GB2210947A - Stopping a flow passage - Google Patents

Abstract

A flow passage (10) containing fluid under high pressure is stopped by a composition (34) with a high expansion rate and long gel time. The composition (34) drives itself from a simple chamber (20) via a conduit (30) into the passage (10). Substantial flow resistance may be provided by having a closed end and lateral apertures (32), in the conduit (30) or by leading the composition (34) into an inflatable bag (42). <IMAGE>

Description

STOPPING A FLOW PASSAGE The present invention relates to a method and apparatus for use in stopping a flow passage. It is applicable to stopping a flow passage along a gas pipe, particularly a high-pressure gas pipe.

Our earlier British patents, Nos. 2,123,919 and 2,157,390, concern stopping a flow passage in a gas pipe by injecting a sealant foam composition which sets to provide a barrier to flow. They disclose the use of injection guns by means of which an expanding foam composition can be pumped into a pipe. The earlier patent discloses an arrangement whereby the outlet from the gun is closed off by a rupturable member. Thus, when the foam composition endeavours to expand, this is initially prevented, until a predetermined pressure is reached at which the membrane ruptures. This pressure is selected such that the sealant is then ready for delivery. It is then pumped steadily into the pipe. The second patent is primarily concerned with a technique in which the sealant foam is entrained within a porous bag within the pipe to be sealed.Once again, the foam composition is pumped in by means of a gun.

These techniques have been found difficult to apply with gas pipes under high pressure. If, for example, the pressure in a gas pipe is two bar above ambient, it is extremely difficult to pump anything into the pipe with a hand pump. For that matter, it is quite hazardous for the operator to be manipulating a gun in direct communication with such high pressures, particularly since the pressure applied to the foam for pumping must be substantially greater than the gas pressure. This is also true if, in place of a mechanical pump, pressurised gas (e.g.

nitrogen) is employed to apply pressure for injecting a sealant. Furthermore, our previous technique employing a rupturable membrane to ensure that the foam composition is delivered when it reaches the correct state does not work well, since a much higher pressure is required to rupture the membrane against the counter-pressure of the gas in the pipe. Matters seem to be made still worse by the effect of the pressure acting on the foam composition. It increases the rate of gelling, possibly because the foam does not expand and consequently heats up more rapidly.

Thus, not only is operation at high pressures potentially hazardous, but the known methods are difficult to apply, with the compositions gelling before substantial amounts get into the zones where seals are required. Even pressures 100 millibar above ambient can cause problems with known techniques.

In one aspect the present invention provides a method of stopping a flow passage containing fluid at a pressure at least 100 millibar (104cm'2) above ambient (particularly within a conduit under high pressure) comprising providing a chamber in communication with the flow passage; charging the chamber with a composition which expands to provide a settable foam material; and allowing or causing the composition to expand and drive itself into the flow passage by the pressure generated by its expansion. Generally, a suitable foam composition will have a higher expansion rate and a longer gel time than the compositions disclosed in our earlier patents.

For example, there may be a gel time of from 3 to 6 minutes, preferably 3.5 to 4.5 minutes, at 25 C. The expansion at atmospheric pressure may be 5 to 20-fold, preferably at least 8-fold.

It is desirable to provide a resistance to flow of the composition from the chamber to the flow passage.

This may be achieved by suitable dimensioning of the connecting conduit and/or by causing the foam to enter an inflatable bag, which is thereby inflated to stop the flow passage. Preferably at least a portion of the bag is porous. This allows resin foam to come in direct contact with the pipe surface giving an adhesive sealing effect in addition to the mechanical, compressive action of the bag.

In another aspect the invention provides apparatus for carrying out a method as indicated above, comprising an expansion chamber assembly for coupling to a flow passage containing fluid at a pressure at least 100 millibar (104cm'2) above ambient. The chamber assembly may comprise a simple chamber with an exit conduit and a closable filling port through which the chamber can be filled. Thus the chamber can be filled and the port can then be closed, so that expanding foam passes out through the exit conduit once it has generated sufficient pressure.

Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings in which: Fig. 1 is a schematic view in elevation of a first embodiment of the invention; and Fig. 2 is a similar view of a second embodiment.

Fig. 1 shows a high pressure gas main 10 provided with a pipe clamp 12 to which are coupled a gland seal 14 and a closure valve 16. A chamber assembly 18 comprises a chamber 20 having an open upper end (which provides a filling port) closed by a lid 22, and a lower exit conduit 24 which leads to a valve 26 operable by a lever 28 to control communication between the conduit 24 and a main delivery tube 30. At its lower end, the delivery tube 30 is closed, and there are-a plurality of apertures 32 in an angular portion of its cylindrical wall at the lower region. For use, the delivery tube 30 is passed through the gland seal 14 (the valve 16 being opened for the purpose), so that the apertured lower region is within the gas main 10, with the apertures 32 -facing generally upstream. The valve 26 is in its closed state, so that the pressure in the gas main does not extend above that valve.A foaming composition is prepared, suitably by mixing a two part resin foam composition, and poured into the cartridge 20 through the mouth. The lid 22 is placed on the cartridge to seal it, and the lever 28 is operated to open the valve 26. Thus the pressure of the gas in the pipe 10 is communicated to the cartridge 20. This restrains passage of the foaming composition down the exit pipe 24 and the delivery tube 30. As the foaming reaction of the composition proceeds, a stage is reached at which the pressure generated thereby can exceed the pressure of the gas. The foam then commences to move down the conduits 24,30 and out through the apertures 32 into the gas main 10. The foam cures rapidly within the pipe to produce a slug of material 34, mostly upstream of the tube 30. This means that, once the foam has set, the pipe can be cut downstream close to the point of injection, leaving intact a substantial proportion of the foam seal. The dimensions of the apertures 32 and the bore of the delivery tube 30 are selected so that the composition passes into the main at a controlled rate.

Such a direct injection system has been found to be suitable for gas mains of moderate size, e.g. up to and including 75mm diameter. For larger mains, the apparatus of Fig. 2 is preferred. Once again, this shows a gas main 10, a cartridge or chamber 20 having a lid 22, a lower exit pipe 24 controlled by a valve 26 having a control arm 28. In this example the delivery tube 30 is of the same diameter as the outlet pipe 24, though this is not essential. It passes through a gland seal 14 in the end of a standpipe 40 projecting from the main 10. A bag whereof at least a portion is porous (and which may be generally as disclosed in Patent 2,157,390) is secured to the end of the delivery tube 30.Thus the cartridge assembly 18' can be engaged with the standpipe by passing the delivery tube 30 in through the standpipe until its end is adjacent the junction of the standpipe 40 and the main 10. The valve 26 is in its closed state, and the (deflated) bag is within the main. As with the first embodiment, a foaming composition is placed in the cartridge 20, which is sealed with its end cap 22. The valve 26 is opened and, when the pressure of the foaming composition exceeds that of the gas in the main 10, the foam is driven by its own pressure down the outlet pipe 24 and the delivery tube 30, and into the bag 42, which is thus inflated with foam. Since the bag 42 has some porosity, some foam can leak through and thus form a seal against the inside of the main 10. The assembly 18' is then withdrawn, leaving the filled bag 42 within the main.

A A suitable foaming composition for use in the present invention is a two component filled polyurethane system which produces a predominantly closed cell semirigid foam. The foam is chemically blown with carbon dioxide and does not contain volatile blowing agents which might interfere with gas detection equipment. A suitable system is made by mixing 100 parts by weight of resin with 87 parts by weight of hardener. These have the following typical properties: Resin This is a filled polyether polyol blend. Its viscosity at 250C is 90-110 poise (Brookfield RVF spindle 3-2 rev/min) or 35-50 poise (Brookfield RVF spindle 3-20 rev/min). Its specific gravity at 250C is 1.3.

Hardener This is a diphenylmethane 4-4' diisocyanate composition containing some higher functionality isocyanates. Its viscosity is 2-2.5 poise (Brookfield RVF spindle 1-20 rev/min). Its specific gravity is 1.24. The isocyanate (NCO) value is 30.7 by weight.

The mixed composition has a cream time at 25 C of from 1 minute to 1 minute 10 seconds for a 25g sample.

The gel time under the same conditions is from 3 minutes 30 seconds to 4 minutes 30 seconds. This is selected so that sufficient foam can flow into the main before gelling. Operation at particularly high or low temperatures will require different compositions to achieve this. The foam volume under the same conditions is such that the 25g sample expands to fill a 200ml plastic cup. The cured product has a hardness 24 hours after mixing at 250C of 80 Shore A. It is resiliently deformable, though markedly harder than the compositions described in our previous patents.

Claims (16)

CLAIMS:

1. A method of stopping a flow passage containing fluid at a pressure at least 100 millibar (104Nm~2) above ambient comprising providing a chamber in communication with the flow passage via a connecting conduit; charging the chamber with a composition which expands to provide a settable foam material; and allowing or causing the composition to expand and drive itself into the flow passage solely by the pressure generated by its expansion.

2. A method according to claim 1 wherein the flow passage contains fluid at a pressure at least 2 bar (2 x 105cm'2) above ambient.

3. A method according to any preceding claim wherein the composition has a gel time at 250C of 3-6m.

4. A method according to any preceding claim wherein the composition has a gel time at 250C of 3.5-4.5m.

5. A method according to any preceding claim wherein the composition has an expansion at atmosphere pressure of 5 to 20-fold.

6. A method according to claim 5 wherein the composition has an expansion at atmospheric pressure of at least 8-fold.

7. A method according to any preceding claim wherein there is provided a resistance to flow of the composition from the chamber to the flow passage.

8. A method according to claim 7 wherein said resistance is achieved by suitable dimensioning of the connecting conduit and/or by causing the foam to enter an inflatable bag which is thereby inflated to stop the flow passage.

9. A method according to claim 8 employing an inflatable bag which is at least partly porous.

10. A method according to claim 8 wherein the connecting conduit has a closed outlet end with lateral apertures.

11. A method according to claim 10 wherein the apertures open towards the upstream side of the flow passage.

12. A method of stopping a flow passage substantially as herein described with reference to and as illustrated in the accompanying drawings.

13. Apparatus for use in a method according to any preceding claim comprising an expansion chamber assembly for coupling to a flow passage containing fluid at a pressure at least 100 millibar (104cm'2) above ambient, the chamber assembly comprising a simple chamber with an exit conduit and a closable filling port through which the chamber can be filled.

14. Apparatus according to claim 13 wherein the exit conduit has a closed outlet end with lateral apertures.

15. Apparatus according to claim 13 wherein the exit conduit terminates i#n an inflatable bag.

16. Apparatus for use in stopping a flow passage substantially as herein described with reference to and as illustrated in the accompanying drawings.