Abstract:
A method of attaching an end termination assembly to a cold lead of a mineral insulated heating cable. the method comprises removing a portion of a metallic sheath of the cold lead from a proximal end of the cold lead, thereby exposing a conductor of the cold lead. In addition sliding a tubular bushing over the proximal end of the cold lead, and sliding a tubular pot over the proximal end of the cold lead, the conductor thereby projecting from a proximal end of the tubular pot. The method further including aligning a proximal end of the sheath of the cold lead with a proximal end of the tubular bushing, and welding the proximal end of the tubular bushing to the sheath at the proximal end of the sheath. In addition, positioning a distal end of the pot over the proximal end of the bushing, and welding the distal end of the pot to the bushing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 62/044,239 entitled SYSTEM AND METHOD FOR FORMING END TERMINATION OF MINERAL INSULATED CABLE, filed, Aug. 30, 2014 which is incorporated herein by reference in its entirety and to which this application claims the benefit of priority. 
     
    
     BACKGROUND 
       [0002]    “Downhole heating” refers to the known practice of providing apparatuses and systems that can be installed in an oil or gas well to heat the well, (a) pipeline(s) within the well, or process media (e.g., oil) retrieved from the well. The well can be thousands of feet deep, and the wellhead can be on land or underwater. In these environments the atmospheric pressure at the wellhead and down the well can be extremely high. 
         [0003]    One type of downhole heating apparatus uses an electric heating cable, or a group or series thereof, to provide thermal energy to the components or media being heated. Electric heating cables connect to a power source and convert an electric current into thermal energy using several known cable structures. One such structure is a mineral-insulated (MI) electric heating cable. A typical MI cable has a round or oval cross-section with several layers. One or more conductors at or near the center of the cable are surrounded by the mineral insulation, which is typically magnesium oxide. The mineral insulation is tightly packed inside a conductive, typically copper or steel, tubular sheath, which in turn may be covered by an insulating polymer or braided overjacket. 
         [0004]    Several MI cables are often spliced together to achieve the necessary length for downhole heating, or to provide zones of differing heating parameters. Near the wellhead, the MI cable is attached to a cold lead, which has a similar composition to the MI cable, including one or more conductors packed with inorganic insulation in a metal sheath. The cold lead is so-called because it does not emit significant thermal energy like the heating cables do. The cold lead is attached at its distal end to the MI cable, and at its proximal end the cold lead must be “terminated” by attaching the cold lead conductor(s) to one or more wires that in turn connect to the heating cable power supply. This termination may be exposed to the surrounding environment, and so must be sealed against ingress of environmental substances, even in high pressure locations. 
         [0005]    Current MI cable terminations are typically wiring kits that include o-ring housings, formed-in-place mastic or epoxy seals, brass, nickel-plated or steel multi-component gland and ferrule assemblies, or combinations thereof. These kits form a seal on the cold lead cable sheath via brazing or application of sealing compound to the sheath. Unfortunately, brazed or epoxied seals against the sheath, while the best existing method, can fail in high pressure environments, or with exposure to corrosive gases and fluids often found in the downhole environment. An improved MI cable end termination for high pressure environments is needed. 
       SUMMARY 
       [0006]    The present methods and apparatuses provide a tungsten inert gas (TIG) welded seal between the cold lead cable sheath and the end termination, which makes other types of sealing locations and features (other than the cable sheath) possible. 
         [0007]    A method of attaching an end termination assembly to a cold lead of a mineral insulated heating cable is disclosed. The method comprising removing a portion of a metallic sheath of the cold lead from a proximal end of the cold lead, thereby exposing a conductor of the cold lead. The method further comprising sliding a tubular bushing over the proximal end of the cold lead, the tubular bushing having a shoulder, the shoulder having a diameter adjacent and proximal to a distal end of the tubular bushing, the tubular bushing having a first portion with a first inner diameter adjacent to a distal end of the tubular bushing and a second portion with a second inner diameter adjacent to a proximal end of the tubular bushing. Additionally, the method comprises sliding a tubular pot over the proximal end of the cold lead, the conductor thereby projecting from a proximal end of the tubular pot, the tubular pot having a length, measured from a distal end of the tubular pot to the proximal end of the tubular pot, that is longer than the distance from the shoulder of the tubular bushing to the distal end of the tubular bushing, the tubular pot having a first portion with a first inner diameter, the first inner diameter approximately equal to a first outer diameter of the tubular bushing. Further, the method comprises aligning a proximal end of the sheath of the cold lead with a proximal end of the tubular bushing; welding the proximal end of the tubular bushing to the sheath at the proximal end of the sheath; positioning a distal end of the tubular pot over the proximal end of the tubular bushing; and welding the distal end of the tubular pot to the tubular bushing. 
         [0008]    Additionally, a further method of attaching an end termination assembly to a cold lead of a mineral insulated heating cable is disclosed. The method comprises, sliding a tubular bushing over a proximal end of the cold lead; sliding a tubular pot over the proximal end of the cold lead; welding a proximal end of the tubular bushing to a proximal end of a metallic sheath of the cold lead; and welding a distal end of the tubular pot to the tubular bushing. 
         [0009]    Furthermore, an end termination assembly for a mineral insulated heating cable is disclosed. The end termination assembly comprises a tubular bushing, the tubular bushing having a shoulder, the shoulder having a diameter adjacent and proximal to the distal end of the tubular bushing, the tubular bushing having a first portion with a first inner diameter adjacent to a distal end of the tubular bushing and a second portion with a second inner diameter adjacent to a proximal end of the tubular bushing. The end termination assembly further comprises a tubular pot having a length, measured from a distal end of the tubular pot to a proximal end of the tubular pot, that is longer than the distance from the shoulder of the tubular bushing to the proximal end of the tubular bushing, the tubular pot configured to be welded to the tubular bushing at the distal end of the tubular pot, the tubular pot having a first portion with a first inner diameter, the first inner diameter approximately equal to an outer diameter of the second portion of the tubular bushing. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a mineral insulated cold lead cable having an exposed conductor. 
           [0011]      FIG. 2  is a top view of a bushing in accordance with an embodiment of the disclosure. 
           [0012]      FIG. 3  is a right side cross-sectional view of the bushing taken along line A-A of  FIG. 2 . 
           [0013]      FIG. 4  is a top view of a pot in accordance with an embodiment of the disclosure. 
           [0014]      FIG. 5  is a right side cross-sectional view of the pot taken along line C-C of  FIG. 4 . 
           [0015]      FIG. 6A  is a right side view of a splice assembly in accordance with an embodiment of the disclosure, attached to a cold lead sheath. 
           [0016]      FIG. 6B  is a right side partial cross-sectional view of the splice assembly of  FIG. 6A . 
           [0017]      FIG. 6C  is a right side full cross-sectional view of the splice assembly of  FIG. 6A . 
           [0018]      FIG. 7  is a flow chart illustrating a method of forming a mineral insulated cable end termination in accordance with the present disclosure. 
           [0019]      FIG. 8  is a right side partial cross-sectional view of the splice assembly of  FIG. 6  with a terminating cap attached. 
           [0020]      FIG. 9  is a right side partial cross-sectional view of the splice assembly of  FIG. 6  with a locking assembly attached. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0022]    The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
         [0023]      FIG. 1  illustrates the proximal (i.e., wellhead) end of a typical mineral insulated (“MI”) cable cold lead  10  that may be spliced to one or more power-transfer conductors, such as insulated wires known as “tails,” using the present methods and apparatuses. It will be understood, however, that the present methods and apparatuses may form end terminations for other cables (e.g., a multi-core MI cable having a plurality of conductors) as well as for other cold leads. The cold lead  10  includes a conductor  12  running the length of the cold lead  10  coaxially within a cylindrical metal sheath  14 . The sheath  14  can be constructed using copper, stainless steel, etc. In some embodiments, the sheath  14  can be a solid metallic sleeve. In other embodiments, the sheath  14  can be a woven metallic covering. In some embodiments, the intervening space within the sheath  14  can be filled with an inorganic insulator  16 . In one example, the inorganic insulator  16  can be magnesium oxide. At a proximal end  18  of the cable  10 , a length of the conductor  12  can be exposed, such as by stripping off a portion of the sheath  14  and the insulator  16 . The length of exposed conductor  12  can provide a connection surface for an end termination. For example, the length of exposed conductor  12  can be connected to an insulated power-transfer conductor or “tail.” The cold lead  10  may be any suitable MI cable cold lead, using any known materials. 
         [0024]    The present methods and apparatuses provide a welded seal between the cold lead  10  sheath  14  and an end termination assembly. The welded seal can be far stronger than existing cold lead termination seals as known in the art. Further, the welded seal methods and apparatuses described herein can make other types of sealing locations and features apart from the sheath  14  possible. The welds described herein may be formed using any suitable welding processes, except where identified. Preferably, TIG welding, electron welding, or laser beam welding can be used. 
         [0025]    Referring to  FIGS. 2 and 3 , an end termination assembly may include a bushing  20 . The bushing  20  can be welded to the outside sheath  14  of the cold lead  10  of a mineral insulated cable. The bushing  20  can be constructed of any suitable metal for welding with the sheath  14 . In one embodiment, the bushing  20  material can be selected to provide pressure and corrosion resistance. Non-limiting examples of the bushing  20  material can include copper, stainless steel, iron, or other applicable materials. In one embodiment, the bushing  20  material can be constructed of the same material as the sheath  14  material. 
         [0026]    The bushing  20  may be substantially tubular with a first portion  22  having a first inner diameter B 1  that is slightly larger than an outer diameter of the sheath  14 , to allow the bushing  20  to be more easily positioned over the sheath  14 . The sheath  14  can typically be straightened by hand, and therefore susceptible to binding up while sliding through the bushing  20  having close tolerances along its entire length. A second portion  24  of the bushing  20 , proximal to the first portion  22  may have a second inner diameter B 2 . The second inner diameter B 2  can be about equal to an outer diameter of the sheath  14 . This close tolerance can provide adjacent surfaces of the bushing  20  and sheath  14  to be in contact. This contact between the bushing  20  and the sheath  14  can increase a quality of a weld, as described below. An inner shoulder  25  can transition between the first inner diameter B 1  and the second inner diameter B 2 . The outer surface of the bushing  20  may have several diameters. A diameter of a distal portion  26  of the outer surface of the bushing  20  can be selected to provide structural stability to the bushing  20 . Additionally, a thickness of the distal portion  26  can provide sufficient material for forming a distal weld, if one is used. The distal portion  26  can end at a distal end  27 . A diameter of a shoulder  28  of the outer surface of the bushing  20  can be adjacent and proximal to the distal portion  26 . The diameter of the shoulder  28  may be selected to project outward from the outer surface of the bushing  20 , with a sufficient distance to receive a pot  40  (see  FIG. 4 ), as described below. In one embodiment, a proximal end  29  of the shoulder  28  can be left as a sharp edge during manufacturing to provide a suitable surface for welding. In one embodiment, the distal portion  26  can have a length, the length equal to a distance between the distal end  27  of the bushing  20  and a distal end  31  of the shoulder  28 . In one example, the length of the distal portion  26  can be about 0.32 inches. Alternatively, the length of the distal portion  26  can be about 10% to about 20% of the total length of the bushing  20 . 
         [0027]    A diameter of a main portion  30  of the bushing  20  can be adjacent and proximal to the shoulder  28 . In one embodiment, the outer diameter of the main portion  30  can be selected to abut an inner surface of the pot  40  when it is positioned over the bushing  20 , as described below. A diameter of a proximal portion  34  may be selected so that the thickness of the bushing  20  at the proximal portion  34  approximately matches the thickness of the cold lead  10  sheath  14 . For example, the thickness of the bushing  20  at the proximal portion  34  can be plus or minus 15% of the thickness of the sheath  14 . In some examples, a more uniform and higher quality weld can be achieved when the thickness of the sheath  14  and the bushing  20  are approximately the same. In one embodiment, the proximal portion  34  can be about 0.35 inches in length to about 0.39 inches in length. Alternatively, the length of the proximal portion  34  can be about 15% to about 20% of the total length of the bushing  20 . The proximal portion  34  can terminate at a proximate end  35 . A proximal shoulder  36  can be used to transition between the outer diameter of the second portion  24  and the outer diameter at the proximal portion  34 . In one embodiment, the proximal shoulder  36  can be a straight, 90° angle. Alternatively, the proximal shoulder  36  can be tapered at an angle less than 90°. 
         [0028]    Referring to  FIGS. 4 and 5 , the end termination assembly may further include a pot  40 . The pot  40  can serve as a shell for enclosing a splice between the conductor  12  of the cold lead  10  and another conductor (not shown). The pot  40  can be constructed of any suitable metal for welding with the bushing  20  and for providing pressure and corrosion resistance. As non-limiting examples, the pot  40  can be constructed of copper, stainless steel, iron, or other applicable materials. The pot  40  can be substantially tubular with a first portion  42  having a first inner diameter P 1 . In one embodiment, the first inner diameter P 1  can be approximately equal to the outer diameter of the main portion  30  of the bushing  20 . A second portion  44  proximal to the first portion  42  can have an inner diameter P 2  that is larger than P 1 . In some embodiments, the first portion  42  of the pot  40  may have a length approximately equal to the distance from the proximal end  35  of the bushing  20  to the shoulder  28 , so that the proximal end  35  of the bushing  20  approximately abuts the second portion of the pot  40 , when the pot  40  is slid in place over the bushing  20  as described below. A transition shoulder  45  can be used to transition between the first portion  42  and the second portion  44 . In one embodiment, the proximal end  35  of the bushing  20  can extend into the second portion  44  of the pot  40 . This can create a void between the proximal portion  34  of the bushing and the second inner diameter P 2  of the pot  40 , for the length of the proximal portion  34  extending into the second portion  44  of the pot. This void can be filled with an epoxy or adhesive insulation when applied to the pot  40 , as described below. 
         [0029]    The outer surface of the pot  40  may be uniform in diameter, except for a first tapered portion  48  at a distal end  50  and a second tapered portion  52  at the proximal end  46 . The first tapered portion  48  and the second tapered portion  52  can have small lengths in comparison to the length of the pot  40 . For example, the length of the first tapered portion  48  can be about 6% to about 10% of the total length of the pot  40 . In another example, the length of the second tapered portion  52  can be about 3% to about 5% of the total length of the pot  40 . In one embodiment, the lengths of the tapered portions  48 ,  52  can be about 0.09 inches to about 0.25 inches. The angle of the taper of the first tapered portion  48  and the second tapered portion  52  can have a taper angle of about 15%. The tapered portions  48 ,  52  can have reduced outer diameters in relation to the rest of the outer surface of the pot  40 . In one embodiment, the second tapered portion  52  may be beveled at the proximal end  46 , the outer surface reducing in diameter over the second tapered portion  52 . In a further embodiment, the first tapered portion  48  can have a reduced diameter at the distal end  50  to provide an optimal thickness for welding. This thickness can be between about 10% and about 20% of the outer diameter of the first portion  42 . Additionally, a distal edge  51  of the first tapered portion  48  can be left as a sharp edge during manufacturing to facilitate welding. The second portion  44  of the pot  40  may further include one or more grooves  54  in the inner surface of the pot  40 . The grooves  54  may be configured to retain a sealing material, such as epoxy, to create a pot seal as described below. In some embodiments, the outer surface of the pot  40  can have a surface treatment (not shown). The surface treatment can provide protection against corrosion. Alternatively, the surface treatment can prevent scratching or marring of the pot. 
         [0030]    The design of the bushing  20  and pot  40  should meet specific criteria to be able to be welded to the sheath  14  and to each other, and then sealed as described below. For example, the treatment of edges between intersecting surfaces can affect the ease with which parts are slid over each other, as well as the quality of the welds at certain points. In some embodiments, edges that will be welded may be left sharp to provide material for forming the weld, and edges that are not welded may be trimmed to minimize snagging and cutting hazards. 
         [0031]      FIGS. 6A ,  6 B and  6 C illustrate an end termination assembly  60  including the bushing  20  and the pot  40 .  FIG. 8  illustrates an example method for attaching the end termination assembly  60  to the cold lead  10 . At step  100 , the cold lead  10  can be stripped at its proximal end to expose the desired length of conductor  12 . At step  110 , the bushing  20  and the pot  40  can be slid over the proximal end of the cold lead  10  until the exposed conductor  12  projects from the proximal end of the pot  40 . At step  120 , the conductor  12  may be spliced to the tail(s), cable conductor, or other conductor using any suitable conductor splicing technique, such as crimping, soldering, and the like. 
         [0032]    At step  130 , the cold lead  10  can be fed distally back through the bushing  20  until the exposed conductor  12  projects from the proximal end of the bushing  20  and the proximal end of the sheath  14  is approximately or entirely flush with the proximal end  35  of the bushing  20 . In this position, the splice of the conductor  12  will be inside the pot  40 . At step  140 , the bushing  20  can be welded to the sheath  14  at the proximal end of the bushing  20 . In another embodiment, the bushing  20  can be welded to the sheath at the proximal ends of each component, particularly at the proximal end  35  of the bushing  20 . The bushing  20  can also be welded to the sheath  14  at a distal end  27  of the bushing  20 . Alternatively, the bushing  20  can be brazed to the sheath  14  at a distal end  27  of the bushing  20  to provide strain relief at the distal end  27 . Welding the bushing  20  to the sheath  14  at the distal end  27  can provide a “backup” seal to support the weld at the proximal portion  32  of the bushing  20 . At step  150 , the pot  40  can be positioned over the bushing  20  so that the distal end  50  of the pot  40  contacts the shoulder  28  of the bushing  20 . At step  160 , the pot  40  can be welded to the bushing  20  at the distal end  50  of the pot  40 . In one embodiment, the pot  40  can be welded to the bushing  20  at the intersection  64  of the distal end  50  of the pot  40 , and the shoulder  28  of the bushing  20 . An electron beam or laser beam weld can be used to weld the bushing  20  and the pot  40 . Alternatively, other welding techniques, such as TIG welding, can be used to weld the bushing  20  and the pot  40 . 
         [0033]    In other embodiments, the pot  40  can be welded to the bushing  20  as described above before the assembly  60  is slid over the cold lead  10 . Where the pot  40  is welded to the bushing  20 , prior to the assembly  60  being slid over the cold lead, the sheath  12  would be welded to the bushing  20  at the distal end only. In other embodiments, the bushing  20  and pot  40  can both be welded as in steps  140  and  160  above before the splice (step  120 ) is completed. 
         [0034]    Referring again to  FIG. 8 , at step  170  the open proximal end  46  of the pot  40  can be partially or completely filled with an insulating adhesive  56 . The insulating adhesive  56  can be seen in  FIG. 6C . The insulating adhesive  56  can be used to coat, secure and protect the splice. The insulating adhesive  56  can create a hermetic seal which can be used to protect the insulation material of the mineral insulated cable from degrading over time. The insulating adhesive  56 , prior to curing, can cover the splice and flow into the grooves  42  to create a tight seal. In one embodiment, the insulating adhesive  56  can be an epoxy or similar temperature-resistant insulating adhesive. Additionally, polymers, such as DURALCO and/or other polyether ether ketone can be used to create the hermetic seal. These polymers, however, are typically not resistant to harsh chemicals or high pressure, especially if the environment is warm. In a preferred embodiment, the pot  40  can be welded to the bushing  20  to form a sealed and protected space for the insulating adhesive  56 . In a further embodiment, a high temperature heat shrink  58  can be applied to the conductor  12  to provide strain relief to the conductor  12  where it leaves the insulating adhesive  56 . Further, the high temperature heat shrink can also provide additional electrical insulation between the conductor  12  and the pot  40 . In one example, the high temperature heat shrink  58  can be a fluoropolymer, such as Sumitube® KH 230. Further,  FIG. 6C  illustrates a void  66  between the sheath  14  and proximal portion  34  of the bushing, as discussed above. The adhesive insulation  56  can therefore surround the sheath  14  as shown in  FIG. 6C . This can provide an additional seal between the pot  40  and the proximal portion  34  of the bushing  20 . 
         [0035]    Optionally, the outer surface of the insulating adhesive  56  at the proximal end  46  of the pot  40  can be used to connect (step  180  of  FIG. 8 ) another environmental seal. The additional environmental seal can be used to provide additional protection against high pressures and harsh chemicals. Referring to  FIG. 9 , a additional environmental seal can be seen in the form of a terminator cap  80 . The terminator cap  80  can be attached to a stub tube  82 . In one embodiment, the stub tube  82  can be inserted into the proximal end  46  of the pot  40 . In one embodiment, the stub tube  82  can be a hollow tube which can allow for one or more conductors (not shown) to pass through the stub tube  82  to the terminator cap  80 . Additionally, one or more conductors (not shown) may project distally from the terminator cap  80  for splicing with the conductor  12  of the cold lead  10 . In one embodiment, the terminator cap  80  can be welded or otherwise sealed against the proximal end  46  of the pot  40 . Alternatively, the terminator cap  80  can have grooves which can correspond to the grooves  54  of the pot  40 . The grooves of the terminator cap  80  can matedly couple with the grooves  54  of the pot  40  to seal the terminator cap  80  to the pot  40 . 
         [0036]    Referring to  FIG. 10 , a SWAGELOK or ferrule gland locking system  90  can be used. A back nut  92  may tighten against the pot  40  using a ferrule (not shown), as is known in the art, by matedly threading with a front nut  94 . An adapter  96  may be welded to the front nut  94  at point  95 . The adapter  96  includes a bore  98  that conforms and can be attached to a sleeve  99  of the stub tube  82 . Threading the nuts  92 ,  94  together tightly can relieve strain on the splice within the pot  40 . In one embodiment, the back nut  92  can be welded to pot  40 . Finally, other known sealing methods, such as oil field pressure balance sealing methods can be used as well to seal the proximal end  46  of the pot  40 . 
         [0037]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
         [0038]    Finally, it is expressly contemplated that any of the processes or steps described herein may be combined, eliminated, or reordered. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.