GB2201464A

GB2201464A - Vacuum support safety pressure relief member and method for making the same

Info

Publication number: GB2201464A
Application number: GB08802488A
Authority: GB
Inventors: Dixit B Kadakia; Wayne V Wright
Original assignee: BS&B Safety Systems LLC
Current assignee: BS&B Safety Systems LLC
Priority date: 1987-02-24
Filing date: 1988-02-04
Publication date: 1988-09-01
Anticipated expiration: 2008-02-04
Also published as: GB8802488D0; GB2201464B; FR2611247B1; CA1286565C; JPS63232832A; FR2611247A1; DE3805546A1; JPH06104191B2; DE3805546C2

Description

2z 1464 0 ?i-- W 1 -1VACUUM SUPPORT SAFETY PRESSURE RELIEF MEMBER AND

METHOD FOR MAKING THE SAME This invention relates to a vacuum safety'support for a pressure relief member, the member being designed for positive rupture in one direction at a pre-determined pressure differential to protect a pressure vessel and to method for making such vacuum supports.

One known form of safety pressure relief assembly includes a rupture disk supported between a pair of complementary supporting members or flanges which are in turn.connected to a vessel or system containing fluid pressure.

These devices are often used in environments having elevated temperatures, alternating pressure and vacuum and corrosive conditions. When such disks are exposed to alternating internal and external pressures the central portion of the disk fluctuates responsive to the pressure differentials thus stressing the disk and ultimately leading to disk rupture at a pressure differential other than that for which the disk was designed. As used herein, the term "positive pressure" refers to a condition in which pressure in the vessel is greater than pressure on the other side of the safety pressure relief assembly while the term nreverse pressuren refers to a condition'in which the vessel pressure is less than the pressure on the other side of the pressure relief assembly.

In order to stabilise the rupture disk against fluctuating in response to alternating internal and external pressure differentials, a vacuum support it positioned internally of the rupture disk and clamped between the complementary flanges. In some constructions, a sealing member is interposed between the vacuum support and the rupture disk. Examples of such supports are shown in US-A-2523068.and US-A-2953279.

In many applications, the vacuum support must be thick enough to support the rupture disk or seal in the f -2presence of a high reverse pressure. At the same time, the vacuum support must also be able to open completely upon the occurance of the positive pressure at which the rupture disk is designed to open. When the rupture disk is designed to open at a relatively low positive internal pressurep the vacuum support may be so thick that rupture of the disk or full opening of the assembly at the pre-determined positive pressure is prevented thus precluding or restricting flow.

Prior art vacuum supports typically include a plurality of petals defined by radial cuts in the vacuum support. Lugs are welded onto the vacuum support adjacent the cuts in order to maintain the structural integrity of the vacuum support in the presence of reverse pressure whil a sufficient pre-determined positive pressure opens the petals upon bursting of the rupture disk. In the past, it has been necessary to-design vacuum supports of varying thicknesses dependent upon the level of reverse pressure the vacuum support must withstand.

In addition, the lugs which are spot welded onto the prior art vacuum supports constitute surface irregularities upon which process materials in the vessel may accumulate.- When such process is corrosive, especially in the presence of high temperatures, the effective life of the vacuum support is reduced.

It is important that, when the internal pressure in the vessel reaches the pre-determined positive pressure at which the rupture disk opens, the vacuum support opens completely and fully while at the same time retaining parts so that vacuum support fragments are not sent downstream of the safety pressure relief device.

According to the present invention, there is provided a vacuum support for use with a safety pressure relief' rupture member, said vacuum support comprising a disk having a convex.side and a concave side, said convex side being positionable against one side of said rupture member e 1; 701 i o, -3for supporting the rupture member when the pressure on the concave side of said disk-is lower than the pressure on the other side of said rupture member, at least one slit is formed in said disk, said at least one slit being defined by a pair of opposed substantially parallel edges being urged against one another by said rupture member when the pressure on the concave side of said disk is lower than the pressure on the other side of said rupture member, said disk edges providing the sole means of support for the portions against one another when so urged.

By the present invention, a vacuum support is provided which is simply and easily constructed, which can open completely and positively at low rupture disk pressures while supporting the rupture disk in the presence of a high reverse pressurer which is usable with rupture disks-having -a wide range of reverse pressure and rupture pressure ratings. and which can open positively and completely without fragmenting when internal vessel pressure exceeds the design rupture disk opening pressure.

According to another aspect of the invention there is provided a method for making a vacuum support for use in a safety pressure relief device of the rupturable type said method comprising the steps of forming a did k having a convex upper side and a concave lower side; forming at least one slit through said disk which divides the same into generally lower and upper portions, said slit being narrow enough relative to said disk thickness to close and prevent said upper,portion from collapsing downwardly into said lower portion responsive to downward pressure applied to said upper portion.

In order that the present invention may more readily be understood, the following description is given, merely by way of examplei with reference being made to the accompanying drawings:

Figure 1 is a partially sectioned perspective i -4view of safety pressure relief device incorporating one embodiment of vacuum support according to the present invention, with portions thereof broken away:

Figure 2 is An exploded perspective view of the 5 safety pressure relief device of Figure 1; Figure 3 is an enlarged partial cross-sectional view of a portion of the safety pressure relief device of Figure 1; Figure.4 is a top plan view of the vacuum support 10 of the safety pressure relief device of Figure 1; Figure 5 is a section taken along line 5-5 in Figure 4; Figure 6 is an enlarged view of a portion of Figure 5; Figure 7 is a cross-sectional view of the safety pressure relief device of Figure 1; Figure 8 is a view similar to Figure 7 after rupture of the safety pressure relief device; Figure 9 is a cross-sectional view of a second embodiment of a vacuum support construct.ed in accordance with the instant invention; and - Figure 10 is an enlarged view of a portion of Figure 9.

The structure 10 shown in Figure 1 includes a base flange 12 threaded to a pipe 14 which serves as the relieving outlet for a pressure vessel to be protected. A safety pressure relief device 16 includes a vacuum support 18, a sealing member 20, and a rupture disk 22 together installed between base flange 12 and a hold-down flange 24.' The hold-down flange is shown provided with threads 26 or other suitable means of connecting piping (not shown) to vent fluids away from the vessel area when required. Flanges 12, 24 are secured together by bolts 28, the device 16 serving as a gasket between flanges 12, 24 to provide a sealed connection for the pressure vessel.

t, M I 7k Rupture-disk 22 includes an upper convex-side 30 (Figure 2) and a lower concave side (not visible in Figure 2), and an anchoring flange 32 (Figure 7). A plurality of slots 34 extend radially outwardly from a solid central portion and a hole 38 is drilled or punched at the upper end of each of the slots to prevent stress concentrations at the upper slot ends.

Rupture disk 22 is constructed to positively burst when the pressure in tubular member 14 exceeds the pressure on the other side of the pressure relief device by a pre- determined amount, which, for any diameter of the safety pressure relief device, may be selected by Varying metal thickness, tensile strength of the metal being considered, and varying the length of the slots 34. For example, the longer the slots, the closer their proximity'at central portion 36 of rupture disk 22, the smaller the area will be between the slots to resist the internal pressure of the vessel.

Sealing member 20 is made to conform with the shape of rupture-disk 22 or must be of sufficient flexibility to assume such a shape when assembled as part of the unit. Since the function of the sealing member is simply to prevent leakage through device 16 and to prevent corrosion of rupture disk 22, it may be made from a wide variety of materials, the material being chosen individually for each installation with caution taken to ensure the protection of rupture disk 22 from corrosion. Furthermore the sealing member-20 and rupture disk 22 may be combined into a single rupture disk which also seals to prevent leakage.

As shown in more detail in Figures 4-6 vacuum support 18 includes a circular disk 39 having a generally convex upper side 40 and a generally concave lower side 42, these sides each being part spherical. A substantially 3 horizontal (as viewed in Figure 5) slit 44 is formed though i -6vacuum support 18 and defines an arc centered about the central ax,is 46 of disk 39. One end of slit 44 terminates in a hole 45 to relieve stress concentrations. Slit 44 divides disk_39 into'an uppr disk portion 48 and a lower disk portion 50.

An anchoring flange 52 is formed about the radially outer circumference of disk 39 and includes an outermost flat annular portion 54, which is clamped between flanges 12, 24 when va-cuum support 18, sealing member 20, and rupture disk 22 are nested together as shown in Figures 1 and 7.

Slit 44 is defined by upper and lower di-sk edges 56 and 58, which are substantially parallel to one another and, as shown, each defining an angle of substantially 60 0 with respect to axis 46. A second axis 60 is shown in Figure 6, such being normal to axis 46 and parallel with annular portion 54. A third axis 62 is parallel to disk edges 56, 58. Thus, in the particular embodiment of the invention, the angle 64 between axes 60, 62, is 0 substantially 30 It has been found that the safety pressure relief device of the invention will operate particularly successfully when disk edges 56, 58 are 0 oriented so that angle 6A is within the range of 0-45 A second slit 66 is formed through disk 39 and is symmetrical with respect to slit 44 and includes a hole 68 at one end thereof to relieve stress concentrations. Although not visible in the drawings, slit 66 includes upper and lower edges 56,.58, which are parallel to one another and form an angle of substantially 60 0 with respect to axis 46. Each of slits 44, 68 has one end which terminates in holes 45, 68 and another end 70, 72, respectively. That portion of the disk between holes 45, 68 is referred to herein as a vacuum support hinge portion 69 and that portion of the disk between ends 70,. 72 is referred to herein as a vacuum support positioning portion 73, the latter ?A Y C -011 1.

-7maintaining upper portion 48 in alignment with lower portion 50 when vacuum support 18, sealing member 20, and rupture disk 22 are nested together for assembly as shown in Figures 1 and 7.

In operation, vacuum support 18, sealing member 20, and rupture disk 22 are assembled between flanges-12, 24, the pressure on the vessel to be protected operating on the concave side of sealing member 20 through slits 44, 46 and holes 45, 6-8 in vacuum support 18. When properly assembled, sealing member 20 nests in the concave side of rupture disk 22 so that pressure transmitted to sealing member 20 is.exerted b the sealing member against the concave side of rup.ture disk 22.

When the pressure in tubular member 14 falls below the pressure on the convex side of rupture disk 22, vacuum support 18 prevents substantial flexing of rupture disk 22 and sealing member 20 in response to fluctuating pressure. In response to the lower pressure internal-of tubular member 14, a downward force is exerted by seal 20 against vacuum support 18 thus pressing upper edge 56 of slit 44 against lower edge 58 and likewise pressing the upper and lower edges of slit 66 together so that the vacuum support assumes the configuration of Figure 3. Due to the dome shape of vacuum support 18 and the abutment of the slit edges flat against one another. vacuum support 18 is able to maintain the configuration of Figure 3 even in the presence of very high reverse pressures. This is so even when the vacuum support is made from thinner material than used in prior art vacuum supports.

Pressure interior of tubular member 14 which is greater than pressure on the other side of safety device 16 acts against sealing member 20 on the lower side of rupture disk 22. When such pressure reaches the level at which disk 22 is designed to burst, the metal between the holes (like hole 38 in the upper portion of disk 22) separates, except 1 1 -8for one set of holes as shown in Figure 8, thus permitting the disk to open as shown. When rupture disk.22 opens, the pressure causes seal 20 to tear and vacuum support 18 to hinge open, the material between slit ends 70, 72 breaking thus permitting the vacuum support to hinge open as shown in Figure 8.

Vacuum support 18 may be designed.to ensure that it will withstand a reverse pressure differential of a selected value without collapsing. The strength of the vacuum support when exposed to reverse pressure is determined by the radial distance between axis 46 and slits 44, 66; angle 64; the thickness of the disk and the width of the slits# i.e. the distance between edges 56, 58. The degree of reverse pressure which the vacuum support will withstand is a function of the thickness of the disk and the length of the hinge, i.e. the distance between holes 45, 68.

It is to be appr-eciated that the slit width will vary dependent upon the thickness of the disk from which the vacuum support is made and the distance between ends 70, 72 will vary dependent upon the diameter of the vacuum support -disk which in turn is dependent upon the diameter of the rupture disk with which the vacuum support is used.

Thus the structure of the vacuum support of the inventi on is able to withstand high reverse pressures because of the manner in which the slit closes with lower disk portion 50 supporting upper disk portion 48 as shown in Figure 3, Because the vacuum support structure can be formed from thinner material than previous vacuum supports. it can open positively and completely at low positive pressures. Thus, unlike prior art vacuum supports, for a given rupture disk size. the vacuum support of the instant invention may be used over a wide range of positive and reverse pressure ratings for its associated rupture disk.

Figures 9 and 10 show a second embodiment 75 of a vacuum support constructed in accordance with the invention, 1 1 v c -.t -g- which includes a pair of symmetrical slits, one of which is slit 76, formed through a dome shaped portion of the vacuum support similar to vacuum support 18. Vacuum support 74 includes a substantially planar radial annular flange 78 which- is used to mount the vacuum support in a type of mounting flange different from flanges 12, 24 in Figure 1. Otherwisep vacuum support 74 functions in the same manner (with an associated rupture disk and seal, each of which have planar flanges similar to flange 78) as the embodiment of Figure 1. Other means than those disclosed herein-for mounting a vacuum support of. the invention may be utilised.

Turning now to Figure 6, included therein is a laser 80. When making vacuum support 18, laser 80 is used to form slits 44, 66 with a laser light beam being aligned with axis 62 thereby forming the slit edges 56, 58 at an angle dependent upon the orientation of laser 80. Laser 80 provides precision control in selecting both the angle of edges 56, 58 and the width of slit 44 thus enabling the vacuum support to be precisely designed to withstand a given amount of reverse pressure. A vacuum support so constructed includes fewer parts than vacuum supports of the prior art which typically have lugs spot welded thereto adjacent cuts which are formed through disk 39 in order to withstand reverse pressure to a preselected amount. As shown the axis 62 passes through the centre of curvature of the partspherical domed portion of the vacuum support, so that the slit edges are perpendicular to the adjacent surface of the dome, thus reducing any tendency for the edges to ride up over one another during a reverse pressure condition.

1 1 1

Claims

-10C L A I M S

A vacuum. support for use with a safety pressure relief rupture member, said vacuum support comprising a disk having a convex side and a concave side, said convex side being positionable against one side of said rupture member for supporting the rupture member when the pressure on the concave side of said disk is lower than the pressure on-the other side of said rupture member, at least one slit is.formed in said disk, said at least one slit being defined by a pair of opposed substantially parallel spaced disk edges, dividing said disk into portions said edges being urged against one another by said rupture member when the pressure on the concave side of said disk is lower than the pressure on the other side of said rupture member, said disk edges providing the sole means of support for the portions against one another when so urged.
2. A vacuum support according to claim 1, wherein the distance between the disk edges is less than the thickness of said disk.
3. A vacuum support according to claim 1 or 2, wherein said vacuum support includes a first and a second slit# said slits have a first pair of opposing ends defining a vacuum support hinge portion therebetween and a second pair of opposing ends defining a vacuum support positioning portion therebetween. 25
4. A vacuum support according to claim 3, wherein said vacuum support positioning portion is substantially shorter than said vacuum support hinge portion.
5. A vacuum support according to any preceding claim, wherein said at least one slit defines an arc.
6. A vacuum support according to claim 5, appendant-on claim 3, wherein said first and second slits 0 together define an arc greater than 270
7. A vacuum support according to claim 5 or 6, said convex side said concave side. and said arc or arcs are \-I- :17 z I IF o, centered on a common axis.
8. A vacuum support according to claim 7, wherein said disk edges form an angle of between 45 0 to 900 with said axis.
9. A vacuum support according to claim 8, 0 wherein said angle is substantially 60
10. A vacuum support according to claim 8 or 9, wherein the concave and convex sides of the disk are part spherical and the disk edges are formed on surfaces passing through the centre of curvature of the spheres, whereby the disk edges are perpendicular to the adjacent portions of the concave and convex sides.
11. A vacuum support according to any preceding claim, wherein said at least one slit is substantially horizontal, to form upper and lower disk portions.
12. A method for making a vacuum support tor use in a safety pressure relief device of the rupturable type said method comprising the steps of forming a disk having a convex upper side and a concave lower side; forming at least one slit through said disk which divides the same into generally lower and upper portions, said slit being narrow enough relative to said disk thickness to close and prevent said upper portion from collapsing downwardly into said lower portion responsive to downward pressure applied to said upper portion.
13. A method according to claim 12, wherein the step of forming a slit is effected by cutting with a laser beam.
14. A method according to claim 12 or 13, wherein said slit is cut narrower than the thickness of said disk.
15. A method according to claim 12. 13 or 14. wherein said slit is cut as an arc.
16. A method according to claim 12, 13, 14 or 15. wherein said slit is cut with a pair of opposed 9 1 -12substantially parallel disk edges on either side of said slit.
17. A method according to'claim 16, wherein said at least one sift is cut to form edges at an angle of between 45 0 and 90 0 with respect to the longitudinal axis of said disk.
18. A method for making a vacuum support for use with a safety pressure relief member, said method being substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
19. A vacuum support for use with a safety pressure relief member, said vacuum support being substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
20. A safety pressure assembly including a vacuum support accordint to any one of claims 1 to 11 or claim 19 and a safety pressure relief member supported thereby.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WClR 4TP. Further copies may be obtained ftm The Patent Oince, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con- 1/87.

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