A111DS 21 1

Examination of Failed Four-Inch

Diameter Cast Iron Pipe Natural

Gas Main, Fort Payne, Alabama

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

Mational Measurement Laboratory

J.S. Department of Commerce

Mational Bureau of Standards

Washington, DC 2C234

September 1980

Issued February 1981

Failure Analysis Report

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• U56 iai Transportation Safety Board

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NBSIR 81-2211

EXAMINATION OF FAILED FOUR-INCH

DIAMETER CAST IRON PIPE NATURAL

GAS MAIN, FORT PAYNE, ALABAMA

NATIONAL BUREAU

OF STANDARDS

LIBRARY

APR 3 0 1981

n D-t 0_cr . - /

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

September 1980

Issued February 1981

Failure Analysis Report

Prepared for

National Transportation Safety Board

Washington, DC 20594

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
u as/s era -<

y* »*tfi !
TABLE OF CONTENTS

SUMMARY

1 . INTRODUCTION

1.1 Reference

1.2 Background Information

1.3 Parts Submitted

2. PURPOSE AND PLAN OF THE EXAMINATION

3. RESULTS OF THE EXAMINATION

3.1 Photographic Documentation

3.2 Fractographic Examination

3.3 Examination for Graphitization

3 .

b

Metallographic Examination

3.5 Chemical Analysis

3.6 Hardness Measurements

3.7 Ring Tests

3.8 Talbot Tests

h. DISCUSSION

5. CONCLUSIONS

6 . ACKNOWLEDGEMENT

REFERENCES

FIGURES

1. The two pieces of the fractured four-inch diameter cast iron pipe

as received at NBS.

2. Mating fracture surfaces of the failed pipe as received at NBS.

3. Fracture surface after cleaning with buffered hydrochloric acid.

U. SEM fractograph. from the region indicated by arrow B in figure 3

near the inside edge of the fracture.

l

5. SEM fractograph from the region indicated, by arrow G in figure 3.

6. Low magnification SEM fractograph from the region indicated hy

arrow A in figure 3.

7. SEM fractograph from the region indicated hy arrow B in figure 3

near the outside edge of the pipe.

8. Polished cross section through the pipe sample ranging from about

1/2 to 2 inches from the fracture.

9. Longitudinal section through the pipe at arrow A, figure 3, showing

the fracture profile horizontally at the top.

10. Longitudinal section through the pipe at arrow G, figure 3, showing

the fracture profile horizontally at the top.

11. Longitudinal section through the pipe at arrow H, figure 3, showing

the fracture profile horizontally at the top.

12. Longitudinal section through the pipe at arrow B, figure 3, showing

the fracture profile horizontally at the top.

13. Longitudinal section through the pipe wall showing the representative

microstructure of the material near the outside wall surface.

lb. Longitudinal section through the pipe wall showing the representative

microstructure of the material near the midthickness of the wall.

15- Longitudinal section through the pipe wall showing the representative

micro structure of the material near the inside wall surface.

l6. Longitudinal section through the pipe wall showing a representative

field of essentially total graphitization.

17- Longitudinal section through the pipe wall at arrow H, figure 3,

showing the fracture profile horizontally at the top.

l8. Longitudinal section through the pipe wall at arrow B, figure 3,

showing the fracture profile horizontally at the top.

li

SUMMARY

At the request of the National Transportation Safety Board, the

Fracture and Deformation Division of the National Bureau of Standards

performed an examination of a fractured four-inch diameter cast iron

pipe natural gas main from Fort Payne, Alabama. An explosion and fire

reportedly occurred in an apartment building at the location of the

failure on November IT, 1979*

The pipe had suffered a transverse fracture. Only one of the

fracture faces was examined at the National Bureau of Standards. Most

of the corrosion product on the fracture surface was rather easily

removed indicating the likelihood that most of the fracture was recent.

There was some graphitization on the fracture surface in a region near

the bottom of the pipe suggesting the existence of at least a partthrough crack before the time of the final failure. Failure appeared to

be due to the application of a bending load at the location of the

apparent pre-existing crack.

In addition to the graphitization observed at the fracture, some

graphitization was found in other regions of the submitted pipe.

Graphitization, however, does not appear to have been a major contributing

factor to the failure.

The chemical composition of the pipe material was typical for gray

cast iron. Except for material adjacent to the inside wall surface of

the pipe, the hardness was typical for ordinary gray cast iron. Material

adjacent to the inside wall surface of the pipe was softer than . expected

for ordinary gray cast iron. The microstructure of the material varied

considerably across the pipe wall thickness.

iii

Examination of Failed Four- Inch Diameter Cast Iron

Pipe Natural Gas Main, Fort Payne, Alabama

1.1 1. INTRODUCTION

Reference

National Transportation Safety Board, Washington, DC 2059^+. This

investigation was conducted at the request of Mr. Jerry A. Houck,

Metallurgist, National Transportation Safety Board.

1.2 Background Information

Information in this section was furnished by the National Transportation

Safety Board.

On November IT, 1979, there was an explosion and fire in a fourunit apartment building in Fort Payne, Alabama attributed to the ignition

of natural gas leaking from a four-inch diameter cast iron pipe gas

main. Upon exposure, the gas main was found to be cracked circumferentially

from about 1:00 to 11:00 o'clock, where 12:00 o'clock is at the top as the pipe lay in the ground. The crack exhibited a maximum width of 0.35

inch at the bottom of the pipe when the pipe was uncovered.

The pipeline had been in service for 26 years. The maximum allowable

operating pressure was 25 psig.

1.3 Parts Submitted

Two pieces of the' fractured four-inch diameter cast iron pipe, each

containing one of the mating fracture surfaces, were submitted to the

NBS Fracture and Deformation Division on March 20, 1980. These pieces

are shown in figure 1 as received at NBS. It is to be noted that although

it was reported that the pipe had cracked circumferentially from about

the 1:00 to 11:00 o'clock positions when exposed at the site, complete

fracture and separation had occurred before the samples were submitted

to NBS. On that same day (March 20, 1980), the smaller piece (on the

right in figure l)_ was given to Tim G. Dunn of Dunn Laboratories, Inc., as per instructions from Jerry Houck of the National Transportation

Safety Board. Therefore, except for some documentary photographs, this

examination was limited to the larger piece of pipe (on the left in

figure 1 )

2. PURPOSE AND PLAN OF THE EXAMINATION

The National Transportation Safety Board requested that the NBS

Fracture and Deformation Division perform a failure analysis and material

characterization of the fractured pipe. At a meeting at NBS on March 20, 1980

attended by Jerry Houck of the National Transportation Safety Board,

Tim G. Dunn of Dunn Laboratories, Inc. and T. Robert Shives of the

National Bureau of Standards, it was agreed that the pipe examination

would include the following tasks

1. Photographic documentation

2 . Fractographic examination

3. Examination for graphitization

b. Metallographic examination

5. Chemical analysis

6. Hardness measurements

7. Ring tests

8. Talbot tests

3. RESULTS OF THE EXAMINATION

3.1 Photographic Documentation

A documentary photograph of the pieces of pipe containing the

mating fracture surfaces is shown in figure 1. The fracture surfaces

themselves are shown in figure 2. Documentation of various aspects of

the examination is found in other figures throughout the report.

3. 2 Fractographic Examination

As indicated in the previous section, the two mating fracture

surfaces are shown as-received at KBS in figure 2. The top of the pipe

in the figure corresponds to the top of the pipe (12 o'clock position)

as it was oriented in service. The fracture surface shown at the left

in the figure is the one retained at KBS for examination.

The fracture surface of the pipe was covered with a dark reddish

brown corrosion product when submitted to KBS. Two regions, indicated

by arrows A and B in figure 2, were somewhat different in appearance

from the rest of the fracture surface suggesting the possibility of

graphitization.

To facilitate a fractographic examination, the fracture surface was

cleaned in an ultrasonic bath with buffered hydrochloric acid. The

fracture is shown in figure 3 after cleaning. Most of the reddish brown

corrosion product was rather easily removed by the cleaning procedure,

indicating that much of the corrosion was of a superficial nature, and

therefore that most of the fracture was rather recent. However, some of

this corrosion product remained after cleaning, especially in the region

near the bottom of the pipe indicated by arrow B in figures 2 and 3

The fact that the corrosion product remained on the fracture surface

after cleaning suggests that a crack may have been present near the

bottom of the pipe for some time before final failure. Since the corrosion

product was concentrated over the outside 2/3 of the fracture in the

region indicated by arrow B, the crack probably was only part-through,

starting at the outside of the pipe. As compared to most of the rest of

the fracture surface, the region indicated by arrow A in figures 2 and 3

remained darker in color after cleaning and appeared to be an area of

graphitization.

2

Regions near the top and bottom of the pipe were examined with the

scanning electron microscope (SEM). The locations of these regions are

indicated in figure 3. The primary feature of the fracture surface at

both top and bottom where it was not masked by corrosion product was

cleavage, which is normally observed in gray cast iron fractures. SEM

fractographs of two representative areas are shown in figures h and 5.

A fractograph. from the area indicated by arrow A in Figures 2 and 3 is

shown in figure 6. Again, this region appears to have been graphitized

and shows evidence of separating from the pipe. A fractograph from the

area indicated by arrow B in figure 2 is shown in figure J. Corrosion

product on the fracture surface is evident at this location.

3.3 Examination for Graphit ization

A cross section ranging from about 1/2 to 2 inches from the fracture

was cut from the pipe sample. The polished section is shown in figure

8. Some localized graphit ization adjacent to the outside wall surface

of the pipe is evident, especially in the region between 12:00 and 2:00

o'clock. At one location in this region, the graphitization penetrates

about 1/3 of the pipe wall thickness. Except for this one location,

graphitization was rather shallow in this section.

In order to check for graphitization at the fracture surface,

longitudinal sections intersecting the fracture were taken in regions

near the top and bottom of the pipe in locations indicated by arrows A,

G, H, and B in figure 3. These sections were taken through the specimens

used for the fractographic examination. Low magnification photographs

of each of these sections are shown in figures 9 through 12. There was

some graphitization at the outside wall surface in each section, and in one section from the top of the pipe (figure 9), the graphitization had

penetrated about k0% of the pipe wall thickness adjacent to the fracture.

This section was taken through the pipe at the location indicated by

arrow A in figure 3 and was through the area of apparent graphitization

shown in the fractograph of figure 6. When the SEM sample was sectioned

for the metallographic examination, this area of graphitization separated

from the pipe. There was, however, very little graphitization along the

fracture surface. There was very little graphitization on the fracture

surface of the other section from the top of the pipe (figure 10), but

there appears to be a substantial secondary crack leading from and

parallel to the fracture at the location indicated by the arrow.

In the sections from the bottom of the pipe, graphitization at the

outer wall surface in the vicinity of the fracture was not nearly as severe as in the one region near the top shown in figure 9, hut graphitization

on the fracture surface itself extended across about 2/3 of the pipe

wall thickness in both sections. The layer of graphitization on the

fracture surface is strong evidence that at least a part-through crack

had existed at the bottom of the pipe at the location of the fracture

for some time before final failure of the pipe.

3 • h Metallographic Examination

The longitudinal sections that were examined for graphitization

were also examined met allographic ally in order to characterize the

- 3 -

microstructure of the pipe material. There was considerable variation

in the microstructure across the pipe wall thickness. The micro structure

near the outside wall surface not in a region of graphitization is shown

in figure 13. It consisted essentially of type B graphite flakes in a matrix of ferrite with a small^amount of steadite (iron- iron phosphide

eutectic) in rounded particles . Near the center of the wall thickness,

shown in figure Ik, the micro structure consisted primarily of type E

graphite flakes in a ferrite matrix with steadite at the boundaries of

the solidification cells. Adjacent to the inside wall surface, the

micro structure consisted primarily of type A graphite flakes in a ferrite

matrix with some apparent steadite. A representative example of the

micro structure in this region is shown in figure 15. Note that the

graphite flake size is much larger near the inside wall surface than in

the rest of the material. A representative region of essentially complete

graphitization is shown in figure 1

6

.

Unetched fields exhibiting parts of the fracture profile in the

sections taken at arrows H and B in figure 3 are shown in figures IT and

18, respectively. Graphitization at the fracture surface is evident.

3 . 5 Chemical Analysis

A sample of the pipe material was submitted to a commercial laboratory

for chemical analysis. The results of that analysis are as follows:

Element

Total carbon

Graphitic carbon

Manganese

Phosphorus

Sulfur

Silicon

Nickel

Chromium

Molybdenum

Copper

Weight Percent

3.60

3.25

0.39

0.775

0.080

1.86

< 0.01

0.05

< 0.01

0.19

The chemical composition requirements of proposed ANSI Standard

A21. 9-1970 for cast iron pipe centrifugally cast in sand lined molds for

gas service limit the phosphorus and sulfur contents to 0.90 and 0.12$

maximum, respectively. These are the only chemical requirements of this

standard, and this cast iron material satisfies them. The standard or specification under which the pipe was produced is not known; ANSI

Standard A21.9-70 is quoted only for comparison of the pipe material

with that produced in accordance with today's practices. The composition

of the material appears to be typical for gray cast iron.

The carbon equivalent [% total carhon + 1/3 LI silicon + % phosphorus)]

is equal to about U.5, which indicates that this cast iron is hypereutectic. Hypereutectic cast irons usually contain coarse graphite

flakes, although this does not appear to he true for this material

except near the inside wall surface. These cast irons are generally of

lower strength than hypoeutectic cast irons, but they are good for

vibration damping applications

.

3 . 6 Hardness Measurements

Hardness measurements were made on the cross section through the

pipe shown in figure 8. Brinell measurements were attempted, but the

material cracked rather badly when the load was applied. Therefore,

Rockwell B (HRB) hardness measurements were made. The material adjacent

to the inside wall surface of the pipe was considerably softer than

either the material at the center or the material adjacent to the outside

wall surface. The hardness near the inside wall surface averaged about

HRB 6k, whereas the hardness at the center and near the outside wall

surface was HRB Qk and 86, respectively. Approximate Brinell equivalent

hardness values are Ilk, l62, and 169, respectively, for material adjacent

to the inside wall surface, material at the center, and material adjacent

to the outside wall surface. Brinell hardness values of 162 and 169 are

typical for ordinary gray cast iron, whereas a Brinell hardness value of

llU low for ordinary gray cast iron and is more typical for soft gray

iron .

3 . T Ring Tests

Three ring specimens, each about 21/2 inches wide, were machined

from the pipe sample. The modulus of rupture was calculated in accordance

with ANSI A21. 9-1970 from the results of ring tests performed on these

specimens. The modulus of rupture values are as follows:

Specimen No. Modulus of Rupture, psi

The standard requires a minimum of U0,000 psi for the modulus of

rupture and is quoted for comparison of the pipe material with today's

requirements. Therefore, the results from all three specimens satisfy

the requirement of the standard.

3 . 8 Talbot Tests

Both the modulus of rupture and the secant modulus of elasticity

were determined from the results of Talbot tests in accordance with ANSI

Standard A21.9-70. Tests were performed on four specimens - one from

the top, one from the bottom, and one from each side of the pipe sample

as the pipe had been oriented in service. The modulus of rupture and

the secant modulus of elasticity results are as follows:

1 71,900

62,900

7^,100

2

3

Specimen Modulus of Rupture, psi Secant Modulus of Elasticity, psi

Bottom

Side 1

Side 2

Top

63,600

i+7,^00

61,800

3^,600

7 , 380,000

12.975.000

8 , 790,000

13.875.000

The standard requires a minimum value of U0,000 psi for the modulus

of rupture as calculated from the results of the Talbot tests. Therefore,

the results from the specimens from both sides and the top satisfy the

standard, but the results from the specimen from the bottom failed to

meet the minimum requirement of the standard.

Further, the standard states that the secant modulus of elasticity

must not exceed 250 times the actual value of the modulus of rupture for

any given specimen. The results from the top and side 1 are satisfactory,

but the results from side 2 and the bottom exceed the maximum permissible

value. Again, the standard is quoted only for comparison of the pipe

material -with today’s requirements.

This four-inch diameter gray cast iron pipe natural gas main fractured

transversely while in service. When the pipe was uncovered, it was

found to be cracked from about 1:00 o’clock to 11:00 o’clock, although

the fracture was complete when the pipe samples were received at NBS.

When the pipe was received at NBS for examination, there was a considerable amount of corrosion product on the fracture surfaces. Most

of the corrosion product was easily removed indicating that corrosion

was primarily superficial, and therefore that most of the fracture was

rather recent. In a region near the bottom, however, all of the corrosion

product was not removed by the cleaning procedure. This region consisted

of a thin layer of reddish brown corrosion product over a relatively

thin layer of graphitization on the fracture surface. The graphit ization

extended in about 2/3 of the pipe wall thickness starting at the outside

wall surface. Its presence as a thin layer on the fracture surface

strongly suggests the existence of at least a part-through crack for

some time before final failure of the pipe. A small region at the top

was found to be a patch of graphitization.

Failure of the pipe due to the application of bending stresses at a location in the pipe weakened by the presence of the apparent partthrough crack, and probably to a much lesser degree by graphitization,

is consistent with the observations of this examination. The pipe

failed in a brittle manner with cleavage being the primary fracture

mode. Although the origin of the fracture crack was not definitely

established, it appears very likely that fracture initiated at the

apparent pre-existing crack at the bottom of the pipe.

In addition to the graphitization at the fracture, there was some

localized graphitization in a cross section slightly removed from the

fracture. Also, graphitization appears to have contributed to the

rather poor performance of two of the Talbot specimens which will be

h. DISCUSSION

discussed later. Although, there was graphitization present in the pipe

sample, there was a relatively small amount at the outside wall surface

at the fracture. Therefore, graphitization does not appear to have heen

a major factor in the failure of the pipe.

The chemical composition of the pipe material appeared to he typical

for gray cast iron. The microstructure of the pipe material varied

considerably across the wall thickness - possibly due to a cooling rate

gradation across the thickness during the casting process. Hardness was typical for ordinary gray cast iron except adjacent to the inside wall

surface where the material was softer than expected for ordinary cast

iron.

The modulus of rupture as calculated from the results of ring tests

easily satisfied the requirement of the present day standard, ANSI

Standard A21.9-70. The modulus of rupture calculated from the Talbot

test results satisfied the standard in three out of four cases, and the

secant modulus of elasticity satisfied the standard in two out of four

cases. An examination of the Talbot specimens after testing indicated

that there was significant graphitization at the fractures of the specimens

that resulted in values- that failed to satisfy the standard.

5.

CONCLUSIONS

1. This failed gray cast iron gas main pipe had fractured transversely

around about 5/6 of the circumference while in service. (The

fracture had been completed before the pipe was submitted to NBS

for examination.

)

2. There was an apparent part-through transverse crack near the bottom

of the pipe in existence before final failure through which the

fracture passed.

3. The fracture origin was not definitely established, but is probably

associated with the apparent pre-existing crack near the bottom of

the pipe.

b. Failure appeared to be due to a bending load applied to the pipe.

5. Except for a small region near the top and a somewhat larger region

near the bottom of the pipe, corrosion product on the fracture

surface was rather easily removed indicating that most of the

fracture was probably recent.

6. The fracture mode was primarily cleavage, which is normal for

overload fractures in cast iron.

7. There was some graphitization at the fracture and in other regions

of the pipe that were examined, but graphitization does not appear

severe enough, to have been a major factor in the failure.

8. The chemical composition of the material appeared to be typical for

gray cast iron.

- 7 -

9 . Except for material adjacent to the inside wall surface of the

pipe, hardness was typical for ordinary cast iron. Hardness adjacent

to the inside wall surface was lower than expected for ordinary

cast iron and is- more typical of soft gray iron.

10. There was a considerable variation in microstructure across the

wall thickness of the pipe.

11. The modulus of rupture based on the results of ring tests satisfies

MSI Standard A21.9-70.

12. One of four modulus of rupture values and two of four secant modulus

of elasticity values based on the results of Talbot tests did not

meet today’s requirements of MSI Standard A21.9-70. (ANSI A21.9-

70 is quoted for comparison of this pipe with present day requirements.)

6. ACKNOWLEDGMENT

Leonard C. Smith of the NBS Fracture and Deformation Division

performed the metallographic work, prepared the SEM specimens, made the

hardness measurements, and assisted in performing the ring and Talbot

tests. Joel C. Sauter, also of the NBS Fracture and Deformation Division,

and Mr. Smith, performed the photographic work.

REFERENCES

1. Metals Handbook, 8th Edition, Volume 7, American Society for Metals

1972.

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

Gray and Ductile Iron Founders’ Society, Inc., 1971.

- 8 -
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Figure

2.

Mating

fracture

surfaces

of

the

failed

pipe

as

received

at

NBS

.

The

piece

of

pipe

on

the

left

was

retained

at

NBS

for

examination.

The

top

of

the

pipe

in

the

figure

corresponds

to

the

top

of

the

pipe

as

it

was

oriented

in

service.

The

arrows

indicate

regions

of

the

fracture

surface

where

there

is

possible

graphitization

or

more

severe

corrosion

than

on

the

rest

of

the

fracture

surface.

Figure 3. Fracture surface after cleaning with buffered hydrochloric

acid. Arrows A and B indicate the same regions as arrows

A and B, respectively, in figure 2. The regions between

lines C and D and between lines E and F were examined with

the SEM. Longitudinal sections for metallographic examination

were taken at arrows A, G, H, and B.

Figure b. SEM fractograph from the region indicated by arrov B in

figure 3 near the inside edge of the fracture. The primary

fracture mode is cleavage. X 550

Figure 5. SEM fractograph from the region indicated by arrov G in

figure 3. The primary fracture mode is cleavage. X ^75

Figure 6. Low magnification SEM fractograph from the region indicated

by arrow A in figure 3. A region of graphitization can be

seen about to separate from the pipe. X 20

Figure 7- SEM fractograph from the region indicated by arrow B in

figure 3 near the outside edge of the pipe. Corrosion

product is covering the fracture surface. X 950

Figure 8. Polished cross section through the pipe sample ranging from

about 1/2 to 2 inches from the fracture. Some localized

graphitization is evident, especially between 12:00 and

2:00 o’clock. The top of the pipe in the figure corresponds

to the top of the pipe as it was oriented in service.

I

Figure 9. Longitudinal section through the pipe at arrow A, figure 3, showing the

fracture profile horizontally at the top. Graphitization at the outside

wall surface (vertical at the left) is evident. The inside wall surface

is vertical at the right. The vertical line at the far left represents

the original outside wall surface. The other vertical line represents

the approximate extent of graphitization at the fracture.

Etchant: 1 % nital X 10

Figure 10. Longitudinal section through the pipe at arrow G, figure 3, showing the

fracture profile horizontally at the top. Graphitization at the outside

wall surface (vertical at the left) away from the fracture can he seen. The inside wall surface is vertical at the right. The vertical line at

the far left represents an extension of the original outside wall

surface. The other vertical line represents the approximate depth of

graphitization at the fracture. The arrow indicates a secondary crack.

Etchant: 1% nital X 10

Figure 11. Longitudinal section through the pipe at arrow H, figure 3, showing the

fracture profile horizontally at the top. The outside wall surface is

vertical at the left and the inside wall surface is vertical at the

right. Graphitization at the fracture surface is evident. The vertical

line at the far left represents an extension of the original outside wall

surface. The other vertical line represents the approximate depth of

graphitization at the fracture.

Etchant: 1% nital X 10

Figure 12. Longitudinal section through the pipe at arrow B, figure 3, showing the

fracture profile horizontally at the top. Graphitization is evident

doth on part of the fracture surface and at the outside wall surface

(vertical at the left). The inside wall surface is vertical at the

right. The vertical line at the far left represents an extension of

the original outside wall surface. The other vertical line represents

the approximate depth of graphitization at the fracture.

Etchant: 1 % nital X 10

Figure 13. Longitudinal section through the pipe wall showing the representative

micro structure of the material near the outside wall surface. The

micro structure consists primarily of type B graphite flakes in the

ferrite matrix. There are some rounded particles of apparent steadite

(iron- iron phosphide eutectic).

Etchant : 1 % nital X 500

Figure lU. Longitudinal section through the pipe wall showing the representative

micro structure of the material near the midthickness of the wall. The

micro structure consists primarily of type E graphite flakes in a ferrite

matrix. There is a small amount of what appears to "be steadite

(iron-iron phosphide eutectic) present in interdendritic patches.

Etchant: 1 % nital X 500

Figure 15. Longitudinal section through the pipe vail shoving the representative

microstructure of the material near the inside vail surface. The

micro structure consists primarily of type A graphite flakes in a ferrite matrix. There are some patches vhich appear to he steadite

(iron- iron phosphide eutectic).

Etchant: 1% nital X 500

Figure l6. Longitudinal section through the pipe vail shoving a representative

field of essentially total graphitization.

Etchant: 1% nital X 500

Fig-are IT. Longitudinal section through the pipe vail at arrow H, figure 3,

shoving the fracture profile horizontally at the top. Graphitization

at the fracture surface can he seen. As polished X 100

Figure l8 . Longitudinal section through the pipe vail at arrow B, figure 3,

shoving the fracture profile horizontally at the top. Graphitization

at the fracture can he seen. As polished X 100

I

. ^ C._l 6 l

AKAj_iYo IS r^Hjir'uRT .LjIjIv jlaO U a.

1 Uij -L.R Examination of Failed Four- Inch Diameter Cast Iron Pipe

Natural Gas Main, Fort Payne, Alabama

Author: T. Robert Shives

Sponsoring Agency: NTSB

rpt~ /’V./r

i? jl\vJiva . Initial &

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MAT I ONAL BUREAU OF STANDARDS

Febr-Uc.i'-v 4> 1981

Memorandum to Author 2 T« Robert Shives

( T h r o ub h Ce n t e r 0 f f i c e > From R„ F, Blunt. Executive Secretary

;hi net on Editorial Review Board

SubJ cts -RB Approval of NBSIR Mani crii

Y o u r in a n u s c r i f t

8 h i ve 5; . T . R

Examination of Failed F o u r— Inch Diameter Cast Iron Pipe Natural

Gas Main. Fort Payne. Alabama

NBSIR 80- (NTSBXR)

BSIR nui ber « sponsors NBSIR 81-22 (NTSBXRj

ha s been approved and/or noted by the Washington Editorial Review

Board for issuance as an MBS I nte rase ncv/ Internal Report. (See toe

.January 16. 1 973 revision of Section 5 of the MBS Manual for Sclent.,.. . a : i d 7e c h n i c a 1 Co mm u n i c a t i o n s .

)

Anv required security or sponsoring asencv release should be obtained

b y y o u r d i v i s i o n i n a d va n c e o f r e pr o d u c t i 0 n

I f this report is to be reproduced by NBSv arrangements are to be aac .. by the or i Tinatins organization directly with Printing and DupI leaf in •; • Pr i. nt ins and Duplicating will supply the Technical Information and Pub 1 ion (TIR'D) with required* r .. . - of copies for appropr . inter no 1 MBS distribution. If the report is for unlimited distribution

VI PD will arrange for input to NT IS.

NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 2.Gov't Accession No.

A” .

3. Recipients Accession No.

4. TITLE AND SUBTITLE

EXAMINATION OF FAILED FOUR-INCH DIAMETER CAST IRON

PIPE NATURAL GAS MAIN, FORT PAYNE, ALABAMA

5. Publication Date

6L Performing Organization Code

7. AUTHOR(S)

T . Robert Shives

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

: -n -f ^ -

V .

11. Contract/Grant No.

No. 5640-42

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, zip)

National Transportation Safety Board

Washington, D.C. 20594

13. Type of Report & Period Covered Failure Analysis

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-v/ord or less [actual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) At the request of the National Transportation Safety Board, the Fracture and

Deformation Division of the National Bureau of Standards performed an examination of a fractured four-inch diameter cast iron pipe natural gas main from Fort Payne,

Alabama. An explosion and fire reportedly occurred in an apartment building at the

location of the failure on November IT, 1979*

The pipe had suffered a transverse fracture. Only one of the fracture faces was examined at the National Bureau of Standards. Most of the corrosion product on the

fracture surface was rather easily removed indicating the likelihood that most of the

fracture was recent. There was some graphitization on the fracture surface in a region near the bottom of the pipe suggesting the existence of at least a part-through

crack before the time of the final failure. Failure appeared to be due to the

application of a bending load at the location of the apparent pre-existing crack.

In addition to the graphitization observed at the fracture, some graphitization

was found in other regions of the submitted pipe. Graphitization, however, does not

appear to have been a major contributing factor to the failure.

The chemical composition of the pipe material was typical for gray cast iron.

Except for material adjacent to the inside wall surface of the pipe, the hardness was

typical for ordinary gray cast iron.

17. 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 gas pipe; cleavage; graphitization

18. AVAILABILITY Unlimited

For Official Distribution. Do Not Release to NTIS

I

i Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

I | Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS

(THIS REPORT)

21. NO. OF

PRINTED PAGES

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

22. Price

UNCLASSIFIED

USC O MM- D C