Boss for composite pressure vessel having polymeric liner

A boss for a pressure vessel with an outer reinforcing shell and an inner liner has a radially extending flange and a tubular neck projecting outwardly to provide a fluid communication port. The flange is embedded in and structurally integrated with the material of the inner liner during molding. The flange is divided by a conical annular groove into an outer skirt and an inner skirt. The inner skirt protrudes from the outer skirt and has a flattened end facing toward the vessel wall. The flattened end and/or the surfaces of the annular groove are textured, knurled or otherwise unevenly surfaced for gripping the liner material. A number of apertures extend from inside the groove to the opposite side of the flange. The liner material is molded on and in the groove of the flange and fills the apertures to form anchoring segments integral with the liner, extending through the flange to liner material on both sides.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a boss fitting which reinforces the structural 
interface between the preferably filament-wound outer shell of a pressure 
vessel and a polymeric inner liner of the pressure vessel, and which 
provides a conduit for transferring fluid to or from the interior of the 
pressure vessel. A boss comprises a radially extending flange located at 
the base of an outwardly extending tubular neck. The flange is embedded in 
the polymeric liner and comprises an upper (axially outer) skirt and a 
lower (axially inner) skirt. The skirts are spaced to define an annular 
groove with a textured or knurled surface at the edges of its outer or 
open end. A plurality of radially spaced apertures extend from the inner 
or closed end of the groove to a flat under surface of the radially 
extending flange. The boss is securely integrated with the polymeric liner 
in a molding procedure. During molding of the polymeric liner, polymeric 
material flows into the groove and through the apertures, forming a 
plurality of polymeric anchors whereby the flange is surrounded by and 
embedded in the polymer on the inside and outside of the boss fitting. 
2. Prior Art 
It is desirable to make gas storage pressure vessels that are light in 
weight and yet highly resistant to fragmentation and corrosion damage. To 
achieve these qualities, pressure vessels can be fabricated from laminated 
layers such as wound fiberglass filaments or various types of synthetic 
filaments, bonded together by a thermosetting epoxy resin. An elastomeric 
or polymeric liner is provided within the filament wound shell to seal the 
vessel and to prevent fluids in the vessel from contacting and potentially 
interacting with the composite material. 
Filament wound vessels can be constructed in a variety of shapes and 
typically are cylindrical with a partly spherical end. A boss at the end 
provides a flowpath to the interior and also structurally joins the 
internal polymeric liner to the outer composite shell in a way that 
prevents fluid from penetrating between the liner and the shell. The boss 
generally comprises a circular flange or support member at the base of a 
neck that protrudes axially outwardly from the end of the vessel. The 
support member is attached to the internal liner so as to anchor the boss 
to the internal liner. A port is defined along the central axis of the 
neck and the support member. The contents of the pressure vessel 
communicate with the external environment through the port. 
In many applications, composite pressure vessels as described are required 
to contain fluids at very high pressures. The internal pressure subjects 
the interface of the boss, the liner and the outer shell to structural 
loading, which can be extreme. As pressure within the vessel is increased 
from ambient pressure, bearing stress is generated as the vessel tends to 
inflate due to the differential pressure between the vessel interior and 
the ambient pressure. This stress includes forces that operate between the 
boss and the composite shell. In addition to a stress normal to the plane 
of the vessel wall (i.e., in a direction that would expel the boss along a 
line parallel to its axis), shear stress develops between the boss and the 
internal liner in the plane of the vessel wall, tending to retract the 
liner radially away from the boss. These stresses also tend to bend the 
circular flange support member of the boss, outwardly of the vessel toward 
the center and/or inwardly toward the radial edges. 
Sufficient stress can detach the boss from the liner, at least locally. Any 
such detachment reduces the structural integrity of the vessel, may expose 
the outer shell or the surfaces between the inner and outer shells to the 
fluid contents, may contribute to separation of the shells, and may result 
in leakage from the pressure vessel. It is important to anchor the boss 
securely to the liner to reduce the possibility of separation. 
It has been proposed to include locking structures in a boss for a pressure 
vessel to better anchor the boss to the liner. For example, U.S. Pat. No. 
5,429,845--Newhouse discloses a boss with a support flange having one or 
more annular grooves for gripping complementary locking tabs formed in the 
liner. The hub portion or throat is tapered inwardly on its outer surface, 
providing an inverted inclined bearing surface which engages the outer 
shell. U.S. Pat. No. 5,476,189--Duvall similarly discloses a boss having a 
radially projecting support flange with annular grooves. Duvall does not 
employ a tapered hub but the support flange has annular grooves which mate 
with tab locks formed in the liner. 
Annular locking grooves are helpful to anchor the boss to the liner. 
However, the respective locking structures, namely the annular grooves and 
liner tab locks, may not prevent the liner from separating from the boss 
with sufficient deformation of the vessel in general and the boss in 
particular. The surfaces of the support flange, which are smooth but for 
the annular grooves, may permit relative displacement of the inner liner 
and the support flange under some circumstances, leading to separation. 
U.S. Pat. No. 5,518,141--Newhouse discloses another design with annular 
grooves in the support flange for mating with tab locks in the liner. 
Newhouse supplements the annular groove locking structure using bolts 
threaded into the hub of the boss through a support dome disposed inside 
of the liner. The bolted support dome holds the inner locking tab on the 
liner captive in its locking groove to resist separation even in the event 
of deformation of the boss structure. It is not clear how the support dome 
could be inserted into the vessel and installed from inside the liner to 
engage over the locking tab and groove, and presumably the liner is molded 
after the support dome has been attached to the hub. 
The foregoing patents are hereby incorporated for their teachings of 
alternative structures and materials for the polymer lining, the 
reinforcing shell and the boss. 
It would be advantageous to improve the structural connection between the 
liner of a pressure vessel and a boss having a support flange in a manner 
that is relatively uncomplicated but produces a robust mechanical 
attachment of the liner and the boss, and is insensitive to or even 
improved under conditions in which stresses produce deformation of the 
boss and its supporting flange, such that relative displacement of the 
liner and the boss is substantially eliminated. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a boss which improves the 
structural connection between the liner of a pressure vessel and an outer 
shell by integrating the structure of the liner with that of a support 
flange on the boss. 
It is another object of the invention to provide a conically downward and 
inward annular groove in the support flange, which is penetrated by the 
liner material during molding and to which the liner material is 
structurally integrated by flow of the liner material against, into and 
through surface formations and through openings in the support flange. 
It is a further object of the invention to enhance the mating surface 
between the boss and the liner of a pressure vessel by providing the boss 
with a textured surface. 
It is another object of the invention to provide a boss which is securely 
and structurally integrated with an integrally formed polymeric liner of a 
pressure vessel, by using polymeric segments joined integrally with the 
liner on opposite sides of the support flange, thereby integrally 
anchoring the liner to the flange. 
These and other objects are accomplished by a boss disposed in the opening 
of an end portion of a pressure vessel. The pressure vessel generally 
comprises a filament wound outer shell and a preferably polymeric internal 
liner. The boss comprises a hub or neck forming a port communicating 
between the interior of the vessel and the outside, and an annular support 
flange extending radially from the neck. The flange is embedded in the 
material of the inner liner during molding, so that the neck extends 
outwardly from the pressure vessel. 
A slanted annular groove is formed in the flange, the groove dividing the 
flange into an upper skirt (i.e., axially outer) and a lower skirt 
(axially inner) spaced from one another by the groove. The annular groove 
slants conically inwardly relative to the axis of the boss and forms 
gripping surfaces which prevent movement of the boss relative to the liner 
in radial and vertical directions when the vessel is stressed. The lower 
skirt comprises a flattened upper (outer facing) surface adjacent an open 
end of the annular groove and a conically slanted underside extending 
inwardly from the edge of the flattened upper surface to a flat underside 
of the annular flange extending to the inside opening of the port. The 
gripping surfaces of the annular flange are enhanced by texturing, 
knurling or similar irregularities of the flat upper portion of the lower 
skirt and the inner surface of the annular groove, at least in the area 
immediately adjacent the open end of the groove. 
A plurality of through apertures are provided through the annular groove 
along its circumference. The apertures are preferably evenly spaced 
angularly, and are preferably oriented in a conical direction 
substantially parallel to the side walls of the groove. The apertures 
extend through the inner radius or closed end of the annular groove to 
open on the underside of the annular flange, preferably in the flat 
underside area. 
The apertures aid in structurally integrating the liner of the pressure 
vessel with the boss. The liner is molded onto the preformed boss. During 
molding the polymeric material flows into and fills the groove in the 
annular flange, and flows through the plurality of apertures to join 
integrally with the material of the liner on opposite sides of the flange. 
After curing, the polymeric material remaining in the apertures forms a 
plurality of polymeric anchors or connecting webs which extend through the 
flange to integrally join the polymeric material inside the annular groove 
to the polymeric material adjacent the underside of the annular flange. 
These anchors or connecting webs, like the groove, are oriented downwardly 
and inwardly. In the event of stress on the pressure vessel tending to 
force the boss axially outwardly, to bow the flange outwardly and/or to 
draw the liner radially away from the boss, the grooves, the flattened and 
textured surfaces and the connecting anchors cooperate to prevent relative 
movement of the liner and the boss and consequent failure of the pressure 
vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention is described in detail with reference to the accompanying 
drawings in which the same reference numerals are used throughout to 
identify corresponding elements. The drawings present the invention in an 
arbitrary orientation. Directional designations such as "upper" and 
"lower" as used in this description are intended to refer to the drawings 
and not to require any particular orientation. 
FIGS. 1-3 show a boss 10 according to the invention. FIG. 3 illustrates the 
boss 10 in place, namely in the spherical end section of a partially shown 
pressure vessel 50. Pressure vessel 50 comprises a preferably polymeric 
inner liner 36 and an outer shell 38 that preferably comprises a fiber 
reinforcement. 
Outer shell 38 of pressure vessel 50 can comprise a known composite 
reinforcement made of fiber reinforcing material in a resin matrix, such 
as fiberglass, ARAMID, carbon, graphite, or the like, or another fibrous 
reinforcing material capable of providing the fragmentation resistance 
required for the particular application in which the vessel is to be used. 
The internal liner 36 is constructed from a polymeric or elastomeric 
material. The liner is gas impervious when cured and is constructed by 
compression molding, injection molding, parison molding or a similar 
technique in which a hardenable or curable material flows as a part of the 
molding process. 
Boss 10 comprises an outwardly projecting hub or neck 12, which extends 
through an opening in the outer shell 38, and a radial or annular flange 
20 located at the base 28 of neck 12. Flange 20 is embedded in liner 36 
during the formation of liner 36. Neck 12 and flange 20 of boss-10 define 
a port 18 which extends through the center of neck 12 and flange 20. Fluid 
is extracted from or loaded into pressure vessel 50 through port 18. Neck 
12 preferably has a downwardly and inwardly tapered outer surface 14, 
thereby forming a groove at the base 28 for receipt of the inner liner 36 
and the fiber and resin matrix outer shell 38. Tapering surface 14 and the 
groove formed thereby, as backed by flange 20 inside the vessel, restrict 
relative displacement of the shell 38, liner 36 and neck or hub 12. Thus 
the structure tends to engage between boss 10 and the laminated shell 
38/liner 36 vessel wall, to keep boss 10 from moving into or out of 
pressure vessel 50. At angularly spaced intervals around the circumference 
of neck 12, tapered outer surface 14 can be flattened to form a gripping 
surface 16 for receiving various lever or gripping devices such as 
wrenches, fork lift tines or the like, depending upon the size of the 
pressure vessel 50. 
Boss 10 is mounted at a polar opening in the typically hemispherical end of 
an elongated pressure vessel. The radial or annular flange 20 extends from 
base 28 of neck 12 and provides a surface by which loads are distributed 
in the area of boss 10 when the vessel is pressurized. 
Pressurization of the pressure vessel 50 tends to expand the vessel due to 
differential pressure as compared to ambient, distorting the vessel 
including its hemispherical end. The associated stress tends to favor 
relative movement in radial and axial directions between boss 10 and the 
vessel wall including liner 36 and shell 38. Internal pressure urges boss 
10 outwardly in an axial direction relative to the vessel wall. With 
inflation of the vessel and resulting expansion of the hemispherical end, 
the vessel wall and particularly inner liner 36 are pulled radially 
outwardly relative to boss 10. The inflation stresses also tend to bow 
annular support flange 20. 
Annular support flange 20 defines a slanted or angled annular groove 22, 
directed conically inwardly and downwardly. In the embodiment shown, the 
conical groove is oriented at about 60.degree. relative to the axis of 
boss 10 and 40.degree. relative to the outwardly sloping outer side of 
flange 20. Flange 20 provides a plurality of engagement and gripping 
surfaces between inner liner 36 and boss 10 to prevent relative movement 
between boss 10 and liner 36 in the radial and vertical directions in 
which stresses are produced by pressurization of the vessel. 
Annular groove 22 separates radial flange 20 into an upper skirt 42 and a 
lower skirt 44. Referring to FIG. 2, upper skirt 42 adjacent neck 12 forms 
a groove 29 with the inwardly sloping tapered outer surface 14 of neck 12, 
located at the base of neck 12. Thus the radial dimension of neck 12 
increases proceeding axially outwardly or upwardly in FIG. 2. Upper skirt 
42 defines an opposed surface such that hub 10 is axially fixed relative 
to the vessel wall as shown in FIG. 3. 
FIG. 3 shows the polymeric liner 36 and reinforced shell 38 with hub 10 in 
place. During formation of polymeric liner 36, for example by molding a 
flowable curable resin, polymeric material flows up to and against the 
bottom of groove 29. The filaments of reinforcing shell 38 are wrapped and 
woven over boss 10 to fix boss 10 relative to the vessel wall. Groove 29 
acts as a bearing surface against the filament windings of outer shell 38. 
Lower skirt 44 terminates in a flattened upper surface 48 adjacent to an 
open end 34B of annular groove 22 and has a slanted underside 30 extending 
inwardly from the edge of the flattened upper surface 48 to a flat 
underside 32 of annular flange 20. The flattened surface 28 is 
substantially parallel to the vessel wall but is spaced from the outer 
shell 38 by a relatively thick portion of polymeric liner 36. This thick 
portion leads continuously into the material that extends into conical 
groove 22. 
Boss 10 is anchored to and integrated with inner liner 36 to prevent 
separation of liner 36 and boss 10 during pressurization of the vessel. 
This is accomplished by a number of surfaces of boss 10 engaging with 
inner liner 36, by gripping and/or abutment, and resisting lateral or 
axial movement of the boss 10 relative to inner liner 36. Gripping 
surfaces are provided including both sides of the inner and outer skirts 
42, 44, namely the inner surface of annular conical groove 22, the top 
surface of upper skirt 42, the bottom of lower skirt 44, and the flat 
underside of flange 20. Abutment surfaces include the flat terminus 48 of 
lower skirt 44, the outer edge of upper skirt 42 and the opposite sides of 
flange 22. Engagement of liner 36 and the gripping surfaces of boss 10 
preferably is enhanced by texturing or knurling the respective surfaces 
including the flattened upper surface 48 of lower skirt 44 and the inner 
surface of the annular groove 22, especially immediately adjacent opening 
34B of groove 22. 
Annular groove 22 has an open end 34B and a substantially closed inner end 
or radius 34A, shown in FIG. 3. A plurality of through apertures 26 are 
provided to extend the opening provided by annular groove 22 inwardly from 
the circumference of closed end 34A. Apertures 26 are preferably evenly 
spaced angularly around the circumference as shown in FIG. 1. Apertures 26 
extend through the inner radius or closed end 34B of annular groove 22 to 
the flat underside 32 of annular flange 20. Inasmuch as liner 36 of the 
pressure vessel is molded using a flowable polymeric or elastomeric 
material, for example by compression or injection molding, the liner 
material is distributed and flows into apertures 26 during the forming 
process. Therefore, after molding of liner 36, flange 20 is embedded in 
and run through with anchoring connecting paths that couple liner material 
on both sides and through flange 20. Thus flange 20 and boss 10 are 
securely integrated with the integral material of liner 36. 
Liner material extending through apertures 26 forms a plurality of 
polymeric anchors 40 which connect the polymeric material from inside the 
annular groove to the polymeric material adjacent the opposite side, 
namely flat underside 32, of the annular flange 20. Thus, the apertures 26 
act as molds which create polymeric anchors or pins 40 which anchor liner 
36 to boss 10. Apertures 26 are oriented in substantially the same 
direction as the walls of groove 22. Under pressurization stress, a 
tendency of distortion to push boss 10 axially outwardly is opposed by 
skirts 42, 44 and flat terminus 48, and a tendency for liner 36 to draw 
radially away from boss 10 is opposed by liner material held in groove 22 
and also by liner material in apertures 26, extending integrally through 
flange 20 to lock the liner to boss 10. 
The invention having been disclosed in connection with the foregoing 
variations and examples, additional variations will now be apparent to 
persons skilled in the art. The invention is not intended to be limited to 
the variations specifically mentioned, and accordingly reference should be 
made to the appended claims rather than the foregoing discussion of 
preferred examples, to assess the scope of the invention in which 
exclusive rights are claimed.