NATIONAL BUREAU OF STANDARDS REPORT

6367

A STUDY OF THE CAUSES -OP FAILURE OP THE BUHNERS

AND UPPER AIR TUBES IN THE ARMY TENT STOVE

by

Selden D, Cole

and

Paul R, Achenbach

Report to

Mechanical Engineering Division

Headquarters,

Quartermaster Research and Engineering Command

Natick, Massachusetts

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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3, 1901, as amended b) Congress in Public l.aw 619, 19S0. These include the development and

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

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problems; invention and development of devices to serve special needs of the Government; and the

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

NBS PROJECT

1003-20-4885 April 10, 1959

NBS REPORT

6367

A STUDY OF THE CAUSES OF FAILURE OF THE BURNERS

AND UPPER AIR TUBES IN THE ARMY TENT STOVE

by

Selden D. Cole and Paul R, Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Mechanical Engineering Division

Headquarters,

Quartermaster Research and Engineering Command

Natick, Massachusetts

IMPORTANT NOTICE

NATIONAL BUREAU OF

intended for use within tl to additional evaluation ar listing of this Report, eith the Office of the Director, however, by the Governme

to reproduce additional cc

r progress accounting documents Approved for public release by the Nrmaiiy published it is suojected

Director of the National Institute of -jission is obtained in v/riting from Standards and Technology (NIST) • Such permission is not needed, on October 9, 2015.

prepared if that agency wishes <NB^

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

A STUDY OF THE CAUSES OP FAILURE OP THE BURNERS AND

UPPER AIR TUBES IN THE ARMY TENT STOVE

by

Selden D. Cole and Paul R, Achenbach

ABSTRACT

A study of the causes of failure In the vaporizing pot

burners and upper air tubes used in the MI94I Army tent stove

was made for the Quartermaster Research and Engineering Command,

A group of pot burners made of low carbon steel except for the

low fire ring and combustion ring were operated until failure

occurred by oxidation and other groups having some components

of stainless steel and some of low carbon steel in various combinations were operated for a period of 3OOO hours at a firing

rate above the recommended value for the stove. New upper air

tubes from three procurements of commercial tubes by the QMR&E

Command, others from an experimental batch cast by the QMR&E

Laboratory, and others cast by the NBS foundry; and used upper

air tubes submitted by Jeffersonville Quartermaster Depot as

having been discarded, were subjected to prolonged operation at

normal and excessive firing rates and to extreme thermal shock

conditions to determine the factors causing the prevalent deformation of the tubes by bending that had been reported in field

use. The tests showed the desirability of using stainless

steel in the vaporizing pot burners for the combustion ring,

the burner support ring, the low fire ring, the air casing,

and the wall of the pot above the low fire ring to resist oxidation at high temperature. It was further shown that the

commercial upper air tubes could be operated in excess of 4QQC

hours at firing rates up to 24 ml/min without deformation. Three

tubes deformed by bending after operation at firing rates of

35 ml/min or higher for periods ranging from a few hundred

hours to 3OQQ hours. At this firing rate the center of the

tube operated at a temperature between I3QC°F and l4CQ°F which

is near the transformation temperature for gray cast iron. All

the deformed tubes were eccentric between inner and outer surfaces, but not all the eccentric tubes used for the tests deformed. Microstructures of the deformed tubes indicated that the

thinner side of the deformied tubes m.ight have reached a higher

temperature than the thicker side. A discussion of the possible

causes of deformation is included and some recommendations regarding composition of the upper air tubes, materials for the burner

pots, and oil control valve design have been made.
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I. Introduction

At the request of the Quartermaster Research and Engineering Command, Natick, Massachusetts, a study was made of the

Flame Spreader (Upper Air Tube) of the vaporizing pot burner

in the Army tent stove M1941 to determine the cause of reported

deformation of this component in field use. The gasolineburning MI941 tent stove is used for space heating in temporary and semi-permanent military housing over a wide geographical area. Failure of the upper air tube incapacitated the

stove and contributed to the 'destruction of the pot burner,

thus multiplying the problems of Immediate replacement in the

field. It had been reported that the stock upper air tube of

the MI941 tent stove did not have a service life commensurate

with that of the stove burner.

The objectives of this study were as follows:

(1) To determine by laboratory tests of the stove,

the service life of four groups of upper air

tubes supplied by the Quartermaster Research

and Engineering Command, using three firing

schedules, and

(2) With the guidance obtained from these results

and from metallurgical tests, to determine and

recommend material or materials for the upper

air tube that would yield a satisfactory service

life, taking into consideration the following

factors

(a) Producibllity by either large or small

foundries;

(b) Probable availability of materials under

the restrictions of wartime;

(c) Machinabillt y of the part; and
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After completing the laboratory tests outlined above and

after obtaining information on the availability of castings from

a group of small and medium-sized foundries^ the study was extended to include the following three tasks:

(1) To operate twelve pot burners with selected components

of stainless steel and low carbon steel for a period

of 3000 to 4000 hours at high fire;

(2) To operate twelve upper air tubes representing a range

of chemical composition proposed by the National Bureau

of Standards for a period of 2000 to 3OOO hours.

These specimens were to be cast in the experimental

foundry of the National Bureau of Standards; and

(3) To make appropriate metallurgical examinations of the

pot burners and upper air tube specimens at the beginning and periodically during the life tests.

II. Description of Test Specimens

The upper air tubes used for the tests came from the following sources.

(1) Twelve tubes were sent initially from the Quartermaster

Research and Engineering Command at Natick^ Mass.

These were commercial samples from three different

batches of upper air tubes procured during recent years

under the existing specifications.

(2) Five new tubes from a group cast at the QMR&E laboratories for experimental purposes.

(3) Twenty- five used tubes furnished by the Jeffersonville

Quartermaster Depot on request^ as representing tubes

that were no longer satisfactory for use.

(4) Thirty-six new tubes of three different compositions

cast at the National Bureau of Standards experimental

foundry to represent a range of carbon and silicon

content

.

-3-

The shape of the upper air tube is shown by the vertical

cross section in Fig. 1. It was 7 1/8 inches high; the vertical

column was about 1 1/2 inches in diameter; and the flame spreader

at the top was 3 inches in diameter and 3/‘4-inch in vertical

dimension. The sidewalls of the tube were about 3/l6-inch thick.

The holes near the top of the center column were 1/4-inch in

diameter and the slot in the cap was 9/32-inch wide. Pour cast

pins connected the top of the cap to the remainder of the tube.

The base of the tube was bored to provide a good fit over the

air inlet tube in the center of the oil burner pot.

Twenty four experimental pot-type burners were submitted

for the latter part of the study. Various combinations of low

carbon steel and stainless steel components miade of two thicknesses of sheet metal were fabricated to provide six burner

styles. The combinations and identification of the six styles

are summarized in Table 1. It will be noted'' that the air casing

was of l8 gage low carbon steel in all styles^ and that the

low fire rlngj combustion ring,, and burner support ring were

of 20 gage stainless steel in all styles. The other three components varied in material or thickness in the various styles.

Ill, Test Apparatus and Procedure

The operational tests were conducted in a special building

designed to Incorporate specific fireproof and explosion-proof

features. Except for wood doors,, the structure employed only

galvanized sheet steel and cement asbestos board components.

The building was about 50 feet long and 16 feet wide with

walls 10 feet high and a sloping roof reaching to a height of 13

feet at the ridge. An 8-foot space at one end was created by

a f loor-to-roof metal dividing partition and metal exterior

walls to serve as an observation room. The two side walls of

the testing space were made of cement asbestos boards lightly

secured to the framing so an Internal explosion could be readily

relieved. The end wall was of metal. An opening 8-in. high

was left both at the floor level and eave height to provide

copious ventilation. A 2-foot wide opening was left at the ridge

and this opening was covered with a hood 1 foot above the roof.
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The large floor space was divided into three equal areas^

approximately l4 ft by 16 ft, by two 4 ft by 8 ft sheets of

galvanized sheet steel serving as radiant shields between adjoining sections. These shields were suppbrted lengthwise

8 Inches above the floor, as shown in the foreground in Pig. 2,

allowing a passageway 4 ft wide at each end of the shields.

Each of these three spaces was divided into four cells

by supporting a piece of sheet metal four feet square on each

side of a square center post leaving a clearance of 8 inches

between the floor and the lower edge of each sheet. This division

of the floor space provided twelve cells each with a gross floor

area of 7 ft by 8 ft. When one of the specimen stoves was

supported 8 inches above the floor and one foot from the sheets

affixed to the center post in each cell, it was radiantly

shielded from each of the other eleven stoves. The stovepipe

of all twelve stoves terminated inside the structure just

beneath the ventilating cap at the ridge of the roof. The compartmentatlon of the building can be seen in Fig. 2. Fig. 3 illustrates one of the stoves mounted in the corner of one of

the twelve cells.

A battery of twelve float valves mounted on the outside of

one of the sidewalls metered the fuel to the twelve stoves.

Fuel was supplied to these float valves through a single line

from a storage tank located some distance away and at a higher

elevation to provide gravity feed of the fuel. A solenoid

valve and shut-off valve, was located upstream of each float

valve in that order. An additional solenoid valve was located

in the main fuel line. A vertical burrette was connected to

a tee in the fuel line between the float valve and solenoid

valve for each stove. These burrettes could be filled from

the supply line and then isolated from the supply by the shutoff valve. By allowing the burrettes to empty through the

float valves the rate of fuel supply to each stove was measured

Independently. Four of the float valves were controlled by a

time clock which energized rotary actuators to alternate the fuel

supply rate between high and low rates. The fuel metering system

and rotary actuators are shown in Fig. 4.

The interior of the structure was equipped with six photoconductive cells sensitive to the flicker of a hydrocarbon flame,

such that each pair of adjacent stoves was monitored by one

cell. When the unsteady flame of the burning gasoline was viewed
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by one of these cells it actuated a relay to close the solenoid

valves in all of the fuel supply lines.

The fuel used for the tests was an 80-octane leaded gasoline .

IV. Two Thousand Hour Operational Test of Upper Air Tubes

The twelve commercial upper air tubes received from the

QMR&E Command representing three procurements under existing

specifications were operated for 2000 hours or more using

three different firing schedules. The identification numbers

of the twleve stoves and the twelve tubes are shown in Table 2.

Four of the stoves were operated continuously at a high

fire fuel rate of 24 ml/mln, four others were operated continuously at a low fire fuel rate of about 8 ml/min^ and the

_

remaining four were cycled every 2 hours between these two

rates of fuel flow. The fuel rate for each stove and upper

air tube is shown in Table 2 along with the total duration of

the test.

Table 2

Fuel Rate

Stove number Air Tube number ml per min Total hours burned

1 23926-10

2 23926-6

3 23926-4

6 23926-8

8 22981-10

9 23926-3

10 23926-11

11 23926-12

13 23926-9

16 23926-5

24 23926-1

30 24490-8

24 2173

24 2176

24 2238

24 2261

8-24 2008

8-24 2034

8-24 2054

8-24 2181

8 2161

8 2067

8 2154

8 2222
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At the end of I 50, 750j 1550j ^-nd 2000 hours of operation,

the tubes were removed from the stoves for Inspection and

measurement for deformation. At none of these inspection

periods was any visible deformation noted nor did any of the

measurements show a change from those recorded before firing.

The jig used for determining whether or not any deformation

had occurred is shown in Fig. 5 . During these tests the measured temperature at midheight

of the tube averaged about 1150°F during high fire operation

(24 ml/min) and about 950 °^ during low fire operation (8 ml/min).

Tubes numbered 23926-10, having operated continuously

on high firej 23926-3# having operated under a cycling condition; and 23926 -I, having operated continuously on low fire,

were removed from the stoves after the 2000-hour test for

crystal analysis by the Mechanical Metallurgy Section. Two

used tubes from the group received from the Jeffersonville

Quartermaster Depot and 1 new tube from the group of five

received from the QMR&E Command were also included in the

crystal analysis study.

The microstructures of these six specimens indicated the

following conclusions:

( 1 ) The variation in the decomposition of the steadite

and pearllte constituents of the cast iron from the

bottom to top of the tubes indicated that they had

been heated in a temperature gradient with the highest

temperature at the top of the tube.

( 2 ) None of the specimens had been heated to the transformation temperature as indicated by the absence

of pearlite patches in the microstructure of the

top portions of the tube.

( 3 ) The two tubes from Jeffersonville Quartermaster Depot

with unknown operational history appeared to have a

thermal history not unlike that of the specimens tested

at the National Bureau of Standards.

( 4 ) Heating of portions of two of the tubes to 1500°F for

one hour followed by air cooling and quenching of

alternate specimens further substantiated the con-

Fig 5

-7-

clusion that the tubes had not been heated above

l450°P during testing or use.

The complete report of the Mechanical Metallurgy Section

on these six tubes is attached as Appendices I and II.

V. Thermal Shock Tests

In the opinion of metallurgists at the National Bureau of

Standards the conditions most likely to produce change in crystal

structure and deformation of the tubes are extremely high operating temperatures and thermal shock. Therefore,, a series of

tests were performed involving higher firing rates and sudden

heating and cooling operations. For this series of tests six

of the original group of twelve commercial tubes^, four additional

used tubes from the Jeffersonville Quartermaster Depot,, and

two of the group of five tubes cast at the QMR&E Command,, were

used in the twelve stoves.

Two of the stoves,. No. 2 and 10,, were operated at the same

firing rates as during the first 2000-hour test as controls. The

upper air tubes in the other ten stoves were subjected to more

severe temperature and thermal shock conditions. These may be

summarized as follows:

(1) Five were operated continuously at a firing rate of

65 ml/min producing a temperature on the upper air

tubes in the range from 1300°F to l400°F. Five

others were put on intermittent operation alternating

between a firing rate of 65 ml/mln for 1 1/2 hours

and chilling in the freezing compartment of a refrigerator at -5°F. After 50 hours of such operation

the firing rate was reduced because the fire was

being extinguished by soot accumulation in less than

24 hours at a fuel rate of 65 ml/min.

( 2 ) The high fire fuel rate was reduced to 40 ml/min for

about three days and then to 35 ml/min at which setting

smoking of the stoves was imminent. The same stoves

were operated continuously as before and the same

stoves were operated cyclically as before,, except that

the tubes in two of the latter group were chilled in

solid CO^ for about 80 cycles of the total 250 cycles
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-8 -

Instead of chilling in a refrigerator at -5°F throughout the test. The ten stoves were operated at a fuel

rate of 35 ml/min for periods ranging from 200 to

400 hours.

( 3 ) The tubes in four stoves were heated for one hour at

a firing rate of 35 ml/min and then quenched in water

at room temperature.

(4) The four-inch stovepipe on one stove was replaced with

six-inch stovepipe by connecting it to the opening

for the stove lid on the top of the stove^ and the

firing rate was Increased to 80 ml/min. The temperature of the upper air tube was not increased^ however^

by increasing the size of stovepipe and Increasing

the firing rate from 35 ml/min to 80 ml/min.

The only damage to the upper air tubes caused by this series

of tests at high firing rates or by exposing them to thermal

shock occurred when the heated tubes were quenched in water.

The cap on one tube broke off after 4 quenchings; a second,, after

7 quenchings; and a third was full of hairline cracks and about

to break after 13 quenchings.

VI. Failure of Vaporizing Burner Pots

At the conclusion of the thermal shock tests described above^

six of the twelve vaporizing burner pots had failed by oxidation.

The remaining six burner pots were fitted with upper air tubes

and operated at a fuel rate of 35 ml/min^ until all the burners

had failed. All twelve burners failed in the same way by oxidation of the low carbon steel in the sidewalls of the burner

between the upper row of air holes and the top flange of the

burner. Fig. 6 shows one of the pot burners after failure. The

zone of oxidation was at the upper edge of the portion of the

burner shown at the left in the photograph.

The total hours of operation of each of the twelve stoves

prior to failure is summarized in Table 3.

Pig 6

-9-

Table 3

Summary of Vaporizing Pot Burner Life

Stove Number Hours of Burner Operation

1 2677

2 4457

3 2747

6 2757

8 2331

9 2245

10 4094

11 2455

13 2662

16 2570

24 3417

30 2514

Stove No. 2 was operated continuously at a fuel rate of

24 ml/mln during the entire life of the burner and stove No. 10

was alternated between high and low fuel rates of 24 ml/min and

either 8 or 12 ml/mln_, respectively,, during the entire burner

life. All the other stoves and burners were operated for periods

of time at fuel rates ranging from 35 to 65 ml/min.

At the time of failure of all of the burners, several of the

commercial upper air tubes and one of the used upper air tubes

from Jeffersonville Quartermaster Depot had been operated for

an extended period. These operational periods are summarized

in Table 4. No deformation had occurred in any of the upper

air tubes at this time.

Table 4

Stove Number Tube Number Hours of Tube Operation

2 23926-6 4457

6 G* 1493

10 23926-11 4094

13 23926-9 2938

16

* Used tube

23926-5 2852

- 10 -

VII. Chemical Composition of Upper Air Tubes

The chemical composition of several of the upper air tubes

used for the tests was determined for comparison with the purchase specifications used by the Quartermaster Research and

Engineering Command and for correlation with the operational

test results. The chemical composition in percent by weight

specified by the QMR&E Command in procurements during recent

years was as follows:

Total carbon 3.00 - 3-60

Silicon 1.80 - 2.50

The sum of total carbon and silicon shall not exceed 5-5

nor shall the silicon at any time be less than I.80.

Phosphorous

Sulphur

Chromium

Manganese--

Nickel

0.60 max.

0.10 max.

0.30 - 0.60

0.60 - 1.00

0.00 - 2.00

The chemical determination for carbon^ phosphorous^ and

sulphur and the spectrochemical determination of manganese,

silicon, nickel, and chromium for six upper air tubes furnished for the tests are summarized in Table 5. The first

three specimens listed in the table were commercially procured upper air tubes furnished by the QMR&E Command and the

last three; A, J, and P, were used specimens furnished by the

Jeffersonville Quartermaster Depot. The first three tubes

were samples from different procurements purchased under the

specified chemical composition shown above.

Table 5

Tube

1 (23926-10)

8 (22981-10)

30 (24490-8)

A (Jeffersonville

J ( P (

Percent Hrs

.

c Si P S Or Mn Ni- burned

3.39 1.9 0.27 0.12 0.12 0745 0.07 2173

3.52 1.8 .40 .12 .5* .46 .03 2280

3.46 1.8 .30 . 11 .5* .66 .7* 2222

3.37 1.9 .29 .13 .12 .70 .07 — 3.51 1.9 .41 .11 .5* .73 .05 --+280

3.46 1.9 .32 . 11 .09 .66 .06 —

* Approximate values. Suitable cast iron standard samples not

available (steel standards used).

- 11 -

In this group of upper air tubes those numbered 1^ 8 and

30 had been operated at controlled firing rates under the following respective conditions: continuous at 24 ml/min; in twohour cycles alternating between 8 ml/min and 24 ml/mln; and

continuously at 8 ml/min. The operational histories of tubes

Aj Jj and P were unknown except that tube J had been operated

at NBS for 28 O hours at high firing rates (35 to 65 ml/min).

These six tubes represented at least four, and perhaps six,

different procurements of upper air tubes. All six tubes met

the specified requirements on carbon, silicon, phosphorous,

and nickel. All. had slightly more sulphur than the maximum

specified and some were deficient in chromium and manganese.

None of the tubes was visibly deformed and all measured true

in the special jig at the time of the chemical analysis.

A review of known specifications for cast iron for this

duty led the Mechanical Metallurgy Section to suggest that

Class I or II castings of Type B as described in ASTM Standard

Specification A319-53 covering Grey Iron Castings for Elevated

Temperatures for Non-Pressure Containing Parts would probably

withstand the thermal shock and temperature requirements of

this application. Thereupon, Inquiries were sent to twentyfive foundries, distributed over all sections of the country,

asking if they could furnish castings having the composition

shown in Tables 6 and 7 below and in the quantities typical

of previous military purchases. The composition shown is

within the range of the requirements for Class I and II, Type B,

castings of ASTM Specification A319-53 S-^d is similar to the

currently used specification except that it raises the upper

limit of the carbon, silicon, and sulphur contents a little.

Table 6

Element Percent by Weight

C

Si

P

S

Cr

Mn

Nl

3.20 - 3.70

1.80 min.

0.60 max.

0.12 max.

0.4l - 0.65

0.40 - 1.00

0.00 - 2.00

- 12 -

The allowable silicon content in relation to the various

permissible carbon contents was further prescribed as shown in

Table 7 *

Table 7

Class Carbon % Silicon %

I 3.50 1.80 - 2.70

3.70 1.80 - 2.10

II 3.20 1.80 - 2.70

3.40 1.80 - 2.10

Sixteen foundries cooperated with replies,, in some cases

adding their own remarks,, as follows:

Foundry State Availability Remarks

Colorado Fuel & Iron

Emmaus Foundry &

Corp. Colorado Yes None

Machine Co.

Klrkland-Weathers Foundry

Penn. Yes Add . 4-.

5

Np

. 2-.

3

Mq

Co. Alabama Yes Exception

requested

0.75 P

Inland Foundry Co. Idaho Yes Chemistry

too complicated

Taylor and Fenn Co. Conn

.

Yes Suggested

nodular iron

R. D. Cole Mfg. Co. Georgia No No reason

Yale & Towne Mfg. Co. New York No Do not make

castings

anymore

General Metals Corp.

Duncan Foundry &

California Yes

Machine Works Inc. Illinois No Do not produce castings

Indiana Foundry Corp. Indiana Yes

Macaulay Foundry Co.

Sterling Mfg. Co.

.Wise .

)

California Yes

Suggest

(Klrsch Foundry Inc Nebraska Yes stainless

steel

U. S. Pipe & Foundry Co. Alabama Yes

-13-

Foundry State Availability Remarks

A. G. Williams Co. Ohio Yes

Sterling Casting Co. Indiana Yes

Gulf Star Foundries Texas No Too large

quantities

After completing the survey of foundries for availability

of castings it was agreed between the sponsor and this Bureau

that 12 upper air tubes of each of three chemical compositions

falling within the range of ASTM Specification ASTM 319-53 would

be cast in the foundry of the National Bureau of Standards for

further tests. The three compositions were as follows:

Table 8

Element Type 1 Type 2 Type 3

C 3.20 - 3.30 3.40 - 3.50 3.60 - 3.70

Si 2.50 - 2.70 2.20 - 2.30 2.00 - 2.10

P max 0 .

6

0 .

6

0 .

6

S max 0.12 0.12 0.12

Cr 0.5 0.5 0.5

Mn 0.5 0.5 0.5

Ni 0.3 0.3 0.3

The three compositions were selected to cover a range of

carbon and silicon contents. The compositions are similar to

that now in use by the Quartermaster Research and Engineering

Command except that the sum of the carbon and silicon is higher

and the permissible maximum sulphur content is slightly higher

in these three compositions.

Analysis of the finished castings showed the following compositions for the three types. It will be noted that the carbon

content was lower and the silicon content was higher in each

case than the selected range.

- 14 -

Table 9

Element Type 1

C 3.13

Si 2.8

P 0.50

S 0.040

Or 0.40

Mn 0 . 64

Ni 0.3

Type 2 Type 3

3.06 3.29

3.2 2.4

0.045 0.56

0.013 0.051

0.24 0.36

0.53 0.80

0.3 0.3

VIII. Deformation of Upper Air Tubes

While awaiting completion of the experimental upper air

tubes by the NBS foundry twelve of the vaporizing pot burners

composed of different combinations of low carbon steel and

stainless steel components were operated for approximately

1000 hours using the original twelve stoves and a selection of

the original commercial and used upper air tubes. The identification of the tubes used for this period is shown in Table 10 . The fuel burning rate was 33 ml/min for half of the specimens

and 38 ml/min for the other half of the specimens.

Table 10

Stove Number Tube Identification* Hours of Operation

1 B 1045

2 2(23926-6) 1059

3 E 1091

6 T 1063

8 F 1016

9 M 968

10 10(23926-11) 1082

11 L 1090

13 G 959

16 D 1087

24 N & C 789 & 188

30 J 624

Tubes Identified with a capital letter were used tubes

received from the Jeffersonville Quartermaster Depot.
m

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r.n ft 7ei» .«? /fitw hettlirt^sbi
-15-

During this period three of the upper air tubes deformed

by bending in the column below the cap. Two of these are

shown in photographs 7 and 8. One of the tubes that deformed

was from the original group of twelve commercial specimens

submitted by the QMR&E Command and was identified as No. 2

and also as 23926-6. It had been operated for 4457 hours

at a firing rate of 24 ml/min followed by a period of 1059

hours at a firing rate of 35 ml/min for a total of 5516 hours.

It deformed at the higher firing rate.

A second deformed specimen was identified as tube 13-G

and was a used tube received from Jeffersonville Quartermaster

Depot with unknown history of use. It was operated during

these tests for a period of 2951 hours at a firing rate of

35 ml/min and deformed during this period. The third specimen which deformed,, Identified as specimen 30-J,, was a used

tube received from Jeffersonville Quartermaster Depot. It

was operated for several hundred hours during these tests at

a firing rate of 38 ml/min. In addition to being bent^ tube J

had increased in height by about 1/4-inch during the tests at

this firing rate. This is not the same J specimen chosen for

chemical analysis^ as reported in Section VII of this report.

These three tubes were studied by the Mechanical Metallurgy Section to determine whether or not the microstructures were

similar to those for tubes studied earlier.

The horizontal sections of the three tubes showed that the

inner and outer surfaces were circular^ but not concentric.

The vertical sections of tubes No. 2 and 13-G showed that the

axis of the bend was in line with the section of minimum and

maximum wall thickness with the minimum wall thickness occurring on the convex side of the bend. These sections are shown

photographically in Appendix III^, which is the complete report

of the Mechanical Metallurgy Section on these 3 tubes.

The microstructurps of tubes No. 2 and 13-G near the bend

showed that the pearlite in these sections was completely decomposed indicating that these tubes had been operated at higher

temperatures than those previously examined but that they had

not reached the transformation temperature. There were differences

in the microstructure on the thin and thick sides of these two

specimens near the bend that could be explained if the tempera-

Fig 7
t

i' f %

•4

r

4
Fig 8

-16-

ture of the thin side had been slightly higher than that of the

thick side and was near l450°F.

The photographs in Appendix 111 show that the layer of

iron oxide on the inside of the tube increased in thickness

progressively from the bottom to the top of the tube. There

was little oxide on the exposed outer surface of the tube^

probably because the tubes were cleaned at regular intervals

during the test.

The reason for the deformation of these tubes could not

be positively established from the operational tests and the

metallurgical studies^ but a theory is advanced in the Section

on Discussion and Conclusions which is generally supported by

the observed results.

Horizontal sections of four additional tubes^ specimens

T^ 3 , 10^ and 30 ^ were made and photographed to show the degree

of eccentricity of the inner and outer surfaces^ the thickness

of wall section^ and the thickness of the oxide layer on the

inner surface. None of these four specimens was deformed.

IX. Tests of Experimental Cast Iron Tubes

Upper air tubes cast in the NBS foundry were placed in the

twelve experimental burner pots containing stainless steel and

low carbon steel components as summarized in Table 1 replacing

those tubes that had been in the pots for about 1000 hours of

operation

.

The new tubes were of the three different compositions reported in Table 9 and were labeled Types 1^ 2^ and 3.

Pour tubes of Type 1 were placed in four pots such that

2 tubes were operated at a fuel rate of 33 ml/mln in style

1 and 2 pots and 2 tubes were operated at a fuel rate of 38

ml/min in style 1 and 2 pots.

Four tubes of Type 2 were placed in four pots such that 2

tubes operated at a fuel rate of 33 ml/mln in style 3 and 4 pots^

and 2 tubes operated at a fuel rate of 38 ml/mln in style 3 and

4 pots.

-17-

Four tubes of Type 3 were placed In four pots such that

2 tubes operated at a fuel rate of 33 ml/min in Style 5 and

6 potSj and 2 tubes operated at a fuel rate of 38 ml/mln in

Style 5 and 6 pots.

The following table gives the stove number^ the pot style

number, the firing rate, the upper air tube number and the

number of hours each tube operated in the pot and stove. In

somie cases more than one tube was used in a particular stove.

Table 11

Stove No. Pot Style No.

Firing rate

ml/min

Type

Tube

1 1 33 1

6 1 33 1

2 2 38 1

3 2 38 1

10 3 33 2

8 3 33 2

11 4 38 2

9 4 38 2

13 5 33 3

24 5 33 3

16 6 38 3

30 6 38 3

Hours of

Operation*

2055

2064

694

453

2078

1140

561

454

316

595

486

1106

2077

2023

2046

* Less than 2000 hours of operation indicates that the tube or

tubes in that stove and pot exfoliated. Other tubes were

placed in the pots for the remainder of the 2000-hour test

period

.

The tests of the experimental upper air tubes cast by the

NBS foundry were continued for slightly over 2000 hours. During

this period none of the tubes failed by bending; but six tubes

of Type 2, two tubes of Type 1, and one tube of Type 3 failed

by exfoliation at the base. The appearance of these exfoliated

tubes is shown clearly in Pig, 1 of Appendix IV. A spectrochemical

analysis of the exfoliated region showed a lead content of O.O5

to 0.5 percent, probably attributable to the leaded gasoline used
Ir'"i
-18-

as fuel. Microstructures of the exfoliated region showed considerable slag penetration and voids. The 2 tubes of Type 1

that falled_, had operated for 453 and 694 hours, respectively;

the one tube of Type 3 that failed, had been fired for 1106

hours; and the 6 tubes of Type 2 failed after firing periods

ranging from 316 to ll40 hours.

The tests showed the superiority of Type 1 and 3 tubes

as compared to Type 2 tubes. It Is probable that the superior

quality of Types 1 and 3 is dependent on differences In chemical composition and microstructure. Differences In cooling

rate of the castings would also affect the microstructures.

It will be noted that the highest Incidence of failure occurred

In the Type 2 tube with ' the highest silicon content and the

lowest phosphorous content. Conversely, the fewest failures

occurred In the Type 3 tubes with the lowest silicon content

and the highest phosphorous content. These relative frequencies

of failure may or may not be significant but It Is known that

high carbon and/or silicon contents decreases the growth resistance of ordinary gray Irons while phosphorous will resist

growth and oxidation to some extent.

The composition of the Type 3 tubes approximated most

nearly the composition of the commercial and used tubes submitted for the Initial tests of this study. These comparisons

can be made from the data In Tables 5 9.

The complete report of the Corrosion Section on the examination of the exfoliated tubes Is attached as Appendix IV.

X. Tests of Twelve Experimental Vaporizing Burner Pots

The twelve new vaporizing burner pots were Installed In

the twelve stoves and operated for 3000 hours. These burner

pots were fabricated In six different styles using some components of low carbon steel and the remainder of stainless

steel of one or the other of two thicknesses of sheet metal.

The combinations of stainless steel and low carbon steel parts

In the several styles are summarized In Table 1. Fig. 9 is a

photograph of one of the burner pots when new.

Fig 9

-19-

'l^wo burner pots of each style were operated for 3 OOO hours

with the firing rate set at about 33 ml/mln for one of each

style and at 38 ml/min for the other of each style.

The burners were examined for corrosion at the end of 500,

1000, 1500 , 2000, and 30OO hours of operation. Those that appeared

to be damaged the most were removed from the stove for careful

Inspection at each Interval. At the 500-hour and 1000-hour inspections there was little visible change in the appearance of

the burners. After I 5 OO hours of operation the upper edge of

the low carbon steel air casing on both style 6 burners had

buckled in some places between the spot welds that held it to

the burner support ring. All twelve burners showed signs of

scaling and oxidation of the low carbon steel air casing.

At the end of 2000 hours of operation both Style 2 burners

and one Style 6 burner had holes in the upper edge of the air

casing. All remaining parts in all twelve burners were in good

condition.

At the end of 3 OOO hours of operation, which was the conclusion of the tests, the low carbon steel air casings had

all suffered noticeable deterioration ranging from partial

separation near the support ring to complete oxidation of the

steel. All other components of the burners were in good condition. Flg» IO-I6 inclusive show the nature of the deterioration of the air casings. The numbers below the burners are

the corresponding stove numbers and can be used to identify

the styles of the burners by referring to Table 11. Fig, 11

shows a style 2 burner and Fig. I 3 a style 4 burner before

cleaning and reveals the carbon deposits near the air holes on

the inside walls of the burner and the considerable amount of

soot and scale that had fallen into the burner. Fig. I 5 shows

a style 6 burner fully assembled after cleaning and Fig. I 6 shows

the same burner with the combustion ring, low fire ring, and

upper air tube removed to indicate the condition of the interior.

The analysis of the air casing material at the end of the

test is reported in Appendix IV as determined by a metallographic

examination.

Fig 10
f
Fig 11

Fig 12

Fig 13

“T'S,v

i i J> '

iS*

"ib.^,;;i:'.##.

Fig 14

Fig 15

Fig 16

- 20-

XI, Discussion and Conclusions

The burner pots with low carbon steel sidewalls were found

by test to have a life of less than 3 OOO hours when fired for

any appreciable length of time at 35 ml/min or higher. One

such pot lasted for 4457 hours when operated steadily at a firing

rate of 24 ml/min and another lasted 4094 hours when operated

cyclically at firing rates of 8 and 24 ml/min. Ten other specimens failed after operating from 2245 to 3417 hours of which

,2000 hours employed firing rates of 24 ml/min or less. The

average life of all twelve burners was 2910 hours. All of the

burners failed similarly by complete oxidation and separation

of the metal in the sidewall of the pot between the top row

of air holes and the top rim of the pot.

Twelve experimental burners containing stainless steel components and low carbon steel components in various combinations

were in good condition at the end of 3 OOO hours of operation at

firing rates of 33 or 38 ml/min except for the air casing which

was made of low carbon steel for all specimens. This component

oxidized at the upper edge where it was welded to the burner

support ring to the extent that separation occurred for distances of a few Inches in some cases and fully half the periphery

in other cases. The entire air casing component suffered from

severe oxidation and scaling. These tests showed that the floor

of the pot_, the sidewall of the pot below the low fire ring^ and

the burner shield under the floor could be made of low carbon

steel_, but that all other components of the burner should be

made of austenitic corrosion resisting steel in order to obtain

a satisfactory burner life. Based on these test results_, burners

of this construction would probably have a useful life twice as

long as the lov^ carbon steel burners used for the initial tests

in this investigation.

The tests of twelve commercial upper air tubes _5 twelve or

more used tubes that had been discarded as unserviceable ^ and

several other new experimental tubes cast at the QMR&E Comjnand

indicated the following conclusions:

(a) The commercial tubes could be operated in excess of

4000 hours with continuous firing at a rate of 24

ml/min or on intermittent high and low fire of 24

ml/min and 8 ml/min^ respectively^ without deformation.

- 21 -

(b) Operation of the stoves at firing rates of 35 ml/mln

or higher produced temperatures on the upper air tubes

at midheight In the range from 1300°F to l400°F^ which

approached the transformation temperature of gray

Iron and usually accelerates the growth of ordinary

gray Iron by graphltlzatlon,

(c) All of the used tubes functioned as well as the new

tubes submitted as test specimens. None of the used

tubes were deformed as received,

(d) Three tubes defomed by bending after operating at

a firing rate of 35 ml/mln for periods of time ranging

from a few hundred hours to about 3000 hours. One of

these tubes was a tube from commercial procurement

that had been operated during the tests for more than

4400 hours at a firing rate of 24 ml/mln and for more

than 1000 hours at 35 ml/mln_, whereas the other two

were used tubes whose usage was unknown prior to their

submittal here. The Inner and outer surfaces of all

three of the bent tubes were eccentric relative to

each other resulting In thinner metal on one side

than on the other. The observed differences In the

microstructure of the thin and thick portions of the

tube near the bend could be explained If the temperature In the thin section was a little higher than

that In the thick section and If the temperatures were

at or very near the transformation temperature. However^ a number of other specimens that were eccentric

did not deform.

(e) The oxidation of the cast Iron In the upper air tubes

continues throughout the life of the tubes; It progresses faster at higher temperatures; and It progresses more rapidly at the middle and top of the

tubes than at the base where the temperature Is lower.

The Iron oxide remains on the Inside of the tube and

becomes thicker and thicker whereas It Is likely to

be scraped or brushed off the exterior during cleaning

operations

,

The observations suimmarlzed above and other experience during

these tests suggests the following hypothesis regarding the cause

of bending In the upper air tubes.
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-22

At the firing rates recommended for these stoves the gray

iron in the upper air tubes will oxidize progressively with

time,, with more rapid oxidation occurring in the upper half

of the tube because of the higher temperatures produced there.

Eventually any gray iron tube would fall after sufficiently long

usage from this progressive oxidation. However, when a tube

is eccentric because the sand core and sand m.old were not

concentric during the casting process, failure is likely to

occur earlier because the amount of unoxidlzed metal is always

less on one side than on the other. The oxide that forms on

the inside of the tube probably has a thermal conductivity of

the order of 1/20 of that of the cast iron itself and therefore.

Insulates the cast iron from the cooling effect of the air stream

moving upward inside the tube. Furthermore, the thin side of

an eccentric tube cannot conduct heat to the cooler base as

rapidly as the thick side. Thus, under the fluctuating temperature conditions that exist in such a burner the thin side

of an eccentric tube would attain a somewhat higher temperature

than the thick side during a temporary rise in the surrounding

gas or flame temperature. Since the tendency of cast iron to

"grow” as a result of graphitlzation Increases progressively

in the tem.perature range from 900 °P up to the transformation

temperature of l400°F, more or less, variations in temperature

between the two sides of an eccentric tube could produce deformation, The tendency to deform would probably increase with

the amount of eccentricity, with increased firing rates, and

with increasing thicknesses of oxide on the inside of the tube.

In our opinion most of the results observed during thisinvestigation support the above hvpothesis. The principal contradictory considerations are, (a) that not all of the eccentric

tubes deformed even though some were extensively oxidized and

(b) that the expected differences in temperature that would

develop between the thin and thick sides of an eccentric tube

because of differences in heat conduction to the base, would

be relatively small.

The upper air tubes of three compositions cast at the NBS

foundry did not fall by bending in 2000 hours of operation at

firing rates of 33 and 38 ml/mln, but did fall by exfoliation

at the base. No specific reason for the exfoliation was found

by chemical analysis or from the microstructures. All three of

the compositions were higher in silicon content than the other

tubes used for the tests and the incidence of failure by exfoliation Increased with Increase in silicon content. Whereas
' ’ C'i'iX
-23-

a direct cause and effect relationship was not established between

these two factors^ it is known that increasing the silicon content in gray iron increases the rate of growth of the iron at

elevated temperatures. In general^ the performance of the experimental tubes cast at the MBS foundry is considered Inferior

to that of the other specimens used in the investigation.

Inasmuch as the commercial and used tubes employed for these

tests exhibited fairly good resistance to bending and typically

contained sulphur ranging from 0.11 to 0.13 percent it is suggested that the permissible sulphur content in the specifications

be raised to 0.12 maximum which agrees with the limit specified

in ASTM Standard A319-53 for gray castings for this type service.

In view of the relatively good performance of the commercial and

used tubes used during these tests in which the sum of the carbon

and silicon ranged from 5.26 to ^ . hi percent^ as compared to that

of the experimental tubes cast at the MBS foundry in which the

sum of these two components ranged from 5-69 to 6.26 percent^ it

is recommended that the limit of 5.5 percent for the sum of these

two elements be retained in the specification. It is further

recommended that the specification limit the permissible eccentricity of the tubes. A suggested limit is that the difference

in wall thickness at opposite ends of any diameter not exceed

1/32-lnch in the middle third of the tube length.

The float valves used on the stoves for control of the fuel

flow rate permitted a flow rate upwards of JO ml/min at their

highest setting. The flow rate was further adjustable by turning a set screw in the top of the valve mechanism which was accessible through a hole in the adj'ustlng knob. These flow rates

are excessive because the burner will not admit enough combustion

air for complete combustion at these operating conditions^ the

stoves extinguish themselves with soot and carbon accumulations^

the upper air tubes attain temperatures of approximately l400°P^

and the stovepipes operate red hot and deteriorate rapidly. Hie

life of the upper air tubes^ the burners^ the stovepipe^ and

the stove Itself could be extended considerably if the float valves

were designed for a maximum setting ^of about 30 ml/min which literally could not be Increased in the field without boring out

the orifice in the valve. It seems highly probable that the stoves

will typically be operated at a maximum setting of the float valve

in the field in cold weather. Thus, a fixed maximum setting more

commensurate with a reasonable life of the stove and its components

is recommended.
L
APPENDIX I

Interdlvislon Work

U. S. DEPARTMENT 0E COMMERCE Order No. IO -676

NATIONAL BUREAU OF STANDARDS Project No. 4885

Washington 25^ D. C,

NATIONAL BUREAU OP STANDARDS REPORT

on

Examination of

CAST IRON AIR -TUBES

Submitted by

Division 10.3 (P. R. Achenbach)

By

H. C. Vacher

C. K. Speller

P. D. Sarm.iento

Mechanical Metallurgy Section

UNITED STATES DEPARTMENT OP COMMERCE

WASHINGTON

NATIONAL BUREAU OP STANDARDS

Report

on

Examination of

CAST IRON AIR TUBES

Submitted by

Division 10.3 (P. R. Achenbach)

Reference ; Division 10.3 Interdivlslon Work Order of 11/4/57.^

Requisition No. 10-676^ Project No. 4885

Identification of Tubes:

Tube

X

A and H

9.

History

This tube was cast at Natick QMR&E Command wlth

the composition shown In their specifications. It

has not been fired.

These tubes were sent In from Jeffersonville

Quartermaster Depot as no longer serviceable. They

were purported to have been fired until they no

longer performed satisfactorily.

This tube fired with gasoline at NBS for 2170

hours at 24 cc/mln firing rate,, or high fire^ at a

temperature about 1150°P avg.

This tube fired with gasoline at NBS for 2034

hours at 8 - 24 cc/mln firing rate, or cycling fire,

changing every two hours. About 1000 °P & 1150°P.

This tube fired with gasoline at NBS for 2154

hours at 8 cc/mln firing rate, or low fire, at a

temperature about 950 °P avg.

24 ,
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- 2

-

Work Requested : Perform metallurgical examinations of six upper

air tubes to determine changes in crystal structure

and size and distribution of graphite Inclusions

Examinations should be made at three sections on

each specimen, viz. (l) at the base^ (2) near rn.idheight and (3) near the top.

Nominal Composition : 3.3^ to 3.6^ carbon^ 2.2^ silicon^ 0.6^

manganese^ 0.5^ chromium^ 0,8% nickel^ 0.6% max,

phosphorus,, 0.1% max, sulphur.

Metallographlc Examination : The metallographic specimens were

cut from the tubes at locations indicated in Figure 1„

Surfaces parallel to the tube axis were polished

according to a procedure developed by Samuels (J, Iron

and Steel Institute,, Vol, l80^ May 1955:* P* 23).

The polished surfaces were examined in the unetched

condition and after etching with 1 percent nital.

Definitions of the principal microconstituents that

were in the microstructure are given in the appendix.

The size and type of distribution of the graphite

flakes are shown in Figures 2 and 3. A comparison

of the microstructures in Figure 2 with the graphiteflake size chart in the American Society for Testing

Materials Standards 1955j showed that the longest

flakes varied between size 5 (l/'^ to 1/2 in. in length)

and size 6 (I/8 to 1/4 in, in length). The shorter

flakes were in the bottom portion of the tube. The

comparison also showed that the distribution and

orientations of flakes in tube X were a mixture of

ASTM types Bj and E, Types B and E predominated

near the surfaces of the tubes whereas type A predominated in the interior. The size and type of

graphite flakes did not vary appreciably from tube to

tube as can be seen from typical microstructures in

Figure 3.

Appreciable differences were observed in the miicrostructures of the top portions of the tubes. These

differences were mainly in the pearllte and steadlte

structures and to some extent in the character of the

boundaries of the graphite flakes.

-3-

The stable micro structure of gray cast iron at

room temperature is graphite plus ferrite. It can

be formed by very slow cooling from l450°P or by

reheating a meta or unstable structure for a prolonged period at temperatures below l450°F, Graphitization_, that is_, the decomposition of the meta and

unstable structure to form graphite and ferrite, is

fastest around 1330°P. If the stable structure is

reheated to temperatures above 1450 °F austenite will

be formed which on cooling at a rate approxlm-atlng

air cooling or in a sand cast mold, would form

pearlite.

The pearlite and steadite microstructures shown

in Figure 4 were typical of tube X and also typical

of gray cast iron that had been cast in a sand m.old.

Typical microstructures of the top, midheight, and

bottom portions of tubes A and 1 are shown for com.- parlson in Figure 5. It can be seen that the pearlite

and steadite constituents were in progressive stages

of (Recomposition and spheroldizatlon. The advanced

stages at the top nearly approached the stable structure whereas the initial stage at the bottom corresponded to the structures observed in tube X, These

structures Indicated that the tubes had been heated

in a temperature gradient in which the top of the tubehad been at the highest temperature. The absence of

pearlite patches in the microstructure of the top

portions indicated that the highest temperature had

not been above the transformation temperature, t!^at

is, 1450 °F, The close similarity of the structures

in corresponding portions indicated that the theim'ial

histories of tubes A and 1 were similar.

The microstructures of the top and bottom, portions of tube shown in Figure 6, indicated that

it also had been heated in a temperature gradient

but that the highest temperature in the top portion

had not been as high as in the tops of tubes A and 1.

The close similarity of the microstructures in

corresponding portions and in the top and bottom

portions of tubes H and 24, Figure indicated t.l.at

the tubes had similar thermal histories but that tl.e

- 4-

Appendlx;

time at maximum temperature had not been sufficient

to change the Initial character of the pearllte and

steadlte constituents. Evidence that tubes H and 24

had been heated to elevated temperatures was shown

by the formation of scale, see Figure 8.

Metallurgical examinations have Indicated that

tubes A, 1, and 9 were heated In temperature gradients In which the maximum temperature of the tubes

was In the top portions, that the thermal histories

of tubes A and 1 were similar, also that the thermal histories of tubes H and 24 were similar but

that the maximum temperature was lower than that

of tubes A, 1, and 9 . Definitions of microconstituents:

Austenite : Austenite Is a solid solution phase Ir. whlch the face-centered cubic form of Iron Is tlie

solvent. In ordinary gray cast Iron austenite Is

stable between approximately 2500 °F and l450°F, The

solubility of carbon In austenite at the austenlteIron carblde-ferrlte eutectold temperature, l 450 °F,

Is approximately 0 . 85^ and at the liquid Iron - austenite - graphite eutectic temperature, 2150°F,

It Is approximately 1,5^. This silicon content of

the gray Iron Is soluble In both the face-centered

cubic and body-centered cubic forms of Iron. Austenite Is not ordinarily a microconstituent of gray

cast Iron at room temperature.

Ferrite : Ferrite Is a solid solution phase In which

the body-centered cubic form of Iron Is the solvent.

The solubility of carbon at 1450 °F Is approximately

0.03^. Ferrite not associated with the ferrite In

the ferrlte-lron carbide eutectold structure (pearllte)

Is sometimes referred to as ’’free" ferrite and Is

Indicated by F In Figure 4. Ferrite Is the matrix

In the microstructure of slowly cooled gray Iron.

Graphite : In gray Iron graphite Is In the form of

flakes that appear In micro structure as dark bands,

see Figure 4. The graphite flakes are part of the

austenite-graphite structure that Is formed In tl-.e freezing of the eutectic liquid.
’ i-i.

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Pearllte ; Pearlite appears In the ml c restructure;,

see Figure 4_, as an aggregate of dark (iron carbide)

and light (ferrite) bands, Pearlite Is formed In

gray Iron when It Is cooled at an appropriate rate

below the eutectold temperature, l 450 °F.

Steadlte ; Steadlte results from the presence of

phosphorus In the Iron. As gray Iron cools, a

ternary eutectic structure consisting- of austenite.

Iron carbide, and Iron phosphide freezes about 1750 °P

This subsequently decomposes Into a "pseudo binary”

Iron, Iron phosphide eutectic structure plus graphite

The boundaries of steadlte generally are fluted

because the phosphorus eutectic freezes after the

austenite dendrites have formed.
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APPENDIX II

Interdlvlsior: Wcrk

U. S. DEPARTMENT OF COMMERCE Order No. 1 0-8 1.8 NATIONAL BUREAU OF STANDARDS Project No, 4885

Washington 25j D, C.

NATIONAL BUREAU 0F STANDARDS REPORT

(Supplement

)

on

Examination of

CAST IRON AIR TUBES

Submitted by

Division 10.3 (P. R. Achenbach)

By

H. C. Vacher

P. D. Sarmiento

Mechianical Metallurgy Section
Ir

.I.J

ii
APPENDIX III

NATIONAL BUREAU OF STANDARDS REPORT

No. 2

(Supplement

)

on

Exam.ination of

CAST IRON AIR TUBES

Submitted by

Division 10.3 (P. R. Achenbach)

by

H. C. Vacher

C. K. Speller

Mechanical Metallurgy Section

August 26

f

1958

Interdivision Work Order

No. 10-50

Project No, 4885

August I;, 1958

NBS

U, S. DEPARTMENT OP COMMERCE

NATIONAL BUREAU OP STANDARDS

UNITED STATES DEPARTMENT OP COMMERCE

WASHINGTON

NATIONAL BUREAU OP STANDARDS

Report

Supplement No. 2

Examination of

CAST IRON AIR TUBES

Submitted by

Division 10.3

P. R. Achenbach and S« D. Cole

References ; (l) Division 10.3 Interdlvlslon Work Order No.

10-50, Project 4885.

(2) Division 8.3 report dated 2/IO/58 on Interdlvlslon Work Order No. 10-676^ dated 11/4/57.

(3) Division 8.3 report dated 3/13/58 on Interdlvlslon Work Order No. IO-818, dated 2/I2/58.

Work Requested : Examine two upper air tubes to determine If

the bend in the air tubes could be correlated with

wall thickness and if the microstructures in different portions of the tubes vSere similar to the

microstructures in the tubes described in two ' previous reports (Ref. 2 and 3).

Material Submitted ; Three tubes were submitted; I3 G, 2 and

J, all of which had been fired.

Examination : Tubes I3 G and 2 were cut so that the cut surfaces coincided with the plane of the bend, photographs 581709 9-nd 581712, and then cut to show

the cross sections near the top of the tube, photographs 581711 3-nd 581715:> 9-nd at the bend, photographs 581710 and 581716. These photographs show

that the maximum wall thickness is on the concave

side of the bend in tubes I3 G and 2,

- 2 -

Tube J was cut to show the cross sections

throughout the length of the tube^ photograph

581708, The sections showed that the outside

and inside surfaces were cylindrical but were

not concentric. The maximum wall thickness was

on the concave side of the bend as in tubes 13 0

and 2.

Specimens for metallographlc exam.l nation were

cut from tubes I3 G and 2 near the bottom, and in

the bent portion near the positions of maximum and

minimum wall thicknesses. See photographs 581709

and 581712 for location and identification of the

specimens. The microstructures were exam.lned l"i

the unetched and etched conditions at both low and

high magnifications. They were photographed in

the etched condition at 100 and 250 magnifIcatlon,

The size and distribution of the graphite flakes

in tubes I3 G and 2 were similar to that in the tubes

described in the previous reports. This indicates

that the cooling rates in the molds during freezlrig

were approximately the same for all of the tubes

examined. The pearllte in tube 13 G near the bottom

was nearly completely decomposed, only a sm.all

amount of spherodized cementite remaining, Tl.is

differs from the microstructure at the bottom, of

the tubes previously examined^ Ref, 2^, and Indicates

that the reheating temperatures were higher for tube

13 G. The pearllte in tube 2 at the bottom was

similar to that in the tubes previously examined,

that ISj the pearllte was fine but resolved at XIOOO

with no indications of spherodized cem*entlte, Tl.e

microstructures of tubes I3 G and 2 near the bend

were similar but both differed from that in corresponding locations in the tubes previously exa.mined.

In tubes I3 G and 2 the pearllte was com.pletely decomposed, This was not the case in the rr;lddle portions of the tubes previously examined and indicates

that the reheating temperatures were higher an.d the

periods at the reheating temperatures were probably

longer in tubes I3 G and 2,

The appearance of the graphite flakes in t:..e thick wall section near the bend was different from

that in the thin wall region in both tube I3 G and

-3-

Discussion:

Summary;

tube 2. In the former the graphite flakes were

thinner and the boundaries smoother than in the

latter.

The observed differences in microstructure between

the thin and thick portions of the tubes could be

explained if the temperature In the thin section

was slightly higher than in the thick portion and

at or very close to the transformation temperature,

approximately l450°F, It may, of course, be m.erely

coincidence that the thin sides of the three tubes

examined had been exposed to higher temperatures,

due to non-uniform conditions of heating. It

appears more probable that other factors influence

the temperature distribution so that the thin

sections are generally hotter. It seems possible

that if the temperature in the furnace was fluctuating there would be a lag in the temperature of

the thicker wall thus causing the maximum temperature in the thin side to be slightly higher than

in the thick side, as indicated by the microstructure.

It has been established that graphltlzatlon of

pearllte causes gray iron to expand or "grow". If

the thin portion of the tube was hotter than the

thick part, graphltlzatlon and growth would occur

more rapidly, causing the tube to bend toward the

thick side.

Sectioning of the tubes showed that the tubes had

bent towards the thick side.

Metalio graphic examination showed that the

bottom of tube 13 G had been heated to a higher

temperature than the bottom of tube 2 and the ones

previously examined. It also showed that the middle portions of tubes 13 G and 2 had been reheated

to higher temperatures than the tubes previously

examined. The appearance of the graphite flakes

in the thick and thin sides of the tubes 13 G and

2 indicated that the temperature in the thin side

was higher than the thick side and was probablry^

approximately l450°P.

- 4-

A possible explanation for the bend In tubes

13 G and 2 Is that the thin side grew at a faster

rate than the thick side. This might result If

the temperature In the furnace had fluctuated at or

close to the transformation temperature, 1450®F,
I

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I

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s.: k tr.^ ^ £/

^o.hl ^ e,i?. ' ^44:?' <5rfjsr

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tj. S. DEt’ARTMKNT OK COMMlvUCE

Iipwld Ij. Sll'OitSfl, Srcrrlni-y

MATtONAK mmKAU OF STANDAUDS

A. V. Aflflil, Dirrct.or THE ]VATI«XAL KIJUEAU OE STANB6AIS WS

The scope of activities of the National Bureau f>f Slarularrls at its hoaH(|uarters in Wiisliin^lon,

f). C., dnd its major laboratories in Botihler, Colo., is sufjtpesled in (he following listing of die divisions and sections engaged in technical work. In general, each section cariics out sj)eciali/.<'<i research, development, and engineering in the field indicated by its title. A brief 'deseription of

the activities, and of (he resultant publications, appears on the inside front cover. WASHINGTOIV, n. c.

KlftCtrIcIty nml KloetrHlilES. Resistance and Reactance. fCleetron Devices. Electrical In- struments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

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

Technology. Length. Engineering Metrology.

Hont* Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research.

Atomic and Radiation Pliysics. Spectroscopy. Radiometry. Mass Spectrometry. Solid

State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory.

Radioactivity. X-rays. High Energy Radiation. Nucleonic Instrumentation. Radiological

Equipment. ' Clscsillstry. Organic Coatings. Surface Chemistry. Organic Chimistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical

Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Moclinnics* Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Ma.ss and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Organic and FiliroiSN Mai<‘ii*ial!H. Rubber. Textiles. Paper. Leather. Testing and

.Specifications. Polymer Structure. Plastics. Dental Research.

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

Metal Physics.

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

Materials. Constitution and Microstructure.

Iluildiug Tecliunlngy# Structural Engineering. Fire Protection. Air Conditioning, Healing,

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heal Transfer. A|»|»liod MatlimiintiCN. Numerical Analysis. Compulation. Statistical Engineering. Mathematical Physics.

Hat a l*’ro<M*8Slng Sysl.riinw. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Anolog Systems. Application Engineering.

• Office of Basic Instrumentation. * Office of Weights and Measures.

i'ryogonic KnginmiM'itlg. Cryogenic Eipiipnuml. Cryogenic Proees.ses. P/operties of Maleriols. Gas Liquefaction.

llSadi<» fi*l‘0|>ugaiimi Upper Almos|»here Research, lonosiiherij Research. Regular Propagation Services. Sun-Earth Relationship.'^. VIIF Research. Ionospheric Connmniieal ion Systems.

Iludi<» B“rO|iagaii«»n IfCiagiiHS'irBiirii. Data Reduction InsirmiK'iitalion. Modulalion Sy."tcins.

Navigation Sysl(un.s. Ratlio Nois(,‘. I’ropospheric. MeasnrcnnMils. ’I'ro|iospheric Analysis. Radio

Systems Application Engim'*'ring. Radio-MiUcorology.

Uindio Si.atndar<lN. High Fre<picncy Elc.clrical Siandards. Radio Broadcast Service. High

Frc(|uency Impedance Siandards. Eleclronii' Calihral ion (icnicr. Microwave I'liysics. Microwave

Circuit .Standards.
NBS