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OCR for page 235
APPENDIX
GFluid-let Cutting of Ordnance and High-Pressure
Clean-Out of Energetic Materials
Fluidjet cutting
is a topic of interest to many groups.
The fluid used is usually water, and high-pressure wa-
ter jets have been used by industry to cut through many
materials (e.g., metal and plastic) for more than 25
years (Summers, 1997~. As part of the ACWA pro-
gram, Teledyne-Commodore and Parsons-AlliedSignal
have proposed using fluidjet cutting to (1) shear fuzes;
(2) precisely section munitions; and (3) gain access to
energetic materials by washing out "demilitarized"
chunks, slivers, or sections of energetic materials from
warheads and rocket motors. Parsons-AlliedSignal pro-
poses using water; Teledyne-Commodore proposes
ammonia.
The use of high-pressure water or ammonia to cut
explosive-loaded ordnance and/or to wash out energetic
materials from ordnance casings is a proven technol-
ogy. When shearing fuzes or sectioning munitions, the
fluid jet often contains an abrasive, such as garnet, and
the fluid pressure is normally about 2,722 aim (40,000
psi) to cut through the metal casing. When removing
explosives or propellants from inside warheads or
rocket motors, the fluid usually does not contain abra-
sives, and the pressure is normally much lower, about
680 atm (10,000 psi). Critical issues include (1) identi-
fication of hazards associated with the specific task;
(2) design of the fluidjet cutting system; (3) determi-
nation of processing parameters; (4) containment and
segregation of residual metal, downloaded energetic
materials, and other refuse; and (5) the development of
a preventive maintenance schedule.
235
DESIGN PARAMETERS AND HAZARDS
IDENTIFICATION
Some of the design parameters for fluidjet cutting
of ordnance and some of the hazards associated with its
operation are well known. Target responses to the im-
pact of high-velocity, nonabrasive water jets have been
analyzed (Kang et al., 1993~; the mechanisms and pa-
rameters of abrasive waterjet (AWJ) cutting have been
examined (P.L. Miller, 1992a); some AWJ explosive
safety tests have been evaluated (P.L. Miller, 1992b);
and the effects of ultra high-pressure water jets on high
explosives have been determined (P.L. Miller, 1992c).
Some design issues associated with fluidjet cutting
systems have been reviewed by a team from Lawrence
Livermore National Laboratory and the Pantex Plant in
Amarillo, Texas (Kang et al., 1993), who were inter-
ested in identifying the physics governing the most
efficient mass-removal process when a material is sub-
jected to waterjet impact. Theoretical and experimen-
tal investigations were performed on the effects of a
nonabrasive water jet impinging on a solid surface. At
jet velocities below 1,500 m/s, the maximum impact
pressure can be calculated from the pressure across a
one-dimensional water-hammer compression wave
(Cook et al., 1962~. The test data have been correlated
to the following expression (Heymann, 1968~:
AP = Pc - Pu = PUCuVj [1 + 2 (vi/cu)]
where P denotes the pressure, r the liquid density, C
the speed of sound, and Vj the jet velocity. The
OCR for page 236
236
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
subscripts u and c signify conditions in the undisturbed
liquid region and the compressed liquid region, respec-
tively. Impact and machining experiments were con-
ducted on various materials with waterjet reservoir
pressures up to 2,720 aim (40,000 psi). Test results in-
dicated that a maximum mass-removal rate takes place
when the distance between the target piece and the
nozzle exit (stand-off distance) is several hundred
nozzle diameters. At this long stand-off, the jet disinte-
grates into a series of ligaments and droplets impinging
on the surface.
Typical nozzle diameters are about 0.35 mm (0.014
in) to 1.5 mm (0.060 in), depending on the material to
be cut and the cutting technique. The techniques can
either be optimized for removing material or for cut-
ting and pulverizing material simultaneously for recla-
mation and reuse. If multiple port nozzles are used, the
sum of the port diameters should not exceed a maxi-
mum design criterion, such as 1.5 mm (0.060 in). The
length-to-diameter ratio of nozzles used for nonabra-
sive fluidjet cutting depends on the fluid pressure and
cutting attributes but is usually about 50: 1.
The parameters that affect safety and risk include
water pressure, nozzle design, abrasive concentration
and particle size, and cutting procedure. Several hun-
dred thousand explosive-loaded projectiles have been
safely cut using fluidjet technology. Metals ranging
from aluminum 6061 to titanium Ti-6Al-4V have been
cut using waterjet streams laced with garnet grit. The
optimum particle size of garnet grit depends on the
metal being cut. The softer the metal, the larger the grit
size. A grit size of about 150 microns has been found
to be very close to optimal for cutting through steel
casings.
Two cutting techniques have also been investigated,
cutting laterally across the projectile (like a saw) and
cutting rotationally (similar to a lathe). The rotational
method is faster. An average time for AWJ cutting
through 4.2 inch, Composition B-loaded mortars was
33 seconds using the rotational method and 57 seconds
using the lateral method (P.L. Miller, 1992a). Ammo-
niajet cutting appears to be even faster. Abrasive am-
moniajet cutting has been reported to be about 25 per-
cent faster than AWJ cutting (Teledyne-Commodore,
1998~.
Both waterjet and AWJ cutting of booster and main-
charge explosives have been demonstrated to be safe
and practical. Even though the impact values from wa-
terjet velocities exceed the threshold impact limits for
explosives, the energetic initiation mechanism for wa-
terjet impingement/cutting is different than for "con-
ventional" solid-solid impacts and is well understood.
When both projectile diameters and impedance mis-
matches are taken into account, the results agree with
published models for impact velocities (P.L. Miller,
1992b). A substantial safety margin for using nonabra-
sive waterjet cutting of main-charge explosives has
also been documented by the Naval Surface Warfare
Center (NSWC) Crane Division (Liddard and Roslund,
1993; Worsey et al., 1990~. A graph of the impact ini-
tiation probabilities for several high explosives is pro-
vided in Figure G- 1 as a log-log plot of velocity versus
fluidjet diameter. The lines represent the velocities at
which initiation would be expected to occur 50 percent
of the time (Verb.
Jet impact is the most likely cause of initiation of
energetic materials during fluidjet cutting. The maxi-
mum pressure for continuous water flow, with existing
equipment, is believed to be about 10,200 aim (150,000
psi). The water jet generated by this driving force has a
sonic velocity of about 1,475 m/s (4,900 ft/s), which
represents an upper bound for water because it is also
the pressure at which water freezes at 25°C (77°F).
In testing by Alliant Techsystems, pentaerythritol
tetranitrate (PETN) and trinitrotoluene (TNT) were
2x1 o4
104
1 o 3
Fluid-jet
regime
5 10~1 10° 1o1 2X101
Diameter (mm)
TNT
Exp D
Picric acid
Comp B
HEX
Tetryl
RDX
PETN
FIGURE G-1 Waterjet velocity at which explosives will
initiate 50 percent of the time as a function of the fluidjet
diameter.
OCR for page 237
APPENDIX G
selected to represent the sensitivity range of explosives
of interest in demilitarization. PETN is an impact-sen-
sitive booster explosive component; TNT is a relatively
impact-insensitive explosive used as a main charge.
Fifty waterjet impact tests were performed on pressed
PETN samples and cast TNT samples. Neither PETN
nor TNT was initiated by the impact of water jets at
this pressure (P.L. Miller, 1992c).
SURVEY OF PRACTICE AND PRODUCTION
The use of fluidjet cutting to gain access to muni-
tions for demilitarization and/or resource, reclamation,
and reuse has been demonstrated and/or used by the
Department of Defense (DOD) and many contractors.
The user community can be separated into uses of non-
abrasive jets and users of abrasive jets.
A limited survey of nonabrasive waterjet cutting of
energetic materials was recently published (Estabrook,
1994~. Nonabrasive water jets have been used to down-
load explosives from warheads by the NSWC Indian
Head Division at Yorktown, Virginia (Lowell, 1986),
and the NSWC Crane Division in Crane, Indiana (Sum-
mers et al., 1988; Burch, 1998), as well as at the West-
ern Area Demilitarization Facility in Hawthorne, Ne-
vada (Day and Zimmermann, 1994~. Nonabrasive
water jets have also been routinely used in the propel-
lant industry to download composite rocket motors to
reclaim cases. This technology has been demonstrated
by Thiokol, Aerojet GenCorp, and many others. Non-
abrasive ammonia jets have been used by the Army in
Huntsville, Alabama, to download rocket motors from
cases as a first step in a novel recovery process (Melvin,
1992; Morgan, 1994~. Carbon dioxide pellets have been
entrained in a pressurized pneumatic jet at velocities of
20 m/s to 300 m/s to demonstrate an "environmentally
friendly" means of downloading (or "blasting out")
explosives from projectiles by the Army at Picatinny
Arsenal in New Jersey (Hwang, 1995~. The Air Force
has even investigated using high-pressure liquid nitro-
gen as a cryogenic jet to remove propellant from large
rocket motors (Coppola,1995~. AWJ has been recently
reviewed in the literature (Summers, 1997~. In the
United States, the AWJ technique combines abrasive
with the high-velocity jet stream after it leaves the ini-
tial acceleration nozzle. The resulting mixture is then
refocused through a second nozzle. AWJ has been used
237
/
/
L/
/
\
Entrainment abrasive
water-jet cutting
DIAJET abrasive
water-jet cutting
FIGURE G-2 Comparison of the AWJ and ASJ (DIAJET)
abrasivejet cutting techniques.
by Alliant Techsystems to section thousands of projec-
tiles without incident. In the United Kingdom, an alter-
native method of abrasive slurry jetting (ASJ), mar-
keted under the name "DIAJET," is being developed
(D. Miller, 1995~. In the ASJ method, the abrasive is
fed into the waterjet stream before it is accelerated
through a nozzle. These two techniques are compared
in Figure G-2. The ASJ technique is potentially more
efficient than AWJ because of higher cutting rates at
reduced pressures and reduced operating costs. For ex-
ample, the AWJ operating pressure is typically in the
range of 2,382 to 3,743 atm (35,000 to 55,000 psi) for
sectioning ordnance; the ASJ operating pressure is be-
tween 238 and 680 aim (3,500 and 10,000 psi). ASJ is
being implemented by the Defense Evaluation and Re-
search Agency (DERA) in the United Kingdom to de-
militarize obsolete ordnance and "render safe" un-
exploded ordnance, such as abandoned mines. ASJ is
also being considered for implementation in the United
States as a more efficient method for demilitarizing
ordnance (Fossey, 1998).
INCIDENTS ASSOCIATED WITH
DEMILITARIZATION OF ORDNANCE
A few incidents have been associated with the de-
militarization of ordnance using jet-cutting techniques.
OCR for page 238
238
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
Five recent, diverse incidents are discussed here. The
first incident, which occurred in 1996 at the Alliant
Techsystems Proving Grounds (Blixrud, 1996), hap-
pened during the mechanical defuzing of obsolete 8-
inch Navy projectiles immediately prior to demilitari-
zation by jet cutting. The cause of the incident was
pinching picrates in the threads while unscrewing a
corroded fuze. The lesson learned was that all ordnance
must be carefully inspected before processing to iden-
tify and remove ordnance that require special treatment
from routine operations. This incident might not have
occurred if jet cutting had been used to remove the fuze
(rather than unscrewing it mechanically).
A second incident involved the fluidiet nozzle be-
coming detached from the lance during the high-pres-
sure water wash-out of explosive from a munition war-
head. When the nozzle impacted the explosive, it
initiated and deflagrated. The lesson learned was that
metal parts must be routinely inspected for signs of
fatigue.
The third and fourth incidents occurred at Aii~ant
Techsystems during system trials and safety demon-
strations. Both incidents involved abrasive water-Jet
cutting of 20 mm ammunition that contained lead azide,
which was press-loaded at high density and deliber-
ately chosen to determine whether initiation would oc-
cur. During abrasive waterjet cutting, the lead azide
initiated and detonated. After this happened the first
time, some design parameters were altered and the tests
were repeated. The results were the same the second
time.
A fifth incident, which occurred at DERA West
Freugh in Scotland in 1995 (Moore, 1999), involved
handling ordnance that had been demilitarized by
abrasive jet cutting. About three days after explo-
sive-loaded ordnance had been sectioned, workers
performing normal procedures were injured when
the ordnance unexpectedly initiated. Evidently, the
cause of the initiation was embedded particles from
the abrasive jet cutting operation that had sensitized
the explosive to impact, especially when the explo-
sive surface was dehydrated. The lessons learned are
that sectioned ordnance should be kept wet while
applying impact, shear, or other forces to it and that
spent abrasive should not be allowed to "dry out"
while it may still be contaminated.
PREVENTATIVE MAINTENANCE
The high-pressure pumps used for jet cutting require
extensive preventative maintenance and are, thus, re-
sponsible for most of the down time for jet-cutting sys-
tems. Wear of the nozzle is a primary concern for safety
and performance. Nozzle wear is worst with the AWJ
method, followed by the ASJ method, and least with
nonabrasive techniques. For AWJ, the nozzle usually
clogs at least once during start-up. The more often the
system is shut down and restarted, the worse the wear.
However, for AWJ, the average service life of a nozzle
is about 1,000 hours of operation.
Any closed-loop fluidjet cutting system has "dead
spots" in which sediment, energetic material, metallic
particles, and spent abrasive can accumulate. The num-
ber of dead spots should be minimized when the sys-
tem is designed and built. Filter housings, traps, and
other solids-capture features in closed-loop systems
should have a preventative maintenance plan based on
actual processing data or experience to ensure that un-
desired combinations of trace .se~iment. ener~et.ic mn
· . . ... .. .
_ ~ _ A-- - - - ---I --- --D-
terlals, metallic particles, and spent abrasives do not
dry out sufficiently to undergo exothermic reduction-
oxidation reactions. If ammonia jets are used, precau-
tions must be taken to minimize the residence time
of materials awaiting further processing to prevent
exothermic ammonolysis.
REFERENCES
Blixrud, C. 1996. Investigation Report, 8" Demilitalization. Memo-
randum from Craig Blixrud, Alliant Techsystems, to M. Dolby
and B. Ford, Alliant Techsystems, May 21, 1996.
Burch, D. 1998. Recovery of RDX and HMX from Military Muni-
tions. Presented at the JANAF PDCS/S&EPS Joint Meeting,
NASA Johnson Space Center, Houston, Texas, April 21-24,
1998.
Cook, M.A., R.T. Keyes, and W.O. Ursenbach. 1962. Measure-
ments of detonation pressure. Journal of Applied Physics 33:
3413-3421.
Coppola, E.N. 1995. Cryogenic Propellant Removal System (PRS).
Pp.324-332 in Proceedings of the 3rd Global Demilitarization
Symposium. Arlington, Va.: Joint Ordnance Commanders
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ity. Pp. 300-332 in Proceedings of the 2nd Demilitarization Sym-
posium. Arlington, Va.: Joint Ordnance Commanders Group
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Estabrook, L.C. 1994. Water-Jet Cutting of Energetic Materials.
Pp. 200-209 in Proceedings of the Life Cycles of Energetic
OCR for page 239
APPENDIX G
Materials 1994 Conference. Paper LA-UR-95-1090. Los
Alamos, N.M.: Los Alamos National Laboratory.
Fossey, R.D. 1998. The use of an Abrasive Waterjet System at 700
bar for the Cutting of Military Munitions as Part of a Demilita-
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national Conference on Jetting Technology. Brugge, Belgium:
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Heymann, F.J. 1968. On the shock wave velocity and impact pres-
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Hwang, M. 1995. Carbon Dioxide Blast Demilitarization of Explo-
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Kang, S-W., T. Reitter, G. Carlson, J. Crutchmer, D. Garrett, P.
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239
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Representative terms from entire chapter:
energetic materials
