Note: Descriptions are shown in the official language in which they were submitted.
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ANTIEXTRUSION DEVICE
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates in general to elastomeric seals having an
antiextrusion device
molded integrally into or onto the low pressure side of the seals. More
particularly, the invention
relates to the integration of a corrugated strip into an elastomeric seal. One
embodiment of the
invention has the strip positioned with the midplane of its corrugations
normal to the mating seal
surfaces and parallel to the midplane of the seal groove. Another embodiment
of the invention has the
midplane of the corrugations canted within the seal. The antiextrusion device
is applicable to annular
seal rings, linear seals, or seals of more complex configuration.
BACKGROUND OF THE INVENTION
Elastomeric seals are in very common use in a wide variety of applications as
a means for
closing off a flow passageway (gap) between two parts. The parts are usually
metallic and will, unless
measures are taken, allow fluids to pass through the gap where the two pieces
are joined. To prevent
the escape or loss of fluid at these gaps, flexible elastomeric seals are
typically used to close the gap
between the two parts. To achieve this function, the elastomeric seal is
placed in a cavity or groove in
a first part and the exposed side of the seal is comated with the surface of a
second part. The
prevention of fluid passage through a gap between such parts generally relies
upon the maintenance
of an initial interference fit of the seal with attendant interface biasing
forces between the sealing
element and the two parts.
Previously this initial interference fit, which is termed 'presqueeze' and
refers to the condition
prior to the application of fluid pressure, has been obtained either: a)
passively from displacement-
induced forces due to the size and protrusion of the elastomeric seal when
mounted in the groove, or
b) actively by compressing the elastomeric seal after it is mounted in the
groove. Sanders et al. U.S.
Patent 5,437,489 shows examples of passively presqueezed seals, while Reneau
U.S. Patent
4,728,125 discusses an example of an actively presqueezed seal.
As fluid pressure is applied to one side of the elastomeric seal, the seal
will deform and shift in
the direction of the fluid pressure forces. With time under high pressure
loads and/or as the pressure
increases, the seal will continue to displace toward the low pressure side of
the groove and become
further distorted and "cold flow" or "creep" into the gap. This time-dependent
behavior is further
enhanced if the elastomeric seal shrinks in volume or is softened by heat or
its interaction with
retained fluids. This problem is intensified when the elastomeric material
begins to shear off into the
gap to be sealed. In some cases the entire seal is displaced into the gap.
Shearing and tearing of the
elastomeric material from the extrusion of the seal into the gap can cause the
seal to fail. These
problems are significantly amplified as the size of the gap to be sealed is
increased.
The industry has implemented a number of improvements in seals to help solve
the problems
of creep and extrusion, which lead to seal failure. Such improvements have
enhanced elastomeric
seal performance, but none of the improvements have fully solved the problem
of creep and extrusion,
particularly for large gaps and for high pressure situations.
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A frequent improvement used for large gap or high-pressure situations has been
to provide an
antiextrusion device on the low-pressure side of the seal. This approach can
minimize static and
creep deflections of the seal into the seal gap. The typical antiextrusion
device is made of a stiffer,
stronger material than the seal elastomer. The antiextrusion device is either
integrally bonded to the
external surface of the seal or retained in the seal groove as a separate
item. Either way, the
antiextrusion device is generally positioned on the downstream face of the
seal to protrude into the
gap and back up the seal. Antiextrusion devices assist in reducing sensitivity
of the elastomer seal to
creep, thereby aiding in the maintenance of the initial interference fit.
The antiextrusion device ideally should provide low resistance to distortion
(i.e., low stiffness)
across the seal gap to permit large deflections of the device in that
direction without the device
undergoing permanent deformation. Concurrently, the antiextrusion device must
provide both high
stiffness and high strength to resist bending and shear distortion of the seal
element into the gap.
Sealing the gap and resisting creep of the seal into the gap requires some
embedment or entrapment
of the antiextrusion device in the seal to permit the seal to react against
the low-pressure end wall of
the seal groove to provide resistive forces to pressure loading. These
requirements are very difficult to
satisfy for linear, annular or circumferential seals for large gaps, because
provision of adequate
stiffness and strength for resisting movement into the gap generally requires
that the antiextrusion
device (ring) be provided with a geometry which causes the ring to have
undesirably high resistance to
distortion across the gap. Generally, only a very limited gap size can be
spanned by currently used
antiextrusion devices without permanent distortion of the devices.
Two types of non-integral, metallic antiextrusion devices are used for large
gaps for both linear
and annular seals. One type uses non-integral, bendable metallic fingers on
the downstream side of
the seal. These fingers have a common base strip which serves as anchor, while
each finger
functions independently. In certain antiextrusion rings of this type, the
individual metallic fingers
undergo excess bending and are not reliable for multiple sealings. In fact,
they have been known to
evert due to inadequate bending strength or excessive gap in severe cases. The
second type of non-
integral, metallic antiextrusion rings are knitted metal annular antiextrusion
rings (Metex, Edison, New
Jersey). These knitted metal rings are suitable for relatively large gaps and
are used for oilfield
downhole packers. However, these knitted antiextrusion rings have very little
elastic rebound, so that
resetting of the seal is not advisable or necessarily feasible due to
inability to fully retract.
The use of antiextrusion rings made of more flexible materials, such as a
stiff elastomer or
plastic material, for large circumferential seal gaps requires that the size
of the antiextrusion ring and
seal be significantly increased in order to provide sufficient embedment of
the antiextrusion ring to
resist creep, bending, and shearing of the rings. For active mechanically
compressed seals, such as
in Reneau U.S. Patent 4,728,125 or the Oceaneering "Smart Flange Plus"T "
(Oceaneering
International, Inc., Houston, Texas), the larger rings and seals require
larger seal compression
hardware and a significantly larger and much more expensive housing. Again,
provision of
satisfactory resistance to bending distortion in the seal gap will impede the
ability of the antiextrusion
ring to adequately distort to span a large gap. Stiffer ring materials have
improved creep and stiffness
performance, but are less conformable to large gaps and generally will
permanently distort when
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spanning larger gaps. Less stiff ring materials require even larger seal
cavities to adequately embed
them.
The significant areas of performance difficulty cited for large gaps and high
pressures with
conventional seals frequently lead to leaks or complete seal failures. For
critical service conditions,
such as deep water subsea pipeline repair clamps or hot-tap pipeline fittings,
revisiting the clamp for
adjusting the compressional preload on installed seals is prohibitively
expensive. Further, providing
more compressional preload in such cases is not practical for passive seals
for reasons of installation
damage to the seal due to excessive interference and an increased tendency of
the seal to creep and
extrude through the gap with high preloads.
Thus, a need exists for seals that can perform in large gap and high pressure
situations.
SUMMARY OF THE INVENTION
The invention contemplates a simple, inexpensive device for solving the
problems and
disadvantages of the prior approaches discussed above. The present invention
provides a simple,
reliable means for avoiding seal extrusion for large gaps and high pressures.
One aspect of the present invention is an antiextrusion device made of a rigid
corrugated
material substantially in a circular planar arrangement.
A second aspect of the present invention is an antiextrusion device made of a
rigid corrugated
material substantially in a right frustroconical pattern.
A third aspect of the present invention is an antiextrusion device made of a
rigid corrugated
material in a linear strip.
A fourth aspect of the present invention is an antiextrusion device made of a
rigid corrugated
material and positioned within a seal at a fixed distance from the low
pressure lateral face of the seal.
In accordance with another aspect of the invention, an elastomeric seal is
described having
one or more antiextrusion devices made of a rigid corrugated material embedded
in and bonded to the
elastomeric material in the seal.
In accordance with yet another aspect of the invention, a sealing unit is
described that has an
elastomeric seal containing an embedded antiextrusion device, a static seal
end and a movable seal
end. The movable seal end can be moved from its original position to stretch
the elastomeric seal and
displace the antiextrusion device. The movable seal tension can then be
released to permit the seal
and the embedded antiextrusion device to attemp to return to their original
positions.
The foregoing has outlined rather broadly several aspects of the present
invention in order
that the detailed description of the invention that follows may be better
understood. Additional features
and advantages of the invention will be described hereinafter which form the
subject of the claims of
the invention. It should be appreciated by those skilled in the art that the
conception and the specific
embodiment disclosed might be readily utilized as a basis for modifying or
redesigning the structures
for carrying out the same purposes as the invention. It should be realized by
those skilled in the art
that such equivalent constructions do not depart from the spirit and scope of
the invention as set forth
in the appended claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
The novel features which are believed to be characteristic of the invention,
both as to its
structure and methods of operation, together with the objects and advantages
thereof, will be better
understood from the following description taken in conjunction with the
accompanying drawings,
wherein:
FIG. 1A shows a frontal view of a first embodiment of an annular corrugated
antiextrusion device;
FIG. I B shows a perspective view of a second embodiment of a right frusto-
conical corrugated
antiextrusion device;
FIG. 2 shows a side view of the embodiment of the corrugated antiextrusion
device of FIG. 1A;
FIG. 3A illustrates a quarter-sectional view of the first embodiment, shown in
FIGs. 1A and 2, of an
antiextrusion device embedded in an annular seal assembly unit;
FIG. 3B illustrates a perspective view of the annular seal assembly shown in
FIG. 3A partially cut
away to show a corrugated antiextrusion device embedded in the seal;
FIG. 4A illustrates a quarter-sectional view of the first embodiment of the
antiextrusion device
embedded in another annular seal in which the midplane of the corrugations of
the antiextrusion
device is normal to the comating sealing surface of the seal;
FIG. 4B illustrates a quarter-sectional view of an antiextrusion device of
FIG. 1 B embedded in an
annular seal in which the midplane of the corrugations of the antiextrusion
device is at an angle of 45
to 1350 to the stretched comating surface of the seal;
FIG. 4C illustrates a perspective view of the seal element shown in FIG. 4B
where the seal has been
partially cut away to show the placement of the antiextrusion device shown in
FIG. 1 B embedded in
the seal;
FIG. 5 shows a view of a linear embodiment of the antiextrusion device along
the midplane of
corrugations transverse to the wave pattern;
FIG. 6 shows a view of the antiextrusion device of FIG. 5 normal to the
midplane of the corrugations;
FIG. 7A shows a linear embodiment of a seal with the antiextrusion device of
FIGs. 5 and 6 embedded
in the seal wherein the midplane of the corrugations of the antiextrusion
device is normal to the
comating sealing surface of the seal;
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FIG. 7B shows a linear embodiment of a seal with the antiextrusion device of
FIGs. 5 and 6 embedded
in the seal wherein the midplane of the corrugations of the antiextrusion
device is at an angle of 45 to
135 to the comating sealing surface of the seal;
FIG. 8 shows the seal of FIG. 7A installed in a linear seal groove; and
FIG. 9 illustrates the installed seal of FIG. 8 preloaded against its comating
seal surface.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides elastomeric seals having an antiextrusion
device molded
integrally into the low pressure side of the seals. By strengthening the low
pressure side of the
elastomeric seal, it becomes resistant to both any initial displacement into
the seal gap and any time-
dependent continued deformation through the seal gap resulting from "creep."
The present invention integrates an antiextrusion limiting means with seals to
assist in the
control of relative displacements into the seal gap and to provide reversible,
repeatable displacements
across the seal gap under varying pressures and gaps. Various antiextrusion
ring designs were
studied for their suitability to be integrally molded into an elastomeric
seal. Most of the available
antiextrusion ring designs are not suitable for integral molding into an
elastomeric seal, and even if
they were incorporated into seals they would not provide both the low
resistance to distortion across
the seal gap (necessary for stability in large gaps) and the necessary
stiffness and high strength to
resist extrusion and creep into the gap under high pressure.
For example, Crane Packing Company, Morton Grove, Illinois has bonded an
elastomer to a
metal reinforcing washer. The metal washer serves as an internal antiextrusion
ring, but the radial
inflexibility of the washer causes the ring to be unsatisfactory for large
gaps.
Conventional metal piston rings and laminar sealing rings exhibit a high ratio
of radial wall
thickness to thickness in the axial direction to enhance the support provided
by the seal cavity and the
stiffness of the rings. However, the attendant high resistance to change of
the ring diameter makes
metal piston rings and laminar rings unable to readily conform to large gaps.
Using split rings results
in shear of the elastomer adjacent the split.
Three types of U-cup seal expander springs are marketed by American Variseal,
Broomfield,
Colorado. These U-cup seal expander springs provide low circumferential
stiffness to permit
conformance to large annular gaps. However, the slanted helical spring and the
flat-wire helical coil
spring would be difficult to mold into an elastomeric seal and offer both very
low torsional stiffness and
low bending and shear strength. Additionally, the bonding surface for the
slanted helical spring is very
limited. The third type has an alternating radially-oriented cantilever
spring. This spring would be
easy to mold into a seal with the cantilever beam axes in either a planar or
conical configuration.
Hirschmann Gmbh (Hirschmann Engineering, Chandler, Arizona) also uses this
same type of relatively
weak alternating cantilever spring in a non-integral planar configuration
retained by detent grooves in
an elastomer as a low-pressure axial shaft seal. However, this type of ring
has insufficient beam
strength and stiffness to elastically resist distortion of the seal into a
large gap under high pressure.
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Corrugated metal-to-metal seals with the midplane of the coplanar
circumferential corrugation
waves parallel, rather than normal, to the faces to be sealed have been used
for annular flange face
seals (Parker Hannifin Corporation, Sulphur, Louisiana and Metallo Gasket
Company, New Brunswick,
New Jersey). The corrugations are multiple concentric annular ridges of
different diameters. The
crests of the corrugation waves bear on the surfaces of the flanges to provide
multiple annular seal
lines. Use of the corrugations provides multiple possible sealing lines and
adds very low level
flexibility to deal with flange gap irregularities and disturbances. However,
this situation is not similar
to the spanning of a large circumferential or linear gap.
Mildly corrugated wave springs for axially preloading a wedge expander to
spread and engage
the sealing lips of a circular U-cup type of seal with its comating sealing
surfaces has also been used.
For this case, the midplane of the corrugation waves is normal to the
cylindrical sealing faces, but the
wave spring is used only for force application and does not provide a backup
function.
Hydrodyne, a division of F.P.I., Hollywood, California produces corrugated
metallic seals as
flange face seals with a cylindrical midsurface normal to the flat comating
sealing faces. These seals
provide only a minor flexibility to the seals to compensate for irregularities
and variations in the seal
gap. Other Hydrodyne metallic seals are not actually corrugated, but use the
central rib to stiffen the
U-shaped cross-section of the ring against axial deflection. None of these
seals are suitable as
antiextrusion devices.
Corrugated Marcel wave spring expanders have been used to radially expand a
relatively rigid
split plastic piston ring. However, the midsurface of the corrugation waves is
cylindrical and parallel to
the cylindrical seal mating faces. Although these expanders provide a radial
force on the ring, they are
not suitable for antiextrusion service.
Microdot/Polyseal of Salt Lake City, Utah makes a seal having a corrugated
four-piece
construction which mounts in a standard groove for an 0-ring with two 0-ring
backup rings. The
relatively rigid seal ring itself is continuous with an essentially corrugated
pattern and has a
rectangular cross-section relatively small compared to the overall seal
groove. The midsurface of the
corrugations is planar and transverse to the comating cylindrical sealing
surfaces. The abutment rings
are also relatively rigid and are split, with one transverse face planar and
the other face corrugated to
closely mate with the seal ring. An elastomeric expander ring is used
underneath both the seal ring
and the abutment rings to preload the relatively rigid seal onto the sealed
surface. This arrangement
permits easy assembly of the substantially unstretchable seal into its groove,
since its diameter is
effectively increased whenever the corrugations are straightened under
assembly tension (for male
seals) or compression (for female seals). The seal is sufficiently rigid to
not require antiextrusion
rings, so the abutment rings function not as antiextrusion devices, but rather
serve only to maintain the
corrugated geometry of the installed seal ring necessary to take up the excess
seal length provided to
permit assembly. The abutment rings and the sealing element in this case are
unsuitable for handling
large gaps, since increasing the cross-sectional sizes of the elements to
handle large gaps and high
pressures makes this seal system very large and much harder to assemble.
The present invention uses a unique corrugated metallic seal molded into an
elastomeric
material that provides both the low resistance to distortion across the seal
gap (necessary for seal
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stability in large gaps) and the necessary stiffness and high strength to
resist creep and extrusion into
the gap under high pressure.
Referring now to the drawings, and initially to Figures 1A and 2, it is
pointed out that like
reference characters designate like or similar parts throughout the drawings.
The figures, or drawings,
are not intended to be to scale. For example, purely for the sake of greater
clarity in the drawings, wall
thickness and spacing are not dimensioned as they actually exist in the
embodiment.
A first embodiment of the present invention suitable for application in either
a female or male
circumferential seal is showr, in Figures 1A and 2. Figure 1A shows a view in
the axial direction of a
substantially planar annular antiextrusion ring prior to molding, while Figure
2 shows a radial side
view.
In Figures 1A and 2, the antiextrusion device 10 of this embodiment is
preferably constructed
of a relatively thin metallic strip material such as carbon or stainless
steel. For example, a corrugated
metal strip that is formed in a generally circular pattern and is
approximately 0.016 to 0.031 inch thick
would be suitable for a 12-inch pipeline clamp at a maximum operating pressure
of 3000 psi. The ratio
of radial annular thickness of the corrugated material of the antiextrusion
device 10 to the wave height
of the corrugations (axial thickness) is on the order of 3 to 20, largely
depending on the pressure
capabilities required.
The midplane of the corrugations is normal to the axis of the ring. The
corrugations may be
formed by rolling, pressing, or other similar means so that they are uniform.
It is desirable to form the
corrugations in a pattern such as the ring that will be approximately stress-
free at the diameter at
which it will be molded and used. The freedom from large locked-in stresses
will ensure that the ring
will remain substantially planar during molding, rather than becoming conical
or otherwise distorting as
a consequence of buckling.
Figure 1 B illustrates another embodiment of an antiextrusion device 20.
Antiextrusion device
20, like the antiextrusion device 10 of Figure 1A, is constructed of a
corrugated rigid material, such as
a thin metallic strip. The planar ring of Figure 1A is a degenerate of the
conical ring (i.e., having a 900
angle between the cone axis and the generating ray of the cone. The
antiextrusion device 20 is
formed in substantially a right frusto-conical ring pattern having an outer
conical side 22 and an inner
conical side 24, where the angle between the axis of the cone and its sides is
typically 45 to 900.
Antiextrusion devices having right frusto-conical ring patterns provide the
desirable reduced seal
circumferential stiffness and can offer comparatively reduced elastomer-to-
ring bond stress. Although
conical antiextrusion devices are somewhat more complex to mold than planar
ones, the use of
conical ring patterns is not otherwise precluded.
The corrugations provide significant increases in bending stiffness normal to
the midplane of
the corrugations when compared to the stiffness of a flat strip of the source
material. Simultaneously
the corrugations markedly decrease the circumferential stiffness of the ring,
so that resistance to
changes in the diameter of the overall antiextrusion device 10 are
significantly smaller when compared
to an uncorrugated ring with the same material thickness.
Figure 3A shows an annular elastomeric sealing unit 36 in which the annular
seal 32 is
bonded to a first and second metallic end rings 33 and 35. This sealing unit
is further described in co-
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pending patent application entitled "Seal Unit and Its Installation." Figure
3B is a perspective view of
the sealing unit 36 where the elastomeric seal 32 and end rings 33 and 35 have
been partially cut
away to show the placement of the antiextrusion device 10 within the seal. The
antiextrusion device
is totally embedded in and bonded to the elastomeric seal 32.
5 Figure 4A shows another embodiment of an annular elastomeric sealing unit 46
in which the
annular seal 42 is bonded to first and second metallic end rings 43 and 45.
The antiextrusion device
10 is integrally molded into and bonded to an elastomeric seal 42 suitable for
use with the large gaps
commonly found in pipeline repair clamps. One or more antiextrusion devices 10
can be molded into
the elastomeric matrix of a seal 42 on the low pressure side of the seal, as
shown in detail to the left,
10 low pressure side of seal 42 in Figure 4A.
Figure 4B shows a similar annular elastomeric sealing unit 56 in which the
circumferential seal
52 is bonded to first and second metallic end rings 53 and 55. The corrugated
conical antiextrusion
device 20 is integrally molded into and bonded to an elastomeric seal 52 with
its conical axis
substantially concentric with the axis of the annular seal 52. The corrugated
wave crests run parallel
to the conical generating rays, with the wave pattern of the corrugations
being uniform and regular.
Typical wave profile patterns would be either substantially sinusoidal,
rectangular, or trapezoidal.
The antiextrusion device 20 of Figure 4B is embedded such that the midplane of
the
corrugations of the device 20 is at an angle of 45 to 135 to the bore
surface 51 and axis of the
second end ring 55. One or more antiextrusion devices 20 can be molded into
the elastomeric matrix
of the seal 52 on the low pressure side of the seal as shown in Figure 4B.
Figure 4C shows a
perspective view of the antiextrusion device 20 embedded in the seal 52 where
the elastomeric seal
52 has been partially cut away to show the placement of the antiextrusion
device 20 within the seal.
The outer conical side 22 of the device 20 is directed toward the low pressure
side of the seal 52.
The particular configuration of the seals shown in Figures 3A, 4A and 4B is a
novel
unidirectional type which is axially tensioned during installation and then
relaxed to seal against a
cylindrical surface. The type of seal shown in Figures 3A, 4A and 4B works in
a female annular recess
and seals against a male plug. The elastomeric seal elements 42 and 52 are
bonded to static seal
ends 43 and 53 on their low pressure sides and to first and second movable
seal ends 45 and 55 on
their high pressure sides to form sealing units 46 and 56 respectively. To
assist in maintaining a good
connection between the elastomer of seals 42 and 52 and static seal ends 43
and 53 and movable
seal ends 45 and 55, undercut face grooves 44 and 54 with rounded edges are
provided in on the
inside traverse faces of ends 43 and 53 and 45 and 55.
The inner diameter of the antiextrusion device or antiextrusion ring 10 is
recessed slightly from
the inner diameter of the elastomeric seal 42 so that it is covered on all
sides and bonded to the
elastomeric matrix. This provision of coverage of the antiextrusion device 10
by elastomer protects
both the material of the antiextrusion element and the elastomer-to-
antiextrusion element bond from
attack by the fluids to be sealed, while also protecting any comating seal
surface from contact damage
from the antiextrusion element.
One or more of the antiextrusion rings 10 can be molded into elastomeric seal
42 with
separations in the axial direction of approximately twice the corrugation wave
height or more to further
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enhance extrusion resistance. Also, one or more antiextrusion rings 10 can be
used on both sides of
a bi-directional seal so that antiextrusion resistance is available for both
pressure directions. Radial
distortions of the elastomer of the seal element 42 are not strongly resisted
by the antiextrusion ring
10, so the seal unit 42 is readily conformable to varying diameters,
imperfections, and ovalities of a
comating pipe or mandrel. Yet because the antiextrusion ring 10 is essentially
anchored into the
matrix of the elastomer at its outer diameter, the antiextrusion ring 10
strongly resists bending out of its
plane and extrusion of the relatively unsupported portion of the elastomeric
seal spanning the seal gap
is strongly resisted by the beam strength of the embedded antiextrusion ring.
The wave crests of the corrugations runs radially for a planar annular
antiextrusion device 10.
The wave profile of the corrugations of antiextrusion ring 10 at a given
radius may be sinusoidal or flat
folded plate segments or another suitable, repetitive profile; the ring wave
height may be made greater
for the smaller radius portion of the ring to facilitate the fabrication of
the ring from straight flat strip
material. The wave profile shown in Figures 1 and 2 is composed of flat
segments with radiused
intersections for reductions of stress risers at the corners. This type of
corrugation has been
commonly used in steel fabrication to increase both bending stiffness and
bonding strength in steel
sheets. For the antiextrusion ring 10, the strength and stiffness are much
enhanced over that of flat
material for bending about a tangential local axis normal to the wave crests.
Simultaneously, the compressive stiffness of the corrugations in the
circumferential direction is
much reduced from flat material. Since the resistance of the ring to diameter
change is directly
controlled by this circumferential stiffness, the corrugated ring 10 may be
changed appreciably in
diameter without significant resistive forces. Further, the diameter of
corrugated ring 10 may be
changed over a much larger range without experiencing permanent deformations
than would be the
case for planar, non-corrugated material. Diameter changes of antiextrusion
ring 10 are
accommodated by relatively low stress bending and twisting of the
corrugations.
In Figure 4A, an annular female sealing unit 46 is molded with one or more of
the
antiextrusion rings 10 molded integrally within the elastomeric seal 42 in an
axially-spaced array on
the low pressure side of the seal. The elastomeric seal 42 will be distorted
somewhat from its
unstressed, molded condition when released from its tensioned installation
condition to assume its
presqueezed but unpressurized position against the surface of a pipe. Further
distortion from
pressure biasing and retained pressure will occur as pressure against the seal
increases above its
zero initial value during installation.
The outer diameter region of embedded antiextrusion rings 10 is well anchored
in the
elastomer matrix in a region where there is not much distortion of the
elastomer. Thus, although the
elastomer will tend to distort into the gap to be sealed, the level of axial
distortion of the elastomer
adjacent the pipe will be strongly limited by the radial beam strength and
stiffness of the corrugated
disks of the integral antiextrusion rings 10. The radial movement of the
elastomer is not strongly
resisted by the antiextrusion rings 10, so that the rings will move with
minimal resistance radially
inwardly to minimize the unsupported portion of the elastomer in the extrusion
gap.
The bond of the elastomer of seal 42 to well anchored antiextrusion ring 10
aids in preventing
excessive distortion of the elastomer into the seal gap on the low pressure
side. Both the stability and
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relatively low stress levels of the elastomer matrix around the outer diameter
end of antiextrusion ring
and the beam strength and stiffness of ring 10 help to maintain the inner
diameter region of the ring
in a stable position, thereby providing substantial support to the elastomer
adjacent the seal gap and
minimizing distortion and creep tendencies of the elastomer in that region. In
the event of elastomer
5 volume change due to interaction with the fluids around the seal 42 or
thermal expansion effects, ring
10 is able to flex to accommodate the elastomer distortions without
overstressing while still providing
substantial support to the elastomer adjacent the seal gap.
Figures 5 and 6 show a second embodiment of this invention suitable for use
with linear seals,
such as those shown as longitudinal seals in the split pipeline repair clamp
of Sanders, et al. U.S.
10 Patent 5,437,489. Figure 5 shows a view along the midplane of a corrugated
antiextrusion strip 100,
while Figure 6 shows a view of the same strip 100 normal to the midplane of
the corrugation waves.
The corrugations of rigid antiextrusion strip 100 are regular in profile and
are formed by rolling or
pressing or other suitable means.
Figures 7A and 7B show the antiextrusion strip 100 of Figures 5 and 6 molded
into the matrix
of a passive linear elastomeric seal 102. The term 'passive' indicates that
the seal 102 has no means
provided for adjusting its presqueeze other than bringing the seal closer to
or farther from the surface
against which it will seal. The cross-section of linear elastomeric seal 102
is basically rectangular with
the two corners 104 which will be inserted into a seal groove typically
radiused. The other two corners
may also be radiused. The length of the elastomeric seal 102 is slightly more
than that of
antiextrusion strip 100 to ensure full embedment.
Antiextrusion strip 100 is covered on all sides by elastomer for corrosion
protection and to
minimize any possible deterioration of the bond between the elastomer and the
strip. Antiextrusion
strip 100 is positioned closer to the low-pressure side of elastomeric seal
102 than it is to the high-
pressure side. Proportions may vary somewhat, depending on the stiffness of
the elastomer,
maximum pressure, expected seal gap range, and the like. Typically the ratio
of the height normal to
the comating surface to the width parallel to the comating surface of the seal
102 will range from about
0.2 to about 2Ø The width of the antiextrusion device will range from about
0.75 to about 0.90 times
the height of the seal 102. Approximate proportions for a typical seal vary.
For example, the width of
a seal may be approximately 1 inch and the height of the seal about 1.25
inches with an embedded
corrugated strip being about 1 inch wide and about 0.024 inch thick with
corrugations 0.25 inch from
peak-to-peak with a wavelength of 0.5 inch. The strip would be covered with a
minimum of
approximately 0.063 inch to 0.188 inch of elastomer.
In Figure 7A, the antiextrusion strip 100 is embedded such that the midplane
of the
corrugations of strip 100 is normal to the comating surface 106 of the seal
102. In Figure 7B, the
antiextrusion strip 100 is embedded such that the strip 100 is canted to
reduce the bond stress under
presqueeze and pressure between the elastomeric matrix of the seal 102 and the
antiextrusion strip
100. The antiextrusion strip 100 is embedded in the elastomeric matrix so that
the midplane of the
corrugations of strip 100 is at an angle 0 to the comating surface 106 of seal
102. Angle 0 preferably
ranges between 45 degrees and 135 degrees.
WO 01/63153 CA 02404469 2002-09-25 pCT/US01/05411
Figure 8 shows the linear elastomeric seal 102 of Figure 7 positioned into a
seal groove 105
such as would be used in the longitudinal seal groove of a split pipeline
repair clamp. The groove 105
is provided in face 106 of the carrier body 108, with its throat narrower than
the seal width to provide a
close fit between seal 102 and the inner portion of the groove 105 so that
seal retention is ensured.
The depth of groove 105 is less than the height of the cross-section of seal
102 so that sufficient seal
protrusion will exist in order to ensure adequate presqueeze, even with large
seal gaps. The low
pressure side 109 of groove 105 is inclined towards the high pressure side 110
at its outer end, while
the inner groove side 111 is parallel to the face 106 and the surface against
which the seal will be
presqueezed. The high pressure side 110 of groove 105 is normal to the face
106 and shorter than
the low pressure side depth of groove 105. Groove relief face 112 is parallel
to face 106. Groove
relief face 112 is also closer to inner groove side 111 than is face 106.
Relief volume for absorbing the
elastomer displaced volume when the seal gap is reduced or varied is provided
by the increased
separation relative to face 106 of groove relief face 112 from the surface
against which elastomeric
seal 102 will be presqueezed. All groove corners are radiused in order to
avoid elastomer tearing or
shearing.
Optionally, seal 102 may have elements having high frictional coefficients
integrally bonded
into the elastomeric matrix of the seal on the comating surface. For example,
silica flour may be
incorporated onto the comating surface of seal 102. An increase in friction
between the comating
surfaces may increase the resistance of the seal to creep.
Figure 9 shows the elastomeric seal 102 in groove 105 of Figure 8 sealing
against the
adjacent comating surface 114 of body 116. Sufficient presqueeze on
elastomeric seal 102 has been
provided by bringing comating surface 114 close enough to obtain a suitably
high interface pressure
between seal 102 and comating surface 114. The elastomer of seal 102 has
distorted into the high
pressure side relief volume provided between relief face 112 and comating
surface 114 due to the
presqueeze compression. The presence of antiextrusion strip 100 adjacent low
pressure side 109 of
groove 105 and firmly embedded in the elastomer of seal 102 which is in turn
entrapped in groove 105
ensures that antiextrusion strip is well anchored to resist forces which would
tend to displace its end
adjacent comating surface 114.
The major advantage of this invention for linear seals accrues primarily from
enhancement, by
means of providing corrugated construction, of structural strength and
stiffness of the antiextrusion
strip for resisting pressure loads normal to the midplane of the corrugations.
The same advantage
applies generally to face seals and other seals of more complex pattern. A
linear seal is essentially a
segment of a circular face seal of infinite radius. The use of the linear
antiextrusion strip is particularly
advantageous for large gap situations and high pressures, both of which occur
in pipeline repair
clamps.
The basic advantages of this invention for annular seals accrue primarily
from: a)
enhancement, by means of providing corrugated construction, of structural
strength and stiffness of
the antiextrusion ring for resisting pressure loads normal to or with vector
components normal to the
midplane of the corrugations, and b) simultaneous reduction of circumferential
ring stiffness through
provision of the same corrugations so that large diametric changes can be
accommodated without
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WO 01/63153 PCT/US01/05411
either high resistance or overstress and permanent distortion of the ring. The
corrugated integrally
molded antiextrusion ring can be used with any large gap seal, including the
conventional active and
passive types.
In all cases, the embedded corrugated antiextrusion device dramatically
increases the
extrusion resistance of the seal for large gaps without markedly decreasing
the desirable
conformability of the seal to the comating seal surface. Accordingly, these
seals provide low
resistance to distortion normal to the comating seal surface in response to
both tensioning and
pressure biasing. However, the integral corrugated antiextrusion ring can
render an otherwise
marginal conventional passive or active seal satisfactory for higher
pressures. The improved stiffness
properties of the annular seal antiextrusion ring for resisting bending and
thereby minimizing elastomer
extrusion into the seal gap markedly improve the performance of seals for
large gaps and high
pressures. At the same time, the corrugations appreciably enhance the radial
flexibility of the
antiextrusion ring by changing its mode of resistance from direct stress
(tension or compression) to the
much less stiff combined bending and twisting mode of the corrugated disk.
Although the flexibility of
the integrally molded corrugated antiextrusion insert for motion normal to the
comating seal surface is
unimportant for linear or near linear seal configurations, the corrugations
still provide an enhanced
bending stiffness for resisting extrusion for linear or near linear seals.
It is readily understood that the corrugation patterns of this invention, the
seal types, and the
positioning and number of the antiextrusion members in a seal may be varied to
meet different
demands. For example, the antiextrusion elements can be adapted readily to
both semicircular and
circular annular seals, linear or near linear or irregularly shaped seals,
stretched or unstretched seals,
and both male and female annular seals. The material for the antiextrusion
member may likewise be
nonmetallic or of composite construction and the positioning of the
antiextrusion device(s) may be
varied as necessary and practical. The corrugated antiextrusion means
described herein offers a
practical, easily applied, and economical solution for large gap seals,
particularly for high pressure
situations.
Having described several embodiments of seals with embedded antiextrusion
devices, it is
believed that other modifications, variations, and changes will be suggested
to those skilled in the art
in view of the description set forth above. It is therefore to be understood
that all such variations,
modifications, and changes are believed to fall within the scope of the
invention as defined in the
appended claims.
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