THE TESTING OF THE INTEGRITY OF A FLUID COUPLING

Abstract: A fluid coupling (20) is provided in a fluid pressure line e.g. a hydrocarbon production line connected to an underground reservoir, in which the sealing integrity of the coupling can be tested after shut-down of flow through the pressure line for repair or maintenance purposes and dis-assembly of the coupling, and in which the coupling (20) comprises: an upstream part (21) and a downstream part (22) which are releasably coupled together, one of said parts defining a cylindrical socket (23) and the other of said parts comprising a tubular portion (24) slidably received by the socket (23); first and second axially spaced circumferential seals (28, 29) arranged to seal the interface between the outer surface of the tubular portion (24) and the inner surface of the socket (23); a pressure chamber (33) defined in the interface between the first and second seal (28, 29); and a fluid inlet testing port (34) provided in said one coupling part (21) and communicating with the pressure chamber (33); in which the testing method comprises introducing a fluid pressure testing medium to the chamber (23) via the testing port (34), in order to test the sealing integrity of the coupling upon re-assembly of the coupling.

Description: THE TESTING OF THE INTEGRITY OF A FLUID COUPLING This invention relates to a method of testing the sealing integrity of a fluid coupling in a fluid pressure line. The invention has been developed primarily in connection with the testing of the sealing integrity of a fluid coupling in a pressure line leading to an underground reservoir of hydrocarbons (in liquid and / or gaseous form) , and which usually comprises a Christmas tree, a blow-out preventer (BOP) , a wireline lubricator, and a surface stuffing box. In a pressure hydrocarbon line, it is usual to employ so- called "quick unions" which assemble a wireline service lubricator and related equipment, and known examples of which include the OTIS and the Bowen unions. Unions of this type are provided on a so-called "box end", and which receive a coupling pin carrying an externally mounted sealing ring. The pin is slidably received by an internal socket in the box end, and the depth of insertion of the pin is limited by an internal abutment or shoulder in the socket. An internally threaded collar is mounted on an external threaded portion of the box end, and is then manually tightened in order to complete the coupling. The sealing ring is housed in an external circumferential groove on the pin, and engages sealingly against the internal wall of the socket of the box end. The internal thread on the collar matches the external thread on the box end, and this thread makes-up quickly by hand, and should be kept clean. The sealing ring is preferably an O-ring, which forms the seal to contain the pressure, and which should be thoroughly inspected periodically for damage, and replacement if necessary. A light film of oil (or grease) helps to make up the union and prevent cutting or chafing of the O-ring. It is important that only manual tightening, and untightening of the collar should take place, and pipe wrenches, chain tongs or hammers should never be used to loosen the collar of the union. If it cannot be turned by hand, all precautions must be taken to make sure that the well pressure has been completely released. The collar of the coupling is therefore tightened manually, when the pin end, with an O-ring mounted thereon, is stopped by the internal abutment or shoulder in the socket. When the collar has been fully tightened, it normally should be backed-off approximately one quarter of a turn, to eliminate any possibility of it sticking due to friction when it is required subsequently to be removed. Also, rocking of the lubricator assembly, to ensure it is perfectly straight, will assist in loosening the coupling. In existing arrangements of hydrocarbon pressure lines, the wellhead lubricator assembly usually consists of several sections of equipment, all screwed together by means of quick unions, in various sizes, and which are designed to be hand- operated. After each operation, the connection above the blowout preventer is broken out, to change out the various tools inside. When re-assembled, the one seal which has been broken out needs to be re-tested, which means that the entire assembly needs to be filled with glycol and then pressure tested. This takes a lot of fluid, and additional down time, with consequent costs, and delays in production. The present invention has therefore been developed with a view to improving the design of a "quick union" type of coupling in a fluid pressure line, in order to provide an improved method of testing the sealing integrity. A method according to the invention is defined in claim 1. Preferred features of the method are set out in the dependent claims. A fluid coupling according to the invention is defined in claim 10. A preferred embodiment of coupling will now be described in detail, by way of example only, for use in a testing method according to the invention, and with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a typical arrangement of fluid pressure line to which a testing method according to the invention may be applied, the pressure line comprising a pressurised hydrocarbon line running from an underground reservoir via a borehole and to surface equipment; and, Figure 2 is an enlarged view of a coupling device in the form of a "quick union" to be incorporated in the pressure line of the surface equipment. Referring first to Figure 1 of the drawings, this sets out the background to the invention, and shows a typical arrangement of surface equipment of a hydrocarbon extraction line, comprising a usual borehole extending to the surface (not shown), a Christmas tree 10, a tree connection 11, a blow-out preventer 12, a wireline lubricator 13 and a stuffing box 14. So-called "quick unions" are incorporated in the surface equipment, one of which is shown by reference numeral 15 immediately above the blow-out preventer 12, and the other of which is shown by reference 16, below wireline lubricator 13. As described in the introduction, typically "quick unions" are manually operated, and comprise a box having an externally threaded box end, which defines an internal socket into which can be slidably received a pin coupling. The pin coupling has an external circumferential groove in which a sealing ring is received, and which engages sealingly against the internal wall of the socket. A manually operated collar is provided, having an internal thread which mates with the external thread on the box end, and which is simply tightened manually to complete the coupling assembly. The depth of insertion of the pin end into the box is limited by an internal shoulder or abutment, at an inner end of the socket, and when the pin end reaches the required entry position, the collar is then tightened manually. In use of surface equipment, as shown in Figure 1, it is necessary, from time to time, to cease production, and to check the operating components. After each operation, the connection above the blow-out preventer 12 is broken out, and when reassembled, the one seal which was broken out needs to be retested. With the existing equipment, this means that the entire assembly needs to be filled with glycol, and then pressure tested. This takes a lot of fluid, and downtime of the system, with consequent impact on costs, as well as delays in production. In order to overcome these drawbacks of existing equipment, a new design of coupling has been developed, as will now be described with reference to Figure 2, and which enables an improved method of testing to be carried out. Referring now therefore to Figure 2 of the drawings, the improved coupling is designated generally by reference 20, and comprises a first coupling portion 21 and a second coupling portion 22 which are slidably interengageable between release and sealingly engaged positions. Typically, coupling portion 21 comprises a "box end", and coupling portion 22 comprises a coupling pin. The coupling portion 21 defines a receiving socket 23 having a cylindrical surface, and which receives slidingly the free end 24 of the coupling portion 22. The socket 23 is cylindrical, but merges at its inner end into an internal shoulder or abutment 25 which forms one means of limiting the depth of insertion of the end 24, and at its outer end merges into an external abutment or shoulder 26 which forms an alternative, or additional means of limiting the depth of insertion of the end 24. As shown in Figure 2, a circumferential rib 27 of the coupling portion 22 engages shoulder 26, to limit the depth of insertion of the end 24. The outer surface of end 24 carries a first sealing ring 28, which is housed in a circumferential groove 29, and which engages sealingly with the internal wall of the socket 23, in order to seal the coupling between coupling portions 21 and 22. Sealing ring 28 therefore functions as a primary seal, but in order to retest the sealing integrity of the primary seal 28, additional components are provided in the coupling 20. A secondary seal 29 is therefore provided, spaced downstream of primary seal 78, with respect to the normal flow direction, and which is housed in a further circumferential groove 30 formed in the outer surface of end 24. Secondary seal 29 functions as a retainer seal, and facilitates the testing procedure which will be described below. The coupling between portions 21 and 22 is completed by provision of a manually rotatable coupling collar 31, which is rotatably mounted on circumferential rib 27, and which has an internal thread which mates with an external thread on coupling portion 21, the interengagement between these two threads being shown by reference 32. Manual tightening and untightening only is required, in order to complete the coupling assembly. In order to test the sealing integrity of the primary seal 28, the coupling 20 shown in Figure 2 can be tested by introduction of pressure testing fluid into an annular testing chamber 33 defined between the outer surface of pin end 24 and the inner wall of socket 23. In practice, it is preferred that the annular chamber 33 is formed in the wall of the socket 23, as shown in Figure 2. The pressure testing fluid is introduced into chamber 33 up to a required pressure, by application of fluid pressure to an external injection port 34. Monitoring of the testing fluid pressure will show whether there is any leakage, and therefore enable the sealing integrity or otherwise of the coupling to be tested, after temporary shutdown of the surface equipment. The testing method achievable with the new coupling shown in Figure 2 is quick and clean, and results in a saving of both time and material. The equipment is left in situ, and normal operations are carried out with the test unit in place. On each occasion that the assembly needs to be "broken-out", it is done on this coupling, so the test is carried out each and every time that the assembly is broken out. The fluid coupling shown in Figure 2 is preferably located above the blow-out preventer, when the coupling forms a "quick union" incorporated in a hydrocarbon production line. However, it is within the scope of the invention to apply the quick union coupling to other forms of fluid pressure line, and in application to a hydrocarbon production line, to releasable couplings arranged below the blow-out preventer.

Claims: CLAIMS 1. A method of testing the sealing integrity of a fluid coupling in a fluid pressure line, said coupling being tested after shut-down of flow through the pressure line for repair or maintenance purposes and dis-assembly of the coupling, and said coupling comprising: an upstream part and a downstream part which are releasably coupled together, one of said parts defining a cylindrical socket and the other of said parts comprising a tubular portion slidably received by said socket; first and second axially spaced circumferential seals arranged to seal the interface between the outer surface of the tubular portion and the inner surface of the socket; a pressure chamber defined in said interface between the first and second seals; and, a fluid inlet testing port provided in said one coupling part and which is communicable with said pressure chamber; in which the method comprises introducing a fluid pressure testing medium to said chamber via the testing port, in order to test the sealing integrity of the coupling upon reassembly of the coupling. 2. A method according to claim 1, in which the fluid pressure line is a hydrocarbon production line connected to an underground reservoir. 3. A method according to claim 2, in which the fluid pressure line includes a blow-out preventer. 4. A method according to claim 3, in which the fluid coupling is arranged above the blow-out preventer. 5. A method according to claim 3, in which the fluid coupling is arranged below the blow-out preventer. 6. A method according to any one of the preceding claims, in which the first and second seals comprise O-rings housed in circumferential slots formed in the outer surface of the tubular portion. 7. A method according to any one of the preceding claims, in which the pressure chamber is an annular chamber defined in the inside surface of said socket. 8. A method according to any one of the preceding claims, in which the upstream and downstream parts of the coupling are releasably coupled together by an external rotatable coupling collar. 9. A method according to claim 8, in which the collar is internally threaded to engage with an external thread on said upstream part, said collar also engaging with a circumferential rib of said downstream part to couple the upstream and downstream parts of the coupling together. 10. A fluid coupling to be fitted in a fluid pressure line, and of which the sealing integrity can be tested after shut-down of flow through the pressure line for repair or maintenance purposes and dis-assembly of the coupling, and in which the coupling comprises: an upstream part; a downstream part which is releasably coupled to said upstream part; a cylindrical socket defined by one of said parts; a tubular portion provided on the other of said parts and slidably received by said socket; first and second axially spaced circumferential seals arranged to seal the interface between the outer surface of the tubular portion and the inner surface of the socket; a pressure chamber defined in said interface between the first and second seals; and, a fluid inlet testing port provided in said one coupling part and which is communicable with said pressure chamber to allow introduction of a fluid pressure testing medium to the chamber in order to test the sealing integrity of the coupling upon reassembly of the coupling.

Inventors: MCKAY FREDERICK D, MCKAY, FREDERICK, D.
Applicants: CROMAR SALES AND SERVICE LIMIT, MCKAY FREDERICK D, CROMAR SALES AND SERVICE LIMITED, MCKAY, FREDERICK, D.
Application year: 1998
Main classification: G01M3
IPC codes: G01M3