GB2145489A - Connecting tubes to walls - Google Patents

Abstract

A method of connecting a tube 1 to a wall 2 comprises friction welding the tube to the wall 2; and puncturing that portion of the wall 2 surrounded by the tube 1 to enable fluid communication from one side of the wall 2 to the other through the tube 1. A conventional drill bit 5 connected to a drill 6 may be used to puncture the wall. The method may also be used for connecting a branch pipe to a main pipe, as shown in Fig. 2. For highly curved walls part of the wall surface (12, Fig. 2) of the main pipe is machined flat in a preliminary stage before friction welding. <IMAGE>

Description

SPECIFICATION Improvements relating to welding The invention relates to methods and apparatus for making connections with a wall of a body or vessel primarily to enable fluid communication via the connection with the body or vessel.

In order to make the connection it is necessary to puncture a wall of the body or vessel and this can be dangerous where the body or vessel contains fluid under pressure, particularly a hazardous fluid since leakage of the fluid can occur.

Problems also arise where the connection with the body or vessel must be made in a liquid environment, particularly at considerable depth. For example, at depths of 600 feet in water it is not practical to arc weld a tubular connection to a surface.

In accordance with the present invention, a method of connecting a tube to a wall comprises friction welding the tube to the wall; and puncturing that portion of the wall surrounded by the tube to enable fluid communication from one side of the wall to the other through the tube.

This invention is particularly applicable to making connections in a liquid environment at depth where arc welding is impractical.

Preferably, where the connection is made in a liquid environment, a tubular shroud is mounted around the friction joining zone to prevent liquid impinging on the friction joining zone. When friction welding at depth in a liquid environment, it is preferable for the shroud to comprise polyurethane foam or a thermoplastic material such as nylon. The shroud prevents external quenching and thus improves the friction weld.

In some cases, the tube may first be friction welded to the wall and subsequently a drill bit is inserted into the tube to puncture the wall.

In these cases, the tube may serve as a guide for the drilling bit. However, where liquid under pressure is contained behind the wall it may be desirable for the wall to be punctured before welding has finished since the liquid released after puncturing will quench the joint zone internally and reduce internal flash.

In one particularly convenient method, the friction welding and drilling steps are carried out in a single operation. Preferably, a cutting tool is mounted in and protrudes from a leading end of the tube, rotation of the tube causing rotation of the cutting tool. With this arrangement as soon as the wall is punctured, the cutting tool will move rapidly into the opening and the tube will engage the wall around the puncture and will be friction welded to the wall. Thus, significant leakage of fluid through the puncture is prevented.

Conveniently, in this case, the cutting tool may include a passage communicating with the interior of the tube through which fluid can pass from one side of the wall to the other. Additionally, closure means are preferably associated with the tube to prevent fluid flow through the tube while the connection is being made. The closure means may comprise a valve such as a non-return valve and conveniently is a ball valve. The provision of a closure member is particularly useful where the connection is made with a pipe or vessel containing fluid at a higher pressure than the environment.

An example of an application of this technique is, as previously mentioned, underwater welding, particularly the connection of a tube to a larger pipe. The connection may be used to draw fluid from a pipe, (as in so-called hot tapping), or to allow compressed air to be forced into the pipe or other closed container, or even to execute regrouting by forcing in liquid concrete. The underwater operations may include salvage.

Preferably the tube to be joined is fitted with rotary driving means such as a hexagon protrusion on the outside of the tube, with further thread connecting means on the outside or the inside for joining to extension tubes, pipes, hoses or other connectors connected to suitable containment vessels. In the examples where the attachment tube contains cutting means with the hole being obtained at the same time as the joining operation, relative dimensions can be chosen such that the drill cuts through first with the tube subsequently bonding to the wall, or alternatively the friction weld can commence before the final breakthrough is achieved. In this connection it is noted that significant material is displaced from the tube such that an axial movement of typically 3-5 mm is obtained for a tube of nominally 3-6 mm thickness.

In joining a connection tube to an existing pipe or curved wall of a vessel some tolerance in mismatch of curvature is acceptable such as 1 mm gap depending on the wall thickness of the connector and of the pipe or vessel wall. If the mismatch is sufficiently excessive to impair the friction joining operation then the curved surface is preferably machined flat or a matching patch added with one external flat surface. This patch is first hermetically joined to the curved surface, preferably by arc welding all around its periphery.

Many other applications are possible using similar methods wherewith the connection is made to the pipe or vessel concerned in conjunction with a drilling or cutting operation to gain access to the remote side of such pipe or vessel. The methods described minimise the loss of fluid and are executed much more expeditiously compared with, for example, cutting and threading a hole in the wall to allow a tubular connection to be made. Furthermore, the friction welded zone can be significantly smaller than the sizes required for subsequent threaded connection to pressure vessels or other plant. This is particularly the case with relatively thin wall pipes or pressure vessels where the wall thickness is inadequate for sufficiently strong threaded joining, but where the friction joints can be stressed to relatively high levels.Thus for example the friction joint may be only 15 mm diameter whereas an extended threaded joint on the tubular connector may be 25 mm diameter and so forth.

Some examples of methods in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Figures 1A-1C are partial cross-sections illustrating different stages in one method according to the invention; Figure 2 is a partial cross-section illustrating part of a second method according to the invention; Figure 3 is a schematic part-sectional view of a completed connection made using a third method according to the invention; and, Figures 4A-4C illustrate the friction welding of a stud under different conditions.

Figures 1A-1C illustrate different stages in the connection of a metal tubular connector 1 to a wall part 2 which may be part of a pipe or other vessel. The tubular connector 1 is mounted between external jaws 3 of a conventional friction welding machine clamped relatively to the wall part 2 and is secured in position when the jaws 3 are urged against a mandrel 4 forming part of the welding machine. In a conventional manner, the welding machine causes the jaws 3 to rotate relatively to the wall part 2 thus causing the tubular connector 1 to rotate. At the same time, the tubular connector 1 is urged against the wall part 2 and rotation is continued for a duration sufficient for the frictional heat generated to achieve an interfacial temperature at which the metal in the joint zone where the connector 1 abuts the wall part 2 is in the plastic state.Once this condition has been achieved with a sufficient build-up of heat rotation is stopped and the tubular connector 1 is urged under considerably greater force against the wall part 2 and welding occurs.

The jaws 3 are then released and the friction welding machine is removed. A conventional drill bit 5 (Figure 1 B) connected to a drill 6 (only part of which is shown in Figure 1 B) is inserted into the tubular connector 1 now welded to the wall part 2. The drill bit 5 is rotated by the drill 6 so that an aperture 7 (Figure 1C) is formed in the wall part 2 within an area defined by the wall of the tubular connector 1. As may be seen in Figure 1 B, the tubular connector 1 helps to guide the drill bit 5 during the drilling operation.

The drill bit 5 is then removed and a hose 8 having an externally screw-threaded ferrule 9 is screwed into the free end of the tubular connector 1 which is provided with an internal screw-thread 10. Fluid communication is thus achieved between the hose 8 and the side of the wall part 2 remote from the tubular connector 1.

Where the operation is carried out underwater or the side of the wall part 2 remote from the tubular connector 1 is under pressure then a seal 11 (Figure 1 B) may be provided around the free end of the tubular connector 1 and engaging the drill 6 to prevent fluid flow occurring at the moment when the aperture 7 is formed. This seal 11 is conveniently self-sealing so that on withdrawal of the drill bit 5 the seal closes the free end of the tubular connector 1 thus preventing fluid communication from occuring. Subsequently, when the hose 8 is connected, the seal 11 will be removed. A valve arrangement could be used instead of the seal 11 in a manner well known to a person skilled in the art.

In some cases, the wall part 2 will not present a plane face to the tubular connector 1. As has previously been mentioned, if there is only about a 1 mm gap then there will be no difficulty during the friction welding operation. However, for more highly curved walls part of the wall surface 12 is machined flat in a preliminary stage before friction welding.

This is shown in Figure 2.

Another example of a method in accordance with the invention is illustrated in Figure 3. In this case, a tubular connector 13 of a hard metal having a first portion 14 and a second integral portion 15 is used. The leading end of the portion 15 is provided with a set of cutting teeth 16. The connector 13 is screwthreaded onto a tubular member 17 the trailing end of which 18 is internally screwthreaded and will initially be gripped between jaws 3 and a mandrel 4 of friction welding apparatus similar to that shown in Figure 1A.

A ball member 19 is urged against a seat 20 by a compression spring 21. The seat 20 is formed by an internal, integral flange 22 of the tubular member 17. The compression spring 21 has a conical shape with its end remote from the ball member 19 engaging a trailing end 23 of the tubular connector 13.

Initially, the ball member 19 closes an aperture 24 in the flange 22.

In use, the friction welding machine causes the tubular member 17 to rotate thus causing the tubular connector 13 to rotate via the screw thread connection so that the cutting teeth 16 cut into the wall part 2. Eventually, the teeth 16 will cut through the wall part 2 to form an aperture 25.

Once a shoulder 14' of the connector portion 14 abuts the wall part 2 (when the aperture 25 has been formed) further rotation of the tubular connector 13 relatively to the wall part 2 will generate frictional heat causing abutting portions of the connector 13 and wall part 2 to become plastic. When enough frictional heat has been generated rotation can be stopped and the tubular connector 13 can be urged under a high force against the wall part 2 to which it will be friction welded.

When the tubular connector 13 has been friction welded in place, the friction welding machine is disconnected from the tubular member 17. At this point, fluid communication through the aperture 25 is prevented since the ball member 19 is still against the seat 20. A pipe 26 may now be connected to the tubular member 17. The pipe 26 has a ferrule 27 having an externally screw-threaded spigot 28 and a central nose 29. The spigot 28 is screwed into the trailing end 1 8 of the tubular member 17 so that the nose 29 protrudes through the aperture 24 and engages the ball member 19. As the spigot 28 moves in an axial direction the nose 29 pushes the ball member 19 away from the the seat 20 thus allowing fluid communication through the aperture 24.

In an alternative arrangement, not shown, a hollow drill bit is push fitted in the leading end of the tubular connector 1 and protrudes from the end of the connector 1. This represents a hybrid between the example shown in Figures 1A-1C and the example shown in Figure 3 since in this case an aperture will be formed in the wall part prior to friction welding taking place. Essentially, the drill bit replaces the cutting teeth 16 of the Figure 3 example.

One of the important applications of these methods is in the field of underwater welding in which case the friction welding machine may be the machine presently manufactured and sold by the applicants.

Furthermore, where the connection is to be made in a liquid environment, such as underwater, it is preferable to provide a tubular shroud such as polyurethane foam or nylon around the friction joining zone. An example of such a shroud is indicated by reference numeral 29 in Figures 1A-1C. The advantage of such a shroud may be appreciated by referring to Figures 4A-4C. These figures illustrate the friction welding of a stud 30 to a wall part 31 although similar results will occur with tubular connectors. Figure 4A illustrates the formation of a weld in air between the stud 30 and the wall part 31. Figure 4B illustrates the same weld being formed underwater at 21 bar pressure and without a shroud and it will be seen that due to quenching, the weld formation is impaired. Figure 4C illustrates the same weld being performed underwater and at 21 bar pressure but with a polyurethane shroud and it will be seen that this closely conforms to that shown in Figure 4A.

Claims (7)

1. A method of connecting a tube to a wall, the method comprising friction welding the tube to the wall; and puncturing that portion of the wall surrounded by the tube to enable fluid communication from one side of the wall to the other through the tube.

2. A method according to claim 1, wherein the method is carried out in a liquid environment, the method further comprising providing a tubular shroud around the friction joining zone to prevent liquid impinging on the friction joining zone.

3. A method according to claim 1 or claim 2, wherein a leading end of the tube is provided with cutting teeth.

4. A method according to claim 1 or claim 2, wherein a cutting tool is initially push fitted in and protrudes from the leading end of the tube.

5. A method according to any of the preceding claims, further comprising preventing fluid flow through the tube while the connection is being made.

6. A method according to claim 5, wherein a non-return valve is associated with the tube to prevent fluid communication.

7. A method of connecting a tube to a wall substantially as hereinbefore described with reference to any of the examples shown in Figures 1 to 3 of the accompanying drawings.