NBSIR 77-1292 (£.

Examination of Failed Six

Inch Cast Iron Pipe Natural

Gas Main, Public Service

Electric and Gas Company,

Fairview, New Jersey

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

June 1977

Failure Analysis Report

Prepared for National Transportation Safety Board

Washington, D.C. 20594

NBSIR 77-1292

EXAMINATION OF FAILED SIX

INCH CAST IRON PIPE NATURAL

GAS MAIN, PUBLIC SERVICE

ELECTRIC AND GAS COMPANY,

FAIRVIEW, NEW JERSEY

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

June 1977

Failure Analysis Report

Prepared for National Transportation Safety Board

Washington, D.C. 20594

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

TABLE OF CONTENTS

Page

SUMMARY ii

1. INTRODUCTION 1

1.1 Reference 1

1.2 Parts Submitted 1

2. PURPOSE 1

3. RESULTS OF ANALYSES AND EXAMINATIONS 1

3.1 Visual Examination 1

3.2 Metallographic Examination 2

3.3 Chemical Analysis 3

4. DISCUSSION 3

5. CONCLUSIONS 4

6. ACKNOWLEDGEMENT 4

REFERENCE 4

FIGURES

1. The two pieces of pipe showing the fracture surfaces as received at

NBS from the NTSB

.

2. Fracture surface designated W as received at NBS.

3. Fracture surface designated W after ultrasonic cleaning.

4. Transverse section through the piece of pipe designated W one inch

from the fracture.

5. Longitudinal section through pipe intersecting fracture at location

of deepest penetration of graphitization.

6. As-polished section through pipe in a partially graphitized region.

7. Representative microstructure of the pipe material in an area that

has not been graphitized.
SUMMARY

The submitted six inch diameter cast iron pipe in service as a natural gas main had fractured transversely. The transverse fracture

and the very low operating pressure in the pipeline, (0.25 psig)

indicate that failure was not caused by hoop stresses due to internal

gas pressure. Therefore, failure was probably caused by stresses from

an unknown external source, although there was no distinct evidence of

mechanical damage to the pipe.

Parts of the fracture surfaces at the top and bottom of the pipe were

covered with a poorly adherent deposit that had the feel of oily soil.

There were jogs in the fracture path at both the top and bottom of the

pipe. There was no f ractographic evidence to indicate the location of

the fracture initiation site.

One region of graphitization of the pipe material was found at the

fracture surface near the bottom of the pipe. The maximum penetration

of the graphitization was about three-fourths of the pipe wall thickness.

It was not possible to draw any conclusions on the relation between the

fracture and this graphitized region.

The microstructure of the material appeared to be satisfactory

except for a large amount of steadite (iron-iron phosphide eutectic).

The chemical composition appeared to be satisfactory except for a rather high phosphorus content.

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

Public Service Electric1. and Gas Company, Fairview, New Jersey

INTRODUCTION

1.1 Reference

National Transportation Safety Board, Washington, D.C. 20594. This

investigation was conducted at the request of Mr. Richard G. Marini,

Pipeline Safety Specialist, National Transportation Safety Board (NTSB)

.

The requesting letter was dated April 12, 1977.

1.2 Parts Submitted

Two pieces of the failed six inch diameter cast iron pipe were submitted to the NBS Mechanical Properties Section for examination.

The nominal wall thickness was 3/8-inch. Each piece contained one of

the two mating fracture faces. The two pieces, designated E and W

before being received at NBS, measured approximately 91/2 and 9 inches,

respectively, in length. The piece designated W was used for most of

this examination. The piece designated E was not cleaned or sectioned.

Both pieces were marked before being submitted to NBS to indicate the

top of the pipe as it had been oriented in service. The parts are shown

in figure 1 as they were received at NBS.

It was reported by the NTSB that the operating pressure in the

pipeline was 0.25 psig.

2.

PURPOSE

The National Transportation Safety Board requested the NBS Mechanical

Properties Section to examine the submitted failed pipe and perform a visual examination, chemical analysis, metallographic examination,

determination of depth of graphitization, and determination of the

location of the fracture origin.

3.

RESULTS OF ANALYSES AND EXAMINATIONS

3. 1 Visual Examination

The submitted pipe had fractured transversely. The outside surface

of the pipe had apparently been cleaned for a length of about six to seven inches on either side of the fracture before being submitted to

NBS. About four to five inches of the cleaned surface on either side

of and adjacent to the fracture exhibited bare metal with essentially

no corrosion product or other deposit. The remainder of the apparently

cleaned surfaces were coated with what appeared to be superficial general

corrosion with patches of a black, tarry deposit adjacent to the regions
of bare metal. Beyond the cleaned regions, the pipe was covered with

what appeared to be relatively tightly adhering soil deposits. There

was no evidence of mechanical damage.

There was a dark gray deposit on the inside of the pipe at the

bottom. Otherwise, the inside of the pipe appeared to be relatively

clean with little corrosion.

There were slight jogs in the fracture path at both the top and

bottom of the pipe as it reportedly had been oriented in service. The

mating fracture surfaces can be seen in figure 1. The jogs are indicated

in the figure by arrows.

Similar regions of both of the mating fracture surfaces were covered

with what appeared to be an oily soil deposit. The deposit covered about

an 80° length of the fracture at the top and about a 60° length at the

bottom. The fracture surface on the piece of pipe labeled W was cleaned

ultrasonically with detergent and water. Most of the deposit was removed

in a short time. Some of the deposit near the top was not removed, but

that which remained still appeared to be oily soil.

Cleaning revealed the features over most of the fracture surface.

There was, however, no f ractographic evidence revealed to indicate the

site of fracture initiation.

The fracture surface designated W is shown before and after cleaning

in figures 2 and 3, respectively. The cleaning operation revealed one region of graphitization at the fracture near the bottom of the pipe (dark

region indicated by the arrov? in figure 3) . The dark appearing regions

near the top of the pipe are areas where the oily deposit had not been

removed during the cleaning procedure.

A transverse section was taken through the length of pipe designated

W about one inch from the fracture. As shown in figure 4, no evidence of

graphitization was found at that section location. There was, however,

a small amount of porosity in that section in the region indicated by the arrow.

3 . 2 Metallographic Examination

A longitudinal section intersecting the fracture at the location of

the deepest penetration of graphitization was taken through the pipe.

This section is shown in figure 5. The fracture profile is vertical at

the right in the figure. At the location of maximum depth, graphitization

had penetrated about 75% of the wall thickness of the pipe. A gradient of

graphitization was found across the pipe wall, with the most severe graphitization at the outside.

2
The unetched microstructure in a partially graphitized region is

shown in figure 6. The very dark areas have become graphitized, whereas

the light regions have not. The dark gray thin particles are graphite

flakes.

A photomicrograph showing the representative etched microstructure

of the pipe material away from the region of graphitization appears in

figure 7. The microstructure consists of graphite flakes (thin dark

particles), pearlite (fingerprint and gray regions), cementite (light

areas), and steadite — iron- iron phosphide eutectic (small rounded

particles)

.

3.3 Chemical Analysis

One sample of the cast iron material from the pipe was submitted to a commercial laboratory for chemical analysis. The results of that

analysis are as follows:

The submitted six inch diameter cast iron pipe had completely

fractured transversely. Because of the low operating pressure of the

pipeline (0.25 psig) it would appear likely that failure occurred as

a result of stresses from an external source and not from stresses

generated internally. There was one region of graphitization at the

fracture near the bottom of the pipe. Maximum penetration of

graphitization was about 75% of the approximately 3/8 inch wall

thickness. The graphitization was most severe at the outside surface

of the pipe and became less severe with distance from the outside

surface.

There was no f ractographic evidence to indicate the probable

initiation site of the fracture.

Element Weight Percent

Total carbon

Combined carbon

Manganese

Phosphorus

Sulfur

Silicon

Nickel

Chromium

Molybdenum

Copper

3.79

1.29

0.77

0.960

0.074

1.63

< 0.01

0.04

0.01

0.07

4. DISCUSSION

3 -
The chemical composition of the pipe material appears to be satisfactory

except for a high phosphorus content. A phosphorus content above about

0.

50. is undesirable since it may lead to the formation of excessive

steadite, a brittle phase consisting of iron-iron phosphide eutectic^.

Indeed, the microstructure appeared to be satisfactory where there was

no graphitization.

5. CONCLUSIONS

1. The transverse fracture and the low operating pressure in the pipe

indicated that failure probably occurred as a result of stresses

from an external source.

2. The fracture initiation site could not be determined from the

available evidence.

3. There was one region of graphitization at fhe fracture location.

Maximum penetration of graphitization from the outside wall was about 75% of the pipe wall thickness. It was not possible to

draw any conclusions on the relation between the fracture and the

graphitized region.

4. The pipe material had a high phosphorus content; otherwise, the

chemical composition appeared to be satisfactory.

5. The microstructure of the pipe material was satisfactory except

for an excessive amount of steadite.

6

.

ACKNOWLEDGEMENT

The metallographic work was performed by Leonard C. Smith of the

NBS Mechanical Properties Section. The photographic work was performed

by Mr. Smith and Todd Eudy, also of the NBS Mechanical Properties

Section.

REFERENCE

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

Gray and Ductile Iron Founders' Society, 1971.

4
Figure

1.

The

two

pieces

of

pipe

showing

the

fracture

surfaces

as

received

at

NBS

from

the

NTSB.

The

piece

labeled

E

is

at

the

left

and

the

piece

labeled

W

is

at

the

right.

Arrows

indicate

jogs

in

the

fracture

path

near

the

top

and

bottom

of

the

pipe.

X

1/2

Figure 2. Fracture surface designated W as received at NBS.

The top of the pipe, as marked before the pipe was

sent to NBS, is at the top in the photograph. X 1

Jim

Figure 3. Fracture surface designated W after ultrasonic

cleaning. The designated top of the pipe is at

the top in the photograph. The arrow indicates

the region of graphitization near the bottom of

the fracture. The dark regions near the top are deposits that were not removed by the cleaning

procedure. X 1

OJ

Figure 4. Transverse section through the piece of pipe

designated W one inch from the fracture. The

top of the pipe is at the top of the photograph.

(The notch appearing at the top was put in with

a file in order to identify the orientation.)

The arrow indicates a region of porosity. X 1

I

Figure 5. Longitudinal section through pipe intersecting fracture at

location of deepest penetration of graphitization. Fracture

profile is vertical at the right. The outside surface of

the pipe is horizontal at the top. Region A has been

graphitized, whereas region B has not. The very dark

areas indicated by arrows are deposits on the inside

surface of the pipe.

Etchant: 1% nital X 4

Figure 6. As-polished section through pipe in a partially graphitized

region. The darkest areas have been graphitized. The

light gray thin areas are graphite flakes.

Unetched X 100

Figure 7. Representative microstructure of the pipe material in an area that has not been graphitized. The thin, dark

particles are graphite flakes. White areas are cement ite.

Fingerprint areas and gray areas are pearlite. Small

rounded particles are steadite (iron-iron phosphied

eutectic)

.

Etchant: 1% nital X 500

i NBS-114A (REV. 7-73)

! U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 77- 1*98

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

EXAMINATION OF FAILED SIX INCH CAST IRON PIPE NATURAL GAS MAIN,

PUBLIC SERVICE ELECTRIC AND GAS COMPANY, FAIRVIEW, NEW JERSEY

•

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

T. R. Shives

8. Performing Organ. Report No. NBSIR

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3120412

11. Contract/Grant No.

[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

16. 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 submitted six inch diameter cast iron pipe in service as a natural gas main had

fractured transversely. The transverse fracture and the very low operating pressure in

the pipeline, (0.25 psig) indicate that failure was not caused by hoop stresses due to

internal gas pressure. Therefore, failure was probably caused by stresses from an unknown external source, although there was no distinct evidence of mechanical damage to

the pipe.

Parts of the fracture surfaces at the top and bottom of the pipe were covered with

a poorly adherent deposit that had the feel of oily soil. There were jogs in the

fracture path at both the top and bottom of the pipe. There was no fractographic evidence to indicate the location of the fracture initiation site.

One region of graphitization of the pipe material was found at the fracture

surface near the bottom of the pipe. The maximum penetration of the graphitization was

about three-fourths of the pipe wall thickness. It was not possible to draw any

conclusions on the relation between the fracture and this graphitized region.

The microstructure of the material appeared to be satisfactory except for a large

amount of steadite (iron- iron phosphide eutectic). The chemical composition appeared to

be satisfactory except for a rather high phosphorus content.

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 pipe; graphitization.

18. AVAILABILITY \Z2 Unlimited

I X

' For Official Distribution. Do Not Release to NTIS .

I Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl

3

1 ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

22. Price

USCOMM.DC 29042-P74

NBSIR 77-1293

Analysis of Housing Data

Collected in A Lead-Based

Paint Survey in Pittsburgh,

Pennsylvania — Part II

Douglas R. Shier

and

William G. Hall

Applied Mathematics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

June 1977

Final

Prepared for: Housing Technology Programs

Center for Building Technology

Institute of Applied Technology, NBS

Sponsored by:

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410