System and method for sealing leaks in vessels

A system and method are disclosed for sealing leaks in electrical insulators and other equipment without the need for depressurizing that equipment. The system and method may be readily adapted to seal any joint, regardless of its configuration. In addition, while the system and method provide an effective and sure seal, the seal may be readily removed in order to change out the leaking component at a future date. A tubular seal is maneuvered into position to encircle the leaking joint. A reinforcing layer is applied over the seal. The seal is then filled with sealant under pressure. The seal isolates the sealant and its direct hydraulic pressure from the operating components to prevent the sealant from contacting those components, while simultaneously providing sufficient force against the leaking joint to stop the leak.

BACKGROUND OF THE INVENTION
 1Field of the Invention
 The present invention relates to systems and methods for sealing leaks.
 More particularly, the invention relates to a system and method for
 sealing leaks in vessels containing hazardous coolants, insulants, and
 other potentially harmful compounds.
 High voltage electrical equipment, such as large circuit breakers and
 transformers, include conductors that are typically encased in an
 insulator, also known as a bushing assembly, which comprises one or more
 sections of cylindrical porcelain pipe that surround the high voltage
 conductors. The sections of pipe define respective joints at the pipe
 interfaces which are sealed with compression seal o-rings and the like.
 The insulators are often filled with inert, non-conductive gasses and/or
 oils for cooling and insulating purposes. One such gas is sulfur
 hexafluoride (SF.sub.6).
 While SF.sub.6 is quite effective as an insulant, the gas also suffers from
 at least one significant shortcoming. It has been found that SF.sub.6, if
 it escapes from its containment and is released into the atmosphere,
 depletes the ozone layer. Therefore, the gas has been targeted by the
 Environmental Protection Agency (EPA), and strict regulations have been
 imposed on its use, both in the United States and throughout the world.
 Moreover, SF.sub.6 has recently become very expensive. Therefore, a leak
 is not only an environmental concern, but can also be very costly.
 Some high voltage electrical equipment, in particular transformers and some
 circuit breakers, utilize "transformer oil", which is a mineral oil that
 is an effective insulant and coolant for the electrical equipment.
 However, transformer oil also has drawbacks, one being that it degrades
 gaskets, o-rings, and seals, often causing them to leak. Transformer oil,
 if allowed to leak for continued periods of time, is potentially damaging
 to the environment as well.
 Others have attempted to solve the above-described leaks with various
 methods and devices. One proposed method was to simply ignore the leak
 until the electrical equipment could be taken off line, removed from the
 site, transported to a repair facility, and repaired by disassembling the
 bushing and replacing the leaking seal. Typically, the amount of time that
 elapsed before such action was taken was on the order of decades. Not only
 is this method very burdensome and expensive, but with increasing
 environmental concerns and strict regulations, this method is no longer
 feasible, as an SF.sub.6 leak may no longer be ignored for such an
 extended period of time.
 Yet another method practiced by others in the past was to depressurize the
 electrical equipment, apply a layer of silicone caulk or the like onto the
 outside of the leaking joint, repressurize the electrical equipment, and
 put it back into service. This method rarely, if ever, works because often
 the surface of the equipment cannot be properly prepared in the field, and
 thus the caulk does not bond sufficiently well to the insulator surface.
 In addition, the caulk often does not have sufficient inherent strength or
 bonding strength to withstand the stresses resulting from the pressurized
 gas trying to escape, and therefore the caulk fails after a relatively
 short operating life. Furthermore, such a method suffers from the
 shortcoming that the electrical equipment must be fully depressurized for
 a period of time while the caulk is applied and allowed to cure.
 Still another proposed method is to apply a layer of caulk or the like to
 the joint, and then apply a reinforcing layer over the caulk. However, the
 caulk still tends to fail as a result of differences in the coefficient of
 thermal expansion between the caulk and the leaking surface, such that
 during the first thermal swing (usually the same day), the caulk either
 cracks or debonds, thereby destroying the seal.
 Yet another method involves the fabrication of a close-fitting housing that
 encloses the leaking joint. The housing is constructed with a passageway
 extending fully around the leaking joint, directly over the joint and
 opening toward it. Thus, once the housing is in place over the leaking
 joint, a pump is connected to the housing and sealant is pumped into the
 passageway. The sealant is pressurized to a level higher than the pressure
 of the leaking fluid. The wall of the leaking components and the walls of
 the housing serve to hold the sealant in place until it cures.
 While this method has proven somewhat effective at sealing the leak, it has
 a number of shortcomings. In the first place, the sealant actually adheres
 the opposite sides of the leaking joint together, which makes it more
 difficult to take the joint apart at some later date in order to perform a
 permanent repair of the leaking joint. In addition, leaking joints
 typically have different configurations and different dimensions. Even
 similar joints on the same equipment often have significant dimensional
 differences. Thus, each joint requires a specially configured housing,
 which is obviously burdensome, inefficient, and expensive. Furthermore,
 because the sealant is pressurized to a level higher than that of the
 leaking fluid, the sealant may actually be forced into the electrical
 component through the leak itself, which can result in a dangerous
 equipment failure.
 In addition, the assignee of the rights in the present invention proposed a
 method and system marketed under the name "Power Band 1". The method
 involved wrapping plural turns of tape about the leaking joint, with a
 number of small tubes extending from beneath the tape to the atmosphere to
 allow SF.sub.6 gas passing through the leaking joint to escape from under
 the tape so that the tape properly lays down over the joint. A composite
 layer is placed over the tape, and the small tubes are crimped. While this
 method has enjoyed success, it has been found that the small tubes often
 leak. In addition, the method requires precision in laying down the tape.
 Accordingly, it will be apparent to those skilled in the art that there
 continues to be a need for a system and method that effectively stops
 leaks without the need for depressurizing the equipment. Furthermore,
 there exists a need for such a system and method that can be readily
 adapted in the field to stop a leak in any joint, regardless of the
 dimensions of that joint. The present invention addresses these needs and
 others.
 SUMMARY OF THE INVENTION
 Briefly, and in general terms, the present invention provides a system and
 method for sealing leaks in vessels such as electrical insulators without
 the need for depressurizing the associated equipment. The system and
 method may be readily adapted in the field to seal any joint, regardless
 of its dimensions. In addition, while the system and method provide an
 effective seal, the seal may be readily removed when desired in order to
 change out the defective, original equipment o-ring or gasket. In
 accordance with one embodiment of the invention, a tubular seal is
 maneuvered into position to encircle the leaking joint. A reinforcing
 layer is applied over the seal. The seal is then filled with sealant under
 pressure, and the sealant is preferably allowed to cure inside the seal.
 Thus, the seal isolates the sealant from the electrical components to
 prevent the sealant from coming into direct contact with the electrical
 components, while simultaneously providing sufficient force against the
 leaking joint to stop the leak.
 Thus, the system of the present invention in one preferred embodiment
 comprises: an inflatable seal adapted to cover the leak, the seal defining
 an interior chamber and including an inlet in communication with the
 chamber; a reinforcing layer adapted to be applied over the seal; and a
 quantity of sealant adapted to be delivered into the chamber through the
 inlet.
 In an alternative embodiment of the invention, the seal comprises a segment
 of extruded tubular rubber stock including first and second ends adapted
 to be adhered together to form a circular seal encircling a leaking joint.
 In a preferred embodiment, the method of the present invention comprises
 the steps of: positioning a tubular seal about a vessel over a leak, the
 seal defining an interior chamber and including an inlet in communication
 with the chamber; placing a reinforcing layer over the seal; and
 introducing an amount of a sealant into the chamber through the inlet.
 Other features and advantages of the present invention will become apparent
 from the following detailed description, taken in conjunction with the
 accompanying drawings which illustrate, by way of example, the features of
 the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 In the following detailed description, like reference numerals will be used
 to refer to like or corresponding elements in the different figures of the
 drawings. Referring now to the drawings, and particularly to FIG. 2, there
 is shown a sealant system 10 comprising a preferred embodiment of the
 invention. The sealant system comprises, generally, a strip of barrier
 tape 12, an inflatable seal 14, and a reinforcing layer 16. The sealant
 system is operative to plug a leaking joint of a vessel, for example an
 insulative bushing 18 of a high voltage electrical device 20 such as a
 circuit breaker (FIG. 1).
 Referring to FIG. 1, the bushing assembly 18 of the high voltage electrical
 device 20 is illustrated to show one possible application of the sealant
 system 10 of the present invention. The bushing assembly comprises plural
 porcelain pipe segments 22 that define joints 24 between the respective
 pipe segments. The porcelain pipe assembly includes a lower end connected
 to a metal connector flange 26 of the circuit breaker device. The lower
 end of the pipe assembly and the flange define a joint therebetween as
 well. The pipe assembly further includes an upper end connected to a metal
 cap 28, with the upper end and metal cap also defining a joint
 therebetween.
 The joints between the respective porcelain pipe segments 22, between the
 metal cap 28 and the porcelain pipe, and between the connector flange 26
 and the porcelain pipe are all common leak sites. The joints are typically
 sealed by compression seal o-rings 29, gaskets, and the like. Over time,
 the o-rings, gaskets, or other seals can deteriorate and begin to leak,
 for example from normal aging, or from prolonged exposure to transformer
 oil which tends to degrade the seals. The sealant system of the present
 invention is operative to stop such leaks, as is described in greater
 detail below.
 The circuit breaker 20 includes an electrical conductor 30 extending
 through the pipe segments 22 of the bushing assembly 18 and through a
 central opening 32 formed in the metal cap 28. The pipe segments define an
 interior compartment that contains pressurized SF.sub.6 gas (or,
 alternatively, transformer oil). The compartment is bounded at the lower
 end by the connector flange 26, and at the top by the metal cap 28. Thus,
 as described above, as one or more of the o-rings and/or gaskets
 deteriorate, the compartment is no longer air-tight and SF.sub.6 gas (or
 transformer oil) may escape from the compartment and into the atmosphere,
 creating an unacceptable environmental hazard. In that event, the sealant
 system 10 may be used to stop the leak, as is now described.
 As described above, in a preferred embodiment the sealant system 10
 includes the strip of barrier tape 12 (FIGS. 2 and 3). The barrier tape
 serves as a joint bridge between two adjacent segments of porcelain pipe
 22, or between the porcelain pipe and metal cap 28 or metal connector
 flange 26. The barrier tape preferably comprises high strength tape,
 composite sheeting, engineering plastic, or the like, and preferably is
 formed with a preselected length such that it only extends about a portion
 of the periphery of the bushing assembly. The barrier tape is preferably
 applied at a location along the joint away from the actual leak, as
 described in greater detail below. In order to ensure a strong connection,
 the surface of the bushing assembly may be prepared in a well known
 manner, and a sealant may be applied to the surface. The barrier tape is
 then laid over the sealant. In the event a portion of the leak is aligned
 with the barrier tape, once the barrier tape is securely in place, the
 leak will be diverted to a path of less resistance, allowing the barrier
 tape to properly bond to the surface of the bushing.
 Referring now to FIGS. 2 and 6, there is shown the inflatable seal 14. In
 one embodiment, the seal is formed of extruded tubular rubber stock with a
 cross-sectional shape selected to complement that of the leaking joint so
 as to make a suitable connection with the surface of the bushing assembly
 18. In a preferred embodiment, the seal has a generally D-shaped
 cross-section, with the straight side 34 bearing against the surface of
 the bushing assembly over the leaking joint 24. In order to form the seal,
 the circumference of the bushing assembly at the leaking joint is
 measured, and a corresponding length of rubber stock is bias-cut and
 extended about the leaking joint to make a relatively tight fit about the
 leaking joint. The open ends of the rubber stock are then preferably
 adhered together in any well known manner to form a seal joint.
 Alternatively, the ends may be cold butted together, vulcanized together,
 joined by a mechanical joiner or plug inserted into each end, joined by
 extending a joining collar over the two ends, or any other well known
 manner for attaching the two ends together in a fluid-tight arrangement.
 This results in a hollow, annular seal with an interior passageway or
 chamber 35 adapted to receive a sealant.
 In one embodiment, a layer of pressure-sensitive adhesive (not shown) is
 applied to the joint-contacting surface of the seal 14, in order to adhere
 the seal to the adjacent pipe segments 22 of the bushing assembly 18 and
 ensure that the seal remains in proper position over the leaking joint 24.
 In the preferred embodiment, the seal 14 further includes an L-shaped
 filler tube 36 and an L-shaped vent tube 38, each of which extends through
 an opening 40 in the seal wall and into the chamber 35 for communication
 therewith. The filler tube is configured for engagement with a source of
 sealant (not shown) to deliver sealant into the chamber. The vent tube is
 provided for evacuating displaced air from the chamber. Alternatively, the
 seal 14 could simply be formed with the pair of openings 40, one of which
 could be engaged by the sealant delivery device while the other opening
 remains unengaged to serve as the vent.
 While in the preferred embodiment the seal 14 includes one filler tube 36
 and one vent tube 38, the seal could be formed with only a filler tube, or
 with plural filler tubes and plural vent tubes, or any such combination.
 Because the filler tube 36 is located adjacent the vent tube 38 in the
 preferred embodiment, a portion of the sealant being injected into the
 chamber 35 through the filler tube may actually extrude through the vent
 tube before all or most of the air inside the chamber has been evacuated.
 To avoid this, a thin rubber membrane 42 may be interposed between the
 ends of the seal (FIG. 6). Accordingly, the sealant being introduced into
 the chamber must travel through the entire chamber before it reaches the
 vent tube. In that manner, substantially all of the air inside the chamber
 is displaced before any sealant escapes through the vent tube.
 The sealant used to fill the seal 14 may take many different forms, such as
 a curing or non-curing sealant, for example a fast-setting, low exothermic
 thermoset polymer. Alternatively, the sealant could comprise water,
 grease, or virtually any liquid.
 Referring to FIG. 2, the composite reinforcing layer 16 is applied over the
 seal 14 to provide strength and support for the seal, while being
 sufficiently flexible to bend in complex angles and offer significant
 strain relief. Preferably, the reinforcing layer comprises the combination
 of a reinforcement and a matrix applied to the reinforcement, such as a
 fiberglass layer. The reinforcement may take many different forms, such as
 a woven substrate, fiber tape, fiber fabric, metal window screen, and the
 like. In one preferred embodiment, the reinforcement comprises a
 fiberglass yarn that is aligned and stitched together. The matrix may
 likewise take many different forms, such as a simple adhesive, for example
 glue, or more complex compositions such as liquid metal matrix.
 Preferably, the matrix is a highly toughened (nearly elastomeric) epoxy,
 as it provides sufficient strength, ease of application, minimal health
 risk, and controllable cure, while being relatively economical.
 Alternatively, the reinforcing layer may comprise a channel shaped metal
 band capable of assuming a circular configuration to back the seal 14.
 The reinforcing layer 16 not only holds the seal 14 in place, but also
 confines the seal and controls any differential thermal expansion problems
 that may otherwise be experienced with the seal 14. The reinforcing layer
 is the backing for the seal and forces the seal radially inwardly against
 the leaking joint 24 to seal the leak. Furthermore, the reinforcing layer
 provides a long useful life, maintains a low profile, and is relatively
 easy to clean and maintain.
 The composite reinforcing layer 16 is preferably allowed to cure, which may
 occur in several different ways. One is to simply allow the reinforcing
 layer to cure at room temperature. However, a preferred method is to
 thermally cure the reinforcing layer with portable heater bands and
 controllers, as is well known in the art.
 In addition, the reinforcing layer 16 may be subjected to compression, for
 example mechanical pressing, in order to force air out of the composite
 and to press the reinforcement and matrix tightly together. Alternatively,
 the reinforcing layer may be encapsulated in plastic sheeting and a vacuum
 established inside the sheeting to allow the air pressure to force the
 sheet down onto the composite reinforcing layer, thereby forcing the
 reinforcing layer down onto the seal.
 In a preferred embodiment, a protective, UV-blocking paint or polymer is
 applied over the reinforcing layer 16 (not shown), because many of the
 matrix materials used in the reinforcing layer, as well as some fiber
 reinforcements, are susceptible to UV rays, as well as to ozone and common
 urban pollutants.
 The sealant system 10 may include plural thermocouples or temperature
 indicating pills, tags, or similar devices (not shown), with those devices
 disposed at spaced apart locations into, around, and on the seal 14 and
 reinforcing layer 16, so that the curing temperatures may be monitored.
 Referring now to FIG. 2, a preferred method of assembling the sealant
 system 10 will be described. Initially, the strip of barrier tape 12 is
 applied over the leaking joint 24, preferably at a location spaced from
 the actual leak, as described above. The circumference of the leaking
 joint is measured, and a corresponding length of the rubber stock is cut
 to size, and the pair of openings 40 formed in the tube. Next, the filler
 and vent tubes 36 and 38 are inserted into the respective openings 40. The
 rubber stock is maneuvered into position about the circumference of the
 leaking joint. Preferably, this is achieved by wrapping the rubber stock
 about the joint and attaching the two ends of the rubber stock together,
 as described above, in order to form the annular seal 14.
 Next, the reinforcing layer 16 is applied over the seal 14 and allowed to
 cure, again as described above. In a preferred embodiment, the reinforcing
 layer and the seal are cooled down after the thermal cure step to the
 operating temperature of the component being repaired and are held at that
 temperature during the sealant injecting step.
 The seal 14 is then filled with a sealant by connecting the source of
 sealant (not shown) to the filler tube 36 and injecting pressurized
 sealant into the chamber 35, while the air in the chamber is displaced
 from the chamber and out through the vent tube 38. It is not crucial that
 all of the air be displaced from the chamber; in fact, in some instances
 it is preferable to trap some air in the sealant. As the pressurized
 sealant is injected into the chamber, the trapped air bubbles will be
 compressed. After the sealant cures, not only will the reinforcing layer
 16 force the seal down onto the leaking joint, the compressed air bubbles
 will provide an auxiliary pressure against the leaking joint 24.
 As the sealant is injected into the seal 14, the hydraulic pressure within
 the seal is preferably raised to and maintained at a controlled pressured,
 such as 10 psi above the pressure inside the bushing assembly 18. In the
 preferred embodiment, the sealant is curable, and thus the next step is to
 allow the sealant to cure. Once the sealant has cured, the pressure
 providing pump can be disconnected from the filler port 36 without any
 plug or valve being required to seal that port. If any of the components
 of the sealant system 10 should happen to stress crack in the future, the
 sealant will remain in place and continue to cover the leaking joint. In
 the case of a non-curing sealant, a pair of caps, plugs, or the like are
 engaged with the respective tubes 36 and 38 to seal off the tubes.
 Alternatively, the tubes can be pinched, crimped, shut off by a bead or a
 valve, or sealed by any other suitable method.
 Once the seal 14 is completed, the protective layer is preferably applied
 over the reinforcing layer 16 to prevent the reinforcing layer from being
 exposed to UV rays. The sealant system 10 is then completed, and is
 effective to prevent further leaking through the covered joint 24.
 Preferably, during the assembly of the sealant system 10, a quantity of air
 or other gas is maintained inside the seal 14 as the reinforcing layer 16
 is applied over it, to prevent the chamber 35 from collapsing as the
 reinforcing layer is applied, thereby ensuring that the chamber extends
 about the periphery of the joint 24. This may be accomplished by simply
 capping the filler and vent tubes 36 and 38, or by any other suitable
 method.
 In an alternative method, a bead of sealant is circumferentially applied
 directly to the leak in the leaking joint 24 before the barrier tape 12 is
 applied. When subjected to the forces of the inflated seal, this bead of
 sealant plugs the leak at its source, lowering the pressure-induced load
 against the entire sealant system 10. Such direct contact of sealant to
 the leaking joint is compatible with the spirit of this invention, because
 the type of sealant used and the small quantity applied would prevent the
 sealant from being forced into the leaking system, nor would it result in
 the opposite sides of the leaking joint being adhered together. Therefore,
 such a method does not suffer from the same shortcomings as do the prior
 art methods mentioned above in the Background section.
 While the sealant system 10 has been primarily described for use with a
 bushing assembly containing SF.sub.6, it will be apparent to those of
 ordinary skill in the art that the sealant system may also be used to stop
 leaks in insulators that contain transformer oil or any other fluid or
 gas, as well as to stop gas or liquid leaks in fluid-handling components,
 or to stop vacuum leaks in those components. In addition, the sealant
 system may be used to add structural stability to component joints, for
 example as a seismic reinforcement.
 Referring now to FIG. 3, there is shown another typical leaking joint 24 in
 an electrical insulator, namely between the metal connector flange 26 and
 the lowest pipe segment 22. The sealant system 10 of the present invention
 is also suitable for sealing a leak in such a joint, as is now described.
 Referring to FIG. 3, a strip of barrier tape 44 is applied over the joint,
 with a segment 46 thereof being connected to the porcelain pipe segment 22
 and extending in a vertical direction, and a segment 48 thereof being
 connected to the connector flange 26 and extending in a horizontal
 direction. As with the embodiment described above, the barrier tape
 extends only partially about the circumference of the joint, and is
 preferably adhered to the bushing assembly 18 at a location spaced from
 the actual leak site, as with the previously described embodiment.
 A seal 50 is provided and is extended about the periphery of the joint. The
 seal is preferably formed from extruded tubular rubber stock, similar to
 the embodiment described above. In this embodiment, however, the rubber
 stock has a generally wedged or triangular cross-sectional shape (FIG. 4)
 for making positive contact with both the porcelain pipe segment 22 and
 the connector flange 26. It will thus be apparent that the seal may take
 many different forms to complement the configuration of the insulator at
 the site of the leaking joint. In fact, in each of the specifically
 disclosed embodiments the rubber stock may initially be circular in cross
 section, if desired, and achieve the cross-sectional shapes described
 above only when applied to the device being sealed.
 In the alternative embodiment of FIGS. 3 and 4, a composite reinforcing
 layer 52 is applied over the seal 50 (FIG. 5) so that the layer bonds to
 both the porcelain pipe segment 22 and connector flange 26. The seal is
 injected with sealant through a filler tube 54 while displaced air is
 evacuated through a vent tube (not shown).
 Referring to FIG. 7, there is shown an alternate method of constructing a
 seal 56. Rather than attaching the two ends together to form an annular
 seal, the ends are separately sealed, preferably with plugs 58 inserted
 into the respective open ends and adhered to the seal. The filler and vent
 tubes 60 and 62 extend through the respective plugs, or may be extended
 into the seal adjacent the respective ends of the seal. In this
 embodiment, the injected sealant will be forced to travel through the
 entire chamber until it reaches the vent tube, and thus there is no
 concern that the sealant will be prematurely ejected through the vent
 tube. Because the seal does not extend about the entire periphery of the
 joint, the strip of barrier tape 64 is preferably placed over that portion
 of the joint not covered by the seal. As with the above-described
 embodiments, a reinforcing layer (not shown) is applied over the seal to
 keep the seal in place over the leaking joint and force the seal radially
 inwardly against the leaking joint.
 Referring now to FIGS. 8 and 9, there is shown an alternative embodiment of
 the sealant system of the present invention. A disk-shaped, inflatable
 seal 100 in the form of a pillow is provided (shown in phantom in FIG. 9)
 and includes an interior chamber 102. A filler tube 104 includes an open
 first end disposed inside the chamber and an open second end disposed
 outside the chamber for injecting pressurized sealant into the chamber. A
 reinforcing layer 106 is applied over the seal and is connected to the
 bushing assembly 108 by an adhesive matrix or the like. Alternatively, the
 reinforcing layer can be bolted down onto the bushing assembly, or
 connected in any other suitable manner. Such a system is used to seal
 small cracks or holes 110 and the like in fluid containing assemblies that
 are not associated with a joint between two pipe segments. While the seal
 is shown having a disk shape, it will be apparent that the seal could
 assume virtually any shape, so long as the seal defines an interior
 chamber to receive a quantity of sealant.
 From the foregoing, it will be apparent that the sealant system 10 provides
 a reliable, efficient system for sealing leaks in electrical insulators
 and other vessels. The sealant system does not require that the leaking
 component be depressurized, nor does the system require that a unique part
 be machined to accommodate the configuration of a leaking joint.
 While forms of the invention have been illustrated and described, it will
 be apparent to those skilled in the art that various modifications and
 improvements may be made without departing from the spirit and scope of
 the invention. As such, it is not intended that the invention be limited,
 except as by the appended claims.