NBSIR 73-264

Examination of Failed One Inch

Black Iron Pipe Natural Gas

Service Line, Iowa Public Service

Company, Eagle Grove, Iowa

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

August 30, 1973

Failure Analysis Report

Prepared for Office of Pipeline Safety

Department of Transportation

Washi gton. D. C. 20590

NBSIR 73-264

EXAMINATION OF FAILED ONE INCH

BLACK IRON PIPE NATURAL GAS

SERVICE LINE, IOWA PUBLIC SERVICE

COMPANY, EAGLE GROVE, IOWA

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

August 30, 1973

Failure Analysis Report

'"^his 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

Affairs at the National Bureau of Standards."

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

TABLE OF CONTENTS

Page

SUMMARY iii

1 . INTRODUCTION 1

1.1 Reference 1

1.2 Background Information 1

1.3 Parts Submitted 2

2. PURPOSE 2

3. EXAP4INATI0NS, TESTS, AND MEASUREMENTS PERFORMED 2

4. RESULTS OF EXAf^INATIONS , TESTS AND MEASUREMENTS 3

4.1 Visual and Macroscopic Examination 3

4.1.1 Submitted fracture 3

4.1.2 NBS produced fractures 3

4.2 Scanning Electron Microscope Examination 4

4.3 Metallographic Examination 4

4.4 Hardness Measurements 5

5. DISCUSSION OF RESULTS 5

6. CONCLUSIONS 6

7. ACKNOWLEDGEMENTS 7

REFERENCES 7

FIGURES

1. Submitted failed natural gas service line pipe parts

as received 8

2. Setup for bend test of pipe length 9

3. Setup for uniaxial tensile test of pipe length 10

i

Page

FIGURES (Continued)

4. Fracture surfaces of the submitted failure as

received 11

5. SEM of the fracture surface of the submitted

failure in the area of densest rust 12

6. SEM of the fracture surface of the submitted

failure in the area of densest rust 12

7. SEM of the fracture surface of the submitted

failure in area B 13

8. SEM of the fracture surface of the submitted

failure in an area away from that containing

the densest rust 13

9. SEM of the fracture surface of the submitted

failure in an area away from that containing

the densest rust 14

10. SEM of the fracture surface of the NBS

produced bend test 14

11. SEM of the fracture of the NBS produced

uniaxial tensile test of material from the

submitted failure 15

12. Unetched longitudinal cross section through

the submitted failed pipe 15

13. Etched longitudinal cross sections showing

fracture profiles 16

14. Etched longitudinal cross section through

submitted fractured pipe showing deformation

at and near the root of the thread one thread

removed from the fracture 17

15. Etched longitudinal cross section through

submitted failed pipe showing representative

microstructure 18

16. Etched representative longitudinal cross section

through stock standard weight black iron pipe ... 18

ii

SUN11ARY 1

A fractured one inch black iron pipe natural gas

service line which connected to a building involved in an

explosion and fire in Eagle Grove, Iowa on February 2, 1973

was examined in order to determine the mode of fracture and

whether there was a pre-existing crack.

The fracture was ductile in nature and appeared to have

occurred due to bending stresses caused by loading from an

external source. There was no evidence found to indicate

the presence of a pre-existing crack.

The material in the submitted pipe was clean with few

inclusions. The microstructure appeared normal for a very

low carbon steel in the normalized heat treatment condition.

The pipe appeared to satisfy currently applicable ASTM

standards for ultimate tensile strength (determined

indirectly from hardness measurements) for grade A electric

resistance welded steel pipe, and carbon content (by visual

comparison of microstructures ) for both grades A and B

electric resistance welded steel pipe.

Examination of Failed One Inch Black Iron

Pipe Natural Gas Service Line, Iowa Public

Service Company, Eagle Grove, Iowa

1. INTRODUCTION

1.1 Reference

Office of Pipeline Safety, Department of Transportation,

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

request of Mr. Lance F. Heverly of OPS under order number

DOT-A.'5-10041 . The request was made on February 28, 1973.

1 . 2 Background Information

The information in this section was furnished by

Mr. Lance F. Heverly of the Office of Pipeline Safety.

At 6:18 P.M. on February 2, 1973, there was an explosion

followed by a fire that destroyed two buildings and severely

damaged another at 218-222 West Broadway Street, Eagle Grove,

Iowa. An accumulation of natural gas apparently provided an

atmosphere conducive to explosion and fire. At the time of

the incident, the ground was frozen. Pressure in the Eagle

Grove gas distribution system in that area was seven psig.

Two days after the incident, the service line to one of

the destroyed buildings v/as pressure tested for gas leaks.

At the time of the explosion, the building wall had fallen

on the service line above ground outside the building, and a bulldozer had apparently hit the service line inside the

basement before the leak test was performed. Two leaks were

found. One of these was in the threaded portion of a horizontal pipe at the downstream edge of a buried 90° elbow

located just outside the basement wall of the building. The

riser pipe and the elbow were broken off by fracturing the

horizontal pipe at the edge of the elbow. At the point of

fracture, the pipe was about two feet deep in the ground.

The horizontal piece was removed with a mass of concrete

attached to it. The concrete had apparently been used to fill

a void in the stone wall around the service line. The void

was evidently produced when the line was installed.

Examination of the fracture surfaces of the one inch pipe

service line by an OPS representative in the field indicated a superficial coating of rust on both surfaces, except for one

mating area on each surface where the rust appeared to be

denser. The region of densest rust (corrosion product) was

between the 6 o'clock and 9 o'clock positions when looking into

the downstream end of the 90° elbow with the pipe positioned

as it had been in service.

- 1 -

1.3 Parts Submitted

Two items were submitted for examination: 1) the length

of one inch black iron riser pipe connected to the 90° elbow

which in turn was connected to one end of the fractured

horizontal one inch black iron pipe, and 2) the remainder of

the fractured horizontal pipe to which the mass of concrete

was attached. These parts are shown as received at NBS in

figure 1. The material was delivered to the NBS Mechanical

Properties Section by Mr. Heverly on February 28, 1973.

2 . PURPOSE

The Office of Pipeline Safety, DOT, requested that the

Mechanical Properties Section, NBS, determine the nature of

the fracture, whether there had been a pre-existing crack,

and the probable cause of failure.

3 . EXAMINATIONS, TESTS, AND MEASUREMENTS PERFORMED

Several tests were performed in order to produce fracture

surfaces for comparison with the submitted fracture surfaces.

These tests, all conducted at about 70° F, were as follows:

A) A ten inch length of stock, standard v/eight, one

inch diameter black iron pipe threaded at one end

tested to fracture in bending as shown in figure 2.

B) A ten inch length taken from the submitted horizontal

fractured pipe threaded at one end tested to fracture

in bending in the same manner as in "A" above.

C) An eleven inch length of stock, standard weight, one

inch diameter black iron pipe threaded at both ends

and pulled to fracture in uniaxial tension as shov/n

in figure 3.

D) An eight inch length taken from the undamaged

remainder of the bend test specimen threaded at both

ends and pulled to fracture in uniaxial tension as

in "C" above.

The fracture surfaces of the submitted failure and the

failures produced in "A" through "D" above were examined

visually and macroscopically . Selected areas of the fracture

surfaces of the submitted failure and of test pieces from "B"

and "D" v;ere examined with the scanning electron microscope

(SEM) . In addition, cross sections, some of which intersected

the fracture surfaces of the submitted fracture and the NBS

produced fractures "A", "B", and "D", v;ere examined metallographically . Hardness measurements were made on transverse

cross sections through the submitted failure and the stock

black iron pipe.

- 2 -

Specimens for SEN examinations, for tests "B" and "D",

and the cross sections for hardness measurements and metallographic examinations from the submitted failed pipe were

all taken from the lor.g portion of the horizontal pipe piece

to which the concrete had been attached. The small threaded

portion of the horizontal pipe that remained in the elbow

was examined visually and macroscopically , but was otherwise

undisturbed

4 . RESULTS OF EXAMINATIONS, TESTS AND MEASUREMENTS

4 . 1 Visual and Macroscopic Examination

4.1.1 Submitted fracture

The two opposing fracture surfaces of the submitted

failure are shown as received in figure 4. The pipe had

fractured in the threaded end at the root of a thread at the

end of a 90° elbow as can be seen in figure 4a. The short

part of the fractured piece remained in the elbow.

The concrete was removed from the horizontal pipe piece

in order to examine the entire submitted length. The

horizontal piece, the riser, and the elbow were all covered

with what appeared to be a mixture of fiberglass and coal tar.

The pipe appears to have been fabricated by an electric

resistance welding process.

Both of the fracture surfaces were covered with corrosion

product (rust) which for the most part appeared to be superficial except for the region discussed in Section 1.2 where

the rust appeared to be denser. This region was between the

6 o'clock and 9 o'clock positions when looking into the downstream end of the 90° elbow with the pipe positioned as it

had been in service. The heaviest concentration was at about

the 7-7:30 o'clock position (arrow A, figure 4a) . The dense

rust appeared on the mating position of the opposing fracture

surface (arrow A, figure 4b) . There were mating areas on both

fracture surfaces adjacent to the region of densest rust which

appeared to have suffered mechanical damage (arrows b, figure 4) . The apparent last part to fail is indicated by arrows C,

figure 4

4.1.2 NBS produced fractures

Each of the four pipe specimens tested at NBS ("A"

through "D", Section 3) failed at the root of a thread adjacent

to the outside of the threaded fixture to which it was attached,

for testing. A considerable amount of ductility was exhibited

in each case.

- 3 -

After the submitted fracture surface was cleaned, the

appearance of it and the appearance of the NBS produced

fracture surfaces were very similar. The tearing and

deformation at the apparent last part to fail in the submitted fracture farrow C, figure 4a) more closely approximated

that of the NBS bend test fractures than those produced by

uniaxial tensile testing. Since the rust was easily removed

from the submitted fracture by ultrasonic cleaning with v/ater

and detergent, the rust over the entire fracture surface was

apparently superficial.

4 . 2 Scanning Electron microscope Examination

The submitted failure and the NBS produced failures "B"

and "D" all exhibited dimpled rupture over essentially their

entire fracture- surfaces indicating that all the fractures

were ductile in nature. Scanning electron photomicrographs

(sen's), shov;ing features representative of the submitted

fracture, are shown in figures 5 through 9. Figures 5 and 6

were taken in an area which appeared to exhibit the densest

rust (area A, figure 4b) . They show dimpled rupture. Figure

7 (area B, Figure 4b) shows dimpled rupture with considerable

mechanical damage. The edge of the thread root can be seen

near the bottom of the figure. Figures 8 and 9 were taken in

two different areas away from that exhibiting the dense rust.

Dimpled rupture again is essentially the only fracture

feature exhibited. No evidence was found to indicate the

presence of a pre-existing crack.

SEN photomicrographs representative of the fracture

features of specimens from "B" and "D" are shov:n in figures

10 and 11, respectively. Both fracture surfaces exhibited

essentially all dimpled rupture.

4 . 3 Metallographic Examination

Figure 12 shows a representative unetched field from a

longitudinal cross section through the submitted failed pipe.

The concentration and size of the inclusions are small and

are not considered excessive for this material.

Low magnification photomicrographs of etched, longitudinal

sections showing fracture profiles of the submitted failure

and NBS produced failures "B" and "D" are shown in figures 13a,

b, and c, respectively. The fracture profile in each case is

shown vertically at the right of the figure. A considerable

amount of deformation and necking can be seen in all three

specimens, indicating ductility in the material. Some

- 4 -
on ^ v 3

.- ....
deformation was exhibited in the interior of the cross

section adjacent to the root of the first thread beyond the

fracture of the submitted failure (figure 14) . Some of the

deformation near the surface at the thread root appears to

have been induced into the material by the threading

operation. There are a few large stringers (inclusions) in

this field which is not typical of the material in the

submitted pipe.

An etched microstructure representative of the material

away from the deformed regions is shown in figure 15. The

microstructure consists of ferrite (white) and a small amount

of pearlite (dark patches) . This is the microstructure of a normalized very low carbon steel.

Metallographic examination of the stock black iron pipe

material revealed a considerably higher inclusion content

than found in the submitted material. An etched microstructure

from a longitudinal cross section through the stock pipe is

shown in figure 16. The microstructure consists of ferrite

(white) and pearlite (dark patches) . There is some evidence

of a Widmanstatten structure. Comparison of microstructures

indicates that the material from the stock pipe has a significantly greater amount of pearlite, and consequently,

a significantly higher carbon content than that of the

submitted pipe.

4 . 4 Hardness Measurements

The Rockwell hardness of the submitted pipe ranged from R45T

23 to 3 0.5 (based on 18 measurements) while that of the stock

pipe ranged from R45T 32 to 38 (based on eight measurements)

5. DISCUSSION OF RESULTS

Even though there were relatively small areas of fairly

dense rust on the opposing fracture surfaces of the submitted

failure, the rust was easily removed when the fracture was

cleaned with detergent and water in an ultrasonic cleaner.

A f ractographic examination revealed no evidence to indicate

the presence of a pre-existing crack in the pipe. The

fracture was quite ductile, with dimpled rupture being

essentially the only fracture feature exhibited (except for

some mechanical damage)

- 5 -

When tested to failure both in bending and in tension,

samples of the stock black iron pipe and samples from the

submitted failed pipe produced fractures which exhibited

dimpled rupture as essentially the only fracture feature

present. This indicates that all the fractures were ductile.

The bend specimens had more of a tear lip than did the

tensile specimens. Comparison of the submitted fracture to

the NBS produced fractures indicated that the failure in the

submitted pipe was probably due to bending stresses caused

by loading from an external source.

The microstructure of the submitted pipe material,

consisting of ferrite and pearlite, appears to be normal for

a normalized very low carbon steel. An ASTM specification

giving heat treatment requirements for black iron pipe could

not be found

One of the ASTM Standards^ which currently applies to

pipe of the type used in applications such as that of the

submitted pipe specifies a maximum carbon content of 0.25%

for grade A and 0.3 0% for grade B. There is no minimum

carbon requirement. The microstructure of the submitted pipe

indicates that the carbon content is well below the maximum

allowed

The greater hardness of the stock pipe compared to the

submitted pipe is probably due to the higher carbon content

of the stock pipe. There appear to be no hardness requirements in the ASTM Standards.

1 2 3 The current strength requirements ' ' for electric

resistance welded steel pipe specify a minimum ultimate

tensile strength of 48 ksi for grade A pipe and 60 ksi for

grade B pipe. The approximate ultimate tensile strength

equivalent to an average Rockwell 45T hardness of 26.7 (as

determined for the submitted pipe) is about 49 to 50 ksi

when compared to data for an AISI 1008 steel. The pipe

material thus appears to satisfy current ultim.ate tensile

strength requirements for grade A electric resistance welded

steel pipe.

6 . CONCLUSIONS

1. The fracture of the submitted pipe was essentially

completely ductile, dimpled rupture being the only

fracture feature exhibited (except for some mechanical

damage)

- 6 -

2. Since the rust was easily removed in an ultrasonic bath

with water and detergent, it was essentially all of a superficial nature.

3. There was no evidence to indicate the presence of a preexisting crack.

4. Comparison of the submitted fracture with laboratory

produced fractures indicates that the submitted failure

was probably due to bending caused by loading from an

external source.

5. The carbon content and ultimate tensile strength of the

material from the submitted pipe appear to satisfy

current ASTM requirements for grade A electric

resistance welded steel.

6. The microstructure appears normal for a normalized very

low carbon steel.

7. ACKNOWLEDGEMENT

Dr. M. L. Picklesimer, Chief of the NBS Mechanical

Properties Section, provided a number of suggestions for

the conduct of this investigation. Mr. L. C. Smith, also of

the NBS Mechanical Properties Section, prepared the specimens

for the mechanical tests and for the metallographic and SEM

examinations

REFERENCES

^ ASTM Standard A53-71, American Society for Testing and

Materials, Book 1, 1972.

^ ASTM Standard A120-71, American Society for Testing and

Materials, Book 1, 1972.

^ ASTM Standard A135-69, American Society for Testing and

Materials, Book 1, 1972.

'* Metals Handbook, 8th Edition, Volume 1, American Society

for Metals, 1961.

- 7 -
..' J. :^

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.Setup for bend test of pipe length. Pipe

specimen is indicated by arrow A. Arrows B

indicate the direction of load application.

The specimen is threaded on the left end.

Figure 3. Setup for uniaxial tensile tost of pipe

length. Pipe is threaded on both ends.

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submitted failure in the area of

densest rust (area A, figure 4b)

showing dimpled rupture. X 650

Figure 6. SEJV. of the fracture surface of the

submitted failure in the area of

densest rust (area A, figure 4b)

showing dimpled rupture . A secondary

crack can be seen in the lower left

portion of the figure. X 1300

Figure 7. SEM of the fracture surface of the

submitted failure in area B, figure

4b, showing mechanical damage (arrows)

and dimpled rupture. Edge of thread

root can be seen at lower left. X 550

Figure 8. SEM of the fracture surface of the

submitted failure in an area away

from that containing the densest

rust showing dimpled rupture. X 110 0
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submitted failure in an area away

from that containing the densest

rust showing dimpled rupture. X 600

Figure 11. SEM of the fracture surface of the

NBS produced uniaxial tensile test

of material from the submitted

failure (test D) showing dimpled

rupture. X 750

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through the submitted failed pipe

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Figure 14. Etched longitudinal cross section

through submitted fractured pipe

showing deformation at and near

the root of the thread one thread

removed from the fracture.

Etch: ammonium molybdate. X 100

Figure 15. Etched longitudinal cross section

through submitted failed pipe showing

representative microstructure which

consists primarily of ferrite (white)

and a small amount of pearlite (dark

patches)

Etch: ammonium molybdate. X 10 0

Figure 16. Etched representative longitudinal cross

section through stock standard weight

black iron pipe used for tests A and C.

The microstructure consists of ferrite

(white) and pearlite (dark patches)

There is some evidence of a Widmanstatten

structure

Etch: 3% Nital. X 100

FORM NBS-n4A ,1.711 U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Cov't Accession

BIBLIOGRAPHIC DATA ^^^^^^

3. Recipient's Accession No.

4. TI'l Ll- AND SU li l lTLK

hj AAiM±lN/\i lUW Ur rAXJ-iijU L'iNiL _i>ICxi rSLiACJS. XKUJN FxirLj

NATURAL GAS SERVICE LINE, IOWA PUBLIC SERVICE

LOJyPANY , LACiLiri CiKUVh , iUVJA.

5. l^ublication D.ite AUgUSL. jU, ly 1 J

6. Performine Organi:^ation Code

7. AUTHOR(S)

T. Robert Shives

8. Performing (Jrgan i ^.i tuTi NBSIR 73-2G4

9. PERFOR.MING 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 I'Jo.

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

bibliography or literature survey, mention it here.)

A fractured one inch black iron pipe natural gas service line v/hich

connected to a building involved in an explosion and fire in

Eagle Grove, Iowa, on February 2, 1973, was examined by the NBS

Mechanical Properties Section. The fracture was ductile in nature.

There was no evidence found to indicate the presence of a preexisting crack. The fracture appeared to have been due to

bending stresses caused by loading from an external source.

17. KEY TORDS (Alphabetical order, separated by semicolons)

Black iron pipe; dimpled rupture; ductile fracture*, gas pipe.

18. AVAILABILITY STATEMENT 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF P.^GES

UNLIMITED.

UNCLASSIFIED

23

lX! FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 66a44.P7I
I-