Note: Descriptions are shown in the official language in which they were submitted.
CA 02548828 2006-05-29
OPTICAL WAVEGUIDE FEEDTHROUGH ASSEMBLY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to feedthroughs for optical waveguides, and more
particularly, to hermetically sealed feedthroughs suitable for use in high
pressure, high
temperature, and/or other harsh environments.
Description of the Related Art
In many industries and applications, there is a need to have small diameter
wires or
optical waveguides penetrate a wall, bulkhead, or other feedthrough member
wherein a
relatively high fluid or gas differential pressure exists across the
feedthrough member. In
addition, one or both sides of the feedthrough member may be subjected to
relatively high
temperatures and other harsh environmental conditions, such as corrosive or
volatile gas,
fluids and other materials.
In the case of electrical systems, these devices, called feedthroughs or
penetrators,
typically are constructed by using metal 'pins' exhibiting high conductivity
and a low
thermal coefficient of expansion. The pins are concentrically located within a
hole in a
housing, and the resulting annular space is filled with a suitable sealing
glass or other
material. Critical to the success of such seals is the selection of the metal
housing, sealing
glass, and electrical pin to ensure completion of a compression seal around
the ductile
inclusion (pin). As the operating temperature range of the feedthrough
increases, the control
of thermal expansion rates becomes increasingly important in order to avoid
failure of the
feedthrough by excessive thermal stress at the interface layers between the
various materials.
This technology is relatively mature for electrical feedthroughs, and
commercial devices are
readily available that meet service temperatures in excess of 200 C.
More recently, with the introduction of optical sensors, particularly sensors
for use in
oil and gas exploration and production and for life in harsh industrial
environments, a need
has emerged for a bulkhead feedthrough that can seal an optical fiber at high
pressures of
- 1 -
CA 02548828 2010-06-07
20,000 psi and above, and high temperatures of 150 C to 300 C, with a service
life
of 5 to 20 years. An exemplary sensing assembly for use in harsh environments
is disclosed
in U.S. Patent No. 6,439,055, which issued on August 27, 2002, entitled
"Pressure Sensor
Assembly Structure To Insulate A Pressure Sensing Device From Harsh
Environments",
which is assigned to the Assignee of the present application.
There are several problems associated with constructing such an optical fiber
feedthrough. One of these problems is the susceptibility of the glass fiber to
damage and
breakage. This is due to the flexibility of the small size fiber, the brittle
nature of the glass
material, and the typical presence of a significant stress concentration at
the point where the
fiber enters and exits the feedthrough. Attempts to use a sealing glass, such
as that used
with electrical feedthroughs, have had problems of this nature due to the high
stress
concentration at the fiber-to-sealing glass interface.
Another problem with sealing an optical fiber, as opposed to sealing a
conductive
metal "pin" in an electrical feedthrough, is that the fused silica material of
which the optical
fiber is made, has an extremely low thermal expansion rate. Compared to most
engineering
materials, including metals, sealing glasses, as well as the metal pins
typically used in
electrical feedthroughs, the coefficient of thermal expansion of the optical
fiber is essentially
zero. This greatly increases the thermal stress problem at the glass-to-
sealing material
interface.
One technique used to produce optical fiber feedthroughs is the use of a
sealed
window with an input and an output lensing system. In this technique, the
optical fiber must
be terminated on each side of a pressure-sealed window, thus allowing the
light to pass from
the fiber into a lens, through the window, into another lens, and finally into
the second fiber.
The disadvantages associated with this system include the non-continuous fiber
path, the
need to provide two fiber terminations with mode matching optics, thus
increasing
manufacturing complexity and increasing the light attenuation associated with
these
features.
- 2 -
CA 02548828 2015-04-07
It is often desirable to mount fiber optic based sensors in harsh environments
that are
environmentally separated from other environments by physical bulkheads. An
exemplary
such fiber optic based sensor is disclosed in co-pending U.S. Patent
Application Serial No.
09/205,944, entitled "Tube-Encased Fiber Grating Pressure Sensor" to T. J.
Bailey et al.,
which is assigned to the Assignee of the present invention. This exemplary
optical sensor is
encased within a tube and certain embodiments are disclosed wherein the sensor
is
suspended within a fluid. The sensor may be used in a harsh environment, such
as where the
sensor is subjected to substantial levels of pressure, temperature, shock
and/or vibration. In
certain environments, such sensors are subjected to continuous temperatures in
the range of
150 C to 250 C, shock levels in excess of 100Gs, and vibration levels of 5G
RMS at typical
frequencies between about 10 Hz and 2000 Hz and pressures of about 15 kpsi or
higher.
However, as discussed above, the harsh environments where the sensors are
located
generally must be isolated by sealed physical barriers from other proximate
environments
through which the optical fiber communication link of the sensor must pass. It
is important
to seal the bulkhead around the optical fiber to prevent adjacent environments
in the sensor
from contaminating the optical fiber communication link. If the optical
communication
fiber is compromised by contamination from an adjacent harsh sensor
environment, the
optical fiber and all sensors to which it is connected are likely to become
ineffective.
There is a need therefore, for an optical waveguide feedthrough assembly
capable of
operating in relative high temperature and high pressure environments.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide an optical waveguide feedthrough
assembly, and a method of making such an assembly, which overcomes one or more
of the
above-described drawbacks and disadvantages of the prior art, and is capable
of relatively
long-lasting operation at relatively high pressures and/or temperatures.
An optical waveguide feedthrough assembly passes at least one optical
waveguide
through a bulk head, a sensor wall, or other feedthrough member. The optical
waveguide
- 3 -
CA 02548828 2006-05-29
feedthrough assembly comprises a cane-based optical waveguide that forms a
glass plug
sealingly disposed in a feedthrough housing. For some embodiments, the optical
waveguide
includes a tapered surface biased against a seal seat formed in the housing.
The feedthrough
assembly can include an annular gold gasket member disposed between the
conical glass
surface and the metal seal seat. The feedthrough assembly can further include
a backup seal.
The backup seal comprises an elastomeric annular member disposed between the
glass plug
and the housing. The backup seal may be energized by a fluid pressure in the
housing. The
feedthrough assembly is operable in high temperature and high pressure
environments.
The conical taper of the glass waveguide surface is designed to be
complementary to
the bulkhead seal seat. The role of the gold gasket is to accommodate
practical
manufacturing tolerances on the surface finishes of the glass plug and the
bulkhead seal seat.
Furthermore, the role of the backup elastomeric seal is to accommodate
practical
manufacturing tolerances on the shape functions the glass plug and the
bulkhead seal seat.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present
invention are
attained and can be understood in detail, a more particular description of the
invention,
briefly summarized above, may be had by reference to the embodiments thereof
which are
illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of this invention and are therefore not to be considered limiting
of its scope,
for the invention may admit to other equally effective embodiments.
Figure 1 illustrates a cross section view of an optical waveguide feedthrough
assembly.
Figure 2 illustrates a cross section view of an optical waveguide feedthrough
assembly having diagnostic sensors disposed therein.
Figures 3-5 illustrate graphs of signals received from the diagnostic sensors
where
the feedthrough assembly is at a fixed temperature and different pressure for
each graph.
- 4 -
CA 02548828 2006-05-29
Figures 6-8 illustrate graphs of signals received from the diagnostic sensors
where
the feedthrough assembly is at a fixed pressure and different temperature for
each graph.
Figure 9 illustrates a cross section view of an optical waveguide feedthrough
assembly that provides bi-directional seal performance.
Figure 10 illustrates a cross sectional view of an optical waveguide
feedthrough
assembly that includes a compression seal element.
Figure 11 illustrates the optical waveguide feedthrough assembly shown in
Figure 10
after compression of the compression seal element.
Figure 12 illustrates a cross section view of another optical waveguide
feedthrough
assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Epoxy-free optical fiber feedthrough assemblies applicable for use in high
temperature, high pressure environments are provided. In one embodiment, a
feedthrough
assembly includes a glass plug disposed in a recess of a feedthrough housing.
The glass
plug is preferably a large-diameter, cane-based, waveguide adapted to seal the
recess in the
housing and provide optical communication through the housing. All embodiments
described herein provide for sealing with respect to the housing at or around
the glass plug
of an optical waveguide element passing through the housing.
As used herein, "optical fiber," "glass plug" and the more general term
"optical
waveguide" refer to any of a number of different devices that are currently
known or later
become known for transmitting optical signals along a desired pathway. For
example, each
of these terms can refer to single mode, multi-mode, birefringent,
polarization maintaining,
polarizing, multi-core or multi-cladding optical waveguides, or flat or planar
waveguides.
The optical waveguides may be made of any glass, e.g., silica, phosphate
glass, or other
glasses, or made of glass and plastic, or solely plastic. For high temperature
applications,
optical waveguides made of a glass material is desirable. Furthermore, any of
the optical
waveguides can be partially or completely coated with a gettering agent and/or
a blocking
- 5 -
CA 02548828 2015-04-07
agent (such as gold) to provide a hydrogen barrier that protects the
waveguide. In
addition, the feedthrough assemblies can include a single such optical
waveguide or may
include a plurality of such optical waveguides.
AN EXEMPLARY FEEDTHROUGH ASSEMBLY
Figure 1 shows a cross section view of an optical fiber feedthrough assembly
100
that includes a front housing 10 coupled to a back housing 12. An optical
waveguide
element 14 passes through a passageway 16 common to both housings 10, 12. The
passageway 16 is defined by bores extending across the housings 10, 12. The
optical
waveguide element 14 includes a glass plug 18 defining a large-diameter, cane-
based,
optical waveguide preferably having an outer diameter of about 3 millimeters
(mm) or
greater. The glass plug 18 can have appropriate core and cladding dimensions
and ratios to
provide the desired outer large-diameter.
For some embodiments, first and second fiber pigtails 19, 20 extend from each
end
of the glass plug 18. Each of the pigtails 19, 20 preferably include an
optical waveguide
such as an optical fiber 26 encased or embedded in a carrier 28 or larger
diameter glass
structure allowing the fiber 26 to be optically coupled to the glass plug 18.
U.S. Patent
Application Serial No. 10/755,722, entitled "Low-Loss Large-Diameter Pigtail",
describes
exemplary pigtails that can facilitate subsequent optical connection of the
fiber 26 to other
fibers, connectors, or other optical components by suitable splicing
techniques known in the
art. Further, U.S. Application Serial No. 10/755,708, entitled "Large Diameter
Optical
Waveguide Splice," describes a large-diameter splice suitable for splicing the
fiber pigtails
19, 20 to the glass plug 18. For some embodiments, the glass plug 18 can be
spliced to or
otherwise optically coupled with fibers in optical communication with each end
of the glass
plug 18 by other techniques and methods.
Sealing of the optical waveguide element 14 with respect to the front housing
10
occurs at and/or around the glass plug 18 to enable isolation of fluid
pressure in
communication with a first end 22 of the passageway 16 from fluid pressure in
communication with a second end 24 of the passageway 16. This sealing of the
glass plug
- 6 -
CA 02548828 2006-05-29
, =
18 with respect to the front housing 10 provides the feedthrough capabilities
of the
feedthrough assembly 100. In the embodiment shown in Figure 1, the glass plug
18 has a
cone shaped tapered surface 50 for seating against a complimentary tapered
seat 51 of the
front housing 10. Engagement between the tapered surface 50 and the
complimentary
tapered seat 51 that is located along the passageway 16 forms a seal that
seals off fluid
communication through the passageway 16. The glass plug 18 can be machined to
provide
the cone shaped tapered surface 50. Additionally, the glass plug 18 is
preferably biased
against the tapered seat 51 using a mechanical preload.
A recess 30 formed in one end of the front housing 10 aligns with a
corresponding
recess 31 in one end of the back housing 12 where the housings 10, 12 are
coupled together.
Preferably, the front housing 10 is welded to the back housing 12 along mated
features
thereof. The housings 10, 12 preferably enclose the glass plug 18, a biasing
member such as
a first stack of Belleville washers 34, and a plunger 32, which are all
disposed within the
recesses 30, 31.
The first stack of Belleville washers 34 supply the mechanical preload by
pressing
the plunger 32 onto an opposite end of the glass plug 18 from the tapered
surface 50. Since
the plunger 32 is moveable with the glass plug 18, this pressing of the
plunger 32 develops a
force to bias the glass plug 18 onto the tapered seat 51 of the front housing
10 located along
the passageway 16 that passes through the front housing 10. Transfer of force
from the
plunger 32 to the glass plug 18 can occur directly via an interface 54 between
the two, which
can include mating conical surfaces. The first stack of Belleville washers 34
compress
between a base shoulder 44 of the recess 31 in the back housing 12 and an
outward shoulder
46 of the plunger 32 upon make-up of the front housing 10 to the back housing
12. Once the
back housing 12 is welded or otherwise attached to the front housing 10 in
order to keep the
front and back housings 10, 12 connected, the first stack of Belleville
washers 34 maintains
the compression that supplies force acting against the plunger 32.
In some embodiments, the feed through assembly 100 further includes a gasket
member 52 disposed between the tapered seat 51 and the tapered surface 50 of
the glass plug
18. As shown in Figure 1, the gasket member 52 comprises an annular gasket.
The gasket
- 7 -
CA 02548828 2006-05-29
member 52 may be a gold foil that is shaped to complement the tapered surface
50 and the
tapered seat 51. The gasket member 52 deforms sufficiently to accommodate
imperfections
on the tapered surface 50 and/or the tapered seat 51, thereby completing the
seal and
reducing stress between contacting surfaces due to any imperfections on the
surfaces. Gold
is preferred because of its ability to withstand high temperature, its
ductility and its inert,
non-reactive, non-corrosive nature.
However, other materials possessing these
characteristics may also be suitable, including aluminum, lead, indium,
polyetheretherketone
("PEEKTm"), polyimide, other suitable polymers, and combinations thereof.
An additional gasket member (not shown) may be disposed between the interface
54
of the glass plug 18 and the plunger 32 for some embodiments to reduce the
surface stress
that may occur between these two components. In further embodiments, a layer
of gold or
other suitable material is deposited on the contact surfaces as an alternative
to using the
gasket member 52. For example, the gold may be deposited using chemical vapor
deposition, physical vapor deposition, plating, or combinations thereof to
reduce surface
stress and maximize the seal performance. Other embodiments utilize the gasket
member 52
punched from sheets of a gasket material.
For some embodiments, the housings 10, 12 additionally enclose a cup-shaped
backstop sleeve 36, a second stack of Belleville washers 38, a perforated
washer 40, and a
centering element 42 that are all disposed within the recesses 30, 31. An
outward shoulder
56 of the backstop sleeve 36 is trapped by the end of the front housing 10 and
an inward
shoulder 57 along the recess 31 in the back housing 12. Contact upon
sandwiching of the
shoulder 56 of the backstop sleeve 36 provides the point at which the housings
10, 12 are
fully mated and can be secured together. Clearance is provided such that the
end of the back
housing 12 does not bottom out prior to the housings 10, 12 being fully mated.
The centering element 42 includes an elastomeric sealing component disposed
between the glass plug 18 and the front housing 10 that can act as a back-up
seal in addition
to facilitating alignment of the glass plug 18 with respect to the seat 51.
Although the
centering element 42 is described as providing a back up seal to the tapered
surface 50 of the
glass plug 18 seated with the gasket member 52 on the complimentary tapered
seat 51, the
- 8 -
CA 02548828 2006-05-29
centering element 42 can be omitted or used independently to seal off the
passageway 16
through the housings 10, 12 in other embodiments.
In some applications, the pressure in the recesses 30, 31 entering from the
second
end 24 of the passageway 16 is higher than the pressure entering from the
first end 22 of the
passageway 16. This pressure differential advantageously causes the centering
element 42
to deform and press against the wall of the recess 30 and the wall of the
glass plug 18,
thereby creating a pressure energized seal. In some embodiments, one or more
holes or
annular channels 43 are formed on the outer surface of the high pressure side
of the
centering element 42. These holes or channels 43 facilitate the deformation of
the centering
element 42 and the formation of the seal between the centering element 42 and
the walls of
the recess 30 and the glass plug 18. Additionally, the perforated washer 40
enables
pressurized fluid to fill the centering element 42 for providing the energized
seal.
Preferably, force transferred through the perforated washer 40 biases the
centering
element 42 into the recess 30. The second stack of Belleville washers 38
pressed by the
backstop sleeve 36 supplies the preloading force to the perforated washer 40.
The second
stack of Belleville washers 38 allow a maximum pressure force to act on the
centering
element 42 such that pressure of the centering element 42 against the wall of
the glass plug
18 does not override force being put on the glass plug 18 to press the tapered
surface 50
against the seat 51.
Embodiments of the feedthrough assembly 100 are capable of performing in
temperature environments of between -50 C and 300 C. Additionally, the
feedthrough
assembly 100 is capable of withstanding pressure up to about 30 kpsi.
EMBEDDING DIAGNOSTIC SENSORS
Figure 2 illustrates a cross section view of an optical waveguide feedthrough
assembly 200 that operates similar to the feedthrough assembly 100 shown in
Figure 1.
However, the feedthrough assembly 200 includes first and second diagnostic
sensors 201,
202 disposed within a glass plug 218. The diagnostic sensors 201, 202 can
include any
optical sensing element, such as fiber Bragg gratings, capable of reflecting
or transmitting an
- 9 -
CA 02548828 2006-05-29
=
optical signal in response to a parameter being measured. The first diagnostic
sensor 201 is
disposed within the glass plug 218 proximate an interface 254 where a plunger
232 pushes
on the glass plug 218. The second diagnostic sensor 202 is disposed within the
glass plug
218 proximate where a tapered surface 250 of the glass plug 218 mates with a
seat 251.
Preferably, each of the diagnostic sensors 201, 202 span a length of the glass
plug 218
across the respective feature that the sensor is proximate.
Interpreting the signals generated by the sensors 201, 202, such as by use of
a
suitable algorithm or comparison to a calibration, enables monitoring of
temperature and/or
pressure. This detection ability allows real-time monitoring of the state of
the feedthrough
assembly 200. Information derived from the sensors 201, 202 can be beneficial
both during
fabrication of the feedthrough assembly 200 and during use thereof. For
diagnostic
purposes, signals received from the second sensor 202 can be monitored to
identify when
and/or if proper contact of the tapered surface 250 with the seat 251 occurs
to ensure that
sealing is established or maintained. Further, monitoring one or both the
sensors 201, 202
can ensure that excess force that might break the glass plug 18 is not applied
to the glass
plug 18 in embodiments where the amount of force can be controlled. Monitoring
signals
received from the first sensor 201 can detect the presence and condition of
hydrostatic loads
from surrounding fluid since these hydrostatic loads dominate the response of
the first
sensor 201. When the feedthrough assembly 200 is part of a wellhead outlet of
an oil/gas
well, the sensors 201, 202 can be used to detect pressure increases and set an
alarm
indicating that seals have been breached in the well.
Figures 3-5 illustrate graphs of signals received from the diagnostic sensors
201, 202
where the feedthrough assembly 200 is at a fixed temperature but has different
pressures
introduced at end 224 for each graph. In all of the graphs herein, first
sensor responses 301
correspond to signals received from the first sensor 201 while second sensor
responses 302
correspond to signals received from the second sensor 202. In Figure 3, an
initial distortion
or spreading of the second sensor response 302 visible specifically as a
spectral chirp 303,
providing positive feedback that preload of the glass plug 18 at the tapered
surface 250
against the seat 251 has been established.
-10-
CA 02548828 2006-05-29
As visible in Figures 4 and 5, this distortion in the second sensor responses
302
grows relative to pressure due to non-uniform seal loads. However, the first
sensor
responses 301 show little change as pressure increases since uniform
hydrostatic pressure
dominates the first sensor 201. Additionally, the first sensor responses 301
provide an
indication of a thermo-mechanical state of the housing of the feedthrough
assembly 200 and
a small pressure driven change in the preload of the plug 232.
Figures 6-8 show graphs of signals received from the diagnostic sensors 201,
202
where the feedthrough assembly 200 is at a fixed pressure but is at a
different temperature
for each graph. The graphs show that as temperature increases both of the
responses 301,
302 shift in wavelength relative to the temperature increase in the same
direction. For
example, the peak at approximately 1534.5 nanometers (nm) in the first
responses 301 at 25
C shifts to approximately 1536.5 nm at 194 C. Other than small changes from
temperature
driven changes in the preloads, shapes of the responses 301, 302 do not change
with
temperature changes.
With reference to Figure 1, pressure entering the first end 22 of the
passageway 16
may be significantly higher than the pressure entering the second end 24 of
the passageway
16 in some applications. In this instance, if the higher pressure from the
first end 22 exceeds
a threshold value, then the seals formed by the seated tapered surface 50 of
the glass plug 18
and/or the centering element 42 may be unseated. Accordingly, non-epoxy
feedthrough
assemblies in some embodiments can be adapted to seal against pressure from
either side of
a glass plug.
A BI-DIRECTIONAL SEAL ASSEMBLY
Figure 9 shows an exemplary feedthrough assembly 900 having a bi-directional
pressurized seal assembly 930. A cone shaped glass plug 920 is disposed in a
recess 925 of
a feedthrough housing 910 formed by two body sections 911, 912. The body
sections 911,
912 can be coupled together using a weld or various other coupling
configurations. A bore
915 sized to accommodate portions of an optical waveguide element 922 on
either side of
the glass plug 920 extends through the feedthrough housing 910. A tapered seat
913 can be
formed on each body section 911, 912 for receiving the glass plug 920. Similar
to the
-11-
CA 02548828 2006-05-29
embodiment shown in Figure 1, a gasket member 945 such as an annular gold foil
can be
disposed between the glass plug 920 and the tapered seats 913 of the body
sections 911, 912.
The symmetrical configuration of tapered seats 913 in sections 911, 912
creates the primary
bidirectional seal design.
In one embodiment, a back-up bi-directional seal assembly 930 is disposed in
the
recess 925 to provide an additional seal against any leakage from either body
section 911,
912. The seal assembly 930 includes two cup-shaped, annular sealing elements
931, 932
and a positioning device 940 to maintain the sealing elements 931, 932 in
their respective
seal seats 941, 942. The sealing elements 931, 932 are positioned such that
their interior
portions are opposed to each other and the positioning device 940 may be
disposed in the
interior portions of the sealing elements 931, 932. The positioning device 940
may
comprise a preloaded spring to bias the sealing elements 931, 932 against
their respective
seal seats 941, 942, or against the body sections 911, 912. In one embodiment,
the sealing
elements 931, 932 are made of an elastomefic material. The sealing elements
931, 932 can
also comprise other suitable flexible materials capable of withstanding high
temperature and
high pressure.
In operation, if fluid leaks through the tapered surfaces between the glass
plug 920
and the first body section 911, then the fluid pressure forces the glass plug
920 against the
tapered seat in the body section 912 to activate the reverse direction seal.
The fluid pressure
will also act against the second sealing element 932, which is biased against
the second body
section 912. Particularly, the fluid pressure acts on the interior portion of
the second sealing
element 932 and urges sealing lips 934 of the second sealing element 932
outward, thereby
sealing off any fluid path between the second sealing element 932 and the
glass plug 920
and between the second sealing element 932 and the body section 911. In this
manner, the
leaked fluid is prevented from entering the bore of the second body section
912 because of
redundant seals.
Similarly, if fluid leaks through the tapered surfaces between the glass plug
920 and
the second body section 912, then the fluid pressure forces the glass plug 920
against the
tapered seat 913 in body section 911. The fluid pressure will also act against
the first
- 12-
CA 02548828 2006-05-29
sealing element 931 biased against the first body section 911. In this
respect, the fluid
pressure causes sealing lips 933 of the first sealing element 931 to sealingly
engage the glass
plug 920 and the body section 911. Thus, the leaked fluid is prevented from
entering the of
bore of the first body section 911 because of redundant seals.
FEEDTHROUGH ASSEMBLY WITH COMPRESSION BUSHING
Figure 10 illustrates a cross sectional view of an optical waveguide
feedthrough
assembly 500 that includes a housing 110, an externally threaded bushing 102,
a
compression driver bushing 104, a compression seal element 106, and a glass
plug 118
portion of an optical waveguide element that sealingly passes through the
housing 110. The
bushings 102, 104 and the seal element 106 are disposed adjacent to one
another in a recess
130 in the housing 110 and encircle a portion of the glass plug 118.
Specifically, the
externally threaded bushing 102 threads into a portion of the recess 130 in
the housing 110
defining mating internal threads. The seal element 106 is located next to the
driver bushing
104 and proximate an inward tapering cone 131 along the recess 130 in the
housing 110.
A seal can be established with the glass plug 118 with respect to the housing
110 by
driving the seal element 106 down the cone 131. To establish this seal,
rotation of the
threaded bushing 102 with respect to the housing 110 displaces the threaded
bushing 102
further into the recess 130 due to the threaded engagement between the
threaded bushing
102 and the housing 110. The driver bushing 104 in turn moves further into the
recess and
pushes the sealing element 106 toward the cone 131. One function of the driver
bushing 104
includes reducing torque transferred to the seal element 106 from the threaded
bushing 102.
Preferably, the glass plug 118 has a cone shaped tapered surface 150 for
seating
against a complimentary tapered seat 151 of the housing 110. The engagement
between the
tapered surface 150 and the complimentary tapered seat 151 can also or
alternatively seal off
fluid communication through the housing 110 around the glass plug 118 in a
redundant
manner. A gasket member 152 such as an annular gold foil can be disposed
between the
tapered surface 150 of the glass plug 118 and the tapered seat 151 of the
housing 110 to
reduce stress risers.
- 13-
CA 02548828 2006-05-29
Figure 11 illustrates the optical waveguide feedthrough assembly 500 after
compressing the seal element 106. The seal element 106 packs within an annulus
between
an exterior of the glass plug 118 and an interior of the housing 110 after
being driven down
the cone 131. Once packed in the annulus, the seal element 106 provides
sealing contact
against both the glass plug 118 and the housing 110. Examples of suitable
materials for the
seal element 106 include TEFLONTm, VESPELTM, polyimide, PEEKTM, ARLONTM, gold
or
other ductile metals for high temperature applications. During lower
temperature usage,
element 106 can be nylon, DELR1NTM or metal such as tin or lead. The driving
of the seal
element 106 can additionally move the glass plug 118 to force the tapered
surface 150 to
mate with the seat 151. The glass plug 118 is of sufficient diameter and
structural integrity
that the compression of the seal element 106 around the glass plug does not
disturb the
optical qualities thereof. The feedthrough assembly 500 is capable of sealing
the glass plug
118 with respect to the housing 110 regardless of which side of the housing
110 is exposed
to a higher pressure.
AN ADDITIONAL EXEMPLARY FEEDTHROUGH ASSEMBLY
Figure 12 shows a cross-section view of a feedthrough assembly 400 that
includes a
feedthrough housing 410 for retaining a glass plug 418. A recess 425 is formed
in one end
of the housing 410 to receive the glass plug 418. Preferably, the recess 425
has a
corresponding tapered seat 451 for receiving a cone shaped tapered surface 450
of the glass
plug 418. The glass plug 418 is preferably biased against the tapered seat 451
that is located
along a bore 416 that connects to the recess 425 and provides a passageway
through the
housing 410.
In one embodiment, a fitting 436 having an axial bore 437 extending
therethrough is
disposed between the glass plug 418 and a washer cap 412. One end of the
fitting 436 has a
surface that mates with the glass plug 418 and an outer diameter that is about
the same size
as the inner diameter of the recess 425. In this respect, the fitting 436
assists with
supporting the glass plug 418 in the recess 425. The other end of the fitting
436 has a neck
435 that connects to the washer cap 412. Particularly, a portion of the neck
435 fits in a hole
of the washer cap 412. The washer cap 412 may be attached to the feedthrough
housing 410
- 14-
CA 02548828 2006-05-29
by any manner known to a person of ordinary skill in the art, such as one or
more screws or
bolts. For example, bolts 438 (two of three are visible in Figure 12) may be
used to attach
the washer cap 412 to the feedthrough housing 410 via three screw holes 440
(only one is
visible in Figure 12) formed through the washer cap 412 and into the
feedthrough housing
410.
The inner portion of the washer cap 412 facing the feedthrough housing 410 has
a
cavity 431 for retaining a preload member such as a spring. In one example,
the preload
member is a Belleville washer stack 434. The washer stack 434 may be disposed
on the
neck 435 of the fitting 436 and between the washer cap 412 and an outward
shoulder 446
formed by a reduced diameter of the neck 435 of the fitting 436. In this
manner, the washer
stack 434 may exert a preloading force on the glass plug 418 to maintain a
seal between the
glass plug 418 and the tapered seat 451 of the feedthrough housing 410.
Similar to the
embodiments described above, a gasket member such as an annular gold foil (not
shown)
can be disposed between the glass plug 418 and the tapered seats 451 and/or
the glass plug
418 and the fitting 436.
The feedthrough assembly 400 may further include a centering element 442 to
act as
a back-up seal. The centering element 442 comprises an elastomeric sealing
component that
is disposed between the glass plug 418 and the feedthrough housing 410. A
pressure
differential across the glass plug 418 advantageously causes the centering
element 442 to
deform and press against the wall of the recess 425 and the wall of the glass
plug 418,
thereby creating a pressure energized seal. Although the centering element 442
is described
as providing a back up seal, the centering element 442 may be used
independently to seal off
the bore 416 of the feedthrough housing 410.
The invention heretofore can be used and has specific utility in applications
within
the oil and gas industry. Further, it is within the scope of the invention
that other
commercial embodiments/uses exist with one such universal sealing arrangement
shown in
the figures and adaptable for use in (by way of example and not limitation)
industrial,
chemical, energy, nuclear, structural, etc. While the foregoing is directed to
preferred
embodiments of the invention, other and further embodiments of the invention
may be
-15-
CA 02548828 2006-05-29
devised without departing from the basic scope thereof, and the scope thereof
is determined
by the claims that follow.
-16-
