Reverse buckling rupture disk apparatus and manufacturing methods

A reverse buckling rupture disk apparatus, adapted to be clamped between inlet and outlet companion bolted flanges, the operation of which is unaffected by the torque applied to the bolts of the companion flanges. The apparatus is comprised of a reverse buckling rupture disk which is welded at its periphery to an annular support ring. The annular support ring is in turn welded to an annular support member. Methods of manufacturing the apparatus are also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to reverse buckling rupture disk 
apparatus, and more particularly, but not by way of limitation, to 
improved reverse buckling rupture disk apparatus adapted to be clamped 
between campanion bolted flanges and methods of manufacturing such 
apparatus. 
2. Description of the Prior Art 
Reverse buckling rupture disk apparatus have been developed and utilized 
heretofore. Such apparatus generally include a reverse buckling rupture 
disk having a concave-convex portion connected to an annular flange 
portion by a transition connection. In most of the prior apparatus, the 
annular flange portion of the rupture disk is clamped between inlet and 
outlet support members which are in turn adapted to be clamped between 
companion bolted flanges. Knife means for severing the rupture disk upon 
the reversal thereof are attached to the outlet support member or 
otherwise held in the apparatus. Various other arrangements have also been 
developed and used whereby one or both of the support members are omitted 
and/or other structure is substituted therefor. 
In all of such prior apparatus wherein the annular flange portion of the 
reverse buckling rupture disk is clamped between companion bolted flanges 
with or without support members or other structure therebetween whereby 
the clamping pressure of the flanges is transmitted to the flange portion 
of the rupture disk, the operation of the rupture disk is adversely 
affected by changes or differences in the torque applied to the flange 
bolts. That is, changes or differences in the clamping pressure exerted on 
the rupture disk produce changes in stresses in the disk, particularly in 
the area of the transition connection, whereby the fluid pressure required 
to cause the disk to reverse and rupture is altered. Thus, when such a 
reverse buckling rupture disk apparatus is claimed between companion 
flanges, if too much or too little torque is applied to the flange bolts, 
the fluid pressure level at which the rupture disk fails can be changed 
appreciably from the predetermined design rupture fluid pressure level. 
This, in turn, can result in premature failure of the rupture disk or the 
existence of an overpressure condition in the vessel or system being 
protected without failure of the rupture disk. 
In order to overcome or reduce changes in rupture pressure due to 
overtorquing or undertorquing the flange bolts, such reverse buckling 
rupture disk apparatus have been preassembled at the factory whereby the 
proper torque is applied to the rupture disk. In cases where the apparatus 
cannot be preassembled, precise instructions relating to the proper amount 
of torque to be applied to the flange bolts have been furnished to users 
of the apparatus. While these procedures have been effective to some 
extent, once a reverse buckling rupture disk apparatus has been installed, 
the disk cannot be removed for inspection purposes and reinstalled without 
inducing new stresses in the disk which alter its operational 
characteristics. Consequently, it has been the practice in the industry 
that once a reverse buckling rupture disk has been clamped between support 
members and/or flanges and removed, it is discarded and replaced. 
By the present invention an improved reverse buckling rupture disk 
apparatus is provided which is adapted to be clamped between companion 
bolted flanges, the operation of which is unaffected by changes or 
differences in the torque applied to the flange bolts. 
SUMMARY OF THE INVENTION 
A reverse buckling rupture disk apparatus comprising a reverse buckling 
rupture disk having a concave-convex portion connected to an annular 
flange portion by a transition connection, an annular support ring 
positioned adjacent the annular flange portion of the rupture disk on the 
convex side thereof welded to the annular flange portion and an annular 
support member adapted to be clamped between companion bolted flanges 
positioned adjacent to concave side of the rupture disk and welded to the 
support ring. Methods of manufacturing the apparatus are also provided. 
It is, therefore, a general object of the present invention to provide an 
improved reverse buckling rupture disk apparatus and methods of 
manufacturing the same. 
A further object of the present invention is the provision of a reverse 
buckling rupture disk apparatus adapted to be clamped between companion 
bolted flanges, the operation of which is unaffected by the torque applied 
to the flange bolts. 
Yet a further object of the present invention is the provision of methods 
of manufacturing a reverse buckling rupture disk apparatus adapted to be 
clamped between companion bolted flanges which is unaffected by the torque 
applied to the bolts of the flanges. 
Another object of the present invention is the provision of reverse 
buckling rupture disk apparatus which can be installed between companion 
bolted flanges, removed, inspected, and reinstalled between such flanges 
without the operational characteristics of the apparatus being affected. 
Other and further objects, features and advantages of the present invention 
will be readily apparent to those skilled in the art upon a reading of the 
description of preferred embodiments which follows when taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings and particularly to FIGS. 1-3, the apparatus 
of the present invention, generally designated by the numeral 10, is 
illustrated clamped between inlet and outlet companion bolted flanges 12 
and 14, respectively. The apparatus 10 and the flanges 12 and 14 are 
clamped together by means of the usual plurality of bolts or studs and 
nuts 16. A pair of gaskets 18 and 20 are disposed between the apparatus 10 
and the flanges 12 and 14 for providing sealing engagement therebetween. 
The apparatus 10 is comprised of a reverse buckling rupture disk 22 having 
a concave-convex portion 24 connected to an annular flange portion 26 by a 
transition connection 28. An annular support ring 30 having a width 
corresponding to the width of the annular flange portion 26 of the rupture 
disk 22 and an outer diameter equal to the outer diameter of the rupture 
disk 22 is positioned adjacent the annular flange portion 26 on the convex 
side of the rupture disk 22. As will be described in further detail 
herein, the rupture disk 22 is welded to the support ring 30 at the 
periphery of the rupture disk 22. A support member 32 is provided which is 
adapted to be clamped between the inlet flange 12 and outlet flange 14. 
That is, the support member 32 has an outer diameter substantially equal 
to the outer diameter of the flanges 12 and 14 and includes openings 
around the periphery thereof for passage of the bolts or studs and nuts 16 
therethough. As will be understood, seating surfaces are provided on 
opposite sides of the support member 32 for engaging the seating surfaces 
of the companion flanges 12 and 14 and the gaskets 18 and 20 positioned 
between the flanges and the support member. The internal diameter of the 
annular support member 32 is smaller than the internal diameters of the 
flanges 12 and 14 so that a portion of the annular support member 32 
extends inwardly within the flanges 12 and 14. The inwardly extending 
portion of the support member 32 provides an annular surface 34 within the 
interior of the flanges 12 and 14. Projecting from the surface 34 of the 
support member 32 and extending longitudinally into the interior of the 
flange 12 is an annulet 36. The annulet 36 is preferably integrally formed 
as a part of the support member 32. 
The rupture disk 22 and support ring 30 welded thereto have substantially 
equal outside diameters which are slightly less than the inside diameter 
of the annulet 36. The rupture disk 22 and support ring 30 are positioned 
adjacent the surface 34 of the support member 32 interiorly of the annulet 
36 and the support ring 30 is welded to the annulet 36. 
As shown in the drawings, knife means generally designated by the numeral 
38 can optionally be welded to or otherwise attached within the support 
member 32 whereby the knife means 38 are positioned so that the 
concave-convex portion 24 of the rupture disk 22 is severed by the knife 
means 38 upon reversal. In a preferred form, the knife means 38 includes 
four sharpened blade legs 40 positioned at right angles to each other with 
the internal ends connected together and the external ends welded to the 
interior of the support member 32. In this configuration, when the 
concave-convex portion 24 of the rupture disk 22 reverses itself and 
contacts the knife blade means 38, the convcave-convex portion 24 is 
severed into four petals. However, as is well understood, other 
configurations of blade legs and other forms of knife means can be 
utilized in the apparatus 10 and rather than being attached to the support 
member 32 the knife blade means can be independently clamped within and/or 
between the flanges 12 and 14. 
Referring now specifically to FIG. 4, an enlarged portion of the apparatus 
10 is illustrated. As shown in FIG. 4, the annular flange portion 26 of 
the rupture disk 24 is preferably welded to the annular support ring 30 at 
the periphery of the annular flange portion 26 by a continuous weld 42. 
The weld 42 is preferably formed using a low heat welding technique 
whereby a minimum of stresses are set up in the annular flange portion 26 
of the rupture disk 22, the particularly, so that no stresses are formed 
in the area of the transition connection 28. As is well understood, in the 
failure of a reverse buckling rupture disk, the reversal of the disk 
begins at the transition connection, and therefore, as long as stresses 
are not produced in the rupture disk at the transition connection area 
thereof during the welding process, the fluid pressure level at which the 
reversal process takes place is unaffected. As is also shown in FIG. 4, 
the support ring 30 is preferably welded to the annulet 36 of the support 
member 32 at the top outside portion of the support ring 30 so that heat 
and stresses from the welding operation are not transmitted to the rupture 
disk 22. Preferably, the support ring 30 is continuously welded to the 
annulet 36 of the support member 32 by a continuous weld 44. 
A preferred technique for forming the welds 42 and 44 in the apparatus 10 
is a technique known as electron beam welding. Electron beam welding 
produces low heat and minimum stresses in the welded parts and 
consequently can be achieved without setting up stresses in the rupture 
disk 22 which affect the operation thereof. However, any low heat welding 
technique can be utilized. 
In manufacturing the apparatus 10, the rupture disk 22 can be preformed 
whereby it includes the concave-convex portion 24 connected to the annular 
flange portion 26 by the transition connection 28 prior to welding it to 
the support ring 30 and prior to welding the support ring 30 to the 
annulet 36 of the support member 32. Preferably, however, the rupture disk 
22, in a flat state prior to having the concave-convex portion 24 formed 
therein, is welded to the support ring 30 followed by the welding of the 
support ring 30 to the annulet 36 of the support member 32. After the 
completion of the welding, fluid under pressure such as compressed air is 
caused to flow by way of the internal portion of the support member 32 
into contact with the flat rupture disk 22. The air pressure is increased 
to a level whereby the concave-convex portion 24 is formed at a desired 
crown height, etc. This latter manufacturing technique whereby the 
concave-convex portion 24 is formed in the rupture disk 22 after welding 
insures that any stresses which may have been formed in the rupture disk 
22 by the welding process are relieved. 
In operation of the apparatus 10 when clamped between companion inlet and 
outlet bolted flanges as illustrated in FIG. 1, pressurized fluid from the 
vessel or system being protected (to which the inlet flange 12 is 
sealingly connected) is exerted on the convex side of the concave-convex 
portion 24 of the rupture disk 22. When the fluid pressure level within 
the vessel or system and exerted on the rupture disk 22 reaches or exceeds 
the predetermined design rupture pressure of the rupture disk 22, the 
rupture disk 22 reverses itself and is severed by the knife means 38 
whereby the pressurized fluid is relieved through the apparatus 10 into 
the outlet flange 14. The outlet flange 14 is normally connected to a 
conduit which leads the relieved fluid to the atmosphere or to another 
system or vessel for containing such fluids. 
Because the rupture disk 22 is welded to the support member 32 and is not 
clamped between the support member 32 and the inlet flange 12, the 
operation of the rupture disk 22 is independent and unaffected by the 
clamping pressure exerted on the flanges 12 and 14 and the support member 
32. This in turn allows the apparatus 10 to be installed between companion 
bolted flanges and the flange bolts to be torqued indiscriminately without 
affecting the operation of the apparatus 10. In addition, the apparatus 10 
can be removed and inspected and then reinstalled many times without 
affecting its operation. 
In order to facilitate a clear understanding of the methods and apparatus 
of the present invention, the following example is given. 
EXAMPLE 
A steel annular support ring having an external diameter of 31.5 inches, an 
internal diameter of 30 inches and a thickness of 0.5 inches is welded to 
a 0.050 inch thick flat metal disk having a diameter of 31.3 inches. The 
weld is a continuous weld located at the periphery of the disk and is 
accomplished using a conventional low heat electron beam welding 
apparatus. The disk with support ring welded thereto is positioned on an 
annular support member within the area defined by an integral annulet 
formed thereon. The support member has an external diameter of 37.8 
inches, an internal diameter of 30 inches and a thickness of 1.4 inches. 
The support member includes 40 equally spaced 1.2 inch bolt holes on a 
bolt circle diameter of 35.6 inches and the integral annulet is 1.38 
inches high, 4 inches thick and has an internal diameter of 29.5 inches. 
The support ring is welded to the annulet of the support member by a 
continuous weld located at the top of the annulet using a conventional low 
heat electron beam welding apparatus. 
After the welding operations are completed, compressed air at a pressure 
level of 435 psig is applied to the disk by way of the internal portion of 
the support member whereby the central portion of the disk is formed into 
a concave-convex shape having a crown height (distance from the base to 
the highest point of the concave-convex portion) of 6.9 inches. A knife 
means having four blade legs welded together at right angles is welded 
onto the support member. 
The resulting reverse buckling rupture disk apparatus has a design rupture 
pressure (fluid pressure level at which reversal occurs) of 68.6 psig+3% 
and can be clamped between conventional 30 inch, 150 psig ASA bolted 
flanges without being affected by the torque applied to the flange bolts. 
The conventional low heat electron beam apparatus is comprised of a Vickers 
10 KV Welder including an electron beam gun and focusing lens, a 
3.25'.times.3.25'.times.4.92' vacuum chamber including a rotary table and 
fixturing and a control panel for set welding the parameters of the 
various welds. 
The welding of the disk to support ring is accomplished by locating the 
disk and support ring, in special fixturing which is mounted on the rotary 
table. The rotary table is then placed on tracks which guide it into the 
vacuum chamber. When the rotary table is in close proximity to the 
electron gun, the chamber is evacuated down to 10.sup.-3 torr. Accurate 
positioning of the disk and support ring under the electron gun is 
achieved by horizontal movement of the rotary table in mutually 
perpendicular directions while being viewed under the application of a 
very low powered Electron Beam Weld. This technique ensures that the beam 
tracks the disk to support ring joint along the entire circumference. Once 
optimum positioning has been achieved several Electron Beam tacks are 
applied. With the beam tracking the circular joint accurately, the main 
weld is performed in one continuous run and a slight overlap is permitted 
at the end of the run to ensure the integrity of the joint. 
The welding parameters for the disk-support ring weld are as follows: 
1. Accelerating Voltage--125 KV+5 KV. 
2. Electron Beam Current--13 mA+1 mA 
3. Distance between workpiece and gun--292 mm+3 mm. 
4. Welding travel speed--23+2 mm/sec. (With beam spin to obtain suitable 
spot shape). 
5. Welding vacuum (minimum)--10.sup.-3 Torr with beam 
6. Focusing Current--879 mA+5 mA. 
7. Penetration--The weld penetration needs to be of the order or 
0.080"-120" for consistent results. 
The welding of the support ring with disk welded thereto to the support 
member is accomplished in the same manner as described above with the 
exception that the assembly is positioned in the chamber at 20.degree. to 
horizontal due to the geometric constraints of the vacuum chamber. 
The welding parameters for the support ring to support member are as 
follows: 
1. Accelerating Voltage--140 KV+5 KV 
2. Electron Beam Current--25 mA+2 mA 
3. Distance between workpiece and gun--276 mm+4 mm 
4. Welding travel speed--23.28 mm per second (With beam spin to obtain 
suitable spot shape). 
5. Welding Vacuum--10.sup.-3 Torr with beam 
6. Focusing current--929 mA+5 mA. 
7. Penetration--In order to provide rigidity the penetration of the second 
weld needs to lie between 0.2 in. and 0.24 in. 
In welding the support ring to the support member, if the gap between the 
support ring and the integral annulet of the support member exceed 0.3 mm, 
a slight depression in the head of the weld will occur. A cosmetic weld is 
therfore permitted, which entails using a low power beam to remelt the 
surface of the weld and give it a more uniform finish. 
The welding parameters for the cosmetic weld are as follows: 
1. Accelerating Voltage--110 KV+5 KV 
2. Electron beam current--10 mA+1 mA 
3. Distance between workpiece and gun--276 mm+4 mm 
4. Welding travel speed--23.28 mm/sec 
5. Welding Vacuum--10.sup.-3 Torr 
6. Focusing current--788 mA+5 mmA. 
Thus, the present invention is well adapted to carry out the objects and 
attain the ends and advantages mentioned as well as those inherent 
therein. While the particular arrangement of parts, location of welds and 
configuration of the apparatus 10 shown in the drawings and described 
above is preferred, numerous changes can be made in such arrangement of 
parts and construction details which will suggest themselves to those 
skilled in the art and which are included within the spirit of this 
invention as defined by the appended claims.