WO1997021052A1

WO1997021052A1 - Sealing gasket arrangement

Info

Publication number: WO1997021052A1
Application number: PCT/GB1996/002808
Authority: WO
Inventors: Gary Briggs
Original assignee: Flexitallic Limited
Priority date: 1995-12-02
Filing date: 1996-11-18
Publication date: 1997-06-12
Also published as: GB9524691D0; GB2307962A

Abstract

A sealing gasket (30), for disposing between raised flange faces (11, 12) bolted together, comprises a known sealing element (31) disposed between the raised flange faces (16, 17) and outwardly thereof compression control means (40), in the form of compression stop arrangements (41A, 41B, 41C ...), associated with individual connecting bolt directions (A, B, C ...) and apertured to pass the respective connecting bolts, joined to the sealing portion by joining parts (43A, 43B ...). The compression stop arrangements are of thickness equal to the operational thickness of the sealing portion plus the height of the raised faces (16 and 17) and conveniently the associated joining part is of the same thickness, providing support for auxiliary seals (46, 47) and having shoulders (50, 51) for locating and centering the gasket arrangement with respect to the raised faces rather than the connecting bolt circle. The joint is not dependant upon accurate tensioning of the connecting bolts to prevent overstressing the flanges and the bolts may be tensioned to much higher levels to use the resilience thereof in accommodating mechanical and tensile forces acting on the pipes and flanges without compromising sealing.

Description

Sealing Gasket Arrangement

This invention relates to gasket arrangements for use with so- called raised face flange joints and in particular addresses problems caused by overstressing such flange joints.

It has long been known to join the ends of axially aligned pipes by providing at the end of each a radially extending flange surrounding the pipe, providing a circular array of bolt holes about the periphery of each flange and drawing the flanges together by means of connecting bolts extending through the bolt holes, a sealing gasket arrangement between the flanges being compressed by the axial loading of the connecting bolts to prevent the passage of service fluid from the pipes by way of the flange faces. The bolt circle, that is the locus of the circle defined by the radially inner surfaces of the connecting bolts, usually serves as a boundary for a guide ring surrounding the sealing element and locating it centrally with respect to the flanges.

When such flange faces are substantially flat the considerable load which may be applied by the connecting bolts is spread over a significant area of interface between the gasket and flange. Some materials used in the past, such as compressed asbestos fibres bound in a rubber, were found not to seal efficiently at the specific loading obtainable from standard sizes of flange and connecting bolts, and to overcome this, the raised face design was introduced which concentrates loading on the sealing element of the gasket to an annular region of reduced radius immediately surrounding the pipe, whilst maintaining overall flange diameter, connecting bolt sizes and number. Such raised face flange form has been used to such extent that it is specified in various industry standards, such as ANSI B16.5 in respect of materials, dimensions, loading forces etc for different classes of service.

However, with such raised face flange arrangement it is seen that the axial loading applied by the connecting bolts must be kept within closely defined limits for particular sealing element compressibility, as once the gasket sealing element is fully compressed, possibly when the raised flange faces abut a compression limiting part of the sealing portion, any further axial loading by way of the connecting bolts near the periphery of the flanges tends to cause deformation of the flanges themselves such that the loading on the sealing element is compromised.

However, with modern sealing materials and forms, such as the spiral wound gasket element, it is possible to effect a seal at a flange face without unduly high specific loading, but the raised face flange design is specified in many situations where a sealing gasket is to be provided.

It is of course feasible, having regard to the compression characteristics of a particular sealing gasket, to specify the axial loading and thus tensile stress to be induced and retained in the tightened connecting bolts and to assemble the joint with care such that the appropriate loading is not exceeded.

However, it is found that the bolts specified by the Standards for a particular class of service are tensioned to achieve the axial loading on a raised face flange only to a low percentage of the maximum tension each such bolts can tolerate. Whereas such highly loaded bolts are able to withstand temporarily increased loading imposed by external mechanical or thermal effects, such bolts cannot tolerate reduced loading without the above described compromise of sealing efficiency. Furthermore, the relatively low residual tension in the bolts does not help in resisting or recovery from such external forces.

It has been proposed to mitigate such disadvantages associated with raised face flanges by providing a spacer washer about each connecting bolt to limit the ability to compress the flanges beyond the axial length of the spacer. The provision of such spacer washer does enable the connecting bolts to be tightened to sustain a greater residual tension, and thus act as a restoring spring against induced deflections of the pipes and flanges. However, this is not itself without disadvantage. There is the additional complexity of assembling the joint, manipulating a spacer into position with respect to each connecting bolt. Also, each spacer, being of necessity a clearance fit on the connecting bolt assumes a somewhat indeterminate position and provides a similarly indeterminate effective boundary to the bolt circle, making it difficult to accurately centre a sealing element that depends on the bolt circle for such centring. Furthermore, it will be appreciated that the spacing of the connecting bolts from the sealing faces by the relatively thin flanges could result, at the loads the higher stressed bolts are now able to withstand, in deformation of the flanges.

It is an object of the present invention to provide for use with such a raised face flange joint a sealing gasket arrangement of simple construction which offers improved sealing performance with simplicity of use.

According to the present invention a sealing gasket arrangement, for use with a raised face flange joint in which facing flanges surrounding adjoining pipe ends each have a raised face of predetermined height with respect to radially outward parts of the flanges containing a circle of bolt holes by way of which a plurality of connecting bolts extend between the flanges and apply axial compressive loading to the gasket arrangement, the gasket comprising (i) an annular, radially inner sealing portion radially dimensioned to be disposed between, and co-operate with, the raised faces and responsive to a predetermined level of axial loading from the flanges to assume a predetermined operational thickness at which a desired degree of sealing between the sealing portion and raised faces is achieved, and (ii) compression control means comprising, associated with each connecting bolt of the joint, a compression stop arrangement, of axial thickness egual to the sum of the height of each raised face and said operational thickness of the sealing portion, to at least partially surround the connecting bolt, and joining means connecting said compression stop arrangement and the sealing portion.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which

Figure 1(a) is a sectional elevation through half of a raised face flanged pipe joint and including a gasket arrangement in accordance with the present invention disposed between the flanges prior to applying axial loading between them by way of connecting bolts, the gasket arrangement having compression control means in which the compression stop arrangement and joining means to the sealing portion are formed integrally within a compression control ring of substantially uniform thickness,

Figure 1(b) is a sectional elevation, similar to Figure 1(a) but of the other half of the raised face flanged pipe joints and after axial loading has been applied by the connecting bolts,

Figure 1(c) is a plan view of part of the gasket arrangement of Figure 1(a) ,

Figure 2(a) is a sectional elevation, similar to Figure 1(b) showing an alternative form of gasket arrangement, also in accordance with the present invention, illustrating a different form of sealing portion and centring thereof with respect to the flanges,

Figure 2(b) is a sectional elevation of a fragment of the joint of Figure 2(a) illustrating circumferential location of the gasket arrangement with respect to the flanges and flange bolt holes.

Figure 3 is a sectional elevation similar to Figure 2(a) but of yet another form of gasket arrangement in accordance with the present invention, in which the compression control means has joining means of reduced thickness,

Figure 4 is a plan view similar to that of Figure 1(c) but showing yet another form of gasket arrangement compression control means having compression stop arrangement and joining means in the form of discrete, substantially radially extending, bolt limbs associated individually with the connecting bolts,

Figure 5(a) is a plan view, generally similar to that of Figure 1(c) or 4 but illustrating variants of the compression stop arrangement based upon a radially extending slot aperture for each connecting bolt,

Figure 5(b) is a further variant on the embodiment of Figure 5(a) in which each connecting bolt slot extends radially inwardly to the sealing portion bifurcating each notional compression control limb associated with each bolt direction, and

Figure 6 is a sectional elevation through yet another form of gasket arrangement in accordance with the present invention in which the compression stop arrangement associated with the individual connecting bolts are discrete members carried by the joining means.

Referring to Figures 1(a) and 1(b) a raised face flange joint 10 comprises facing flanges 11, 12 each surrounding adjoining pipe ends 13, 14 which share a common longitudinal axis 15. Each flange has a raised face, 16, 17 respectively, immediately surrounding the pipe, which is of predetermined height h with respect to radially outward parts of the flanges. These radially outward parts have flange faces 18, 19 respectively and contain a circle of bolt holes 20, 21 respectively, uniformly arrayed about the longitudinal axis 15.

A plurality of connecting bolts 22 extend through the axially aligned flange bolt holes and by way of head 23 and nut 24 (or such nuts at each end) apply axial load to draw the flanges together .

Such raised face flanged joint arrangement per se is well known and the dimensions of the flanges, raised faces, bolts circles, as well as the size and number of connecting bolts is defined for different classes of service by Standard ANSI B16.5.

In operation a gasket arrangement is disposed between the raised flange faces, usually located centrally by reference to the circle of connecting bolts, and appropriate axial loading applied such that the sealing part of the gasket is fully compressed to seal with respect to the raised faces.

Referring also to Figure 1(c) a sealing gasket arrangement 30 in accordance with the present invention comprises an annular, radially inner sealing portion 31 of conventional form, being dimensioned to be disposed between, and co-operate with, the raised faces 16 and 17. In the form illustrated the sealing portion comprises an incompressible steel core 32 of predetermined thickness t_c which serves as a carrier for compressible spiral wound gasket elements 33 and 34 in annular recesses 35 and 36 respectively in its radial faces. The structure of each spiral wound element is such that when subjected to a predetermined level of axial loading by the flanges the elements contract axially until the raised flange faces abut the core 32, which acts as a compression limiter to prevent further compression of the spiral wound elements, that is, the predetermined axial loading causes the sealing portion to assume a predetermined operational thickness t₀ that happens to egual core thickness t_c.

The gasket arrangement 30 also comprises compression control means indicated generally at 40. Associated with each connecting bolt of the joint, say bolts 22_A, 22_B, 22_c... illustrated in Figure 1(c) , is a radial bolt direction A, B, C ... passing through the axis of the respective bolt. For each bolt direction the compression control means is defined by a compression control limb 40_A, 40_B, 40_c ..., centred circumferentially on the bolt direction, each limb comprising a circumferentially and radially extending compression stop arrangement 41_A, 41_B, 41_c ... apertured at 42_A, 42_B ... to surround the associated connecting bolt and a joining part 43_A, 43_B, 43_c connecting the sealing portion 31 with the compression stop arrangement.

The joining parts 43_A, 43_B ... together thus comprise joining means connecting the compression stop arrangement and the sealing portion.

In this embodiment, the compression control limbs are of such circumferential extent that the compression stop arrangement and joining parts of adjacent limbs are contiguous and integral at notional boundaries 44 to define a compression control ring 45 surrounding the sealing portion. Furthermore, the limbs are of substantially uniform thickness, so that such joining part inwardly of each compression stop arrangement is of the same axial thickness t, as each compression stop arrangement, and t, is egual to the sum of the height of each raised face and the operational thickness of the sealing portion, that is, t, = 2h + t₀. Put another way, the compression stop arrangements are formed within an integral ring and effectively extend circumferentially and radially in accordance with the dimensions of the non-raised flange faces 18 and 19.

Optionally, as shown in Figure 1(b), the joining means, insofar as it comprises a circumferentially complete ring which lies adjacent to flange surfaces 18 and 19, may support auxiliary sealing elements 46, 47 respectively. Furthermore, such ring, extending radially outwardly of the connecting bolt circle to the edges of the flanges, may support environmental seals 48 and 49 to prevent damage to the flange faces, raised faces, bolts and/or aperture 42_A etc from operating in an unsuitable environment.

It will be seen from Figures 1(a) and 1(b) that the joining means 43, being thicker than the operational thickness of the sealing portion 31, has axially extending shoulders 50 and 51 at which it reduces in thickness to core 32, the shoulders providing a means for locating the gasket arrangement radially with respect to the flanges, that is, centring the sealing portion with respect to the longitudinal axis 15. Such arrangement also means that the apertures 42_A, 42_B ... of the compression stop arrangement may be a generous clearance fit on the connecting bolts, and thus facilitate easy passage of the bolts between the flange bolt holes, without such clearance from the well-defined bolt circle being detrimental to centring accuracy.

It will also be appreciated that such shoulders 50 and 51 not only provide a means of locating the gasket arrangement centrally with respect to the pipes and flanges but also provide, when in position, a restraint to radial movement between the flanges before the connecting bolts are inserted, provided they are together axially. Referring also to Figure 2(a), the assembly of the flanged joint with the gasket arrangement therebetween may be improved by providing one of the shoulders, indicated by broken line 50', inclined to the axis 15 such that it forms a guidance funnel. With the gasket arrangement located on flange 12 by way of shoulder 51 and raised face 17, then as the flange 11 is brought axially towards it, and notwithstanding a limited degree of axial misalignment, the edge of raised face 16 is guided by shoulder 50' into the correct axial and radial position.

Referring also to Figure 2(b) it will be seen that the shoulder 51 and edge of raised face 17 may include a co-operating notch 17' and projection 51' to align the gasket arrangement in a circumferential direction, with the compression stop apertures in line with the connecting bolt holes in the flange.

It will be appreciated that when the flanges are loaded axially by tensioning, the connecting bolts, the force applied to any sealing element cannot exceed the predetermined desired extent, irrespective of the magnitude of the loading above the minimum required to achieve operational compression of the sealing elements.

As discussed hereinbefore, if the connecting bolts are highly tensioned, say to the order of 70% of yield point, they behave as high rate resilient elements to the extent that lateral or bending forces applied to the joint by way of the pipes are accommodated within the connecting bolts by changes in the residual tension levels of individual bolts without this being manifested between the flanges and sealing portion and potentially detrimental to the sealing function.

Notwithstanding the advantages realisable from having the connecting bolts exerting a residual tension greatly in excess of that normally permissible with raised face flange joints, the precise level of bolt tension is not critical and thus the joint can be assembled and loaded without the extreme care and skill levels hitherto required.

It will be appreciated that this structure of the gasket arrangement may be varied to suit different sealing conditions.

For instance, in Figure 2(a) it is seen that the sealing portion 31' comprises a spiral wound element 53 which extends directly between the raised flange faces, being surrounded by a compression limiter 54 in which operates between the raised faces 16 and 17, being equivalent to core 32 of gasket 30, and integral with the compression control means 40. It will be appreciated that the compression limiter 56 associated with the sealing element 40 may be omitted, the sealing element extending radially to the edges of the raised faces and being located directly into the compression control means.

Referring to Figure 3, this shows in sectional elevation a further form of gasket arrangement 55, in which the sealing portion 56 includes a compression limiter 57 joined to the radially outward compression stop arrangement 41' surrounding the connecting bolts, by an axially thin joining means 58. Clearly such an arrangement precludes the use of auxiliary sealing elements between the raised faces and the bolt circle and the joining means to centre the gasket arrangement with respect to the flanges.

Referring now to Figure , which is a plan view somewhat similar to Figure 1(c) but showing a section of an embodiment of gasket arrangement 60 in which the compression control limbs 60_A, 60_B, 60_c ... associated with the aforementioned bolt directions A, B, C ... are discrete and of circumferentially limited extent, the compression stop arrangements 61_A, 61_B, 61_c ... preferably having a face area adjacent the flange corresponding to the area of the bolt head or nut. Such discrete limbs not only prohibit the use of an auxiliary sealing elements but also environment sealing elements, except in the form of O-rings (not shown) surrounding the individual bolt apertures 62_A, 62_B, 62_c ... .

Referring to Figure 5(a), which is a schematic plan view of the modified form of the arrangements of Figure 1(c) and 4, the Figure illustrates that the compression stop arrangements may have apertures 42'_A, 42'_B in the form of radially extending slots rather than holes totally surrounding the connecting bolts. It will be appreciated that provided the flanges are supported by the compression stop means at least to the radial distance corresponding to the locus of the centres of the connecting bolts, the axial loading will not manifest as deflection of the flanges.

It will be appreciated that the radial slots may extend inwardly of the bolt circle, the flange loading from the bolt head and nut being transmitted each side of the bolt and slot.

This may be taken to the extreme shown in Figure 5(b) where the compression control limbs, discrete or defined notionally in a compression control ring, are bifurcated by bolt aperture slots 14^,'_A, 42' '_B ... extending radially to the sealing portion.

It will be understood that other such modifications may be effected without departing from the scope of the invention.

The compression stop arrangement may be secured to the connecting means but formed other than integrally. For instance, as shown in the sectional elevation of Figure 6, the compression stop arrangements may comprise individual spacer washers 70_A etc supported by a carrier 71 which provides the joining parts of the joining meanε as individual limbs or a continuous ring, the spacer washers being a press fit through a relatively thin joining part and/or secured thereto, for example by welding.

The compression control means may also include one or more passages (not shown) extending radially therethrough to permit the detection of leakage past, or to pressure test, any one of the sealing elements.

Claims

1. A sealing gasket arrangement (30,55,60), for use with a raised face flange joint (10) in which facing flanges (11,12) surrounding adjoining pipe ends (13,14) each have a raised face (16,17) of predetermined height (h) with respect to radially outward parts of the flanges containing a circle of bolt holes (20,21) by way of which a plurality of connecting bolts (22_ABC) extend between the flanges and apply axial compressive loading to the gasket arrangement, the gasket comprising

(i) an annular, radially inner sealing portion (31,31' ,56) radially dimensioned to be disposed between, and co-operate with, the raised faces and responsive to a predetermined level of axial loading from the flanges to assume a predetermined operational thickness (t„) at which a desired degree of sealing between the sealing portion and raised faces is achieved, and

(ii) compression control means (40), characterised in that the compression control means comprises, associated with each connecting bolt of the joint, a compression stop arrangement (41_ABC;41' ;61_ABC;70_A) of axial thickness (t.) equal to the sum of the height of each raised face and said operational thickness of the sealing portion, arranged operably to at least partially surround the connecting bolt, and joining means (43;58;71) connecting said compression stop arrangement and the sealing portion.

2. A sealing gasket arrangement as claimed in claim 1 characterised in that the compression control means comprises, associated with each radial direction (A,B,C) passing through the axis of a connecting bolt (22_A,22_B,22_C) , a compression control limb (14_AB._C;60_ABC) centred circumferentially on the bolt direction, comprising a radially and circumferentially extending compression stop arrangement (41_ABC;41' ;61_ABC;70_A) , operable to permit passage of the connecting bolt and joining part (43_ABC;71) extending radially between the sealing (31;56) portion and the compression stop arrangement and supporting the compression stop arrangement.

3. A sealing gasket arrangement as claimed in claim 2 characterised in that for each compression control limb (⁴⁰ _A,B,C?⁶⁰ _A,B,C) ^tne compression stop arrangement (41_ABC;61_ABC; 70_A) is integral with the joining part (43_ABC;71) .

4. A sealing gasket arrangement as claimed in claim 2 or claim 3 characterised in that the compression stop arrangement (41_ABC) and joining part (43_ABC) of each compression control limb are (40_ABC) of substantially uniform thickness.

5. A sealing gasket arrangement as claimed in any one of claims 2 to 4 characterised in that, the compression control limbs ( ⁰ _A,B,C) are of such circumferential extent that the compression stop arrangements (41_{A Bc} ;41')of adjacent limbs are contiguous and integrally formed to define a compression control ring surrounding the sealing portion.

6. A sealing gasket arrangement as claimed in claim 5 characterised in that the joining parts (43_ABC) of adjacent limbs (40_ABC) are contiguous and integrally formed in defining said compression control ring.

7. A sealing gasket arrangement as claimed in claim 5 or claim 6 characterised in that at least one surface of the compression control ring radially inwardly of the bolt circle carries auxiliary sealing means (46,47) co-operable with the flange (18,19) face outwardly of the raised face (16,17).

8. A sealing gasket arrangement as claimed in any one of the preceding claims characterised in that the compression stop arrangement (41_ABC;41' ;60_ABC) associated with each connecting bolt extends radially outwardly of the connecting bolt.

9. A sealing gasket arrangement as claimed in claim 8 when dependent on claim 5 chracterised in that at least one surface of the compression control ring radially outwardly of the bolt circle carries environmental sealing (48,49) means co-operable with the flange face (18,19) .

10. A sealing gasket arrangement as claimed in any one of the preceding claims characterised in that the joining means (43,58) is integral with a radially extending core (32) of the sealing portion, said core carrying upon radially extending faces (35,36) thereof primary sealing means.

11. A sealing gasket arrangement as claimed in any one of the preceding claims characterised in that the joining means (43) has an axial thickness greater than the operational thickness of the sealing portion and extends radially inwardly to at least one raised face (16,17) and surrounds it by a centring shoulder (50,51;50' ) .