Abstract:
An apparatus for amorphous bonding of tubulars ( 110,111 ) comprises a double skin jacket ( 2,113,114 ) which can be placed around said tubulars ( 110,111 ) which skins define a sealed inner fluid space ( 11,121 ) which contains shield gas and a heating element ( 1,129 ) and a sealed outer fluid space ( 9,119 ) surrounding the inner fluid space ( 11,121 ) to reduce the risk of explosion during the amorphous bonding process.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for amorphous bonding of tubulars. 
     During the construction of oil and gas wells it is usual to connect a large number of tubulars. Conventionally this is effected by screw couplings. One of the disadvantages of this construction is that the couplings are prone to corrosion with the result that a whole string of tubulars may have to be replaced every few years, particularly in high temperature, high pressure wells containing corrosive vapours. 
     It has been suggested that the longevity of such tubulars could be greatly increased, perhaps up to 25 years, if the couplings could be dispensed with. 
     One proposal for dealing with this problem has been to weld tubulars together. However, this is extremely hazardous at the head of an oil or gas well. Furthermore, normal manual welding does not result in a homogeneous metallurgical structure and the corrosion problem remains. 
     A technique of joining metal components known as “amorphous bonding” has been successfully utilised in the automotive industry. The surfaces of the components to be joined are ground into parallism. A foil of a metal alloy is then placed between the components which are mechanically pressed together. The joint is then subjected to local heating by an induction heater. The resulting structure is nearly metallurgically homogeneous. 
     It will be appreciated that it would be extremely desirable to be able to join tubulars by amorphous bonding. However, the technical difficulties are daunting insofar as it is necessary to transfer a process suited to a precision engineering shop to an area where inflammable and often explosive gas mixtures are present and where the rigidity of an engineering shop floor is replaced by a drilling platform which may well be offshore and which may be in continuous motion in heavy seas and inclement weather. 
     It is observed that UK patent specification No. 540,519 discloses a welding device comprising a ring burner which is surrounded by an annular water cooling jacket to reduce explosion hazards during the welding process. 
     European patent application No. 157131 discloses a double chambered sealing system for welding pipe end which injects inert shield gas in radial and axial directions into unsealed areas around the welding zone to prevent air contamination of said zone. 
     European patent application No. 418606 discloses an amorphous bonding apparatus in which nitrogen shield gas is injected into a jacket surrounding the bonded tubular ends and also nitrogen gas is injected into the interior of the bonded tubulars to create a virtually oxygen free atmosphere in the region of the bond. 
     Although the known devices provide some protection against explosion hazards they do not provide sufficient protection in an hazardous environment at the head of an oil or gas well. 
     The present invention is primarily concerned with reducing the risk of explosion while the amorphous bonding is taking place. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an apparatus for amorphous bonding the ends of tubulars which are in substantial axial alignment and surrounded by a shield gas, said apparatus comprising a jacket which in use is placed around said adjacent tubular ends, said jacket having an inner skin which, in use, defines a sealed inner fluid space containing a heating element and shield gas, and an outer skin which surrounds the inner skin such that in use a sealed outer fluid space is defined between said inner and outer skin. 
     It is preferred that said jacket is formed by two parts which are slidably mounted on a support frame and which can be urged together to form said jacket and that the inner skin is provided with fluid communication means which allow in use fluid to flow in a controlled manner from the inner fluid space into the outer fluid space or vice versa. 
     In one embodiment the apparatus comprises means to introduce a shield gas into the inner fluid space and means to introduce water into the outer fluid space and the fluid communication means comprises a conduit which, in use, can convey said shield gas to within said outer fluid space at a selected depth between the water level in the outer fluid space so that a selected pressure difference is maintained between the inner and outer fluid spaces. 
     In an alternative embodiment the apparatus comprises an inlet pipe for introducing a shield gas into the outer fluid space, an orifice in the inner skin for allowing the shield gas to flow from the outer fluid space into the inner fluid space and an outlet pipe for allowing the shield gas out of the inner fluid space, wherein preferably pressure control means are provided which in use control the pressure in the inner and outer fluid space such that the pressure in the inner fluid space is higher than the ambient pressure and the pressure in the outer fluid space is higher than in the inner fluid space. In this manner a high pressure gas shield is created in the outer fluid space which prevents air to flow into the inner fluid space and hot shield gases to leak from the inner fluid space into the atmosphere. 
     Suitably the apparatus further comprises a packer which in use is inserted into the interior of the tubular ends that are bonded by the apparatus, which packer comprises an elongate mandrel having a resilient packer element adjacent each end thereof, means to enable an inert shield gas to be introduced into an end of said elongate mandrel and to leave said elongate mandrel between said resilient packer elements, and means to enable water to be introduced into said end of said elongate mandrel and to leave said elongate mandrel between said resilient packer elements. 
     It will be understood that the external double skin jacket and the internal packer provide an adequate protection against explosion hazards during the amorphous bonding process since they prevent explosive gases to reach the area of the heating element and the tubular ends heated thereby and also prevent hot shield gases or other fluids to escape into the surrounding atmosphere. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which: 
     FIG. 1 is a vertical section through an amorphous apparatus according to the present invention; 
     FIG. 2 shows, to an enlarged scale, a view on line II—II of FIG. 1; and 
     FIG. 3 shows a schematic cross-sectional view of an apparatus according to the present invention in which pressurized shield gas is injected via the outer fluid space into the inner fluid space and then vented into the atmosphere. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1 there is shown an amorphous bonding apparatus which is generally identified by reference numeral  101 . 
     The amorphous bonding apparatus  101  comprises a support frame  102  which is provided with wheels  103  which run in channels (not shown). 
     Two clamps  104  and  105  are disposed towards the bottom of the support frame  102  whilst another two clamps  106  and  107  are mounted near the top of the support frame  102  and can be displaced vertically by two piston-and-cylinder assemblies  108  and  109 . 
     In use, a lower tubular  110  is secured in slips (not shown). The support frame  102  is then advanced towards the lower tubular  110  and the clamps  104  and  105  secured thereto. 
     An upper tubular  111  is then maneuvered into position using an elevator or a positioning device and gripped in the clamps  106  and  107 . The piston-and-cylinder assemblies  108  and  109  are then actuated to bring the lower end of the upper tubular  111  into close proximity to the upper end of the lower tubular  110 . The adjacent ends of the upper and lower tubulars are then brought into substantial alignment and machined such that the adjacent ends are substantially flat and parallel to each other. 
     Then a foil of alloy is placed on the upper surface of the lower tubular  110  and the upper tubular  111  is urged downwardly by the piston and cylinder assemblies  108 ,  109  with a predetermined pressure which varies according to the composition of the tubulars and the composition of the foil. 
     At this point the sealable beating apparatus  112  is mounted on the tubulars straddling the foil. The sealable heating apparatus  112  comprises two halves  113  and  114  which can be advanced and retracted by hydraulic rams. In particular, the half  113  can be advanced and retracted by hydraulic rams  115  while the half  113  can be advanced and  114  can be advanced and retracted by hydraulic rams  116 . 
     As can be seen from FIG. 2 the half  113  comprises an inner skin  117  and an outer skin  118  which define an outer fluid space  119  therebetween. The faces of the inner skin  117  and the outer skin  118  are each provided with resilient seals  120  which engage on sealing surfaces on the half  114  and together define a jacket which surrounds the lower tubular  110  and the upper tubular  111 . The resilient seals  120  also extend around the lower tubular  110  and the upper tubular  111  respectively. As indicated above, after the ends of the lower tubular  110  and the upper tubular  111  have been prepared for bonding a film of a suitable alloy is placed therebetween and the upper tubular  111  pressed against the lower tubular  110 . 
     The halves  113  and  114  are then moved into position either side of the tubulars  110 ,  111  and pressed together with the hydraulic rams so as to form an inner chamber  121  enclosed by the inner skin  117 . The two halves  113  and  114  are then fastened together with six mechanical fasteners (not visible) to ensure that the halves do not inadvertently come apart. 
     The outer fluid space  119  is then filled with water (H 2 O) from inlet pipe  122 . The water fills the outer fluid space  119  and leaves through outlet pipe  123 . The water is continually pumped through the outer fluid space  119  and its presence is detected by a sensor  124  which is designed to inhibit the remainder of the process if no water is present or the temperature of the water exceeds a predetermined temperature. 
     The outer fluid space  119  can be emptied via drain line  125 . An emergency water tank  126  and emerging water supply  127  are provided so that the outer fluid space  119  can be deluged with water in an emergency, for example catastrophic failure of a. seal resulting in loss of water from the outer fluid space  119 . 
     The inner fluid space or chamber  121  is cooled by a flow of shield gas which is introduced through a manifold  128  situated below an induction heating ring  129 . The shield gas is supplied via gas supply pipe  130  which is, in turn, connected to a source of compressed air via air line  131  and a source of argon shield gas via argon line  132 . 
     The inner chamber  121  is also provided with two gas exit pipes  133 ,  134  which are connected to an exit manifold  135 . The exit manifold  135  is connected to an argon flushing line  136  and a line  153  which opens into the outer fluid space  119  well below outlet pipe  123 . 
     A sampling pipe  137  is provided to allow samples of gas from within the inner chamber  121  to be continually taken and analysed. 
     The induction heating ring  129  is independently water (H 2 O) cooled by a water supply which is pumped through inlet pipe  138  and leaves through outlet pipe  139 . The induction heating ring  129  is provided with power via heavy metal conduits which are symbolised by wires  140  and  141 . 
     While the heating apparatus  112  is being prepared an internal packer  142  is lowered down the upper tubular  111 . The purpose of the internal packer  142  is threefold, viz: 
     (1) to prevent inflammable, and possibly explosive, vapour rising up the lower tubular  110 ; 
     (2) prevent air coming down the upper tubular  111 ; and 
     (3) allow a desired atmosphere to be created in the vicinity of the joint. 
     With these purposes in mind the internal packer  142  comprises an elongate mandrel  143  with a resilient packer element  144 ,  145  at each end thereof. Each resilient packer element  144 ,  145  is connected to a source of pressurized water via packer element control line  146 . When pressurized water is supplied through packer element control line  146  both the packer elements  144 ,  145  expand and form a seal between the elongate mandrel  143  and the upper tubular  111  and lower tubular  110  respectively thereby forming an isolated chamber  147 . 
     The centre of the elongate mandrel  143  is provided with an elongate bore  148  which is connected to a water (H 2 O) inlet tube  149  and is provided with a multiplicity of radial outlet tubes  150  which open into the isolated chamber  147 . An argon supply pipe  151  also passes downwardly through the elongate mandrel  143  and opens into the isolated chamber  147  immediately above the resilient packer element  145 . 
     After the apparatus  112  has been properly positioned, the internal packer  142  positioned, and the resilient packer elements  144 ,  145  set, the amorphous bonding process proceeds as follows: 
     1. Water flow is established through the outer fluid space  119 . 
     2. The inner chamber  121  is purged with air for a fixed time and in any event until the gas sampled through the safety device  137  does not record an unacceptable level of hydrocarbons. 
     3. The air supply is switched off and argon is passed through the inner chamber  121  to form an atmosphere of argon shield gas to the outside of the joint. 
     4. When the sample of gas being taken through the sampling pipe  137  indicates that the atmosphere in the inner chamber  121  is substantially pure argon the inner chamber  121  is ready. During steps 3 and 4 argon leaves the system via argon flushing line  136  and can, if desired, be recovered for use in other application. 
     5. During steps 2, 3 and 4 the isolated chamber  147  is purged by the introduction of argon shield gas through argon supply pipe  151 . The argon purges the isolated chamber  147  and leaves via an outlet tube (not visible). A sensor in the outlet tube checks the argon content of the gas passing through the outlet tube and inhibits activation of the induction heating ring  129  until the gas passing through the outlet tube is substantially pure argon. Air is also introduced into the upper tubular  111  via pipe  152  to purge any combustible gases from inside the upper tubular. 
     6. At this stage power is applied to the induction heating ring  129  to heat the metal in the area of the joint to a temperature in the range of about 1000-1300° C. for a predetermined period. However, safety requirements necessitate the surrounding area being kept as cool as practicable. With this in mind argon is pumped through the inner chamber  121  and the isolated chamber  147  throughout the heating process. Furthermore, air is pumped through the pipe  152 . 
     The argon which leaves the inner chamber  121  via gas exit pipes  133 ,  134  is directed through line  153  by closing valves  154  and opening  155 . The argon bubbles through the water and is cooled thereby before venting into the atmosphere. Furthermore, the pressure of argon in the inner chamber  121  can be controlled by varying the depth of the outlet of the line  153  below the water level. This provides a simple and effective method of controlling the pressure in the inner chamber  121 . 
     After the requisite period the induction heating is ceased and the joint allowed to cool whilst the flow of argon continues. 
     When the joint has been cooled sufficiently the supply of argon through argon supply line  151  is terminated and cooling water is introduced through water inlet tube  149 . The supply of water is continued until the tubulars  110  and  111  are suitably cooled at which time the supply of argon to the inner chamber  121  via gas supply pipe  130  is stopped. The supply of water to the outer fluid space  119  is also stopped and the outer fluid space  119  drained by opening a valve  156  in the drain line  125 . 
     The halves  113  and  114  are then withdrawn. 
     Only when it is determined that it is safe to do so is the water supply to the packer  142  via water inlet pipe  149  terminated. The resilient packer elements  144 ,  145  are then deflated and the packer  142  withdrawn. 
     The tubulars  110  are then released from the clamps  104 ,  105   106 ,  107  and the amorphous bonding apparatus  101  rolled back. 
     The joint is then tested. If the test is successful the tubulars are lifted to enable the slips to be released and lowered into the hole. The slips are then applied and the process repeated. 
     Various modifications to the embodiment described are envisaged, for example air, or preferably, as described with reference to FIG. 3, an inert shield gas such as nitrogen could be circulated through the outer fluid space  119  instead of water. Instead of purging the isolated space  147  with argon it could be initially purged with air subsequently argon for the heating step. If desired, after the induction heating is completed and cooling has commenced the resilient packer element  144  (but not the resilient packer element  145 ) could be released prior to the introduction of cooling water. This would allow any steam found to rapidly escape and further purge the inside of the upper tubular. 
     Turning now to FIG. 3 an amorphous bonding heating coil is identified by reference numeral  1 . 
     The amorphous bonding heating coil  1  surrounds a tubular  110  and is surrounded by a jacket enclosure  2  having a first half  3  and a second half  4 . 
     Each half  3 ,  4  comprises an inner skin  7  and an outer skin  8  defining an annular outer space  9  therebetween. 
     The halves  3  and  4  are provided with seals which interengage when the halves  3  and  4  are clamped together and which are intended to form the sealed jacket enclosure  2 . However, to facilitate understanding the present invention it will be assumed that there is a small gap  5  between the halves  3 ,  4 . 
     In use, an inlet pipe  6  conveys inert shield gas into the annular outer space  9  between the inner skin  7  and the outer skin  8 . The annular outer fluid space  9  is maintained at a pressure P 1  which is slightly greater than the ambient pressure P 0 . An orifice  10  allows part of the inert shield gas to pass into an inner fluid space  11  inside the inner skin  7 . The inert gas can then pass from the inner fluid space  11  to an isolated outlet pipe  12 via an orifice  13  which is set to maintain the pressure P 2  in the chamber  11  between P 1  and P 0 . 
     In use, cool inert gas is passed through inlet pipe  6 . Part of the cool inert gas passes into the annular outer fluid space  9  whilst the balance flows through the inner fluid space  11  via orifice  10  and orifice  13 . When the induction heater  1  is operational the inert gas in the inner fluid space  11  is heated and the heated inert gas leaves via insulated outlet pipe  12  which vents to atmosphere in a safe area optionally after being indirectly cooled. 
     As can be seen from the arrows  14 ,  15  in the event of a leak in the outer skin  8  cool inert gas from the annular outer fluid space  9  passes through the gap into the ambient air since the pressure P 1  in the space  9  is higher than the ambient pressure P 0 . Similarly, in the event of a leak in the inner skin  7  cool inert gas passes from space  9  through the inner skin  7  into the inner fluid space  11 . 
     It will be appreciated that with the arrangement disclosed the probability of hot shield gases leaking to the atmosphere surrounding the enclosure  2  is small. 
     Various modifications to the embodiment claimed are envisaged, for example the inlet pipe  6  and the orifice  10  could be disposed to help ensure that the annular outer fluid space  9  is constantly replenished with cool inert gas, thus reducing the possibility of small pockets of hot inert gas accumulating in the outer fluid space  9 . If desired several inlet pipes  6  and several orifices  10  could be provided. 
     It will be appreciated that the orifices  10  and  13  could be formed by adjustable valves or pressure relief valves. 
     If desired flow and temperature sensors may be provided which are arranged to stop the amorphous bonding process and drench the entire area with water if a signal is detected indicative of a major leak. 
     Such sensors could comprise flow sensors in the inlet pipe  6  and the insulated outlet pipe  12 .