IMBSIR 77-1198 (R)

Examination of 3/4 Inch Steel

Pipe Natural Gas Service Lines,

Delmarva Power and Light

Company, Wilmington,

Delaware

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

Failure Analysis Report

December 1976

Prepared for Office of Pipeline Safety Operations

Department of Transportation

Washington, D. C. 20590

NBSIR 77-1198 (R)

EXAMINATION OF 3/4 INCH STEEL

PIPE NATURAL GAS SERVICE LINES,

DELMARVA POWER AND LIGHT

COMPANY, WILMINGTON,

DELAWARE

T. Robert Shives

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

Failure Analysis Report

December 1976

Prepared for Office of Pipeline Safety Operations

Department of Transportation

Washington, D. C. 20590

U S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director
'
Table of Contents

Page

SUMMARY iv

1. INTRODUCTION 1

1.1 Reference 1

1.2 Background Information 1

1.3 Parts Submitted 1

2. PURPOSE 2

3. REPORT FORMAT 3

4. RESULTS OF EXAMINATIONS AND TESTS 3

4.1 Pipe Sample from 13 Clayton Court 3

4.1.1 Visual and Macroscopic Examination 3

4.1.2 Wall Thickness Measurements 4

4.1.3 Metallographic Examination 4

4.1.4 Hardness Measurements 5

4.2 Pipe Samples Other Than That From 13 Clayton Court 5

4.2.1 Visual and Macroscopic Examination in the

As Received at NBS Condition and After

Cross Sectioning 5

4.2.2 Leak Tests 7

4.2.3 Pipe Condition After Rust Removal • 7

4.2.4 Wall Thickness Measurements 8

4.2.5 Metallographic Examination 8

4.2.6 Hardness Measurements 9

5. DISCUSSION 9

5.1 Pipe Sample From 13 Clayton Court 9

i
Table of Contents (continued)

Page

5.2 Pipe Samples Other Than That From 13 Clayton Court 10

5.3 General Discussion 11

6. CONCLUSIONS 11

6.1 Pipe Sample From 13 Clayton Court 11

6.2 Pipe Samples Other Than That From 13 Clayton Court 12

7 . ACKNOWLEDGEMENT 13

REFERENCE 13

TABLES

1. Results of Wall Thickness Measurements.

2. Results of Hardness Measurements.

3. Cross Sectional Deformation at the Bend in the Pipe.

FIGURES

1. Steel pipe natural gas service line from 13 Clayton Court, Edgemoor

Gardens, Wilmington, Delaware as received at NBS.

2. Thirteen steel pipe natural gas service lines from Edgemoor Gardens,

Wilmington, Delaware as received at NBS.

3. Four views around the circumference of the pipe from 13 Clayton Court

showing extensive corrosion.

4. Cross section through severely corroded region of pipe from

13 Clayton Court.

5. Unetched cross section through pipe from 13 Clayton Court.

6. Etched cross section through pipe from 13 Clayton Court.

7. Pipe from 1 Clayton Ct.

8. Pipe from 2 Clayton Ct.

9. Pipe from 5 Clayton Ct.

ii
FIGURES (continued)

10. Pipe from 6 Clayton Ct.

11. Pipe from 7 Clayton Ct.

12. Pipe from 8 Clayton Ct.

13. Pipe from 9 Clayton Court.

14. Pipe from 12 Clayton Ct.

15. Pipe from 31 S. Bennywell.

16. Pipe identified as 7.

17. Pipe identified as 10.

18. Pipe from 13 S. Cannon Dr.

19. Pipe from 18 S. Cannon.

20. Pipe from 18 S. Cannon before and after cleaning.

21. Pipe from 31 S. Bennywell before and after cleaning.

22. As-polished cross section through the pipe from 8 Clayton Ct.

showing inclusion content representative of the sections examined.

23. As-polished cross section through the pipe from 31 S. Bennywell

showing porosity.

24. Etched cross section through the bend of the pipe sample from

8 Clayton Ct. showing cracking of the weld at the inside of the pipe.

25. Etched cross section through pipe sample designated 10.

26. As-polished cross section through pipe sample from 31 S. Bennywell

showing corrosion product on the inside of the pipe.

27. Etched cross section through pipe sample from 8 Clayton Ct.

showing microstructure consisting of ferrite and a small amount of

pearlite.

28. Etched cross section through pipe sample designated 7 showing

microstructure consisting of ferrite and a small amount of pearlite.

29. Etched cross section through pipe sample designated 10 showing the

microstructure at the weld and on both sides of the weld.

30. Etched cross section through pipe sample from 8 Clayton Ct. showing

decarburization adjacent to the pipe surface in a slightly corroded

region.

iii
SUMMARY

The Office of Pipeline Safety Operations requested that the NBS

Mechanical Properties Section examine fourteen 3/4 inch diameter steel

pipe natural gas service lines from Edgemoor Gardens, Wilmington,

Delaware. The submitted samples had all been installed in crawl spaces

under houses. An explosion had been attributed to the ignition of gas

leaking from one of these pipes. All of the pipe samples exhibited

corrosion to some extent. Two samples, including the one reportedly

involved in the explosion, had been perforated. Many others were

severely corroded. A reportedly high concentration of water vapor in

the poorly ventilated crawl spaces is suggested as the source of the

corroding medium. Measurements in essentially uncorroded regions

indicated that the original pipe wall thickness would meet current

(1976) ASTM specifications. All but one of the longitudinal seam welds

appeared to be in satisfactory condition. The unsatisfactory weld was cracked at a bend in the pipe where there was a considerable amount of ross sectional deformation. Several samples exhibited cross sectional

deformation at the bend. The hardness and microstructure of the weld

and parent materials appeared to be compatible. The microstructure of

all the samples examined appeared to be satisfactory except for one sample that exhibited a large amount of porosity. All except the two

perforated samples withstood a leak test at 30 psig natural gas.
Examination of 3/4 Inch Steel Pipe Natural Gas Service Lines,

Delraarva Power and Light Company, Wilmington, Delaware

1.1

Reference

1. INTRODUCTION

Office of Pipeline Safety Operations, Materials Transportation Bureau,

Department of Transportation, Washington, D.C. 20590. This investigation

was conducted at the request of Mr. Cesar DeLeon, Acting Director of the

Office of Pipeline Safety Operations, under agreement number DOT-AS-60053

.

The request letter was dated July 1, 1976.

1 . 2 Background Information

The information in this section was furnished by Mr. Lance F. Heverly

of the Office of Pipeline Safety Operations and Messrs. J. Benjamin Roy, Jr.

and Daniel R. Kiley, Fire Marshal and Deputy Fire Marshal, respectively,

of the State of Delaware.

On February 25, 1976, there was an explosion at 13 Clayton Court,

Edgemoor Gardens, Wilmington, Delaware. The explosion was attributed to

the ignition of an accumulation of natural gas that had escaped from a 3^4 inch diameter steel pipe gas service line in the crawl space under

the house at 13 Clayton Court.

The service line at 13 Clayton Court, as well as those at other houses

in the Edgemoor Gardens development, entered the crawl space by passing

horizontally through the foundation wall of the house. The pipe then

turned 90° to a vertical position and then passed through a concrete slab

floor to the house above.

It was reported that the crawl spaces under the residences in the

Edgemoor Gardens development were poorly ventilated and damp.

Schedule 80, extra heavy wall, longitudinally seam welded black steel

pipe had been used for the service lines. The diameter of the pipe was

3/4 inch. The lines were installed in 1942.

1 . 3 Parts Submitted

Two pieces of 3/4 inch diameter steel natural gas service line pipe

from 13 Clayton Court, Edgemoor Gardens, Wilmington, Delaware were delivered

to the National Bureau of Standards (NBS) Mechanical Properties Section on March 2, 1976 by J. Benjamin Roy, Jr., and Daniel R. Kiley, Fire Marshal and

ueputy Fire Marshal, respectively, of the State of Delaware. Present at the

time of the delivery, in addition to Messrs. Roy and Kiley, were Lance F. Heverly and Robert F. Langley of the Office of Pipeline Safety

Operations, and Bruce W. Christ and T. Robert Shives of the NBS Mechanical

Properties Section.

1
These two pieces of pipe are shown in figure 1 as received at NBS.

As described by the Delaware Fire Marshal's Office, item 1 (bottom piece

in figure 1) was about 38 1/2 inches in total length with a 90° bend

having one leg approximately 12 inches in length and the other leg

approximately 26 1/2 inches in length. Item 2 (top piece in figure 1) was approximately 17 inches in length. Item 2 had been separated from

item 1 by sawing at the scene. At the top of item 2 (at the right in

figure 1) is the service cock for the gas system at 13 Clayton Court. A

sleeve was also attached to item 2 where it passed through the concrete

floor separating the house from the crawl space under it.

On March 3, 1976, thirteen additional pieces of 3/4 inch diameter

steel pipe natural gas service line were delivered by Lance F. Heverly

to the NBS Mechanical Properties Section. All of these pipe samples were

from crawl spaces under houses in Edgemoor Gardens in Wilmington, Delaware.

These pieces of pipe, shown in figure 2 as received at NBS had the

following identification tags attached to them.

1 Clayton Ct.

2 Clayton Ct.

5 Clayton Ct.

6 Clayton Ct.

7 Clayton Ct.

8 Clayton Ct.

9 Clayton Court

12 Clayton Ct.

31 S. Bennywell (Beanywell?) with sleeve

7 10

13 S. Cannon Dr. with two sleeves

18 S. Cannon

Each of the above pieces of service line pipe had a 90° bend, but the

radius of curvature of the bend differed among the various pieces. The

total length of the various pieces also varied.

In addition to the pipe and sleeves, one repair coupling was submitted.

2. PURPOSE

The Office of Pipeline Safety Operations requested that the NBS

Mechanical Properties Section perform the following tasks:

1. Establish and maintain sample identification and custodial record

for documentation.

2. Provide six documentary photographs showing the physical condition

of the failed pieces as soon as practical to 0PS0 for its information

and for trqnsmittal to the Delaware State Fire Marshal.

2
3. Prepare similar documentary photographs of the 13 samples submitted

on March 3, 1976, before and after rust removal.

4. Make other photographic representations as deemed appropriate from

examination or testing.

5. Test selected samples from the 13 additional pieces prior to rust

removal for leakage with natural gas at 30 psig and, if found to be

leaking, determine total and unit length average leakage rates at

20 and 30 psig.

6. Determine original wall thickness of the failed pieces and other samples.

7. Remove rust scale from selected samples of the 13 samples delivered on March 3 and determine the remaining wall thickness at representative

locations of approximate maximum and average pitting.

8. Inspect pieces and samples for any apparent mechanical damage, including

cross sectional deformation, due to bending and incipient or existing

opening of the longitudinal seam weld, if any. Evaluate the effect

on the serviceability of the pipe where applicable.

9. Cut and macroscopically inspect specimens of fracture face of cracks

and breaks. Based on this inspection, perform metallographic analysis

as deemed necessary.

10. Determine such other tests or analyses which appear necessary or desirable from the foregoing examination or other evaluation. Advise

OPSO accordingly and perform same pursuant to concurrence.

In compliance with item 2 above, documentary photographs of the pipe

samples from 13 Clayton Court were sent to the Office of Pipeline Safety

Operations on July 14, 1976.

3. REPORT FORMAT

In this report, the results of the examination of the pipe from 13

Clayton Court will be presented separately from the results of the examination of the other 13 service lines.

4. RESULTS OF EXAMINATIONS AND TESTS

4. 1 Pipe Sample from 13 Clayton Court

4.1.1 Visual and Macroscopic Examination

Both pieces of pipe from 13 Clayton Court exhibited evidence of

noth general and pitting corrosion. Corrosion was essentially superficial

near the top of the pipe close to the service cock. The severity of the

- 3 -
corrosive attack increased with the distance from the top of the pipe. It was most severe in the region of the 90° bend, with several perforations

being evident. Some of the results of corrosion can be seen in figure 1.

In figure 3, four higher magnification views of the circumference of the

pipe in the vicinity of arrow A in figure 1 show corrosion at the bend

where the pipe has been perforated.

Arrows B in figure 1 indicate two areas of mechanical damage.

The damage has the appearance of rather shallow saw cuts. The bottoms of

both of these regions exhibited some shiny metal when submitted to NBS,

indicating that the damage may have occurred shortly before the pipe was

submitted. Neither of these regions of mechanical damage would be expected

to have a significant adverse effect on the integrity of the pipe.

4.1.2 Wall Thickness Measurements

The approximate original wall thickness of the pipe was determined

at a cross section through one of the regions least affected by corrosion.

As given in Table 1, the average of four measurements was 0.155 inch and the

range was 0.152 to 0.156 inch. The specified nominal wall thickness for

schedule 80 3/4 inch diameter steel pipe is 0.154 inch! The minimum

acceptable wall thickness is 0.135 inch}

In order to determine the wall thickness in a severely corroded region,

the pipe was sectioned through the region of perforations in the vicinity of

arrow A in figure 1. This cross section is shown in figure 4. The wall

thickness ranged from zero at a perforation to 0.139 inch. The corrosion was non-uniform at this cross section, with the maximum wall thickness being

greater than the minimum required in reference 1.

As can be seen in figure 4, there is no apparent cross sectional

deformation at the part of the bend where the cross section was taken.

There did not appear to be any significant deformation anywhere else in

the bend, either.

4.1.3 Metallographic Examination

The cross section shown in figure 4 was examined metallographically

.

Part of the cross section is shown in figure 5 in the unetched condition.

The steel is relatively free of inclusions and there is no evidence of

porosity. There is a heavy layer of corrosion product on the outer surface

>f the pipe. The inside surface of the pipe is not shown, but the corrosion

was negligible.

Part of the cross section is shown at a higher magnification in the

etched condition in figure 6. The microstructure consists primarily of

ferrite with a very small amount of pearlite.

4
4.1.4 Hardness Measurements

Rockwell B (HRB) hardness measurements were made on the cross section where the "original" wall thickness measurements were made. The

results of measurements away from the weld ranged from HRB 67 to 72. The

average was HRB 69 as indicated in Table 2.

4 . 2 Pipe Samples Other Than That From 13 Clayton Court

4.2.1 Visual and Macroscopic Examination in the As Received at NBS

Condition and After Cross Sectioning

Although the welded longitudinal seam was quite obvious on the

surface of some of the pipe samples, in no case, with visual or macroscopic

examination, did the welded seam appear to be open or opening. (As

discussed later, metallographic examination revealed an apparent crack in the

weld in one sample.) Corrosion was no more severe at the welds than

elsewhere.

Several of the samples exhibited cross sectional deformation at

the bend. This deformation, expressed as the difference between the maximum

and minimum inside diameter of the pipe at a cross section through the bend,

is shown in Table 3 for some of the samples that exhibited the greatest amount

of cross sectional deformation.

Because of differences in condition among the various pipe samples,

each sample will be described individually.

1 Clayton Ct. There was mild general corrosion over the entire

submitted pipe length. Corrosion was somewhat more severe at the

bend (figure 7a) than elsewhere. No significant mechanical damage

was observed. Some cross sectional deformation was evident at the

bend (figure 7b).

2 Clayton Ct. There was moderate general corrosion over the entire

submitted pipe length and there was significant pitting corrosion

both at the bend (figure 8) and away from the bend. No significant

mechanical damage or cross sectional deformation was observed.

5 Clayton Ct. There was slight general corrosion over the entire

submitted pipe length and a small amount of moderate pitting at

the bend (figure 9a). No significant mechanical damage was observed.

Some cross sectional deformation at the bend was evident (figure 9b).

6 Clayton Ct. There was mild general corrosion over the entire

submitted pipe length. Pitting was significant at the bend

(figure 10a). In addition, in a region about 8 inches from the

bend, corrosion was severe (figure 10b). A cross section through

the pipe in this region is shown in figure 10c. The arrow in

figure 10a indicates a cut in the pipe probably made by a pipe

cutting tool. This cut was quite deep and had penetrated the

- 5 -
entire wall thickness in at least one place. This mechanical damage

appeared to be recent and may have been done when the pipe was

removed from service. No other significant mechanical damage was

observed. Cross sectional deformation was insignificant.

7 Clayton Ct. There was mild general corrosion over the entire

submitted pipe length with some relatively mild pitting at the

bend (figure 11a). No significant mechanical damage was observed,

although there were what appeared to be some shallow pipe wrench

marks (not shown in the figure). Some cross sectional deformation

at the bend was evident (figure lib).

8 Clayton Ct. There was significant general corrosion and some pitting over the entire submitted pipe length (figure 12a).

Corrosion was more severe at one end of the bend than elsewhere

(figures 12b and 12c). No significant mechanical damage was

observed. Some cross sectional deformation at the bend was evident (figure 12d)

.

9 Clayton Court. There was slight general corrosion over the entire

submitted pipe length (figure 13a). Corrosion was somewhat more

severe with pitting at the bend. No significant mechanical damage

was observed. There was some cross sectional deformation at the

bend (figure 13b).

12 Clayton Ct. There was a significant amount of corrosion over the

entire submitted pipe length (figure 14a). Some scale and pitting

were evident. Corrosion did not appear to be more severe at the

bend than elsewhere. Neither any significant mechanical damage

nor cross sectional deformation was observed (figure 14b)

.

31 S. Bennywell(?) . There was moderate general corrosion and

significant pitting over the entire submitted length of pipe not

covered by the sleeve (figure 15a). The cross section shown in

figure 15b was taken through one of the most severely corroded

regions, but not at the bend. Some porosity was observed at this cross section and at other cross sections from this pipe sample.

Apparently, there was a line of porosity extending over at least

the entire submitted length of pipe that had not been covered by

the sleeve. No significant mechanical damage was evident. There

was a slight amount of cross sectional deformation at the bend.

7. Corrosion was mild away from the bend. At the bend, however,

corrosion was very severe with a large loss of material and perforation of the pipe (figure 16a). At the location of the perforation,

the pipe appears to have suffered some mechanical damage, manifested

in the form of a depression in the pipe. A cross section through

the pipe at the depression is shown in figure 16b. It is not clear

when the depression was formed. If it was formed after corrosion

- 6 -
had thinned the pipe wall to the point shown, it would have been

relatively easy to push the pipe in to form the depression. No

other significant mechanical damage was observed. Significant

cross sectional deformation was observed at the bend, although

this deformation is not evident in figure 16b.

10. Corrosion was severe in the vicinity of the bend

(figure 17a). There were large diameter, round pits. Corrosion,

in general, was less severe as the distance from the bend increased,

although there were some large pits well removed from the bend.

Part of the pipe that had been covered with the sleeve was examined.

Corrosion was very slight where the sleeve had been except near the

end of the sleeve where some pitting was observed (figure 17b). No

significant mechanical damage or cross sectional deformation was observed (figure 17c).

13 S. Cannon Dr. There was a considerable amount of soil adhering

to this pipe sample, indicating that, unlike the other samples,

it had been under a soil cover. Both general corrosion and pitting

were rather severe in the relatively short length of pipe exposed

between the two sleeves (figure 18a). A cross section through one

of the more severely corroded regions is shown in figure 18b.

Mechanical damage and cross sectional deformation were insignificant.

18 S. Cannon. General corrosion appeared as a gradient ranging

from slight away from the bend to severe approaching the bend

(figure 19a). There was severe pitting at the bend and adjacent to

the sleeve. No significant mechanical damage or cross sectional

deformation was observed (figure 19b).

4.2.2 Leak Tests

Except for the pipe sample identified as "7", all of the pipe

samples submitted on March 3, 1976, were leak tested. Pipe sample 7 was

not tested because it had an obvious perforation. The leak tests were

made at a pressure of 30 psig with natural gas used as the pressurizing

medium.

Each pipe sample was tested individually. Appropriate fittings were

affixed to the pipe ends for admitting gas and sealing the system from the

atmosphere. Before being pressurized, the pipe samples were flushed with

natural gas. After being pressurized, the pressure was monitored for at

least three hours. No leak was observed in any of the samples.

4.2.3 Pipe Condition After Rust Removal

Selected parts of several of the submitted pipe samples were

cleaned of rust (and adhering soil where necessary) with a wire wheel in

order to facilitate the examination of the pipe surfaces with the rust

7
removed. The parts selected for cleaning were those that exhibited the

severest corrosion. Two representative examples of pipe samples both

before and after cleaning are shown in figures 20 and 21. In no case

did the condition of the pipe appear to be significantly altered by the

removal of the rust. Therefore, except for the change in appearance due

to the loss of the corrosion product itself, the descriptions of the pipe

samples presented in Section 4.2.1 of this report apply equally well to

the cleaned pipe. Because there appeared to be no significant change in

condition, the cleaned pipes were not leak tested.

4.2.4 Wall Thickness Measurements

Wall thickness measurements of each of the thirteen pipe samples

other than that from 13 Clayton Court were made at a cross section through

the pipe in a region least affected by corrosion. The wall thickness at

these cross sections very closely approximated the original wall thickness

of the pipe. Four measurements about 90° apart were made at each cross

section. The average measurement and the range for each pipe sample are given in Table 1. All measurements were greater than the 0.135 inch

minimum acceptable wall thickness for schedule 80 pipe^.

The minimum wall thickness was determined for each of the same

13 pipe samples at a cross section taken where the corrosion appeared to

be the most severe. These cross sections are shown in figures 7 through

19. The results of the minimum wall thickness measurements are given in

Table 1. In all cases except for the samples from 1 Clayton Ct. and

5 Clayton Ct., the minimum wall thickness was less than the specified

minimum of 0.135 inchl.

4.2.5 Metallographic Examination

Several of the cross sections where the minimum wall thickness

measurements were made or where cross sectional deformation was determined

were examined metallographically . For the most part, the material was rather clean and free of porosity. An example representative of the

inclusion content of the samples examined is shown in figure 22.

In all the cross sections examined, the only significant

porosity observed was in the pipe sample from 31 S. Bennywell. This

porosity was referred to earlier and can be seen in figure 15b. Part

of the cross section shown in figure 15b appears in the as-polished

condition at higher magnification in figure 23.

In the sections examined, only one of the welded seams exhibited an opening or incipient opening the pipe sample from

8 Clayton Ct. The welded seam had begun to crack at the inside of

the pipe. An etched cross section showing the crack appears in figure 24.

The crack path appears to be transgranular . This same weld exhibited a small imperfection at the outside of the pipe. This imperfection does

8
not look like a crack and it does not appear to be of any significance.

There was a considerable amount of cross sectional deformation in the

pipe where the crack had formed (figure 12d). Because of the location

of the weld with respect to the deformation, the transverse tensile

stress on the inside of the pipe at the weld would have been increased

by the deformation.

As expected, all of the sections examined exhibited corrosion

product in varying amounts on the outside pipe surface. The sample

designated 10 had one of the heaviest layers of corrosion product

(figure 25).

Of those examined, the cross section of the sample from 31 S.

Bennywell was the only one to exhibit a significant amount of corrosion

product on the inside (figure 26).

The microstructure of all the sections examined consisted

primarily of ferrite with a small amount of pearlite. There were

differences in grain size and texture as can be seen in figures 27 and

28 which show different cross sections at the same magnification. There

were only minor differences in microstructure at the welded seams as can

be seen in figures 24 and 29. In these two figures, the relationship

between the parent material and the weld is typical of those sections

examined

Some of the cross sections examined exhibited evidence of

decarburization adjacent to the inside and original outside pipe

surfaces. An example is shown in figure 30.

4.2.6 Hardness Measurements

Rockwell B (HRB) hardness measurements were made on the cross sections through each pipe sample where the original wall thickness

measurements were made. The results of these measurements are given in

Table 2. Each of the average values presented is based on three

measurements. There was considerable variation in hardness among the

different pipe samples. None of these measurements was taken at a bend in the pipe; therefore, differences in hardness can not be

attributed to strain • hardening of the material due to the bending

operation. In all cases, the hardness at the weld was lower than or equal to the hardness elsewhere in the cross section for a given sample.

5. DISCUSSION

5.1 Pipe Sample From 13 Clayton Court

The pipe sample from 13 Clayton Court was very severely corroded.

There were several perforations in the most severely corroded region

which was located at the bend. No significant corrosion was observed

on the inside of the pipe.

- 9 -
There was some slight mechanical damage, although not near the

perforations. This damage appeared to have occurred a short time before

the pipe was submitted to NBS. It should have had little adverse effect

on the integrity of the pipe.

The original wall thickness of the pipe would satisfy the current

requirements of appropriate ASTM Standards.

The microstructure, consisting of ferrite and some pearlite,

appeared to be satisfactory. The microstructure of the weld appeared

to be compatible with that of the parent material. The hardness of the

weld and parent material also appeared to be compatible.

The weld appeared to be sound. There was no evidence to indicate

that the weld was opening. Cross sectional deformation which could have

increased the stress in the weld was negligible.

5 . 2 Pipe Samples Other Than That From 13 Clayton Court

All of the pipe samples had suffered corrosion to some extent. The

degree of corrosive attack varied considerably among the various samples.

Some samples such as those from 1 Clayton Ct. and 7 Clayton Ct. were

corroded only mildly, whereas others had been much more severely

corroded. The sample identified as 7 had been perforated in one place.

No significant corrosion was observed on the inside of any of the pipe

samples except for the one from 31 S. Bennywell.

The sleeves that covered the pipe where it passed through a wall or floor appeared to have no deleterious effect on the condition of the pipe

itself. Actually, the pipe appeared to be less severely corroded where

it had been covered than where there had been no sleeve.

The average wall thickness measured in the least corroded regions

would satisfy the current ASTM requirements for the original wall thickness

for all of the pipe samples. In severely corroded regions, the minimum

wall thickness of only two samples satisfied the current minimum wall

thickness requirements.

The only observed instance of significant mechanical damage that may

have influenced the deterioration of any of the samples was in the pipe

identified as 7. This pipe sample appeared to have been "pushed in"

around the perforation. It is not clear when this damage occurred, but

there was corrosion product over the entire "pushed in" area much like

that is surrounding areas. There was no shiny metal in evidence to

indicate that the pipe had been recently struck in this area.

Removal of rust from the surface of some of the pipe samples

revealed no significant change in the apparent condition of the samples.

10 -
Except for the one sample that had been perforated (sample 7), all

of the samples satisfactorily withstood a leak test at a pressure of..

30 psig natural gas.

All the welds appeared to be in satisfactory condition except for

the one in the sample from 8 Clayton Ct. This weld was cracked on the

inside of the pipe at the bend where there was a considerable amount of cross sectional deformation. For the cross sections examined, the

microstructure of the weld was very similar to that of the parent

material for any given sample. For all of the samples, the hardness of

the weld material was either less than or the same as that of the parent

material. The hardness of the weld and parent materials appeared to be

compatible

.

Cross sectional deformation was observed in the bends of a number

of the samples. This deformation evidently occurred when the bends were

made. None of the cross sections examined exhibited an excessive

inclusion content. There was a significant "line" of porosity in the

sample from 31 S. Bennywell. The microstructures of all the samples

examined consisted of ferrite and some pearlite, but there were some differences in grain size and texture. There was some apparent

decarburization in varying degrees adjacent to both the inside and

outside wall surfaces. This decarburization should have had no significant effect on the pipe.

Since all of the pipes tested withstood the leak tests, they should

have been performing satisfactorily in service. Several of the samples

had deteriorated seriously, however, and if they had been left in service

and the corroding conditions had persisted, in time others may have

perforated in the same manner as sample 7. Even before perforation

occurs, the load bearing ability of the material is decreased by the

thinning of the walls by corrosion. The decrease in load bearing ability

increases the susceptibility of the pipes to fracture from an externally

applied force.

5. 3 General Discussion

It was reported, as indicated in the section on background information

that the crawl spaces where these pipes were located were poorly ventilated

Therefore, a rather high concentration of water vapor would be expected to

be present. A suggested source of the corroding medium is water vapor that

condensed on the vertical part of the pipe and ran down to the bend or to

the more nearly horizontal part of the pipe where it would concentrate.

6. CONCLUSIONS

6.1 Pipe Sample From 13 Clayton Court

1. The sample from 13 Clayton Court was severely corroded over the entire

length submitted. Corrosion was severe enough in one region to result

in perforation of the pipe wall.

11
2. Corrosion of the inside wall of the pipe was negligible except for one sample

.

3. No mechanical damage that might have contributed to the failure was observed

.

4. Cross sectional deformation at the bend was negligible.

5. The initial wall thickness of the pipe would have met current specifications.

6. The weld exhibited no evidence of opening.

7. The microstructure and hardness of the weld appeared to be compatible

with those of the parent material.

6 . 2 Pipe Samples Other Than That From 13 Clayton Court

1. All of the pipe samples were corroded, but the degree of corrosion

among the various samples varied from mild to severe. One of

the samples had corroded severely enough that it had been perforated.

2. Corrosion of the inside of the pipes was negligible.

3. There was significant mechanical damage in one sample at a perforation.

4. Except for the sample that was perforated, all the samples withstood

a leak test at 30 psig natural gas.

5. Removal of the rust from the pipe surfaces did not reveal any

significant change in the condition of any of the samples.

6. There was a considerable amount of cross sectional deformation at the

bend in several of the samples.

7. The initial wall thickness of all the pipe samples would have met

current specifications.

8. The minimum wall thicknesses in regions of- severe corrosion were less

than that currently specified except for two samples.

9. The weld in the sample from 8 Clayton Ct. had cracked on the inside

of the pipe.

10. All of the welds except for the one in the sample from 8 Clayton Ct.

appeared to be in satisfactory condition.

11. The microstructure and hardness of the welds appeared to be

compatible with those of the parent material.

12
12. There was a significant amount of porosity in the sample from

31 S. Bennywell.

7. ACKNOWLEDGEMENT

The wall thickness measurements, hardness tests, metallographic

specimen preparation and photographic work were performed by L. C. Smith

of the NBS Mechanical Properties Section. Mr. Smith also assisted in

the leak testing.

REFERENCE

1. Standard A53-73 or Standard A120-73, 1976 Book of Standards, American

Society for Testing and Materials, Philadelphia, Pennsylvania, 1976.

13 -
Table 1. Results of Wall Thickness Measurements

Pipe Sample

In Least

Wall Thickness,

Corroded Region

inches

In Most Severely

Corroded Region

Average Range Minimum

13 Clayton Court 0.155 0.152-0.156 0.000*

1 Clayton Ct. 0.154 0.153-0.155 0.140

2 Clayton Ct

0.153 0.150-0.157 0.080

5 Clayton Ct. 0.155 0.154-0.156 0.141

6 Clayton Ct. 0.154 0.148-0.155 0.023

7 Clayton Ct. 0.152 0.150-0.155 0.129

8 Clayton Ct. 0.156 0.154-0.158 0.079

9 Clayton Court 0.155 0.154-0.158 0.121

12 Clayton Ct. 0.158 0.155-0.160 0.122

31 S. Bennywell(?) 0.141 0.140-0.145 0.035

7 0.152 0.148-0.153 0.000*

10 0.152 0.150-0.154 0.022

13 S. Cannon Dr. 0.151 0.150-0.152 0.067

18 S. Cannon 0.154 0.152-0.155 0.068

Perforation

14 -
Table 2. Results of Hardness Measurements

Pipe Sample Rockwell B Hardness (HRB)

In weld Average away from weld

13 Clayton Court 63 69

1 Clayton Ct. 55 64

2 Clayton Ct. 58 66

5 Clayton Ct. 60 72

6 Clayton Ct. 67 74

7 Clayton Ct. 59 65

8 Clayton Ct. 67 70

9 Clayton Court 70 74

12 Clayton Ct. 59 70

31 S. Bennywell(?) 52 65

7 58 61

10 50 53

13 S. Cannon Dr. 59 61

18 S . Cannon 59 59

Table 3. Cross Sectional Deformation at the Bend in the Pipe

Pipe Sample Inside Diameter, inches

Maximum Minimum Difference

1 Clayton Ct. 0.82 0.58 0.24

5 Clayton Ct. .81 .60 .21

7 Clayton Ct. .86 .54 .32

8 Clayton Ct. .84 .53 .31

9 Clayton Court .78 .64 .14

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Figure 3. Four views around the circumference of the pipe from 13 Clayton

Court showing extensive corrosion. These views are approximately

at the location of arrow A in figure 1. X 1 1/2

Figure 4. Cross section through severely corroded region of pipe from

13 Clayton Court. The welded seam is indicated by the arrow. X 2

Figure 5. Unetched cross section through pipe from 13 Clayton Court.

Light region is pipe material. Light gray region adjacent

to the pipe material is corrosion product.

As polished. X 100

Figure 6. Etched cross section through pipe from 13 Clayton Court.

Dark gray material at the top is corrosion product.

Microstructure consists primarily of ferrite with some

pearlite.

Etchant: 1% nital X 200

a

b

Figure 7. Pipe from 1 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through bend showing cross sectional

deformation. The welded seam is indicated by

the arrow. X 2

Figure 8. Pipe from 2 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through a corroded region not at

the bend in the pipe. The welded seam is indicated

by the arrow. X 2

b

Figure 9. Pipe from 5 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through bend showing cross sectional

deformation. The welded seam is indicated by the

X 2 arrow.

a

Figure 10. Pipe from 6 Clayton Ct.

a. Bend region of pipe as received at NBS showing corrosion.

Arrow indicates partial cut apparently made by a pipe

cutting tool. X 1

b. Region of severe corrosion about 8 inches from the bend. X 1 c. Cross section through region shown in figure 10b. The

welded seam is indicated by the arrow. X 2

a

b

Figure 11. Pipe from 7 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through bend showing cross sectional

deformation. The welded seam is indicated by the arrow. X 2

b

Figure 12. Pipe from 8 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Region of severe corrosion at end of bend

(arrows) . X 1 c. Cross section through pipe in region of severe corrosion shown in figure 12b. The welded seam is

indicated by the arrow. X 2 d. Cross section through bend showing cross sectional

deformation. The welded seam is indicated by the arrow. X 2

b

Figure 13. Pipe from 9 Clayton Court.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through bend showing cross sectional

deformation. The welded seam is indicated by the

arrow. X 2

b

Figure 14. Pipe from 12 Clayton Ct.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through bend showing essentially

no cross sectional deformation. The welded seam

is indicated by the arrow. X 2

b

Figure 15. Pipe from 31 S. Bennywell.

a. Bend region of pipe as received at NBS showing

corrosion. X 1

b. Cross section through one of the more severely

corroded regions not in the bend. The dark

areas between about 10 and 11 o'clock represent

porosity. The welded seam is indicated by the arrow. X 2

a

b

Figure 16. Pipe identified as 7.

a. Bend region of pipe as received at NBS showing corrosion,

depression, and perforation (arrow). X 1

b. Cross section through perforation showing extent of

depression. Except for the depression, there is little

evidence of cross sectional deformation in this figure.

The welded seam is indicated by the arrow. X 2

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Figure 18. Pipe from 13 S. Cannon Dr.

a. Bend region of pipe as received at NBS showing soil

and corrosion. X 1

b. Cross section through one of the more severely

corroded regions adjacent to the bend. The welded

seam is indicated by the arrow. X 2

b

Figure 19. Pipe from 18 S. Cannon.

a. Bend region of pipe as received at NBS showing

corrosion. The end of a sleeve can be seen at

the right. X 1

b. Cross section through one of the more severely

corroded regions of the bend. The welded seam is

indicated by the arrow. X 2

b

Figure 20. Pipe from 18 S. Cannon before and after cleaning. X 1

a. Before cleaning.

b. After cleaning.

b

Figure 21. Pipe from 31 S. Bennywell before and after cleaning.

Pipe has been rotated slightly between figures a and

b. XI

a. Before cleaning.

b. After cleaning.

Figure 22. As-polished cross section through the pipe from 8 Clayton Ct.

showing inclusion content representative of the sections

examined. X 100

Figure 23. As-polished cross section through the pipe from 31 S.

Bennywell showing porosity. The location of the porosity

in the pipe wall can be seen in figure 15b. The two

parallel, nearly horizontal lines about 1/3 the distance

from the bottom of the figure are polishing scratches

caused by foreign material being dragged from the pores. X 40

Figure 25. Etched cross section through pipe sample designated 10.

The light gray material covering approximately the upper

one-half of the figure is corrosion product.

Etchant: 1% nital X 160

Figure 24. Etched cross section through the bend of the pipe sample

from 8 Clayton Ct. showing cracking of the weld at the

inside of the pipe. The inside wall surface of the pipe

is vertical at the right.

Etchant: 1% nital X 40

Figure 26. As-polished cross section through pipe sample from 31 S. Bennywell showing corrosion product on the inside of the

pipe. The corrosion product is light gray. X 100

Figure 27. Etched cross section Figure

through pipe sample

from 8 Clayton Ct.

showing microstructure consisting of

ferrite and a small

amount of pearlit e. Etchant: 1% nital

X 100

28. Etched cross section through

pipe sample designated 7 showing

microstructure consisting of

ferrite and a small amount of

pearlite. The grain size is

smaller and the grains are more nearly equiaxed than in

the microstructure shown in

figure 27.

Etchant: 1% nital X 100

wpP?

Figure 29. Etched cross section through pipe sample designated 10

showing the microstructure at the weld (between arrows)

and on both sides of the weld.

Etchant: 1% nital X 100

Figure 30. Etched cross section through pipe sample from 8 Clayton Ct.

showing decarburization adjacent to the pipe surface

(vertical at the right) in a slightly corroded region.

Note that there are fewer of the small dark areas near the

surface than in the left of the figure.

Etchant: 1% nital X 50
-

-

-

-

--

•
NBS-1 14A (REV. 7-73)

_ U.S. DEPT. OF COMM.

bibliographic data

SHEET

1. PUBLICATION OR RE! PORT NO.

NBSIR 77-1198 (R)

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

EXAMINATION OF 3/4 INCH STEEL PIPE NATURAL GAS SERVICE

LINES, DELMARVA POWER AND LIGHT COMPANY, WILMINGTON,

DELAWARE

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

T. Robert Shives

8 . Performing Organ. Report No. NBSIR

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3120418

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office of Pipeline Safety Operations

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.)

The Office of Pipeline Safety Operations requested that the NBS Mechanical Properties

Section examine fourteen 3/4 inch diameter steel pipe natural gas service lines from

Edgemoor Gardens, Wilmington, Delaware. The submitted samples had all been installed

in crawl spaces under houses. An explosion had been attributed to the ignition of gas

leaking from one of these pipes. All of the pipe samples exhibited corrosion to some

extent. Two samples, including the one reportedly involved in the explosion, had been

perforated. Many others were severely corroded. A reportedly high concentration of

water vapor in the poorly ventilated crawl spaces is suggested as the source of the

corroding medium. Measurements in essentially uncorroded regions indicated that the

original pipe wall thickness would meet current (1976) ASTM specifications. All but

one of the longitudinal seam welds appeared to be in satisfactory condition. The

unsatisfactory weld was cracked at a bend in the pipe where there was a considerable

amount of cross sectional deformation. Several samples exhibited cross sectional

deformation at the bend. The hardness and microstructure of the weld and parent

materials appeared to be compatible. The microstructure of all the samples examined

appeared to be satisfactory except for one sample that exhibited a large amount of

porosity. All except the two perforated samples withstood a leak test at 30 psig

natural gas.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Corrosion; natural gas pipe; natural gas pipe failure; steel pipe.

18. AVAILABILITY Cunlimited

[* For Official Distribution. Do Not Release to NTIS sponsor is

responsible for its further use.

[

! Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl 3

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1 Order From Nati onal Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

22. Price

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