GB2345524A

GB2345524A - A pipe coupling with intermediate pipe tensioning means

Info

Publication number: GB2345524A
Application number: GB9827843A
Authority: GB
Inventors: Graeme Staniforth
Original assignee: SPF ENGINEERING Ltd
Current assignee: SPF ENGINEERING Ltd
Priority date: 1998-12-17
Filing date: 1998-12-17
Publication date: 2000-07-12
Anticipated expiration: 2018-12-17
Also published as: GB9827843D0; GB2345524B

Abstract

A pipe coupling comprises a coupling body 10, a resilient seal 30a, 30b, and tensioning means 40a, 40b adapted to hold the resilient seal in sealing contact between the coupling body and an end of a pipe to be coupled 1a, 1b. The tensioning means comprises an annular tensioning member 40a, 40b and intermediate pipe tensioning means 50a, 50b. The intermediate pipe tensioning means are disposed between the resilient seal and the annular tensioning member, and are arranged such that tensioning movement of the annular tensioning member towards the coupling body causes the intermediate tensioning means to urge the seal into sealing engagement between the exterior surface of the pipe and the coupling body. The intermediate pipe tensioning means has means for adjustment of its effective circumferential length, so permitting the intermediate pipe tensioning means effective circumference to more closely conform to the external diameter of the pipe end.

Description

The invention relates to sealing apparatus for use in joining pipes to other pipes and to other equipment such as vessels, valves and the like to accomplish a fluid-tight seal.

There are two fundamental approaches to the problem. One is to fabricate a sealing apparatus to match the exact dimension (s) of the pipe (s) to be connected.

This is an effective but relatively expensive solution compared to the second approach, which is to provide a range of sealing apparatus each with sufficient tolerance so that members of the range can accomplish seals on the complete spectrum of pipe size requirement.

In the United Kingdom (and also elsewhere) a particular problem arises in that historically pipe dimensions have been specified in terms of the internal pipe diameter, the wall thickness being chosen to suit the pressure loading and the material from which the pipe is made. Thus for, say, a nominal 100mm pipe (internal diameter) a wide variety of external pipe diameters must be catered for. Also a wide variety of different pipe materials must be catered for. In the interest of economy it is highly desirable to minimise the number of pipe sealing apparatus in a given range and this inevitably means that each seal in a range must have a wider tolerance than is the case for ranges of pipe sealing apparatus having a larger number of different sizes.

In this specification the ter'pipe coupling'will be used to indicate a piece of apparatus for joining two (or more) pipes (e. g. straight runs, bends, junctions) together or for joining one or more pipes to another piece of equipment such as a vessel, tank or valve.

A known coupling generally comprises a substantially rigid coupling body with which at least one pipe end is to be sealingly coupled in use; and for each joint a resilient seal is disposed between the coupling body and the pipe end and there is also provided tensioning means to hold the resilient seal in sealing relationship between the pipe end and the coupling body.

In known, typical pipe couplings the resilient seal is typically of generally triangular cross section (though'0'rings are also used) and of a shape having a smooth cylindrical inner surface to abut the surface of the pipe, a rear (relative to the pipe end) radial surface for abutment with an annular tensioning ring, and a frustoconical surface for abutment with a complementary bevelled surface provided in the pipe coupling body so that when urged into sealing engagement there is a wedge effect. Sometimes surface ribs are provided, said ribs deforming as the resilient seal is tensioned. Other shapes and profiles of resilient seal are well known.

The tensioning means usually comprises some form of substantially rigid annular element disposed and arranged to abut the resilient seal and force it into sealing engagement between the pipe end and the coupling body. This is usually achieved by connecting the annular element to the coupling body by bolts or other screw threaded adjustment means. Where pipe couplings are intended to join two pipe ends, two seals are provided and the tensioning means may be provided to independently tension respective seals relative to the coupling body or common tensioning means may be used to tension both seals, for example by bolts acting to 'compress'the coupling body and both seals between annular elements of respective seals. The common tensioning means is often more favoured by fitters because it is quicker to adjust. However, structurally, the independent tensioning arrangement is often desirable and sometimes essential, due to pressure requirements and the ease of adjusting each seal independently of any other.

Where a range of couplings is to be provided then a particular size of coupling, and the annular element provided thereon, must be capable of accomplishing seals on a range of external diameter sized pipes. Thus the annular element may be a close, interference, fit on the largest pipe end in the range of pipes which it can accommodate, whereas in relation to the smallest pipe diameter in the range to be accommodated, the annular element may have an internal diameter appreciably bigger than the external pipe diameter of the smallest pipe, thus leaving an annular gap. In this latter case there is a tendency for the resilient seal, under tension, to be forced out through the annular gap, so that the seal is ineffective. In practice, most coupling ranges have a tolerance in terms of the annular gap width of a maximum of about 17-25mm which is about the maximum gap width for an operable seal in most cases, especially at high pressure where the normal high pressure loading is often exceeded significantly by the normally higher test pressure criteria. A known type of coupling with an annular gap larger than this is likely to be ineffective.

Therefore the number of couplings in a range is effectively determined by this tolerance and by the size range of pipe diameters to be catered for.

The invention seeks to reduce the number of pipe coupling sizes required to accommodate a given range of pipe diameters by effectively increasing this tolerance for a given pipe coupling.

The invention provides in its broadest aspect a pipe coupling comprising a coupling body, a resilient seal and tensioning means adapted to hold the resilient seal in sealing contact between the coupling body and an end of a pipe to be coupled, wherein the tensioning means comprises an annular tensioning member and intermediate pipe tensioning means, the intermediate pipe tensioning means being disposed between said resilient seal and said annular tensioning member, the intermediate pipe tensioning means being arranged such that tensioning movement of the annular tensioning member towards the coupling body causes the intermediate tensioning member to urge the seal into sealing engagement between the exterior surface of the pipe end and the coupling body, the intermediate pipe tensioning means having means for adjustment of its effective circumferential length so permitting the intermediate pipe tensioning means'effective circumference to more closely conform to the external diameter of the pipe end.

It will be seen that the resilient seal is urged by the annular tensioning member through the agency of the intermediate pipe tensioning means.

It is to be understood that the intermediate pipe tensioning means is essentially an annular element which may be composed of one, or of a plurality of segment (s), the means for adjustment being so as to enable the intermediate pipe tensioning means to be disposed in relation to the pipe end such that on urging of the seal into said sealing engagement any gap between said intermediate pipe sealing means and the exterior surface of the pipe is sufficiently small to prevent the seal being forced out of that gap and thus making the seal of the pipe coupling ineffective.

Preferably said means for adjustment of the effective circumference length of the intermediate pipe tensioning means is provided by disposing an end of the segment to overlap an opposite end of the segment, or where a plurality of segments are provided to allow an end of each segment to overlap an end of an adjacent element.

Desirably the or each segment is provided at one end with a cut away portion and at an opposite end with a projection; said cut away portion and projection being dimensioned such that the cut away portion at the end of the or one of the segment (s) may in use receive at least a part of the projection at the opposite end of said segment or of another similar segment. The amount of overlap and so the spacing between the segments is variable depending upon the extent to which the projection (s) is/are received in the cut away portion (s). In this way the effective circumferencial length of the intermediate pipe tensioning means is made variable to adjust to fit various external pipe diameters.

It is to be understood that where a plurality of segments is provided such overlaps need not be provided on every segment to accomplish the necessary adjustment though this is desirable. The overlap is preferably arranged such that it occurs at least in a radial direction relative to the pipe, and optionally also in an axial direction of the pipe. Preferably the or each projection is of'L'shape in cross section and the cut away (s) correspondingly shaped.

Typically the pipe joint assembly is delivered for use fully assembled but untightened.

The segments (s) of which the intermediate pipe tensioning means is comprised may be made from any suitable substantially rigid material, amongst which are metals such as mild steel, ductile iron, and plastics and composite materials. It is envisaged that for light duties where the pipe is at a relatively low pressure differential the segment (s) may be of plastics and/or comprise only one segment, though this may well depend upon the external diameter of the pipe.

Typically a 600mm external diameter pipe would have an intermediate pipe tensioning means provided by twelve identical segments giving a substantial range of adjustment to fit a larger range of pipe external diameters than previous couplings.

Annular gaps between the pipe external surface and the annular tensioning ring of 40mm or more have been possible whilst the coupling gave a proper fluid-tight seal.

It is envisaged that for larger pipe diameters (e. g. 600mm upwards) where the exterior circumference of the pipe more closely approaches a flat plane, a set of said segments may be provided from which a number are used the number being chosen to suit the application. Each element may be either straight or have a radius of curvature not closely similar to that of the external pipe radius, yet a fluid-tight seal may be obtained.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a schematic partially cut away cross sectional view though a first pipe coupling according to the invention shown in sealing engagement with two pipe ends of different external diameters.

Fig. 2a is an axial view on a reduced scale of an assembly of segments forming part of intermediate tensioning means of the coupling shown in Fig 1.

Fig. 2b is an axial view shown partly broken away of a few segments forming part of intermediate tensioning means of the coupling shown in Fig. 1.

Fig. 3 is a front view of one of said segments shown in Fig. 2.

Fig. 4 is an end view on line X of Fig. 3.

Fig. 5 is an end view on line Y of Fig. 3.

Fig. 6 is a cross-section on line c-c of Fig. 3, and Fig. 7 is a partial axial view shown partly broken away of a single segment intermediate tensioning means according to a second embodiment of the invention.

The pipe coupling shown in Figs 1-7 is one designed to couple two pipe ends 1 a, 1 b and therefore comprises two couplings shown generally as Sa 5b, according to the invention each comprising a coupling body shown generally as 10 having a central cylindrical portion 12 provided with an inwardly projecting annular lip 14 which provides an end stop for 16 ends of pipes received therein; opposed bevelled portions 18a, and 18b, and radial (relative to the central cylindrical portion 12) annular flange portions 20a, 20b.

The flange 20a, portions 20b are provided with bores to receive bolts 22, these being provided at circumferentially-spaced intervals (see Fig. 2). For each pipe end 1 a, 1 b, to be sealed there is provided an annular resilient seal 30a, 30b of wedge shaped cross-section (in this embodiment both resilient seals are of identical shape), and respective tensioning means provided by respective annular steel rings 40a, 40b these again being of identical shape, and respective intermediate tensioning means provided by a plurality of linked steel segments 50a, 50b of arcuate shape and of generally L shaped cross-section linked to from an annular each being adapted to receive a respective one of said seals 30aa 30~. It will be noted that the external diameters of pipes 1 a and 1 b are different.

The pipe coupling is supplied assembled but with the bolts untightened and is fitted by inserting the pipe ends 1 a and I b into respective ends of the central cylindrical portion 12 of the coupling through respective annular rings 40a, 40b resilient seals 30a, 30b and annulus'of steel segments 50a, 50b : the pipe ends la, I b, being inserted until they abut the lip 14 from opposite sides. The steel segments 50a, 50b have oblique rear surfaces 51 51b such that a frustoconical socket is provided into which the pipe ends la, Ib, inserted and on movement of the pipe ends la, 1 b, towards lip 14 the steel segments are forced radically automatically to receive the pipe ends la, 1~. The resilient seals 30a, 30b are pushed down into the bevelled portion 18a 18b and the steel annularly linked segments pushed to abut the resilient seals 30= 30b. Bolts 22 inserted through annular steel rings 40a, 40b and flange portions 20 are then tightened to urge resilient seals 30a, and 30b into wedging sealing engagement between the bevelled portions 18a. 18b and the exterior surfaces of the pipe ends lylb. As the bolts are tightened, the segments 50a, 50b respectively tighten to form a close fit on the pipe ends although it is not necessary for the segments to contact the pipe ends surfaces. This occurs as tightening commences, the bevelled portions force the segments down to the pipe ends exterior surfaces and so the segments overlap one another more and more until tightening ceases, at which point the seals are engaged in fluid-tight manner between bevelled portions 18a, 18b and exterior surfaces of pipe ends la, and I b.

It should be understood that instead of a single bolt 22 provided at each circumferentially spaced position, a pair of bolts could be provided each one linking a respective annular steel ring 40a, 40b with a respective flange. This increases the load on the central cylintrical portion 12 of the coupling body but enables independent adjustment of the respective pipe couplings 5av 5b.

It will be noted that in this embodiment the annular steel rings 40aF 40~ are identical and that the inner radius of the ring 40a is larger by a significant amount than the external radius of pipe end 1 a leaving a gap G. With a conventional (known) coupling the resilient seal would escape through through this gap and the seal of Fig. 2a shows a plurality of the segments 50a shown in Fig. l. These are shown in closed-up formation and thus in a position of minimum annular radius of the intermediate tensioning means.

Fig 2b shows parts of a pair of segments 50a shown in their maximum open position where the overlap between segments is at its minimum.

Each of the segments 50a (and 50~) comprises an arcuate steel element of L shaped general cross-section (Fig. 3-6). At one end 51 of each element there is provided a cut away portion 52 and at an opposite end 53 there is provided a projection 54. Projection 54 and cut away portion 52 are dimensioned so that projection 54 can overlie, to a greater or lesser extent, cut away portion 52. Figures 3 4,5, and 6 show the shape of the segments 50a, 50b.

The lip 14 is optional. In certain circumstances such as where e. g. a branch, coupling is to be inserted into an existing pipeline, its presence is not desirable.

Fig. 7 shows another embodiment in which the intermediate pipe tensioning means comprises a single segment 50c with overlapping ends. This segment is of plastics and the single end overlap gives only a relatively small degree of circumferential length adjustment compared with that shown in Figs 1-6 Any convenient number of segments may be used for the intermediate tensioning means, and the overlapping construction shown in the embodiments is onl one of many overlapping variations which will be apparent to those skilled in the art.

The segments may be of plastics or ductile iron or of any suitable material.

Claims

CLAIMS 1. A pipe coupling comprising a coupling body, a resilient seal and tensioning means adapted to hold the resilient seal in sealing contact between the coupling body and an end of a pipe to be coupled, wherein the tensioning means comprises an annular tensioning member and intermediate pipe tensioning means, the intermediate pipe tensioning means being disposed between said resilient seal and said annular tensioning member, the intermediate pipe tensioning means being arranged such that tensioning movement of the annular tensioning member towards the coupling body causes the intermediate tensioning means to urge the seal into sealing engagement between the exterior surface of the pipe end and the coupling body, the intermediate pipe tensioning means having means for adjustment of its effective circumferential length so permitting the intermediate pipe tensioning means'effective circumference to more closely conform to the external diameter of the pipe end.
2. A pipe coupling as claimed in claim 1, wherein the intermediate pipe tensioning means is an annular element which may be composed of one. or of a plurality of segment (s), the means for adjustment being so as to enable the intermediate pipe tensioning means to be disposed in relation to the pipe end such that on urging of the seal into said sealing engagement, any gap between said intermediate pipe sealing means and the exterior surface of the pipe is sufficiently small to prevent the seal being forced out of that gap and thus making the seal of the pipe coupling ineffective.
3. A pipe coupling as claimed in claim 2, wherein said means for adjustment of the effective circumference length of the intermediate pipe tensioning means i s provided by disposing an end of the segment to overlap an opposite end of the segment, or where a plurality of segments are provided to allow an end of each segment to overlap an end of an adjacent segment.
4. A pipe coupling as claimed in claim 3, wherein the or each segment is provided at one end with a cut away portion and at an opposite end with a projection; said cut away portion and projection being dimensioned such that the cut away portion at the end of the or one of the segment (s) may in use receive at least a part of the projection at the opposite end of said segment or of another similar segment, so providing said means for adjustment of the effective circumferential length of the intermediate pipe tensioning means.
5. A pipe coupling as claimed in claim 3 in which a plurality of segments is provided and wherein the overlap is arranged such that it occurs at least in a radial direction relative to the pipe, and optionally also in an axial direction of the pipe.
6. A pipe coupling as claimed in claim 4 or 5, wherein the or each projection is of'L'shape in cross section and the cut away (s) are correspondingly shaped.
7. A pipe coupling as hereinbefore described and/or as shown in the accompanying drawings.