GB2282422A - Closure especially for a pressure vessel and seal therefor - Google Patents

Abstract

A seal for a pressure vessel comprises first and second walls (20, 21) integrally attached to each other and to first and second flanges (22, 23), the walls and flanges forming a hollow elongate extrusion (14), suitably of a high pressure elastomer, which has a mouth (27) formed by the flanges. When placed under pressure, i.e. when the pressure vessel is closed and pressurised, the seal deforms such that the flanges (22, 23) make total sealing Contact with the pressure vessel and the closure. In a preferred embodiment the seal has an annular reinforcing spring (24) embedded in it, the reinforcing spring bridging the gap between the closure and the pressure vessel when the vessel is pressurised and the seal deformed. <IMAGE>

Description

CLOSURE ESPECIALLY FOR A PRESSURE VESSEL AND SEAL THEREFOR This invention relates to closures, especially for pipes and pressure vessels, and to seals for such closures.

In U.K.Patent Specification No:1,508,998 there is disclosed a closure member for a pipe or pressure vessel comprising a door adapted to fit an aperture in the body of the pipe or the pressure vessel, a plurality of blocks slidably mounted adjacent the periphery of the door and movable from a position at least substantially wholly within the said periphery to a position in which a part of each block protrudes beyond the periphery for engagement with the said body, the said parts of the blocks together forming a protrusion extending substantially entirely around the periphery of the door, and means for moving the blocks from the withdrawn to the protruding position.

The closure member of that Specification was particularly designed for relatively large apertures in pipes and pressure vessels which are subject to high pressures. The complexity of the construction of the closure member, however, prevents a similar design from being readily used in closures for small apertures.A closure for small apertures is described in U.K.Patent Specification 1,594,935, wherein the closure comprises a door adapted to fit into an aperture in the pipe or pressure vessel, an arcuate locking member disposed around the periphery of the door for locking the door to the pipe or pressure vessel, the ends of the locking member being movable towards and away from each other to cause radial contraction and expansion of the locking member, whereby the locking member may be brought into and out of locking engagement with the pipe or pressure vessel, and a hinge assembly by means of which the door may be mounted on the pipe or pressure vessel, said hinge assembly comprising a main bracket adapted to be secured to the pipe or pressure vessel, a secondary bracket pivotally mounted on the main bracket and a support for the door mounted on the secondary bracket for movement about an axis parallel to the pivot axis of the secondary bracket.

In U.K.Patent Specification o.

there is described a closure for a pipe or pressure vessel which comprises a door adapted to fit into an aperture in the pipe or pressure vessel and an arcuate locking member disposed around the periphery of the door for locking the door to the pipe or pressure vessel, the ends of the locking member being movable towards and away from each other to cause radial contraction and expansion of the locking member, whereby the locking member or attachments thereto may be brought out of and into locking engagement with the pipe or pressure vessel, and wherein the arcuate locking member and/or attachments, when in locking engagement with the pipe or pressure vessel is or are locked between surfaces of the pipe or pressure vessel and the door which are at an acute angle relative to the plane of the door. The locking member usually comprises a generally annular or C-shaped body.

It is of course of vital importance that the closure between the door and the pipe or pressure vessel should be a hermetic one, and various forms of seal have been designed for this purpose. For example, in the closure of U.K.Patent Specification NoEt2q345the seal, which is located between two opposed faces on the door and the wall of the aperture of the pipe or pressure vessel respectively, comprises an annular ring of resilient material having first and second flanges adapted to engage respective opposed faces of the door and aperture, the radially outer flange having greater flexibility than the radially inner flange. The seal is held captive within a groove around the periphery of the door, and engages with either a flat face or a concave toroidal groove formed in the inner wall of the aperture.

It is an object of the present invention to provide a pipe or pressure vessel with a pressure-retaining closure in which a seal ensures total sealing between the vessel and the closure when the pipe or vessel is both under pressure and under vacuum.

According to the present invention a pressure vessel is provided with a pressure-retaining closure and a seal located between the vessel and the closure, the seal having a form such that, when the pressure vessel is closed and put under pressure, the seal is deformed so as to be in full face sealing contact with the pressure vessel and the closure.

In a preferred embodiment the seal comprises first and second walls integrally attached to each other and to first and second flanges respectively, the walls and flanges forming a hollow elongate extrusion having a mouth formed by the first and second flanges, the seal being made of an elastomeric material deformable when placed under pressure such that said first and second flanges make total sealing contact with the pressure vessel and the closure.

Preferably the first and second walls form a right angle and the seal is contained within an annular rectangular groove in the closure facing a planar wall of the pressure vessel.

The said planar wall is suitably part of a separately-formed neck member which is permanently welded to the pressure vessel.

Preferably an annular reinforcing member is embedded in the seal at the junction of the first wall and the first flange. This may take the form of a solid metal wire, but preferably it is a hollow metal spring, and it has the dual function of reinforcing the seal and also providing fireresistance to the structure.

The seal is suitably made from a high pressure elastomer such as a nitrile rubber. The fluoroelastomer sold under the trade name VITON is particularly useful for this purpose. The two walls of the seal are preferably of substantial equal thickness and their outer surfaces, i.e.

those facing the walls of the annular retaining groove, may be slightly concave, to assist initial pressure-induced deformation.

The invention will now be determined in more detail with reference to the accompanying drawings, showing one embodiment of a pressure vessel closure. In the drawings, Figure 1 shows an aperture for a pipe or pressure vessel, with a hinged door in the open position; Figure 2 shows the door in the closed and locked position; Figure 3 is a cross-section on the line 3-3 of Figure 2 showing the door, aperture and hinge, with the door in the locked position; Figure 4 is an enlarged cross-section through the annular seal; and Figures 5 and 6 are details showing the seal in position in the groove in the door when the door is initially closed and when the vessel is put under pressure, respectively.

Referring to the drawings, Figures 1 and 2 show a circular access port 1, which is adapted to be welded to the end of a pipe or a pressure vessel, having an annular strengthening collar 2. A door 3 is mounted on brackets 4 attached to the annular collar 2. Pivotally mounted on brackets 4 are secondary brackets 5 the ends of which remote from brackets 4 are pivotally mounted on door supports 6.

Brackets 5 are braced by tube 5a. The distance between the pivot axis of the brackets 5 on the brackets 4 and the pivot axis of the brackets on the supports 6 is approximately 65% of the distance between the pivot axis of the brackets 5 on the brackets 4 and a line parallel thereto and passing through the centre of the door 3. This enables the door 3 to be removed from the access port 1 by means firstly of an axial outwards movement followed by a rotational movement.

Relatively small doors may be moved manually. Larger doors may be moved by a handwheel-operated gearbox mounted in the tube 5a.

A C-shaped locking member 7 is disposed around the periphery of the door 3. As best seen in Figure 3, the locking member is in the form of a hollow frusto-cone, with a rectangular cross-section. In the example illustrated the cone angle is 20 .

The marginal portion of the external face of the door 3 is in the form of a frusto-conical flat face 8, the angle between face 8 and the plane of the door being about 200.

An internal bearing surface 10 formed in the access port 1 slopes at a similar angle to the plane of the door, i.e.

faces 8 and 10 are parallel. Bearing face 10 forms one side of a triangular-shaped recess 11 machined out of the inside wall of the access port 1. This triangular recess 11 houses the locking ring 7 when the ring 7 is in fully engaged, locked position.

An annular rectangular groove 12 is formed on the internal wall 13 of the door 3 and retains an elastomeric seal 14. The structure of seal 14, suitably made from a nitrile rubber, is shown in detail in Figure 4. It is an annular extrusion comprising an upper wall 20 and a back wall 21, the thicknesses of which, x and z respectively, are substantially equal. Integrally formed with wall 20 is a front flange 22, and integrally formed with wall 21 is a bottom flange 23, the flanges 22 and 23 being relatively flexible whilst walls 20 and 21 are relatively rigid. The surfaces of the walls 20 and 21 may be slightly concave in form.

Embedded within the seal 14, at the junction of upper wall 20 with front flange 22, is a reinforcing member in the form of a hollow metal spring 24. The spring 24 has a diameter larger than the maximum gap between the door 3 and the access port 1, as will be explained below.

The outer extremities of flanges 22 and 23 taper to wedge-shaped lips 25,26 respectively. Flanges 22 and 23 bound by a substantially semi-circular mouth 27 forming a relief groove.

The geometry of the seal 14 is important to the proper operation of it. Thus, as mentioned, the thicknesses of the walls 20 and 21, i.e. x and z, are substantially the same; the radius r of the groove 27 is substantially ; x is suitably 1.4 to 1.6 times the thickness of the flange 22 at its upper end, i.e. w, and preferably x=1.5w; and preferably the thickness of the seal at the junction of walls 20 and 21, i.e. y, is substantially 1.4 to 1.6 times the thickness of each wall, most preferably y=1.5x.

Seal 14 is retained in the groove 12 on door 3, and the method of closing door 3 is as described in U.K.Patent Specification No: The position of the seal on closing the door, and before the vessel is put under pressure, is shown in Figure 5. The front of the seal protrudes slightly from the groove 12 to stand proud of the face of the wall 13 by, e.g., 0.25mm.

When the pressure vessel is put under pressure, as shown in Figure 6, initial low pressure sealing is obtained by lip 25 of flange 22 contacting the sealing face 30 of the neck 31 of the access port 1. Lip 26 ensures that no leakage occurs into the groove 12. Further increase in pressure deforms the relief groove 27 and causes the anti-extrusion spring 24 to move across the gap between the wall 13 and the sealing face 30, so as to form a barrier to extrusion of the elastomer of the seal 14 into the gap 32 radially outwards of the seal. This allows the seal to retain pressures up to 10,000 psig.

The radius r and position of the relief groove 27 are such as to provide sufficient seal lip flexibility and yet retain adequate strength across the sections x and z and rigidity at section y. The relationship between sections x,z and y is such as to prevent the faces of walls 20 and 21 from being pulled out of groove 12 when under pressure. With these relative dimensions seal-rotation is presented by the corners of the seal being effectively "locked" in the groove. The relationship between section w and x ensures that lip contact occurs progressively along the outer face of flange 22 and sealing face 30 before the pressure at section x causes the anti-extrusion ring 24 to move to straddle the gap between the door and the neck of the access port (Figure 6).

The closure of the invention is equally useful for vessels which operate under vacuum. For such applications the flange 22 has sufficient strength to enable an initial seal to form, and the resulting external atmospheric pressure on the door causes axial movement to close the gap between door and neck. Since the seal 14 protrudes from the groove 12 an effective seal is made along the entire outer face of the flange 22.

It will of course be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope and spirit of the invention.

Claims (10)

1. A pressure vessel provided with a pressure-retaining closure and a seal located between the vessel and the closure, the seal having a form such that, when the pressure vessel is closed and put under pressure, the seal is deformed so as to be in full face sealing contact with the pressure vessel and the closure.

2. A pressure vessel as claimed in claim 1 wherein the seal comprises first and second walls integrally attached to each other and to first and second flanges respectively, the walls and flanges forming a hollow elongate extrusion having a mouth formed by the first and second flanges, the seal being made of an elastomeric material deformable when placed under pressure such that said first and second flanges make total sealing contact with the pressure vessel and the closure.

3. A pressure vessel as claimed in claim 2 wherein the first and second walls form a right angle and the seal is contained within an annular rectangular groove in the closure facing a planar wall of the pressure vessel.

4. A pressure vessel as clained in clan 3 wherein the said planar wall is part of a separately-formed neck member which is permanently welded to the pressure vessel.

5. A pressure vessel as claimed in any of claims 2 to 4 in which an annular reinforcing member is embedded in the seal at the junction of the first wall and the first flange.

6. A pressure vessel as claimed in claim 5 wherein the reinforcing member is a hollow metal spring.

7. A pressure vessel as claimed in any of claims 2 to 6 in which the first and second walls of the seal are of substantially equal thickness and their surfaces facing the pressure vessel are of slightly concave form.

8. A pressure vessel as claimed in any of claims 2 to 7 wherein the radius of the mouth formed by the first and second flanges is substantially half the thickness of each wall.

9. A pressure vessel as claimed in any of claims 2 to 8 wherein the thickness of the seal at the junction of the walls is substantially 1.4 to 1.6 times the thickness of each wall.

10. A pressure vessel as claimed in any preceding claim wherein the seal is made of a high pressure elastomer.