GB1562329A

GB1562329A - Safety pressure relief apparatus

Info

Publication number: GB1562329A
Application number: GB629777A
Authority: GB
Original assignee: Black Sivalls and Bryson Inc
Current assignee: Black Sivalls and Bryson Inc
Priority date: 1977-02-15
Filing date: 1977-02-15
Publication date: 1980-03-12

Description

(54) SAFETY PRESSURE RELIEF APPARATUS (71) We, BLACK, SIVALLS & BRYSON INC., a corporation organised and existing under the laws of the State of Delaware, United States of America, of 4242 Southwest Freeway, P.O. Box 27125, Houston, County of Harris, State of Texas, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a safety pressure relief apparatus.

Many forms of such apparatus of the rupture disc type have been developed, these including a rupture disc supported between a pair of supporting members which are in turn connected to a relief connection in a vessel or system containing fluid pressure. When the fluid pressure exceeds the design rupture pressure of the disc, it ruptures, causing the fluid pressure to be relieved. Such assemblies have hitherto been welded, soldered, bolted or otherwise clamped together, and the rup ture discs have generally been formed of a thin frangible metal or other material having a concave-convex shape.

The disc can be placed so that fluid pressure from the vessel or system to be protected is exerted against the concave side of the disc, so that the disc is in tension and, in order to prevent premature stress failures in the disc, the operating fluid pressure exerted on the disc, i.e., the normal operation pressure of the vessel or system, must be considerably less than the pressure at which the disc is designed to rupture.

In more recent years, rupture disc assemblies of the so-called "reverse buckling" type have been developed which are capable of operating at 90 per cent or more of the pressure at which the disc is designed to rupture. As before, the various parts are welded, soldered, bolted or otherwise clamped together and the rupture disc is positioned so that fluid pressure from the system or vessel to be protected is exerted on the convex side of the disc. The disc is thus under compression during operation and allows the normal fluid pressure exerted on the disc to be relatively close to the pressure at which the disc is designed to rupture. Reverse buckling rupture discs can withstand pressure fluctuations within the vessel or system over a long period of time without premature failure.Knife blades can be provided upon which the disc impales when reversed by excess fluid pressure, or scores or grooves can be formed on a surface of the concave-convex portion of the disc so that upon reversal, the concave-convex portion tears along the lines of weakness thus formed and opens.

In substantially all such apparatus the various parts are assembled and clamped together. In reverse buckling rupture disc assemblies, the rupture disc is often clamped between a pair of annular members which are in turn clamped between inlet and outlet flanges. Regardless of the particular techniques used for clamping the rupture disc between supporting members, the pressure at which the disc ruptures is often affected and can be changed appreciably by variables in the clamping means. When assembly is by welding or soldering, this pressure is effected by variations in the welding or soldering heat, the speed at which the welding or soldering is accomplished and the force exerted on the rupture disc by the supporting members.In bolted assemblies the pressure is affected and often substantially changed by variations in the flange configuration, the bolting load exerted on the rupture disc and misalignment of the rupture disc within the supporting members.

According to the present invention, we provide a method of forming a safety relief apparatus, having a concave-convex rupturable member, which comprises making a body of ductile material, forming a recess at at least one of the ends of said body, so that a substantially flat integral relatively thin portion is formed at the inner end of said at least one recess, and deforming said portion by pressure to form a concave-convex rupturable portion.

There is also provided, according to the invention, a safety pressure relief apparatus made by the method of the invention and comprising a body formed of ductile material and having opposite ends, a recess extending inwardly from at least one of said opposite ends, the internal end of said at least one recess being formed by an integral relatively thin rup turable portion and said portion having a concave-convex shape formed by applying pressure thereto when it is in a substantially flate state.

With such a construction the need to clamp the parts as in prior apparatus, is eliminated.

It should be noted that prior knawn assemblies can only be used in applications wherein the fluid pressure exerted on the rupture disc is limited, usually below 2,000 psig. This limitation has generally been due to the fact that a reverse buckling rupture disc designed for a high pressure application must include a relatively thick concaveconvex portion connected to an annular flange portion by a transition connection having a large radius. When high pressures are exerted on the disc, unpredictable failure often occurs at the large radius transition connection in that the diameter of the concave-convex portion is reduced as the pressure forces exerted thereon cause the radius portion to roll inward until the disc fails by rolling off the supporting member.

By the present -invention, an integral reverse buckling fluid pressure rupturable apparatus is provided which includes only a single part thereby eliminating the problems mentioned above. Further, the apparatus of the present invention is particularly suitable - in high pressure applications in that the rupturable portion of the apparatus does not include a large radius transition connection and consequently the heretofore experienced problems of unpredictable failure are obviated.

In order that the present invention will be more readily understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of one embodiment of apparatus according to the present invention; Figure 2 is a cross-sectional view of the apparatus of Figure 1; Figure 3 is a view similar to Figure 2 showing the apparatus after reversal of its rupturable portion; Figure 4 is a similar view after reversal and rupture of the rupturable portion; Figure 5 is an enlarged partial crosssectional view of the apparatus of Figure 1 prior to forming the rupturable portion thereof into a concave-convex shape; Figure 6 is a similar view after forming the rupturable portion thereof into a concave-convex shape;; Figure 7 is a perspective view of a further form of apparatus of the present invention; Figure 8 is a cross-section through the apparatus of Figure 7; Figure 9 is a view similar to Figure 2, showing further arrangements of the rupturable portion thereof; Figure 10 is a view similar to Figure 9 showing a further arrangement; and Figure 11 is a cross-sectional view similar to Figure 10 showing yet another arrangement.

The apparatus illustrated in Figures 1 through 4 comprises a cylindrical support body 12 formed of a ductile material and having opposite parallel ends 14 and 16.

An inlet cylindrical recess 18 and an outlet cylindrical recess 20 are provided in the body 12 extending from t.tne ends 14 and 16 respectively, the recesses terminating within the body 12, whereby a relatively thin integral rupturable portion 22 is formed within the body 12. When portion 22 is formed into a concave-convex shape, the convex side 24 faces the inlet recess 18 and the concave side 26 faces the outlet recess 20. The cylindrical body 12 and the cylindrical inlet and outlet recesses 18 and 20 are coaxial so that the rupturable portion 22 of the body 12 is connected to the remaining outer annular portion 28 of the body 12 by an annular connection 30 lying in a plane perpendicular to the axis of the body 12.

The rupturable portion 22 of the body 12-is formed by first machining it to a flat configuration as shown in Figure 5.

Pressure is then applied by way of the outlet recess 20, so that the rupturable portion 22 is stretched or bulged into the desired concave-convex shape. While this can be accomplished mechanically, i.e., forcing a plug having a convex surface against the rupturable portion 22 by way of the outlet recess 20, the bulging is preferably accomplished by exerting fluid pressure on the side 26 thereof by way of the outlet recess 20.In either technique, in order to ensure that the connection 30 of the rupturable portion 22 to the outer annular portion 28 of the body 12 is of proper strength i.e. resists tearing or cracking when the rupturable portion 22 is formed into the concave-convex shape, the recesses 18 and 20 are machined or otherwise formed in the body 12 whereby the connection 30 includes smoothly curved portions on both sides of the rup turable portion 22 and the rupturable portion 22 is substantially flat. The curved portion of the connection 30 on the sides 26 and 24 of the rupturable portion 22 corresponds with arcs of circles having radiuses R and R' respectively.

The thickness of the rupturable portion 22, the material from which the apparatus is formed, e.g. stainless steel, carbon steel, inconel, and the fluid pressure utilised to form the concave-convex shape as well as the diameter of the rupturable portion 22 determine the fluid pressure level at which the latter will reverse and rupture.

These variables are adjusted to give the desired results in the manufacture of the apparatus. It is advantageous that the radii R and R' be of specific size to avoid cracking or other stress failure during formation of the rupturable portion 22 and to ensure that the rupturable portion 22 tears away from the outer annular portion 28 of the body 12 after reversal. The radius R is more critical and should be sufficiently large so that during formation into the concave-convex shape, the connection 30 does not become weakened due to the stretching of the material from which the body 12 is formed at the curved portion of the connection 30 within the outlet recess 20.Preferably, the radius R is at least equal to half of the thickness of the rupturable portion 22 prior to forming so that upon forming the connection 30 includes a smooth unbroken transition on its side facing the outlet recess 20 as illustrated in Figure 6. The radius R' must be small as compared to the radius R so that upon reversal of the rupturable portion 22, the stress created in the connection 30 at the radius R' causes the connection to shear and the rupturable portion 22 to tear away from the portion 28 of the body 12. Preferably the radius R' -is as small as the machining process used in forming the inlet recess 18 will allow.

In operation, the apparatus is sealingly positioned in a pressure relief area with the fluid pressure from the vessel or system which is being protected exerted on the convex side 24 of the portion 22. In the form illustrated in Figures 1 to 6, the apparatus can be conveniently clamped between conventional pipe flanges or other similar clamping means. When the fluid pressure exerted on the convex side 24 of the portion 22 exceeds the design rupture pressure, the portion 22 reverses itself as shown in Figure 3 which causes the formation of cracks 31 in the connection 30 on the side thereof facing the inlet recess 18. As a result, the entire portion 22 tears away from the outer annular portion 28 of the body 12 at the connection 30 as illustrated in Figure 4 thereby providing full relief of fluid pressure from the system or vessel being protected.

The configuration of the body 12 can take a variety of forms. As illustrated in Figures 7 and 8, it can include threads 15 on the lower outside surfaces thereof for direct threaded connection to a pipe fitting, and the upper outer portion 17 can be formed into a hexagonal head for facilitating the threading of the body 12 into the pipe fitting. Threads can be provided on the outside surfaces of the body 12 at either end and/or either or both of the recesses 18 and 20.

Further, the position of the rupturable portion 22 within the body 12 can vary as can the diameters of the recesses 18 and 20 to produce different desired results.

For example, as illustrated in Figure 9 the apparatus can be formed with a single recess 18 or 20 whereby the rupturable portion 22 is positioned at either end of the support body 12, or as illustrated in Figures 10 and 11, the inlet and outlet cylindrical recesses 18 and 20 can be of different diameters. In Figure 10, the outlet recess 20 is of a larger diameter than the inlet recess 18, and in Figure 11 the outlet recess 20 is of a smaller diameter than the inlet recess 18.

The forming of the rupturable portion 22 of the body 12 into a concave-convex shape by applying pressure thereto when in the flat state by way of the outlet recess 20 is particularly well suited for producing a large number of substantially identical apparatus. Since, if the apparatus are of substantially the same size, when portions 22 are formed into concave-convex shapes using the same forming pressure, slight variations in the thickness of the repturable portions do not materially affect the pressure level at which the units will rupture.That is, the rupturable portions 22 of units which are slightly thinner than others are formed into concave-convex shapes having greater apex heights which increases the fluid pressure at which the rupturable portions reverse, but those units having thicker rupturable portions are formed into concave-convex shapes of less apex height which reduces the fluid pressure at which the rupturable portions reverse. Further, because the diameter to thickness ratios of the rupturable portions 22 can be closely controlled, the apparatus can be utilised in extremely high pressure applications and can withstand operating pressures at up to 90 percent of the design rupture without premature failure of the rupturable portions 22.

WHAT WE CLAIM IS: 1. A method of forming a safety pressure relief apparatus, having a concaveconvex rupturable member, which comprises making a body of ductile material, forming a recess at at least one of the ends of said body, so that a substantially flat integral relatively thin portion is formed at the inner end of said at least one recess, and deforming said portion by pressure to form a concave-convex rupturable portion.

2. A method according to claim 1, wherein a smoothly curved transition section is formed on each side of said portion where it joins said body.

3. A method according to claim 2, wherein the radius of curvature, prior to deformation, on the concave side is at least half the thickness of said portion.

4. A method according to claim 1, 2 or 3, wherein the pressure applied is fluid pressure.

5. A safety pressure relief apparatus made by the method of claim 1 and comprising a body formed of ductile material and having opposite ends, a recess extending inwardly from at least one of said opposite ends, the internal end of said at least one recess being formed by an integral relatively thin rupturable portion and said portion having a concaveconvex shape formed by applying pressure thereto when it is in a substantially flat state.

6. Apparatus according to claim 5, wherein the or each recess is cylindrical in shape..

7. Apparatus according to claim 6, wherein the or each recess is positioned coaxially within said body.

8. Apparatus according to claim 5, 6 or 7, wherein a recess is formed adjacent each end.

9. Apparatus according to claim 8, wherein the recesses have different diameters.

10. Apparatus according to claim 8 or 9, wherein the rupturable portion is positioned nearer the one end than the other.

11. Apparatus according to any one of claims 5 to 10, wherein the body is provided with a screwthread on its external surface.

12. Apparatus according to any one of claims 5 to 11, wherein said rupturable portion is connected to the body by an annular connection disposed in a plane perpendicular to the axis of the body.

13. Apparatus according to claim 12, wherein said annular connection includes smoothly curved surfaces, on each side of said rupturable portion, when said portion is in the flat state, at the junction with the body.

14. Apparatus according to claim 13, wherein the smoothly curved surface on the side of the rupturable portion which is concave has a radius when said portion is flat, at least equal to half the thickness of said portion.

15. Safety pressure relief apparatus substantially as hereinbefore described reference to and as illustrated in Figures 1 to 6 of the accompanying drawings.

16. Safety pressure relief apparatus substantially as hereinbefore described with reference to and as illustrated in Figures 7 and 8 of the accompanying drawings.

17. Safety pressure relief apparatus substantially as hereinbefore described with reference to and as illustrated in Figures 9 and 10 of the accompanying drawings.

18. Safety pressure relief apparatus substantially as hereinbefore described with reference to and as illustrated in Figure 11 of the accompanying drawings.

19. A method of forming safety relief apparatus according to claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reverse. Further, because the diameter to thickness ratios of the rupturable portions 22 can be closely controlled, the apparatus can be utilised in extremely high pressure applications and can withstand operating pressures at up to 90 percent of the design rupture without premature failure of the rupturable portions 22. WHAT WE CLAIM IS:

1. A method of forming a safety pressure relief apparatus, having a concaveconvex rupturable member, which comprises making a body of ductile material, forming a recess at at least one of the ends of said body, so that a substantially flat integral relatively thin portion is formed at the inner end of said at least one recess, and deforming said portion by pressure to form a concave-convex rupturable portion.