Note: Descriptions are shown in the official language in which they were submitted.
s~i~
SAFET~ PRESSURE RELIEF DEVICE
AND METHOD FOR MAKING THE SAME
BACKGROUND OF THE INVENTION
_. Field of the Invention
This invention relates generally to safety pressure relief
devices and more particularly, but not by way of limitation, to a
safety pressure relief device designed for positive rupture in one
direction at a pre-determined pressure differential to protect a
pressure vessel. The invention also relates to methods for making
such safety pressure relief devices.
2. Description of the Prior Art
A variety of safety pressure relief devices of the rupture
disk type have been developed. Generally, these devices includ a
rupture disk supported between a pair of complementary supporting
members or flanges which are in turn connected to a relief connec-
1~ tion in a vessel or system containin~ fluid pressure.
Safety pressure relief devices of the rupture disk type areoften used in environments having elevated temperatures, alter-
nating 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 diferentials thus stressing the disk and ultimately
leading to disk rupture at a pressure differential other than that
for which the dislc was designed. ~s used herein, the term
"positive pressure" refers to a condition in which pressure in the
..
:
" :
,, . ~ - . . ~ .
-', , ' . . ' ~ :'
65fir,;
vessel is greater than pressure on the other side of the safety
pressure relief device while the term "reverse pressure" refers to
a condition in which the vessel pressure is less than the pressure
on the other side of the presure relief device.
In order to stablize the rupture disk against fluctuating in
response to alternating internal and external pressure differen-
tials, a vacuum support is clamped between the complementary
flanges which contain the rupture disk with the vacuum support
being positioned internally of the rupture disk. ~n some
constructions, a sealing member is interposed between the vacuum
support and the rupture disk. Thus, the vacuum support prevents
fluctuation of the rupture disk or seal when a vacuum occurs in
the pressure vessel in which the safety pressure relief device is
installed. Examples of such supports are shown in U.S. Patents
No. 2,523,068 to Simpson et al. and No. 2,953,279 to Coffman.
A problem occurs with such prior art vacuum supports. In
many applications, the vacuum support must be thick enough to sup-
port the rupture disk or seal in the presence 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
pressure, the vacuum support may be so thick that ~ull opening of
the assembly at the pre-determined positive pressure is prevented
thus restricting flow.
. .
. . . . .
~3~
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 main-
tain the structural integrity of the vacuum support in the pre
sence of reverse pressure while 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 sup-
ports of varying thicknesses dependent upon the level of reverse
pressure the vacuum support must withstand. Moreover, some design
parameters are not achieveable using prior art vacuum supports.
In other words, when it is desired to have the vacuu~ support
withstand a very high reverse pressure while opening in the pre-
sence of a very low positive pressure, the vacuum support may be
so thick that rupture of the disk at the positive pressure may not
occur.
In addition to the foregoing problems, the lugs which are
spot welded onto the prior art vacuum supports constitute surface
irregularities upon which process 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 o the safety pressure relie~ device.
36~
sy the present invention, a safety pressure relief device of
the rupture disk type is provided which includes a vacuum support
which is simply and easily constructed, which opens completely and
positively at low rupture disk pressures while supporting the rup-
ture disk in the presence of a high reverse pressure, which is
useable with rupture disks havinq a wide range of reverse pressure
and rupture pressure ratings, and which opens positively and
completely without fragmenting when internal vessel pressure
exceeds rupture disk opening pressure.
S~M~ARY OF THE INVENTION
The present invention relates to a vacuum support for use
with a safety pressure relief rupture member. The vacuum support
comprises a disk having a generally convex upper side and a
generally concave lower side and a slit formed therethrough. An
upper disk edge defines a generally upper side of the slit and a
lower disk edge defines a generally lower side of the slit. The
slit edges are pressed together with the lower disk edge sup-
porting that portion of the disk generally above the slit respon-
sive to downward force applied to the disk.
Another aspect of the invention comprises a method for making
a vacuum support for use in a safety pressure relief device of the
rupturable type. The method includes the steps of forming a disk
having a conve~ upper side and a concave lower side. Thereafter a
; slit is formed through the disk which dlvides the same into
generally lower and upper portions. The slit is narrow enough
.
relative to the disk thickness to close and prevent the upper por-
tion from collapsing downwardly into the lower portion responsive
to downward pressure applied to the upper portion.
It is, therefore, an object of the present invention to pro-
vide an improved safety pressure relief device of the rupturabletype.
It is a further object of the present invention to provide
such a safety pressure relief device in which the rupture disk is
supported in the presence of high reverse pressure and which opens
positively and completely at a pre-deter~ined positive low
pressure.
It is another object of the present invention to provide such
a safety pressure relief device which includes a vacuum support
that is useable over a wide range of rupture disk reverse pressure
and positive pressure ratings.
It is yet another object of the present invention to provide
such a safety pressure relief device which is easily constructed
and which incorporates fewer parts than those in the prior art.
It is still another object oE the invention to provide such a
safety pressure relief device having a vacuum support whlch is
formed of thinner material than those in the prior art.
It is another object of the invention to provide such a
safety pressure relief device which opens positively and comple-
~ tely at a pre-determined positive press~re and which does not
fragment upon opening.
~'
'':
'
.
56~
_IEF DESCRIPTION OE THE DRAwINGS
Figure 1 is a partially sectioned perspective view of a
safety pressure relief device constructed in accordance with the
instant invention with portions thereof broken away.
Eigure 2 is an exploded perspective view of the 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 of the
saety pressure relief device of Figure 1.
Figure S is a view 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 ~ i5 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 constructed in accordance with the instant inven-
tion.
Figure 10 is an enlarged view of a portion of Figure 9.
DETAILED DESCRIPTION OF THE PREEERRED EMBODIME~TS OF THE INVENTION
Indicated generally at 10 is structure incorporating a safety
pressure relief device constructed in accordance with the instant
invention. A base flange 12 is threaded or otherwise su:itabl~
connected to a pipe or tubular member 14 which servex as the
~ ~ . . . .
i`5
relieving outlet for a pressure vessel to be protected.
Indicated generally at 16 is a safety pressure relief device
constructed in accordance with the instant invention. Device 16
includes a vacuum support 18, a sealing member 20, and a rupture
member or disk 22. Device 16 is installed between base flange 12
and a hold-down flange 24. The hold-down flange is generally pro-
vided 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 bolted together via bolts, like bolt
28, as shown. Safety pressure relief device 16 serves as a gasket
between flanges 12, 24 to provide a sealed connection for the
pressure vessel.
Turning attention now to Figure 2, rupture disk 22 includes
an upper convex side 30 and a lower concave side (not visible in
Figure 2). Rupture member 22 includes an anchoring flange 32,
such also being viewable in Figure 7. A plurality of slots, like
slot 34, extend radially outwardly from a solid central portion
36. A hole, like hole 3~ is drilled or punched at the upper end
of each of the slots, like slot 34, to prevent stress con-
centrations at the upper slot ends.
Rupture disk 22 is constructed to positively burst when the
pxessure in tubular member 14 exceeds the pressure on the other
side oE the pressure relief device by a pre-determined amount.
The pre-determined pressure at which such bursting occurs for any
~5 diameter o~ the safety pressure relie~ device may be selected by
-7-
. . . . : , . :, ~.
', .. '
varying metal thickness, tensil strength of the metal being con-
sidered, and varying the length of the slots, like slot 34. For
example, the longer the slots, the closer their proximity at
central portion 36 of rupture disk 22 and 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 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 selection of a material as
; a sealing member should be made individually for each installation
with caution taken to assure ~he protection of rupture disk 22
from corrosion. It should be appreciated that it is known to com-
bine sealing member 20 and rupture disk 22 into a single rupture
disk which also seals to prevent leakage.
Vacuum support 18 is shown in more detail in Figures 4-6 and
attention is directed thereto for a description of the vacuum sup-
port structure. Vacuum support 18 includes a circular disk 39having a generally convex upper.side 40 and a generally concave
lower side 42. A substantially horizontal (as viewed in Figure 5)
; slit 44 is formed through vacuum support 18 and defines an arc
centered about an axis designated by dot-dash line 46. One end of
slit 44 terminates in a hole 45 to relieve stress concentrations.
.
'''.' ' '' '' '
~65~;~
Axis 46 also comprises the central axis for disk 39. Slit 44
divides disk 39 into an upper disk portion 48 and a lower disk
portion 50.
~n anchoring flange 52 is formed about the radially outer
circumference of disk 39 and provides a means for anchoring device
16 between flanges 12, 24 when vacuum support 18, sealing member
20, and rupture disk 22 are nested together as shown in Figures 1
and 7. A flat arcuate portion 54 comprises the radially outermost
edge o disk 39 and assists in anchoring the vacuum support bet- :
ween flanges 12, 24.
~lit 44 is defined by an upper edge 56 and a lower edge 5~,
such being referred to herein as an upper disk edge and a lower
disk edge, respectively. The disk edges are substantially
parallel to one another and in the instant embodiment of the
invention each defines an angle of substantially 60 with respect
to axis 46. A second axis 60 is shown in Figure 6, such being
normal to axis 46 and parallel with arcuate portion 54. A third
axis 62 is parallel to disk edges 56, 58. Thus, in the instant
embodiment of the invention, the angle between axes 60, 62,
designated by arc 64 (hereinafter angle 64) is substantially 30.
It has been found that the safe~y pressure relief device of the
invention will successfully operate, as will hereinafter be
described in more detail, when disk edges 56, 5~ ar~ oriented so
that angle 64 is within the range of 0-45.
A second slit 66 is forlned through disk 39 and is symmetrical
_g_
' ' ' ' ' ' '
r;~E;tl~
with respect with slit 44. Like sli~ 44, slit 66 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, like edges 56, 58, which are parallel to one another and
which, like edges 56, 58, form an angle of substantially 60 with
respect to axis 46. Each of slits 44, 68 have one end which ter-
minates 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 and that portion of the
10 disk between ends 70, 72 is referred to herein as a vacuum support
positioning portion. The vacuum support positioning portio~ main-
tains upper portion 48 in alignment with lower portion S0 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 rup~
ture disk 22 are assembled between flanges 12, 24 as previously
described and as shown in Figures 1 and 7. The pressure on the
vessel to be protected operates on the concave side of sealing
member 20 through slits 44, 46 and holes 45, 68 in vacuum support
20 18. When properly assembled, sealing member 20 nests in the con-
cave side of rupture disk 22 so..that pressure .transmitted to
sealing member 20 is exerted by the sealing member against the
concave side o~ rupture disk 22.
When pressure in tubular member :L4 falls below the pressure
on the convex side oE rupture disk 22, vacuum support 18 prevents
--10--
.~ .
:: '
~2~
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 ~4 against lower edge 58 and likewise pressing the
upper and lower edges of slit 66 together so that the vacuum sup-
port 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 Fiyure 3 even in the presence of very hi~h
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 for one set o~ 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 as shown in Figure 8. As can be seen, the
material between slit ends 70, 72 breaks thus permitting the
' vacuum support to hinge open as shown in Figure 8.
Vacuum support 18 may be designed to assure that it will
wlthstand a reverse pressure dif~erential of a selected amount
:`
'
,
~6S6~
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., for slit 44, 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 width, i.e., the distance
between holes 45, 68.
It is to be appreciated that the slit width will vary depen-
dent 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.
It can be seen that the structure of the vacuum support of
- the invention is able to withstand high reverse pressures because
of the manner in which the slit closes with lower disk portion 5Q
supporting upper disk portion 48 as shown in Figure 3. This
improved vacuum support structure withstands higher reverse
pressures than previous vacuum supports and can be formed from
thinner material than previous vacuum supports. Thus, the vacuum
support of the invention withstands very high reverse pressures
while at the same time, because of the thin material from which
the vacuum support disk is made, opens positively and completely
at low positive pressures. Thus, unlike prior art vacuum sup-
.
-12-
.
:
".:
~`
~f~
ports, for a given rupture dis~ 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.
Indicated generally at 74 in Figures 9 and 10 is a second
embodiment of a vacuum support constructed in accordance with
the instant invention. Vacuum support 74 includes a pair of sym-
metrical 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 flange 78
which is used to mount the vacuum support in a type of ~ounting
flange different from flanges 12, 24 in Figure 1. Otherwise,
vacuum support 74 functions in the same manner (with an associated
rupture disk and seal, each of which have planar ~langes similar
to flange 78) as the embodiment of Figure 1. It is to be appre-
ciated that means other than those disclosed herein for mounting avacuum support constructed in accordance with the instant inven-
tion may be utilized without departing the scope of the invention.
Turning now to Figure 6, included therein is a laser 80.
~hen 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 a~, an angle dependent upon the
orientation of laser 80. ~aser 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
-13-
'
.
~l~f3~SG~
constructed includes fewer parts than vacuum supports of the prior
art which typically have luqs spot welded thereto adjacent cuts
which are formed through disk 39 in order to withstand reverse
pressure to a preselected amount.
It is to be appreciated that additions and modifications may
be made to the embodiments disclosed herein without departing from
the spirit of the invention which is defined in the following
claims.
-14-
.
. , , ~, . .
.
