NBSIR 73-299

Examination of Failed Eight Incli

Welded Steel Pipe Natural Gas Main,

UGI Corp., Coopersburg, Pennsylvania

M. L. Picklesimer and T. R. Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

November, 1973

Failure Analysis Report

Prepared for Office of Pipeline Safety

Department of Transportation

Washington. D. C. 20590
I

I
NBSIR 73-299

EXAMINATION OF FAILED EIGHT INCH

WELDED STEEL PIPE NATURAL GAS MAIN.

UGI CORP., COOPERSBURG, PENNSYLVANIA

M. L, Picklesimer and T. R. Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

November, 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

Affairs at the National Bureau of Standards."

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

IMATIOIMAL BUREAU OF STANDARDS. Richard W. Roberts, Director

TABLE OF CONTENTS

Page

SUMMARY iv

1. INTRODUCTION 1

1.1 Reference 1

1.2 Background Information 1

1.3 Part Submitted 2

2. PURPOSE 2

3. EXAMINATIONS AND TESTS PERFORMED 3

3.1 Plan of the Examination 3

3.2 Other Examinations and Tests Performed 3

3.3 Summary of Mechanical Tests Performed at NBS ... 4

4. RESULTS OF EXAMINATIONS AND TESTS 5

4.1 Visual and Macroscopic Examinations 5

4.1.1 Surfaces of pipe and weld 5

4.1.2 Service failure fracture surface 5

4.2 Fractographic Examination 6

4.2.1 Service fracture 6

4.2.2 Fracture through weld metal pulled in

tension after cooling in liquid

nitrogen 7

4.2.3 Tensile fracture through weld metal

at 70" F 7

4.2.4 Weld metal fractured in impact at 38° F . 7

4.2.5 Fracture through weld metal pulled in

tension at 35° F 7

4.3 Metallographic Examination 8

4.4 Hardness Measurem.ents 9

i

7. ACKNOWLEDGEMENT

FIGURES

1. Part of the welded steel gas main pipe still in

the ditch

2. Length of gas pipe containing the cracked weld as

received at NBS

3. Part of the pipe length

4. Four views of the outside of the pipe in the weld

area

5. Part of the inside wall surface of the pipe in

the area of the weld

6. Part of the fracture surface of the pipe with

several specimens having been removed

7. Part of the service fracture surface near one of

the crack arrest areas . . .

8. SKM photomicrograph of service fracture surface ....

9. SEM photomicrograph of service fracture surface ....

10. SEM photomicrograph of fracture surface of weld

material pulled after cooling in liquid nitrogen .

11. SEM photomicrograph of fracture surface of tensile

specimen failed through weld at 70® F

12. SEM photomicrograph of fracture surface of impact

specimen tested at 3S° F

13. SEM photomicrograph of fracture surface of weld

metal pulled in tension at 35** F

14. Etched longitudinal side of tensile specimen

15. Etched longitudinal sections through pieces of

pipe on either side of the weld

16. Etched microstructure of longitudinal section

through weld

FIGURES (Continued)

17. Etched microstructure of longitudinal section

through pipe material adjacent to weld . . .

.

18. Representative etched area of longitudinal

section through heat affected zone

19. Etched longitudinal sections through both

pieces of pipe adjacent to the heat

affected zone

20. Unetched longitudinal sections through vreld

.material

21. Unetched longitudinal section through pipe

material showing inclusion content . . . .

.

SUMNARY

The Office of Pipeline Safety, Department of

Transportation, submitted a four foot length of eight inch

diameter welded steel pipe natural gas main containing a

crack in the weld to the NBS Mechanical Properties Section

for examination. The apparent crack origin was located at

about the 4:30 o'clock position, assuming the top of the

pipe to be at twelve o'clock and the outside of the bend

of the pipe as installed was at three o'clock. The crack

had propagated about two-thirds of the way around the pipe

circumference. Optical and scanning electron microscopy

revealed the fracture to have been predominantly brittle

in nature. There was lack of weld penetration around a

large part of the weld circumference and the weld metal

exhibited some porosity. These features are normal for

steel pipe welded by the oxy-acetylene practice used at

the time the weld was made. While these features of the

weld helped to define the path of the fracture, they

probably did not contribute to it. Examination of the

fracture and comparison of its features with those of

fractures produced in the laboratory indicated that

failure was probably brought about as a result of a single

event, impact loading from an external source.

iv

Examination of Failed Eight Inch Welded Steel Pipe

Natural Gas Main, UGI Corp., Coopersburg, Pennsylvania

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-AS-10041 . The request was made on March 1, 1973.

1 . 2 Background Information

The information in this section was furnished by Mr.

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

John Flaherty of the Pennsylvania Public Utility Commission,

and Tpr. George F. Umberger, Fire Marshall, Pennsylvania

State Police, at a meeting at the National Bureau of

Standards with M. L. Picklesimer of NBS on March 1, 1973.

On February 21, 1973 at 11:52 A.M., there was a natural

gas explosion involving two duplex apartment buildings at

41-43 and 45-47 North Main Street in Coopersburg, Pennsylvania.

The explosion resulted in the loss of life, personal injuries,

and property damage. After the explosion, pressure testing

of the eight inch diameter welded steel pipe natural gas main

in North Main Street with air caused water to squirt from the

ground, indicating the location of a leak which was found to

be at a cracked weld. This crack is shown in figure 1 with

the pipe still in place in the ditch after that part of the

pipe containing the cracked weld had been uncovered. The

photograph shown in figure 1 was reported to have been taken

looking straight down on the pipe. (Photograph furnished by

and used with permission of the Pennsylvania State Police.)

The pipeline had been installed in 1924 and was under 30

inches of soil consisting primarily of shale, on top of which

was an eight inch layer of concrete. The welds in the line

were assumed to have been made by the oxy-acetylene torch

process, since arc welding was not used in the construction

of gas distribution lines in Pennsylvania prior to 1929. Gas

pressure in this area of the Coopersburg gas distribution

system was maintained at 45 psig.

- 1 -

During the process of removing the cover material from

the cracked part of the pipe, a water main was broken and

the cracked weld in the gas pipe was submerged for more

than three hours. After the water was removed from the

ditch, the gas pipe was clamped around the crack with a rubber gasket. When pressure tested with air, water came

out at the break. With the clamp left in place, a length

of pipe containing the crack was cut by torch from the

pipeline and removed for examination.

Prior to the explosion, blasting holes had been drilled

in the vicinity of the gas main and blasting charges had

been set off. The nearest blasting hole was 4 feet 10 inches

from the gas main. The dynamite sticks used in the blasting

charges were 2 inches by 16 inches and were inserted to a

depth of 7 1/2 inches into the holes. A 2 1/2 pound charge

was used in each hole. The last six charges were set off at

11:15 A.M. on February 21, 1973, which was 37 minutes before

the explosion.

1.3 Part Submitted

A four foot length (approximately) of the eight inch

diameter pipe which had been cut from the gas pipeline was

submitted to the NBS Mechanical Properties Section for

examination. The cracked weld was in the approximate

center of the submitted length. The clamp and gasket were

still in place (figure 2) when the pipe length was delivered

to the Mechanical Properties Section on March 1, 1973 by

Tpr. George F. Umberger.

2 . PURPOSE

The Office of Pipeline Safety requested that NBS

determine the following:

1) Whether there was a pre-existing crack.

2) Whether the crack initiated and propagated over

a period of time or formed in a single event.

3) Whether the crack formed from shock or

vibration loading.

4) The quality of the v/eld.

5) The probable properties of the welded joint.

- 2 -

3. EXAMINATIONS AND TESTS PERFORMED

3 . 1 Plan of the Examination

At a meeting at NBS on June 11, 1973 attended by Mr.

Lance Heverly of OPS, Dr. Amos J. Shaler representing the

UGI Corporation, and Dr. M. L. Picklesimer of NBS, the

plan of the examination of the failed gas pipe discussed

in this section was agreed upon.

The pipe would be cut transversely by band saw on one

side of the weld and about two inches from it. The piece

containing the weld was then to be cut longitudinally on a

diameter starting at the transverse saw cut face to allow

a portion of the pipe to be removed so that part of the

fracture surface would be exposed for examination. It was

proposed to cut the uncracked welded part of the pipe longitudinally into several pieces, one of which was to be used

for two strips welded back to back for tensile testing by

Dr. Shaler. (This material was given to Dr. Shaler at NBS

on June 15, 1973.) A second piece was to contain partly

cracked weld and partly uncracked weld and was to be

fractured through the weld in tension at liquid nitrogen

temperature. A third piece was to be used for a strip

tensile specimen with the reduced section being weld metal.

This specimen was to be tested at room temperature (70° F)

.

After photographing the fracture surface, the cutoff

piece which contained the fracture surface was to be cleaned

ultrasonically with detergent and water and then, if

necessary, would be cleaned with sodium citrate to remove

the remaining corrosion product. The specimen was to be

examined after every step in the cleaning process.

The direction of further work would depend upon the

results up to that time.

3 . 2 Other Examinations and Tests Performed

In addition to the planned examinations discussed in

Section 3.1, a visual examination of the pipe wall surfaces

was made, particularly in the area of the weld. The

fracture surface was examined visually, macroscopically

,

and with the scanning electron microscope (SEM)

.

- 3 -

A specimen was broken through weld material in impact

at 38° F (to approximate the soil temperature at the time of

the explosion) . A specimen containing some cracked weld and

some uncracked weld metal was fractured through the weld in

tension at 35° F (again to approximate the soil temperature

at the time of the explosion) . The fracture surfaces produced

from these tests and the two other tests performed at NBS

(discussed in Section 3.1) were examined visually and with

the SEM.

The relative amounts of quasi-cleavage (brittle fracture)

and dimpled rupture (ductile fracture) were determined on the

SEM for selected areas of various fracture surfaces by point

counting with a ten point grid. At least twenty fields were

used for each determination.

Hardness measurements were made on longitudinal sections

through the pipe and the weld, and metallographic examinations

were performed in selected areas.

3 . 3 Summary of Mechanical Tests Performed at NBS

A summary of the mechanical tests (except hardness tests)

that were performed at NBS and discussed in Sections 3.1 and

3.2 is presented below. The specimen locations referred to

are shown in figure 3.

A. Weld metal pulled to fracture in tension near

liquid nitrogen temperature. Specimen had been

located between 6 and the end of the tail of the

chalk arrow (piece second from the right in figure

3b) .

B. Tensile specimen v/ith reduced section being all

weld metal, tested at 70° F. Specimen had been

located between 3 and 4 (piece second from the

left in figure 3b)

.

C. Specimen broken through weld metal in impact at

38° F. Specimen had been located between 2 and 3

(right part of the piece at the far left in figure

3b) .

D. Weld metal pulled to fracture in tension at 35° F.

Specimen had been located left of 2 (piece to the

far left in figure 3b with the impact specimen

removed)

.

The two pieces given to Dr. Shaler were located between

4 and 6.

- 4 -

4. RESULTS OF EXAMINATIONS AND TESTS

4 . 1 Visual and Macroscopic Examinations

4.1.1 Surfaces of pipe and weld

The crack in the weld traversed about two-thirds

of the circumference of the pipe. One end of the crack was

near the top of the pipe. The length of the crack is indicated in figure 4. This figure shows four views of the pipe

in the weld area as seen from the top, both sides, and the

bottom with the pipe in the as received condition except for

the clamp having been removed. The weld bead around the

outside of the pipe appeared to have been made in a single

continuous pass while the pipe was rotated. The surface

topography of the weld bead appears to be typical of welds

made with an oxy-acetylene torch used manually.

The outside wall surface of the pipe length was covered

with a heavy scale (corrosion product) . There were areas

that were also covered v/ith what appeared to be tightly

adhering soil. The top of the pipe appeared to have less

scale and fewer soil deposits than the rest of the pipe.

According to OPS, the bolts holding the clamp on the pipe

were at the top of the pipe. The clamp is shown in place

in figure 2. The letter "T" in figure 4a indicates this

position, which is somewhat at variance with the top of the

pipe as indicated in figure 1.

The inside wall surfaces of the pipe had patches of

light scale, but in general were relatively clean. There

appeared to be somewhat more corrosion product in the region

near the weld (probably due to welding flux) than in other

areas as can be seen in figure 5. The area shown in this

figure contains both cracked and uncracked weld. There is

evidence of lack of weld penetration, since over much of the

pipe circumference, the weld material does not come through

to the inside pipe v/all.

4.1.2 Service failure fracture surface

Part of the fracture surface, after being cut from

the pipe length, is shown in figure 6. Several specimens had

been removed before this photograph was taken. General areas

of incomplete weld penetration are indicated by arrows 1. The

fracture surface was covered with corrosion product which

masked most of the fracture features. There were some spheres

of slag on top of the rust which were probably from the oxyacetylene torch cutting of the pipe section to allow removal

from the ditch.

- 5 -

The fracture surface was cleaned ultrasonically with

water and detergent, which removed most of the rust. When

examined with a low-power optical microscope, the fracture

surface appeared to exhibit quasi-cleavage . A photomacrograph

of part of the fracture surface is shown in figure 7 at

higher magnification than in figure 6. Careful examination

of the cleaned fracture surface indicated that the features

were flat and finer in the region about midway in the length

of the crack (measured circumferentially) than closer to the

crack arrest regions. Based on this observation, it is

probable that the crack origin was about midway between the

crack arrest regions or at about the 4:30 o'clock position

assuming the top of the pipe to be at 12 o'clock as shown in

figure 1 and the outside of the bend of the pipe as installed

to be at three o'clock.

4 . 2 Fractographic Examination

4.2.1 Service fracture

The service fracture was examined in several areas

with the SEM. These included regions near both crack arrest

sites, an area near the apparent crack origin, and an area

about halfv/ay between the apparent crack origin and one of the

crack arrest sites. Each of these areas exhibited quasicleavage as the primary fracture feature, indicating that the

fracture was basically brittle in nature. There was, however,

some dimpled rupture exhibited by each of the areas, indicating

some degree of ductility. In order to determine quantitatively

the relative amounts of dimpled rupture and quasi-cleavage, a point counting method referred to in Section 3.2 was employed

with the following results:

1. Near one crack arrest site: 9% dimpled rupture,

remainder quasi-cleavage.

2. Near the other crack arrest site: 15% dimpled

rupture, remainder quasi-cleavage.

3. Apparent crack origin: 3.5% dimpled rupture in

one area, 4% dimpled rupture in another area,

remainder quasi-cleavage.

4. About half way between the apparent crack origin

and one of the crack arrest sites: 9 1/2%

dimpled rupture, remainder quasi-cleavage.

- 6 -

Thus, the fracture appeared to be less ductile near the

apparent crack origin than away from the origin. Representative SEM photomicrographs of the service fracture are shown

in figures 8 and 9. Quasi-cleavage is the primary fracture

feature exhibited, but some dimpled rupture can be seen in

both figures.

4.2.2 Fracture through weld metal pulled in tension

after cooling in liquid nitrogen

The fracture surface produced by extending the

service crack through weld metal under a tensile load at

near liquid nitrogen temperature exhibited quasi-cleavage

as essentially the only fracture feature, indicating a completely brittle fracture. An SEM photomicrograph

representative of this fracture surface is shown in figure 10.

4.2.3 Tensile fracture through weld metal at 7 0° F

The fracture surface of the tensile specimen with

an all weld metal reduced cross section exhibited essentially

all dimpled rupture indicating a ductile fracture. The

specimen had an ultimate tensile strength of about 50,800 psi

and an apparent elongation in 2 inches of 5 percent. Since

one face of the specimen had been curved to a radius of 3.5

inches to eliminate voids in the root of the weld and to

assure fracture through the weld, the true elongation was

somewhat greater than 5 percent. This amount of elongation

indicates that the weld metal was ductile, which agrees with

the results of the f ractographic examination. An SEM

photomicrograph showing a representative area of the tensile

specimen fracture surface is shown in figure 11.

4.2.4 Weld metal fractured in impact at 38° F

The fracture surface of the specimen fractured in

impact through weld metal at 38" F exhibited 6 percent dimpled

rupture, the remainder being quasi-cleavage. A representative

area of this specimen fracture surface is shown in figure 12.

4.2.5 Fracture through weld metal pulled in tension

at 35° F

The fracture surface produced by extending the

service crack under tensile loading at 35° F exhibited 11 percent dimpled rupture compared to 9 percent dimpled rupture for

the service crack adjacent to it. The remainder of the fracture

features at each point exhibited quasi-cleavage, indicating that

the fracture was primarily of a brittle nature. A representative area of this fracture surface is shown in figure 13.

- 7 -

4 . 3 Metallographic Examination

A longitudinal side of the tensile specimen tested at 70° F

was prepared metallographically before the test was conducted.

A low magnification view of this in the etched condition (figure

14) indicates that the weld was made in one pass. There is a small amount of mismatch between the two pieces of pipe at

this point, as the planes of the wall surfaces of one piece do

not quite coincide with the corresponding planes of the wall

surfaces of the other piece.

Longitudinal sections through both pieces of pipe intersecting the fracture surface are shown in figure 15. The

microstructure of the weld material (area A) is similar for

both pieces and consists of a ferrite matrix in a Widmanstatten

pattern with a little cementite and some pearlite in the grain

boundaries. A representative area of the v/eld material is

shown in figure 16. The microstructure of the pipe material

adjacent to the weld (area B) , again similar for both pieces,

is shown in figure 17. The microstructure appears to have

undergone phase transformation (austenite to ferrite) as a

result of heating during welding. It consists of a ferrite

matrix with some cementite and pearlite in the grain boundaries.

The heat affected zones (area C, figure 15) on both sides of

the weld exhibit similar microstructures . A representative

area is shown in figure 18. This microstructure, consisting

of small grains of ferrite and some pearlite and cementite in

the grain boundaries, appears to have been heated into the

lower part of the ferrite plus austenite temperature range.

There were some differences between the microstructures of

the two pieces of pipe in area D (fig. 15) just beyond the

heat affected zones. In both cases, ferrite is the primary

constituent with some pearlite and cementite in the grain

boundaries, but one exhibits a Widmanstatten structure and

the other does not. Examples of these microstructures are

shown in figure 19.

There was some porosity in the weld material. An example

of this in an unetched longitudinal section is shown in figure

20a. An area more typical of the weld material is shown in

an unetched longitudinal section in figure 20b. Such porosity

is normal in manual torch welding.

There were some inclusions in the pipe material as shown

in figure 21. This is an area of a longitudinal section

about midway between the inner and outer walls of the pipe.

- 8 -

4.4 Hardness Measurements

Rockwell SOT hardness measurements were made on the

longitudinal sections shown in figure 15. Each value given

below is an average of at least four measurements.

Area ^3 0T ^^^^^^^^^ Section shown in

figure 15a figure 15b

A - Weld material 55.5 54.5

B - Heat affected zone showing

results of phase transformation 59.0 61.0

C - Heat affected zone showing

results of phase transformation 62.0 61.0

D - Parent pipe material 62.5 59.0

The range for any given area was never greater than three

R3OT points.

5. DISCUSSION

The crack in this eight inch welded steel pipe natural

gas main initiated and propagated in a weld and traversed

about two-thirds the circumference of the pipe. Examination

of the fracture surface indicated that the crack had probably

initiated at the approximate midpoint between the two ends of

the crack. This would be at approximately the 4:30 o'clock

position, assuming the top of the pipe as shown in figure 1

to be 12 o'clock. The entire fracture appeared to be

essentially brittle in nature, but there was less ductility

exhibited in the area of the crack origin than away from the

origin. The fracture surface appeared to be flatter in the

area of the origin.

The weld appeared to have been made in a single pass by

manual oxy-acetylene torch welding. There was lack of weld

penetration over a large part of the pipe circumference.

This could be seen at the inside wall surface of the welded

joint and on the fracture surface. There was some porosity

in the weld material. The Widmanstatten structure found in

the microstructure of the weld material was produced by

- 9 -

relatively rapid cooling of the weld. While all of these

features might be considered somewhat undesirable, their

presence is probably consistent with welding practices

employed at the time the weld was made. The weld metal

exhibited adequate ductility in the 70° F tensile test.

There was some mismatch between the two pieces of pipe at

the weld, but this was not considered to be unacceptably large.

The microstructure of the steel pipe on each side of the

joint consisted of the same phases as that of the weld material;

namely, a ferrite matrix with some cementite and pearlite.

In general, the cementite and the pearlite were found in the

grain boundaries. The presence of a Widmanstatten structure

in one of the pieces of pipe indicates that this pipe may have

been cooled rapidly from the hot rolling temperature at the

time of manufacture.

The scale on the outside wall surfaces of the pipe did

not appear to have had a detrimental effect on the welded

joint and it is not likely that it contributed significantly

to the failure of the pipe.

While there were some differences in hardness among the

pipe materials, the heat affected zones, and the weld material,

the differences were not large and were probably insignificant.

Comparison was made of the fracture features of the

service crack and the laboratory produced fractures through

weld metal from the submitted pipe length in order to determine the relative amounts of ductile fracture (dimpled rupture)

and brittle fracture (quasi-cleavage) present for each case.

A summary of these determinations is presented below.

Fracture % dimpled % quasirupture cleavage

Service fracture

Near origin 3.5-4.0 96 - 96.5

Near one crack arrest site 9 91

Near other crack arrest site 15 85

Halfway between initiation

point and crack arrest site 9.5 90.5

Impact specimen (33° F) 6 94

Tensile specimen (70° F) 100 0

Tensile fracture (near liquid

nitrogen temperature, ~ -320° F) 0 100

Tensile fracture (35° F) 9 91

The temperature of the soil around the pipe at the time

of the accident was reported (by the Office of Pipeline

Safety) to be approximately 35 to 40° F. The area of the

fracture surface of the service failure near the probable

crack origin exhibited less ductility than the impact specimen

tested at about the temperature of the pipe environment at the

time of the accident. The impact specimen fracture surface

exhibited less ductility than that of the tensile fracture

produced at the approximate temperature of the soil. Based

on the determinations of the relative amounts of ductility

and the appearance of the features of the service fracture,

the pipe failure appears to have initiated as the result of

impact loading by an external source. The entire crack

appears to have occurred in a single event. As the crack

spread from the point of initiation, the rate of propagation

probably decreased, which accounts for the increased ductility

exhibited by the fracture surface near the crack arrest sites.

6. CONCLUSIONS

1. The submitted length of eight inch welded steel pipe

natural gas main had cracked in a weld and the crack

traversed about two-thirds of the circumference of the

pipe. The apparent crack origin was at about the 4:30

o'clock position, assuming the top of the pipe as shown

in figure 1 to be at 12 o'clock and the outside of the

bend of the pipe as installed to be at three o'clock.

2. The fracture was predominantly brittle in nature.

3. There was a heavy scale on the external pipe wall surface,

but this does not appear to have contributed to the

failure.

4. There was a lack of weld penetration around much of the

circumference of the pipe on the inside, a feature

normally produced in the welding technique used at the

time

.

5. Although there was some porosity in the weld, it is not

considered to be excessive in light of v/elding techniques

used at the time the weld v^as made

.

6. The microstructures of the weld material and the pipe

material appear to be compatible and normal.

7. The weld material appeared to exhibit adequate ductility

in a 70° F tensile test.

8. Failure appears to have been caused by a single event,

impact loading from an external source.

- 11 -

7 . ACKNOWLEDGEMENT

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

performed most of the photographic work, made the hardness

measurements, and prepared the specimens for metallographic

examination

- 12 -

Figure 1. Part of the welded steel gas main pipe still

in the ditch showing the crack in the weld.

A mirror had been placed to the right and

near the bottom of the pipe in order to show

that part of the crack which extended to the

pipe bottom. This photograph was taken looking

straight down on the pipe, and was furnished

by and used with permission of the Pennsylvania

State Police. Approx. X 3/8

Figure 2

Length of gas pipe containing the cracked

weld as received at NBS . The clamp is still

in place. X 1/10

Figure 3a." Part of the pipe length with a portion of

the fracture surface exposed. The numbers

indicate the locations of specimens referred to in Section 3.3.





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Figure 6. Part of the fracture surface of the pipe with several

specimens having been removed. The lettered arrows

indicate the same areas as in figure 4. Arrows 1 indicate general areas of incomplete weld penetration

(flat areas on the fracture surface adjacent to the

inside wall of the pipe)

'Figure 7. Part of the service fracture surface near

one of the crack arrest areas, X 7

Figure 10. SEM photomicrograph of fracture surface

of weld material pulled in tension after

cooling in liquid nitrogen. Quasi-cleavage

is essentially the only fracture feature

exhibited. X 25 0

Figure 11. SEM photomicrograph of fracture surface

of tensile specimen failed through weld

metal at 7 0** F. Dimpled rupture is

essentially the only fracture feature

exhibited. X 140

Figure 12 . SEM photomicrograph of fracture surface

of impact specimen tested at SS'* F showing

primarily quasi-cleavage and a small amount

of dimpled rupture. X 135

Figure 13. SEM photomicrograph of fracture surface

of weld metal pulled in tension at 35° F.

Quasi-cleavage is the primary fracture

feature exhibited, but there is some

dimpled rupture. X 190

Figure 14. Etched longitudinal side of tensile specimen

encompassing the weld before testing. Lack

of penetration is indicated by the arrow.

The weld appears to have been made in a single

pass . Etch: 20% nitric acid in water. X 2

b

Figure 15. Etched longitudinal sections through pieces

of pipe on either side of the weld. The

sections intersect the fracture. Letter

designations are as follows:

A. Weld material.

B. Pipe material adjacent to the weld

in the heat affected zone.

C. Heat affected zone somewhat removed

from the weld.

D. Parent pipe material.

Etch: 10% nitric acid in water. X 3

Figure 16. Etched microstructure of longitudinal

section through weld. Microstructure

consists primarily of ferrite, some of

which is in a Widmanstatten pattern,

with some cementite and pearlite in the

grain boundaries.

Etch: 1% nital. X 100

Figure 17. Etched microstructure- of longitudinal

section through pipe material adjacent

to the weld. Microstructure consists of

ferrite with some cementite and pearlite

in the grain boundaries. A phase transformation has taken place.

Etch: 1% nital. X 100

Figure 18. Representative etched area of

longitudinal section through heat

affected zone. Microstructure

consists of ferrite and some

pearlite and cementite in the

grain boundaries.

Etch: 1% nital. X 100

Figure 19. Etched longitudinal sections through

both pieces of pipe adjacent to the

heat affected zone. In both cases,

the microstructure consists primarily

of ferrite with some pearlite and

cementite in the grain boundaries. In

figure 19a, some Widmanstatten structure

can be seen.

Etch: 1% nital. X 100

b

Figure 20. Unetched longitudinal sections through

weld material. X 100

a . Area containing more than average

porosity

.

b. Area representative of the weld

material.

Figure 21. Unetched longitudinal section

through pipe material shov/ing

the inclusion content. X 100

Font.- NT 5-114

A

.VI

)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

"] t;

I

1 > 'J i'. Lie; AT ION OR HHPORr NO. NBSIR 73-299

t Accession

4. in LE AND >UHT! rLE EXAMINATION OF FAILED EIGHT INCH WELDED STEEL

PIPE NATURAL GAS MAIN, UGI CORP., COOPERSBURG,

PENNSYLVANIA.

3. Recipient's A-ccessmn No.

5. Publication Date November, 197 3

6. Performing Organization Code

7. AUTHOR(S)

„ M. L. Picklesimer and T R. Shives

8, Performing Or>3an i za tion NBSIR 73-299

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL HL'REAU' OF STANDARDS

DEPARTMENT OF CO.MMERCE

WASHINGTON, D.C. 20234

10. Project/ I'ask; '••'ork Unit No. 3120418

11. Contract/Grant No.

12, Sponsoring Organization .\arr.e and Address Office of Pipeline Safety

Departn^ent of Transportation

Washington, D. C. 20590

13. Type of Report & Period Covered Failure

Analysis Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

lu. .\BiTKACT -A 2JC--.ord or less factual sum.-nary of most significant information. If document includes a significant

bibliography or literature survey, mention it tiero.) The Office of Pipeline Safety, Department of Transportation,

submitted a four foot length of eight inch diameter welded steel pipe

natural gas main containing a crack in the v/eld to the NBS Mechanical

Properties Section for examination. The apparent crack origin v/as

located at about the 4:30 o'clock position, assuming the top of the

pipe to be at tv/elve o'clock and the outside of the bend of the pipe as

installed v/as at three o'clock. The crack had propagated about tv/cthirds of the v/ay around the pipe circumference. Optical and scanning

electron microscopy revealed the fracture to have been predominantly

brittle in nature. There v/as lack of v;eld penetration around a large

part of the weld circumference and the weld metal exhibited somie

porosity. These features are normal for steel pipe welded by the oxyacetylene practice used at the time the weld v/as made. While these

features of the weld helped to define the path of the fracture, they

probably did not contribute to it. Examination of the fracture and

comparison of its features with those of fractures produced in the

laboratory indicated that failure was probably brought about as a result of a single event, impact loading from an external source.

17. KEY WORDS >' Alphabetical order, separated by semicolons)

Brittle fracture; gas main pipe; v/elded steel pipe.

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