This invention relates to a method and apparatus for drilling a hole in an internally lined container such as a fluid conduit pipe. Particularly, but not exclusively, this invention is for application to conduit pipes used in the gas, oil and water industries which are connected in service.

It is often necessary in pipe conduit networks to add pipes, fittings and servicing equipment. For instance, it is frequently necessary to provide additional service lines to existing mains pipes. The first stage in any such installation is to cut a hole in the existing pipe. This can be a particularly problematic process if the pipe has been fitted with an internal lining.

Fitting fluid conduit pipes with a lining is common practice in the industry, such linings being employed as an anti-corrosion support and to aid in leak prevention. Typical pipe linings used comprise fibre woven into a tube and impregnated or coated with a polymer to provide an impervious surface.

Problems can arise with all know methods and machinery for cutting holes in such pipes because the hole saws used are chosen for their ability to cut through the pipe material and are therefore generally unsuitable for cutting the liner material. This can result in the liner suffering considerable damage as a hole is drilled through it, making it extremely difficult to reseal the lining around the finished hole. Furthermore, it is generally necessary when cutting a hole through an internally lined pipe to require that the pipe is first isolated from the system. This results in a complicated, time consuming procedure and can cause significant inconvenience to users of the service in question.

It is an object of the present invention to obviate or mitigate the above problems.

According to the present invention there is provided a method for cutting a hole of a predetermined diameter into a container having an internal lining, comprising the steps of:

a) drilling a first pilot hole in the said container without cutting a hole through the said internal lining, the diameter of the pilot hole being less than the said predetermined diameter; b) inserting a holding member through the pilot hole to push the lining away from the inner wall of the container in the vicinity of the pilot hole; c) drilling a second hole with said holding member in position, the second hole having the said predetermined diameter; d) removing the holding member from the second hole; and e) inserting a cutter through the second hole to cut a hole in the lining.

The invention also provides apparatus for cutting a hole of a predetermined diameter in a container having an internal lining, the apparatus comprising means for drilling a first pilot hole in the container without cutting through the lining, a holding member insertable into the pilot hole to push the lining away from the inner wall of the container in the vicinity of pilot hole, means for drilling a second hole of the said predetermined diameter in the container with the holding means in position, and means insertable through the second hole for cutting a hole in the container lining.

Preferably the pilot hole drilling means comprises a hollow spindle, having a drive end for engagement with a drive mechanism and a drill end fitted with a tubular hole saw, wherein the hollow spindle houses a pushing member and a biasing means, said biasing means biasing the pushing member so as to extend through the said drill end of the spindle and coaxially through the tubular hole saw. Preferably the pushing member comprises a plunger provided with a body portion in slidable engagement with the internal surface of the hollow spindle and an elongate portion extending from the body portion through the hole saw. Preferably the biasing means comprises a coil spring disposed along the axis of the spindle between the drive end thereof and the body portion of the pushing member.

Preferably the said holding member comprises an elongate member dimensioned to pass through the pilot hole without piercing the pipe lining.

Preferably a second hole drilling means comprises a spindle having a drive end for engagement with a drive mechanism and a drill

end fitted with a tubular hole saw. The said spindle may support the said holding member such that it extends through the tubular hole saw. Preferably the holding member comprises a plunger fixed to the drill end of the spindle. Preferably, at least one end of the holding member is free to rotate with respect to the spindle.

Preferably the lining cutting means comprises a first spindle having a drive end to engage a drive mechanism and a cutting end supporting a cutting element. Preferably the said first spindle is rotatably housed within a hollow second spindle. Preferably the lower end of the second spindle is arranged to enable pressure to be applied to the first spindle whilst the first spindle rotates to cut the container lining. Preferably the second spindle is fitted at its upper end with an auxiliary bridle engageable by a feed screw to apply the necessary axial pressure to the second spindle.

The container may be connected in service at the time the holes are cut. In such circumstances, the various drilling and cutting components are used when mounted in a chamber sealed onto part of the container. Such chambers are well known.

This invention therefore provides a method and apparatus in which different cutting elements are used to cut the container and the lining. This has the advantage that the lining cutter can be chosen specifically for its ability to cut a clean hole in any particular lining material, therefore avoiding any unnecessary damage to the lining.

A specific embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is an axial section of a first pilot hole drilling assembly which may be used in accordance with the present invention;

Fig. 2 shows a part sectioned second hole drilling assembly which may be used in accordance with the present invention; and

Fig. 3 shows a part sectioned liner cutting assembly which may be used in accordance with the present invention.

Referring to the drawings, Figs. 1, 2 and 3 respectively show three interchangeable assemblies that may be used in place of a conventional hole cutter of a conventional drilling machine (not shown). All three of the operating assemblies are used sequentially in the method described below.

Referring to Fig. 1, a pilot hole drilling assembly comprises a hollow spindle 1 fitted at one end with a drive end piece 2 and at the opposite end with a drill end piece 3.

The drive end piece 2 has a threaded body section 4, a circumferential flange 5 and a square head 6. The body 4 of the drive end piece 2 is screwed into the end of the pilot spindle 1 such that the flange 5 seats on the spindle 1. The square head 6 receives an adapter 7 which is used to drive the spindle 1 and against which a feed screw 8 bears.

The drill end piece 3 has an insert portion 9, a circur. rential flange 10 and a central circular threaded boss 11. An axia. bore 12 extends through the drill end piece 3, opening into the centre of the boss 11. The insert portion 9 fits into the end of the pilot spindle 1 with the flange 10 seating on the spindle 1. The drill end piece 3 supports a small diameter tubular pilot hole saw 13 which is screwed onto the boss 11.

The interior of the hollow spindle 1 houses a plunger 14 which has a head 15 of substantially the same diameter as the interior of the spindle 1, and a rod 16 disposed coaxially with the spindle 1. The plunger rod 16 extends through the bore 12 of the drill end piece 3 and into the centre of the tubular pilot hole saw 13. The plunger 14 is biased by a coil spring 17 housed axially within the spindle 1 between the drive end piece 2 and the plunger head 15. The action of the spring tends to push the end of the plunger rod 16 beyond the cutting end of the pilot hole saw 13.

Referring to Fig. 2 the illustrated drilling assembly comprises a solid spindle 18 which has a square head piece 19 at the drive end and a radially extending flange 20 at the drill end. In use the square head 19 receives the adapter 7 (Fig. 1). The drill end supports a hole saw 21 which is located by pegs 22 fixed on the spindle 18. A plunger having a main body portion 23 and a tip 24 is screwed onto a threaded stud 25 on the end of the spindle 18. An apertured washer 26 is sandwiched between the body 23 and the hole saw 21 such that the hole saw 21 is clamped to the spindle 18 by the force applied to it via the washer 26. The plunger tip 24 is supported on bearings 27 and 28 so as to be rotatable relative to the body 23.

Referring to Fig. 3, the illustrated liner cutting assembly

comprises two coaxial spindles 29 and 30. The inner spindle 29 supports a square head portion 31 at the drive end to receive the adapter 7 (Fig. 2) and a lining cutter 32 at the opposite end.

The outer spindle 30 supports an auxiliary bridle 33 at its upper end, and is provided with a flange 34 at its lower end. The auxiliary bridle 33 is adapted to receive a feed screw (not shown). The arrangement allows for rotational force to be applied to the inner spindle 29 via the head portion 31 whilst an independent axial force is applied to the external spindle 30 via the auxiliary bridle 33. A washer 35 enables axial force applied to the spindle 30 to be transmitted to the spindle 29.

The procedure for drilling a hole into a lined conduit pipe involves three steps using each of the above described operating assemblies in turn. Each of the three operating assemblies can be driven by the same conventional drilling machine (not shown). The procedure for drilling the hole is as follows:

The pilot hole drilling assembly of Fig. 1 is fitted to the drilling machine and is pushed towards the surface of a pipe (not shown) until the pilot hole saw 13 locates on the surface of the pipe wall. This pushes the plunger 14 into the hollow spindle 1 against the action of the spring 17. The end of the plunger rod 16 bears against the pipe wall under the force of the spring 17. Drilling is then commenced with the feed screw 8 applying axial force to the spindle 1. As the drill saw breaks through the pipe wall, the plunger rod 16 is thrust through the pilot hole in the pipe wall under the action of the spring 17, pushing the pipe lining away from the cutting edge of the saw 13. Thus a pilot hole is drilled into the pipe wall without cutting the pipe lining. The small pilot hole coupon is then removed from the hole and any swarf is cleaned away.

For the second stage of the procedure the pilot hole drilling assembly is removed from the drilling machine and the drilling assembly of Fig. 2 is fitted in its place. The drilling assembly is then positioned against the pipe wall with the plunger tip 24 located within the pilot hole. Drilling is then commenced. The plunger tip bears against the pipe liner as the hole is drilled into the pipe, thereby pushing it away from the inner wall of the pipe and thus away from the cutting edge of the saw The tip 24 of the plunger is free to

rotate relative to the spindle 18 and thus does not have . any tendency to bore its way through the liner. This therefore enables a full size pipe fitting hole to be cut in the pipe wall without cutting the liner. The drilling assembly is then removed from the hole. The resulting coupon is either retained within the tubular saw 21 or removed as a separate operation.

For the final stage of the procedure, the hole drilling assembly of Fig. 2 is removed from the drilling machine and the liner cutting assembly of Fig. 3 is fitted. The spindle 29 is driven in rotation, and the assembly is forced through the liner as a result of a feed screw (not shown) bearing against the bridle 33.

The apparatus and method described above can be used to drill holes in pipes that have first been isolated from the system or can be used in conjunction with known machinery to drill holes in lined pipes that are connected in service, i.e. that are filled with pressurised fluid. In the latter case the pressure in the pipe will actually aid the procedure by providing an internal pressure that opposes the pressure applied by the liner cutting assembly and thereby supports the lining as it is cut. This will both increase the ease with which the lining is cut and result in a cleaner cut edge.

It will be appreciated that the possible applications of the apparatus and method described are not limited to fluid conduit pipes. For instance, they could be used to cut holes through lined fluid storage tanks.