Sealing hollow structures

Abstract

A method of sealing a hole in a wall of a hollow structure comprises providing a sealed chamber that is external to the structure and that is in fluid communication with an internal space of the structure via the hole. The structure may be a pipe-in-pipe structure and the internal space may be an annulus between outer and inner pipes. Fluid flows through the hole into or out of the chamber as the pressure and/or composition of fluid in the internal space is adjusted. Then, a plug is spun and friction-welded into the hole. The plug is inserted into the hole from within the chamber.

Claims

1. An apparatus for sealing a hole in a structure, the apparatus comprising: a fitting defining a chamber, the fitting having an opening that communicates with the chamber; an attachment system for removably attaching the fitting to the structure with the opening facing the structure; a control system arranged to control the pressure and/or composition of fluid in the chamber; and a friction plug welding machine, which machine is arranged to advance a plug from the chamber and through the opening to seal the hole in the structure; wherein the welding machine is disposed within a housing that is attachable to the fitting to define an auxiliary volume in fluid communication with the chamber.

2. The apparatus of claim 1, wherein the opening is surrounded by a seal.

3. The apparatus of claim 1, wherein the welding machine is disposed within the chamber.

4. The apparatus of claim 1, wherein the welding machine is movable relative to the housing between a retracted position within the housing and a deployed position extended from the housing and into the chamber.

5. The apparatus of claim 1, further comprising a partition that is movable to seal the chamber from the auxiliary volume.

6. The apparatus of claim 1, wherein the fitting is shaped to define at least one saddle formation on an end of the fitting containing the opening.

7. The apparatus of claim 1, wherein the attachment system comprises one or more tensionable straps.

Description

(1) In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

(2) FIG. 1 is an exploded cross-sectional view of a clamp fitting in accordance with the invention, aligned with a port that penetrates the outer pipe of a length of PiP pipe;

(3) FIG. 2 corresponds to FIG. 1 but shows the fitting mounted on the pipe to surround the port in the outer pipe, and connected to a source of vacuum or gas;

(4) FIG. 3 corresponds to FIG. 2 but shows a housing attached to the fitting, that housing containing a welding tool;

(5) FIG. 4 corresponds to FIG. 3 but shows the welding tool advanced from the housing and through the fitting to weld a plug into the port;

(6) FIG. 5 shows the fitting, housing and welding tool removed from the pipe to leave the welded plug protruding from the pipe; and

(7) FIG. 6 shows the protruding part of the plug cut away and ground down flush with the outer pipe.

(8) FIGS. 1 to 4 of the drawings show a clamp fitting 10 of the invention that is arranged to be mounted onto a pipe 12 like a saddle.

(9) The pipe 12 is of PiP configuration and so comprises an outer pipe 14 that is concentric with and spaced from an inner pipe 16. The outer and inner pipes 14, 16 are commonly both of steel, although the inner pipe 16 could instead be of a composite material. A thermally-insulating annulus 18 is defined in the space between the outer and inner pipes 14, 16.

(10) As is conventional, the thermal insulation provided by the annulus 18 may be improved by altering the pressure and/or composition of the atmosphere in the annulus 18. For example, thermal management may involve evacuating air from the annulus 18 to draw down a partial vacuum in the annulus 18. Alternatively, thermal management may involve introducing other gases into the annulus 18 that reduce heat transmission, such as xenon or other rare or noble gases. Such gases may be at ambient pressure or below or above ambient pressure.

(11) To modify the atmosphere in the annulus 18 in these ways, the outer pipe 14 is penetrated by a drawdown hole or port 20 that communicates with the annulus 18. This allows air or other gases to be drawn from or pumped into the annulus 18 as appropriate. In accordance with the invention, the port 20 tapers so as to narrow in a radially-inward direction toward the central axis 22 of the pipe 12.

(12) In this example, the port 20 is aligned with the central axis 22 of the pipe 12. Such alignment between the port 20 and the central axis 22 is preferred but is not essential.

(13) The clamp fitting 10 comprises a tubular body 24 that surrounds a longitudinal axis 26. The longitudinal axis 26 is shown here intersecting the central axis 22 of the pipe 12 and in radial alignment with the port 20 in the outer pipe 14.

(14) The hollow interior of the body 24 opens to opposite ends to define a lumen 28 that extends longitudinally through the body 24. Those opposed ends of the body 24 are identified in the following description as outer and inner ends, expressed in a radial direction along the longitudinal axis 26 with respect to the central axis 22 of the pipe 12. The lumen 28 defines openings in the outer and inner ends of the body 24.

(15) In this example, the fitting 10 is capable of serving as an isolation valve. Thus, the lumen 28 of the body 24 can be closed by a partition 30 that is disposed between the outer and inner ends. The partition 30 is movable transversely across the longitudinal axis 26 between an extended, closed position shown in FIGS. 1 to 3 and a retracted, open position shown in FIG. 4. In the closed position, the partition 30 is sealed gas-tightly to the body 24 and thereby serves as a gate valve element.

(16) When in the closed position, the partition 30 seats into and seals against a complementary groove 32 in the body 24. A chamber 34 is thereby defined within the body 24 on the radially inner side of the partition 30. When the fitting 10 has been sealed to the pipe 12 and the partition 30 is closed as shown in FIGS. 2 and 3, the chamber 34 is a gas-tight space that communicates with the annulus 18 of the pipe 12 through the port 20 in the outer pipe 14.

(17) When in the open position, the partition 30 is accommodated by a hollow lateral extension 36 of the body 24. The interior of the extension 36 communicates with the lumen 28 of the body 24 but is otherwise isolated from the exterior of the body 24.

(18) Movement of the partition 30 between the closed and open positions is driven by a drive mechanism 38 that may be operable manually or by a motor. The drive mechanism 38 may, for example, comprise a screw 40 that acts between the partition 30 and the body 24.

(19) The outer end of the body 24 is surrounded by a mounting flange 42. Conversely, the inner end of the body 24 is shaped as a rigid skirt that extends toward the pipe 12 and surrounds the lumen 28 of the body 24. The skirt supports a continuous, resiliently-flexible gasket 44 in a saddle formation with concave cylindrical edge curvature to complement the outer radius of the pipe 12.

(20) The gasket 44 is shaped to surround the port 20 in the outer pipe 14 and to seal against the outer surface of the outer pipe 14 when the fitting 10 is pressed radially inwards against the pipe 12. For this purpose, the body 24 of the fitting 10 has attachment formations 46 that support respective ends of a chain, band or strap 48 that embraces the pipe 12. In this example, the attachment formations 46 extend from the body 24 substantially tangentially with respect to the outer diameter of the pipe 12. The strap 48 is tensioned to pull the fitting 10 toward the pipe 12 and hence to compress the gasket 44 gas-tightly against the pipe 12 as shown in FIGS. 2, 3 and 4.

(21) A side wall of the body 24 on a radially inner side of the partition 30 is penetrated by an opening 50 to which a pipe or hose 52 can be coupled to communicate with the chamber 34, as shown in FIGS. 2, 3 and 4.

(22) At its other end, the hose 52 communicates via a valve 54 with an atmosphere control system 56 for determining the pressure and/or composition of the atmosphere in the annulus 18. As is conventional, the valve 54 is shown as white when open and as black when closed.

(23) The system 56 may, for example, comprise a pump that is arranged to draw air from the chamber 34 and hence, via the port 20, from the annulus 18 to draw down a partial vacuum in the annulus 18. The system 56 may also, or alternatively, comprise a source of a thermally-insulating gas such as xenon that is pumped into the chamber 34 and hence, via the port 20, into the annulus 18 to replace air in the annulus 18.

(24) The hose 52 may be coupled to the opening 50 to connect the system 56 to the fitting 10 either before or after the fitting 10 has been attached to the pipe 12 as shown in FIG. 2.

(25) Turning now to FIG. 3, this shows a removable housing 58 attached to the fitting 10. The housing 58 defines an auxiliary volume that contains a friction taper plug welding tool 60.

(26) The housing 58 has an open inner end that is attached to the mounting flange 42 at the outer end of the body 24 of the fitting 10, such that the lumen 28 of the body 24 extends into the housing 58. The housing 58 thereby closes the open outer end of the body 24 while cooperating with the body 24 to define a continuous sealed enclosure that comprises the lumen 28 of the body 24 and the interior of the housing 58.

(27) The housing 58 is preferably attached to the fitting 10 after the fitting 10 has been attached to the pipe 12. In principle, however, the housing 58 could be attached to the fitting 10 before the fitting 10 is attached to the pipe 12, so that the housing 58 and the fitting 10 may be attached to the pipe 12 together. Similarly, the housing 58 and the fitting 10 may also be removed from the pipe 12 together or the housing 58 may be removed from the fitting 10 before the fitting 10 is removed from the pipe 12.

(28) The welding tool 60 is mounted to move relative to the housing 58 in directions parallel to the longitudinal axis 26. In this example, the welding tool 60 is mounted on rails 62 within the housing 58.

(29) A drive system 64 is operable move the welding tool 60 longitudinally within the housing 58. The drive system 64 may, for example, comprise a stepper motor that drives a pinion along a rack extending along at least one of the rails 62.

(30) The welding tool 60 comprises a motor 66 that is operable to turn a chuck 68 about the longitudinal axis 26 as shown in FIG. 4. The chuck 68 has jaws 70 that can be moved laterally to clamp a mandrel or welding plug 72 that is centred on the longitudinal axis 26.

(31) The plug 72 comprises a cylindrical body 74 and a tapered head 76. The taper angle of the head 76 substantially matches the taper angle of the port 20 in the outer pipe 14. The length of the head 786 substantially matches the thickness of the outer pipe 14. The diameter of the body 74, and hence of the widest part of the head 76, substantially matches the maximum width of the port 20 at the outer surface of the outer pipe 14.

(32) FIG. 3 shows the partition 30 in the closed position and the welding tool 60 retracted within the housing 58 to the extent that the head 76 of the plug 72 is on the radially outer side of the partition 30. Conversely, FIG. 4 shows the partition 30 now retracted into the open position. This allows the plug 72 to advance to the radially inner side of the partition 30 when the drive system 64 moves the welding tool 60 relative to the housing 58 in a radially inward direction.

(33) The atmosphere control system 56 may be activated before or after the partition 30 has been retracted. With the valve 54 in the hose 52 kept open, the system 56 draws air out of the chamber 34 and/or pumps a replacement gas into the chamber 34. This controls the pressure and/or composition of the atmosphere in the chamber 34 and hence in the annulus 18 that communicates with the chamber 34 through the port 20 in the outer pipe 14.

(34) FIG. 3 shows the atmosphere control system 56 activated before the partition 30 has been retracted, and drawing air from the chamber 34 and hence from the annulus 18 that communicates with the chamber 34 through the port 20. It would also be possible to activate the atmosphere control system 56 before the housing 58 is attached to the fitting 10, when the partition 30 is in the closed position to enclose and seal the chamber 34 as in FIG. 2.

(35) When the atmosphere in the annulus 18 is at the appropriate pressure and/or composition, the valve 54 in the hose 52 is closed as shown in FIG. 4. Next, the port 20 must be closed to seal the annulus 18 and hence to trap the atmosphere in the annulus 18 with the desired pressure and/or composition. For this purpose, the partition 30 is retracted into the open position to allow the drive system 62 to deploy the welding tool 60 from the housing 58 and into the chamber 34.

(36) The welding tool 60 is advanced from the housing 58 and into the chamber 34 to the extent that the heed 76 of the plug 72 enters the port 20 in the outer pipe 14. As the welding tool 60 is advanced in this way, the motor 64 turns the chuck 66 of the welding tool 60. This spins the plug 72 about the longitudinal axis 26 around which the port 20 is also centred.

(37) When the tapered head 76 of the spinning plug 72 encounters the similarly-tapered stationary wall that surrounds the complementary port 20, friction generates heat that quickly melts the interface between the head 76 and the surrounding outer pipe 14. The motor 64 is then stopped so that the now stationary plug 72 and the outer pipe 14 fuse together. As the molten interface cools, the port 20 is thereby sealed by virtue of a strong and continuous weld between the head 76 of the plug 72 and the outer pipe 14.

(38) After venting the chamber 34 to equalise pressure in the chamber 34 with the ambient air pressure, the fitting 10, housing 58 and welding tool 60 may be removed from the pipe 12. This leaves the body 74 of the welded plug 72 protruding from the outer pipe as shown in FIG. 5. Finally the body 74 of the plug 72 is cut away and ground down flush with the outer pipe 14 as shown in FIG. 6, leaving the head 76 of the plug 72 welded in the port 20.

(39) Many variations are possible within the inventive concept. For example, the inner pipe 16 could be lined with a polymer lining or other corrosion-resistant lining or coating. The outer pipe 14 could be coated with a protective or thermally-insulating coating of, for example, polypropylene. The annulus 18 could contain heating elements and/or insulating material. However, all such optional additions have been omitted from the drawings for clarity.

(40) The atmosphere control system 56 that determines the pressure and/or composition of the atmosphere in the annulus 18 could be configured to supply a gas into the chamber 34 whose composition supports the welding operation.

(41) The gasket 44 could be supplemented by a rigid locating structure that is shaped to match the curvature of or otherwise to engage the outer surface of the pipe 12 when the gasket 44 has been compressed by tightening the strap 48.

(42) In principle, it would be possible for the housing 58 to be integrated with the fitting 10 so that the housing 58 and the welding tool 60 form part of the fitting 10 and are attached to and removed from the pipe 12 as a single unit. In that case, the partition 30 could be omitted.

(43) Whilst the invention has been illustrated in the context of a pipe-in-pipe system, the invention could be used in other contexts. In particular, the invention could be used in other applications to seal a hole that is provided in a wall of a hollow structure for ingress or egress of fluid into or from a space within the structure, while managing the pressure or composition of the fluid and providing for the fluid to flow into or out of that space before the hole is sealed. In a broad sense, the fluid needs not be a gas but could be another fluid such as a liquid, a gel or a particulate mass.