NBSIR 74-625

Examination of Failed Two Inch Steel

Pipe Natural Gas Main, Columbia Gas

Company, Spring Garden Township,

York County, Pennsylvania

T. R. Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

January 1975

Failure Analysis Report

Prepared for Office of Pipeline Safety

Department of Transportation

Washington, D. C. 20590

NBSIR 74-625

EXAMINATION OF FAILED TWO INCH STEEL

PIPE NATURAL GAS MAIN, COLUMBIA GAS

COMPANY, SPRING GARDEN TOWNSHIP,

YORK COUNTY, PENNSYLVANIA

T. R. Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

January 1975

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 Affairs at the National Bureau of Standards."

Prepared for Office of Pipeline Safety

Department of Transportation

Washington, D. C. 20590

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

TABLE OF CONTENTS

Page

SUMMARY .

1. INTRODUCTION ..... 1

1.1 Reference . 1

1.2 Background Information 1

1.3 Parts Submitted 2

2. PURPOSE . 2

3. PLAN OF EXAMINATION 2

3.1 General Plan 2

3.2 Soil Corrosivity Characterization 3

3.2.1 Background 3

3.2.2 Procedure 3

3.3 Impact Tests 5

4. RESULTS OF EXAMINATIONS, TESTS, AND ANALYSES .... 5

4.1 Visual and Macroscopic Examination 5

4.1.1 Submitted length of pipe 5

4.1.2 Pipeline in the field 6

4.2 Fractographic Examination 7

4.2.1 Visual and Macroscopic 7

4.2.2 Scanning Electron Microscope

Examination 7 .

4.3 Metallographic Examination 8

4.4 Chemical Analysis 9

4.5 Hardness and Dimensional Measurements .... 9

i
Table of Contents (Continued) Page

4.6 Soil Corrosivity Characterization 10 '

4.7 Impact Tests ; 10

5. DISCUSSION 11

6. CONCLUSIONS 13

7. ACKNOWLEDGEMENT 15

REFERENCES 15

TABLES

1. Results of Chemical Analysis of the Pipe Material . .

2. Results of Hardness Measurements

3. Results of the Measurements Made at the Site of

the Pipeline

4. Results of Chemical Analysis of Soil Samples . . . . FIGURES

1. Pipe length as received at NBS with the clamp in

place

2. Longitudinal piece cut from the pipe length about

24 inches south of the fracture

3. Part of the pipe length as received showing bow

south of the clamp . . .

4. Four views of the pipe in the area of the crack

after removal of the clamp

5. Sections through the pipe length in locations where

pits appeared to be among the deepest

6. Top view of part of the pipeline excavated at

site 2

7. Bottom half of the south side of the fracture . . . .

8. Scanning electron fractograph taken in region of

"fresh" fracture

ii
Figures (Continued) Page

9. Scanning electron fractograph taken in region

of "fresh" fracture

10. Scanning electron fractograph taken in region

of "fresh" fracture .

11. Scanning electron fractograph taken in the older

appearing part of the fracture

12. Scanning electron fractograph taken in the older

appearing part of the fracture

13. Scanning electron fractograph taken in the older

appearing part of the fracture

14. Scanning electron fractograph taken in the older

appearing part of the fracture

15. Longitudinal section through the pipe near the

south fracture surface

16. Longitudinal section intersecting the south fracture

surface

17. Areas B, C, and D in figure 16 are shown

18. Fracture surface of laboratory impact specimens . .

19. Scanning electron fractographs of the brittle region

of the laboratory specimen fracture surfaces . . .

20. Scanning electron fractograph from the specimen

tested in impact at 45°F

21. Scanning electron fractograph showing the transition

from essentially brittle fracture to ductile

fracture

iii
SUMMARY

The Mechanical Properties Section of the National Bureau of

Standards examined a length of a cracked two inch diameter

plain carbon, welded steel natural gas main pipe at the request

of the Office of Pipeline Safety. The pipe had a transverse

crack extending about 85% of the circumference. The pipeline

had suffered considerable mechanical damage in the vicinity of

the failure, and the crack, which propagated in an essentially

brittle manner, appeared to have initiated in a gouged area

near the bottom of the pipe. There was a considerable amount

of corrosion product on the surface of the pipe in the gouged

area. The amount and distribution of corrosion product on

the fracture surface indicated that the crack had formed in

at least two stages, and that a crack was present prior to

the time of failure. During the first stage, the crack may

have penetrated the entire wall thickness of the pipe in one

region opposite the crack origin near the bottom of the pipe.

The likely mechanism of fracture for the first stage of the

crack appears to be stress corrosion cracking. For the second

stage of the crack, either stress corrosion cracking or impact

appears to be the likely mechanism of failure.

The pipeline was installed in 1949. In 1971, a sanitary sewer

system was installed in the same street with the sewer laterals

passing under the gas main. Failure in the gas main occurred

at the location of one of these laterals about three years

after the installation of the sewer system.

There was a considerable amount of pitting on the pipe surface,

some of the pits penetrating more than half the wall thickness

of the pipe. Analysis of soil samples taken from three sites

along the pipeline indicated that the soils were of low

corrosivity. Pit depths of the magnitude found are consistent

with the expected corrosive attack for exposure of plain carbon

steel in soils of low corrosivity.

A length of the gas main pipe, still in service and located

about 51 feet from the site of the failure, showed no evidence

of significant mechanical damage. This length contained fewer

pits than the submitted length, and the pits were less severe.
Examination of Failed Two Inch Steel Pipe Natural Gas

Main, Columbia Gas Company, Spring Garden Township,

York County, Pennsylvania

1. INTRODUCTION

1.1 Reference

Office of Pipeline Safety, Department of Transportation,

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

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

Safety (OPS) under order number DOT-AS-1 004 1 . The request was

made on January 16, 1974.

1.2 Background Information

The information in this section was furnished by Mr. Lance

F. Heverly of OPS and Mr. William E. Smeigh, Jr., of the

Pennsylvania Public Utility Commission.

On January 8, 1974, there was an explosion which essentially

destroyed a house located at 1324 South Ogontz Street in Spring

Garden Township in York County, Pennsylvania. The house was

on the southwest side of the street. The explosion v/as attributed to an accumulation of natural gas which had leaked from a crack in a two inch steel gas main pipe under South Ogontz

Street in front of the house in which the accident occurred.

The gas main had been installed in 194 9 and was reported

to have been about 4 2 inches below the paved street at the

location of the failure. At the time of failure, gas pressure

was estimated to be about 35 psig and the soil temperature was

estimated to be 45''F. The pipeline was constructed of schedule

40, two inch diameter welded steel pipe. Cathodic protection

was provided for the pipeline. The installation dates and the

locations of the three closest anodes are given below:

A sanitary sewer system had been installed in South Ogontz

Street in 1971 with the lateral service lines to houses on the

southwest side of the street passing under the gas main. At

the time of the explosion, the residence at 1324 South Ogontz

Location Installation Date

135 feet south of fracture

195 feet south of fracture

216 feet north of fracture

8/13/71

5/8/73

11/30/71

- 1 -
street was connected to a septic system in front of the house

(between the house and the street). The sewer lateral, which

passed about 1 1/2 feet under the gas main, had never been

connected to the residence and was capped at the approximate

location of the property line.

The crack in the gas main pipe occurred at the approximate

location where the sewer lateral passed under the pipe.

1.3 Parts Submitted

A length of the two inch gas main pipe about six feet long

was delivered to T . R. Shives of the NBS Mechanical Properties

Section on January 15, 1974 by Trooper Thomas R. Minnich, Fire

Marshall, Pennsylvania State Police. The length of pipe is

shown as received in figure 1. Before delivery to NBS the

region containing the crack had been covered with a rubber

gasket and a metal clamp which can be seen in the' photograph

(figure 1)

2 . PURPOSE

The Office of Pipeline Safety requested that the

Mechanical Properties Section determine the mechanism

and, inasfar as possible, the cause of failure.

3. PLAN OF EXAMINATION

3 . 1 General Plan

At a series of three meetings at the National Bureau of

Standards among representatives of the Office of Pipeline

Safety, the Pennsylvania Public Utility Commission, the

Columbia Gas Company, and the Mechanical Properties and

Corrosion and Electrodeposition Sections of NBS, the general

plan of the examination was discussed. These meetings were

held on January 16, May 7, and June 7, 1974. It was agreed

that any cleaning or cutting of the fracture surface would be

confined to the south side of the fracture. As set forth at

the first meeting, the analysis of the failure was to include

documentation of the deformation and other mechanical damage

to the surface of the pipe, f ractographic examination of the

south fracture surface, metallographic examination, and other

tests or analyses that were deemed advisable as the examination

progressed. At the second meeting a program to determine the

corrosivity of tne soil \n the vicinity of the pipe failure was

presented by Mr. Edward Escalante of the NBS Corrosion and

Electrodeposition Section. This program was agreed to at the

third meeting.

NBS

of fracture

- 2 -
It was also decided that when the soil samples were being taken,

a small length of the pipeline away from the failure would be

exposed for visual examination. Because of the brittle and

fresh appearance of the second stage of the fracture, a series

of impact tests were run on some of the pipeline material in

order to characterize its fracture behavior at high strain rates.

Most of the tests, examinations, and analyses employed in

this investigation are routine methods which do not require

further explanation here. Exceptions to this generalization

are the soil corrosivity characterization program and the impact

tests

3 . 2 Soil Corrosivity Characterization

3.2.1 Background

The soil corrosivity characterization program was

devised by and, with the exception of the chemical analyses,

was carried out by Mr. Edward Escalante of the NBS Corrosion

and Electrodeposition Section. The following is taken from

his report of the results of the soil characterization:

The corrosivity of a soil might be defined as

the ease v;ith which a soil can destroy a given metal.

The degree of corrosivity is largely determined by a

number of measurable parameters which are inherent in

the makeup of the soil . Experience has shown that

these parameters are soil resistivity, redox potential.,

and pH^-'-) . Further insight about the corrosivity of a soil can be gained from a chemical analysis of the

soil and from measurement of the corrosion potential

of the metal in the ground (2).

3.2.2 Procedure

Three sites along the gas main pipeline under South

Ogontz Street were selected for the soil corrosivity characterization measurements. They are as follows:

Site 1: In undisturbed soil adjacent to and just east of

the location of the failure.

Site 2: Directly over the gas main 51 feet north of site 1.

Site 3: Adjacent to and just east of the gas main pipe 27

feet north of site 2

- 3 -
The failure (adjacent to site 1) had occurred where

a capped sanitary sewer lateral at 1324 South Ogontz Street

passed under the gas main pipe. Site 2 was selected to be at ^ the location of another capped sewer lateral at 1320 South

Ogontz Street where again the lateral passed under the gas

pipe. The residences at 1320 and 1324 South Ogontz Street were

both utilizing septic systems.

Site 3 was essentially half-way between the sewer

laterals to 1320 and 1316 South Ogontz Street. All three sites

were selected to be away from all anodes that had been installed

to provide cathodic protection for the pipeline, except for

two anodes that were installed near the site of the failure when

the length of failed pipe was replaced. These latter two anodes

had been installed for such a short time before our examination

that they would not be expected to have any effects on results

of the examination except for the pipeline potential.

At each site, a six inch square hole was cut through

the blacktop by Columbia Gas Company personnel. A small hole

was bored with a two inch diameter soil auger to a depth that

eventually reached about 38 inches at sites 1 and 3. At site

2, the initial hole was enlarged to three feet by four feet

and was dug to a depth sufficient to expose about a two foot

length of the pipeline for examination. At this location, the

top of the gas pipe was about 34 1/2 inches below the top of

the blacktop. At all three sites the soil contained a considerable

amount of shale. At site 2, there was a special fill material

to a depth of about one foot below the pavement. This material

is not thought to have a significant effect on the corrosivity

of the soil at the level of the pipe.

The following is paraphrased from Nr. Escalante's

report:

I^ox potential and pH measurements were made at

the site at the approximate depth of the pipeline.

Resistivity measurements were made on soil samples

removed from the excavations adjacent to the pipeline

. using a standard soil cup and an AC wheatstone bridge

circuit. The potential of the pipeline was measured

versus a CU-CUSO4 electrode. All potential measurements

v;ere made using a high impedance {10^^ olim) voltmeter.

Samples for chemical analysis in the laboratory were

transported in 500 cm^ glass jars with plastic lids.

The soil samples were analyzed for water soluble carbonates,

nitrates, sulfates, and sulfides. A total acid determination was also made on two samples

- 4 -
3 . 3 Impact Tests

The pipe material is a plain, low carbon, relatively low

strength steel v/hich would be expected to exhibit good ductility.

Indeed, a longitudinal piece cut from the pipe about 24 inches

south of the fracture could be bent double at room temperature

with only slight cracking, as shown in figure 2, indicating

that the material did possess good ductility, at least at

relatively low strain rates.

In order to determine the fracture behavior of this pipe

steel at the relatively high strain rates characteristic of

a Charpy impact test, several longitudinal specimens were cut

from a length of the submitted pipe material between 7 and 10

inches south of the fracture. Geometric restrictions imposed

by the shape of the pipe and the wall thickness of the pipe

resulted in specimens much smaller than the standard ASTM

Charpy specimen. The impact specimen dimensions were 3 inches

long, slightly less than 1/4 inch wide, and about 1/10 inch

thick (the thickness direction being a radius eminating from

the longitudinal axis of the pipe) . The scale was removed

from both the inside and outside wall surfaces by surface

grinding. The specimens were "notched" transversly in the

center on the side corresponding to the outside wall surface

of the pipe with a jevfeler"s saw. The saw-cut notch was

approximately 0.02 inch deep. Then the specimens were

cyclically stressed in reversed bending to initiate a fatigue

crack at the base of the saw-cut notch. Specimens so "notched"

were then broken in a Charpy impact machine.

4 . RESULTS OF EXAMINATIONS, TESTS, AND ANALYSES

4 . 1 Visual and Macroscopic Examination

4.1.1 Submitted length of pipe

The submitted length of pipe was bowed down and to

the west as it lay in the soil. The center of the bow was just

south of the fracture. The bow can be seen in figures 1, 3a,

and 3b which show the top, east side, and bottom of the pipe,

respectively. Before being submitted to NBS , the pipe length

had been marked with the letters "S" (south) and "N" (north) on

the top to indicate orientation. The "S" can be seen at the

left end of the pipe length in figure 1.

When the clamp was removed from the pipe, a transverse

crack was exposed in the approximate center of the submitted

length. The crack had traversed about 85% of the circumference

of the pipe, extending clockwise from about the one o'clock

- 5 -
position to the eleven o'clock position, assuming the letters

"S" and "N" marked on the pipe when it was received to be in

the twelve o'clock position. The two ends of the crack can be ^ seen in figure 4a which shows the top of the pipe after the

clamp had been removed

Looking from the south toward the north, the right

side, bottom, and left side of the pipe in the area of the

crack are shown in figures 4b, 4c, and 4d, respectively. As

can be seen in figure 4c (arrow A) , the pipe had been dented

near the bottom in the vicinity of the crack. Other mechanical

damage was evident, especially on the bottom of the pipe and

again in the vicinity of the crack. Some of this damage can be

seen in figures 4c and 4d . Tliis damage appears to have been

caused by something scraping or gouging the pipe in the transverse

direction. The crack passed through one of these gouged areas.

There was a heavy deposit of corrosion product on the pipe

surface where the damage had occurred. Mechanical damage was

found on other areas of the pipe length, but it did not appear

to be as severe as that near the crack.

There was a considerable amount of pitting on the

outside surface of the entire length of pipe submitted for

examination. Examples of pitting in the vicinity of the crack

are quite evident in figures 4a and 4b. Cross sections two and

five inches south of the crack and a longitudinal section taken

between 22 and 24 inches south of the crack are shown in figures

5a, 5b, and 5c, respectively. Each of these sections was cut

through what appeared to be one of the deeper pits. As can be

seen in figure 5, some of the pits had penetrated more than half

the wall thickness of the pipe, or approximately 0.08 inch. Some

macroscopic deformation is evident in figure 5c, indicating

probable mechanical damage in this area.

The inside wall surface of the pipe length was

covered with a light scale, but this scale was considered to

have an insignificant effect on the integrity of the pipe.

4.1.2 Pipeline in the Field

At site 2 (described in Section 3.3.2) , about a two

foot length of the pipeline was excavated and cleaned of loosely

adhering soil with a small, stiff bristle bursh. Part of the

exposed pipe is shov/n after cleaning in figure 6. The pipe

length was examined in place visually and with a hand magnifier

on the top, both sides, and (with the aid of mirrors) on the

bottom for general condition. The pipe was covered with a black,

sooty substance that could be easily rubbed off on the hands.

- 6 -
There was no mechanical damage evident such as that detected

in the submitted pipe length. There were some pits, particularly near the south end of the excavated length, but these

pits did not appear to be nearly as severe as those on the pipe

length that was submitted for examination.

4 . 2 Fractographic Examination

4.2.1 Visual and Macroscopic

Taking precautions to prevent further propagation of

the crack during handling, the pipe length was cut transversly

about two inches on either side of the crack. The remaining

four inch length of pipe containing the crack was then cut

longitudinally on a three o'clock-nine o'clock diameter from

the south saw-cut face in to the crack. This dissection

exposed the crack over about 180° of the pipe circumference.

The wall thickness of the pipe at the crack at the bottom of

the pipe in the gouged area had been reduced by more than 70%

at one point, apparently by a combination of mechanical damage

and corrosion. This can be seen in figure 7 where part of

the south side of the fracture surface is shown. The crack

apparently initiated at this gouged area.

Both the north and south opposing fracture surfaces

were covered with corrosion product in an essentially similar

pattern. There appeared to be a distinct change part way

across the fracture surface (as viewed radially) in the degree

of corrosive attack. Corrosion product was heavier on the outside

circumferential part of the fracture surface than on the inside

circumferential part. This indicates that the part of the

fracture intersecting the outside wall surface of the pipe had

probably formed at an earlier time than the more recent appearing part adjacent to the inside v/all surface. The distinction

between the severity of the corrosive attack was evident over

the entire 180° portion of the fracture exposed, with the

possible exception of a small region adjacent to the gouge at

the bottom of the pipe where the older part of the crack may

have penetrated the entire wall thickness. The older and

recent parts of the fracture can be seen in figure 7.

4.2.2 Scanning Electron Microscope Examination

The primary feature exhibited by the entire exposed

portion of the more recent appearing part of the fracture was

quasi-cleavage (indicating brittle fracture) . There was a small amount of dimpled rupture (indicating ductile fracture)

,

most of which was found adjacent to the inner wall surface.

- 7 -
Thus, the recent part of the fracture was principally brittle;

i.e., very low ductility. Two areas exhibiting features

typical of the recent fracture away from the inner wall are

shown in figures 8 and 9. One area adjacent to the inner

surface of the pipe exhibiting a mixture of quasi-cleavage

and dimpled rupture is shown in figure 10.

Regions of the older appearing part of the fracture

were covered with a rather heavy film of corrosion product

which obscured the fracture features. An area exhibiting this

film is shown in figure 11. After cleaning the fracture

surface in an ultrasonic cleaner, enough of the corrosion film

had been removed so that many of the fracture features could

be seen. Quasi-cleavage was the primary feature exhibited

(figures 12 and 13) , but there was some dimpled rupture near

the apparent fracture origin (figure 14)

4 . 3 Metallographic Examination

An area of an as-polished longitudinal section through the

pipe adjacent to the south fracture surface exhibiting a typical

inclusion content for the pipe material in the areas examined

is shown in figure 15. The average inclusion content in this

typical area does not appear to be abnormally high.

An etched longitudinal section intersecting the fracture

near the apparent fracture origin near the bottom of the pipe

is shown in figure 16. The outside surface of the pipe is

horizontal at the top of the figure, and the fracture profile

is at the right in the region designated "D". Macroscopic

deformation near the fracture is evidenced by the upward

curvature. This deformation apparently was caused mechanically

by an external source. Deformation on a finer scale can be

seen in a gouged area adjacent to the outside surface of the

pipe in the region designated "A" in figure 16. Areas

designated "B", "C", and "D" in figure 16 are shown at higher

magnification in figures 17a, 17b, and 17c, respectively.

Area B (figure 17a) , at the periphery of the gouge through

which the crack passed, had suffered mechanical damage and

subsequent corrosive attack. The area adjacent to the fracture

shown in figure 17b (area C, figure 16) is in the gouged region

through which the crack passed. There is a relatively heavy

deposit of corrosion product at area C.

Although corrosion product is evident on the outside wall

surface in both figures 17a and 17b, none could be seen on the

profile of the fracture shown in figure 17c. The fracture

had been ul trasonically cleaned before the section shown in

figures 16 and 17 was prepared. This cleaning operation may

have removed enough of the corrosion product so that it could

- 8 -
not be seen in profile or, indeed, the corrosion product may

have been too thin even before cleaning to be detected in

profile. As indicated in figure 17c, the fracture appears to

be primarily intergranular in nature in this region, which is

in contrast to the results of the f ractographic examination.

The areas of the fracture examined with the scanning electron

microscope exhibited primarily transgranular quasi-cleavage

Apparently both intergranular and transgranular fracture modes

are exhibited by different areas of the fracture.

The wall thickness of the pipe adjacent to the fracture

had been reduced by about 7 0% in the section shown in figure

16. This was apparently due to a combination of mechanical

damage (gouging) and subsequent corrosion, which may have been

accelerated by the material in the deformed region being in a

relatively high stress condition. There appears to be some

evidence of microscopic deformation adjacent to the gouged

area, which would be expected from the mechanical damage.

The material that had probably suffered the most severe

deformation may have been corroded away. There appears to be

a secondary crack perpendicular to and away from the fracture

(arrow E, figure 16). The corrosion product was unusually

heavy in this region.

The micros true ture of the material consists primarily of

ferrite (light phase) with some pearlite (dark phase)

4 . 4 Chemical Analysis

A chemical analysis was performed by a competent commercial

laboratory on a sample of the pipe material. The results of

that analysis are given in Table 1. The pipe was fabricated

from a plain, low carbon steel. It meets the chemical composition requirements of ASTM Standard A53-73 for type F welded

pipe, and it meets all the requirements for type E except for

a high phosphorus content (3). The standard specifies a maximum phosphorus content o.f 0 . 050% for type E pipe.

4 . 5 Hardness and Dimensional Measurements

Rockwell B hardness measurements were made on three

transverse sections through the pipe length located 2,5, and

24 inches south of the fracture. A minimum of ten measurements

was made on each section. The results are given in Table 2

along v/ith approximate equivalent ultimate tensile strength

(UTS) values^^^. In each cross section, the lowest hardness

values were obtained at the location of the longitudinal weld

in the pipe. The approximate ultimate tensile strength based

on hardness is above the minimum required for type F and grade

- 9 -
A, type E welded pipe as specified in ASTM Standard A53-73 (3) . ASTM Standard A53-73 specifies that the outside diameter of

the pipe should be 2.375 inches within mill tolerances. The

outside diameter of the submitted pipe v;as 2.38 inches for an

average of four measurements made at 4 5® intervals on a

transverse plane. The average wall thickness in a region away

from the fracture measured 0.150 inch, which is well above the

minimum 0.135 inch required by ASTM 53-73.

4 . 6 Soil Corrosivity Characterization

Data from measurements made at the site of the pipeline

are given in Table 3. The results indicate that the soil is

slightly alkaline. The redox potential is above +500 mv and,

therefore, considered noncorrosive from the standpoint of

anaerobic bacterial attack (5). The resistivities at sites 1

and 3 were well over 10,000 ohm-cm which would indicate nonaggressive soil . The soil at site 2 with a resistivity of just

under 5000 ohm-cm is judged to be moderately aggressive. The

potential of the pipeline indicated that it is under very weak

cathodic protection in the area of site 1 where, according to

the Columbia Gas Company, magnesium anodes were installed at

the time the failed length of pipe was replaced. This protection

was reduced at site 2 and further reduced at site 3.

The results of the chemical analysis of the soil samples

are given in Table 4. The carbonate content is high, but not

abnormal for an alkaline soil, as indicated by the pH. The

nitrate, sulfate, and sulfide contents are low for all of the

samples. The sulfate content at site 2 is two or three times

higher than at sites 1 and 3, but nevertheless, low compared to

National Bureau of Standards soils (6), The low values of these

acid forming anions is reflected in the low total acid

determinations

4 . 7 Impact Tests

Impact tests were run on three of the pre-cracked specimens

described in Section 3.3. One each was tested on a Charpy

impact machine at 25 , 45, and 65**F. The 25° temperature

approximated the temperature of the air in York on the day of

the explosion, and the 4 5° temperature approximated the estimated

temperature of the soil at the site of the failure. The fracture

surfaces produced at the three temperatures are shown in

figure 18. For about the first 90% of the impact fracture in

each case, the dominant feature was quasi-cleavage indicating

low-ductility or brittle fracture. Scanning electron fractographs

- 10 -
showing examples of this part of the fracture surfaces are shown

in figures 19a, b, and c for the specimens tested at 25, 45, and

65°F , respectively. For each specimen, however, there was an

abrupt change in the fracture mode with the fracture going from

brittle to ductile. There was a band of dimpled rupture at the

last part of the fracture to form. This part of the fracture

was farthest from the notched surface and may be related to

specimen configuration. The width of the band of ductile

fracture (dimpled rupture) was about 11, 8, and 9% of the total

fracture produced in impact at 25, 45, and 65°F, respectively.

A scanning electron fractograph representative of the ductile

regions of the specimen fractures is shown in figure 20. A

fractograph showing the transition from quasi-cleavage to

dimpled rupture in the specimen tested at 4 5*'F is shown in

figure 21.

5. DISCUSSION •

This two inch steel gas main pipe failed in a brittle

manner at a location of the pipeline where the pipe had suffered

rather severe mechanical damage. This damage consisted of

bowing, denting, and gouging of the pipe. The crack causing

failure passed through, and probably initiated at, a gouge that

was adjacent to a dent near the bottom of the pipe. The wall

thickness of the pipe had been reduced by about 70% near the

apparent origin of the crack, and there was a significant amount

of corrosion product on the outside of the pipe in the gouged

region

The crack leading to final failure appears to have formed

in at least two stages at different times, as evidenced by the

amount and distribution of corrosion product on the fracture

surfaces. Thus, apparently there was a crack present prior to

the time of final failure of the pipe. Both the older and recent

parts of the crack were essentially brittle in nature, but the

older part of the crack, which had penetrated about half of

the wall thickness of the pipe over most of the approximately

180° portion of the fracture surface examined, and perhaps

penetrated the entire wall thickness of the pipe near the crack

origin, exhibited somewhat more ductility than the part of the

crack that formed later. This was shown by comparison of

fractographs which indicated somewhat more dimpled rupture in

the older part of the crack than in the more recent part.

Since this normally ductile steel failed in a brittle

manner, the apparent mechanism of fracture for the older part of

the crack was likely stress corrosion cracking. Failure occurred

in a relatively highly stressed area of the pipe, the stressed

condition having been created by mechanically deforming the

- 11 -
material (the mechanical damage mentioned above) . There was

more corrosion product in the gouged area of the pipe through

which the crack passed than in other areas of the submitted

length, which is probably due to a combination of the stress

condition of the pipe at the gouged area and the absence of any

surface protection for the pipe. Even though this pipe is

classed as a "bare" pipe, there was a light protective coating

consisting of a black, tarry appearing substance on the outside

surface of the pipe. This coating was missing in the gouged

area.

The mechanism for the more recent part of the crack was

probably either stress corrosion cracking or impact. The impact

tests conducted in the laboratory resulted in primarily

c leavaae fractures at temperatures similar to those to which

the pipe was subjected at the time of the failure. There was

some dimpled rupture exhibited by the more recent part of the

field fracture adjacent to the inner wall surface of the pipe.

This part of the fracture was likely the last to form. This

region of dimpled rupture in the field fracture was much smaller

than that observed in the laboratory -produced fractures. The

fact, however, that the laboratory fractures were primarily

cleavage indicates that impact may be a possible fracture

mechanism for the more recent part of the field fracture.

Compared with data gathered by the National Bureau of

Standards on soils throughout the United States, the results

of the soil analyses indicate that the soil in the areas of

the pipeline examined is of low corrosivity. This fact would

not necessarily eliminate the possibility of failure due to

stress corrosion cracking.

The submitted pipe length had a number of corrosion pits

on the outside surface, some of which were about 0.080 inch

deep. This represents more than half of the wall thickness of

the pipe. National Bureau of Standards soil data (6) reveal

that maximum pit depths of from 0.060 to 0.400 inch over a period of thirty years exposure might be expected in this soil.

This is consistent with the maximum pit depths found in the

cross sections of the. submitted pipe length examined. Although

the examination was essentially superficial, there appeared to

be fewer pits in the length of pipeline that was still in service

(at site 2) than in the submitted length, and those pits observed

appeared to be less deep. Both this length of pipe and the

submitted length were located where capped sewer laterals leading

to 1320 and 1324 South Ogontz Street, respectively, crossed

under the gas main. There were septic systems in the front yards

of both 1320 and 1324 South Ogontz Street. The pipe at site 2

- 12 -
(1320 South

the pipe in

Ogontz) had not

the vicinity of

suffered the mechanical damage

the failure had sustained.

that

At the outset of this investigation, it was thought that

possible seepage from the septic system or the capped sewer

lateral at 1324 South Ogontz Street may have provided a medium

to accelerate the corrosion process or to promote stress

corrosion cracking. This suspicion was not borne out by the

results of the soil analysis.

The inclusion content and the microstructure of the pipe

material appeared to be satisfactory. The chemical composition

meets the requirements of ASTM Standard A53-73 for type F

welded steel pipe and the ultimate tensile strength (based on

hardness measurements) meets the requirements of the same ASTM

Standard for type F and grade A, type E welded steel pipe.

The pipe diameter and wall thickness satisfy tlie requirements

of this Standard for schedule 4 0 pipe.

6. CONCLUSIONS

1. There was a transverse crack in the approximate center of

the submitted length of pipe. This crack traversed about

85% of the pipe circumference, extending in a clockwise

direction from one o'clock to eleven o'clock.

2. There was a considerable amount of mechanical damage to

the pipe consisting of a bow, dents, and gouges on the

outside surface in the vicinity of the failure. The

mechanical damage produced a region in the vicinity of the

crack that was more highly stressed than was most of the

material away from the crack.

3. The crack appeared to initiate at a gouge near the bottom

of the pipe. At the apparent origin, the wall thickness

of the pipe had been reduced by about 70%, likely by a combination of mechanical damage and corrosion.

4. As evidenced by the corrosion product on the fracture

surface, the crack had formed in at least two stages. Both

parts of the crack were essentially brittle in nature, but

the older part exhibited slightly more ductility than the

more recent part. This indicates that part of the crack

had been in existence prior to the time of failure. The

older part of the crack may have penetrated the entire wall

thickness of the pipe.

- 13 -
5. The likely fracture mechanism of the older part of the

fracture was stress corrosion cracking. The likely fracture

mechanism of the more recent part of the fracture was either ' stress corrosion cracking or impact.

6. There were numerous pits in the outside wall surface of the

submitted length of pipe. Some of these pits penetrated

more than half the wall thickness of the pipe, but the pit

depths appear to be consistent with NBS data for exposure

in nonaggressive soils.

7. Pitting appeared to be much less severe and there was no

evidence of significant mechanical damage on the pipe length

examined which was located about 51 feet from the site of

the failure.

8. The soils examined in areas along the pipeline are considered

to be of low corrosivity.

9. There was no evidence from the soil analysis of any leakage

from the septic system or the sewer lateral that may have

contributed to the failure.

10. Laboratory impact tests on non-standard pre-cracked impact

specimens machined from the pipe material resulted in

fractures which were about 90% quasi-cleavage and 10%

dimpled rupture. The dimpled rupture was essentially all

in a band at the last part of the fracture to form and may

be related to specimen configuration. These fractures were

somewhat similar to the more recent part of the field

fracture, although the field fracture exhibited less dimpled

rupture than the laboratory impact specimens.

11. The chemical composition of the pipe material meets the

requirements of ASTM Standard A53-73 for type F welded steel

pipe.

12. The ultimate tensile strength (based on hardness data) meets

the requirements of ASTM Standard A53-73 for type F and

grade A, type E welded steel pipe.

13. The outside diameter and the wall thickness of the pipe meet

ASTM Standard A53-73 for schedule 4 0 pipe.

14. Nothing abnormal was noted concerning the microstructure or

inclusion content of the pipe material.

- 14 -
7 . ACKNOWLEDGEMENT

The soil corrosivity characterization program and the

analysis of the data from that program were carried out by

Mr. Edward Escalante of the NBS Corrosion and Electrodeposition

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

Section performed the photographic and metallographic work

and assisted in other areas of the investigation.

REFERENCES

1. Iverson, W. P., "Tests in Soils," Handbook on Corrosion

Testing and Evaluation (W. H. Ailor"i Editor), Wiley, New

York, 1971.

2. Romanoff, M. , "Underground Corrosion" (NBS Circular 579),

U. S. Department of Commerce Clearinghouse, PB 168 350, 1957.

3. Annual ASTM Standards , Part 1, American Society for Testing

and Materials, Philadelphia , 1974.

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

Metals, Metals Park, Ohio, 1961.

5. Starkey, R. L. , and Wight, K. M. , "Anaerobic Corrosion of Iron

in Soil," American Gas Association, New York, 1945.

6. Schwerdtfeger , W. J., "Soil Resistivity as Related to Underground Corrosion and Cathodic Protection," Journal of

Research, National Bureau of Standards, 69C, No. 1, 1965.

IISCOMM NHS DC - 15 -
Table 1. Results of Chemical Analysis of the Pipe Material

Element ^ Percent (weight)

Carbon 0.09

Manganese 0.45

Phosphorus 0.071

Sulfur 0.022

Silicon < 0 . 05

Nickel < 0.05

Chromium < 0.05

Molybdenum <0.05

Copper . < 0 . 05

Table 2. Results of Hardness Measurements

Hardness, Rg Approx. Equiv,

Cross Section Location Average Range UTS, ksi

2" south of fracture 74 62-79 56-73

5" south of fracture 71 62-77 56-72

24" south of fracture 70 63-72 56-70
cn

(d -P •H

-P 0>

Q) o in o

-P CN o 0 iH

Oh o • • • (U o o o c u 1 1 1 •H 1 rH 13

(D

U

•Hw> ^ CTi • • • o o o

ro ro <N LD LD IT) o o o + + + o o o

ro ro <N n <Ti m

CN

n (N CN rH

a0 rH <N ro •H

-P QJ 0) fd P -p -p u rH •H

Lo cn

0) fH

(tJ Eh

-P

•HOH

O

CO

U

O

U I IT) I I • I I I LD I I • I I rH

(0 u»

rH (U 0 73 CD LO Ll) LO LO LD LO

to -H

MH r—1

CZ5 o o < ' U rH V V V V V V

rH d) 13 CO e e fd

ID

C/3

i-H rH Orr\ Uj CO

0) 0 -p o t—1

r~ 00 o CO fd V ^ IH rH LO 1 1—1

(/) >-l rH \ iH iH H Q) w -P CO g

>i (d rH

fri

«; Q) .H (—1

X)

(d 7i U] o rH 0) •H 0 -p

O CN o O 00 00 ro

CO (d

O ID CN CN CN CN

u rH

5-1 -P \ CD C_) /—\ u 0) H CP

-p e

fd :s

MH e 0 OJ CP H

0] XJ U] o

-P ^3 0) o

iH rH -p -H 0 (d \ 00 00 W CO C CN CN CN iH

0) Ofcn « u XI o

5h

u

-P fd • (d u tp

[2 eco

•H

-p

(duo

(U

O 0) u u

Id fd

14H MH

U 05

W

fd 4H :? ^ MOO P rH rH W 0) Q) XJ X! U

(d = s

(U 00 C <^ CN

0)

w

u

fd

:5 MH o u

O

fd MHwO

0)

W (U XI X! u = fd s O 0) CO

iH rH rg CN c^n

(U (U p -p •H -H

(U QJ •P -P •H -H

CO CO CO CO CO to

00 O QJ \

•H x: o • cu u c

fo &. a)

0) 4J O OJ x: -p -P w

-P to

x: <D x: X!

4J XI -u •H c 5 O -P nj 4J ftJ U

. T3 rH Cl^ q; OJ (T3 g

U -P 4-> (T3 fO H C -H

rH O O U

Q) -H 0) c M M x: •H O -P

03 x: g > O

rH CI, 0) —

u e ? -p

(ti M-l

x: u -P rH

4J rH

0) 0

x: x: X! x:

4-> 4J -P •H OJ 3

-x: o

0) 4-) w

05 u

PQ -H UH 4-> Z > o tn

>H P

(T3 W (DX OJ

0) -H -H > rH a

•H in n3

QJ n3 C 0) u ^ ri x:

OJ -P M -P P

-H +J C

U) -H -H

(13 tn tT>

(T3 a :j x: 0 0

+J T5 -H X5

CP QJ G C 0) <C

Q) 0 x:

t-P -H -P

4-1 QJ -H -P QJ H o x: -H

(1^ Oi-P 04

QJp

•rl

Figure 2. Longitudinal piece cut from the pipe length

about 24 inches south of the fracture. This

piece exhibited good ductility since it was

bent through a sharp angle and exhibited

only slight cracking. X 4

b

Figure 3. Part of pipe length as received showing bow south

of the clamp. X 1/5

a. East side of pipe

b. Bottom of pipe

Figure 4. Four views of the pipe in the area of the crack

after removal of the clamp. X 1

Arrow A indicates dent near the bottom of the pipe

Arrows B indicate gouge near bottom of the pipe

through which the crack passed

Arrows C indicate examples of pitting on the surface

of the pipe

a. Top of pipe

b. East side of pipe

c. Bottom of pipe

d. West side of pipe





\q; ^

XI

<-{ o

0)u

0)

• a,

ac w M

-p u

•H • a • • M Q) XI M u x:

0) O (d -P

(tJ u

(U C U M-l U 0

0)

CD x: x:

x: c c -p 0 -H <H 0

•H 0 03

4-1 Oi 0

nj 0 x; 03 U -P. x: P 0) 0

•H -P 0 u

td 0 03 C

C t/3 •H

•H W 03 H W Q) x: (u x: «N

-P QJ x: u

CP Ou u C 0

c •H 4J rH

rH 0) CN 0 > CM

0) 0

-P 4-1 C

•H 0

a 0 c C -H

Eh 0 0 -P •H rH U

x: -P hj QJ -p • U U 03 -p Q) QJ x: w W 03 H

fd

(D 0) c

0 q; 0) 03 -H

>^ Q) >-l x: 03 :d -p > > -p

0) 03 03 -H

01 x: C

C -P fd (d c 0 u

•H Cn Eh

-P C

U 0

• • • n3 XI U

in

U

•H

Ix,

Figure 6. Top view of part of the pipeline excavated at site 2. X 1/2

Bottom half (as the pipe was positioned in

service) of the south side of the fracture.

Thin area at about 7 o'clock is- where the

crack passed through a gouge. Note lighter

color of the fracture near the inside wall

surface of the pipe. This region is the

recent part of the fracture. X 1 1/2

Scanning electron fractograph taken in region

of "fresh" fracture showing essentially all

quasi-cleavage . X 260

Figure 10. Scanning electron fractograph taken in region

of "fresh" fracture adjacent to the inner wall

surface. The primary fracture feature is

quasi-cleavage . Some dimpled rupture is evident

X 260

Figure 11 . Scanning electron f ractograph taken in the

older appearing part of the fracture before

ultrasonic cleaning. The film of corrosion

product is evident. X 690

Figure 12. Scanning electron f ractograph taken in the

older part of the fracture after ultrasonic

cleaning. Quasi-cleavage is the primary

fracture feature. X 95

Figure 13. Scanning electron fractograph taken in the

older appearing part of the fracture. The

primary feature exhibited is quasi-cleavage

X 137

Figure 14. Scanning electron fractograph taken in the

older appearing part of the fracture near

the apparent fracture origin. There is a small amount of dimpled rupture. X 670
1
Figure 15. Longitudinal section through the pipe near the

south fracture surface showing an average

inclusion content for the areas examined. As

polished. X 100

Figure 16. Longitudinal section intersecting the south

fracture surface near the apparent crack origin,

The outside wall surface of the pipe is at the

top. The fracture profile is at the right (D)

Macroscopic deformation is evident near the

fracture. Deformation on a finer scale can be

seen at A. E indicates a secondary crack.

Areas B, C, and D are shown at higher magnification in figure 17.

Etchant: 1% nital X16

3 . o. o

>irH

rH>Hu

cuw

Q)MU

-H>o

XIo

U)

Q)U

fO

<£>u

CP -H

4-4- rH u

4-1 C

x:ow

•H

PL4

"+-1 oOc

0) T>•H>

cu

•H

Q)

(U X!

EH

OOU 0)0 o 4J •HW 0) o u U fO

)-l Q) o a. u a

c: 0)u

u rti fd • (d -P >-i CU4-> 4-» En o -p fd

4-) fd

0) <U >

X; > -H 4-1 4J -H w x: m 0

4-)

O

M -H

fd >HM V4

U 0

rnnD fl) -HO x;

IW 4-) 0) 4-1 0 a c 4-) -H 0) 0) td Ou 13 0

Q) Q) (1) rH

x: tn 73 rH

4-> XJ -H fd 3 > O •

M-l

W Q) -H 0 -P fd CP 5-1 rH

Q)

C

C Q)

U fd -H >

fd ^ fd

M-l 0) 0 »-( u tj-x: 0) Di p fd tn rH u w 6 -H

fd

a M-i 4-1 rH TJ 0 0

nH -H V4 •H

fO rH Cn Ch ^ fd QJ >i U V4 Q) rH

0) -H

U •H

•H fd 0) 4-> fd w x: cr> o e

4J

u 3 (d •H 3 Q >-i O e c3 fn M • • fd X) O

o

O 0) cn

TJ u H X

o ts

1 •HW

0 0 ua c c tr 0 0

•H 4-1 -p x: 0

u u

Q) -p c M 0 0

•H G •H

-P eg

0) u

U

Eh

aw- tes w td

to u • c 10 •H (1) 0) 'd u g -p c: a

ffl •H -p o u

Q) H u p

in T3

-p u (U u < fd -H u

a, u e e H

•H

>iU H •H 0

0 -p • • • -p rd c Em

(T3 0 4-1 0 0 0 0

»-( -p •H LD IT) in 0 Cn CN

J3 -p 0 0)

tT3 >-i 0) (U (U

(d

i-H u w 3

•H 0) -P P -p 0 e -p fd fd (d 0 fd M >-i U) •H u 0) 0) Q) •H Qj CL Qj u CQ e e e

W c: 0)

14-1 •H -P 4-1 u 0) C U Q Cn CP cn 0 rd C C

•H 4-1 •H •H •H

0) 4-» U <u +J -P 4-> u td Cn. w W to

fd Q) Q)

4-> rd > Eh Eh Eh, 0 a-H fd

(T3 0 -H 0) U fd H • • • a 5 u fd XI U

00

QJU

cr> H

. in

X!

> X

ID u QJ 0 rH

-p U

m 1 u •H 0 (0

(T3 fd rH tr

OJ cn x: H

-p

<D m U

0

-P c fT3 0 (U •H 14H eno -P u c

(T3 o C c

1—

•H Q) -p e Q) +J 0 If) H 'Ti u Q) XI 0) X!

x:

0) C

x: (d

4-> U

U-l QJ 0 U

u

Ui fd x: O, • a, S-i fd ^ o 0 o u W in in in cn0 QJ -p rH QJ QJ QJ u D Oi U U M

<n 4-> e :3 u 0 -H -P -P -p

fd T3 fd fd fd

>-( u u

c U-l Q) QJ QJ 0 0

u c e e

-p QJ -p QJ QJ u e C -P -P

0) -H P

rH U 0 cn tJ^ cn

OJ QJ e c C c

a, fd •H •H •H

cn to -P +J -P c cn (/) U) •H -p i-H QJ 0) QJ c u fd Eh c e

a. w u e • • • w •H fd X5 U

QJP

Cn •H

Figure 20. Scanning electron fractograph from the

specimen tested in impact at 45°F. This

area is in the ductile part of the fracture.

The primary feature exhibited is dimpled

rupture. X 425

Figure 21. Scanning electron fractograph showing the

transition from essentially brittle fracture

(top) to ductile fracture (bottom) . There

is a small area of quas i-cleavage in the

predominantly ductile region. X 165

NtJi-l MA IREV 7-73)

U.S. DEPT. Of COMM.

niBi inr'DA.DMir* data

SHEET

1. IM Hl K A 1 |(),\ OH Kl- POK r NO. NBSIR 74-625

2. Ciov 't A( ( i-sston

IN ( )

.

3. Rcc ipifni 's Accession No.

4. TITLE ANf) SUB I I I I.I EXAMINATION OF FAILED TWO INCH STEEL PIPE NATURAL

GAS MAIN, COLUMBIA GAS COMPANY, SPRING GARDEN

TOWNSHIP, YORK COUNTY, PENNSYLVANIA

5. Fublic aiion Date February, 1975

6, Performing Organization Code

7. Ali rilOK(S)

T. R. Shives

8» Performinc Urcan. Report No. NBSIR 74-625

9. PI;KI-ORMINC. OIU.ANI/.A ITON NAMI- ANH AnnUlvSS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. i'roiect/Task/Work Unit No. 3120418

11. (ontracl /Grant No.

12. Sporisorm^ ( )r^ r/ .m cm N.imc .imt ' i)m[i|<n A,|,lri'ss (Street, City, State, ZIP)

Office of Pipeline Safety

Department of Transportation

Washington, DC 20590

13. Type of Report & Period

( overed FallurG

Analysis Report

14. Sponsoring; Agency (,ode

15. SIjPI-'I.KMKNTARY NOI l-S

16. AHSTRA(."r (A 200-word or less factual summary ol most sif^rnlii ant information. If document includes a sifinificani

hi hi lof^raphy or literature survey, mention it here.)

The Mechanical Properties Section of the National Bureau of Standards

examined a length of a cracked two inch diameter plain carbon, welded

steel natural gas main pipe at the request of the Office of Pipeline

Safety. The pipe had a transverse crack extending about 85% of the

circumference. The pipeline had suffered considerable mechanical damage

in the vicinity of the failure, and the crack, which propagated in an

essentially brittle manner, appeared to have initiated in a gouged area

near the bottom of the pipe. There was a considerable amount of

corrosion product on the surface of the pipe in the gouged area. The

amount and distribution of corrosion product on the fracture surface

indicated that the crack had formed in at least two stages, and that a

crack was present prior to the time of failure. During the first stage,

the crack may have penetrated the entire wall thickness of the pipe in

one region opposite the crack origin near the bottom of the pipe. The

likely mechanism of fracture for the first stage of the crack appears

to be stress corrosion cracking. For the second stage of the crack,

either stress corrosion cracking or impact appears to be the likely

mechanism of failure.

17. KKY WORDS (six to twelve entries; alphabt tn nt order, capitalize only the first letter of the first key word unless a proper name; separated by semic nions ) Brittle fracture; gas main pipe; impact; low carbon steel; stress

corrosion cracking

18. AVAll.AKlLn Y IJnl imitcd 19. SLCIJRl TY CLASS

I THIS REPORT)

21. NO. OF PAGES

Tor Official Distribution. Do Not Release to N'l IS UN(.;L ASSUMED

40

[ Order T rom Sup. of Doc, U.S. Washington, D.f . 20 (0.^ SD ( Ciovernment

at. No. ( 1 ^

'ritit 1 ri^ Office 20. Si:( LRU Y C LASS

(| III SPACE)

22. Price

[ Order I' rom National Technic.

Springfield, Virginia _'2I'>I

1 In f orriia r 1 .11 Service f N 1 IS) L;N( LASSIE'lED

USCOMM-DC 29042-P74