NBSIR 73-273

Examination of Failed Six Incli Cast

Iron Pipe Natural Gas Main; Illinois

Power Company, East Saint Louis,

Illinois

I. J. Femberg and M. L. Picklesimer

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington. D. C. 20234

October 15. 1973

Failure Analysis Report

Prepared for Office of Pipeline Safety

Department of Transportation

Washington. D. C. 20590

NBSIR 73-273

EXAMINATION OF FAILED SIX INCH CAST

IRON PIPE NATURAL GAS MAIN: ILLINOIS

POWER COMPANY, EAST SAINT LOUIS,

ILLINOIS

I. J. Feinberg and M. L. Picklesimer

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

October 15, 1973

Failure Analysis Report

"This document has been prepared for the use of the Office of Pipeline Safety, Department of Transportation,

Washington, D. C. Responsibility for its further use

rests with that agency. NBS requests that if release

to the general public is contemplated, such action be

taken only after consultation with the Office of Public

Affaris at the National Bureau of Standards."

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent, Secretary

IMATIOWAL BUREAU OF STANDARDS, Richard W. Roberts, Director

TABLE OF CONTENTS

Page

SUMMARY iii

1. INTRODUCTION 1

1.1 History 1

1 . 2 Purpose 1

2. EXAMINATION PLAN 1

3. EXAMINATION RESULTS 2

3.1 Visual Examination 2

3.2 Deflection and Gap Measurements 2

3.3 Chemical Analysis 3

3.4 Hardness Tests 3

3.5 Metallography 3

3.5.1 Kacro-examination 3

3.5.2 Microstructural examination 4

4. DISCUSSION 4

5. CONCLUSIONS 6

ACKNOWLEDGEflENTS 6

REFERENCES 6

FIGURES

1. Pipe Material As-received at NBS for Examination 7

2. Photographs of Maximum Gap and Deflection in Section

of Fractured Pipe 8

3. Features Adjacent to Fracture of Cast Iron Pipe,

As-received 9

i

Page

FIGURES (Continued)

4. Views of Cross-sections Adjacent to Point H, Fig. 2b... 10

5. Microstructures at Point H Adjacent to Probable

Fracture Origin 11

6. Microstructure Adjacent to Narrow Band of Pearlite

Shown in Figure 5c at Higher JXIa unification 12

ii

SUMJ^mRY

Examination revealed that the subject pipe had

a microstructure not normally present in material

meeting the usual specifications for the application.

Graphitization probably aided crack initiation and

crack propagation and fracture probably resulted

from an externally applied load.

From the freshness of the fracture surface, it

was concluded that the fracture was of recent origin

when its presence was detected.

iii

Examination of Failed Six Inch Cast Iron Pipe

Natural Gas Main; Illinois Power Company,

East Saint Louis, Illinois

1 . INTRODUCTION

1 . 1 History

The following information relative to the failure has

been excerpted from the Leak Report [1] obtained from the

Office of Pipeline Safety, Department of Transportation.

"A gas leak was detected in an alley north of Illinois

Avenue near 14th Street in East St. Louis, Illinois at

5:57 P.M. on Novem.ber 11, 1971. The source of the gas was

traced to a break in the 3/8 inch thick wall of the 6 inch

I.D. pit-cast iron pipe gas main, approximately six feet

from an adjacent 5 story residential building. The gas

ignited and an explosion occurred as a result of the escape

of the gas .

When the break was uncovered a continuous circumferential

crack was observed. Only a narrow section of the pipe remained

uncracked. The leak report [1] contained no information with

regard to the location of the uncracked section relative to the

position of the pipe as it was placed in service.

1 . 2 Purpose

A 38 inch long section of the pipe containing the undisturbed crack was packed in a supporting box and delivered

by the Power Company to NBS for examination on December 13,

1971 at the request of the Office of Pipeline Safety (OPS)

,

Department of Transportation. OPS requested a metallurgical

examination to determine, if possible, the cause of the crack

and to obtain any other available information that might be

useful in the investigation of the incident. Figure 1 is a

view of the section as-received.

2. EXAMINATION PLAN

(a) Make record photographs of selected positions around

the surface of the pipe section at the fracture

showing the location of gap and deflection

measurements

- 1 -
t
(b) Cut the pipe section near mid-length, obtaining a 20 inch-long segment containing the fracture, for

examination. Saw-cut the segment obtaining a subsection approximately 3 inch x 11 inch, containing

11 inches of the circumferential fracture surface.

From this sub-section prepare one longitudinal

metallographic specimen whose examination face is

parallel to the fracture surface and also shows the

depth of graphitization . Prepare a second specimen

(transverse) whose examination face is parallel to

the fracture surface and also shows the depth of

graphitization. Examine both specimens for microstructural features adjacent to the graphitization.

The boxed area adjacent to H in Figure 2b shows

the location at which the metallographic specimens

were obtained.

(c) Conduct a chemical analysis of a sample from the

pipe.

(d) Check the hardness of the pipe material.

3. EXAMINATION RESULTS

3 . 1 Visual Examination

Large areas covered by a black oxide scale were observed

on the outside surface of the pipe section. Pits ranging from

match-head to thumb-nail in size were found scattered around

the outside surface. Some of the larger pits were quite deep.

Shallow lace-like pitting covered by a film, of red rust was

observed throughout the interior of the pipe section. A

reddish band of rust varying from approximately 1 to 2 inches

in width v/as observed to extend longitudinally from one end

to the other of the interior of the pipe section.

3.2 Deflection and Gap JVIeasurements

A six-foot, flexible steel tape v/as wrapped around the

circumference of the pipe at a distance of about 6 inches

from the crack, with the zero point of the tape located

approximately at the center of the uncracked region, arrow C,

Figure 2a. The tape and a steel scale were used to allow

measurements of deflection and gap at various positions on the

pipe. The maximum deflection occurred at C and measured

between 0.045 and 0.050 inches in 6 inches. The maximum gap

appeared to be at G, approximately 150 degrees from C (see

Figure 2b) . An accurate gap measurement could not be made at

G because the scale used in m.easurement did not fit flatly on

the pipe surface on either side of the fracture.

- 2 -

3 . 3 Chemical Analysis

3.4

The composition of the pipe sample is given in Table 1.

Table 1. Chemical Composition of Pipe Sample

Percent

Combined Carbon 0.35

Graphitic Carbon 3 . 07

Total Carbon 3.42

Silicon 2.06

Phosphorus 0. 6 04

Sulfur 0.079

Manganese 0.35

Tests

The hardnesses of the pipe material are given in Table 2.

Table 2. Hardnesses of Pipe Material

Hardness

Location Rockwell "B"

Adjacent to outside surface 85

Mid-thickness 8 3

Adjacent to inside surface 7 5

3 . 5 Metallography

3.5.1 Macro -examination

Figures 3a and 3b show the fracture surface and

the unfractured section, respectively. Features observed are

described in the legends for these two figures. Figures 4a

and 4b are views of longitudinal and transverse sub-sections,

respectively, adjacent to the probable fracture origin. The

plane viewed in Figure 4a is at a right angle to the fracture

plane while in Figure 4b, the plane viewed is parallel to the

fracture plane. The arrows point to patches of graphitization

present on the outside surface of the pipe. Graphitization is

a phenomenon whereby the iron in the cast iron is progressively

corroded leaving a porous mass of carbon and iron oxide.

- 3 -
I-
3.5.2 JVicrostructural examination

Figures 5a through 5c show the microstructure of

the cast iron pipe adjacent to the fracture surface in a traverse made from the outside surface to the inside surface

of a longitudinal cross-section specimen. The area shown

in Figure 5a is adjacent to the probable fracture origin at

the outside surface of the pipe. Both complete and partial

graphitization were observed at the outside surface. Below

the graphitized zone the structure is essentially a ferrite

matrix containing type B graphite in a rosette grouping.

Graphitization was observed adjacent to the fracture surface

at the center of the section. The core of the pipe wall

consisted essentially of a ferrite matrix containing both

type A and type B graphite (see Figure 5b) . Figure 5c shows

the inside surface of the pipe. An oxide layer (dark) is

present on the inside surface of the pipe wall. A narrow

band of pearlite was observed adjacent to the inside wall.

The remainder of the structure is essentially a ferrite matrix

containing coarse type A graphite. Figure 6 shows the

structure adjacent to the narrow band of pearlite shown in

Figure 5c at a higher magnification. Areas of the iron-iron

phosphide eutectic (small rounded particles in light-colored

ferrite) , coarse type A graphite flakes in a ferrite matrix,

and lamellar pearlite are present.

The microstructure of the pipe v/all was found to be

largely ferritic. A narrow band of pearlite was observed

adjacent to the inside wall surface. The iron-iron phosphide

eutectic was observed, quite heavily concentrated, adjacent

to the inside surface. Graphite flake sizes ranged from

moderate adjacent to the outside of the pipe wall to quite

coarse adjacent to the inside surface.

4. DISCUSSION

The hardness, greatest adjacent to the outside of the

wall and least adjacent to the inside of the wall is

apparently related to the difference in the size and shape

of the graphite flakes [2] . The presence of a large amount

of ferrite in the structure may have contributed some

ductility and may account for the incomplete fracture around

the pipe circumference

_ 4 _

The chemical analysis of a sample of the subject pipe

indicated a low ratio of combined carbon to total carbon and

a high ratio of graphitic to total carbon. The phosphorus

content, 0.604 percent, is quite high and may have contributed to localized embrittlement at the fracture origin.

The ratio of manganese to sulfur content, about 4 to 1, is

low. A ratio of 5 to 1 is usually aimed at in good casting

practice, to minimize deleterious effects from the presence

of sulfur in the composition of gray cast iron [3]

Type A and type B graphite in a ferrite matrix such as

that observed in the microstructure produce a relatively weak

cast iron [2]. The iron-iron phosphide eutectic, also

observed is known to contribute to brittleness [4] . Material

having these structural features does not meet the requirements of the specifications [5] usually required for cast

iron pipe to be used in natural gas service.

The outer surface of the pipe between G and H (area K)

was deeply pitted. It was found that pitting resulting from

graphitization reduced the wall thickness at H, where the

examination specimens were obtained, as much as 56 percent.

A notch was produced within area K that acted as a severe

stress concentrator. For this reason it is believed that

initiation of the pipe fracture was localized at this spot

of graphitization.

As was previously indicated, no information was supplied

with regard to the location of the uncracked section relative

to the position of the pipe as it was placed in service. If

this information had been supplied it could have been useful

in determining positively the location of the crack origin

with respect to the position of the pipe as it was placed in

service. If the band of rust described in paragraph 3.1, and

which may have formed in the pipe bottom, is accepted as a criterion of orientation, then the probable fracture origin,

K, is located approximately 120 degrees from the position of

the pipe bottom as it was placed in service.

Severe graphitization at K in the pipe section produced a

notch that acted as a stress-concentrator and aided crack

initiation in that area. Crack propagation, from the

appearance of the fresh fracture surface, appears to have been

rapid thereafter and probably occurred in a single event. An

externally applied load produced by settlement could have been

of sufficient magnitude to cause the break.

- 5 -

5. CONCLUSIONS

The following conclusions are drawn from this

examination

1. The microstructure of the material does not meet

the minimum requirements of the specifications

usually used for cast iron pipe for natural gas

service [5] , since it consists of a matrix of

ferrite v;ith coarse flakes of types A and B

graphite and a region near the inner surface rich

in iron-iron phosphide eutectic.

2. It is likely that graphitization aided crack

initiation

3. Initiation and propagation of the fracture probably

resulted from the imposition of an overloading

external force that may have been derived from

settlement of the ground.

4. The crack was apparently of recent origin when

its presence was detected.

ACKNOWLEDGEMENTS

The metallographic specimens were prepared by

Mr. C. H. Brady, Mechanical Properties Section, Metallurgy

Division. The photographic prints were also made by

Mr . Brady

REFERENCES

[1] Department of Transportation Leak Report-Distribution

System No. 210843, Operator Information ( Illinois Power

Co.) No. 08012; dated December 1, 1971.

[2] "Gray and Ductile Iron Castings Handbook" (1971) , edited

by Charles F. Walton, published by the Gray and Ductile

Iron Founders' Society, Inc., Cleveland, Ohio; page 201

section 3.

[3] ibid, page 196 b. Alloy Additions.

[4] ibid/ page 104 and page 112, lines 6-21 inclusive.

[5] American Standard Specification for Cast Iron Pit Cast

Pipe for Gas, ASA A21. 3-1953, Section 3-3, Quality of

Iron.

- 6 -

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Maximum Deflection and Gap in

Section of Fractured Pipe.

Approx. 1/3 X

a. Maximum deflection, 0.04-

0.05 inch in 6 inches,

occurred at C.

b. Maximum gap produced in

fracturing occurred

' adjacent to G. An

accurate gap measurement

could not be made because

of surface conditions.

Specimens for metallographi

excimination were obtained

from the boxed area.
b
r

Figure 3. Fractures Adjacent to Fracture of

Cast Iron Pipe, As-received.

a. Area K (within brackets) contains

the probable fracture origin.

Deep pits were observed adjacent

to the fracture surface of the

pipe at arrows G and H. Note

that the fracture surface both to

the left and to the right of the

bracketed area is quite flat.

X 1/2

b. Area C (within brackets) contains

the unfractured section and the

converging crack tips. Shallow

lace-like pitting shown in this

view was present throughout the

interior surface of the pipe

length submitted. X 1/2
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Figure 5. Microstructures at Point H Adjacent

to Probable Fracture Origin

Longitudinal Cross-section. Etched

with nital. X 250

a. Adjacent to outside of pipe wall.

At top is a zone of graphitized

and partially graphitized material

(dark) . Below the graphitized

zone the structure is essentially

a ferrite matrix containing type

B graphite in a rosette grouping.

b. Center of pipe wall. Graphitization

'

. (dark) at fracture surface. Core of

pipe wall is essentially a ferrite

matrix containing both types A and

B graphite

c. Inside edge of pipe wall. At right

is an oxide layer on inside surface

of pipe wall; adjacent to this is a

narrow band of pearlite. Remainder

of structure is essentially a ferrite

matrix containing coarse type A

graphite
0) 0)

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Figure 6. Microstructure Adjacent to Narrow Band

of Pearlite Shown in Figure 5c at a Higher Magnification. Etched with

nital. X 1000

Areas of the iron-iron phosphide

eutectic (small rounded particles in

light-colored ferrite) , coarse type A

graphite flakes in a ferrite matrix,

and lamellar pearlite are present.

U.S. OEP~. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

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

NBSIR 73-273

1

3. Recipient's .Acccs.viun Nu.

4. TITLE .A.\D SUBTITLE

EXAMINATION Or FAILED SIX INCH CAST IRON PIPE

natural' GAS MAIN; ILLINOIS POWER COMPANY,

EAST SAINT LOUIS, ILLINOIS

5. Publication Date September, 1973

6. Performing Organization Code

7. AUTHOR(S)

I. J. Feinberg and M. L. Picklesimer

£, Performing Organization

NBSIR 73-273

9. PERFOR.MLN'G ORGA.\TZATIO.\' .NAME AND ADDRESS 1 NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF C0M:-!ERCE

WASHINGTON, D.C. 20234

10. Project/ Task,- v.crk Unit .No. 3120418

11. Contract/Grant No.

.... J

1 12. Sponsoring Organization Xa.Tic and Address

Office of Pipeline Safety

Department of Transportation

Washington, D. C. 20590

13. Type of Report Period

Covered Failure

Analysis Report

14. Sponsoring .Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTR.\CT ( 2'JO-vvora or less faciual summary of most significant information, if document includes a significant

bibliography or literature survey, mention it here.) Examination revealed that the subject pipe had a microstructure nor norm.ally present in material meeting the usual

specifications for the application. Graphitization probably

aided crack initiation and ' crack propagation and fracture

probably resulted from an externally applied load.

From the freshness of the fracture surface, it v;as concluded that the fracture was of recent origin.

17. KEY 'iiORDS (Alphabetical order, scp.irated bv s ernicolons)

Cast iron; failure analysis; .fracture; graphitization,

microstructure ; pipe.

18. AVAILABILITY STATEMENT

! I UNLIMITED.

!X! FOR OFFICAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL .OSSIFIED

21. NO. OF PAGES

21

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED





i