END CLOSURES FOR FILAMENT WOUND PRESSURE VESSELS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No. 60/977,574, filed October 4, 2007, the disclosure of which is incorporated herein by reference. FIELD OF THE INVENTION

This invention relates to filament wound pressure vessels and more particularly to the fabrication of filament wound pressure vessels wherein end closures can be effectively secured to allow such pressure vessels to operate at desired internal pressures.

BACKGROUND OF THE INVENTION

Pressure vessels, such as those having full bore openings, have been in ever increasing demand with the growth of reverse osmosis, nano filtration, ultrafiltration and micro filtration as ever more important commercial separation processes. The term full- bore-access is used to denote a pressure vessel having an opening of a diameter such that a cartridge or other device of outer diameter close to the interior diameter of the bore of the pressure vessel can be supplied to and removed from the pressure vessel through such entrance. Such pressure vessels are economically made using filaments of high tensile strength that are impregnated with synthetic resinous material such as epoxy resins, vinyl ester resins, polyester resins, acrylic resins and polyurethane resins and are referred to as fiber reinforced plastic (FRP) vessels. They are generally fabricated by winding such resin-impregnated strands about a rotating mandrel in generally helical patterns to create numerous superimposed layers, and pressure vessels made in this manner can be constructed with adequate strength to withstand even high internal pressures, e.g. as high as about 1500 psi. Such vessels are used for a variety of purposes where the interior of the vessel will be subject to high internal pressure.

Pressure vessels of this type having large openings that are made by filament winding methods have generally utilized separate internally grooved rings that are wound into the pressure vessel at the time of fabrication to provide a strong, secure support for a removable end closure. Examples of such are shown in Patents Nos. 5,720,411 and 6,165,303 where the groove in the ring later receives a helical locking ring to secure a circular end plug in place. Instead of a helical ring, a simple snap ring might be used as disclosed in U.S. Patents Nos. 5,866,001 and 6,558,544. Other arrangements have used a plurality of locking ring segments, as taught in U.S. Patents Nos. 2,237,029 and 7,036,674. There have also been attempts made to lathe-cut grooves in the interior surface of such an FRP vessel; however the result has been a weakening of vessel wall that often resulted in lamination separation and closure failure. Moreover, such lathe-grooving was ever thereafter a prospective source of material degradation. A further alternative, shown in U.S. Patent No. 4,140,240, is the use of annular locking segments which carry five parallel ribs that are received in pockets provided in the interior surface of the entrance end region of the pressure vessel.

Regardless of the type of locking ring arrangement used, the receptacle in a filament wound pressure vessel in which the ring is received has generally been that of an internally grooved annular insert, usually made of a strong metal, that becomes bonded as an integral part of the filament wound FRP vessel. Such an arrangement has been felt needed in order to provide adequate strength to prevent blowout of the end closure when the vessel is subjected to high internal pressure. For example, in seawater desalination, pressures of 800-1,000 psi may often be used. With the growing worldwide shortages of fresh water, there is added interest in the use of pressure vessels of this type that can be economically produced in order to render water desalination economically feasible, and the end closure for such a pressure vessel constitutes a substantial portion of the overall

cost. In view of the foregoing, the search has continued for more effective and economical arrangements for providing end closures for filament wound pressure vessels, and particularly for pressure vessels than can be designed to handle a range of internal pressures.

SUMMARY OF THE INVENTION

It has now been found that filament wound pressure vessels for accommodating cylindrical cartridges or like objects may be wound in a manner so as to create an integral circumferential groove of certain size and shape located in the interior cylindrical surface of the entrance end region of the vessel; this groove, when coupled with segmental locking rings of a certain design, will secure an end closure plug in a manner that will very effectively resist high internal pressure. Thus, vessels incorporating such improvements will meet ASME standards for operation at such pressures without the inclusion of a grooved metal ring or the like having been incorporated as a part of the filament wound FRP vessel.

In one particular aspect, the invention provides a filament wound pressure vessel for holding a cylindrical cartridge, which vessel comprises a generally tubular filament wound pressure-resistant casing having an interior bore of circular cross-section and a transverse annular end face, a removable end closure plug of circular cross-section which is received in said bore for closing an end of said casing, said filament wound casing having a circumferential groove formed in its interior surface in an entrance region generally near said end face, and circular locking means received in said groove to secure said removable end closure plug within the casing and close the end of the casing, said circumferential groove, which is created in said casing during filament winding thereof,

having an axially outer wall which is oriented at an angle between about 70° and 45° to the centerline of said casing.

In another particular aspect, the invention provides a filament wound pressure vessel for holding a cylindrical object, which vessel comprises: a generally tubular filament wound pressure-resistant casing having an interior central bore region of circular cross-section and a transverse annular end face, a removable end closure plug of circular cross-section which is received in said bore for closing an end of said casing, said filament wound casing having a bell end section of greater wall thickness than said central bore region and having a circumferential groove formed in its interior surface of said bell end section generally near said end face, said bell end section having an annular bulbous exterior region surrounding the location of said groove, and circular locking means received in said groove to secure said removable end closure plug within the casing and close the end of the casing, said circumferential groove, which is created in said casing during filament winding thereof, having an axially outward wall which is oriented at an angle between about 70° and 45° to the centerline of said casing.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a cross-sectional view of a pressure vessel showing an end closure arrangement embodying various features of the present invention.

FIGURE 2 is an enlarged fragmentary view of the encircled portion of the end closure shown in FIGURE 1.

FIGURE 3 is an enlarged cross-sectional view of the locking ring segment shown in FIGS. 1 and 2.

FIGURE 4 is a fragmentary view, enlarged in size, showing the sidewall of the pressure vessel of FIG. 1 in the region of the end closure, with the end closure and the locking ring segment removed.

FIGURE 5 is a front view of the locking ring segment shown in FIGS. 1-3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the entrance end of a pressure vessel 11 having a full bore opening. The pressure vessel is designed so as can be produced by conventional filament winding about a mandrel, as generally described with respect to FIG. 2 of the '303 patent. As such, the vessel will have a central casing section 13 that has a cylindrical interior bore 15 of circular cross-section that is sized to be just slightly greater than the diameter of the cylindrical filtration cartridges that will be accommodated therewithin. Each end of the pressure vessel 11 is preferably formed as a bell or entrance end section 17 of greater exterior diameter and slightly larger interior diameter than the central casing section 13. It has a thickness over the major portion of its length about three times that of the section 13 which provides the main bore of the vessel 11.

In fabrication of the vessel, a suitable spacer is positioned on the mandrel to provide an interior surface 23 at the entrance end of slightly greater diameter than the central bore 15 and a short frustoconical transition section 25 leading to the central bore 15. The spacer may also be shaped to define an interior groove 21, or the spacer may be made in two parts, e.g. a separate unit might be used to form the groove and the transition section. Following vessel fabrication, removal from the mandrel, and removal of such a spacer, the entrance or bell end section 17 has an interior cylindrical entrance wall 23 of constant diameter which extends from a transverse flat end wall 24 to the short frustoconical transition surface 25 that leads to the interior bore 15 of the pressure vessel.

A bulbous annular region 26 is located in surrounding relationship to the groove 21. The pressure vessel may be provided with one or two side ports by simply cutting two diametrically opposed (or one) circular passageways through the enlarged entrance section sidewall, counterboring such passageways and then installing two side port fittings 27 within these radial passageways, as is well known in this art. For specialty vessels, additional ports, e.g. at 90° thereto, can be provided if desired.

FIG. 1 illustrates an end plug 29 that is used to effectively seal the end of the pressure vessel 11. The end plug 29 is circular in shape, having a peripheral surface formed as a section 31 of a right circular cylinder at its axially inward end, an annular shoulder 33 intermediate its width and a recessed front or axially outward region as a result of a circumferential recess 35 of rectangular, i.e. square, cross section that is formed in the otherwise flat front face 37 of the end plug 29. The diameter of the annular shoulder 33 is just greater than that of the central bore 15, but it is proportionally sized such that the end plug 29 is slidably received in the entrance end of the vessel, i.e. the diameter of the shoulder 33 is just slightly less than the diameter of the vessel entrance surface 23. This surface 23 of constant diameter extends from its flat front face 24 to the groove 21; the radially inward end of the groove is contiguous with the transition section 25. The plug 29 can be slid or inserted into the vessel until an oblique surface 39 on the shoulder abuts against the transition surface 25 of the vessel entrance. An axial passageway extends centrally through the end plug 29 which accommodates a circular cross section portion of a female tubular connector 41. the connector 41 receives a first male connector portion of an adapter 41a which has a second male connector portion that is received in the permeate conduit 43 of a cylindrical filtration cartridge 45, as well known in this art. Locking means in the form of a

segmented ring 47 is received in the groove 21 and secures the end plug 29 in place in the entrance end section 17.

To seal the interior of the pressure vessel, a seal plate 49 of molded polymeric material or the like is preferably provided, which seats against the axially inward surface of the end plug. The seal plate 49 has an interior hub through which the tubular connector 41 passes and is sealed by an O-ring 51 seated therein. An annular flange 53 near the exterior circumferential edge of the seal plate 49 is provided with a short lip 55 to create a pocket in which an annular seal 57 is accommodated. The seal plate 49 is locked in place against the end plug 29 by a shoulder on the connector 41 which seats and bears against an inner peripheral surface on the hub of the seal plate when the connector 41 is locked in place. Locking is effected when a snap ring 59 is received in a groove in the connector, with the snap ring seating against the flat front surface 37 of the end plug, as seen in FIG. 1.

The groove 21 is preferably V-shaped in cross-section. It has been found that, by shaping the groove 21 so its axially outward wall 61 is aligned at an angle between about 45° and about 70° to the centerline of the pressure vessel, a filament wound FRP pressure vessel will exhibit surprising strength in supporting the end plug 29 when under high interior pressure. This is the angle A marked in FIG. 4. Very generally, a groove with an outward wall near the lower end of such range, e.g. about 50° to 55°, would support an end closure that would effectively hold a high internal pressure; vice-versa, low pressure vessels might be formed with grooves with an outward wall with an angle A of about 60° to 65°. Both walls 61, 63 may be oriented at angles between about 45° and about 70° to the centerline; however, the angle of the axially inward wall is less critical. The axially inward wall is depicted on FIG. 4 as angle B and may be steeper by about 5° to 10° than

angle A. The groove 21 preferably has an arcuate innermost bottom surface 65 which interconnects the two walls.

The end plug 29, with the seal plate 49 and tubular connector 41 installed, is secured in closed position in the vessel entrance by a plurality of arcuate locking segments 47. Three segments 47, each being an arcuate segment of about 120°, may be preferred; however, two segments or four or more segments could be used if desired. Although it may be convenient for all of the segments to be the same size, such is not necessary, and different arcuate size segments may be used that preferably add up to about 360°. As best seen in FIGS. 3 and 5, the arcuate segments 47 each have a head portion and a root portion. The head has a radially inner, arcuate surface 67, which has substantially the same radius of curvature as that of the circumferential recess 35 of the end plug 31 (see FIG. 2). The portion of the head which extends forward of the root portion has a radially outer surface 69 with a radius of curvature substantially the same as the interior wall surface 23 of the entrance section of the vessel, and it has a flat front wall 70. The root portion has an angled wall surface that extends from the surface 69 and that is oriented to lie in abutting contact with the axially outward wall 61 of the groove 21. Thus, it is oriented to the arcuate surface 69 at an angle that is supplementary to angle A. The radially outer edge 72 of the root portion of the locking segment 47 is arcuate in cross section having a radius that is substantially the same as the bottom 65 of the groove 21. The axially inward or rear surface 73 of the root portion of the locking segment is preferably a flat wall 73 which extends upward to an arcuate surface 75 that is juxtaposed with the annular shoulder in its operative position. This radially interior surface 75 of the root portion is a right circular cylindrical surface that is essentially coaxial with the radially outer surface 69 of the front portion of the head. As can be seen in FIG. 2, the radially interior arcuate surface 75 of the root portion is aligned coaxially with the head radially outer arcuate surface 69 that lies

in abutting contact with the interior surface 23 of the entrance region of the pressure vessel. The arcuate surface 75 terminates at a flat rear surface 77 of the head portion, and when assembled, this radially interior arcuate surface 75 lies juxtaposed with the outer surface of the shoulder 33 of the end plug 29. Thus, in essence, the locking segment 47, in cross section, constitutes a head portion that lies above the cylindrical surface 23 of the vessel (within the bore region) and a root portion that is seated in the groove 21. The rear section of the head portion is seated in the circumferential groove 35 in the front flat surface 37 of the end plug 29, whereas the front section of the head extends forward thereof. To secure the end closure in locked position, there are three drilled and tapped holes 77 in the front surface 37 of the end plug that accept cap screws 79 or the like, as shown in FIG. 1. As best seen in FIG. 5, there are recessed pockets 81 formed centrally of each of the three locking segments 47 which provide clearance for the head of the cap screw 79. The head of the cap screw, when tightened, bears against the flat front surface 37 and the wall at the end of the pocket in the arcuate segment. Thus, each locking segment, seated in the groove 21, becomes clamped to the front of the end plug 29 when the respective cap screw has been tightened in the pocket 81 to cause engagement between the flat rear surface 77 of the head portion and the transverse wall of the circumferential recess 35 in the end plug.

In operation, the pressure vessel 11 is first loaded with the desired number of cylindrical filtration cartridges 45 or the like, and an adaptor 41a is inserted into the permeate tube 43 of the last one to be loaded. The end plug assembly, with the seal plate 49, the connector 41 and the various O-ring seals installed, is then carefully slid into the entrance end of the vessel so the end of the adapter 41a, which protrudes from the permeate tube of the last cylindrical filtration cartridge, is received in the chamfered end of the connector 41. The first male connector portion of the adapter 41a is elongated, and

its sliding fit with the connector 41 provides clearance to allow the plug assembly to be slid a bit more deeply into the vessel to open up in the region of the groove 21 to allow the three arcuate locking segments 47 to be inserted. The extent of entry of the end plug 29 is limited by engagement of the shoulder's oblique wall 39 with the transition surface 25 of the vessel. The respective right and left hand edges of each arcuate segment 47 are suitably angled (as seen in FIG. 5) to provide clearances to allow them to be individually readily inserted into the region between the installed end plug 29 and the groove 21 as a result of the clearance also provided by the circumferential recess 35 in the front flat face 37 of the end plug. The segments may be similarly indivudally readily removed therefrom. With all three segments 47 in place, the end plug 29 is then pulled slightly axially outward, using the threaded end of the connector 41, to the position shown in FIGS. 1 and 2. The three cap screws 79 are then inserted into the threaded holes 77 in the end plug so their heads enter the open regions provided by the pockets 81 ; the pockets are aligned with the threaded holes when the arcuate segments 47 are installed. Tightening of the cap screws 79 in the threaded holes clamps the head of each arcuate segment 47 against the flat transverse wall of the circumferential recess 35, tightly joining the three segments to the end plug 29.

For pressure vessels to be able to meet the specifications of ASME code and the like for use in such a high pressure environment, it must be shown that the end closures and the wall strength of the vessel itself are sufficient to withstand pressures to a substantial percentage above the rated value to be considered to be safe. In a closure for a full bore access vessel such as that shown in FIG. 1, the internal pressure will be axially outward on the end plug 29. The force of this pressure must be effectively resisted by the combination of the contour of the outer surface of the end plug, the locking segments 47 and the groove 21 in the pressure vessel. Whereas previously it was felt that a metal ring

with an internal groove needed to be embedded in a filament wound FRP pressure vessel to provide adequate strength, it has surprisingly been found that the combination of a V- shaped groove 21 formed in the interior surface of the FRP vessel in combination with appropriately contoured locking ring segments 47 that seat in a circumferential recess of rectangular cross section in the outer surface of the circular end plug 29 provide closure strength sufficient to meet code standards for even high internal pressures.

As depicted in FIG. 2, the axially outward force upon the end plug 29 is transformed into force vectors being exerted by the oblique walls 71 of the locking segments; these walls abut the axially outward wall 61 of the V-shaped groove. Because these force vectors are directed into the slightly bulbous portion of the entrance section 17 of the pressure vessel, they are strongly resisted by the strands of filament that are helically wrapped about the mandrel in the formation of a pressure vessel of this type. Representative vessel manufacture is disclosed in U.S. Patent No. 6,074,595 and international published application WO2006/110754, the disclosures of both of which are incorporated herein by reference. It can be seen from FIG. 2 that the natural result of such axially outward force upon the end plug being transmitted to the heads of the locking segments 47 would tend to create a torsional or twisting moment in the arcuate segments. However, the combination of the double shoulder arrangement, i.e. the three interengaging walls or surfaces aligned at 90° to one another (provided by the walls 67, 77 and 75 of the radially interior region of each locking segment, which walls seat against the three mating surfaces of the circumferential recess 35 of the end plug and the outer surface of the shoulder 33), extremely effectively resists such twisting moments that might otherwise result in deformation of locking segments and failure of the end closure in this fashion. Accordingly, it is found that, by orienting the axially outward wall 61 of the groove 21 at an angle A of between about 45° and 70°, and preferably between about 50° and 65°, the

aforementioned force vectors which are the result of high internal pressure are strongly resisted by the slightly bulbous wall of the entrance section of the pressure vessel. Both walls 61, 63 of the groove 21 may be oriented at the same angle so that angle A would equal angle B; however, it may be preferred to orient the axially inward walls 63 at slightly steeper angle, for example 5° to 10° steeper than angle A.

Although the invention has been described with regard to certain preferred embodiments which constitute the best mode presently known to the inventors for carrying out the invention, it should be understood that various changes and modifications as would be obvious to one having ordinary skill in this art may be made without deviating from the scope of the invention that is set forth in the appended claims. Although the description and illustration is one of a pressure vessel design for holding cylindrical filtration cartridges for use in crossflow filtration, it should be understood that this concept of an end closure for a pressure vessel may be employed likewise for any other types of cylindrical cartridges for filtration or other purposes. Moreover, these end closure arrangements can be effectively incorporated in filament wound FRP vessels that are used for other types of high pressure operations where a cylindrical cavity is desired to house objects of like shape that can be inserted by sliding therethrough.

Particular features of the invention are emphasized in the claims that follow.