Abstract:
An end fitting in which to receive a flexible pipe end to be joined includes an annular seal unit comprised of a resilient elastomeric composition contained in a tapered rigid housing ring force fit in a tapered recess of a surrounding component so as to engage the outer surface of the received pipe end.

Description:
FIELD OF INVENTION 
     The field of art to which the invention relates comprises end fittings that retain and seal at least one open end of flexible plastic pipe for attachment to suitable utilization apparatus. 
     BACKGROUND OF THE INVENTION 
     A flexible flowline is comprised typically of several distinct concentric layers that afford strength and flexibility to the flowline. The innermost layer, known as the carcass, prevents collapse of the flowline due to external hydrostatic pressure. The immediately adjacent layer, known as the barrier, is constructed from a synthetic polymer material and serves to prevent content leakage. There may also be succession of other layers of varying materials forming the overall composite of the flowline. 
     A flexible flowline may be utilized, for example, as a dynamic riser to couple a rigid flowline or another flexible flowline on the seabed to a floating vessel or buoy to convey production fluids such as oil, gas or oil/gas mixtures under pressure from an oil/gas well or platform to the vessel or buoy. An end fitting can be utilized to couple the flexible flowline at each end to an adjacent flowline or wellhead and the vessel or buoy. 
     One or more leak-tight seals contained in the end fitting has been achieved in the manner of the prior art utilizing a seal ring which, for example, encircles and engages the external surface of the barrier layer. This ring holds the barrier and carcass layers in position within the end fitting by a frictional force generated from the pressure of the seal ring on the barrier layer. 
     While functioning well, problems with the foregoing seals have arisen inside the end fitting where the flowline and end fitting are subjected to extreme fluctuations in temperature. Such extremes are known to occur in the flowline and end fitting when they are, for example, subjected to repeated changes in temperature as where, the flowline may be exposed to a temperature in excess 100° C. when production fluid is conveyed through the flowline and subsequently may be exposed to temperatures on the order of 0° C. from sea water when flow of the production fluid is interrupted or discontinued. 
     Repeated thermal cycling in the foregoing manner can result in a loss of seal integrity due to stress relaxation and creep of the barrier layer, followed by loss of compression at the seal. That is, with the seal area being highly stressed in compression, the flowline material at the beginning of service is often in its most highly plasticized state. This, however, deteriorates with time until ultimately a loss in barrier thickness occurs and a state of equilibrium is reached. Once compression at the interface of the seal ring and barrier declines to a low but non-zero level, loss of fluid content in the flowline can occur. Phenomena such as thermal expansion and creep can work to reduce or eliminate compression between the seal ring and the polymer layer. 
     Various forms of end fittings are disclosed in U.S. Pat. Nos. 1,817,776; 2,264,480; 2,341,164; 2,444,380; 3,995,897; 4,773,680; and 5,639,128. 
     Despite recognition of the foregoing, it has not been known heretofore how to satisfactorily eliminate the loss of tension and sealing of the flowline that can occur as described. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the invention to provide an enhanced seal for an end fitting capable of increasing the sealing properties against a flowline received therein. 
     It is further object of the invention to effect the previous object with a seal that is operative to compensate or be unaffected by adverse thermal effects encountered during service. 
     It is a further object of the invention to effect the previous objects with a seal of economical construction so as not to contribute to costly increases in the overall cost of the fitting. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved seal construction for an end fitting in which an open end of flexible flowline is to be received. More specifically, the invention relates to such an end fitting in which a novel seal construction is provided capable of functioning to compensate, offset or be unaffected by the adverse effects of temperature swings to which the fitting is exposed in service. 
     The foregoing is achieved in accordance with the invention by means of one or more seal units containing resilient seals of selected shape and assembled into a seal housing ring having a tapered outer surface received in a complementary recess of a surrounding wall. The housing ring may contain a sole or opposite resilient seals assembled thereon. The ring with seals is then axially forced into the surrounding recess by means of a displaceable drive ring. This reduces the inside diameter of the housing ring by forcing it onto a mating part of the end fitting which has a diameter smaller than that of the housing ring. As a result of the foregoing, the seal, or seals provide a means to seal against an irregular surface which may, for example, be an extruded polymer tube such as the flexbarrier of the received flowline. By forcing the housing ring onto the polymer tube, any surface irregularities are gradually reduced until any gaps between the housing ring and the polymer tube are eliminated. By eliminating the gaps, the problem of potential extrusion of the resilient seal is likewise eliminated. 
     A key to operability of the seal unit is the use of a compressible metal or relatively hard polymer housing for the seal to deform the mating layer in such a way as to eliminate the gaps. For these purposes, the seal housing may comprise an annealed corrosion resistant metal, a relatively hard polymer such as polyphenylene sulfide or other deformable material compatible with fluids to be conveyed through the flowline. Such construction can be used to seal high pressures since extrusion of the resilient seals is precluded. At the same time, the seal is superior to existing mechanical seals used in flexible pipes or hoses since mechanical seals require mechanical compression between the seal ring and the polymer layer. Moreover, the construction is not limited to the fluid sealing layer of flexible pipe since it can be readily applied to any extruded polymer layer of a flexible pipe or hose. 
    
    
     The above noted features and advantages of the invention as well as other superior aspects thereof will be further appreciated by those skilled in the art upon reading the detailed description which follows in conjunction with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a prior art end fitting containing a received pipe end to be secured; 
     FIG. 2 is a sectional view of an exemplary end fitting containing the improved seal unit construction in accordance with the invention; 
     FIG. 3 is a further sectional view of an end fitting containing multiple seal constructions in accordance with the invention; 
     FIG. 4 is an enlarged sectional elevation of a seal hereof as utilized in the end fitting of FIG. 3; 
     FIG. 5 is a further enlarged sectional elevation of a seal construction at a different location in an end fitting in accordance with the invention; 
     FIG. 6 is a sectional elevation of the seal housing of the invention; 
     FIG. 7 is an enlarged sectional view of the encircled portion  7 — 7  of FIG. 6; 
     FIG. 8 is a side elevation of the seal drive ring; and 
     FIG. 9 is a front elevation of the seal drive ring. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals receptively. The drawing figures are not necessarily to scale and in certain views, portions may have been exaggerated for purpose of clarity. 
     Referring now to FIG. 1 of the drawings, there is illustrated a prior art end fitting designated  10  as disclosed, for example, in U.S. Pat. No. 5,639,128 incorporated herein by reference and available from commercial sources such as Wellstream, Inc. of Panama City, Fla. Briefly, the end fitting  11  receives a flexible flowline  12  including a carcass layer  14  and a barrier layer  16 . An inner seal ring  18  presses against the external surface of barrier layer  16 . A sleeve  20  is received intervening between carcass  14  and barrier  16 . As shown, seal  18  is compressed between the interior body wall surface  21  and the exterior surface of barrier layer  16 . 
     Referring to FIG. 2, the exemplary end fitting  10  hereof includes an annular body  22 , an inner collar  24 , a body ring  26  and a barrier sleeve  27 . A counter-bore  28  in body  22  defines a wedge-like tapered recess  30  in which to receive a tapered wedge-shaped seal unit  31  in accordance with the invention as will be described. The seal unit  31  comprises a housing ring  32  and a housing drive-ring  34  both forced into the wedge-like recess  30  in the course of bolts  42  being tightened so as to condense and wedge housing ring  32  inwardly within the recess. On bolts  42  being tightened, elastomer seal  38  between the barrier wall of pipe end  12  and ring  34  is compressed while opposite seal  40  is compressed concomitantly between the inner surface of recess  30  and the ring  34 . 
     As shown in FIGS. 3 and 4, end fitting  10  includes a tubular insert  42  secured via bolts  44  to body  22 . A counter-bore  45  within insert  42  accommodates receipt of flexible pipe end  12  while an internally extending plastic cover  46  encircles the pipe about entrance  48 . Corrugated wires  50  are secured in epoxy  52  that serve to maintain integrity of the unit. Contained within the end fitting are an inner seal unit  31  with its housing ring  32  in tapered recess  30  and an outer seal unit  53  with its housing ring  54  in tapered recess  56 . Both housing rings, are identical with the latter including opposite elastomeric seals  38  and  40  compressed intervening between the surface of recess  56  and plastic cover  46 . As above, the drive ring  34  and housing ring  32  are forced axially inward of recess  30  when tightening bolts  47 . 
     Some end fitting constructions may optionally also include a middle seal unit  60  similar to and axially between inner and outer seal units  31  and  53  above as best seen in FIG.  5 . Housing ring  62  is wedged into tapered recess  64  of a collar  66 . Included within housing ring  62  are opposite elastomeric seals  38  and  40  as above. 
     As best seen in FIGS. 6 and 7, the various housing rings  32 ,  54 , and  62  are formed of hard metal, cross sectionally tapered about their annular peripheries  72 . O.D.  72  of the ring includes an annular groove  74  in which to contain an elastomeric, resilient and preferably O-ring seal  40 . Optionally, one or more of the rings can also include an internal groove  76 , about the interior surface  78  for receiving an additional and similar O-ring seal  38 . It will be appreciated that sealing can be effective with only an inner o-ring  38  using a metal-to-metal seal about the exterior. However, also using an exterior O-ring  40  affords more forgiving of surface imperfections. 
     As shown in FIGS. 8 and 9, the hard metal drive rings  34  are tapered similarly as the housing rings and include side cuts  80  to permit a controlled collapse in the course of being forced into its receptive recess behind a seal ring. The resilient seals  38 ,  40  can be O-ring, cup seal, X-ring, or other suitable shape that can be assembled into a receptive groove within a housing ring  32 ,  54  and  62 . On being forced into an encircling body with a matching taper but having a diameter smaller than that of the housing ring the inside diameter of the housing ring is caused to be reduced. 
     In this manner, sealing is provided and maintained against any irregular surface which may be an extruded polymer tube such as barrier  16 . By forcing the housing ring onto the polymer tube, any irregularities are gradually reduced until gaps between the housing ring and the polymer tube are eliminated. By eliminating the gaps, the potential for extrusion of the resilient seal is likewise eliminated. 
     Significant for the foregoing is the use of a compressible metal seal housing ring or relatively hard polymer housing ring for the seal to deform the mating layer in such a way as to eliminate gaps. The design can be used to seal high pressures since extrusion of the resilient seal is avoided. Moreover, it is superior to existing mechanical seals used on flexible pipes or hoses since mechanical seals require mechanical compression between the seal ring and the polymer layer. Phenomena such as thermal expansion and creep can work to reduce or eliminate such compression. 
     At the same time, such construction is not limited to the fluid sealing layer of flexible pipe, since it can be readily applied to any extruded polymer layer in a flexible pipe or hose. By means thereof, a resilient seal applied directly to an extruded polymer layer, and housed in a metal housing which is forced onto the polymer layer to eliminate gaps, the previous problems associated with temperature induced seal failure in an end fitting is substantially if not completely eliminated. 
     By the above description there is disclosed a novel seal construction for an end fitting that contributes significantly to the overall reliability of the end fitting per se. It achieves the intended result with only minor changes in construction so as not to contribute to any significant cost increase in manufacture of the overall end fitting. The virtues thereof can be readily appreciated by those skilled in the art. 
     Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.