NBSIR 75-704 (J)

Investigation of a 1-Ton Tank-Car

Tank That Leaked Phosgene in

Easton, Pennsylvania on April 24, 1973

C. G. Interrante

Mechanical Properties Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

April 1975

Failure Analysis Report

Prepared for Federal Railroad Administration

Department of Transportation

Washington, D. C. 20590
III
NBSIR 75-704

INVESTIGATION OF A 1-TON TANK-CAR

TANK THAT LEAKED PHOSGENE IN EASTON, PENNSYLVANIA ON APRIL 24, 1973

C. G. Interrante

Mechanical Properties Section

Metal lurgy Division

Institute for Materials Research

National Bureau of Standards

Washington. D. C. 20234

April 1975

Failure Analysis Report

"This document has been prepared for the use of the Federal Railroad Administration, Department of Transportation, Washington, D.C. Responsibility

for its further use rests with that agency. NBS

requests that if release to the public is contemplated, such action be taken only after consultation with the Office of Public Affairs

at the National Bureau of Standards."

Prepared for Federal Railroad Administration

Department of Transportation

Washington, D. C. 20590

U.S. DEPARTMENT OF COMMERCE. Rogers C.B. Morton. Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

TABLE OF CONTENTS

Page

ABSTRACT iii

1. INTRODUCTION 1

2. PURPOSE OF INVESTIGATION .. 2

3. EXPERIMENTAL PROCEDURES 2

4. RESULTS AND DISCUSSIONS 4

4.1 Weight of Tank 4

4.2 Examinations for Cracks 4

4.3 Visual Examinations 4

4.4 Metallographic Examinations 5

4.5 Scanning-Electron-Microscope Examinations 8

5. SUMMARY ON THE NATURE AND CAUSE OF THE LEAK 9

6. ACKNOWLEDGEMENTS 10

7. REFERENCES 10

List of Figures

1. The tank after flame cutting to remove the end that

leaked and the section that contained the leak.

2. The section that contained the leak, as flaune-cut from

the tank.

3. Eight 1-inch segments as saw-cut from the section that

contained the leak.

4. Eight 1-inch segments in the rough-ground condition.

5. Eight 1-inch segments from near the leak and two end

segments taken from the section that contained the

leak, in the cropped, polished, and etched condition.

i
List of Figures (continued)

6. Inside of tank after removal of the end that leaked.

7. Montage of bond region on segment number 2, face 1.

8. Montage of bond region on segment number 4, face 1.

9. Montage of bond region on segment number 5, face 1.

10. Segment number 5 after being wedged open to examine

for cracks, showing the location of a dark region

(at the arrow) which represents a possible preexisting path through the tac weld,

11. Two sections taken in the weld metal on the head-

- plate portion of fractured segment 5, showing surface

(llA) and sub-surface (IIB) defects and oxides that

surround them.

12. SEM fractograph of fracture face of segment 5 taken

at X5 magnification,

13. SEM fractographs taken at X48 (Fig. 13A,) and X240

(Fig, 14B.) showing microporosity in the dull region

and crystalline fracture in the adjacent parts of the

fracture

14 . SEM fractographs of the dull region (Figure 14A)

,

showing microporosity and dimpled rupture, and of

a region representative of the balance of the

fracture (Figure 14B) , showing a crystalline

appearance.

ii
ABSTRACT

At the request of the Standards and Procedures Division,

Federal Railroad Administration, Department of Transportation,

an investigation was conducted at the National Bureau of

Standards (NBS) on a 1-ton tank-car tank, which reportedly

failed in service by leaking phosgene gas in Easton,

Pennsylvania. The tank was shipped to NBS where it was

sectioned and examined to determine the nature and possible

cause of the leak.

No gross defects, through which phosgene gas could have

leaked, were observed and it is believed that the leak

occurred through a path of very small size, which probably

existed either along the fusion boundary of or within the

weld metal of a tac weld present in the region of the leak.

The forged weld present at locations remote from the leak

did not exist in the region of the leak and the available

evidence indicates that this unbonded metal is the result

of corrosion promoted by capillary action at the root of this

weldment. It is believed that the observed leak was

principally the result of corrosion from the inside of the

vessel, and it is speculated that the failure of the vessel may

have been accelerated by hydrotesting of the vessel and/or

by service-related fatigue loads on the weld joint.

Investigation of a 1-Ton Tank-Car Tank That Leaked

Phosgene in Easton, Pennsylvania on April 24, 1973

1. INTRODUCTION

*

A 1-ton tank-car tank failed at Richards Yard in

Easton, Pennsylvania in April 24, 1973, by leaking while

being used to transport Phosgene, a class A poisonous gas.

When this leak was discovered, it was peened shut with a

peening haimner. However, the escape of the gas resulted

in the hospitalization of three railroad employees at

Easton, Pennsylvania. Accordingly, the Federal Railway

Administration requested that the National Bureau of

Standards conduct an inspection and failure analysis of

this failed tank.

The tank was identified as CWS-A-5119, Lot P-479-1,

tested 1/4 3, American Welding Company, Carbondale,

Pennsylvania. Certificates furnished by the Association

of American Railroads indicated that, for the vessel in

question, the files of Robert W. Hunt Company, Engineers,

Chicago, Illinois, show that: (1) the tank had been

fabricated by a process that lapwelded the heads to the

shell by water-gas forging; (2) the heat numbers for the heads,

plates, and bottoms are 59C669, 68C743, 62C730, respectively;

(3) the January, 194 3 tare weight and water capacity were 15 90

pounds and 1680 pounds respectively; and (4) the meohfanical

properties of these steels were as follows:

Heat

No.

Yield

Point

(psi)

Tensile

Strength

(psi)

Elongation

(percent)

Reduction

of Area

(percent) Test

59C669 34,700 50,400 33.0 63.2 Satisfactory

62C730 31,100 51,100 34.0 67.7 Satisfactory

68C743 32,200 49,200 37.0 67.8 Satisfactory

In addition, these files give the following chemical

compositions (percent by weight, ladle analyses) for

these heats of steels:

The material in this Introduction was provided by

Mr. Quentin Banks, FRA.
- 2 -

c q 1Mn111 59C669 .12 .008 .026 .42

62C730 .11 .016 .034 .45

68C743 .12 .009 .030 .45

The tank was reported to have been hydrotested at

500 pounds pressure on each of the following dates: 1/43,

7/60, 2/68, and 3/73. The leak in the tank was discovered

in April of 1973, during the first service after the hydrotest

of March 1973. During this service, the tank-car tank was

reported to have been positioned near the rear of a railroad

car that carried 15 of these 1-ton tanks.

2 . PURPOSE OF INVESTIGATION

The purpose of this investigation is to determine the

nature and possible cause of the leak in the forged weld

seam of this tank-car tank.

3. EXPERIMENTAL PROCEDURES

The tank was weighed. Then it was inspected for cracks

in the region of the leak by four methods : visual exaunination, magnetic-particle testing, dye-penetrant testing, and

metallographic inspection of various sections of the forged

weld seam in the vicinity of the leak. In addition, a

section containing a one-inch (2.5 cm) length of the weld

seam in the vicinity of the leak was fractured and excimined

for a pre-existing corrosion path from the inside to the

outside of the vessel. The inside of the tank was visually

examined.

The visual examinations were done by examining both the

reported region of the leak and the interior of the tank by

eye and with the aid of a hand magnifying lens. The

magnetic-particle test procedure involved the use of iron

oxide powder. When current is passed through the piece being

tested the powder is selectively attracted to discontinuities

at or very near the surface on which the powder is placed.

The localization of the powder, as detected by eye, is taken

as evidence of the location of a discontinuity at or very

near the surface. The dye-penetrant test involved the use

of red dye that penetrates by capillary attraction into any

flaw or discontinuity present on the surface being tested.

A white spray paint is placed onto the test surface and the

dye present, inside of flaws in the surface, stains the
- 3 -

white paint and this stain is taken as evidence of the

presence of a flaw in the surface.

Before these inspections were made, paint was removed

from the end of the tank in the region of the leak and this

region was degreased to provide a clean surface for inspection. When these inspections were completed, the end of

the tank that contained the leak was removed from the tank

by a circumferencial torch cut at a distance of about

9 1/2 inches (24 cm) from the end that leaked in service,

as shown in Figure 1. The section that contained the leak

was removed by another torch cut. This section is the piece

that is missing in Figure 1, and it is shown as Figure 2.

Two arrows are seen in the figure. These were placed to

point to two paint marks on the end of the tank. The paint

marks were present on the tank when it was received at NBS,

and they had been placed about 5 inches (13 cm) apart to

bracket the location of the leak.

The region between the arrows was then saw cut from the

balance of this torch-cut tank segment. Saw cuts were made

at distances of about 1 1/2 inches (4 cm) beyond either end

of the length between the two arrows. This saw-cut tank

segment was about 8 inches (2 0 cm) in length, as measured

along the circumference. This segment was further saw cut

into eight approximately equal segments, which were numbered

1 through 8 , and they are shown in Figure 3 along with the

part of the shell plate that adjoined these eight segments

in the original 9 1/2-inch (24 cm) long flame-cut section.

These eight segments were then rough ground on a 60 grit

paper wheel. The rough-ground segments are shown as

Figure 4. The surfaces shown here are on the right sides

of the segments as viewed on Figure 3, and this surface for

each segment will be referred to as face 1 in the text to

follow; face 2 is the other side of each of these segments.

Face 1 of each of these eight segments was prepared for

metallographic examination by cropping at a distance of about

1 1/2 inches (3 to 4 cm) from the edge of the head-to-shell

forged weld, and two additional sections were then prepared

from the original flame-cut segment of Figure 2. The

locations of these two sections are marked IB and SB in

Figure 2, and IB face 1 and SB face^2 are shown in Figure 5

along with the other eight segments , in the polished-andetched condition in Figure 5,

f

Only the shell piece of segment number 5 is shown in

this figure.
- 4 -

The surfaces shown in Figure 5 were carefully examined

in various conditions of preparation, with the aim of

detecting a continuous path from the interior to the exterior

of the tank. To this end, these samples were also examined

on other surfaces in other cross-sectional planes within

these segments, so as to make possible (through photographic

records) the tracing of voids through various planes within

a segment. In addition, segment 5 was pulled apart

completely severing the bond of a tac weld between the head

and the shell pieces; the fracture surface attached to the

shell was carefully examined by scanning electron microscopy

and the weld metal on the fractured head piece was successively

polished and examined at various depths below the fracture

surface

.

4. RESULTS AND DISCUSSIONS

4 . 1 Weight of Tank

The weight of the tank, as measured at NBS, was 1670

pounds (752 kg) plus 37 pounds (17 kg) for 10 bolts and

1 dome; for a total weight of 1710 pounds (770 kg) . This

contrasts with the 1590 pounds (716 kg) tare weight measured

in 1943. The 10 bolts weighed 1-3/4 pounds (0.8 kg) and the

dome weighed 35 1/4 pounds (16 kg)

.

4.2 Examinations for Cracks

The magnetic-particle and dye-penetrant inspections for

cracks proved negative, and it was concluded that the peening

of the end of the tank to stop the leak also effectively

closed any surface flaws that were present.

4 . 3 Visual Examinations

Visual examination of the external parts of the tank

revealed that the exact location of the leak on the end of

the tank was not readily discernable. Between the two marks

that had been placed on the end of the tank to locate the

leak, there was a region of about 2 inches (5 cm) in length

from which the paint on the surface of the tank had been

removed. It was presumed that the peening hammers used to

close off the leak had chipped this paint loose. This

peened region is contained mainly in segments 4 and 5, and

so it was tentatively concluded that the tank had leaked in

segments 4 and 5.

Midway between segments 4 and 5 inside the tank, a

corrosion line was observed. This line can be seen in

Figure 3 on the plate in front of these segments, and it

can be seen in Figure 6, which shows the inside of the
- 5 -

remainder of the tank after renvoval of the end that leaked.

In Figure 6, this line is marked by an arrow. The line is

bounded by two circles —one is the flame-cut shell plate

and one is the head plate at the far end of the vessel —and

the line is approximately midway between the 10 and the

11 o'clock positions on the circles.

Several cycles of corrosion are apparent in Figure 6

on the inside of the tank. Each cycle is believed to

represent corrosion that occurred while the tank was

partially filled while being stored flat along the long

axis of the tank, and it appears that with each cycle,

corrosion products were formed over a segment of the

inside surfaces of a partially filled cylinder. Thus, at

a previous boundary between the filled and unfilled parts,

there exists a line, which is visible evidence of a difference

in the corrosion experiences of the metal on the two sides of

the line.

Both the rough-ground segments of Figure 4 and the

polished segments of Figure 5 show that the bonded region

extends for less than 0.4 inches (1.0 cm), in segments

numbered 1 through 7, and for about 0.6 inches (1.5 cm),

in segment number 8. The shortness of these lengths of the

bond line are somewhat surprising, especially for segments

2, 4, and 5 which have bond line lengths of less than

0.2 inches (0.5 cm).

In the polished and etched condition (Figure 5)

,

segments numbered 2 , 4 , and 5 were observed to have no

fusion from lap welding, i.e. no forged weld region. The

bonded metal shown here for these three segments is that

of a tac weld at the end of the vessel. The other segments

examined had at least some small length of forged weld

metal along their bond lines. Segments IB and 8B were

taken from the ends of the original flcime-cut section at

distances somewhat remote from the leak, as marked on the

photograph of Figure 2. In Figure 5, the polished and

etched faces of these two segments clearly show forged weld

metal in lengths of 1.3 inches (3.3 cm) for 8B and 0.6

inches (1.5 cm) for IB. Segment 8B is more distant from

the tac weld than any of the other segments examined, and

SB has the longest forged weld region.

4 . 4 Metallographic Examinations

The as-polished-and-etched surfaces of the various

segments were metallographically examined in detail, and

these examinations revealed that the tac weld was present in
- 6 -

sections 1 through 7 inclusive and it was not present in

IB, 8, and 8B . Special attention was focused on segments

4 and 5 in the attempts to determine the location of a

continuous (micro) path for the escape of gas from the

inside of the tank, but none of these attempts conclusively

demonstrated that such a path existed.

A montage of photomicrographs was taken on face 1 of

segments 2, A, and 5, each of which were bonded only by a tac weld with no lap weld being present. These montages

are presented, respectively as Figure 7, 8, and 9. They

show that the unbonded region extends (from inside the

tank) to the root of the tac weld of segment 4 face 1,

and that the unbonded region extends beyond the root of

the weld for a short distance along the fusion line of the

tac weld in the other two segments. They also show, in

the corroded forged weld regions near the tip of the

unbonded part, that somewhat enlarged cavities have formed,

presumably by corrosion that occurred in these regions at a

rate greater than the rate at which it occurred at other

nearby locations. These local regions, such as is shown near

the tip of the crack of Figure 7, have a geometry that

restricts the access to the bulk of the interior space of

the tank. The formation of cavities such as those shown , in Figure 7 is not unlike that observed in crevice corrosion.

It is well known that mild steels are susceptible to crevice

corrosion?^

In the tac weld, the fusion line between the weld metal

and the base metal (head or shell) appears as a line defect

and it seemed that a continuous path of voids might exist

along one of these fusion boundaries. Careful metal lographic

examinations of the various segments showed that these fusion

lines contained strings of intermittant inclusions, which

apparently became localized and aligned at the fusion line

as a result of the tac-welding operation.

These inclusions and the inclusions within the weld

metal, as well as other defects present in the base metal

in the vicinity of the weld metal were observed and

photographed on various surfaces within the 10 segments.

Successive planes of the selected segments were ground,

polished, examined, etched, and reexamined in the search

for a continuous path of voids from the inside to the

outside of the tank.

The intersection of segments 4 and 5 was considered to

be the most likely region for the leak, and attention was
- 7 -

focused on finding a continuous path nearby segment 4 face 1

and segment 5 face 2. On segment 4 face 1, eight successive

planes were prepared and photographed at various depths up

to 0.121 inches (.31 cm) from the original plane examined.

This was also done on segment 5 face 2 using 7 planes up to

a depth of 0.0084 inches (.021 cm); each plane examined in

this instance represented only a small change in the depth

below the previous surface examined.

The results of the observations made on these two

segments follow: Only a tac weld was observed and no lapweld region was present; voids were present predominantly

in the weld metal of the tac weld; the fusion boundary always

contained a string of inclusions, but a continuous path was

not traced through the successive sections examined.

Segment 5, face 2 had been examined on successive

surfaces and after face 1 was also examined, this segment

was separated into two pieces —a thicker head piece with

some weld metal attached and a thinner shell piece with

some weld metal attached. The separation was accomplished

by first separating the two pieces with a small saw cut

in the segment at the end that did not contain the weld metal,

then prying open this saw-cut slit with a chisel, and then

pulling the two pieces in tension until the weld metal was

completely fractured. In this way, it was possible to later

examine the fracture face and to observe the path along

which the two pieces fractured. It was believed, that a

segment fractured in this manner would give evidence of

pre-existing voids in the weld metal.

Segment 5 in the partially fractured condition is

shown in Figure 10, in which the piece of the head is shown

on the right and the shell on the left. The arrow in

between the head and shell pieces points to a dark region

along the bond line. This dark region is a void region in

the partially fractured surface of weld metal, and it is

believed to have existed prior to this separation. After

the pieces were completely separated, the appearance of the

fracture in the region just below this dark region was dull

in comparison to that of the adjacent regions on the balance

of the fracture faces. The balance of the fracture was

bright and crystalline in appearance. The fracture face of

the piece of the shell was observed in detail using the

scanning electron microscope. The head piece of this fracture

was used for metallographic studies.

In the metallographic studies, the head piece with its

weld metal was polished and etched on successive weld-metal
- 8 -

layers beneath the level of the fracture face of the weld

metal. In several of these layers there existed weld-metal

with gross porosity and oxidation which extended from outside of

the tank on the face of the weld to within the tac weld metal.

After successive weld-metal layers were removed microporosity

only was present. Figure llA shows the region of porosity

at one level at which it extended to the outside of the tank

and Figure IIB shows the region at another level at which it

was essentially contained within the weld metal. Surrounding

the pores there is evidence of corrosion. While this

corrosion could have been the result of some externally

prompted corrosive action, we suspect that it may be a result of internally prompted corrosion, and that it may be

the actual site of the leak. However, the micropores

observed at the internal weld metal site were not successfully

traced all the way to the root of the tac weld inside the

vessel

.

4 . 5 Scanning-Electron-Microscope Examinations

Several scanning-electron-microscope (SEN) fractographs

were taken of the fracture faces of the shell portion of the

separated segment number 5. These fractographs showed that

the fracture was crystalline in appearance except for the

region beneath the dark spot shown in the photograph of

Figure 10. The non-crystalline appearance of the metal

beneath this dark spot was observed to be present along a

continuous path from the inside to the outside of the tank

on this fracture face.

Figure 12 shows the fracture face on the shell portion

of segment 5 at a magnification of X5. The arrow on the

figure points in the direction of crack propagation (during

separation from the inside to the outside of the tank) and

it is located at the dark part shown at the arrow on Figure 7.

At higher magnifications. Figure 13 shows that this dull

region is non-crystalline whereas other parts of the fracture

are crystallographic . Microporosity is much more prevalent

in the dull region. This microporosity and the dimpled

appearance of the dull region is shown at X1300 in Figure 14A,

and the crystalline appearance of the balance of the fracture

is represented at X1300 in Figure 14B.

It is believed that the dull region failed in a more

ductile manner than did the balance of the fracture because

constraint was locally decreased in this region due to the

presence of the micropores that existed before the two pieces

were separated to form the fracture faces. This microporosity
- 9 -

was probably present in the original tac weld, just after

the weldment had been deposited. In service, it is believed

that corrosion acted on this region of porosity eventually

to form a continuous path from the interior to the exterior

of the tank,

5 . Summary on the Nature and Cause of the Leak

No gross defects through which phosgene gas could have

leaked from the vessel were observed and it is believed that

the leak occurred through a micropath, which probably existed

either along the fusion boundary of, or within, the weld metal

of the tac weld present in the region of the leak. The forged

weld observed at sites remote from the leak was not present

at the site of the leak, and so the distance through which the

micropath had to form was relatively short in comparison with

that at other locations remote from the leak. It is believed

that this micropath was formed by corrosion which was itself

promoted by capillary action at this site inside the vessel.

Other factors which may have contributed to the leak,

include the stress of the hydrotest and fatigue loads in

service

.

The available evidence indicates that the leak was

promoted by corrosion. In numerous selected sites examined,

there was little or no bond of the forged weld, and

corrosion is believed to have led to this condition. In

these places where the forged weld is expected to have once

been, there is observed evidence of local accelerated corrosion

in the form of pockets (See Figure 8) , We interpret these

findings as indications of corrosion along the forged weld

bond line. Furthermore at the tip or end of the regions

in which there was no forged weld metal, the root of the tac

weld was partially separated along the fusion line and this

separation is also believed to have resulted from local

corrosive attack. In addition, microporosity was observed,

particularly in the region of the tac-weld metal of segment 5,

and this too is believed to have resulted from corrosive

attack.

The corrosion is believed to have been promoted by the

geometry inside the tank at the weld joint. At this location,

the tank head and sheel plates come together in a wedge shape,

with the point of the wedge being at the bond line between

the plates. Thus, a very narrow gap existed inside the tank

at the forged weld bond. We believe that this narrow gap

promotes capillary action and the retention of liquids.

Furthermore, we can conceive of local corrosive attack or
- 10 -

crevice corrosion due to this capillary attraction. For example, water that is retained in this capillary would

react with phosgene and forin4) hydrochloric acid (HCL) in

the capillary, with a resultant expectation of local

corrosive attack along the bond line.

The failure of this tank occurred during the first

"out of plant" service after a hydrotest of this vessel;

it can be argued that the stress of the hydrotest and the

subsequent corrosive attack (by the above mechanism) may

have accelerated the final linking of raicrovoids and voids,

and that the hydrotest thereby accelerated the formation of

the leak observed in service. It can also be speculated that in service, these vessels can receive fatigue loads of

sufficient magnitude to promote the linking of voids over

short distances within the bonded region between the head

and shell plates. However, no direct evidence of fatigue markings were observed in our investigation.

6. ACKNOWLEDGEMENTS

The extensive metallographic studies of this project

were conducted by C. H. Brady, and by G. E. Hicho and

D. E. Harne who also supervised the weighing of the tank

and assisted T. R. Shives in conducting the magnetic-particle

and dye-penetrant tests. T. P. Royston supervised the flame- cutting and sectioning operations and he provided the

photographic documentation of the tank after sectioning. Helpful suggestions were made to the author by Drs.

M. L. Picklesimer, J. H. Smith, and J. R. Ambrose.

7. REFERENCES

1. McCaffery, E. , J. Electronchem Soc. , 1974, 121, p. 1007.

2. Rosenfeld, I. L. and Marshakov, I. K. , Corrosion, 1964,

20, p. list.

3. Evans, Vlick R. , The Corrosion and Oxidation of Metals ; Scientific Principles and Practical Applications^

Edward Arnold (Publishers) Ltd., 1960, p. 528, 529.

4. Wertheim, E. , Textbook of Organic Chemistry , Second

Edition, The Blakiston Company, Philadelphia, 1945,

p. 260.

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Figure 3. Eight 1-inch segments as saw-cut from the

section that contained the leak. Part of

the shell plate that adjoined these

segments is also shown.




f]iiii nil

cm

Figure 5. Eight 1-inch segments from near the leak and two

end segments taken from the section that contained

the leak, in the cropped, polished, and etched

condition.


Figure 6. Inside of tank after removal of the end that leaked. The

arrow marks a faint corrosion line located at saw-cut

boundary of segments 4 and 5, which were taken from the

flame-cut section of the tank. This arrow is also

approximately centered on 2 white marks at 9 o'clock and

12 o'clock. These marks show the limits of the flame-cut

section

Figure 7. Montage of bond region on segment number

Figure 8 Montaqe of bond region on segment number 4, face 1. X 40

—t- ""^^^

VFigure 9. Montage of bond region on segment number 5,

face 1. X 40

Figure 10. Segment number 5 after being wedged open to examine

for cracks, showing the location of a dark region

(at the arrow) which represents a possible preexisting path through the tac weld.

Fig. IIB

Figure 11. Two sections taken in the weld metal on the headplate portion of fractured segment 5, showing surface

(llA) and sub-surface (IIB) defects and oxides

that surround them.

Figure 12. SEM fractograph of fracture face of segment 5 taken

at X5 magnification. The arrow points in the

direction of crack propagation and it is located at

the "dark part .

Fig. 13A

X48

Fig. 13B

X240

Figure 13. SEM fractographs taken at X48 (Fig. 13A.) and X240

(Fig. 14B.) showing microporosity in the dull

region and crystalline fracture in the adjacent

parts of the fracture.

Fig. 14A

Fig. 14B

Figure 14. SEM fractographs of the dull region (Figure 14A)

,

showing microporosity and dimpled rupture, and of

a region representative of the balance of the

fracture (Figure 14B) , showing a crystalline

appearance. X1300

NBS-lUA (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. Fl'MLK ATION OR Kl I'OR I NO. NBSIR 75-704

2. (ii>v't Accession

No.

3. Recipient's Accession No.

4. TH l.i: ANP ,sl B l lTLl: INVESTIGATION OF A 1-TON TANK-CAR TANK THAT LEAKED

PHOSGENE IN EASTON, PENNSYLVANIA ON APRIL 24, 1973

5. Publication Date April 1975

6. Performing Organization Code

7. AL'THORfSl

C. G. Interrante

8. Performing Organ. Report No. NBSIR 75-704

9. PKRFOR.MINC. ORC, ANIZATION NAMF AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3120110

11. Contract /Grant No.

12. Sponsoring Organization Name and ( omplcte Address (Street, City, Stale, ZIP)

Federal Railroad Administration

Department of Transportation

Washington, D.C. 20590

13. Type of Report & Period Covered Failure

Analysis Report

14. sponsoring Agency '.-ode

15. SUPPLEMENTARY NOTES

16. ABSIRAC I (A 200-word or less factual summary of moat aigrtHicant information. If document includes a significant

bibliography or literature survey, mention it here.)

j At the request of the Standards and Procedures Division, Federal

Railroad Administration, Department of Transportation, an investigation

was conducted at the National Bureau of Standards (NBS) on a 1-ton tankcar tank, which reportedly failed in service by leaking phosgene gas in

Easton, Pennsylvania. The tank was shipped to NBS where it was

sectioned and examined to determine the nature and possible cause of the

leak.

No gross defects, through which phosgene gas could have leaked, wer

observed and it is believed that the leak occurred through a path of

very small size, which probably existed either along the fusion

boundary of or within the weld metal of a tac weld present in the

region of the leak. The forged weld present at locations remote from

the leak did not exist in the region of the leak and the available

evidence indicates that this unbonded metal is the result of corrosion

promoted by capillary action at the root of this weldment. It is

believed that the observed leak was principally the result of corrosion

from the inside of the vessel, and it is speculated that the failure of

the vessel may have been accelerated by hydrotesting of the vessel and/

or by service-related fatigue loads on the weld joint.

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; crevice corrosion; failure amalysis; failure by leaking;

fractography ; hydrotest effects; mild steel; 1-ton tamk; phosgene

container; pressure vessel

18. AVAILAfULITY [_ Unlimited

@CX For Official Distribution. Do Not Release to NTI.S

r Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20(02, SD Cat. No. Cl^

{_J2 Order I'rom .National Technical Information Service (NTIS)

Springfield, Virginia 221'il

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SE( URITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

28

22. Price

USCOMM-OC 2e042.P7