US20070131444A1 - Cable seals and methods of assembly - Google Patents

Abstract

A method of sealing a cable penetration includes assembling a cable seal and inserting the cable seal into a cable penetration. Assembling the cable seal includes adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket, and positioning a secondary elastic seal over the heat-shrinkable tubing. An example of a secondary elastic seal could be O-rings. A cap or other means provides the outer sealing surface.

Description

BACKGROUND OF THE INVENTION
• This invention relates generally to methods and apparatus for assembling cable seals.
• Many known industrial facilities have a variety of cable systems used to conduct electrical and electronic signals between field apparatus and non-field apparatus. Some examples of field apparatus are pressure data transmitters and valve position drive motors. Some examples of non-field apparatus include power sources and control system cabinets located in areas such as control rooms and offices. Some examples of cable uses are to transmit data to and from a variety of field apparatus and non-field apparatus, transmit electronic directives to field apparatus from non-field apparatus and to provide electrical power to apparatus regardless of location.
• Many known cable systems include data and power cables that are typically routed through open passages of apparatus, the open passages often referred to as cable penetrations. The cable penetrations typically have seals to maintain the integrity of the cable jackets and to mitigate the potential for vapor ingression into the associated instrumentation/electronics region of the apparatus. The aforementioned seals may also be used in circumstances where separating differing environmental conditions between an electronic device and the cable penetration is not as important as simply providing for a cable support mechanism for facilitating cable routing, for example, cable tray ingress and egress, building wall penetrations and cable vault risers.
• Many facilities have operating environments that include humidity levels that may exceed 50% relative humidity and temperature levels that may exceed 66° Celsius (C.) (150° Fahrenheit (F.)) for extended periods of time. Some facilities may also have apparatus positioned such that a potential for exposure to steam or other vapors may be present. In the aforementioned environmental circumstances, the outer jackets of the cables may experience cold flow, i.e., a time dependent strain (or deformation) of the cable jacket resulting from stress, and allow a subsequent vapor ingression into the associated instrumentation/electronics region of the apparatus.
BRIEF DESCRIPTION OF THE INVENTION
• In one aspect, a method of sealing a cable penetration is provided. The method includes assembling a cable seal and inserting the cable seal into a cable penetration. Assembling the cable seal includes adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket, and positioning a secondary elastic seal over the heat-shrinkable tubing. An example of a secondary elastic seal could be O-rings. A cap or other means provides the outer sealing surface.
• In another aspect, a cable seal is provided. The cable seal includes at least one cable having an FEP outer jacket. The seal also includes at least a portion of a predetermined length of a heat-shrinkable tubing that is inserted over at least a portion of the cable outer jacket. The seal further includes a cap having at least one sealing surface. The cap is inserted over at least a portion of the heat-shrinkable tubing. The seal also includes at least one elastic member. The member includes at least one sealing surface and is inserted over at least a portion of the heat-shrinkable tubing.
• In a further aspect, a cable penetration sealing system is provided. The system includes a cable seal for a cable and at least one apparatus. The seal includes a predetermined length of a heat-shrinkable tubing, a cap, and at least one elastic member. The cable includes an FEP outer jacket. The tubing is inserted over at least a portion of the cable outer jacket. The cap includes at least one sealing surface and the cap is inserted over at least a portion of the heat-shrinkable tubing. The elastic member includes at least one sealing surface and is inserted over at least a portion of the heat-shrinkable tubing. The apparatus includes at least one cable penetration and the cable penetration is configured to receive the seal.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a fragmentary illustration of an exemplary cable seal; and
• FIG. 2 is an enlarged view of the cable seal shown inFIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 is a fragmentary illustration of anexemplary cable seal200.Seal200 is integral to anapparatus202. In the exemplary embodiment,apparatus202 is a proximity probe (sometimes referred to as an eddy current probe and/or a displacement transducer). Alternatively,apparatus202 may be, but not be limited to, an electrical current transducer, a resistance temperature detector (RTD), or any other industrial field instrument. Also alternatively,apparatus202 may be any object having a cable penetration, including a wall, cable tray side member, and a bracket assembly.Apparatus202 is often used to measure bearing (not shown inFIG. 1) vibration on large machines, such as turbines, as a function of the relative movement between the bearing and the journal. As the relative position between the bearing and journal varies, an electrical signal is induced withinapparatus202.Apparatus202 may be used with large machines including, but not limited to steam turbines, and may therefore be exposed to an environment that includes steam exiting a turbine bearing housing. The steam will normally increase the relative humidity and temperature levels within the vicinity of the bearing, and therefore,apparatus202.
• Apparatus202 has ahousing204 that is normally cast from a material that can withstand environments that include extended high temperatures, vibration, humidity, and exposure to steam. In the exemplary embodiment,housing204 is cast from stainless steel. Alternatively, other materials including, but not limited to, titanium alloys may be used.Housing204 has a plurality of cavities formed during the casting process. Alternatively, at least some of these cavities may be formed using standard machining techniques subsequent to the casting process.Apparatus202 also has an instrumentation/electronics cavity206 that is formed by a plurality of interior walls (not shown inFIG. 1) ofhousing204 to a set of predetermined dimensions to house the electronics and instrumentation (not shown inFIG. 1) used to measure the relative movement within the associated component, for example, a journal bearing, and subsequently transform an induced electronic signal into a signal that is transmitted to computer102.Cavity206 typically houses electrical power and electronic interconnections (not shown inFIG. 1). Therefore,cavity206 is normally the largest cavity withinhousing204 and houses the components that may be sensitive to vapor ingression.
• Housing204 also has acable cavity208 that is positioned and dimensioned withinhousing204 to facilitate pulling acable210 intohousing204.Cable210 has anouter jacket212 that surrounds at least one electrical conductor (not shown inFIG. 1).Cavity206 andcavity208 may be formed integrally or as separate cavities. Substantiallyannular cavity208 is formed by a substantially annular cable cavityinterior wall214 and a cablecavity housing neck216. Neck216 extends radially inward from the aforementioned housing inner wall and forms a substantially circular cable cavityopen passage218 and a cable cavity openpassage sealing surface220.Neck216 andpassage218 are discussed further below.
• Housing204 further has a substantially annularopen passage222 that is formed by a substantially annular housing open passageinterior wall224 andneck216. Furthermore,housing204 has anannular housing opening228 that is a widened portion ofopen passage222 that is defined by an annular housing open passagevertical sealing surface230 and an annular housing open passagehorizontal sealing surface232.Sealing surface230 protrudes axially inward from a housingoutermost surface234 and sealingsurface232 extends substantially radially perpendicular tosurface230.Cavity208,open passage218,open passage222 andhousing opening228 define a cable penetration.
• Seal200 includes a plurality of elastic media. In the exemplary embodiment the elastic media is a plurality of O-rings236 and238. Alternatively, elastic media such as tapes, foams, putties, or other materials that meet or exceed the predetermined characteristics of O-rings236 and238 may be used.Seal200 also has a heat-shrinkable tubing240 and ahousing cap226.Housing cap226 is inserted overcable210 and inserted into anannular housing opening228. Alternative, other media and materials that meet or exceed the predetermined characteristics ofcap226 may be used, for example, tapes, foams and putties. O-rings236,238 andtubing240 are discussed further below.
• FIG. 2 is an enlarged view ofexemplary cable seal200.FIG. 2 illustrates many ofseal200 components illustrated inFIG. 1 and discussed above.
• In the exemplary embodiment, heat-shrinkable tubing240 has two layers, tubingouter layer242 and tubinginner layer244.Outer layer242 is formed with polytetrafluoroethylene (PTFE). As a stand-alone material, PTFE heat-shrinkable tubing generally has a shrink ratio in the 2:1 to 4:1 range, i.e., the inner diameter of a section of PTFE tubing will be reduced by approximately 50% to 75% subsequent to heat application at a temperature range of approximately 325° C. to 340° C. (617° F. to 644° F.). PTFE typically has a continuous temperature rating of approximately 250° C. (482° F.) that is usually sufficient to protect an underlying cable from a nearby steam source that may have a temperature of approximately 100° C. (212° F.) at substantially atmospheric pressures. PTFE also is substantially non-porous and normally exhibits chemical resistance properties that are sufficient for many industrial applications. Furthermore, PTFE typically exhibits a smooth outer surface that facilitates a resistance to strain as discussed further below.
• Inner layer244 is formed with fluorinated ethylene-propylene (FEP). As a stand-alone material, FEP heat-shrinkable tubing generally has a shrink ratio in the 1.3:1 to 1.6:1 range, i.e., the inner diameter of a section of PTFE tubing will be reduced by approximately 23% to 37.5% subsequent to heat application at a temperature range of approximately 190° C. to 210° C. (374° F. to 410° F.). FEP typically has a continuous temperature rating of approximately 204° C. (400° F.) that is usually sufficient to protect an underlying cable from a nearby steam source that may have a temperature of approximately 100° C. (212° F.) at substantially atmospheric pressures. FEP, similar to PTFE, also is substantially non-porous and normally exhibits chemical resistance properties that are sufficient for many industrial applications. However, FEP typically does not exhibit as smooth an outer surface as PTFE.
• In the exemplary embodiment, a section oftubing240 is cut to a predetermined length. The length may be determined from the dimensions of the length of housingopen passage222 and the predetermined lengths of heat-shrinkable tubing that extend beyondpassage222 in either of the two axial directions alongcable210 The section oftubing240 is inserted overcable210. Normally, it may be more convenient to slidetubing segment240 over the end ofcable210.
• Heat is applied to dual-layer tubing240 to form a tubing-enclosed cable portion246 (illustrated as the section ofcable210 enclosed bytubing240 inFIG. 2).Inner FEP layer244 melts and flows to encapsulate cableouter jacket212. Sinceouter jacket212 is also formed from FEP,jacket212 also melts slightly and a chemical bond between tubinginner layer244 andjacket212 is formed.Inner FEP layer244 does not shrink as much asouter PTFE layer242 does, therefore,layer242 shrinks tightly overinner FEP layer244 to form a tight, smooth seal in conjunction withinner layer244 on cableouter jacket212. In the exemplary embodiment,tubing240 has a continuous service temperature rating of approximately 200° C. (392° F.).
• Alternatively,tubing240 may have more than two layers, for example a neutral middle layer.Tubing240 may also have one layer of a composite material that obtains substantially similar results as the exemplary embodiment.
• Upon cooling of tubing-enclosedcable portion246,housing cap226 is inserted overcable portion246 in a manner substantially similar to that used to inserttubing240 overcable210 as described above.Cap226 has an open passage (not shown inFIG. 2) of sufficient diameter to facilitate insertion overcable portion246 while having a clearance between anoutermost surface248 ofcable portion246 that is small enough to facilitate a mitigation of vapor ingression betweencap226 andcable portion246 as well as provide additional structural support tocable portion246 to mitigate strain ofcable portion246.Cap226 is positioned overcable portion246 at approximately the midpoint ofcable portion246 so that sufficient length ofcable portion246 extends beyondpassage222 in either of the two axial directions along cable portionoutermost surface248 to facilitate sufficient strength in the layers ofcable portion246, to mitigate strain incable portion246, and to establish a small clearance between theoutermost surface248 ofcable portion246 and the cable cavity openpassage sealing surface220 as discussed below.
• In the exemplary embodiment, two O-rings236 and238 are inserted overcable portion246 to assemble a tubing/O-ring-enclosedcable portion250. O-rings236 and238 are substantially circular and annular. O-rings236 and238 are inserted overcable portion246 in a manner substantially similar to that used to inserttubing240 overcable210 as described above. O-ring236 and O-ring238 expand to mitigate a clearance between asurface252 of O-ring236 and asurface254 of O-ring238 and the radiallyoutermost surface248 ofcable portion246 to mitigate strain ofcable portion246 and facilitate a seal that tends to mitigate vapor ingression intocavity208 along theoutermost surface248 ofcable portion246. The smoothoutermost surface248 of tubing-enclosedcable portion246 formed by tubingouter layer242 facilitates the sealing action between O-rings236 and238 andsurface248. O-ring238 is a redundant backup for O-ring236.
• Tubing/O-ring-enclosedcable portion250 is inserted intohousing204 through housingopen passage222 pulled into cavity206 (shown in FIG.1) for subsequent electrical connection to the appropriate terminals (not shown inFIGS. 1 and 2).Cable210 is pulled throughhousing204 until O-ring236 contacts a housing open passage vertical O-ring sealing surface256. The aforementioned expansion of O-ring236 also tends to mitigate clearances betweensurface252 of O-ring236 and sealingsurface256 and a housing open passage horizontal O-ring sealing surface258. O-ring238 expands in a similar manner, however, instead of expanding against housing open passage vertical O-ring sealing surface256,surface254 of O-ring238 expands againstsurface252 of O-ring236. The expansion of O-ring236 againstsurfaces256 and258 and the expansion of O-ring238 againstsurface258 facilitate a seal that tends to mitigate vapor ingression intocavity208. Housing open passage void260 permits additional expansion of O-rings236 and238 in the axial direction.
• Inserting Tubing/O-ring-enclosedcable portion250 inhousing204 also tends to decrease a clearance between theoutermost surface248 ofcable portion246 and the cable cavity openpassage sealing surface220 to facilitate a mitigation of vapor ingression intocavity208 and to mitigate strain ofcable portion246.
• Assembly ofseal200 is completed by insertingcap226 intohousing opening228 such that a substantial portion ofcap226 sealing surface is in contact with a substantial portion ofsurfaces230 and232 to facilitate a mitigation of vapor ingression intocavity208 and to mitigate strain ofcable portion246. In the exemplary embodiment, cap226 forms a friction seal withsurface232. Alternatively, an adhesive suitable for the associated environment may be used to affixcap226 tosurfaces230 and232. Also alternatively, at least one set screw may be inserted into a channel formed radially throughhousing204 andcap226.
• The methods and apparatus for a cable seal described herein facilitate operation of a cable penetration sealing system. More specifically, designing and installing a cable seal as described above facilitates operation of a cable penetration sealing system by mitigating an cold flow of a cable jacket. As a result, degradation of cable jacket integrity, effectiveness and reliability, extended maintenance costs and associated system outages may be reduced or eliminated.
• Although the methods and apparatus described and/or illustrated herein are described and/or illustrated with respect to methods and apparatus for a cable penetration sealing system, and more specifically, an apparatus cable seal, practice of the methods described and/or illustrated herein is not limited to apparatus cable seals nor to cable penetration sealing systems generally. Rather, the methods described and/or illustrated herein are applicable to designing, installing and operating any system.
• Exemplary embodiments of cable seals as associated with cable penetration sealing systems are described above in detail. The methods, apparatus and systems are not limited to the specific embodiments described herein nor to the specific cable seals designed, installed and operated, but rather, the methods of designing, installing and operating cable seals may be utilized independently and separately from other methods, apparatus and systems described herein or to designing, installing and operating components not described herein. For example, other components can also be designed, installed and operated using the methods described herein.
• While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Claims (20)

1. A method of sealing a cable penetration, said method comprising:

assembling a cable seal, said assembling comprising adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket, positioning a cap over the heat-shrinkable tubing, and positioning at least one elastic member over at least a portion of the heat-shrinkable tubing; and

inserting the cable seal into a cable penetration.

2. A method in accordance withclaim 1 wherein adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket comprises positioning the heat-shrinkable tubing over the cable outer jacket by inserting at least one open end of a predetermined length of a multi-layered heat-shrinkable tubing over at least a portion of the cable outer jacket.

3. A method in accordance withclaim 1 wherein adhering at least a portion of a heat-shrinkable tubing to at least a portion of a cable outer jacket further comprises melting a heat-shrinkable tubing inner layer such that it chemically bonds with the cable outer jacket, thereby increasing the strength of the cable outer jacket and mitigating a potential for cable outer jacket strain and cold flow of at least a portion of the cable outer jacket.

4. A method in accordance withclaim 1 wherein positioning a cap over the heat-shrinkable tubing comprises inserting a cap open passage over the heat-shrinkable tubing outer surface, thereby mitigating a potential for cable outer jacket strain and cold flow of at least a portion of the cable outer jacket.

5. A method in accordance withclaim 1 wherein positioning at least one O-ring over at least a portion of the heat-shrinkable tubing comprises inserting at least one O-ring over a heat-shrinkable tubing outer surface, thereby facilitating a seal between at least a portion of an O-ring substantially annular inner surface and at least a portion of the heat-shrinkable tubing outer surface by expanding the O-ring, thereby mitigating a potential for cable outer jacket strain and cold flow of at least a portion of the cable outer jacket.

6. A method in accordance withclaim 1 wherein inserting the cable seal into a cable penetration comprises inserting at least a portion of the cable seal through at least a portion of a cable penetration and compressing at least a portion of at least one O-ring against a sealing surface within the cable penetration, thereby mitigating stress within at least a portion of the cable outer jacket.

7. A method in accordance withclaim 1 wherein inserting the cable seal into a cable penetration further comprises inserting the cap into the open passage such that a seal between the cable penetration and an external environment is facilitated.

8. A cable seal comprising:

at least one cable, said cable comprising an FEP outer jacket;

at least a portion of a predetermined length of a heat-shrinkable tubing, said tubing being inserted over at least a portion of said cable outer jacket, said tubing comprising an outer layer comprising a first material and an inner layer comprising a second material that is different from said first material, said first layer is chemically bonded to said cable outer jacket;

a cap, said cap comprising at least one sealing surface, said cap being inserted over at least a portion of said heat-shrinkable tubing; and

at least one elastic member, said member comprising at least one sealing surface, said member inserted over at least a portion of said heat-shrinkable tubing.

9. A cable seal in accordance withclaim 8 wherein said inner layer comprises FEP, wherein said chemical bond between said inner layer and said outer jacket facilitates an increase of a strength of said cable outer jacket and facilitates mitigation of a potential for cable outer jacket strain and cold flow of at least a portion of said cable outer jacket.

10. A cable seal in accordance withclaim 8 wherein said outer layer comprises PTFE and an outer surface, surface irregularities being mitigated on said outer surface, and said outer surface facilitates seal formation between said at least one elastic member and said cap and facilitates mitigation of a potential of cold flow of said cable outer jacket.

11. A cable seal in accordance withclaim 8 wherein said cap sealing surface forms a substantially annular open passage, said open passage facilitates receipt of said cable.

12. A cable seal in accordance withclaim 8 wherein said at least one elastic member further comprises a first O-ring and a second O-ring, said first and said second O-rings inserted over at least a portion of an outer surface of said heat-shrinkable tubing such that said first and said second O-rings facilitate mitigation of stress within said heat-shrinkable tubing and facilitate seal formation between said O-rings and an outer surface of said heat-shrinkable tubing.

13. A cable seal in accordance withclaim 12 wherein said second O-ring comprises a redundant O-ring.

14. A cable penetration sealing system, said system comprising:

a cable seal for a cable, said cable seal comprising a predetermined length of a heat-shrinkable tubing, a cap, and at least one elastic member, said cable comprising an FEP outer jacket, said tubing being inserted over at least a portion of said cable outer jacket, said tubing comprising an outer layer comprising a first material and an inner layer comprising a second material that is different from said first material, said first layer is chemically bonded to said cable outer jacket, said cap comprising at least one sealing surface, said cap inserted over at least a portion of said heat-shrinkable tubing, said at least one elastic member comprising at least one sealing surface, said elastic member inserted over at least a portion of said heat-shrinkable tubing; and

at least one housing comprising at least one cable penetration, said cable penetration configured to receive said seal and comprises a substantially annular circumferential interior surface that comprises a protrusion.

15. A cable penetration sealing system in accordance withclaim 14 wherein said substantially annular circumferential interior surface forms an instrumentation/electronics cavity.

16. A cable penetration sealing system in accordance withclaim 14 wherein said protrusion extends radially and orthogonally inward from at least a portion of said circumferential interior surface, said protrusion comprises at least one annular radially innermost protrusion sealing surface and at least one protrusion sealing surface extending radially and orthogonally inward from at least a portion of said circumferential interior surface, said protrusion sealing surface comprising a predetermined axial length, said sealing surface facilitates a seal between said cable and said housing.

17. A cable penetration sealing system in accordance withclaim 14 wherein at least a portion of said interior surface and at least a portion of said protrusion form a housing open passage, said open passage facilitates intrusion of said cable into said housing, said open passage comprising radial dimensions sized to facilitate receipt and compression of said at least one elastic member.

18. A cable penetration sealing system in accordance withclaim 16 wherein said circumferential interior surface and said protrusion sealing surface extend radially and orthogonally inward from said circumferential interior surface to facilitate forming a seal between said cap and said housing.

19. A cable penetration sealing system in accordance withclaim 14 wherein said inner layer comprises FEP and said outer layer comprises PTFE, said PTFE outer layer comprises an outer surface, said chemical bond between said FEP inner layer and said FEP outer jacket facilitates coupling of said tubing to said cable outer jacket to assemble a tubing-enclosed cable portion, said PTFE outer surface mitigates surface irregularities and facilitates mitigation of cold flow of said cable outer jacket.

20. A cable penetration sealing system in accordance withclaim 14 wherein said at least one elastic member further comprises a first O-ring and a second O-ring, said first and said second O-rings inserted over at least a portion of an outer surface of said heat-shrinkable tubing such that said first and said second O-rings facilitate mitigation of stress within said heat-shrinkable tubing and facilitate seal formation between said O-rings and an outer surface of said heat-shrinkable tubing, said second O-ring being a redundant O-ring.

Images