GB2121499A - A pressure compensated breakaway pipe coupling - Google Patents

Abstract

A breakaway pipeline coupling comprises first and second pipe sections 12, 14 which cooperate to form a fluid seal and are designed to separate at a predetermined tensile load. A plurality of piston 20 and cylinder 18 pressure compensating devices are arranged around the exterior of the sections to hold them together until separation. Shear pins or shear studs 52 passing between the pipeline sections fail when the coupling is subjected to external load exceeding the predetermined value. The pressure compensating devices which apply a compression load on the coupling to counteract the tension load exerted by internal pressure in the pipeline include pistons movable axially within cylinders in response to pressure differentials, and tubes 24 for exposing one side of the piston to the internal pressure within the coupling. Shut-off valves 70 installed in one or both of the pipe sections prevent loss of fluid upon coupling separation. <IMAGE>

Description

SPECIFICATION A pressure compensated breakaway pipe coupling This invention relates generally to breakaway pipeline couplings designed to separate when subjected to externally applied tensile loads exceeding a predetermined limit in order to prevent permanent structural damage to other piping components. More particular ly, this invention relates to breakaway pipeline cou- plings utilizing pressure compensating mechanisms to counteract tensile loads produced by internal pressure which might otherwise cause the coupling to separate.

Breakaway pipeline couplings for use in pipelines for transmitting oil, gas and otherfluids are known.

One commercially available breakaway pipe coupling is described in U.S. Patent 4,059,288, issued November 22, 1977 to Harvey O. Mohr. Another commercially available breakaway pipe coupling is described in European PatentApplication Publication No.

0006278A1.

The Mohr patent discloses a separable safety pipeline connectorwhich will separate at a predetermined externally applied tension, but which will be insensitive to variations in tension caused by internal pipeline pressure. The connector includes a housing having one axial end adapted for connection to the pipeline, and with the other axial end open. The connector includes a pipe extension member having one axial end adapted for connection to the pipeline for transmission of line fluids therethrough and with the other axial end arranged to telescope coaxially with the housing in sealed relationship therewith. A shear disc is mounted between the housing and extension memberfor restraining the same against axial separation in response to axial tension loads applied thereto.The shear disc is sized to rupture at a predetermined axial load level, so that axial separation is prevented below such a load level. The housing and extension member define an annular chamber therebetween, whereby fluid pressure within the chamberforcesthe housing and extension member axiallytogetherto thereby balance line pressure. A port is provided through the extension memberto communicate line pressure to the chamber.

The pressure balanced, breakaway pipe couplings disclosed by both the aforementioned Mohr patent and Thompson application recognize the need for compensating internal pipeline pressures, but do not address other structural and functional needs. For example, both the aforementioned couplings are expensive to fabricate and install, due, at least in part, to the several large-diameter, concentric, precision machined surfaces which must be provided in the pressure compensation chamber and piston apparatus. Furthermore, the Mohrcoupling makes no provision forterminating the fluid flow th rough the coupling upon its separation, thus allowing the contents of the pipeline to be discharged into the environment.

With the deficiencies of known breakaway pipeline couplings clearly in mind, the present invention contemplates a breakaway pipeline coupling utilizing a plurality of piston and cylinder mechanisms. These mechanisms provide pressure compensation and are arranged external to the pipeline coupling sections.

These piston and cylinder mechanisms are simpleto manufacture and are easy to maintain. The cylinders are ported to the interiorofthe pipeline to provide compressive forces that counteractthetension forces produced in the pipeline by internal pressure.

The present pipeline coupling utilizes butterfly valves which are positioned to interlock in the open position. Immediately upon relative movement between the coupling sections, the valves are closed in order to stop fluid flow. Thus, excessive spillage of fluid from the separated coupling sections is averted.

Numerous other advantages of the embodiments of the present breakaway pipeline coupling will become apparent from the following detailed description considered in conjunction with the accompanying drawings.

The invention is described with reference to the drawings wherein Fig. 1 is a cross-sectional view through a preferred embodiment of a pressurecompensated breakaway pipe coupling constructed in accordance with the principles ofthis invention; Fig. 2 is an end view of the pipe coupling of Fig. 1, such view being taken along line 2-2 of Fig. 1; Fig. 3 is a view similar to Fig. 1, but showing the coupling sections of the pipeline coupling fully separated; Fig. 4 is a cross-sectional viewthrough an alternative embodiment of a connected pressure-compensated breakaway pipe coupling, said embodiment featuring two butterfly valves, one valve disposed in each coupling section; Fig. 5 is a view of the embodiment of Fig. 4with the coupling sections separated and the valves in a closed position; and Fig. 6 is a schematic view of the breakaway coupling ofthis invention shown in situ ata typical application; an offshore mooring for tankers.

Both embodiments of the present breakaway pipe coupling can be used in diverse marine terminal applications. For example, referring to Fig. 6, the breakaway pipe coupling devices shown in schematic only, could be interposed between sections offloating hose 101 attachedto a buoy 102 in acatenaryanchor leg mooring (CALM), or could be positioned between sections of underwater hose 103 connecting the buoy 103 with an underwater pipeline manifold 104. The breakaway pipe coupling could also be utilized between the underwater pipeline manifold 104 and the pipeline 105 or at any point in the pipeline.

Alternatively, the coupling could be positioned be tween a hose string and the pipeline manifold at a multiple buoy mooring. At a pier, the coupling could be utilized effectively in loading arms, or between hoses and piping on the pier. Several other marine terminal applications and many other pipeline and hose system applications are also envisioned.

Referring to Figs. 1 to 3, sectional views of the The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

pipeline coupling device 10 ofthis invention are shown. The coupling device 10 is designed to fix in a portion of a pipeline or hose system as schematically shown in Fig. 6, and comprises a first coupling cylindrical section 12, which is coaxially fitted (telescoped) within a second coupling cylindrical section 14. These coupling sections are in sealing arrange menu with each other such that fluid will pass through the coupling and said pipeline. Seals 92 prevent leakage offluid from the interface between the two coupling sections. The coupling device 10 may be integral with the pipeline as is coupling section 12 or may be bolted into the pipeline the end flange 22.The coupling sections 12 and 14 are secured together by a plurality of pressure compensation cylinders 16, which structurally bridge between the coupling sections, andwhich comprise a cylinder 18 and a piston 20 disposed therein and a shaft 36 attached to the piston and extending from the cylinder. Pressure lines 24 communicate between the interior 26 of cou pler section 14to the interior 28 of the piston shaft end of each cylinder 28.

Each pressure compensation is connected by a cylinder 16 pin 30 to a trunnion 32 secured to and extending from the outer surface 34 of coupler section 14.

In each pressure compensating cylinder 16the piston shaft 35 extends from the piston 20 through each cylinder 18to asplitcollar40 movably disposed in a fluted opening 42 in a nut retaining flange 44 extending from coupling section 14. The shaft 36 has an annular lip 46 which fits in a groove 48 of said collar 40 and affixes the shaft 36 to the split collar 40.

Aflange 50 extending from coupling section 12 is secured to the flange 44 of section 14 by a plurality of shear pins 52, which are arranged peripherally about and extend radiallythrough mating flanges 44 and 50, as shown in Fig. 2.

Ashaft58 is bolted to flange 50 via nut 54 and is affixed to the split collar40 by means of an annular lip 60, which fits in groove 62 ofthe collar 40.

Coupling section 14 has a butterfly valve disk 70 pivoted therein upon shaft 72 extending through the walls of section 14 as shown. An arm 74 mounted on shaft72 is connected through a spring 78 attached to the nut retaining flange 44. This spring biases the butterfly valve disk 70 against (arrow 75) stop 76 which extends across coupling section 12.

The pressure compensation operation of the invention will be explained with particular reference to Figs.

1 and 2.

Cylinders 16 apply a compression force on the breakaway pipeline coupling 10 to counteractthe tension load exerted by internal pressure. Pressure communicated from the interior of pipe section 14to the cylinders 18 act against the pistons 20 and through shafts 36 and 58 tend to drawflange 50 towards the cylinders.

To illustrate, let N cylinders be used for pressure compensation, each cylinder having an internal diameter d1, and a shaft diameterdz, as shown in Fig. 2.

Thus, at a pressure P, the to compressive force ovortori bathe cviinders is: F = NP

The tension exerted by the internal pressure in the pipe sections 12and 14, which have an internal diameter D, is:

Since it is intended thatthe compression force (Fc) equalsthetensionforce (Ft) in ordertoachieve complete pressure compensation, it follows that: N N (d12 - d22) =D2.

Applying these mathematical relationships to the pressure compensating mechanism of Figs. 1 and 2, four cylinders, each with an internal diameter of 11.75 inches and a 1.25 inch diametershaft,would essentially balance pressure within a 23.25 inch interior diameter pipe.

The pressure compensating cylinder arrangement ensuresthatthere is no appreciable change in the load applied to the shear studs 52 as a result of changes in the internal pressure in the pipe. However, any change in the tension load due to external forces on the pipeline system is applied to the shear studs 52.

The breakaway operation of the breakaway pipe coupling 10 is readily apparentfrom a comparison of Figs. 1 and 2 with Fig. 3.

The shearstuds 52 are sized to separatewhen a predetermined tension load is applied tending to separate coupler sections 12 and 14. When the shear studs 52 separate coupler sections 12 and 14. When the shear studs 52 separate as a result of a tension load higherthan the design load, the pipe sections 12 and 14 begin to separate, as shown in Fig. 3. The separation causes the piston shafts 36to extend and the collar-retaining flange 44 to move back from its normal position overthe split collars 40. The split collars 40thus move out of the openings 42 in flange 44. As soon as the split collars 40 are free from the openings 42 in flanges 44,they separate in halves 40A and 40B, thereby disconnecting the piston shafts 36 and 58.The pipe sections 12 and 14 are then completely separated.

The valve closure operation of the breakaway pipe coupling 10 is readily apparentfrom a comparison of Figs. 1 and 2 with Fig. 3. In the normal position, Figs. 1 and 2 the valve 70 is held against the stop 76 by tension in the spring 78. The butterfly valve disk70 is released from stop 76 and pivots about shaft 72 when the couplersections 12 and 14 separate and seats againstvalve seat 80. (Fig. 3). The spring 78 drivesthe butterfly valve to its closed position against seat 80 and holds itthere. In the closed position the valve preventsflowthrough pipe section 14 when the pipeline coupling sections 12 and 14 are discon nected.

The breakaway pipeline coupling 10 can easily be serviced,forthe cylinders 16 can be removed and replaced without disassembly of the entire coupling.

The cylinders 16can be disassembled, repacked, and reassembled in the field without special tools.

Now referring to Figs. 4 and 5, another embodi ment is shown for the butterflyvalve disk70.lnstead of having the valve disk 70 abut against stop 76 as shown in Fig.I,this 1, this embodimentfeatures a second butterfly valve disk 90 disposed in section 12 which interlocks with the first butterfly valve disk in section 14, that is butterfly valve disk 70 is spring biased (arrow 75) towards valve disk 90, and valve disk 90 is similarly spring biased towards valve disk 70 (arrow 85) such that each valve disk is locked in the open position when coupling sections 12 and 14 are secured, as shown in Fig. 4.

Upon separation of coupling sections 12 and 14, as shown in Fig.5, each butterfly valve disk 70 and 90, respectively is free to close, because the other valve disk is not blocking its rotation to its closed position, that is, valve 70 seats against seat 80, and valve 90 seats against seat 95, as shown.

Claims (20)

1. A pressure compensated pipeline coupling, comprising: (a) first and second coupling sections, normally joined together such that fluid can flow through said coupling sections; (b) locking means between said coupling sections for securing said sections together, said locking meansadaptedto release in responsetotensile loads exceeding a predetermined limit, thus allowing said coupling sections to separate; and (c) pressure compensation means associated with said locking means and said first and second coupling sections for exerting compressive force upon said locking means, said pressure compensation means including a plurality of cylinders mounted externally of said coupling sections, said cylinders in fluid pressure communication with said fluid within said coupling sections.

2. A pressure compensated pipeline coupling as defined in claim 1, wherein said pressure compensation means comprises a plurality of cylinders secured to the exterior of said coupling sections and extending axiallytherealong, each said cylinder containing a movable piston.

3. A pressure compensated pipeline coupling as defined in claim 2, which includesfirstattachment means which are speced circumferentially about an exterior portion of said first coupling section, and wherein each of said cylinders is secured to one of said first attachment means points.

4. A pressure compensated pipeline coupling as defined in claim 3, which includes means defining an end wall in each cylinder having an aperture therein, and a piston shaft extending axially from each of said piston and projecting through each of said aperture.

5. A pressure compensated pipeline coupling as defined in claim 4, which includes second attachment means spaced circumferentially about an exterior of said second coupling section and each said piston being secured to one of said second attachment means.

6. A pressurecompensated pipeline coupling as defined in claim 5, which includes conduit means connected between an interior portion of one of said coupling sections and an interior portion of each of said cylinders on a piston shaft side of said cylinders such that each of said piston shafts exert compressive force on said locking means proportional to the fluid prnssurewithin said coupling sections.

7. A pressure compensated pipeline coupling as defined in claim 6, wherein the sum of effective interior cross-sectional areas on the piston shaft side of said cylinders is essentially equal to an interior cross sectional area of said coupling sections, such that the total compressive force exerted by said piston shafts is essentially equal to the tension force exerted on said locking means by fluid pressure within said coupling sections.

8. A pressure compensated coupling as defined in claim 7, wherein each of said piston shafts separate from said attachment means when said locking means release.

9. A pressure compensated coupling as defined in claim 8, wherein said locking means comprises shear studs arranged between said first and second coupling sections.

10. A pressure compensated coupling as defined in claim 9, wherein each of coupling sections include at least one flange and said shear studs are arranged on each flange.

11. Avalve sealed pipeline coupling, comprising: (a) first and second coupling sections, normally joined together; (b) locking means joining said first and second coupling sections such that fluid can flow through said coupling sections; (c) valving means pivotally mounted in said first coupling section; and (d) means disposed in said second coupling section, for normally holding said valving means in the open position, when said first and second coupling sections are joined.

12. Avalve sealed pipeline coupling as defined in claim 11 wherein said valving means comprises a valve disk, and wherein said holding means bears against said valve disk preventing itfrom moving to the closed position, and wherein said valve disk is free of said holding means when said coupling sections separate, thus allowing said valving means to close.

13. Avalvesealed pipeline coupling as defined in claim 12 which includes a spring associated with said valve disk wherein said valve disk is biased to a closed position by said spring.

14. A valve sealed pipeline coupling as defined in claim 13 wherein said locking means are adapted to release in response to tensile loads exceeding a predetermined limit, thus allowing said coupling sections to separate.

15. Avalve sealed pipeline coupling as defined in claim 14which includes pressure compensation means associated with said locking means for exerting compressive force upon said locking means, pressure compensation means being in fluid pressure communication with said coupling sections.

16. Avalvesealed pipeline coupling as defined in claim 12 wherein said holding means comprises a second valve disk pivotally mounted in said second coupling.

17. A valve sealed pipeline coupling as defined in claim 16, wherein said first and second valve disks mutually prevent each other from moving to a closed position.

18. Avalve sealed pipeline coupling as defined in claim 17, wherein said first and second valve disks are free to close when said coupling sections separate.

19. Avalve sealed pipeline coupling as defined in claim 18, including a spring for each valve disk wherein said valve disks are biased to a closed position by said springs.

20. A pressure compensated pipeline coupling as defined in claim 1 substantially as hereinbefore described with reference to the drawings.