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CORROSION OF MATERIALS IN HYDROSPACE

PART III - TITANIUM AND TITANIUM ALLOYS

BY

Fred M. Reinhart

September 1967

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NAVAL CIVIL ENGINEERING LABORATORY
Port Hueneme, California

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CORROSION OF MATERIALS IN HYDROSPACE
PART III - TITANIUM AND TITANIUM ALLOYS
Technical Note N- 921

Y-FO15-01-05-002a

by

Fred M. Reinhart

ABSTRACT

A total of 475 specimens of 10 titanium alloys were exposed at two
different depths in the Pacific Ocean for six different periods of time
varying from 123 to 1064 days to determine the effects of deep ocean
environments on their corrosion resistance. Specimens of the alloys
were also exposed in surface seawater for 181 days for comparison purposes.

Corrosion rates, types of corrosion, pit depths, effects of welding,
stress corrosion cracking resistance and changes in mechanical properties
are presented.

The alloys were immune to corrosion and stress corrosion cracking
except alloy 13V-11Cr-3Al with unrelieved circular welds. This alloy
with unrelieved circular welds failed by stress corrosion cracking
after 181 days of exposure at the surface, 403 days at 6,780 feet and
402 days at 2,370 feet. The 13V-11Cr-3Al alloy with unrelieved butt welds
failed by stress corrosion cracking when stressed at 75 percent of its
yield strength after 35, 77 and 105 days of exposure at the surface.

The mechanical properties of the alloys were not affected.

Some information from TOTO in the Atlantic Ocean is included for
comparative purposes.

Each transmittal of this document outside the agencies of the
U. S. Government must have prior approval of the Naval Civil
Engineering Laboratory.

PREFACE

The U. S. Naval Civil Engineering Laboratory is conducting a
research program to determine the effects of deep ocean environments
on materials. It is expected that this research will establish the
best materials to be used in deep ocean construction.

A Submersible Test Unit (STU) was designed, on which many test

specimens can be mounted. The STU can be lowered to the ocean floor

and left for long periods of exposure.
Thus far, two deep-ocean test sites in the Pacific Ocean have

been selected. Six STUs have been exposed and recovered. Test Site
I (nominal depth of 6,000 feet) is approximately 81 nautical miles
west-southwest of Port Hueneme, California, latitude 33944'N and
longitude 120945'W. Test Site II (nominal depth of 2,500 feet) is
75 nautical miles west of Port Hueneme, California, latitude 34°06'N
and longitude 120°42'W. A surface sea water exposure site (V) was
established at Point Mugu, California (34°906'N - 119°07'W) to obtain

surface immersion data for comparison purposes.
This report presents the results of the evaluations of titanium

and titanium alloys exposed at the above three test sites. Also,
some information from TOTO is included for comparative purposes.

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INTRODUCTION

The development of deep diving submarines which can stay sub-
merged for long periods of time has focused attention on the deep
ocean as an operating environment. This has created a need for
information concerning the behavior of common materials of construc-
tion as well as newly developed materials with promising potentials,
at depths in the ocean.

To study the problems of construction in the deep ocean, project
"Deep Ocean Studies" was established. Fundamental to the design,
construction and operation of structures, and their related facilities
is information with regard to the deterioration of materials in deep
ocean environments. This report is devoted to the portion of the
project concerned with determining the effects of these environments
on the corrosion of metals and alloys.

The test sites for the deep ocean exposures are shown in Figure
1 and their specific geographical locations are given in Table 1.

The complete oceanographic data at these sites, obtained from NCEL
cruises between 1961 and 1967, are summarized in Figure 2. Initially,
it was decided to utilize the site at the 6,000 foot depth. Because
of the minimum oxygen concentration zone found between the 2,000 and
3,000 foot depths, during the early oceanographic cruises, it was
decided to establish a second exposure site (STU II-l and II-2) ata
nominal depth of 2,500 feet. For comparative purposes, the surface
water site V was included.

A summary of the characteristics of the bottom waters 10 feet
above the bottom sediments at the two deep ocean exposure sites and
at the surface exposure site is given in Table l.

Sources of information pertaining to the biological character-
istics of the bottom sediments, biological deterioration of materials,
detailed oceanographic data, and construction, emplacement and
retrieval of STU structures are given in Reference 1.

The procedures for the preparation of the specimens for exposure
and for evaluating them after exposure are described in Reference 2.

Previous reports pertaining to the performance of materials in
the deep ocean environments are given in References 1 through 7.

This report is a discussion of the results obtained of the
corrosion of titanium and titanium alloys for the six exposure periods
shown in Table 1 and for 181 days of exposure five feet below the
surface.

RESULTS AND DISCUSSION

The results presented and discussed herein also include the
corrosion data for titanium exposed on the STU structures for the
International Nickel Company, Incorporated as granted by Reference 8.
Results from other participants in the NCEL exposures are also in-
cluded; U. S. Navy Marine Engineering Laboratory (Reference 9), the
Chemistry Division, NCEL (Reference 10), and U. S. Naval Air
Engineering Center (Reference 11). Deep ocean data from the
Atlantic Ocean (TOTO) are also included for purposes of comparison;
Naval Research Laboratory (Reference 12) and Naval Applied Science
Laboratory (Reference 13).

The chemical compositions of the titanium alloys are given in
Table 2, their corrosion rates in Table 3, their stress corrosion
behavior in Table 4 and the effect of corrosion on their mechanical
properties in Table 5.

Corrosion

There was no corrosion of any of the alloys at the surface or
at either nominal depth @,500 or 6,000 feet) for any period of
exposure except two alloys; the Navy Marine Engineering Laboratory
reported a corrosion rate of 0.19 MPY for unalloyed titanium and
of 0.18 MPY for the 6 Al-4V alloy after 123 days of exposure at a
depth of 5,640 feet in the Pacific Ocean, Reference 9. They also
reported no visible corrosion. For practical purposes, these values
are considered to be inconsequential.

Alloys 75A, Ti-0.15 Pd, 5A1-2.5Sn, 6A1-4V and 13V-11Cr-3Al were
fusion welded by the inert-gas shielded arc, non-consumable (tungsten-
arc) electrode process (TIG). There were transverse butt welds and
3-inch diameter circular welds in the 6 inch by 12 inch specimens.
The welding stresses of these specimens were not relieved by an
annealing treatment in order to simulate a welded component not
adaptable to stress relieving after welding. There was no visible
corrosion of these welded alloys except for stress corrosion crack-
ing of the 13V-11Cr-3Al alloy with the circular welds. This will
be discuss under stress corrosion.

The 6A1-4V alloy was also exposed as:

a. Wire, 0.020, 0.045 and 0.063 inch diameter
b.** Cables, 1/16"=" 1) x TOseS "6 x19, 3" = 6 x19 with Type

304 stainless steel swaged ends and }" - 6 x 19 tied with mild steel
wire.

c. Flash welded tube.
d. Flash welded sphere.
e. Piece from a broken sphere.

There was no visible corrosion on any of the above specimens except
for the Type 304 swaged fittings and the mild steel wire. The faying
surfaces of the Type 304 swaged fittings were severely attacked by
crevice corrosion. The mild steel wire used to tie the end of one
titanium cable was corroded almost through by galvanic corrosion;

the mild steel wire being anodic to the titanium cable.

The Naval Research Laboratory, Reference 12, and the Naval
Applied Science Laboratory, Reference 13, reported no corrosion of
titanium alloys, both unwelded and welded, at depths of 4,250 and
5,600 feet in the Tongue-of-the-Ocean, Atlantic Ocean after exposures
varying from 102 to 1050 days.

Stress Corrosion

Specimens of the alloys stressed in various ways and to values
equivalent to 35, 50 and 75 percent of their respective yield strengths
were exposed at the surface for 180 days and at nominal depths of
2,500 and 6,000 feet for different periods of time.

The majority of the specimens were deformed by bowing to obtain
the desired tensile stress in the central 2 inch length of the outer
surface of the specimen as described in Reference 2. Many of these
specimens, butt welded by the TIG process, were positioned such that
the transverse weld bead was at the apex of the bow in the 2-inch
length. Other specimens, 6" x 12", had a 3" diameter circular weld
bead placed in the center as shown in Figure 3. The stresses induced
by the welding operation were not relieved in order to retain the
maximum residual stresses in the specimens. Still other specimens
were in the shape of welded rings 9-5/8 inches outside diameter which
were deformed different amounts in order to induce tensile stresses
in the periphery at the ends of the restraining rods as shown in
Figure 4.

The results of the stress corrosion tests are given in Table 4.
There were no stress corrosion cracking failures of any of the
alloys, both unwelded and butt welded, stressed at values equivalent
to as high as 75 percent of their respective yield strengths for 180
days of exposure at the surface, 402 days at the 2,370 foot depth
and 751 days at the 5,640 foot depth, except for the butt welded
13V-11Cr-3Al alloy. The unrelieved butt welded 13V-11Cr-3Al alloy

failed by stress corrosion cracking when stressed at values equivalent
to 75 percent (94,500 psi) of its yield strength after 35, 77 and 105
days of exposure at the surface in the Pacific Ocean. The stress corro-
sion cracks occurred at the edge of the weld bead as shown in Figure 5.

Metallographic examinations of unetched and etched sections in a
plane parallel to the surface of the specimen showed that a secondary
crack which started at the edge of the specimen in the parent metal away
from and parallel to the main fracture was irregular and branching in
mature as well as transgranular as shown in Figure 6. This is typical of
the main fracture.

The Naval Applied Science Laboratory, Reference 10, reported no
stress corrosion cracking of unwelded and butt welded 7A1-2Cb-1Ta alloy
stressed at 100 percent of its yield strength after 199 days of exposure
at a depth of 4,250 feet in the Tongue-of-the-Ocean, Atlantic Ocean.

The 6A1-4V alloy rings stressed as high as 60,000 psi (approxi-
mately 50 percent of its yield strength) (Figure 4) did not fail by
stress corrosion cracking during 402 days of exposure at a depth of
2,370 feet.

Alloys 75A, Ti-0.15Pd, 5A1-2.5Sn, 7A1-2Cb-1Ta, 6A1-4V and 13V-
11Cr-3Al were exposed with an unrelieved 3-inch diameter circular weld
bead in the center of 6" x 12" specimens as shown in Figure 3. Only the
13V-11Cr-3A1l alloy failed by stress corrosion cracking because of the
residual welding stresses. Cracking occurred during surface exposure of
181 days, during 403 days of exposure at a depth of 6,780 feet, during
751 days of exposure at a depth of 5,640 feet, and during 402 days of
exposure at a depth of 2,370 feet. The cracks in all cases were radial
across the weld beads, a typical crack is shown in Figure 7. The crack
in this case changed direction by 90 degrees (left side of Figure) just
outside the weld bead because of the redistribution of the residual
stresses.

Metallographic examination of a polished section of the crack taken
in the plane of the sheet where it changed direction showed that the
path of the crack was irregular and branching in nature as shown in
Figure 8. After etching and reexamination it was found that the crack
was predominantly transgranular as shown in Figure 9.

Mechanical Properties

The effect of exposure in sea water at nominal depths of 2,500 and
6,000 feet on the mechanical properties of the alloys is given in Table
5. These data show that the mechanical properties of the alloys were
not adversely affected by exposure in sea water at nominal depths of
2,500 and 6,000 feet for periods of time as long as 751 days.

SUMMARY AND CONCLUSIONS

The purpose of this investigation was to determine the effects of
deep ocean environments on the corrosion and stress corrosion of titanium
alloys. To accomplish this, 473 specimens of 10 alloys were exposed at
the surface for 181 days and at nominal depths of 2,500 and 6,000 feet
for periods of time varying from 123 to 1064 days.

There was no visible corrosion nor any significant weight losses of
any of the alloys after 181 days of exposure at the surface, 197 and 402
days at a nominal depth of 2,500 feet, and 123, 403, 751, and 1064 days
at a nominal depth of 6,000 feet either in the sea water or the bottom
sediment.

Alloys, unwelded and with transverse butt welds, were not sus-
ceptible to stress corrosion cracking when stressed at values equivalent
to 75 percent of their respective yield strengths after 180 days of
exposure at the surface, 402 days at a nominal depth of 2,500 feet, and
751 days of exposure at a nominal depth of 6,000 feet, except the butt
welded 13V-l1Cr-3Al alloy. This alloy failed by stress corrosion crack-
ing after 35, 77 and 105 days of exposure at the surface. Flash welded
rings of 6A1-4V alloy did not stress corrosion crack when stressed to
60,000 psi and exposed at a depth of 2,370 feet for 402 days. The
residual stresses induced in 13V-11Cr-3Al alloy sheet by a 3-inch
diameter unrelieved weld were great enough to cause stress corrosion
cracking after 181 days of exposure at the surface, 403 days at 6,780
feet, and 402 days at 2,370 feet. The other alloys, 75A, Ti-0.15Pd,
SA1-2.5Sn, 7Al-2Cb-1Ta, and 6A1-4V, similarly welded were not susceptible
to stress corrosion cracking either at the surface or at depth.

The mechanical properties of the alloys were not adversely
affected by exposure in sea water at depth.

Differences in temperature, oxygen concentration, pressure and
velocity of flow between the surface and depths in the Pacific Ocean
appear to have no influence on the corrosion behavior of titanium alloys.

REFERENCES

Le

U. S. Naval Civil Engineering Laboratory Technical Note N-900:
Corrosion of Materials in Hydrospace Part I - Irons, Steels, Cast
Irons and Steel Products, by Fred M. Reinhart, Port Hueneme,
California, July 1967.

U. S. Naval Civil Engineering Laboratory Technical Report R-504:
Corrosion of Materials in Hydrospace, by Fred M. Reinhart,
Port Hueneme, California, December 1966.

U. S. Naval Civil Engineering Laboratory Technical Note N-605:
Preliminary Examination of Materials Exposed on STU I-3 in the

Deep Ocean - (5,640 Feet of Depth for 123 Days), by Fred M. Reinhart,
Port Hueneme, California, June 1964.

U. S. Naval Civil Engineering Laboratory Technical Note N-695:
Examples of Corrosion of Materials Exposed on STU II-1 in the Deep
Ocean - (2,340 Feet of Depth for 197 Days), by Fred M. Reinhart,
Port Hueneme, California, February 1965.

U. S. Naval Civil Engineering Laboratory Technical Note N-781:
Effect of Deep Ocean Environments on the Corrosion of Selected
Alloys, by Fred M. Reinhart, Port Hueneme, California, October 1965.

U.S. Naval Civil Engineering Laboratory Technical Note N-793:
Visual Observations on Corrosion of Materials on STU I-1 after 1064
Days of Exposure at a Depth of 5,300 Feet in the Pacific Ocean, by
Fred M. Reinhart, Port Hueneme, California, November 1965.

U. S. Naval Civil Engineering Laboratory Technical Note N-915:
Corrosion of Materials in Hydrospace Part II - Nickel and Nickel
Alloys, by Fred M. Reinhart, Port Hueneme, California, August 1967.

May, Dr. T. P., Unpublished data, International Nickel Company,
Incorporated, Wrightsville Beach, N. C.

Navy Marine Engineering Laboratory MEL R&D Phase Report 429/66:
Metal Corrosion in Deep-Ocean Environments, by W. L. Wheatfall,
Annapolis, Maryland, January 1967.

10.

11.

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13,

14.

U. S. Naval Civil Engineering Laboratory Technical Note N-859:
Corrosion Rates of Selected Alloys in the Deep Ocean, by

J. B. Crilly and W. S. Haynes, Port Hueneme, California, November
1966.

Naval Air Engineering Center Report NAEC-AML-2132:; Evaluation
of Metallic Materials Exposed to the Deep Ocean Environment at
5,640 Feet for 123 Days, by John J. De Luccia and Edward Taylor,
Philadelphia, Pennsylvania, June 1965.

Naval Research Laboratory NRL Memorandum Report 1634: Marine
Corrosion Studies; Stress-Corrosion Cracking, Deep Ocean
Technology, Cathodic Protection and Corrosion Fatigue. Third
Interim Report of Progress, by B. F. Brown, et al, Washington,
D. C., July 1965.

Naval Applied Science Laboratory, Laboratory Project 9400-72,
Technical Memorandum 3: Corrosion at 4,500 Foot Depth in Tongue-
of-the-Ocean, by E. Fischer and S. Finger, Brooklyn, New York,
March 1966.

Naval Applied Science Laboratory, Laboratory Project 9300-6,
Technical Memorandum 5: Retrieval, Examination and Evaluation
of Materials Exposed for 199 Days on NASL Deep Sea Materials
Exposure Mooring No. 1, by A. Anastasio and A, Macander,
Brooklyn, New York, July 1966.

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Table 4. Stress Corrosion of Titanium Alloys

Specimens

Stress, Percent of Exposure, Depth, Exposed | Failed
i Days Feet

NNO ONDDDOOCOCUW
WWW WD WD W WH fd W fo
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23.8
333}, 9)
50.8
Welding stresses

Fw WH Ww
iS} (2) (2) (S)

SAl-2.5Smr 42.9

SAL-2. 587) 42.9
42.9
42.9
61.3
61.3
61.3
61.3
92.0
92.0
92.0
92.0
43.3
61.8
92.7
Welding stresses
stresses
stresses
stresses
stresses
stresses

SS

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FNUNNNDN WW WW WD WWWD WW WD Ww

15

Table 4. Continued

pecimens

S
Stress, Percent of Exposure,| Depth, Exposed | Failed
KSI Yield Strength} Days Feet

1 0

7al-2¢b-1Tasb/
7A1-2Cb-1Ta—
transverse d
Sees ey
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Tal 20b-1tet
7A1-2Cb-1Tas—

transverse d

Theat ett!
longitudina} jweld
7Al-2Cb-1Tay ,
7AL-2Cb-1 Taz,

7Al-2Cb-1 Tap, |
7A1-2Cb-1Ta= Welding stresses

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16

Table 4. Continued

Stress, Percent of Exposure, | Depth, Exposed Failed
KSI Yield Strength} Days Feet

Welding stresses
Welding stresses
Welding stresses
Welding stresses
Welding stresses
Welding stresses

FNNNN NM
iS) (S) S) (2)
Tes
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LH)
13V-11¢r-3Al>,

13V-11Cr-3Aly,
13v-11¢r-3Al>,
13V-11Cr-3Al,
13V-11Cr-3Al7)
13V-11Cr-3Aly
13V-11Cr-3Al>,
13V-11Cr-3Al7)
13V-11Cr-3Al>"
13V-11Cr-3Al7)
13V-11Cr-3Al>,
13v-11Cr-3Al7
13V-11Cr-3Al7
13V-11Cr-3Al>,
13V-11Cr-3Al5)
13V-11Cr-3Al> Welding stresses
13V-11Cr-3Al,) Welding stresses
13V-11Cr-3Al, Welding stresses
13V-11Cr-3Al> | Welding stresses
13V-11Cr-3Al5 Welding stresses
13V-1iCr-3Al1— Welding stresses

pine wy SS GLS

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8
8
8
8
8
8
8
6
6
6
6
of
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FNNNNDND WW WW WD WH WWD WH WWD Ww

/ Transverse butt weld, unrelieved, across specimen at apex of bow.

/ Circular weld 3 inches in diameter in center of specimen, unrelieved.

/ Two specimens lost when structure was turned on its side and dragged

along the bottom.

4/ One specimen lost when structure was turned on its side and dragged

along the bottom.

5/ Three specimens lost when structure was turned on its side and dragged
along the bottom.
Specimens failed at edge of weld beads after 35, 77 and 105 days.
Specimen partially embedded in bottom sediment cracked radially across
the weld bead.

8/ Specimen in sea water cracked radially across the weld bead.

9/ Three specimens lost during a storm.

10/ Reference 13

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SALINITY

Oxygen, ml/1

0 2 4 6 8 ol 12 14 16 18
Temperature, C
6.4 6.6 6.8 7.0 Tae 7.4 7.6 7.8 8.0 8.2
pH
33.0 33.2 33.4 33.6 33.8 34.0 34.2 34.4 34.6 34.8

Salinity, ppt

Pigure 2. Oceanographic dats at STU sites.

Figure 3. Circular weld (3" diameter) in 6" x 12" specimen.
unrelieved.

Figure 4. Alloy 6A1-4V welded rings deformed to induce stresses.

Figure 5. Stress corrosion crack across specimen of 13V-11Cr-3A1

alloy at the edge of the weld bead. Note secondary
branching cracks extending from main fracture.

Figure 6. Secondary crack in parent metal away from and
parallel to main fracture. Crack is branching in
nature and transgranular. Etched in lactic,
hydrofluoric and nitric acid mixture. X100.

Figure 7. Radial stress corrosion crack across weld bead

of 13V-11Cr-3A1.

Figure 8. Irregular, branching stress corrosion crack in

13V-11Cr-3A1. Unetched. X100.

Figure 9. Same area as shown in Figure 6 etched to show that
crack is predominantly transgranular. Etched in
lactic- hydrofluoric-nitric acids. X100.

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UNCLASSIFIED

Security Classification

DOCUMENT CONTROL DATA- R&D

Security classification of title, body of abstract and indexing: annotation must be entered when the overall report is classified)

5 LASS!IFICATION
ORIGINATING ACTIVITY (Corporate author) Cc IC ATION

Naval Civil Engineering Laboratory
Port Hueneme, California

REPORT TITLE

Gorrosion of Materials in Hydrospace. Part III - Titanium and Titanium Alloys

OCESCRIPTIVE NOTES (Type of report and inclusive dates)

AUTHOR(S) (First name, middle initial, last name)

REINHART, Fred M.

6 REPORT DATE Ja. TOTAL NO. OF PAGES 7b. NO. OF REFS
August 6 Q 1

8a, CONTRACT OR GRANT NO. 9A, ORIGINATOR'S REPORT NUMBER(S)

PROJECT N hni 1 Note N-
peenciee7 No-\ y=FO15=01-05-002a pease a qe

9b. OTHER REPORT NO(S) (Any other numbers that may be assigned
this report)

overnment

11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY

Naval Facilities Engineering Command
Washington, D. C.

13. ABSTRACT

A total of 475 specimens of 10 titanium alloys were exposed at two different
depths in the Pacific Ocean for six different periods of time varying from 123 to
1064 days to determine the effects of deep ocean environments on their corrosion
resistance. Specimens of the alloys were also exposed in surface seawater for
181 days for comparison purposes.

Corrosion rates, types of corrosion, pit depths, effects of welding, stress
corrosion cracking resistance and changes in mechanical properties are presented.
The alloys were immune to corrosion and stress corrosion cracking except
alloy 13V-11Cr-3Al. This alloy with unrelieved circular welds failed by stress
corrosion cracking after 181 days of exposure at the surface, 403 days at 6,780

feet and 402 days at 2,370 feet. The 13V-11Cr-3Al alloy with unrelieved butt
welds failed by stress corrosion cracking when stressed at 75 percent of its
yield strength after 35, 77 and 105 days of exposure at the surface.

The mechanical properties of the alloys were not affected.

Some information from TOTO in the Atlantic Ocean is included for comparative
purposes.

FORM PAGE 1 os
DD 1 NOV 1473 ( Y UNCLASSIFIED
S/N 0101-807-6801 Security Classification

UNCLASSIFIED

Security Classification

Titanium alloys
Mechanical properties
Corrosion

Hydrospace

DD ,2%"..1473 (sack)

(PAGE 2)

UNCLASSIFIED

Security Classification

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