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NATIONAL BUREAU OF STANDARDS REPORT

$*. r/s ed.

7818

THERMAL CONDUCTIVITY OF A SAMPLE OF

TYPE 316 STAINLESS STEEL

by

Thomas W. Watson and Henry E. Robinson

Report to

Applied Physics Laboratory

Johns Hopkins University

Silver Spring, Maryland

<^b|>

U. S. DEPARTMENT OF COMMENCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STAIM!)ARDS REPORT

NBS PROJECT NBS REPORT

1006-30-10642 March 22, 1963 7818

THERMAL CONDUCTIVITY OF A SAMPLE OF

TYPE 316 STAINLESS STEEL

by

T, W. Watson and II, E. Robinson

Heat Transfer Section

Building Research Division

to

Applied Physics Laboratory

Johns Hopkins University

Silver Spring, Maryland

NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, thi whole or in part, is not author Bureau of Standards, Washingt

the Report has been specifically

IMPORTANT NOTICE

ss accounting documents intended Approved for public release by the subi ected t0 additional evaluation Director of the National Institute of e Office of the Director, National Standards and Technology (NIST) the Government agency for which on October 9,2015. opies tor its om> use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Thermal Conductivity of a Sample of

Type 316 Stainless Steel

by

Thomas W. Watson and Henry E. Robinson

1.

INTRODUCTION

This report presents results of thermal conductivity measurements

in the temperature range 90° to 850°C of a sample of fully-annealed

Type 316 stainless steel submitted by the Applied Physics Laboratory,

Johns Hopkins University, Silver Spring, Maryland.

2

.

SAMPLE

The sample submitted was a bar about 2.54 cm in diameter and 46.0

cm long, from which the test specimen was machined to a uniform diameter

of 2.54 cm and a length of 37.0 cm.

The chemical composition and mechanical properties of the specimen

are given in Table 1, as supplied by the Applied Physics Laboratory, on

the basis of a chemical analysis made by Joseph T. Ryerson & Son, Inc.

The steel was identified as Alleghany Heat No. 327268.

3.

TEST APPARATUS AND METHOD

The thermal conductivity of the sample was determined by means of

a steady-state flow of heat longitudinally in a bar specimen, with measurements of the temperatures existing at the ends of six consecutive,

approximately 3.51-cm, spans along the central length of the bar. Each

determination required a pair of tests at moderately different temperature conditions, and yielded values of thermal conductivity at six different mean temperatures.

The test apparatus is shown schematically in Figure 1.—

The specimen, a bar approximately 37 cm long and of uniform external dimensions over the metering length, was supported at the top

(coolant) end concentrically within a stainless steel guard tube of

0.8-cm wall thickness, which in turn was held concentrically within a cylindrical outer container. The specimen was drilled at each end with

a 1.35-cm hole 5.5 cm deep. An electrical heater was inserted and se- cured in the hole at the bottom (hot) end, and the supporting fixture

at the top end provided a liquid-tight connection for circulating a coolant through the top drill-hole.

iy See: "Thermal Conductivity of Some Commercial Iron-Nickel Alloys,"

by T. W. Watson and H. E. Robinson (Trans. ASME(G), 83, 403-408, 1961).
- 2 -

Temperatures along the specimen were indicated by seven thermocouples located symmetrically about the longitudinal center of the specimen, spaced approxima tely 3,51 cm apart, with one additional thermocouple

near the bottom end of the specimen. Thermocouples were similarly located in almost exactly corresponding longitudinal positions on the guard

tube

.

The guard tube was equipped near its lower end with two external,

circumferential electric heaters, as shown. The guard tube was cooled at

the top by means of a copper -tube coil soldered circumferentially at a position corresponding in effect to that of the specimen coolant well.

Coolant (water at 40°C) was pumped through the guard coil and specimen

well in series connection, as shown.

The electrical heater for the specimen consisted of a porcelain

cylinder 1.25 cm in diameter and 5.2 cm long, threaded longitudinally

with 26-gage nichrome heater wire. Its resistance was approximately 22

ohms. Current was brought to the heater through relatively large heater

leads, to which separate potential leads were connected at the point

where they entered the porcelain core. The heater was energized by an

adjustable constant-voltage d~c source. Heater current and voltage

drop measurements were made using standard resistors and the high precision manual potentiometer used for thermocouple observations. The

guard was heated with alternating current governed by a sensitive temperature controller actuated by the guard temperature at a selected

position

.

The thermocouples were made from calibrated platinum: platinum- 10%

rhodium 15-mil wires, welded by gas-oxygen flame to form a butt joint

about 0.042 cm in diameter.

The thermocouple junctions were pressed into transverse grooves

0.04 cm wide by 0.05 cm deep and 0.6 cm in length in the convex surface of the bar and tightly secured by hammering the metal around the

groove. The bare thermocouple leads were individually brought out in

the powder insulation in the same transverse plane as the junction (one

wire in each direction around the bar) forming a 4-cm circle. The wires

were then insulated with alumina tubing, and in cooler regions with

fiberglas sleeving, and brought out through the powder insulation near

the guard tube. The thermocouples in the guard tube were electrically

welded to form a spherical junction about 0.10 cm in diameter. The

junctions in the guard were inserted into radially-drilled holes 0,11

cm in diameter and 0,17 cm deep, and tightly secured by punch-pricking

the metal around the hole. The wires were similarly brought out through

the powder insulation. The longitudinal positions of the thermocouple

junctions were taken as those of the centers of the grooves, or of the

drilled holes, measured to the nearest 0.01 cm with a laboratory

ca thetometer

.
- 3 -

After installation of the specimen, the space between it and the

guard tube was filled with alumina powder insulation, which also was

used to insulate the space surrounding the guard tube. The tests were

conducted with the insulation exposed to atmospheric air.

In principle, if there were no heat exchange between the specimen

and its surroundings, the conductivity could be determined from the

measured power input to the specimen and the average temperature gradient for each of the six spans along the specimen, all of uniform known

cross-sectional area. In practice, a perfect balance of temperatures

between the bar and guard all along their lengths is not possible because of differences in their temperature coefficients of conductivity,

and the effect of the outward heat losses of the guard. In addition to

heat exchanges between the bar and guard from this cause, a relatively

insignificant longitudinal flow of heat occurs in the powder insulation

surrounding the specimen, and the contribution of the specimen to this

heat flow must depend somewhat on the bar-to-guard temperature unbalance.

In order to evaluate the heat flow in the bar at the center points

of each of the six spans, a partly empirical procedure was used. Two

steady-state test-runs were made with slightly different bar and guard

temperatures and power inputs. In the two tests, the heat flow and the

observed temperature drop from end to end of a given span differed, as did also the approximate integral with respect to length of the observed

temperature differences between bar and guard, summed from the hot end

of the bar to the span center point. It is thus possible to write for

each span two equations (one for each test -run) of the form

fS

Ax

Q

where A is the cross-sectional area of the specimen,

k is the specimen conductivity at the mean temperature of the

span.

At is the temperature drop from end to end of the span,

Ax is the length of the span,

fS represents the total net heat loss from the bar from its bottom

end at the heater to the midpoint, x, of the given span, expressed as the product of S, which is the integral J*o ^bar ~ tguard)^x » and an average heat transfer coefficient f for the

thermal path from bar to guard.

Q is the measured power input to the specimen heater.
-4-

The two equations written for each of the six spans of the bar can

be solved simultaneously to determine k and f. For this to be strictly

valid, k and f must have equal values in the two equations. Since the

mean temperatures of the span in the two tests will in general differ

slightly, and the conductivity of the bar may vary with temperature, a slight adjustment is made to the observed values of At so that k corresponds to the mean of the span mean temperatures in the two tests, The

equality of f in the two tests is not so readily assured, but because

the magnitude of fS in these tests was generally on the order of 5 percent of Q, a moderate difference in the values of f in the two equations

would affect the solved value of Ak/Ax only slightly 0

The computation of results directly from the observed data was

effected by an IBM 7090 digital computer suitably programmed to compute

the thermal conductivity and the corresponding mean temperature for each

of the six spans, The computer was used to fit a third-power equation

to the thermal conductivity and temperature results, by the method of

least squares,

4, RESULTS

The results of the thermal conductivity determinations are shown

in Figure 2 and Table 2, The 30 individual values of thermal conductivity plotted represent five sets of tests, each with values for the six

spans. The solid line represents the trinomial fitting the data, as determined by a digital computer, from which the values tabulated in

Table 2 were taken. The trinomial equation obtained is

k = 0.1333 + 0.1727 0.04334(^^00)

2 + 0„0332(Tjj5o ) 3

with k in w/cm C, T in °C (90 < T < 840), The standard deviation of the

departures of the thirty data points from the trinomial equation is

0,001595 w/cm C, The extreme departure of an individual data point

from the smooth curve (at 300°C) is less than 3 percent,

5, DISCUSSION OF RESULTS

The conductivity values obtained for this sample are about 8 percent higher at 100°C, and 2 percent higher at 700°C, than values reported

in NBS Report 5748 (January 1958) for two specimens of another Type 316

sample made by a different manufacturer. The present sample contained

less silicon (0,567, versus 1,27,), The value inferred for the present

sample at 0°C (0,134 w/cm C) compares with the value 0,133 at 0°C given

by Tyler and Wilson, 1952 (NBS Circular 556, pp43 , 44), for Type 316

stainless steel.
-5-

Mn

TABLE I

Chemical Composition

P S Si

- Percent

Ni Cr

0*058

Mo

1.50 0*022 0.019 0.56 13.36 17.51 2.44

Tensile

P si. . .

Mechanical Properties

Yield

psi

Elongation

percent

Reduction

of Area

percent Hardness

80,200 45,700 60 65.6 BHN 143

TABLE 2

Thermal Conductivity of _a Sample of

Type 516 Stainless Steel

°c Watt/ cm°C

90 0.149

130 0.155

170 0.162

210 0.168

250 0*174

290 0*181

330 0.187

370 0.193

410 0*199

450 0.205

°C Watt/ cm°C

490 0.211

530 0.218

570 0.224

610 0*230

650 0.236

690 0.243

730 0.249

770 0*256

810 0.262

850 0*269

US COMM-NBS -DC

370

COOLANT

APPARATUS FOR MEASURING THE THERMAL CONDUCTIVITY OF METALS

Fig 1
THERMAL

CONDUCTIVITY

OF

A

SAMPLE

OF

316

STAINLESS

STEEL
U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

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

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[

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I