GB2221256A

GB2221256A - Bursting disc

Info

Publication number: GB2221256A
Application number: GB8912485A
Authority: GB
Inventors: Cecil Derry; Alan Leslie Hume
Original assignee: Marston Palmer Ltd
Current assignee: Marston Palmer Ltd
Priority date: 1988-06-02
Filing date: 1989-05-31
Publication date: 1990-01-31
Anticipated expiration: 2009-05-31
Also published as: DE3917732C2; DE3917732A1; GB8912485D0; GB8813054D0; GB2221256B

Description

4 _) 1 2221256 Bursting Disc This invention relates to bursting discs and

has particular, but not exclusive, reference to reverse buckling bursting discs specifically adapted to reverse at low pressures and yet be capable of 5 having an identifying tag on the disc.

Reverse buckling discs are well known and certain reverse buckling discs have been produced which are capable of reversing at low pressures whilst simultaneously capable of withstanding working pressures very close to their determined low pressure reversing. An example of such a reverse buckling disc is the MAXIVENT N and MAXIVENT 0 series of bursting discs available from Marston Palmer Limited of Wobaston Road, Fordhouses, Wolverhampton, WV10 6QJ which discs are described in UK patent specification Nos 1 355 486 and 1 444 206.

Although such discs work very satis-factorily, it is not present practice to tag the discs themselves as the discs are completely released from their holders on bursting. Furthermore, because such discs are completely released from their holders, it is necessary to catch the discs downstream if such discs could cause damage to equipment downstream of the disc.

By the present invention there is provided a bursting disc comprising a domed portion and an integral substantially flat peripheral flange around the domed portion, there being a groove within the substantially flat flange portion around at least part of the domed portion, adjacent the domed portion characterised in that, the domed portion lias at least one substantially straight edge where it meets the plane of the flange.

2 Preferably the groove is a part of a circle, but may be substantially parallel to the edge of the domed portion, and domed portion is centrally located within the circle. The substantially straight edges may be chords within the circle on which the groove lies.

There may be more than one substantially straight edge, two or more edges may form intersecting chords. One chord may be longer than the other or others, the longest chord may be so arranged with respect to the groove that no groove is on the outer periphery of the losigest chord.

The groove may be on the convex or the concave side of the disc.

The disc mav be a reverse buckling disc. The domed portion of the disc may be provided with zones of localised weakness. The zones may be score lines. The score lines may be arranged radially across the dome.

By way of example embodiments of the present invention will now be described with reference to the accompanying drawings of which FIGURES 1 and 2 are plan and cross-sectional views respectively of a prior art disc,

FIGURES 3 and 4 are typical plan and cross-sectional views of discs in accordance with the present invention, FIGURE 5 is a part sectional view of an alternative form of disc and groove, and 7 are plan and side elevational views of an alternative form of disc, FIGURE 8 is a plan view of a yet further alternative form of disc, and FIGURES 6 3 FIGURES 9 to 16 are plan profiles of alternative form of dome and groove arrangements.

Referring to Figure 1, this shows a plan view of a typical reverse buckling disc comprising a central domed portion 1 and an integral outer peripheral flange 2. As can be seen in Figure 2, the domed portion 1 is connected to the flange 2 by a relatively sharp transition region indicated by 3.

When the disc is operated in a reverse buckling mode, pressure is applied in the direction of arrow 4. The tag may be connected to the peripheral flange as at 5 to identify the disc. The tag may be eccentrically mounted so as to permit Cie -1i-sc to be installed only the correct way up.

Although simple reverse buckling discs as shown in Figures 1 and 2 work satisfactorily, they are often not capable of reversing adequately to open at very low pressure. It will be appreciated that in any practical bursting disc it is desirable that the disc should be able to withstand a predetermined pressure for normal operation which must of course be below the pressure at which the disc will relieve. It is also desirable that the pressure at which the disc should relieve be as close to the normal working pressure as possible. Thus, if a disc were capable of relief at 4 bars, it would not be very satisfactory if its maximum working pressure were only 1 bar. Ideally, the operating pressure should be up to 90% of the rated bursting pressure and even further preferably is an operating pressure to within 5% of a tolerance band for the rated burst pressure. Thus, for example, if the rated burst pressure is 10 bar, there would normally be a tolerance of 5% on such units so that 4 they would all burst within the region 9.5 to 10.5 bar. Run at 95% tolerance would mean therefore a maximum practical working pressure of 95% x 95%, approximately 90% of the nominal burst pressure rating.

En the embodiment of the invention illustrated in Figures 3 and 4, the reverse buckling bursting disc includes a central domed portion 6 surrounded by an integral peripheral flange 7. A circular groove 8 is provided within the planar portion of tAhe flange aroun;l in arc or approximately 2700. The domed portion 6 is centrally located within the flange and with-in the groove 8, but instead of being a complete circle n plan view as is the domed portion 1, the doined portion meets the planar region of the flange in straight edges as at 9, 10 and 11. The remaining transition region 12 is inside ti-te groove 8 and lies on a circle. It can be seen therefore from Figure 3 that the transition region includes three straight portions 9, 10, 11 with the remainder lying on a circle.

The groove 8 is made by pressing a suitable rigid tool into the metal of the flange and the domed portion 6 is formed by the action of internal pressure into a suitable tool in a manner well known per se.

It has been found that the provision of the straight edges 9, 10 and 11 result in a burst pressure much lower than is provided in the absence of such straight edges. The groove 8 ens-tires that the central domed portion tears from the peripheral flange. If complete removal of the domed portion is required, the groove 8 is a complete circle. However, if it is required that the domed portion is retained on the 1 1 peripheral flange when it opens, then the groove is terminated in a region as is shown.

It has been found that the straight edge 9 initiates the buckling of the disc and that the buckle then travels from the location of the straight edge 9 across the disc so that the disc preferably starts to open at a point 13 directly opposite the chord 9.

The groove 8 may be provided on the pressurised side of the disc as is shown in Figure 4 or may be provided on the opposite side as at 14 in Figure 5. This ensures that the groove is removed fro:-,i tlie. source of pressurised material and may be advantageous in the case of corrosive pressurising media.

is To assist the hinging action of the released portion of the disc, the peripheral groove 8 may be provided with portions 15, 16 which extend away from the groove to enhance the hinging effect.

The profile of the do-me is shown more clearly in Figures 6 and 7 in which the flange 17 incorporates a groove 18 avid in which there is provided 3 smaller flattened portions 19, 20, 21 and one larger straight edged region 22. Figure 7 shows a profile of the disc illustrated in Figure 6 and it can be seen that a tag 23 can easily be attached to the disc.

Alternative forms of profiles are illustrated in Figures 9 to 16 and it can be seen that numerous combinations are possible. In all cases, Figures 9 to 16 show only the outer peripheral groove 24 and the internal profile of the dome with the straight edges where required. In all cases there is an integral peripheral flange. The domed portion nay have 8 regular sides (Figure 14), or 16 sides (Figure 15) with alternate straight and arcuate sides, or 14 sides P 1.

2.

6 - 7 curved, 6 short straights and 1 long straight (Figure 16) or any other suitable combination.

The domed portion may be provided with scores or other zones of weakness if required.

It will be appreciated that the straight lines at the edge of the dome need not be exactly straight.

They may for convenience be so, but they may be merely substantially straight and may be arcs on very large diameter circles compared to the diameter of the periphery of the dome or the flange.

In tests carried out on a disc sifostantially as illustrated in Figures 6 and 7, the following results were obtained:

Using nickel foil in two cases Reversal pressure of a typical circular disc as shown in Figure 1 at a nominal bore of mm a) At the same dome height as the dish of the invention shown in Figu.res 6 and 7 - reversal pressure = 3.24 bar b) At the same ratio of dishing manufacture pressure to burst pressure of foil as the dish of the invention shown in Figures 6 and 7 - reversal pressure = 3.80 bar Reversal pressure of disc of the invention shown in Figures 6 and 7 = 0.76 bar - a reduction of at least 76% At a nominal bore of 50 mm, other factors being the same, for the disc as shown in Figure 1 a) reversal pressure at same dome height 2.48 bar 7 is b) reversal presure at some dishing ratio 3.17 bar Reversal pressure of the disc of the invention - 1.38 bar - a reduction of at least 44% In a further series of tests on different materials mm nominal St Steel 3.45 bar bore (NB) Nickel 1.75 bar Inconel 2.40 bar nm NB St Steel 2.75 bar Nickel 1.40 bar Inconel 2.05 bar Results frotu Maxivent Discs manufactared using the same materials and dishing criteria show:

mm NB St Steel 7.4 bar mm NB St Steel 8.3 bar 8

Claims

CLAIMS: 1. A bursting disc comprising a domed portion and an integral

substantially flat peripheral flange around the domed portion, there being a groove within the substantially flat flange portion around at least part of the domed portion, adjacent the domed portion characterised in that, the domed portion has at least one substantially straight edge where it meets the plane of the flange.
2. A bursting disc as claimed in claim 1 further characterised in that the groove is part of a circle.
3. A bursting disc as claimed in claim 2 further characterised in that the groove is substantially parallel to the edge of the domed portion, the domed portion being centrally located within the circle.
4. A bursting disc as claimed in claim 3 further characterised in that the straight edge is a chord within the circle on which the groove lies.
5. A bursting disc as claimed in claim 4 or claim 5 further characterised in that there is more than one straight edge, with the two or more straight edges forming intersecting Chords.
6. A bursting disc as claimed in claim 5 further characterised in that one claord is longer than the other or others.
7. A bursting disc as claimed in claim 6 further characterised in that no groove is on the outer periphery of the longest chord.
8. A bursting disc as claimed in any one of claims 1 to 7 further characterised in that the groove is on the convex side of the disc.
9. A bursting disc as claimed in any one of claim 1 to 7 further characterised in that the groove is on the concave side of the disc.

1 4 9
10. A bursting disc as claimed in any one of claims 1 to 9 further cInaracterised in that the bursting disc is a reverse buckling disc.
11. A bursting disc as claimed in claim 10 further characterised in that the domed portion of the disc is provided with zones of localised weakness.
12. A bursting disc as claimed in claim 11 further chareterised in that the zones are score lines.
13. A bursting disc as claimed in claim 12 further characterised in that the score lines extend radially over the dome.
14. A bursting disc substantially as herein described with reference to and as illustrated by Figs 3 to 16 of the accompanying drawings.

Published 1990 at The Patent Office, State House. 66 71 High Holborn, London WC 1R 4TP. Purther copies maybe obtained from The Patent 0Moe. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187