Abstract:
Embodiments of a system and method for sealing an end of a flowline to an end fitting are disclosed. Such methods include providing an end fitting housing having a bore, wherein a portion of the bore has a tapered inner surface, inserting an open end of a flexible pipe into the bore, the flexible pipe having an external layer, to create a tapered annular space between the tapered inner surface and the external layer, and positioning a ring into the tapered annular space such that the ring radially contracts upon the external layer causing the external layer to deform to create a seal.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation-in-part of Ser. No. 09/689,075, entitled High Temperature End Fitting and Method of Use, filed on Oct. 12, 2000 now U.S. Pat. NO. 6,592,153 which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates in general to end fittings that retain and seal at least one open end of flexible pipe, and in particular to high temperature end fittings. 
     BACKGROUND INFORMATION 
     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, plasticized state, 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. 
     Despite recognition of the forgoing, it has not been previously known how to satisfactorily eliminate the loss of tension and sealing of the flowline that can occur as described above. 
     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. 
     These and other features, and advantages, will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only form of the invention. 
    
    
     
       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  77  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. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components, signals, messages, protocols, and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to limit the invention from that described in the claims. Well-known elements are presented without detailed description in order not to obscure the present invention in unnecessary detail. For the most part, details unnecessary to obtain a complete understanding of the present invention have been omitted inasmuch as such details are within the skills of persons of ordinary skill in the relevant art. 
     Referring now to  FIG. 1  of the drawings, there is illustrated a prior art end fitting designated  11  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  comprises an annular body  13  adapted to receive a flexible flowline  12  which comprises an interior or carcass layer  14  and an exterior or barrier layer  16 . An inner seal ring  18  presses against the external surface of the barrier layer  16 . A sleeve  20  is received intervening between the carcass layer  14  and the barrier layer  16 . As shown, the seal ring  18  is compressed between the interior wall surface of the annular body  13  and the exterior surface of the barrier layer  16 . The barrier layer  16  may be of a relatively soft material, such as polymer. The polymer may be of many different types, such as polyvinylidene fluoride (PVDF). PVDF has a relatively high thermal expansion coefficient and softens when heated to its maximum service temperature. The sleeve  20  is placed below the seal ring  18  in order to provide increased support for the compressive forces that result from deforming the seal ring  18  into the barrier layer  16 . The carcass layer  14  is typically steel or stainless steel. Because the carcass layer  14  and the body  13  are typically made from steel or stainless steel, their thermal expansion coefficient is much less that the barrier layer  16 . Thus, under heat, the barrier layer  16  undergoes stress relaxation and the compressive forces transferred by the barrier are reduced. When cooled, the barrier layer  16  has lost some of its ability to recover and tends to shrink away from the seal ring  18 , which could cause the connection to fail. On the other hand, some embodiments may not include a sleeve  20 . In this case, the barrier layer  16  is supported by the carcass layer  14 . 
     Referring to  FIG. 2 , there is an illustrated exemplary end fitting  10  incorporating one aspect of the present invention. Only the top half of the end fitting  10  is illustrated in  FIG. 2  because the lower half is symmetrical with the top half. The end fitting  10  includes an annular body  22 , an inner collar  24 , a body ring  26  and a barrier sleeve  27 . An interior surface of a counter-bore  28  in the body  22  and an exterior surface of a barrier layer  16  defines a wedge-like tapered recess  30 . A tapered wedge-shaped seal unit  31  is positioned within the recess  30 . In the illustrative embodiment, the seal unit  31  comprises a housing ring  32  and a housing drive-ring  34 . The housing ring  32  may be made from a compressible metal, such as an annealed corrosion resistant metal, or a relatively hard polymer, such as polyphenylene sulfide or other deformable material compatible with fluids to be conveyed through the flowline. The housing ring  32  is generally wedge shaped so as to fit within the tapered recess  30 . The housing ring  32  may have annular grooves defined on its interior surface, such as annular groove  37 . A compressible seal  38 , such as an elastomeric O-ring, may be positioned within the annular groove  37 . Similarly, the housing ring  32  may have an annular groove  39  defined in its exterior surface. A compressible seal  40  may be positioned annular groove  39 . 
     In operation, a plurality of bolts  42  radially positioned around the fitting  10  are tightened which causes the inner collar  24  to move closer to the annular body  22 . As the inner collar  24  moves closer, the drive ring  34  is also moved closer to the annular body  22 . The movement of the drive ring  34  causes an axial force on the seal unit  31  thereby driving the seal unit  31  further into the recess  30 . The axial force on the seal unit  31  also causes the seal unit to deform in a radially inwardly direction towards the underling barrier layer  16 . This deformation reduces the inside diameter of the housing ring  32  by forcing it onto a mating part of the end fitting which has a diameter smaller than that of the housing ring. This reduction in diameter of the housing ring  32  causes the surface of the barrier layer  16  to deform until all gaps between the barrier layer  16  and the seal unit  31  are eliminated. Flexible seals, such as the seals  38  and  40 , may also be used to further reinforce the seal in the event of additional relaxation of the barrier layer  16 . 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 barrier of the received flowline. By forcing the housing ring  32  onto the polymer barrier surface  16 , any surface irregularities are gradually reduced until the gaps between the housing ring and the barrier layer  16  are significantly reduced or eliminated. By reducing the gaps, the problem of potential extrusion of the flexible seals is also significantly reduced. 
     Alternative embodiments are shown in  FIGS. 3 and 4 . For brevity and clarity, a description of those parts which are identical or similar to those described in connection with the first embodiment will not be repeated here. Reference should be made to the foregoing paragraphs with the following description to arrive at a complete understanding of additional embodiment. 
     Referring now to  FIG. 3 , there is illustrated an end fitting  10  which includes a tubular insert  43  secured via bolts  44  to a body  49 . A counter-bore  45  within the insert  43  accommodates receipt of the flexible pipe end  12  while an internally extending plastic cover  46  encircles the pipe at an entrance  48 . Corrugated wires  50  are secured in epoxy  52  to maintain the structural integrity of the unit. Contained within the end fitting are the inner seal unit  31   a  with its housing ring  32   a  in a tapered recess  30   a.  In this embodiment, there is also an outer seal unit  53 . 
       FIG. 4  is a detail view of the seal unit  31   a  and surrounding components from the embodiment illustrated in  FIG. 3 . An interior surface  41  of a counter-bore defined in the tubular insert  43  and the exterior surface of a barrier layer  16  defines a wedge-like tapered recess  30   a.  The tapered wedge-shaped seal unit  31   a  is positioned within the recess  30   a.  In the illustrative embodiment, the seal unit  31   a  comprises the housing ring  32   a  and a housing drive-ring  34   a.  The housing ring  32   a  is generally wedge shaped so as to fit within the tapered recess  30   a.  The housing ring  32   a  may have annular grooves defined on its interior surface, such as annular groove  37   a.  A compressible seal  38   a,  such as an elastomeric O-ring, may be positioned within the annular groove  37   a.  Similarly, the housing ring  32   a  may have an annular groove  39   a  defined in its exterior surface. A compressible seal  40   a  may be positioned in the annular groove  39   a.    
     The operation of this embodiment is similar to the one described with reference to  FIG. 2 . When a plurality of bolts  47  are tightened, an inner collar  24   a  moves closer to the tubular insert  43 . As the inner collar  24   a  moves closer, the drive ring  34   a  is also moved closer to the tubular insert  43 . The movement of the drive ring  34   a  causes an axial force on the seal unit  31   a  thereby driving the housing ring  32   a  further into the recess  30   a.  The axial force on the seal unit  31   a  also causes the seal unit to deform in a radially inwardly direction towards the underling barrier layer  16 . This reduces the inside diameter of the housing ring  32   a  and the drive ring  34   a  by forcing them onto a mating part of the end fitting which has a diameter smaller than that of the housing ring. This radial deformation causes the surface of the barrier layer  16  to deform until all gaps between the barrier layer  16  and the seal unit  31   a  are eliminated. Flexible seals, such as the seals  38   a  and  40   a,  may also be used to further reinforce the seal in the event of additional relaxation of the barrier layer  16 . 
     Turning back to  FIG. 3 , one skilled in the art would realize that a similar situation occurs with respect to the outer seal unit  53 . When a plurality of bolts  57  are tightened, an outer collar  59  moves closer to the body  49 . As the outer collar  59  moves closer, the housing drive ring  55  is also moved closer to the body  49 . The movement of the drive ring  55  causes an axial force on the seal unit  53  thereby driving the housing ring  54  further into the recess  56 . The axial force on the seal unit  53  also causes the seal unit to deform in a radially inwardly direction towards the underling plastic cover  46 . This reduces the inside diameter of the housing ring  54  and the drive ring  55  by forcing it onto the plastic cover  46  which has a diameter smaller than that of the housing ring. This radial deformation causes the surface of the plastic cover  46  to deform until all gaps between the plastic cover  46  and the seal unit  53  are eliminated. Flexible seals, such as the seals  38   b  and  40   b,  may also be used to further reinforce the seal in the event of additional relaxation of the barrier layer  16 . 
     Some end fitting constructions may optionally also include a middle seal unit similar to and axially between inner and outer seal units  31  and  53 . A detail of one such embodiment is illustrated in  FIG. 5 , which illustrates a middle seal unit  60 . A housing ring  62  is wedged into a tapered recess  64  of a collar  66 . Included within the housing ring  62  are opposite elastomeric seals  38   c  and  40   c,  which are similar to seals  38  and  40  described above. In this embodiment, a collar  67  can be used to drive the housing ring  62  into the tapered recess  64  when a plurality of bolts  69  are tightened. As illustrated, once the housing ring  62  is in place, the layer  16  deforms in a radially inward direction to accommodate the housing ring  62 . 
       FIGS. 6 and 7  are section views of one embodiment of a housing ring, such as the housing ring  32 , which could be used in various embodiments of the invention. Housing rings  54  and  62  could be of a similar configuration but with different diameters. In one embodiment, the housing rings  32 ,  54 , and  62  may be formed of hard metal, having a cross sectionally tapered section as illustrated in  FIG. 6 . An outside surface  72  of the ring may include one or more annular grooves, such as the groove  37  in which to contain an elastomeric or flexible resilient seal, for instance an O-ring seal  38 . Optionally, the housing rings can also include one or more internal grooves, such as groove  39 , on the interior surface  78  for receiving an additional seal, such as an o-ring seal  40 . 
       FIGS. 8 and 9  illustrate one embodiment of a drive ring, such as the drive ring  34 . The drive ring  34  is 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 coupled to 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 the barrier layer  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. 
     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. 
     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. Furthermore, embodiments of the present invention work with flowlines which have barrier layers and flowlines which do not have barrier layers. 
     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. 
     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments. Accordingly, all such modifications are intended to be included in the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.