WO2001016518A1 - Inflatable stopper - Google Patents

Abstract

An inflatable bag for arresting the flow of a liquid such as water within a pipeline carrying and a method for arresting such a liquid flow are disclosed. The inflatable bag (2) consists of an inner flexible bladder (6), at least one outer flexible bag (4), and a spine assembly (8) passing through the centre of the inner bladder (6). The spine assembly (8) has a first blind end (10) and an open end (11) communicating with an inflation/deflation means and is provided with a number of apertures (16) inside the bladder (6) through which an inflating medium passes. The outer bag is constructed from a plurality of pieces of material joined together in simply overlapping regions by being at least doubly stitched through both pieces of material of the said plurality of pieces which form the overlap thus forming a shear joint (30) as opposed to the conventional butt joint.

Description

Inflatable Stopper

This invention relates to Inflatable stoppers, in particular to Inflatable stoppers or stoppers for use in pipe systems for preventing leakage o f fluid therefrom following damage or during general repair work, or for stopping fluid flow within a pipe or passageway temporarily in the case o f water and more permanently in the case o f other fluids.

Inflatable stoppers are currently used in pipelines and passageways to temporarily halt the flow o f fluid therein. The stoppers are generally inj ected into the pipeline from within a mounting means disposed externally of the pipe and subsequently inflated using a gas, for example air, which results in expansion of the device until the external surfaces of the stopper contact the internal surface of the pipe and form a seal therewith. Once sealed, repair work can be undertaken on a section of the pipe downstream of the fluid flow.

Inflatable stoppers have been used in many gaseous fluid pipe systems wherein the stopper is simply inserted at an open end of a pipe and is dependent on gravity thereafter for its correct positioning in the pipe. The most common use however for Inflatable stoppers is in connection with closed pres surised systems in which a launching system is used to inj ect the inflatable stopper into the pipe without any requirement for firstly eliminating or reducing the fluid flow therein. Indeed the gas pipeline industry- most commonly uses the apparatus hereinafter described to both isolate a section of pipeline to be replaced and provide a bypass function so that there is no significant diminution of downstream line pressure which might cause the pilot lights of downstream gas appliances to be extinguished. The closed system comprises a primary stopper which is introduced into the pipeline through a drilled and tapped aperture in the pipe and orientates itself away from the inj ection tube in the same direction to that of the fluid flow within the pipe. The downstream end of the stopper is supported from by an iris plate which requires further launching apparatus and accordingly a further aperture drilling and tapping in the pipeline downstream of the first aperture abovementioned. The iris plate is usually expandable and is inserted through the aperture in the pipe in its un-expanded condition whereafter it is exp anded to partially restrict the fluid flow through the pipe and also to provided a support surface against which the downstream end o f the inflated stopper can react.

Thereafter a secondary inflatable stopper is launched into the pipe using launching devices upstream of the primary stopper, a second set of primary and secondary inflatable stoppers being launched into the pipeline downstream of the first primary stopper to isolate a section o f the pipeline which is to be replaced, repaired or otherwise worked on. The arrangement is in general to provide a double block and bleed facility, as a pair of inflatable stoppers is provided on either side of the faulty pipeline section, and any residual gas remaining in this section after having been sealed o ff is bled away. A double seal approach is used due to the hazardous nature of gas wherein any back flow o f gas could result in an explosion.

The inflated stoppers are held in position and maintain a seal in the pipe purely due to the inflation pressure inside the stopper and the resulting frictional contact with the internal surfaces of the pipe which is dependent on said pressure.

Conventional inflatable stoppers for use in gas systems work at inflation pressures between 2.50 bar and 4.00 bar, with line pressures at approximately 1.00 bar. In certain gas systems offshore line pressures of between 2.00 and 4.00 bar are reached and in order that the stopper can inflate, the inflation pressure needs to be greater than the pressure in the pipe.

The United Kingdom gas authorities have set a safety standard level of 8 bar (giving a safety factor of 4: 1 in most cases) at which the inflatable stoppers must be capable of operating. However conventional inflatable stoppers are not sufficiently strong to withstand such inflation pressures that may be required for them to operate in high pressure systems with working pressures at 8 bar. Raising inflation pressure in the conventional stoppers above 2 bar is likely to result in bursting of the inflatable stopper and therefore leakage of the gas contained therein.

The reason for such significant safety factors is that gas is an explosive medium and any leakage however small could present a very serious explosion risk. In liquid pipe systems, such as those by which mains water and non-flammable liquids are delivered, there is a much les s stringent safety requirement because a leak in the stopping system is highly unlikely to cause a catastrophic failure.

The current construction of the inflatable stoppers described consists of a latex inflatable bladder mounted on a semi-rigid spine which passes through the bladder and is sealed to the closed end thereof. Around the bladder is attached a fabric (e.g. nylon, canvas) cover which is attached to both ends of the spine, but in general is not physically connected to the bladder. The spine is provided along a portion of its length with air outlets through which air can pas s after being pumped into the spine from its open end. Although the current stopper constructions can be used at pressures of up to 2 atmospheres, and in certain circumstances even greater pressures , the inherent bursting strength of the cover and/ or the bladder is insufficient to withstand the inflation pressures which are required when providing a temporary stopper in a pipe in which liquids flow.

Traditionally where a stopping effect is to be effected on a gaseous fluid flow within a pipeline, the inflation medium traditionally used has been a gas such as Nitrogen on account of its inertness . However, it was found when experimenting with liquid flows in pipes that gas was unsuitable for a number of reasons . Firstly, gases are universally less dense than liquids and accordingly during the inflation of the stopper, it was found to float above the fluid rendering correct orientation of said stopper within the pipe more unlikely. Secondly, the kinetic head of the liquid flowing within the pipe made orientation of the stopper significantly more difficult as the stopper tended to be forced downstream of the injection apparatus by the fluid flow and as the stopper was so forced, frictional contact of the cover with the inner surface of the pipe often abraded not only the cover but also caused chafing of the bladder against the cover so giving rise to premature failure of the bladder and/or cover. Thirdly, the kinetic head often gave rise to wild oscillations o f the stopper within the pipe during inflation and while liquid flowed around the partially inflated stopper.

A further disadvantage associated with modern inflatable stopper construction is that there is often insufficient friction between the inner surface of the pipe and the external surface of the nylon/canvas stopper either to prevent the stopper from being dislodged while inflated and being subsequently washed away with the flow o f the fluid within the pipe, or to prevent fluid ingress between the inner surface of the pipe and the outer surface of the stopper into the cavity formed behind the said stopper.

A yet further disadvantage of current stoppers arises from the simple linear stitching of traditional butt joints of the different pieces of nylon/ canvas which constitute the stopper. This type of seam is inherently weak and liable to burst on the application of only moderate internal pressure.

It is an obj ect of the present invention to provide an improved inflatable stopper which is stronger than the conventional types and can operate in pressures at 8.00 bar or above as required by the United Kingdom gas authorities, and also allows the stopper to function in both open and closed water systems (in addition to closed gas systems, but at higher mains pres sures) .

It is a further object of this invention to provide an inflatable stopper construction with enhanced frictional engagement with the inner surface of a pipe when inflated therein, and also to provide a stopper which substantially eliminates seepage of fluid between the outer surface of the stopper and the inner surface of the pipe.

It is a further object of this invention to provide a method of arresting liquid flow within a pipe by means of an inflatable stopper, together with a stopper capable o f achieving this end.

According to the present invention there is provided an inflatable stopper, comprising an inner flexible bladder and one or more outer flexible covers, said bladder having a spine assembly passing therethrough, said spine assembly having a first blind end and a second open end communicating with an inflation/deflation means, characterised in that the said one or more outer flexible covers are constructed from a plurality of pieces of material j oined together in simply overlapping regions by being at least doubly stitched through both pieces of material o f the said plurality of pieces which form the overlap . Preferably the joints between adjacent material portions are lap joints as distinct from butt joints wherein the stitching through respective material portions is subj ected to a shearing force on inflation as opposed to a tensile force.

Preferably the covers are constructed from two end pieces of material and a substantially cylindrical piece which forms the body of the cover, and further preferably the direction o f the stitching is in a plane substantially perpendicular to the axis o f the cylinder. In this construction, the orientation of the lines of double, and preferably treble stitching are most suitably orientated to accommodate the higher pres sures to which the stoppers can now be pressurised without either bladder or cover bursting.

In one embodiment, the shear joint construction of one or more outer flexible covers comprises at least one row of stitching, although in a most preferred embodiment the shear joint construction comprises between two and four rows of stitching. The advantage of two or more rows of stitching of shear joint construction over conventional butt joint construction is increased strength and a reduced risk of bursting o f the inflatable stopper under high pressure.

This method of construction abolishes the need for using threads with larger dimensions which albeit would result in increased strength o f the thread but which would produce larger perforations in the outer flexible covers than would be produced with a finer thread and thereby reduce the total integrity of the joints.

Preferably the cover is constructed from nylon, or alternative high strength fabrics . In one possible embodiment, the inflatable stopper further comprises an outer skin which encloses and inflates with the bladder and the cover. Preferably the skin is of an elastomeric, rubber, latex or other compressible material having high elasticity, and high coefficient o f friction characteristics in the inflated condition when contacting the inner surface of the pipe. The use of such compressible a material in the provision of a skin is advantageous in two respects . Firstly, as the inflatable device is inflated, the skin is compressed into the various imperfections or deposits on the inner surface of the pipe and thus minimises their effect, and secondly, the coefficient of friction between the inner surface of the pipe and the skin is necessarily increased and the stopper is much les s likelv to shift while fully inflated.

Preferably the skin is made of latex.

In circumstances where a latex skin is provided, a perfect seal between the inflatable device and the pipe inner surface can be obtained rendering the device utile for applications which require zero or complete absence of bypass o f fluid around the device after inflation.

It is a further advantage if the latex skin is impregnated with a sterilising and/or cleaning and/or lubricating compound, for example chlorine, which has a surprising lubricating effect on the outer surface of the skin and thus enhances the launchabilitv and/or extraction o f the inflatable stopper from the pipe. The use o f chlorine, which has sterilising qualities, also allows the inflatable stopper to be used in clean/sterile systems such as water systems .

The use of chlorine to impregnate the latex skin not only increases the shelf life of the stopper from 12- 18 months , which is currently the norm, to 2-3 years, but also increases the slippability of the latex skin in its deflated condition which facilitates the launching and retraction of the stopper as a whole into and from a pipe in which fluid is flowing and which is to be the subject of rejuvenation or renovation work behind the inflatable stopper.

In one pos sible embodiment of the invention the inflation/deflation means comprises a fluid inflation/deflation mechanism, wherein the fluid is preferably but not exclusively air.

In a further possible embodiment o f the invention the inflation/deflation means comprises a substantially incompressible fluid inflation/ deflation mechanism, thereby increasing the inflation pressure that can be obtained in the inflatable stopper and permitting the use of the particular incompressible fluid flowing in the pipe for inflation purposes . Preferably the substantially incompressible fluid is water, but a large number of such fluids are currently transported through pipe networks . Included within the definition of substantially incompressible are liquids such as beers, lagers and other alcoholic beverages , sewage and other sludges, finely divided particulate matter such as sands , powders, and dusts , suspensions such as slurries, precipitates, colloids, and the like.

Preferably one or more of the covers are made from nylon which can be provided either coated or uncoated. Alternatively, flame retardant materials or neoprene can be used, or any other material can be used which is suitable for the particular application and the fluid flowing within the pipe.

Preferably the spine assembly is a conventional curved spine assembly to aid exit of the inflatable stopper from a launch tube and aid entry into a pipe system. In a particularly preferred embodiment, the launching apparatus is provided with a clamping head of sufficient width and depth to define a cavity externally of the pipe when clamped thereto which extends in front of the contact area of the inflatable stopper when fully inflated within the pipe. In this configuration, an additional aperture can be drilled in the pipe to allow fluid to flow from upstream of the inflatable stopper into the clamping head cavity and ultimately back into the pipe downstream of said inflatable stopper. This facility for providing such a "bypass " arrangement is a direct result of the enhanced sealing which can be achieved against the inner surface of the pipe using the inflatable devices of the present invention.

According to a further aspect of the invention, there is provided a method of arresting a substantially incompressible fluid flow within a pipe, wherein an aperture is drilled in the pipeline in a sealed manner to prevent liquid escape through said aperture, securing launching apparatus adjacent said aperture, said launching apparatus having dispo sed therein an inflatable stopper sized according to the inner bore dimensions o f the pipe, introducing said inflatable stopper into said pipeline and inflating same to a predetermined pressure so that the outer surface of the stopper sealingly contacts the inner surface of the pipe thus substantially arresting the fluid flow in said pipe, characterised in that the inflating medium is a substantially incompressible fluid.

Preferably the inflating medium is a liquid.

Preferably the liquid inflating medium is water.

Preferably the inflatable stopper is of the type described in the first aspect of the invention. Most preferably the inflation pressure of the fluid is at least partially dependent on the pressure of fluid within the pipe upstream of the inflated stopper when arresting said fluid flow within the pipe. In this manner, any fluctuations in the pipe line pressure can be compensated for in the liquid inflation pressure which is inflating the stopper thus ensuring that a substantially constant pressure differential between inflation pressure and line pressure.

An advantage of using an incompressible inflating medium is that failure is not instantaneous in that the stopper does not immediately collapse and allow full uninhibited fluid flow through the pipe, but gradual as the stopper leaks liquid and inflation pressure inside the stopper can no longer be maintained. During this gradual failure, measures can be taken by operatives noticing the gradual increase of liquid leaking through the bag seal to close the pipe and prevent any significant loss of liquid.

A yet further advantage of using liquid as an inflating medium is that during inflation the stopper increases substantially in mass, and thus the likelihood of wild stopper oscillations is significantly reduced and indeed in the vast majority of circumstances, such oscillations never occur. This increases the life expectancy of the both the stopper and the launching apparatus, and increases the safety with which such can be used. Where the inflating fluid is the same as that flowing in the pipe, the stopper inflates substantially centrally inside the pipe because there is little difference between the density of the stopper and inflating medium and the liquid flowing in the pipe. Correct orientation of the stopper can thus be ensured. Additionally, the increasing mass and volume of the stopper as it is inflated prevents said stopper from being forcibly reversed by the liquid flowing in the pipe when said stopper is introduced in a direction opposite to said liquid flow. It is important to realise here that the cross-sectional area of the stopper, and thus the resistance caused to the liquid flow in the pipe increases as the stopper is being inflated, and the risk of stopper reversal therefore also increases during inflation thereof. The thrust on the stopper as it is inflated thus increases and where the inflation medium is a gas , this thrust is often too great and the stopper deforms and is forcibly reversed inside the pipe.

An additional benefit o f the significantly enhanced structural strength properties of the device of the present invention is that far greater inflation pressures can be used. As mentioned, liquid or other compres sible fluid inflating mediums can be used. For example, conventional inflatable devices have heretofore only been operated at maximum differential pres sures of between 0.25 and 0.5 bar, that is the pressure of the inflation is 0.25-0.5 bar greater than the pres sure of fluid flowing within the pipe. The inflatable devices according to the present invention can easily operate at pres sure differentials o f 1 bar and above. In circumstances where the pressure o f the inflating medium is in communication with or is dependent on the mains fluid pressure within the pipe, the optimum differential pressure can be maintained because any fluctuations in mains pres sure are automatically reflected in the pressure of the inflating medium and thus the inflation pressure within the device.

Perhaps one o f the most important advantages of the present invention is that it is no longer neces sary to provide both a primary and secondary, contingent inflatable device within the pipe. Only a single device is required because the sealing pressure achieved is so great (directly attributable to the capability o f the device to withstand much greater internal inflation pres sures as a result of its construction, and where liquid inflating mediums are used, the relative incompres sibility of such liquids) as to minimise the risk o f bursting or of being reversed internally of the pipe by the fluid flowing therein. Whereas previously cumbersome lifting apparatus was required to orientate and correctly dispose a combine set of launching tubes for primary and secondary devices, now a single human can carry the equipment. Those skilled in the art will immediately recognise the advantages of such an arrangement, particularly as regards mounting time and expense, the size of the hole which is required to be dug around the pipe to be renovated, and the cost of the apparatus in general. It is of course possible to use a pair of inflatable stoppers to effect a double seal on either side of a pipe section to be replaced should this be required.

Such capabilities are unprecedented.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings wherein:-

Figure 1 is a cross section of an inflatable stopper in an inflated condition according to an embodiment of the present invention, and

Figure 2 is a side elevation of an inflatable stopper according to the present invention.

Referring firstly to Figure 1 , there is illustrated an inflatable stopper 2 comprising an outer flexible cover 4, a bladder 6 and a centrally located spine assembly 8 passing therethrough.

Spine assembly 8 has a first blind end 10 and a second open end provided with a threaded connector 1 1 communicating with an inflation/ deflation pipe 14.

The spine assembly 8 includes a solid inner member 12 and a hollow outer member 14 having a plurality of apertures 16 along the length thereo f. Solid inner member 12 and hollow outer member 14 are semi flexible , and these members are preferably pre-formed a curvature to allow for effective launching of the device into a pipe in which fluid is already flowing.

Spine assembly 8 is also provided with a cap 18 at blind end 10. Cap 18, in addition to the curvature of the spine as sembly 8, aid exit of inflatable stopper 2 from a launch tube and entry into a pipe system in an uninflated condition and then allow said stopper means to self centre before being inflated.

Apertures 1 6 o f spine assembly 8 provide a means by which the inflatable stopper 2 can be inflated and deflated. It is also to be mentioned that in certain applications, it is highly desirable for the spine to be provided with additional service conduits or features. For example, in flammable or explosive gas stopping operations, it is desirable to monitor the ambient pressures on either side of the stopper after inflation to check for leaks and upstream and downstream conditions . In this instance, it is possible to pass individual pressure tubes through the spine to emerge in blind end or the rear end o f the spine and thus be open to measure pres sures at these locations . The conduits , which may additionally pas s electrical or electronic signals from either end of the stopper to measuring apparatus provided externally of the pipe, possibly atop the launching apparatus, either pas s through the spine or are physically secured thereto so that a safe watch on conditions within the pipe during the stopping operation can be maintained.

The covers 4 and bladder 6 respectively, have sealing means 20 below the threaded connector 1 1 on the spine assembly 8, thereby fastening and sealing said cover and bladder against said spine assembly. Cap 18 provides fastening and sealing of the cover and bladder 4 and 6 respectively, at the blind end 10 of the spine assembly 8.

A possible example of sealing means 20 is a swaged compression ring.

Referring to Figure 2, there is illustrated a cover 4 having double rows of shear stitching 30 in planes sub stantially perpendicular to the axial direction of the stopper. Use o f shear stitching 30 rather than conventional butt stitching provides the cover 4 with increased strength thereby allowing said stopper to withstand increased levels of pressure and reducing the risk of bursting thereof. A method of increasing the strength of the stitching whilst minimising the diameter of the thread used is advantageous as the size of the perforations made by the stitching are reduced thereby reducing the means by which pressure can be lost from cover 4. Different strength threads can be used.

Preferably the bladder is made of latex. However, other strong but flexible materials could also be used. Different thickness' of the bladder could be used in conjunction with different stitching patterns to increase the strength o f the stopper without impairing collapsibility thereof in order that the stopper can be successfully launched from the launch system and subsequently recovered.

The cover can be made of coated or un-coated nylon, flame retardant materials, latex or neoprenes . The cover or bladder can be impregnated with a sterilising compound or chlorine to allow the stopper to be used in a clean water sys tem, and in a particularly advantageous embodiment, a further chlorine-impregnated latex skin is provided over the cover 4 to enable the stopper to be used in such systems as a complete seal between the latex skin and the inner surface of the pipe can be achieved. The inflatable stopper can be inflated using gas or water and the inflation/ deflation means are adapted accordingly.

The improved inflatable stopper as described above has the advantage in that it can withstand pressures up to 12 bar and flow rates up to 3.7 metres per second thereby making it suitable for use in a closed water system in addition to a closed gas system.

Claims

1 . An inflatable stopper, comprising an inner flexible bladder and at least one outer cover, said bladder having a spine assembly passing therethrough, said spine assembly having a first blind end and a second open end communicating with an inflation/deflation means , characterised in that the said one or more covers are constructed from a plurality o f pieces of material joined together in simply overlapping regions by being at least doubly stitched through both pieces of material of the said plurality of pieces which form the overlap to form a shear joint.

2. A stopper according to claim 1 wherein the cover is constructed from two end pieces of material and one or more partially or totally cylindrical pieces which form the body of the cover.

3. A stopper according to any preceding claim wherein the direction of the stitching is in a plane substantially perpendicular to the axis of the cylinder.

4. A stopper according to any preceding claim wherein the shear joint construction o f one or more covers comprises at least one row of stitching.

5. A stopper according to claim 4 wherein the shear joint construction comprises between two and four rows o f stitching.

6. A stopper according to any preceding claim characterised in that the cover is constructed from nylon.

7. A stopper according to any preceding claim wherein the inflatable stopper further comprises a skin which encloses and inflates with the bladder and the cover.

8. A stopper according to claim 7 wherein the skin is of an elastomeric compressible material.

9. A stopper according to claim 8 wherein the skin made of latex.

10. A stopper according to any of claims 7-9 wherein the skin is impregnated with a sterilising and/or cleaning and/or lubricating compound.

11. A stopper according to claim 9 or 10 wherein the skin is impregnated with chlorine.

12. A stopper according to any preceding claim wherein the inflation/deflation means uses air as the medium for inflating the device.

13. A stopper according to any of claims 1 - 1 1 wherein the inflation/ deflation means uses a sub stantially incompressible fluid as the inflating medium for inflating the device.

14. A stopper according to claim 13 wherein the substantially incompressible fluid is a liquid.

15. A stopper according to claim 14 wherein the liquid is water.

16. A stopper according to any preceding claim wherein the spine assembly is curved to facilitate the correct orientation of said device as it is ejected from the a launch tube and introduced into a pipe.

17. A method of arresting a substantially incompressible fluid flow within a pipe, wherein an aperture is drilled in the pipeline in a sealed manner to prevent liquid escape through said aperture, securing launching apparatus adjacent said aperture, said launching apparatus having disposed therein an inflatable stopper sized according to the dimensions of the pipe, introducing said inflatable stopper into said pipeline and inflating same to a predetermined pressure so that the outer surface o f the stopper at least partially sealingly contacts the inner surface of the pipe thus substantially arresting the fluid flow in said pipe, characterised in that the inflating medium is a substantially incompressible fluid.

18. A method according to claim 17 wherein the substantially incompressible fluid is a liquid.

19. A method according to claim 18 wherein the liquid is water.

20. A method according to any of claims 17- 19 wherein the inflation pressure of the fluid is at least partially dependent on the pressure of fluid within the pipe upstream of the inflated bag when arresting said fluid flow within the pipe.

21. A method according to any of claims 17-20 wherein the stopper is constructed according to any of claims 1 - 16.