GB2093533A

GB2093533A - Transmitting fluid pressure from one fluid to another for use in a sub-sea well head

Info

Publication number: GB2093533A
Application number: GB8105311A
Authority: GB
Original assignee: BRISCO ENGINEERING UK Ltd
Current assignee: BRISCO ENGINEERING UK Ltd
Priority date: 1981-02-19
Filing date: 1981-02-19
Publication date: 1982-09-02

Abstract

A fluids isolating pressure transmitter wherein a bellows unit (14) is guided for longitudinal expansion and contraction within a cylindrical bore (12). The bellows unit (14) is sealingly closed except for entry of a first fluid under pressure through a fluid connector (20) closing one end of the bore, while a fluid connector (24) closes the other end of the bore except for entry of a second fluid under pressure which is contained within the bore to oppose the pressure of the first fluid, which is fully isolated from the second fluid within the bellows unit. The transmitter is especially suited to use at a well head, in particular a sub-sea well head, for transmitting the crude oil pressure to an hydraulic operating fluid, being capable of production as a sealed welded unit avoiding reliance on elastomeric seals either for isolation of the two fluids or their separation from the external environment. <IMAGE>

Description

SPECIFICATION Fluids isolating pressure transducer This invention relates to a fluids isolating pressure transducer, particularly but not exclusively a transducer adapted for operation at a sub-sea well head to transmit the crude oil pressure to an hydraulic operating fluid whilst maintaining isolation of the two fluids.

In the case of a sub-sea well head, a remote control system is provided on a surface rig. Operation of this control system essentially requires an input accurately indicative of the crude oil pressure at the well head, and a convenient means of providing this input is by a hydraulic fluid link extending between the surface rig and the sub-sea well head. At the sub-sea well head, an underwater manifold assembly incorporates a transducer through which the crude oil pressure is transmitted to the hydraulic operating fluid.

A known transducer device for this purpose includes a cylinder/piston unit, the pressure of the crude oil on one side of the piston head being transmitted to the hydraulic operating fluid on the other side of the piston head.

It is to be appreciated that the crude oil contains contaminant gases, waxes and the like which can be very corrosive or otherwise impart undesirable properties. This not only prohibits use of the crude oil as an hydraulic operating fluid, but also means that, ideally, the metering and/or control circuit containing the hydraulic operating fluid should be fully isolated from the crude oil. In an endeavour to achieve this, the known device incorporates a sliding, elastomeric seal in the cylinder/piston assembly.

In practice, it is found that such a seal is not adequate to ensure complete isolation. Furthermore, the elastomeric seal tends to deteriorate rapidly owing to contact with the crude oil. However, it is clearly undesirable for it to be necessary repeatedly to replace this seal in a sub-sea situation. On the contrary, it is preferable for the pressure transducer to be a sealed for life assembly, with all working parts having a maintenance and service free expectation forthe entire period of usage, e.g. 25 years. This is a demanding requirement, especially as the working pressure of the well developed within the device may be as high as 5,000 p.s.i.

It is a primary object of the present invention to provide an improved fluids isolating pressure transducer. It is a further object of the invention to provide such a transducer which is readily capable of production as a sealed assembly for use at a sub-sea well head.

According to the invention, there is provided a fluids isolating pressure transducer which comprises a housing having a bore, a first fluid connector sealed to the housing at one end of the bore, a hollow bellows unit guided for expansion and contraction longitudinally within the bore, said bellows unit being peripherally sealed at one end to the fluid connector for entry of a first fluid under pressure into the bellows and including a closure plate at its other end, and a second fluid connector sealed to the housing at the other end of the bore for entry of a second fluid under pressure into the bore to act against the closure plate counter to the pressure of the first fluid, which first fluid is isolated from the second fluid within the bellows unit.

The guiding of the bellows unit is preferably effected by the closure plate thereof, which slidingly cooperates with the wall of the housing bore. Such closure plate preferably carries a low friction bearing strip at which said plate slides within the bore. As a further feature to avoid wear, the bellows of the bellows unit preferably has clearance within the bore in the most contracted condition of said unit. It is to be noted that the closure plate is not intended to effect a sliding seal against the housing bore; the second fluid is present around the outside of the bellows in the space defined by the above-mentioned clearance, so that balanced pressure conditions exist throughout.

Operating conditions may require a zero setting defined by a predetermined internal pressure differential below which the transducer is non-operative.

Thus, the bellows unit preferably has a maximum contraction which can be preset by an adjustable stop. Such adjustable stop conveniently comprises a pin in screwthreaded engagement with the first fluid connector at one end and extending longitudinally within the bellows unit to cooperate with the closure plate of the latter at its other end. The stop pin preferably has its said other end rounded to make point engagement with the closure plate, thereby to prevent scoring or like damage.

It may also be desirable to protect the transducer and/or second fluid operating circuit against damage in the event of a pressure failure in such circuit. This can be achieved by providing the closure plate with a lapped pressure face for making sealing engagement with the second fluid connector to close said connector against passage of fluid in the event of a pressure failure in the circuit of the second fluid outside the hosusing. With an external pressure failure of the second fluid, the bellows unit will expand sufficiently rapidly to trap a substantial quantity of second fluid within the housing bore before closing said bore at the second fluid connector, so that balanced pressure conditions are maintained around the bellows unit with minimum distortion.By way of example, a typical zero setting will be 60 p.s.i. and a full expansion of the bellows unit will be produced by a pressure differential of 100 p.s.i., while the normal operating pressure of the second fluid to be transmitted through the bellows unit will be of the order of 5,000 p.s.i. Fast sealing at the second fluid connectorwill thereby inevitably result from an external failure in the second fluid unit, sufficiently fast to maintain internally balanced pressure conditions at little more than the normal operating pressure.

The preferred transducer is especially suited to use at a sub-sea well head. For this purpose, in a preferred arrangement, the first and second fluids are isolated from one another and from a third fluid outside the housing by means of non-elastomeric seals. This transducer may be completed as a welded assembly having metallic parts between which said non-elastomeric seals are constituted by welded joints. Thus, the invention also extends to a transducer forming parl of a sub-sea well head manifold assembly wherein the first fluid connector seal ingly connects to the housing a pipe for communicating crude oil from the well head and the second fluid connector sealingly connects to the housing a pipe for communicating a hydraulic operating fluid to remote metering andior control devices.The zero setting of the bellows unit, the connection of the second fluid supply and the associated operation of a bleed port at the second fluid connector may all be effected on shore, the seal welding of the unit, with the exception of completion of the crude oil connection, then being completed before the manifold assembly is taken to sea and lowered to the seabed.

A practical embodiment of fluids isolating pressure tranducer will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows the tranducer in end view, and Figure 2 shows the tranducer in longitudinal cross section.

The transducer shown in the drawings is specially for sub-sea operation at a well head, being intended to transmit the pressure of the crude oil to an hyd raulic operating fluid.

The device comprises a cylindrical housing 10 with a longitudinal bore designated 12, within which is housed a bellows unit generally designated 14. The bellows unit 14 comprises a metallic alloy bellows 16 sealingly closed at its front end by a closure plate 18.

At its rear end, the bellows 16 is sealed to a crude oil connector member 20. Thus, assembly is effected by inserting the welded sub-assembly bellows unit 14 and connector member 20 into one end of the housing bore 12. The sub-assembly 14,20 seals within the bore through an elastomeric "0" ring and backup sealing device 22. At its other end, the housing bore 12 is closed by a connector member 24 for the hydraulic operating fluid. The connector member 24 is seal welded at 25 to the housing 10. A connecting stub pipe for the crude oil is designated 26 and a connecting stub pipe for the hydraulic operating fluid is referenced 28. In practice, the crude oil supply pipe connecting to the stub pipe 26 is butt welded in position on the sea bed.

The closure plate 18 has a peripheral low friction bearing strip 19 which bears on the housing bore 12 to guide the bellows unit 14 in expansion and contraction. It is to be noted that this bearing strip 19 does not effect sealing engagement with the housing bore 12; the bore contains hydraulic operating fluid around the bellows to the rear of the bearing strip.

The front end of the crude oil connector member 20 has four angularly distributed ports 30 through which, in use, crude oil can enter the interior of the bellow unit. Centrally, the front end of the member 20 has a screwthreaded hole in which is received a screwthreaded stop pin 32, which extends forwardly within the bellows unit 14 for engagement with the closure plate 18 in order to define a position of maximum contraction ofthe bellows 16. in this position of maximum contraction, shown in Figure 2, the wall of the bellows 16 has radial clearance within the bore 12. The stop pin 32 is preset to define a minmum operating pressure differential, and locked in the pre-set position by a lock nut 34. It will be noted that the stop pin 32 h as a rounded front end 36 to make point engage; ent with the rear face of the closure plate 18.

The hydraulic operating fluid connector member 24 has an end face 38 having a recess through which operating fluid can enter the housing bore 12 to oppose the pressure of tie crude oil isolated within the bellows. This member 24 is also provided with an air bleed port 40. In the event of a pressure failure in the operating fluid circuit externally of the transducer, the closure plate 18 of the bellows unit 14 very rapidly closes against the end face 38 to seal the connector member 24, trapping operating fluid within the housing to maintain substantially balanced pressure conditions around the bellows. Sealing is ensured by an elastomeric "0" ring 44 on the front face of the closure plate 18, in conjunction with lapped zones 42 of said closure plate front face adja cent the "0" ring 44.

All parts of the transducer (except the elastomeric seals) are made of metal alloy resistantforthe expected life of the device to sea water and crude oil containing contaminants such as waxes and gases, e.g. hydrogen sulphide and carbon dioxide.

Typically, the housing may be about 25 cm long with an 8 cm diameter bore. The bellows unit may be about 11 cm long at maximum contraction and 16 cm long at maximum expansion.

Assembly of the transducer unit, within a manifold centre, is completed on-shore with the exception of connection of the crude oil supply pipe to the stub pipe 26. Thus, having effected a low heat fusion weld at 46 between the housing 10 and the crude oil connector member 20, connected the hydraulic operating fluid supply by seal welding to the connecting stub pipe 28, bled the transducer and seal welded the bleed port 40 in the connector member 24, and pre-setthe minimum operating pressure differential, the sealing and preparation of the unit is complete.

In practice, the device may be designed for a maximum working pressure of the well of 5,000 p.s.i. For a proof pressure factor of two, the unit will then be subjected to an internal pressure test of 10,000 p.s.i.

The manifold centre is then taken out to sea and lowered to the sea bed, where, it will be noted, the external pressure will usually be much less than the internal working pressure, e.g. about 900 p.s.i. at 650 m below sea level. Only the crude oil connection to the stub pipe 28 is effected by welding in position on the sea bed, and when this has been done, a fully seal welded transducer assembly is completed. It will thus be noted that the elastomeric seal 22 is not relied upon for sealing. The elastomeric seal 44 is only operative in the event of a pressure failure in the operating fluid supply, and its slow deterioration will not affect the ma.n sealing effect achieved by the lapped front face 42 of the closure plate 18 in the event of such pressure failure.

Thus, once in operational condition on the sea bed, it is anticipated that the transducer will have an operational life of substantial duration, up to say 25 years, substantially without deterioration.

The above described embodiment of transducer is capable of transmitting the crude oil pressure with an acceptable loss of accuracy. Increased accuracy can be achieved with a bellows of increased flexibility, or bss increasing the cross-sectional area of the bellows unit exposed to the isolated fluids.

It is to be appreciated that the invention is not restricted to a transducer specifically for use as part of a manifold centre on a sub-sea well head, and that, especially for other applications, various mod ifications are possible within the scope of the invention as defined by the appended claims.

Claims

1. A fluids isolating pressure transducer which comprises a housing having a bore, a first fluid connector sealed to the housing at one end of the bore, a hollow bellows unit guided for expansion and contraction longitudinally within the bore, said bellows unit being peripherally sealed at one end to the fluid connector for entry of a first fluid under pressure into the bellows and including a closure plate at its other end, and a second fluid connector sealed to the housing at the other end ofthe bore for entry of a second fluid under pressure into the bore to act against the closure plate counter to the pressure of the first fluid, which first fluid is isolated from the second fluid within the bellows unit.

2. A transducer according to claim 1, wherein the closure plate ofthe bellows unit slidingly cooperates with the wall of the housing bore.

3. A transducer according to claim 2, wherein the closure plate carries a low friction bearing strip at which said plate slides within the bore.

4. A transducer according to any of claims 1 to 3, wherein the bellows of the bellows unit has clearance within the bore in the most contracted condition of said unit.

5. A transducer according to any of claims 1 to 4, including a bleed valve in the second fluid connector.

6. Atransducer according to any of claims 1 to 5, wherein the bellows unit has a maximum contraction which can be preset by an adjustable stop.

7. Atransducer according to claim 6, wherein the adjustable stop comprises a pin in screwthreaded engagement with the first fluid connector at one end and extending longitudinally within the bellows unit to cooperate with the closure plate of the latter at its other end.

8. A transducer according to claim 7, wherein the stop pin has its said other end rounded to make point engagement with the closure plate.

9. Atransducer according to any of claims 1 to 8, wherein the closure plate has a lapped pressure face for making sealing engagement with the second fluid connector to close said connector against passage of fluid in the event of a pressure failure in the circuit of the second fluid outside the housing.

10. Atransducer according to any of claims 1 to 9, wherein the first and second fluids are isolated from one another and from a third fluid outside the housing by means of non-elastomeric seals.

11. Atransducer according to claim 10, completed as a welded assembly having metallic parts between which said non-elastomeric seals are constituted by welded joints.

12. A transducer according to claim 11, forming part of a sub-sea well head manifold assembly wherein the first fluid connector sealingly connects to the housing a pipe for communicating crude oil from the well head and the second fluid connector sealingly connects to the housing a pipe for communicating a hydraulic operating fluid to remote metering and/or control devices.

13. Afluids isolating pressure transducer substantially as hereinbefore described with reference to the accompanying drawings.

13. A fluids isolating pressure transducer sub- stantially as hereinbefore described with reference to the accompanying drawings.

New claims or amendments to claims filed on 11.1.82 Superseded claims: New or amended claims: see attached sheets 12-14 CLAIMS

1. A fluids isolating pressure transducer which comprises a housing having a bore, a connector for a high pressure working fluid sealed to the housing at one end of the bore, a hollow bellows unit guided for expansion and contraction longitudinally within the bore, said bellows unit being peripherally sealed at one end to the fluid connector for entry of the working fluid under high pressure into the bellows and including a closure plate at its other end, and a connector for a high pressure operating fluid sealed to the housing at the other end of the bore for entry of the operating fluid under high pressure into the bore to act against the closure plate counter to the pressure of the working fluid, which working fluid is isolated from the operating fluid within the bellows unit, wherein the operating fluid connector and the closure plate are mutually adapted for sealing engagement with one another whereby, in the event of a pressure failure in the operating fluid supply, the bellows unit is expanded sufficiently rapidly to seal the operating fluid connector whilst trapping high pressure operating fluid within the housing bore around the bellows in order substantially to maintain balanced pressure conditions inside and outside the bellows.

2. Atransducer according to claim 1, wherein the closure plate of the bellows unit slidingly cooperates with the wall of the housing bore.

4. Atransducer according to any of claims 1 to 3, wherein the bellows of the bellows unit has clearance within the bore in the most contracted condition of said unit.

5. A transducer according to any of claims 1 to 4, including a bleed valve in the operating fluid connector.

7. A transducer according to claim 6, wherein the adjustable stop comprises a pin in screwthreaded engagement with the first fluid connector at one end and extending longitudinally within the bellows unit to cooperate with the closure plate of the latter at its other end.

9. A transducer according to any of claims 1 to 8, wherein the closure plate has a lapped pressure face for making sealing engagement with the operating fluid connector to close said connector against passage of fluid in the event of a pressure failure in the circuit of the operating fluid outside the housing.

10. A transducer according to any of claims 1 to 9, wherein the working and operating fluids are isolated from one another and from a third fluid outside the housing by means of non-elastomeric seals.

11. A transducer according to claim 10, completed as a welded assembly having metallic parts between which said non-elastomeric seals are constituted by welded joints.

12. A transducer according to claim 11, forming part of a sub-sea well head manifold assembly wherein the working fluid connector sealingly connects to the housing a pipe for communicating crude oil from the well head and the operating fluid connector sealingly connects to the housing a pipe for communicating a hydraulic operating fluid to remote metering and/or control devices.