back filled with 6 in. of dirt.
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3. TEST PROCEDUEE AND RESULTS

Sintering and Consolidation Temperatures

In the laboratory^ the 9 x 9 x 24 in. box was filled during

separate tests with Gilsulate, (l) as it came from the shipping bag,

(2) after it had been soaked in a container of water, and (3) with

the unconsolidated residue that had been subjected to some heating,

from previous tests. A constant heating temperature of about 525 F,

measured at the heated end of the 1-inch pipe, was maintained for

several days in each test.

At the end of the first test an investigation of the envelope

formed around the pipe revealed the following conclusions as

presented on Fig. 2A-2B and shown on the photograph Fig. 3»

1. Estimated initial sintering temperature was about 193 F.

Material that showed sintering at temperatures lower than 226 F

was too weak to withstand gentle h.andling.

2. The minimum temperature of pipe for sintering to obtain

moderate strength and cohesiveness of the sintering annulus was 226 F.

This sintered material showed only slight fusion of particles

.

3. Glassy consolidation occurred at temperatures higher than

371 F. This material is a voidless "solidified liquid" when cool.

A thin layer of glassy material up to 1/2 in. thick was found on the

top surface of the pipe where the temperature was between 371 F and

491 F. At pipe temperatures above 491 F the material flowed from

above the pipe leaving a void and collected under the pipe. The

void was roofed with granular consolidated material with an inside
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CROSS SECTIONS INDICATED IN TIG. 2

A

SLUMP

UNCONSOLIDATED

UNCONSOLIDATED

SINTERED

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CONSOLIDATED

BOMSPtIDA' CONSOLIDATED

SECTION 8—

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film of glassy material.

4. The sintered material under the pipe, between 3OO F and

371 F slumped away slightly, leaving a gap into which a flow of

plastic material entered from the hotter end. This flow persisted

until it reached a section of the pipe whose temperature was 3 IO F.

5o Pipe temperatures greater than 444 F caused considerable

slumping of the unconsolidated granular material, due to shrinkage

as it consolidated or melted at the pipe.

The second test in this same apparatus using Gilsulate that

was soaked with water indicated that a consolidated core of glassy

material could not be obtained at the temperatures recommended

for Type B but that a sintered material only composed the envelope.

The third test using Gilsulate that had previously been heated,

but not to the point of sintering, indicated that much higher temperatures were needed to obtain a sintering and consolidation

equivalent to that observed with the original material.

The 9 X 9 X 36 in. box, with the heaters internally in the

pipe, was filled with dry Gilsulate as it came from the shipping

bag and the temperature of the pipe brought up to about 450 F for

several hours . The system was then cooled completely to room

temperature and the loose Gilsulate removed from the box, leaving

the core exposed to room air conditions . When heat was again

applied to the system the bottom half of the core dropped away from

the pipe without having been softened by the heat.

Oven Tests

Further effects of heating Gilsulate were observed by placing
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-lithe 2 X 2 X 4 in. aluminum boats random filled with Gilsulate as

obtained from the shipping bag^ into a thermostatically controlled

electric oven with shielded elements . Thirteen samples were

initially placed in the oven at room temperature. The temperature

was increased in nine steps with the temperature being maintained

constant at each successive level for 1 to 8 hours. At the beginning of each of the nine periods at constant temperature, an

additional sample at room temperature was introduced into the oven

and at the end of that period was removed with one of the initial

13 samples. The temperature of the oven was observed with a mercury

in glass thermometer mounted through a hole in the center of the

top surface.

Fig. 4 is a graphical presentation of the temperature each

sample was subjected to during the oven tests and the length of the

exposure. After the removal of the first four boxes, each removal

thereafter consisted of two boxes, one box of the original 13 , and

one box exposed to a fixed temperature for a relatively short length

of time. The exposure of each sample is listed below. For samples

1 through 13 , each sample was exposed to the temperatures of all of

the previous samples for the periods of time shown.

Specimen 1 was removed after 22 hours at 188 F

Specimen 2

tr IT ft 24 ff " 196 F

Specimen 3

ft ft !T 27 ft " 230 F

Specimen 4

»f fl ft 4o ff " 302 F

Specimens 5 & l4 were removed after 4

ft " 358 F

Specimens 6 & 15 " 8

ff " 358 F
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- 12-

Spec iaiens 7 & l6 were removed after 1 hour at 385 F

Specimens 8 85 17 "

Specimens 9 8c iQ "

Specimens 10 & 19 "

Specimens 11 8c 20 "

Specimen 12 was

Specimens I3 8c 21 were

2 hours " 385 F

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" " 401 F

" " 455 F

507 F

tt ft

The visual effect of time -temperature treatment upon Gilsulate

is shown in the photographs number 5“9> inclusive. Fig. 5 shows

that sintering took place at the 302 F temperature level with

specimen 4. Figs. 6 , 7ji 8 , 9 ^show that the initial 13 specimens

sintered but did not consolidate at any temperature up to 507 F

regardless of the length of time of exposure but specimens l4 through

21 consolidated starting at 358 F and 4 hours duration.

This series of time -temperature tests indicates that a gradual

increase in temperature changes the characteristics of Gilsulate so

that it does not flow together into a homogeneous consolidated mass,

whereas a sudden exposure for a short length of time at any temperature above 358 F causes complete consolidation, if the material has

not been previously heated.

Thermal Conductivity

The thermal conductivity of a sample of unconsolidated Gilsulate

was measured by pouring the loose material, as taken from the shipping

bag, between the plates of the hot plate apparatus and redding the

loose material to prevent voids

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Density, as tested, Ib/ft^ 39 •

2

Thickness, as tested, inch 1.00

Thermal conductivity, Btu/hr ft^(deg F/inch) O .636

Mean temperature of specimens, °F 130 •

9

Temperature gradient in specimens, deg F/inch 42.9

The thermal conductivity of the dry dirt used to cover the

Gilsulate conduit was determined in the same manner as the Gilsulate.

The loose dirt was slightly pulverized so that the largest granixLes

were not over 1/8 in. and was then poured between the plates of the

apparatus and settled by considerable rapping of the plates

.

Density, as tested, Ib/ft^ 65.5

Thickness, as tested, inch 1.01

Thermal conductivity, Btu/hr ft^(deg F/inch) 1.55

Mean temperature of specimens, °F 128.1

Temperature gradient in specimens, deg F/inch 33 *0

* Loss of weight on drying, percent 2.3

^Material was tested as received and then was air-dried after the

test to constant weight in an oven at 215 F.

Controlled Underground Tests

For underground studies of the heat transmission factor of

Gilsulate with controlled conditions the manufacturer's recommended

directions for forming the conduit were followed, and simulated

conditions of actual field use were applied in completing the investigation.

With the Gilsulate poured around the pipe and the test box filled
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vith dry dirt to a level approximately 2 feet above the center line^

steam between 325 F and 355 F was turned into the system for a period

of about one week. The steam temperature was then raised to 3^0 F for

a period of four hours after which the steam was turned off.

Fig. 10 is a graphical presentation of this time -temperature

combination used to form the consolidated core in the Gilsulate

envelope

.

After allowing the entire apparatus to cool to a steady state,

steam at 350 F was admitted to the pipe and held at that temperature

for eleven days at which time temperature stations and condensate

rate indicated a steady condition prevailed throughout the Gilsulate

conduit

,

Water was added through the stand pipes until a free water

level of 1 ft was measured in the box. The 1 ft level was maintained

until the earth on the surface about 3 ft above the free water level

became moist. Steam at 350 F was admitted to the pipe while the

1 ft water level was held constant. At the end of 22 days of

constant steam temperature and water level, a steady condensate rate

and temperatures in the conduit again prevailed.

Immediately at the conclusion of the test with a 1-foot water

table, a 1 in, core sample, from top to bottom of the test box,

adjacent to the Gilsulate conduit was taken in increments and the

percent moisture for each increment determined. A second core sample

was taken from directly over the conduit center for comparison with

the moisture content of the first core sample. The core was taken

INITIAL

CONSOLIDATION

TEMPERATURES

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in measured increments with each increment placed in a separate

weighed container. Each container and sample was weighed before

heating in an oven at 215 F again after heating when there was

no more change in weight. Fig. 11 shows the percent of moisture

to dry dirt for each increment of the two cores and the change of

moisture content with height in the test installation. The short

curve B shows the dirt to be slightly drier above the conduit than

the dirt adjacent to the conduit. The percent moisture at both

stations at the level of the top of the conduit and at the surface of

the dirt was about 5 percent, increasing to about 10 percent a few

inches above the conduit and dropping to zero percent at the pipe

level. Below the conduit the percent moisture to dirt indicated by

the core samples increased rapidly from zero at the conduit to about

38 percent at the 2 in. level. It is probable that water drained

from the samples taken below the free water level as they were being

withdrawn. Thus the 38 percent shown at the 2-in. level is probably

not representative of the actual conditions

.

The rates of condensation measured in the measuring section of

the pipe for the tests with dry dirt and with a 1-foot water level were

0.503 lb per hour for the dry dirt and O.765 lb per hour for the

moist dirt.

To determine the thermal conductivity factor, kjj^, the equation

for steady heat transfer through an annulus was used

q In ^ ^m “

, in which

2 TT L AT

q = rate of heat loss in Btu/hr for the measuring section

INCHES

MOISTURE DISTRIBUTION

TtOlt

20 30 40

PERCENT WATER TO DRY SOIL

(average per core sample)

-16-

In = logarithm to base e

To = radius at inside surface of annulus, ft

n = radius at outside surface of annulus, ft

n = 3.1^16

L = length of pipe, ft (measuring section)

At = difference in temperature measured at the two radii, °F

kjj^ = thermal conductivity factor, Btu/hr (sq ft)(°F/ft)

Substituting the appropriate values obtained from the tests of

the underground installation in the equation, the thermal conductivity factors for the Gilsulate envelope surrounded by dry

earth and moist earth are shown below. The thermal conductivity

of the dry dirt and moist dirt surrounding the conduit, expressed

in Btu/hr (sq ft)(°F/in), are also shown below based on the temperature gradient observed in the dirt and assuming that the above

equation is applicable approximately to this case.

Gilsulate surrounded by dry earth, = 1.335 Btu/hr (sq ft)(°F/in)

Gilsulate surrounded by damp earth, kfn = 1*^1^ " " ” " " "

Dry dirt surrounding Gilsulate, kjjj = 2.73 " " " " " "

Moist dirt surrounding Gilsulate, kjj^ =10.03 " " " " " "

Fig. 12 shows the average temperature in the Gilsulate and

earth at the midpoint of the measuring section plotted against the

ratio of the distances to each station and to the pipe surface as

measured from the center of the pipe. The interface between the

Gilsulate conduit and dirt lay between the 3-l/2 in. and 4-l/2 in.

stations . The curve through the dry and moist dirt is a straight

temperature.

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line in Fig. 12 on semi-log paper indicating steady conditions and

a uniform material, and a uniform rate of change of temperature with

the logarithmof the distance from the pipe. While the curve for the

Gilsulate conduit in Fig. 12 approaches a straight line yet, there

is deviation from a straight line indicating a difference in the

thermal conductivity of the material, especially near the pipe,

where a consolidation of some thickness was expected to exist.

Water was again added to the box until the 2 ft level above

the bottom of the box was reached. At this height the water level

was midheight of the 4 in. pipe and Gilsulate conduit. With all

temperature in the system initially at room temperature steam at

350 F was admitted to the pipe and 15 minutes later the inlet and

outlet pipe temperatures were 235 F and I3I F, respectively. Six

hours later the temperatures were 239 F and I80 F, respectively.

3 days and 6 hours after starting the test the temperatures were

230 F and 224 F at the inlet and outlet of the pipe. During this

time the boiler was using maximum energy input, the condensate

rate from the measuring section was averaging 12. 3 lb per hr and

the pressure could only be maintained a little above atmospheric

pressure. Temperatures taken 3 in. below the surface of the dirt

or about I6 in. above the conduit surface and centered over the

conduit ranged from l4o F to l44 F with the ambient temperature at

about 75 F

Water was again added to the box raising the water level to

3 ft from the bottom which completely covered the conduit . Steam at

-18-

350 F was admitted to the pipe and one hour later the inlet and

outlet pipe temperature read 2l8 F and 205 F. This drop in temperature took place with full energy input to the boiler and 5 days

later the temperatures were 221 F and 2lU F and the pressure was

only slightly above atmospheric

Lowering the water level below the conduit caused an immediate

increase in pipe temperature indicating that the conduit was drying

out whereas an increase in the height of the water level to cover

the conduit caused an immediate drop in pipe temperature to about

that of boiling water at atmospheric pressure.

Figs. 13, l4 and 15 show the temperatures observed at equal

distances from the pipe in downward, lateral and upward directions

when the conduit was surrounded with dry dirt, and ^nith moist dirt

and three levels of the water table in the box. The measured rate

of condensate for the four-foot measuring section with dry dirt was

0.50 lb per hr; with the 1 ft water level, O.76 lb per hr^ and with

the 2 ft and 3 water levels, about 12 lbs per hr with the boiler

at full capacity.

Fig. 16 is a photograph of the Gilsulate conduit as it was

being removed from the box after the tests were complete. The

Gilsulate had sintered completely, with a relatively thin layer of

glassy consolidated material surrounding the pipe. There was no

evidence that the consolidated Gilsulate adhered to the pipe.

Fig. 17 is a photograph of three pieces of the conduit showing the

surface that was in contact with the pipe (large center piece) and

12

FROM PIPE

FIG. 13

INCHES

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DISTANCE FROM PIPE. INCHES

FIG. 15

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the cracks that were observed on all pieces adjacent to the pipe.

The upper left piece shows the narrow band of consolidation; the

lower left piece shows the amount of sintering that occurred on the

surface of the conc^uit. The entire conduit broke up into chunks

resembling coke in appearance as it was removed, revealing an

extensive system of cracks and fissures in the Gilsulate envelope

as indicated in Fig. l6.

Trench Tests

For the outside installation of the 20 ft pipe in a trench

18 in. deep and about 13 in. wide, the Gilsulate was moistened

before it was placed around the pipe in the manner recommended by

the manufacturer. The empty paper bags were used to cover ten feet

of the conduit before backfilling with dirt. Thermocouples were

peened into the pipe about 3*5 ft from either end, and in the same

plane on the surface of the Gilsulate and 1 in. below the surface.

Steam at a temperature of about 375 F was turned into the pipe

to consolidate an inner core. After four hours the steam was turned

off and the system allowed to cool for several days . When steam

was again turned into the pipe, the temperature was limited to

352 F automatically.

During the next three weeks a series of heating and cooling

and wetting cycles took place. The time of heating and the time

of cooling varied from one to three days and the amount of water

added varied from complete flooding of the trench to a mild wetting.

Each time the water table was raised, when the pipe was being heated

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steadily, the holler temperature would drop from 350 F to about

212 F at full energy input. As the water table was lowered the pipe

temperature and boiler temperature would increase. Fig. l8 is a

photograph showing the conduit at the inlet end. The glassy consolidation near the pipe is hardly discernible^ most of the core being

a tightly sintered material. Fig. 19 is a photograph of the

outlet end of the pipe showing the cracks in the portion of the

conduit that was covered with paper.

A second installation was m^de using dry Gilsulate as it came

from the shipping bag and curing it immediately after it was

installed at 375-380 F for four hours. After the four hour curing

time the steam temperature was reduced to 352 F and held for 65 hours.

As the steam temperature was being reduced a small hole, large

enough for observation purposes, was dug through the Gilsulate to

the pipe. A second sampling and inspection was made 17 hours later

and a third sampling made 40 hours after the first one.

The first sampling revealed a soft sticky plastic about 3A"

thick adjacent to and adhering to the pipe. The second sampling

and inspection revealed a settlement groove along the center line of

the conduit on the outside surface and the Gilsulate near the pipe

was a sticky plastic with a hard crust on the outside. The third

sampling revealed a coke-like substance on top of the pipe, a

void space at the side of the pipe and apparent filling of a void

at the bottom.

After cooling for 72 hours, about 4-l/2 ft at the inlet end
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vas freed of all loose material leaving the rigid core exposed.

Steam at a temperature of 350 F was admitted to the pipe. As the

pipe and envelope warmed up, a longitudinal crack opened up on the

top of the core followed by a similar one on the side. On adding

water to the trench where the core was exposed for 4 to 5 feet,

vapor was observed about as soon as the water touched the conduit.

By the time the water was level mth the center of the pipe the

boiler steam temperature had dropped to about 212 F. Fig. 20 is a

photograph showing the exposed hard core and the cracks that developed

in it.

Chromatographic Analyses

Four samples of Gilsulation were analyzed chromatographically

and are listed as follows:

No. 1 "Raw". Proposed for use between 300 and 385 F.

This sample is representative of the material as

received before subjection to field test.

No. 2 "Heated". This sample represents No. 1 after

subjection to field test in which steam line was

at 350 F.

No. 3 "Severely Heated". This sample represents No. 1 after

subjection to field test in which steam line was at

380 F.

No. k "Raw No. 2". This sample represents the material

submitted by the supplier after completion of the

referenced field tests. This material proposed as a
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replaeement for Sample No. 1 with the claim it was

definitely known to be Type B.

Chromatographic Analysis of Gilsulate

Sample No. 1 2 3 4

Coke residue, ^ 17.4 19.6 20.8 16.1

Volatile Loss,

^ 0.2 1.1 2.1 --

. (? Composition, %

Asphaltenes 79.2 88.8 97.6 78.2

Water-White Oils 2.6 1.4 0.8 3-0

Dark Oils 8.3 3.7 0.8 6.1

Asphaltic Resins 9.9 5.1 1.2 11.0

Chloroform Desorbed 0.3 0.2 trace 0.9

Total 100.3 99.2 100.4 99.2

Ratio; Asphaltenes to Petrolenes

3. 8/1.0 7. 9/1-0 41/1.0 3. 6/1.0

A.S.T.M. Method DI68-3O

^ 2k hours at kOO F

N.B.S. Method RP2577.

Ordinarily, the hardness of a bituminous substance can be

measured by determining either its consistency or softening point,

or both. Unfortunately, the characteristic hardness and intumescent

(swelling and increase in volume caused by application of heat)

properties of gilsonite made the determination of either softening

point or consistency impractical. An indirect method such as coke
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-23-

residue at 1750 F vas used. The results revealed that a progressive increase in coke residue, and therefore hardness, had

occurred during the field tests

The asphaltenes were hard, brittle, black solids which

intumesce on heating. The petrolenes (combination of water white

oils, dark oils and asphaltic resins) act as dispersing media for

the asphaltenes and are believed to impart fusibility to the bitumen.

In general, the lower the ratio of asphaltene to petrolenes the lower

will be the softening point and therefore the more easily fusible

will be the bitumen. These ratios for the samples marked No. 1

and No. 4 were 3«8/l-0 and 3»6/l.O. While the behavior during the

test for volatile loss and the lower ratio of asphaltene to

petrolene indicate improved fusibility of sample No. 4 over sample

No. 1, it is doubtful whether the improvement would be significant.

Studies at the National Bureau of Standards and other laboratories have shown that 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

Sample No. 1 showed as much as an increase in asphaltenes

content and a corresponding 86.5^ decrease in petrolenes content,

after exposure to field tests as sample No. 3* Since the volatile

loss after 24 hours of exposure to 400 F was 2^, compared with

0.2^ volatile loss of No. 1, it can be assumed that the changes

which occurred during the field tests were due to changes in composition rather than to volatilization losses.
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-24-

4. DISCUSSION AND CONCLUSIONS

The laboratory and simulated field tests of Type B Gilsulate

indicated the following conclusions about the material tested;

(a) The characteristics of Gilsulate change when heated. When

dry Gilsulate is heated rapidly it sinters at a temperature

of about 225 °F and consolidates at a temperature of about

360 °F to 370 °F. When dry Gilsulate was heated slowly it

sintered but did not consolidate at temperatures up to 50? °F.

(b) Wetting Gilsulate before heating inhibits consolidation.

(c) Gilsulate is intumescentj i.e. it swells and increases in

volume as a result of the application of heat

(d) Gilsulate cracks during repeated heating and cooling,

(e) A hard consolidated core is not always formed upon heating.

The Gilsulate does not soften upon heating except during the

initial curing process

(f) Gilsulate does not adhere to steel pipe for the most part

after initial curing and consolidation.

(g) Gilsulate does not resist penetration of water after being

heated and cooled down.

(h) The thermal conductivity of raw granular Gilsulate is about

0.64 Btu/hr (sq ft)(°F/in) at a mean temperature of 130°F.

The thermal conductivity of a sintered and consolidated

envelope of Gilsulate on a steam pipe is about 1.33 Btu/hr

(sq ft)(°F/in) in dry earth and only slightly higher in damp

earth because it is essentially non-hygroscopic

- 25 -

(i) A Gilsulate envelope on a steam pipe permits water to

come in contact with the pipe when the water table is at

the level of the pipe or higher resulting in high condensation rates and possible corrosion.

These findings indicate that Gilsulate might be an economical

and useful insulation for underground steam lines in dry climates

where the water table does not reach the level of the pipe. In

areas where the water table reached the level of the pipe Gilsulate

insulation would permit high condensation rates and might not protect

the steam line against corrosion.

THE NATIONAL BUREAU OF STANDARDS

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

3, 1901, 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

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

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publications should be addressed to tbe Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.
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