Vessel for storing fluid under pressure able to undergo rupture without fragmentation

Vessel for storing a fluid under pressure, such as a gas storage vessel, of the type comprising an internal casing surrounded by an external hooping. The internal casing has symmetry about a longitudinal axis, a central pipe section and two extremity portions, and at least one of the extremity portions protruding outwardly. The hooping is of reinforcing fibers coated with a thermoplastic of thermosetting binder, and opposite the pipe section the hooping has at least one layer of fibers, known as longitudinal fibers, having a flat winding pattern and a winding angle as small as possible, so as to allow a boss, centered on the longitudinal axis of the protruded extremity, to be uncovered with fibers. Further, the hooping has at least one layer of fibers, known as circumferential fibers, having an almost 90.degree. winding angle. Moreover, the pipe section further comprises at least one layer of fibers having a winding pattern that is either flat or helical with a winding angle (.alpha..sub.n) of between the angle (.alpha.) of the longitudinal fibers and 90.degree..

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention concerns vessels for storing fluid under pressure and 
more particularly, but not exclusively, vessels of the bottle type for 
storing gas, such as air, oxygen, nitrogen, carbon dioxide, used in 
various industrial areas. 
More specifically, the invention further concerns bottles of the type 
comprising an internal casing with a form that is symmetric about a 
longitudinal axis and having a cylindrical portion or pipe section and two 
extremity portions, one extremity portion protruding outwardly, and 
further the internal casing is surrounded by a hooping of reinforcing 
fiber windings coated with a suitable binder. 
2. Discussion of Background Information 
When such vessels break, this generally occurs along the pipe section of 
the casing which opens suddenly. This occurs usually when the vessel 
contains a gas under high pressure. Such a rupture may cause the release 
of dangerous metal fragments which pose a threat to persons located 
nearby. Moreover, a recent official standard further imposes that this 
type of vessel is required to satisfy an under pressure rupture test. 
Moreover, the results of the test must produce a rupture without 
fragmentation of the internal casing of the vessel. 
SUMMARY OF THE INVENTION 
The aim of the present invention is to provide a vessel of the type meeting 
the requirements of this official standard. 
To this effect, the invention concerns a vessel for storing fluid under 
pressure of the type comprising an internal casing with a form that is 
symmetric about a longitudinal axis and having one cylindrical central 
portion or pipe section and two extremity portions, where at least one of 
the extremity portions protrude outwardly. In addition, the internal 
casing is surrounded by a hooping of reinforcing fiber windings coated 
with a thermoplastic or thermosetting binder. The hooping opposite the 
pipe section is composed of at least one layer of fibers having a winding 
angle that is circumferential and known as circumferential fibers, and at 
least one layer of fiber wound in a planar manner known as longitudinal 
fibers. The winding angle of the longitudinal fibers is as small as 
possible so as to leave free, at the protruded extremity portion, an 
opening in the internal casing centered on the longitudinal axis. 
Moreover, the pipe section further comprises at least one layer of fibers 
having a winding pattern that is planar or helically and a winding angle 
of between that of the longitudinal fibers and 90.degree.. 
Vessels of this known type resist bursting mainly because of 
circumferential fibers. The longitudinal fibers, wound according to a flat 
or geodesic winding pattern are mainly intended to absorb the axial 
forces, because the longitudinal fibers exhibit a winding angle with 
respect to the longitudinal axis of the vessel which is too small to take 
up the circumferential rupture forces on bursting. 
Whereas a vessel conforming to the present invention is able to satisfy the 
legal requirements concerning bursting without fragmentation of the 
internal casing due to the fact that the rupture forces are no longer 
exclusively borne by the circumferential layers. Instead, the rupture 
forces are partly taken up by the layer of fibers wound under an 
intermediate angle between 90.degree. and that of the longitudinal fibers. 
These fibers take up and distribute the force initially absorbed by the 
circumferential layers when the vessel having a winding pattern that is 
flat or helical can be breaks. 
Advantageously, the layer of fibers having a winding pattern that is flat 
or helical exhibits a winding angle equal to 90.degree. less the winding 
angle of the longitudinal fibers. Moreover, several layers of fibers fiber 
windings having an intermediate angle starting with provided and can have 
different winding angles. For example, the winding angles can vary between 
the value of 90.degree. and that of the longitudinal fibers. These layers 
of fibers actively participate in taking up the rupture forces by 
absorbing and distributing the force from the circumferential fibers, once 
as the circumferential fibers rupture, in turns according to the 
respective winding angle of the fiber windings. 
Thus, instead of having a sudden bursting when the vessel breaks, there is 
a cascade rupture of the circumferential fibers and then of the fiber 
windings having an intermediate angle starting with those fibers with a 
winding angle closest to 90.degree.. The result is a "soft" tearing of the 
vessel without rupture with fragmentation of the internal casing, and thus 
complying with the requirements to the official standards.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1a and 1b diagrammatically show at 1 a vessel formed of a cylindrical 
central body or pipe section 2 extended at its two extremities by an end 
piece 3 protruding outwardly and having a boss of revolution 4 coaxial 
with the axis 5 of the pipe section 2. 
In FIG. 1a, a fiber symbolized at 6 is wound flat in that the bobbin 
unwinding the fiber 6 still moves within a given plane during winding of 
the vessel 1 which rotates around its axis 5. 
The angle .alpha. the plane makes in which the bobbin moves by rotating 
around the vessel with respect to the axis 5 is known as the winding 
angle. 
Having regard to the existence of bosses 4 at the extremities of the vessel 
and which must not be overlapped by fiber, the angle .alpha. shown on FIG. 
1a corresponds to winding fibers flush with the bosses 4 and is the 
minimal winding angle. 
For vessels of the type of those concerned by the present invention, there 
needs to exist, at least at one of the extremities, this type of boss 4 on 
which a connection end piece (not shown) is mounted for filling and 
emptying the vessel. 
This minimal angle .alpha. depends on the morphology and dimensions of the 
vessels. For normal type vessels or bottles, this angle is about 
20.degree.. 
Bottles of the type with an internal casing or a metallic liner covered 
with a hooping of reinforcing fiber windings coated with a suitable binder 
firstly, include layers of fibers placed according to the winding mode 
shown on FIG. 1a and known as longitudinal fibers and having a winding 
angle .alpha., for example of about 20.degree., and secondly layers of 
fibers wound circumferentially on the pipe section of the bottle may 
constitute a danger should accidental bursting occur. In fact, only the 
circumferential fibers of these vessels are able to resist the rupture 
forces on bursting, and the longitudinal fibers do not offer much 
resistance owing to the fact that the rupture stresses on bursting are 
mainly exerted on the pipe section and generate circumferential traction 
forces which the longitudinal fibers are unable to take up owing to their 
winding angle. 
As a result, a sudden rupture of the circumferential fibers when their 
limit of resistance is reached is likely to result in fragmentation of the 
metallic internal casing and projection of splinters. 
In accordance with the invention, with a conventional covering of the 
internal casing or liner, especially a metallic liner, with the aid 
firstly of fibers wound circumferentially around the pipe section and 
secondly fibers wound longitudinally, this covering is to be replaced by 
another covering including, not merely the fibers wound circumferentially 
and longitudinally, but also fibers wound according to one or several 
intermediate angles between the winding angle of the circumferential 
fibers and the winding angle of the longitudinal fibers. 
FIG. 2 diagrammatically shows the pipe section of a vessel with an internal 
casing, and shows various layers of fibers wound on this pipe section 2. 
A fiber is placed circumferentially at C and, along with a generating line 
7 of the pipe section 2, forms an angle almost equal to 90.degree.. A 
longitudinal fiber is shown at L and placed at a minimum angle .alpha. 
with respect to the generating line. 
In accordance with the invention, fibers are wound along intermediate 
angles of between 90.degree. and .alpha., the fibers also being designated 
as longitudinal fibers and allocated with a different index according to 
their angle of winding. 
FIG. 2 shows six fibers, respectively L.sub.1 to L.sub.6, having winding 
angles .alpha..sub.1 to .alpha..sub.6 respectively of increasing values 
stepped between .alpha. and 90.degree.. 
Thus, the layers of longitudinal fibers L to L.sub.6 exhibit between them a 
stress gradient or resistance to progressive bursting gradient. In this 
regard, the maximum stress allowed by the fibers wound along the angle 
.alpha..sub.6 (the closest to 90.degree.) is slightly smaller than that of 
the circumferential fibers C, but significantly larger than that of the 
fibers wound under the angle .alpha..sub.5, and much greater than that of 
the fibers wound along the angle .alpha..sub.4, and so on. 
The result is that should the circumferential fibers C break, it is the 
fibers L.sub.6 which first of all sustain the shock and then, the latter 
releasing, the fibers L.sub.5. The result of this structure is a chain 
rupture of all the longitudinal fibers and in turn a rupture of the pipe 
section of the flying type, that is a "soft" tearing without fragmenting 
the internal casing. 
A single winding angle may be provided between the values of 90.degree. and 
.alpha., in which case it is preferable that this angle has a value 
approximately equal to 90.degree.-.alpha.. 
Several angles are preferably provided whose values are stepped, possibly 
regularly, for example between the value .alpha. and the value of 
90.degree.-.alpha.. 
Nevertheless, it is possible to wind longitudinal fibers with an 
intermediate winding angle of between 90.degree. and 90.degree.-.alpha.. 
According to one embodiment intended to approximately divide into two equal 
shares the circumferential rupture forces between firstly the 
circumferential fibers C and secondly all the longitudinal fibers (L, 
L.sub.1, L.sub.2, L.sub.3 . . . ), it is possible to provide in addition 
to the minimal winding angles nine winding angles .alpha..sub.1 to 
.alpha..sub.9 for nine layers of fibers L.sub.1 to L.sub.9. 
The winding angle .alpha..sub.8 of the layer L.sub.8 may be equal to 
90.degree.-.alpha. and the winding angle .alpha..sub.9 is between 
90.degree. and 90.degree.-.alpha.. 
In the case of a vessel with hemispherical extremities, it is possible to 
envisage having a fanshaped distribution of fibers L.sub.n with graduated 
winding angles of between 90.degree. and .alpha. whilst allowing for a 
winding of fibers geodesically on the extremities. 
The number of winding angles of the longitudinal fibers L.sub.n may vary 
significantly in the same way as the number of fibers wound under the same 
angle, as well as the number and stepping of the layers of fibers wound 
along the various possible angles (L,L.sub.n,C) according to the 
morphology, dimensions and nature of the vessel, the nature of the 
material constituting the casing (metal or thermoplastic material or 
elastomer, for example), the nature of the fibers (glass, carbon, Kevlar, 
for example) and the binder of the matrix (thermoplastic or thermosetting 
material). 
According to the winding angle (.alpha..sub.n), the longitudinal fibers 
(L.sub.n) of the invention are wound either via a flat winding (FIG. 1a) 
or via a helical winding (FIG. 1b). 
It is to be noted that the implementation of the invention does not 
necessarily imply an excess dimensioning of the wall of the vessel, that 
is the adding of additional layers of longitudinal fibers. In fact, it is 
preferable to implement the same number of layers of longitudinal fibers 
for a given type of bottle as in the conventional production mode, but 
this number of layers shall be distributed on the various layers placed 
with the various angles in question (.alpha., .alpha..sub.1, 
.alpha..sub.2, .alpha..sub.3, etc.). 
Thus, the overall weight and thickness of the wall of this type of bottle 
of the invention shall be indentical to those of a given bottle embodied 
according to the prior art. 
The invention is applicable to any vessel, especially any bottle type 
vessel, with a bottom or extremities protruding outwardly, irrespective of 
the shape of the protrusion, that is hemispherical, semi-elliptic, oval of 
Cassini. 
On these protruded extremities, the fiber windings shall be made 
goedesically as far as possible by any method. 
The shape of these extremities could of course be optimized according to 
the number and placing angles of the various longitudinal fibers.