NBSIR 76-1121

r

ft| Examination of Failed Six Inch

Cast Iron Pipe Natural Gas

Main, Brooklyn Union Gas

Company, Queens County,

New York

Bruce W. Christ and T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

Failure Analysis Report

July 1976

Issued September 1976

Prepared for Office of Pipeline Safety Operations

Department of Transportation

Washington, D. C. 20590

NBSIR 76-1121

EXAMINATION OF FAILED SIX INCH

CAST IRON PIPE NATURAL GAS

MAIN, BROOKLYN UNION GAS

COMPANY, QUEENS COUNTY,

NEW YORK

Bruce W. Christ and T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washsington, D C. 20234

Failure Analysis Report

July 1976

Issued September 1976

Prepared for Office of Pipeline Safety Operations

Department of Transportation

Washington, D. C. 20590

U S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director
.

'
Table of Contents

Page

SUMMARY iii

1. INTRODUCTION 1

1.1 Reference 1

1.2 Background Information 1

1.3 Part Submitted 2

2. PURPOSE 2

3. RESULTS OF EXAMINATIONS, TESTS AND ANALYSES 2

3.1 Visual and Macroscopic Examination 2

3.2 Fractographic Examination with the Scanning

Electron Microscope 4

3.3 Chemical Analysis 4

3.4 Wall Thickness Measurements 5

3.5 Metallographic Examination 5

3.6 Hardness Measurements 6

4. DISCUSSION 6

5. CONCLUSIONS 7

6. ACKNOWLEDGEMENT 8

REFERENCES 8

FIGURES

1. Length of six inch diameter cast iron pipe natural gas main reported

to be from Queens County, New York, as received at NBS except that

the top of the wooden shipping crate has been removed.

2. View of what was reported to be the top of the pipe as oriented in

service.

i
FIGURES (continued)

3.

4.

5.

6 .

7.

8 .

9.

10 .

11 .

12 .

13.

14.

15.

16.

Bottom view of the pipe length in the vicinity of the crack (arrow).

View of the pipe near the top showing depressions at the crack.

Partially exposed fracture surfaces of the pipe showing corrosion

product before any cleaning was done.

Scanning electron fractograph showing features typical for the region

of the fracture about midway through the wall thickness.

Scanning electron fractograph near the outside wall surface of the pipe.

Scanning electron fractograph near the outside wall surface of the pipe.

Etched longitudinal section intersecting the W-length fracture at a point 5 cm beyond the 9 cm point on the circumferential metric scale

that can be seen in figure 2.

Part of the longitudinal section shown in figure 9 in the unetched

condition.

Center area of the section shown in figure 9 where there is a concentration of porosity or gas pockets.

An area from the section shown in figure 9 where there is partial

graphitization

An area from the section shown in figure 9 where graphitization is

nearly complete.

Transverse section through the W-length of the pipe about 6 cm from

the fracture exhibiting some graphitization adjacent to the outside

wall surface.

Longitudinal section intersecting the fracture at one of the

depressions shown in figure 4.

Typical microstructure of the submitted pipe material in an area away from graphitization and porosity.

li
SUMMARY

The Office of Pipeline Safety Operations, Department of Transportation,

submitted a length of six inch diameter cast iron natural gas pipeline to

the NBS Mechanical Properties Section for examination. The OPSO indicated

that the pipe length was taken from Kew Gardens, Queens County, New York.

The pipe length contained a transverse crack that had penetrated the

entire wall thickness for about 90% of the pipe circumference. The

nature of the corrosion product on the fracture surface indicated that

the crack was not "fresh." The fracture was brittle typical for gray

cast iron. Failure apparently occurred due to the application of a bending

load from an external source. The material appeared to be normal for gray

cast iron in regard to microstructure and hardness. Chemical composition

also appeared normal, with the possible exception of a slightly high

phosphorus content. In the sections examined, there was one area of high

porosity. There were localized regions of graphitization , but the

discontinuous nature of the graphitization around the circumference of

the pipe suggests that graphitization did not play a significant role in

the propagation of the crack. Measured variation in wall thickness was

within specified tolerances.

iii
.
Examination of Failed Six Inch Cast Iron Pipe Natural Gas Main,

Brooklyn Union Gas Company, Queens, County , New York

1. INTRODUCTION

1.1 Reference

Office of Pipeline Safety Operations, Department of Transportation,

Washington, D.C. 20590. This investigation was conducted at the request

of Mr. Cesar DeLeon, Acting Director of the Office of Pipeline Safety

Operations, under Agreement Number DOT-AS-60053 . The request was dated

April 14, 1976 and was received at NBS on April 28, 1976.

1.2 Background Information

The information in this section was furnished by Mr. Walter Dennis, Jr.,

of the Office of Pipeline Safety Operations, Mr. Robert L. Swartwout of the

New York State Public Service Commission, Mr. Kurt M. Richter of the

Brooklyn Union Gas Company, and Mr. John T. Wynne, Jr., Assistant District

Attorney for Queens County, New York.

On January 30, 1976, there was an explosion followed by a fire

involving four houses on 86th Road between 134th and 135th Streets in

Kew Gardens, Queens County, New York. The houses were identified as follows: 134-14, 134-16, 134-18, and 134-20 86th Road. The explosion

and subsequent fire were attributed to an accumulation of natural gas

that had escaped from a cracked six inch diameter cast iron pipe gas

main located under 86th Road about two feet from and running parallel

to the south curb line of 86th Road.

The gas main had been installed in January 1927. The main was

under three feet of cover at the location of the crack.

Within the last five years, there had apparently been no excavations

within 9 feet east and 14 feet west of the location of the crack in the

gas main pipe. In October 1971, however, excavations were made over the gas

main about 10 feet east and 15 feet west of the location of the crack in

order to put plastic inserts in the service lines to the houses located

at 134-15 and 134-16 86th Road.

It was reported that no unusually heavy traffic had been using the

street. The heaviest vehicles to use the street, at least on a regular

basis, were garbage collecting trucks and fuel oil delivery trucks. The

crack in the gas main pipe occurred in what was described as a quiet

residential area.

The closest pipeline in 86th Road to the gas main in the vicinity

of the fracture was a 12 inch diameter storm sewer. The sewer, which

was installed in 1946, lay essentially parallel to the gas line and

about 7 feet north of it.

1
It was reported by the Brooklyn Union Gas Company that there had

been unusually large settlement of the north curb and a 4 inch settlement

of the south curb line of 86th Road. The west wall of the house located

at 134-14 86th Road had abnormal settlement in the front of the building.

The greatest settlement of the south curb was about 17 feet west of the

location of the crack in the pipe. All points of maximum settlement were

west of the crack in the pipe. The settlement values are based on a comparison between a 1956 survey and a survey made on February 19, 1976.

According to Mr. Richter, the specification to which this cast iron

pipe was manufactured was probably the 1925 edition of the American Gas

Association Standard Specifications For Cast Iron Pipe and Special

Castings. A copy of this specification was provided to NBS by

Mr. Swartwout.

1.3 Part Submitted

A piece of the six inch diameter cast iron pipe about 5 feet-8 inches

(1.7 meters) long containing the crack was delivered in a wooden crate to

the NBS Mechanical Properties Section on February 9, 1976 by

Detective Robert D. Gabriel of the New York City Police Department,

Mr. Mario Martello of the New York State Public Service Commission,

and Mr. Willie Merriweather of the Brooklyn Union Gas Company. The

pipe length was cushioned in foam rubber.

2.

PURPOSE

The Office of Pipeline Safety Operations requested that the NBS

Mechanical Properties Section perform the following tasks in conjunction

with an examination of the cracked pipe.

1. Provide photo documentation and maintain a custodial record.

2. Prepare a test specimen in such a manner so as to preserve the

extremities of the fracture.

3. Examine for possible graphitization.

4. Determine mechanical properties, make a chemical analysis,

and compare results with appropriate standards.

5. Provide f ractographic analysis of the fracture surfaces.

6. Make additional tests or analyses that may be necessary to

determine, if possible, the failure cause.

3.

RESULTS OF EXAMINATIONS, TESTS, AND ANALYSES

3 . 1 Visual and Macroscopic Examination

The submitted pipe length is shown as received at NBS in figure 1,

except that the top of the wooden crate in which it was delivered had

2
been removed. As soon as the pipe length was removed from the crate,

three 2 1/2 cm wide steel straps were placed across the crack to keep

it from propagating further as the pipe was handled. The straps were

held in place with machine screws that were attached to the pipe in

drilled and tapped holes on either side of the crack. One such strap

can be seen in figure 2 which shows what was reported by the Brooklyn

Union Gas Company to be the top of the pipe as it was oriented in

service.

The transverse crack that can be seen in figure 2 had penetrated

the entire wall thickness of the pipe around nearly 90% of the pipe

circumference. With the pipe oriented as shown in figure 2, the

"hinged" portion is near the bottom.

Prior to being delivered to NBS, "top" had been written with chalk

on what was reported to be the top of the pipe as it had been oriented

in service. In addition, the pipe length had been marked on the reported

top with an "E" on one side of the crack and with a "W" on the other side.

The "E" and "W" can be seen in figure 2. For convenience in referring to

the pipe lengths on either side of the crack, one side will be referred

to as the "E-length" and the other side as the "W-length." The crack was

about 96 cm from the end of the "E-length."

When received at NBS, the pipe length (except for an area near the

crack) was covered with what appeared to be a mixture of ashes and soil.

Some of the pipe surface near the crack had been cleaned of the ash-soil

mixture before the pipe had been submitted for examination. The

cleaning was especially evident at the top of the pipe. Some of the

ash-soil mixture on the pipe can be seen in figure 2, and more can be seen

in figure 3 which shows the bottom of the pipe in the region of the crack.

Where the ash-soil mixture had been removed, the pipe surface exhibited

some general corrosion, but this corrosion did not appear to be severe enough to significantly affect the integrity of the pipe. Corrosion of

the inside wall surface of the pipe was negligible.

There were two depressions near the top of the pipe adjacent to the

crack. It appeared as though material had either been chipped out or had

fallen out. These depressions can be seen in figure 4. No other

significant mechanical damage to the pipe was observed.

In order to expose the fracture surface for examination, while

preserving the crack extremities, the pipe length was cut as follows.

A through transverse saw cut was made in the E-length about 33 cm from

the fracture. A similar saw cut was made in the W-length about 6 cm from

the fracture. Then on an approximate pipe diameter, a longitudinal saw

cut was made from the W-length transverse saw cut into the crack. Both

the E-length and the W-length fracture surfaces were then exposed over

about 180° of the pipe circumference. Only the W-length fracture surface

was used in the NBS examination. The E-length side of the fracture was retained in the as-received condition at NBS.

3
The entire exposed fracture surface was covered with what appeared

to be a superficial, light reddish-orange corrosion product as shown in

figure 5. Approximately one-half of the exposed W-length fracture surface

was cleaned ultrasonically . The light colored corrosion product was removed by this cleaning operation. Beneath the light colored product,

the entire portion of the fracture surface that had been cleaned was covered with a more adherent, darker colored corrosion product that was

not removed by the ultrasonic cleaning. Much of this material was removed

from approximately a 2 1/2 cm length of the fracture by repetitive

replication with cellulose acetate, but some of it remained. This 2 1/2 cm length was about 180° circumferentially from the hinged portion and was

in the vicinity of the probable fracture origin near the top of the pipe.

3 . 2 Fractographic Examination with the Scanning Electron Microscope

The 2 1/2 cm length of the W-length fracture that had been cleaned

both ultrasonically and by repetitive replication was examined with the

scanning electron microscope. Figure 6 shows features typical of those

exhibited by the fracture about halfway between the inside and outside

surfaces of the pipe. Two examples of the fracture surface features

near the outside surface of the pipe are shown in figures 7 and 8.

Note, the magnifications of figures 6, 7, and 8 are different.

Some evidence of cleavage appears in figures 6 and 7. The smooth

appearing regions in figure 8 are cavities that may have been porosity or gas pockets. In figure 6, the narrow dark particles are graphite flakes.

Such flakes are a normal constituent in gray cast iron. The graphite

flakes are not as easily seen in figures 7 and 8. Fracture features near

the inside surface of the pipe appeared similar to those shown in figure 8.

3 . 3 Chemical Analysis

A chemical analysis was performed on a sample of the pipe material

by a commercial laboratory with the following results:

Element Percent by Weight

Total carbon 3.61

Combined carbon 2.84

Manganese 0.35

Phosphorus 0.596

Sulfur 0.088

Silicon 1.80

Nickel 0.03

Chromium 0.04

Molybdenum <0.01

Copper 0.07

The 1925 edition of the American Gas Association Standard Specifications

for Cast Iron and Special Castings does not specify a chemical composition

for the pipe material. However, the chemical composition of the Queens

County pipe appears to be normal for a gray cast iron, with the possible

4
exception of a slightly high phosphorus content. A phosphorus content

greater than 0.50% is considered undesirable since it may lead to the

formation of excessive steadite, a brittle phase consisting of iron-iron

phosphide eutectic.

3. - Wall Thickness Measurements

It was reported by the Brooklyn Union Gas Company that the pipe

had been pit cast, a process that generally resulted in a nonuniform

wall thickness around the pipe circumference. There was, indeed, some variation in the wall thickness of the submitted pipe length. As measured

on a cross section about 6 cm from the fracture, the minimum wall

thickness was 0.35 inch near the top of the pipe (as the pipe was reportedly

oriented in service) and the maximum -was 0.48 inch near the bottom of the

pipe. This variation in wall thickness is within the tolerances given in

the 1925 edition of the American Gas Association Standard Specifications

for Cast Iron Pipe and Special Castings.

3 . 5 Metallographic Examination

An unetched longitudinal section through the approximate top of the

W-length of the pipe showing the fracture profile appears in figure 9.

The fracture profile is at the left, the outside surface of the pipe is

at the bottom, and the inside surface of the pipe is at the top as the

section is oriented in the figure. Part of the fracture profile is showm

at higher magnification in figure 10. The apparent lack of deformation

adjacent to the fracture is characteristic of a low ductility or brittle

fracture. The thin dark particles appearing in figure 10 and in several

subsequent figures are graphite flakes.

The mottled region that can be seen in figure 9 in about the center

one-third of the section length, and away from the outside wall surface of

the pipe, is in an area of porosity or gas pockets. Some of this porosity

is shown at higher magnification in figure 11. Of the sections of the

pipe examined, the area shown in figures 9 and 11 contains the greatest

concentration of porosity.

The dark region along the outer wall surface in figure 9 is graphitized.

Two areas from the section appearing in figure 9 showing partial graphitization and nearly complete graphitization appear in figures 12 and 13,

respectively.

Two transverse rings were taken through the W-length of pipe at 6 cm

and 15 cm from the fracture. Both of these rings exhibited some evidence

of graphitization. One of the rings is shown in figure 14.

A longitudinal section intersecting the fracture at one of the

depressions mentioned earlier where material was missing (arrows A,

figure 4) is shown in figure 15. Material adjacent to the depression

(upper left, figure 15) is graphitized.

o
The region of severest graphitization in the sections examined can

be seen in figure 9 near the right side of the photomacrograph.

Graphitization has penetrated about 3/4 of the wall thickness of the

pipe in this region.

The typical microstructure of the pipe material away from the

graphitized regions is shown in figure 16. The microstructure consists

primarily of graphite flakes (long, thin, dark particles) and pearlite

(fingerprint pattern) with small amounts of ferrite (light color) and

steadite (small rounded particles)

3.6 Hardness Measurements

Brinell hardness measurements (HB) were made on a cross section

through the pipe. The results of four measurements averaged HB 153.

The 1925 edition of the American Gas Association Standard Specifications

For Cast Iron Pipe and Special Castings does not specify hardness, but

the measured hardness is reasonable for gray cast iron.

4. DISCUSSION

This six inch diameter cast iron natural gas pipe failed as a result

of the initiation and propagation of a transverse crack that penetrated

the entire wall thickness of the pipe for about 90% of its circumference.

The hinged portion of the cracked pipe was reportedly at the bottom as

the pipe had been oriented in service. Cracks of this nature can be

caused by the application of an external bending load.

Perhaps the most significant feature of the fracture surfaces was

the corrosion products found on them. The entire portions of the fracture

surfaces that were exposed during the examination were covered with a light colored superficial corrosion product that was rather easily removed

by ultrasonic cleaning. Beneath the light colored product, however, was

a darker, more adherent corrosion product. Attempts to remove this darker

material by ultrasonic cleaning were unsuccessful. Much of it was removed

from a 2 1/2 cm length of the fracture by repetitive replication with

cellulose acetate, but some remained. The amount, color, and adherence

of the darker corrosion product on the fracture surface indicates that

the crack was not "fresh."

No significant mechanical damage to the pipe was observed, with the

possible exception of two depressions adjacent to the crack near the top

of the pipe where material appeared to be missing. A metallographic

examination of a section through one of the depressions revealed

graphitized material adjacent to the depressions. It is likely that the

missing material was also graphitized. This graphitized region would

have been rather easily knocked off during handling, which could explain

the forming of the depression. A similar explanation might account for

the second depression.

6
The fracture appeared to be brittle in nature, as expected for a

cast iron. The fracture features and the lack of deformation adjacent

to the fracture are both indicative of a brittle fracture.

/ General corrosion of the inside wall surface of the pipe length

was negligible, and the general corrosion of the outside wall surface

of the pipe length was not considered to be severe enough to significantly

affect the integrity of the pipe.

Graphitization was discontinuous around the two complete

circumferential sections examined. Graphitized regions penetrated the

wall from the outside to depths ranging from essentially zero to 75%

of the wall thickness. Because there is less resistance to crack

formation in graphitized regions, as compared to non-graphitized

regions, the presence of graphitization probably assisted in the

development of the crack. However, the discontinuous nature of

graphitization around the circumference suggests that graphitization

did not play a significant role in the propagation of the crack.

There was a high concentration of porosity in one region of one of

the sections examined. In general, however, the porosity in the pipe

appeared to be low. The porosity did not seem to have had a significant

effect on the fracture.

Except for the regions of porosity and graphitization, the microstructure of the pipe material appeared to be as expected for gray cast

iron. The microstructure consisted primarily of graphite flakes and

pearlite with some ferrite and steadite. The amount of steadite does

not appear to be excessive.

A chemical analysis of the pipe material indicated that there was a slightly greater than desirable phosphorus content. Otherwise, the

chemical composition appeared to be as expected for gray cast iron.

The hardness of the material as measured on a transverse section

was normal for gray cast iron.

There was some variation in wall thickness of the submitted pipe

length which was attributable to the manufacturing process used to make

the pipe, namely, pit casting. This variation in wall thickness is,

however, within specified tolerances.

5. CONCLUSIONS

1. The length of six inch diameter cast iron pipe natural gas main that was submitted to NBS for examination failed as a result of the

formation of a transverse crack that had penetrated the entire wall

thickness of the pipe for about 90% of the pipe circumference.

2. The crack was probably initiated by an externally applied bending load.

7
3 . The nature of the corrosion product on the fracture surfaces

indicates that the fracture was not "fresh."

4. The fracture mode appeared to be brittle.

5. General corrosion of the pipe wall surfaces was slight and was

not considered to have had a significant effect on the integrity

of the pipe.

6. There were localized regions of graphitization, but the discontinuous

nature of the graphitization around the circumference of the pipe

suggests that graphitization did not play a significant role in the

propagation of the crack.

7. In the sections examined, there was one region where the porosity

was quite high; in all other regions, the porosity was low.

Porosity did not appear to have played a significant role in the

fracture

.

8. The microstructure of the pipe material away from the regions of

porosity and graphitization appeared to be as expected for gray

cast iron.

9. The chemical composition of the pipe material was normal for gray

cast iron with the possible exception of a slightly high phosphorus

content

.

10. Variations in wall thickness were within the specified tolerances

set forth in the 1925 edition of the American Gas Association

Standard Specifications For Cast Iron Pipe and Special Castings.

11. Hardness measurements gave results which are as expected for

gray cast iron.

6. ACKNOWLEDGEMENT

Mr. Leonard C. Smith of the NBS Mechanical Properties Section

performed the photographic work, prepared the metallographic specimens,

and assisted in other aspects of this investigation.

REFERENCES

1. Gray and Ductile Iron Castings Handbook, Charles F. Walton, Editor,

Gray and Ductile Iron Founders' Society, 1971.

8
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Bottom

view

of

the

pipe

length

in

the

vicinity

of

the

crack

(arrow).

The

two

white,

horizontal

chalk

marks

indicate

the

approximate

ends

of

the

hinged

portion.

X

1/2
V
Figure 4. View of the pipe near the top showing depressions at the

crack. The depressions are indicated by arrows "A."

Arrow "B" indicates a sawcut made in the laboratory.

This sawcut is not related to the failure. The W-length

of the pipe is to the right of the crack and the E-length

is to the left. X 1

Figure 5. Partially exposed fracture surfaces of the pipe showing

corrosion product before any cleaning was done. The

E-length fracture surface is intact and the W-length

has been cut into two pieces. The white arrows indicate

the approximate extremeties of the crack. X 1/2

Figure 6. Scanning electron fractograph showing features typical

for the region of the fracture about midway through the

wall thickness. Cleavage is evident. X 110

Figure 7. Scanning electron fractograph near the outside wall surface

of the pipe. There is some evidence of cleavage. X 210

Figure 8. Scanning electron fractograph near the outside wall surface

of. the pipe. The smooth areas may have been regions of

porosity or gas pockets. X 490

Figure 9. Etched longitudinal section intersecting the W-length fracture

at a point 5 cm beyond the 9 cm point on the circumferential

metric scale that can be seen in figure 2. The fracture is

vertical at the left. The outside surface of the pipe is at

the bottom, and the inside of the pipe is at the top. Some

adherent soil and ash appear on the outside surface.

Etchant: 1% nital X 2 1/2

Figure 10. Part of the longitudinal section shown in figure 9 in the

unetched condition. The fracture profile is at the left.

There is no evidence of deformation.

As-polished X 100

Figure 12. An area from the section shown in figure 9 where there is

partial graphitization.

Etchant: 1% nital

Figure 11. Center area of the section shown in figure 9 where there

is a concentration of porosity or gas pockets.

As-polished X 50

X 200

Figure 13. An area from the section shown in

figure 9 where graphitization is nearly

complete.

As-polished X 100

Figure 14. Transverse section through the W-length of the pipe about

6 cm from the fracture exhibiting some graphitization

adjacent to the outside wall surface. Arrows indicate

some of the regions of graphitization.

As-polished X 1

Figure 15. Longitudinal section intersecting the fracture at one of

the depressions shown in figure 4. The section was taken

at about 52 1/2 cm on the circumferential scale shown

in figure 4. The fracture is vertical at the left; the outside

surface of the pipe is at the top. The dark region adjacent

to the outside surface is graphitized. The depression is at

the upper left of the section.

Etchant: 1% nital X 2 1/2

Figure 16. Typical microstructure of the submitted pipe material in an area away from graphitization and porosity. The microstructure consists primarily of graphite flakes (long, thin,

dark particles) and pearlite (fingerprint pattern) with

small amounts of ferrite (light color) and steadite (small

rounded particles)

.

Etchant: 1% nital X 400

,.l 1 4 A (REV. 7-73)

U.S. DEPT. OF COMM.

ilBLIOGR APH 1C DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1121

2. Ciov’t Accession

No.

3. Recipient’s Accession No.

TITLE AND SUBTITLE

EXAMINATION OF FAILED SIX INCH CAST IRON PIPE NATURAL GAS

MAIN, BROOKLYN UNION GAS COMPANY, QUEENS COUNTY, NEW YORK

5. Publication Date July 1976

6. Performing Organization C ode

AUTHOR(S)

Bruce W. Christ and T. Robert Shives

8. Performing Organ. Report No. NBSIR 76-1121

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3120418

11. Contract/Grant No.

Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Pipeline Safety Operations

Department of Transportation

Washington, D.C. 20590

13. Type of Report & Period Covered

Failure Analysis

14. Sponsoring Agency Code

SUPPLEMENTARY NOTES

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

The Office of Pipeline Safety Operations, Department of Transportation, submitted

length of six inch diameter cast iron natural gas pipeline to the NBS Mechanical

roperties Section for examination. The OPSO indicated that the pipe length was

aken from Kew Gardens, Queens County, New York. The pipe length contained a transverse

rack that had penetrated the entire wall thickness for about 90% of the pipe

ircumf erence. The nature of the corrosion product on the fracture surface indicated

hat the crack was not "fresh." The fracture was brittle typical for gray cast

ron. Failure apparently occurred due to the application of a bending load from an xternal source. The material appeared to be normal for gray cast iron in regard to

licrostructure and hardness. Chemical composition also appeared normal, with the

'Ossible exception of a slightly high phosphorus content. In the sections examined,

here was one area of high porosity. There were localized regions of graphitization,

iut the discontinuous nature of the graphitization around the circumference of the

•ipe suggests that graphitization did not play a significant role in the propagation

>f the crack. Measured variation in wall thickness was within specified tolerances.

. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

brittle fracture; cast iron; cast iron pipe; natural gas pipe; natural gas pipe

rracture

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