CA1064415A - Pressure release device - Google Patents

Abstract

Abstract of the Disclosure Pressure release means for pressurized containers and particularly electrochemical cell containers subject to pressure eruption conditions in which the pressure release mean-is an integral part of the container wall. This means is actu-ated at predetermined abnormal pressure at which a relatively rigid and undeformed wall area between two deformed portions of the container wall tears to form a vent. This vent can he adapted to provide either slow or rapid pressure release.

Description

; ~06~4~5 This invention relates to pressure release devices for containers and especially to electrochemical cells which are subject to undesirable increases of internal pressure.
Prior art pressure release devices include safety valves, rupture membranes, shearing plugs, sharp points which are forced through sheets and the like. A problem with all these devices is that their inherent properties make it diffi-cult to combine the characteristics of low cost, precision in venting at a specific pressure, adequate sealing for the pres-surized container and a degree of strength against accidental triggering by mechanical abuse or malfunction. For example, a safety valve, which is made to open when the force on the valve exceeds that of a spring, is adequately precise with respect to venting at a specific pressure. However, this is offset by the , : :
costly requirement for added parts, which are susceptible to ~; mechanical accidents, and precise fit for hermeticity which can lead to increased cost. Additionally, such devices rely upon the stability of a seal for hermetic closure and corrosive sùb-r stances within a container could render this seal ineffective.
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~ RupturabLe membrane!J consist of a wea]cenec~ portion of . .
a vessel or contailler wall which provides hermctic closure until tl~e contained prcssurF is sufficient to tear the mem~rcine.
Though it is less compllcated in terms of material than the safety valve, its curvature, thickness and material condition require close control because the pressure at whic~ the membrane tears ..
is deterMined Dot by the stable elastic properties of the memorane `out by its ultimate plastic-deformation behavior which is dependent upon composition and the mechanical and thermal history of the material. Thus whi.le the seal is adequate the cost of precision in the release pressure becomes high. Any ; cost saving realized by requiring less precision in venting pressure is offset by the need for additional strength and weight of the vessel or container to accommodate hiyher pressures.
Additionally, for small openings the membrane m~st be so thin that protection Erom puncture and corrosion would also bécome necessary, thus further increasing the cost. Simple grooves in the wall of con:tainers such as have been used in capacitors have the additional deficiencies of lengthy tear propayations and the absence of vent closure after the excess pressure has been released unless an expensive spring container is used. These deficiencies can be especially detrimental if caustic materials ai-e contained in the container.
Other methods for venting such as shearing the periphery of a plug, or the forcing of a sharp tool through a sheet, remain imprecise to the extent that the venting pressure depends on the varying physicaL characteristics of the material used in actuatincJ the venting process. Additionally, shearing - plugs depend on adding materials of low shear strencJth to the wall and these materials Inust be selected to be compatible with the container contents.

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It is ~:herefore an ol~jec~ of the prc.sen~ lnvention to provide a ~LesSul-e release device which inteyra~es the ~atures of low cost, good precision in venting and an hermetic seal ~cr . pressurized vessels or containers.
It is another object to provide a pressure release device W21ic]l is an integral part of the containeL^ wall and which requires no additional ioreigl~ material.
Another object is to provide a pressure release device which can be formed to vent at a predeteLmined slow or rapid rate.
It is still another object to provide a pressure release device which will s~bstan~ially close af~ter venting to inhibit ~urthe`r egress of container materials or the ingress of foreign matter.
` - Another object is to provide a low cost pressure ; release device ~ihich c~an be formed by die pressiny.
Another cbject is to provide a pressure release device which is based upon the predictable behavior of à bending strain `rather thall a tensile strain.
It is another object to provide a method for pressure ~... . . .
"- venting which is low cost, preclse within acceptable limits, and ~equires no materials other than the walls of a container - . .
to be vented.

It-is yet another object to incorporate all of the above features in a r~ressuriza~ container or vessel.

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Another object is to incorporate all of the above features in an electrochemical cell which because of its con-tents is either in a pressurized state or subject to a high degree of pressure buildup.
According to a broad aspect of the present invention, there is provided a pressure release device comprising channel means having one or more interruptions therein whereby under conditions of increasing pressure the channel means unfolds and ;
simultaneously therewith at least one of the interruptions is stretched to rupture thereby ~orming a vent for release of the pressure.
These and other objects, features and advantages will become more evident from the detailed description below as well as from the drawings, in which~
Figure 1 is a plan view of the end wall of a container embodying the pressure release device of the invention.

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Figure 2 is a perspective view of Figure 1 with a portion, taken along line 2-2 of Figure 1, shown in section.
This figure shows a specific embodiment of the container of the invention wherein it is used for an electrochemical cell.
;~ Figure 3a is an enlarged sectional view taken along line 3a-3a of Figure 1.
Figure 3b is an enlarged sectional view similar to 3a of another embodiment of the invention in which there is provided an additional reinforcing sectionO
Figure 4 shows the portion of the container where venting takes place. In this figure another embodiment of the invention is shown, namely one in which the shape of the vent-ing area differs from that shown in Fig. 1.
- 30 Figure 5 is a perspective view of another embodiment of the invention wherein the pressure release device is incor-porated into a side wall of the container.
_~_ 64g~15 Figure 6 is a perspective view of another embodiment of a container made in accordance with the invention.
Figure 7 is a graph showing the general relationship ;~ between displacement of the disc in the embodiment :hown in Fig. 1 " ' ~

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- ~ ~064415 ,,arid,venting pressui-e.

~ The pl-esent invention envisions a pressure release .

: device integratecl into a container or vessel wall in which a , stress caused by pressure is concentrated and direc~ed at ~
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: preselected portion of the contai.ner wall causing this preselected portion to tear under an undesirable increase of pressure thereby forming a vent for release of the pressure.
- The.concentration of stress is obtained because the normal contour of a container wall llas been a].tered to provide two ,~ 10 deformed and more extensible.sections between WhlCIl is a small undeformed or less deformed and relat-ively inextensible section ., ~ . .
of wall. This undeformed section is adapted to rupture when : - .
.: , the pre,ssure level within the container reaches ,a predetermined level. As the.internal pressure increases either the end or side walls of the container are forced outwardly and the deformed sections of the container wall will tend to unfold :
~: while undergoing relatively slight bending strain. However, .
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thls unfoLding can be achieved only with stretching of the , .
~ ; unde.form~ section of wall that is between tlle two deformed .
portions thereof. This section, referred to herein as a ~,: "bridge", "bridging" or "bridging area", cannot extend in the , ~ ~ , . . .
~ same way as the deformed portions and therefore is subjected to .~. ~ . . . .
~ , . high tens.ile stress which leads ineluctably to the tearing or, . . ;
rupturing of the bridging area thereby forming a vent. The .: .
~ :. deformations will advantageously be elongated and in the form .:of channels arranged so that an end of one is aligned with an . . .
.~ - end of another with a bridge therebetween. The container , .~ . material can be of metal such as steeL or nickel-plated steel or of plastlcs or rubber which can contain pressurizcd contents : 30 and have:predictable movement under stress.
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. Th.e cPntainer materials most suitAb.. le'~ox th.e us~e : .. .. ...
~' of the structuxes are those'that are capa,bl'e Qf under~o~n~
substantial inelastic eLon~ation befoxe b,rea~In~
: ~eferrin~ no~.to th~ drawin~s~ F,i~uxe 1 sh.ows the .
end ~f a container 10 w,hich'has been di.e pxessed and~Qx dee~ ' ' drawn to include annular cha'nnels llr12 as. the de~rmed aXe~s.
Th.e ends 61 a-d, edges. 62 a-d and bases: 63 a-~b ~f the channels are preferably of rounded confi~uxation7 thus th.e ch~nneI~s, can be for~ed by draw,in~ and stxetchin~ pxocesses .with~ut the de~elo~ent . 10 of weak spots that c~uld be susceptible to c~rXQsion ~r ~echanical ,~.
.,~ breaka~e, However Qthex s,h.~pes. cQuld alsQ be u~s:ed. These ,,, :~'' chann~els 11, 12 axe capable~ of un,~old;na undex pre$'sure by .,, under~oin~ bendin~ ,stxain. It m,atters little whether~ the , ch.annels extend ~nwardly into the'containex ~X outw.ardly ~xo~ :.
it, so lon~ as extensibilt,ty undex pressure. I$~ possible, ;. . .
; The brid~es. 13, 14 between the ends of channeIs 11~ 12 are '. .::~
the points at which ventin~ t,a,kesi place because the b~idge ~$ ;~
,' subjected to tensile str~in beyond its rupture point while the ''' '. channels still ha~e substantial extensibility, Gxo~yes. 15~ 16 , . . 20 are either cut Qr pressed as axcuate ~xooVes which'extend ~, across the bxidges and d~wn the ends of th.e adjacent channels ,,. since th.ese are re~i4ns of txansition from the hi~h'stxain .
': at the undeformed portions o~ the'brid~es to thé low stXain ,:`, at the fully de~oxmed portiQns o~ the channels, The ~r~oyes .
15, 16 of the brid~e aXeas 13~ 14 are relatively small yet ~ pxoYide su~icient yent~n~ as Qpposed to the si.~ple ~roQyes `:~. of the prior art whIch m,ust be lar~er to be'effectiye ~nd "'.~ therefoxe would have the dis:advanta~es of bein~ more susceptible ''' : -6-.

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~644~5 tQ mechanical or corr~siQn da~age~and to ~or~ti.on o~ wide openings.
High'tensile:stres,s. is concentrated in the ~ro~ved ~ortiQns 15~ 16 o~ the brid~e areas 13, 14 and not in the adi~inin~ areas such as:the~ Quter' annulus 6S adja,ce'nt the brid~e ~xeas. The depth o~ the ~ro~Ve is substantiall~ detexminative of the de~xee 4~ thi~ concen~tration and a ~roo~e hav~n~ ~ depth at le,a,st ~bQut hal~ o~. th:e'ori~inal w:~ll th.~ckne,ss. is~ usually ~de~uate., : The width'at the~ba'se o~ each ~r~QVe ,i.s m.,a,de ~uch tha't the ru~ture which..occurs.in th.e ~rQo~e t~kes pl~ce durin~
th~t ~t ~ the ~ut,w,a,rd.dis~lacement Q~ the disc 19 ~or ~h~ch the excess~ye internal~pressure yaXies le~s,t, I,n oxde~ to ensu~e ~Qdex~tely unifor~;s:tr~in across the ~r~oYe b~se and tQ ~pid pxe~ature'ru~ture it i,s pxe~exable that the junctuxes p~ the ~r~ave'bas:e with'the side w~lls of the ~X~Ye ~xe rounded~,~nd the ~ateria,l thickness, Q~ the ~Qoye ba,s,e between thes:e juncture.s: is:.appxoxi~ately cQnstante The desixed ba,se width depends upon ~and i:s a function of the contalnex materials characteri.s,tic;elon~ation to rupture. undex tens~le ~ 20 stxess~ and 4f the struc*ure-detexmined pullin~ ~p~xt o~ the ~r~ove w~lls-as~excessive'internal pressuXe ~ncrea,$es~
The m~texi~l o,~ the ~ro~.ve hase is st~ai.ned in direct prop~Xtion to the. di,~s,placement thatl ~idens th.e ~rOQ~e~ ~nd in inYex~s~e pXQ-~xtign tQ its initial ~idth~ Thus~ f~X ex~ple.f the pxe~e~red ~ x~oye b~se width f~r th.e m~:~e'extensible annealed ~ld ~-teel W~ll ,. be .~ade $~Allex than th~t ~sr the sa~e steeI which'h~s been - ~ w~xk-hardened. ~ matexial allowin~ severa~ old extenS~on :~ ~
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before rupture, such as annealed pure copper or fine silver, lead, rubber, or some plastics, would require a much narrower groove, for the same structure, than that suited to mild steel.
If the gr~oves in a metal have been formed by , cold pressing~the base material is hard and relatively ln-extensible, but a simple anneal restores its ductibility and stabilizes i~s mechanical and chemical properties. The grooves, with the adjoining~areas including the bridges and the - ends of the channels, can be annealed by application of heat sufficient to make the entire areas 15,16 red hot for about a second. It has been found that by annealing the metal in the area where rupture is desired it is possible to provide more eAYact control over the mom~nt of venting by counteracting the effects of cold working the metal container. The annealing also provides the groove area,` which is the weakest part of the container structure, and the surrounding area, which has been subjected to forming-stresses, with a degree of resistance against corrosion and attack from materials contained S 20 -within the container of which the groove is a part~and also reduces the susceptibility to mechanical injury.
- ~ In the embodiments shown in Figures 1-4 the channels 11,12 have a central disc 19 therebetween. When the pressure in the conkainer e,xceeds normal operating pressure the central disc 19 will be forced outward. Thls will, ln turn, place botll the c]-allnels 11,12 under ~endinc3 stress and the bridge ~ area 13,14 under tensile stress. Figure 2 shows the movement .~ ' .
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10644~5 of the channels 11, 12 under this stress, by dotted line 20.
The pressure force existing in the container is shown by arrows. The dotted line 20 shows that the channels have been unfolded partially but not completely at the time of venting.
When the venting pressure has been reached, the groove is stretched to the shape as in the embodiment where the container is formed of mild steel, shown by dotted line 21, roughly 35-50% wider than originally, and is ruptured or torn. It is desirable to have the groove tear while the deformed portions are still extensible because this allows further opening of the vent if the excess pressure is not relieved.
However, these tears are limited to the bridge area because as the channels unfold, the ends of the channels do not undergo appreciable tensile stress. The tensile load released by the ruptured bridge does not propagate the tear into the channel regions since the area adjacent to the tear has retained its strength even when the channels have fully unfolded. Simple grooves do not have this characteristic since the areas adjacent to the ends of the groove have been subjected to full tensile stress causing weakening and when the groove ruptures the adjacent area does not have sufficient strength to contain the tearO Limiting of the tears to the chosen vent regions is generally aided by the greater thickness of the channel material. Thus, the groove 16 shown in Figure 3a provides a limited vent in any metal that is sufficiently ductile to allow deep drawing, even when internal pressure after venting remains high enough to unfold the channels fully.
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The channel material will, of course, advantageouisily be o~
such thickness as to permit unfolding without bending fracture.
For homogeneous rigid materials, includiny those for which reinforcement is impractical, means are needed to reduce tensile , stress, across the ends of a vent crack, enough to prevent .
further rupture. Such means are shown in the embodiment of Figure 3b where the end of the groove 35 dips below the lowest level of the rest of the channel. The thinned portions 38, 39 uncler the groove are compressed as the channel unfolds, off-10 ~ setting the tension that otherwise could extend the groove ~, .: , , - crack. Thus, there generally should be a differ-ential in strain between the vent area and the desired end of the vent accomplished by these or other similar means.
: , . , ~ith tlle elastic-recovery movement of the channels ~; after venting, the vent that has opened w~ close sufficiently to inhibit container material from escaping and ` ~ ~ foreiyn material from entering the container . This is especially important with electrochemical cells containing substances , , :
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; ~ which are incompatible with ambient atmospheric materials.
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This latter feature tends not to be present in vents that consLst only of a thinned groove in the wall of a container.
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~ ~ The disc 19, by its mOveMent shown by the dot,ted 7j~ line 20, exerts a pulling force on both the cbannels and the ., ~
iS bridge area. This force produces small, predominately bending strains in the channels with concomltant large outward displacemeht of the disc, and on the groove 15 ln the bridge area 13 a large tensile strain which increases until the groove is eventually ruptured.
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Figure 2 shows container 5 having a pressure release device of this invention as it is used in a typical electro-chemical cell that in some instances can develop excessive ~nternal pressure. The cell shown is one in which the anode ~2 is lithium and the cathode depolarizer is S02. Separator mats 23 separate the anode 22 from the cathode current collector 24, After the cell has been made hermetic the So~ is introduced into it. An insulating disc 25 separates the cell components from the outer cell wall and the pressure release mechanism however this disc is not a hermetic separator and - excess fluid and its concomitant pressure can circumvent this disc and operate on the pressure release device integrated into the cell wall.
Figure 4 relates to an embodiment similar to that of Figure 1 and shows the ends 32 of adjacent channels 71,72 and the bridging area 73 therebetween. Groove 30 is of lenticular shape with its width approaching zero as it approaches the end of the most deformed portion of the channels 71,72. Differing shapes of groove alter the venting process.
A groove of uniform width such as that shown in Figure 1 ruptures first at the center of the bridge area 33 forming a ~;
lenticular slit whose extremities progress down the channel ends, with continued outward motion of disc 19, until they reach the ends of the thinned (or extensible) material at the base of the - groove. The groove embodiment as shown in Figure 4 is strained roughly the same amount throughout its length and ruptures in a roughly full-length but initially very narrow slit extending along the full length of the thinned base of the ,'"r`

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groove. The resulting partial decrease of restraint on the ~isc 19 allo~s more abrupt vent opening than that of the uniform width groove at the time of rupture, with a more rapid decrease of pressure. Thus the venting action can be varied or controlled from a slow, pressure-regulating release to an abrupt opening of a substantial vent.
Figure 5 shows another embodiment of this invention in which a cylindrical container 2 is provided with a pressure release device in the form of circumferential deformations 40,41 in the side wall thereof. Thoug}i the deformations 40,41 are shown as facing outward, th~ direction has little bearing on the pressure release device's operation. In this embodiment ., the direction of the operative tension is axial as shown by the arrows, and the defor~ations can unfold to increase the axial length of the container. In this way the tenslle stress is concentrated on the b}idge area 42 and particularly in the groove 43 which tears under this strain while the deformations 40,41 still are capable of further unbending as previously explained.
Figure 6 shows another variation in structure in which the channels 51,~52 are formed in the cylindrical side - wall of a container but are not circumferential in form.
Instead the channels 51,52 are in a direction parallel to the axis of tlle cylinder. Excessive pressure within the container distends its circumference and the channels 51,52 unfold with only a bendiny strain, while the bridgin~J area 53 is subjected to high tellslle strain causing tile wall ~o rup~ure a~ g~oove 54.

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It should be noted that the structures of Figs. 1-4 havc two characteristics not found in the embodiments of ~igs. 5 and 6. First, in the ormer the vent is formed in a bridge bet-ween two ~uite difEerent members--a central disc l9 and an outer annular rlng 6~5-- rather than between two like members.
The outer annulus, with the adjoining part of tlle container walls, is subjec~ed to a contractile force alony tlle diameter passing through the bridyes, when the disc is forced outward by excesslve internal pressure. The width oE this annulus will d~sira~ly be sufficient to support the contractile force with-out undercJoing plastic deformation so that the force can .! , ' continue to increase and to strain the groove base material until it ruptures. Second, as the disc is displaced outwardly Erom the plane of the outer annulus under e~cessive internal pressure, the bridges ar~ rotated slightly from their original plane but undergo little lnitial elongation, thereby providing a degree of yrotection against acciden-tal release by pressure vent formation in the bridge area.
Figure 7 illustrates the motion o~ disc l9 in~
Figure l as a function of internal pressure. The inclusion of the channeLs in the container end wall allows substantial outward motion of the disc with minor strain of channel material. As the disc moves outward, the internal pressure chanyes only gradually so that a pressure plateau is reached as shown between points A and B ~ollowed by more rapid pressure increase whell the channels arc unfolded to the point .. . .
where ~urther unfoldillg becomes diEEicult. Though su~stantial motion of clisc l9 continues within the plateau, the pressure within tlle cell varies little. 'l'hus the bridcJe area is . . .. .

10644~5 sevexly strained during this ~ove~ent as prev~ously explained and ruptures durin~ th;s predictable pressure plateau makin~ , ,it possible to predeter~ine wi'th xeasonable pxecision the internal pxessuxe at which:the vent will form, In order to .' enSuxe rupture of the groove'w.ith;n a predetermined desired pxeSSure ran~e such as the'p~essure plateau the width.o~ the :
~ro~ye ca,n be varied~ ~ith ,a, ~reater width caus~ng rupture t~wArds, the upper end o~.. th.e cUXve and a lessex ~idth.causin~ ' xupture t~o,w~rds the lowe'r end of the sa~e cUxve. Because of the ~elatiye sizes of the ~rooves and the channeIs the ~reatest p~rt of the force exerted by excessiYe intexnal .
pxes.suxe ~s directed to unfoldin~ the de~oxm~tions or channels ''.
with only a minor part of the force exerted to place the ' ,.
grooves under tensile strain, Once the ~rooYe has been extended beyond ~ts proportional li~it~ both the min~r ~orce that widens this section to ruptuxe and the ma~or foxce un~oldin~ the deformation axe li.ttle chan~ed, Thus;r while the intexnal contai.ner pressure xem.ains s,ubs,tantI.a~
con$tant durin~ the unfolding o~ the de~oxmati,ons~ the bxi.d~e section is sevexeIy strained to rupture. It 1,s thexe~oxe the repxoducible mQVement o~ the de~ormations. ~hich detex.mines ' the pressure at which the yent is ~ormed. The position : :
of the plateau as it relates to ventin~ pressure is dependent~ . :
to a lar~e extent~ upon th.e thickness o~ the w.all o~ the container at the ch.anneIs, Thus the cont~inex can be:~de to yent ~t a hi~her pressuXe if the thicknes.'s of the cha,nnel wall ~.s increased and a,t a lower pressure if decreased, Sim~larl~Y~ i~ the channel ~re annealed the pressure pl~te~u is ~ttained more quickly ~nd at a lowex intern~l pxessure leyel, Ventin~ will thus ~ccuX ~t a lower pres'suxet The follo~w,in~
examples set ~orth the characteristics of a specific type of .

' 10644~5 containex.
Standard D-size'cell containers as shown in Fi~uxe 2 wexe~rmed by deep-drawin~ mild steel to 1.3 inch:outside d~.~eter ,Q2Q inch conta,iner ihicknes's, channels o~ .9 inch rid~e dia~etex and ,08 inch:'depth with the channel sides ~orming an an~le ~ 80, with each~'oth.ex. The ~rooVes, trayexsin~ the ,,, bx~d~es between adjoinin~ ch'annel ridge5, WeXe pressed about ,01 ,i,nch.deep and had a ~axi~um width o~ ~bout~j,a25 inch ~t the centeX Q~ th.e brid~es. ~ter local annealing c~ the bxid~es ,a,nd adjoining cha,nnel ends.~ the cpnt~inexs vented a,t 450 + 25 psi.
~elea,s.e pxessures beyond these'li~its were found when substitution .021 inch stock sti:fened the channels to incXease the vent pres$,ure to 485 + 25 ps~i., Such'yarlables~ o~ cQurSer are controlled in m~nufacturin~ to ~aintaln speci~ied dim,en$ions ~nd ~atexi~l conditiQn, '.These pres'sure ranaes ~oX yenting axe su~icientl~ pxecise and~in the use~ul ra,n~e o,~ opeX~tin~
~es:sures ~X use fox he'x~eti,cally sealedr ~re5$uxized~ electr~-che~ical cells.

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Claims (19)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A container having a pressure release device in a wall thereof with said device comprising a pre-determined venting area defined by the proximate ends of two channels with said channels comprising deformations of said wall and said venting area being relatively undeformed, whereby under conditions within said container of increasing pressure above normal operating pressure said channels tend to undeform and simulta-neously therewith said pre-determined venting area is stretched to rupture thereby forming a vent for release of said pressure.

2. A container as in claim 1 wherein a portion of said pre-determined venting area includes a narrow groove with said groove extending across said area and into said proximate ends of said channels.

3. A container as in claim 2 wherein said pre-determined venting area is annealed.

4. A container as in claim 1 wherein said container contains an electrochemical cell.

5. A container having a pressure release device in a wall thereof with said pressure release device comprising channel means having one or more interruptions therein, whereby under conditions within said container of increasing pressure above normal internal pressure said channel means unfolds and simultaneously therewith at least one of said interruptions is stretched to rupture thereby forming at least one vent for release of said pressure.

6. A container as in claim 5 wherein a portion of said interruption includes a narrow groove with said groove extending across said interruption and extending into said channel means adjacent said interruption.

7. A container as in claim 6, wherein said interruption is annealed.

8. A container as in claim 5 wherein said container contains an electrochemical cell.

9. A container having a pressure release device in a wall thereof, said wall being shaped whereby to form a plurality of channels on one side of the wall with the side of said wall opposite each channel having a shape generally corresponding to the shape of said channel, and said channels being in proxi-mity to each other in at least one place, whereby increasing internal pressure will a) cause said channels to tend to unbend and b) cause rupture in an area of said wall where said channels are in proximity to each other.

10. A container as in claim 9 wherein said rupture area is further weakened by the inclusion of a narrow groove across said area and extending from one of said channels to an adjacent channel in proximity with the other.

11. A container as in claim 10 wherein said rupture area is annealed.

12. A container as in claim 9 wherein said container contains an electrochemical cell.

13. A container having a pressure release device in a wall thereof, said wall being deformed whereby to form channel means for permitting a portion of said wall to move outwardly, and a small, relatively undeformed section of said wall being positioned between adjacent portions of said channel means;
whereby said outward movement causes concentrated forces to act on said relatively undeformed portion, which forces cause said relatively undeformed portion to rupture when said outward movement occurs.

14. A container as in claim 13 wherein said relatively undeformed section includes a narrow groove therein with said groove extending across said section to connect adjacent portions of said channel means.

15. A container as in claim 14 wherein at least one of a) said undeformed section, b) said groove, or c) said adjacent portions of said channel means is annealed.

16. A container as in claim 13 wherein said channel means comprises an interrupted annular channel on an end wall of a container.

17. A container as in claim 13 wherein said channel means comprises an interrupted circumferential channel on the side wall of a container.

18. A container as in claim 13 wherein said channel means comprises an interrupted channel disposed axially along the side of a container.

19. A pressure release device comprising channel means having one or more interruptions therein whereby under condi-tions of increasing pressure said channel means unfolds and simultaneously therewith at least one of said interruptions is stretched to rupture thereby forming a vent for release of said pressure.