NATIONAL BUREAU OF STANDARDS REPORT

NIBS PROJECT NBS REPORT

1003-12-10431 March 22, I960 6691

THERMAL CONDUCTIVITY OF UNIBESTOS PIPE INSULATION

Manufactured by

Union Asbestos and Rubber Company

Bloomington, Illinois

by

T. W. Watson

and

P. R. Achenbach

to

Bureau of Yards and Docks

Office of the Chief of Engineers

Headquarters, U.S. Air Force

Washington, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ST, intended for use within the l to additional evaluation and r listing of this Report, either I the Office of the Director, Na

however, by the Government

to reproduce additional copie

rogress accounting documents Approved for public release by the mal| y published it is subjected

Director of the National Institute of ion js obtained in writing from Standards and Technology (NIST) Such permission is not needed, on October 9, 2015. pre Pared if that agenc ^ wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

THERMAL CONDUCTIVITY OF UNIBESTOS PIPE INSULATION

by

T. W. Watson and P. R. Achenbach

Introduction

As a part of the Tri-Service studies of insulation for underground

heat distribution systems, three separate tests were made of the thermal

conductivity of Unibestos Pipe Insulation manufactured by the Union Asbestos and Rubber Co., Bloomington, Illinois. The several tests were

made to investigate the variability of the material between specimens,

the variability of the thermal conductivity from the interior to the ex- terior surface of a given specimen, and the temperature coefficient of

the thermal conductivity.

Materials

The specimens for the tests were cut from 2 lengths of Unibestos Pipe

Insulation obtained from the manufacturer and identified as follows:

Sample A - Unibestos pipe insulation, 4 in. i . d . , 10 in. o. d . , 36 in. long

Sample B - Unibestos pipe insulation, 8 in. i.d., 18 in. o. d. , 36 in. long

The shipping carton was marked: "No. 1200 Unibestos Pipe Insulation, Grade 3, Class F, 3 ft, Pipe Size 8, Thickness 5,

Navy, Carton 121 Code No. 9906112-675." The overall dry density of a half section of this sample was 15.0 lb/ft^.

Specimens

Flat specimens with dimensions of 8 x 8 inches and about 1-inch thick

ness were cut from the samples for the three series of tests. The origins

location of the specimens in the cylindrical samples are further described

as follows:

Series 1 - The two pieces were cut with one face substantially tangent to

the inside surface of Sample A.

Series 2 - The two pieces were cut with one face substantially tangent to

the cylindrical surface of radius one inch greater than the

inside radius of Sample B. This pair of specimens is identified as B-0 in Table 1.

- 2 -

Series 3 - The attached photograph shows the juxtaposition of the pairs

cut from Sample B to yield three pairs of 8- inch square test

specimens, numbered 1, 2, and 3 in outward progression from

the center of the sample. The inner surface of Specimen 1 was 3/16 in. from the inner surface of the sample; the suc- cessive specimens were contiguous, but separated by the 0.06-in.

width of the sawcut. The specimens numbered 1, 2, and 3 in

the photograph are identified as B-l, B-2, and B-3, respectively, in Table 1.

Procedure

The thermal conductivity of the specimens was measured in an 8-inch

guarded hot-plate apparatus conforming with the requirements of Fed. Spec.

LLL-F-321b and of ASTM C177-45. The specimens were air-dried to constant

weight in an oven at 215°F immediately prior to the conductivity measurements. The pair of specimens taken from Sample A was tested at mean temperatures of about 74°F and 129°F, whereas the specimens taken from Sample B for Test Series 2 and 3 were tested only at the higher mean temperature.

Test Results and Discussion

The results obtained during the 3 series of tests are summarized in

Table 1. The values of thermal conductivity at two mean temperatures for

Specimen A indicate that the temperature coefficient of conductivity a,p , defined by the equation k t = k-pCl + a^Ct - T)), is 0.00066 at T = 129°F,

for this specimen.

It will be noted in Table 1 that the density, as tested, of the five

different insulation specimens. A, B-0, B-l, B-2, and B-3, ranged from

10.9 to 16.3 lb/ft^, a variation of 42 percent of the mean value for the

five specimens. The density of Specimen A, one face of which was tangent

to the inside surface of the cylindrical Sample A, was the highest; and

the density of Specimen B-l was next to the highest. One surface of

Specimen B-l was tangent to a circle with a radius only 3/16-inch greater

than that of the inner surface of the cylindrical sample. The increase

in density near the inner surface was believed to be caused by a greater

concentration of silicate in this zone resulting from the method of manufacture.

In the five tests made at a mean temperature of about 129°F, the

thermal conductivity values, as shown in Table 1, ranged from 0.323 to

0.408 Btu/hr (f tj (deg F/inch), a maximum variation of about 24 percent

-3-

of the mean value for the five tests. The thermal conductivities of the

five different specimens were not directly proportional to their density.

If the five values obtained at the same mean temperature in tests 1, 3,

4, 5, and 6 are corrected to a common density of 15 lb/ft^ by direct proportion, the maximum variation in the resulting computed thermal conductivities is about 29 percent of the mean of the five values.

It should be rioted that the densities of Specimens B-l, B-2, and B-3

were all appreciably below the average dry density of 15.0 lb/f t^ observed

for the half-cylinder from which they were taken. This indicates that the

material in the half-cylinder, not represented by the three pairs of specimens, was considerably more dense than the portions comprising the samples, even though the specimens represented a major part of the cross section of

the half-cylinder.

The variability in thermal conductivity revealed by these test results

indicate that a method for measuring the average thermal conductivity of a complete cylindrical section of insulation might be preferable for materials of this type even though the fit of the specimen on the test cylinder introduces a problem in such an apparatus.

v

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The

average

density

of

one

of

the

halves

of

Sample B

was

measured

as

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lb/ft^

undried,

corres

ponding

to

about

15.0

lb/

ft^

in

an

oven-dried

condition.

1