GB2147425A - Leakage detection - Google Patents

Abstract

Pipe coupling leakage detecting apparatus comprises an elongate tool (76) supporting a coupling (12, chain dotted lines) to be tested. An end assembly (14) carries several elongate members (34) extending parallel to the tool which have an annular collector (36) at their free ends which collects any leakage search gas from the coupling being tested and also restrains the coupling against axial movement. The elongate tool supports an axially compressible seal member (84) and fluid pressure means (90, 92, 106) radially expand the seal into engagement with the pipe by such compression. Means are provided for introducing a search gas into a space (11) defined by the tool and the coupling so that the coupling thread is exposed to the search gas and the collector (36) serves to collect any leakage search gas. A detector such as a mass spectrometer is provided for quantitatively measuring any search gas which has been collected by the collector (36). <IMAGE>

Description

SPECIFICATION Leakage detection This invention relates to leakage detection, for example to leakage from high quality pipe couplings.

The leakage of hydrocarbons whether gaseous or liquid from pipelines and various forms of pipes used in oil and natural gas industries is a serious matter for obvious reasons and because of these hazards it has been conventional practice for many years to use couplings with special thread forms which reduce as far as possible the risk of leakage. In addition various pipe thread sealants or dopes are employed with the aim, but not necessarily the practical effect of reducing the risk of leakage in the event of the presence of dirt or malformation of a screw thread. Certain pipes are operated at extremely high pressures of the order of 500 Kg/cm or even higher and such pressures give rise to an even more pressing need for pipe couplings which are totally free of leaks even down to molecular size.

According to the present invention there is provided pipe coupling leakage detecting apparatus comprising an elongate tool adapted to support a coupling to be tested, a support structure carrying a fluid actuator and operative to carry a plurality of elongate members extending parallel to the tool and having collector means at the free ends and so located as to collect any leakage search gas from a coupling being tested, operation of the actuator serving to adjust the operating length of the tool to accommodate couplings of different lengths, the elongate tool supporting a compressible seal member and means to activate the seal by engagement in compression thereof, means for introducing a pressure fluid capable of actuating the compressible seal, means for introducng a search gas to a space defined by the tool whereby the coupling thread can be exposed to the search gas and the collector means serve to collect any leak age search gas, and detector means such as a mass spectrometer capable of measuring quantitatively any search gas which may leak through the coupling thread and which has been collected by the collector means.

Further according to the present invention there is provided pipe coupling leakage detecting apparatus comprising an elongate tool adapted to support a coupling to be tested, a support structure carrying a fluid actuator and operative to carry a plurality of elongate members extending parallel to the tool and having collector means at the free ends so located as to collect any leakage search gas from a coupling being tested, operation of the actuator serving to adjust the operating length of the tool to accommodate couplings of different lengths and to resist forces generated during tests, the elongate tool supporting a compressible seal member and means to activate the seal by engagement in compression thereof to cause radial expansion and consequent sealing against the internal periphery of a coupling being tested, means for introducing a pressure fluid capable of actuating the compressible seal, means for introducing a search gas to an annular space defined by the tool and the coupling being tested whereby the coupling thread can be exposed to the search gas and the collector means serve to collect any leakage search gas, a mass spectrometer or other detector means capable of measuring quantitatively any search gas which may leak through the coupling thread and which has been collected by the collector means.

Still further according to the present invention there is provided a pipe coupling leakage detecting apparatus comprising an elongate tool assembly adapted to support a coupling to be tested, support means for the tool disposed at one end thereof, a plurality of arms extending parallel to the tool and pivotally mounted at an end remote from the tool on an end assembly, a hydraulic actuator mounted at one end on the end assembly and at the other end on the support means, the actuator being operable to move the arms axially relative to the support means whereby different coupling sizes can be accommodated, and collector means for any leakage search gas mounted at the ends of the arms remote from the support means, the collector means also serving to located a part of the coupling under test, the arrangement being such that the tool, the coupling being tested and the collector means lie to one side of the support means and the actuator and end assembly lie on the other side of the support means.

Pipe coupling leak detection apparatus embodying the invention will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a side elevation, partly in section, of the leak datection apparatus; Figure 2 is a fragmentary view in the direction of the arrow 2 in Fig. 1; Figure 3 is a longitudinal section showing, to an enlarged scale, the interior parts of the tool; and Figure 4 is an end elevation of the tool showing details of an interlock arrangement.

Referring now to the drawing, the apparatus includes support means 10 which is merely intended for carrying the weight of the apparatus and is not required to resist the very large horizontal forces which will be encountered by pressure testing to 500 Kg/cm or possibly higher. A tool part 11, of the apparatus receives a pipe coupling 1 2 and serves to apply directly high pressure search fluid to the threads of the coupling.

Considering the apparatus from left to right in Fig. 1, an end assembly 14 (or hinge bracket) accommodates a cylindrical boss 1 6 having its bore 18 tapped to receive a screwthreaded piston rod 20 of a hydraulic cylinder 22. The piston rod 20 is secured against rotation by a grub screw 21. Four pairs of lugs 24 are welded to the right-hand face (as shown) of the end assembly 14 (two pairs only visible in the drawing) and these lugs have aligned apertures so that respective pairs receive pins 26. The radially inner ones of the pairs of lugs 24 are connected by webs 28 and seam welds 30 to the cylindrical boss 16 to provide additional strength but as will be apparent the webs 28 do not interfere with the insertion of and removal of the pins 26.

The pins 26 are each detachably secured by a cotter pin 32. The end assembly is not in contact with any base support structure and is therefore free to move relative to the support structure 10 which carries the whole weight of the apparatus. The parts of the apparatus to the left of support structure 10 substantially counter balance those to the right.

Each pair of lugs 24 and the corresponding pin 26 receive an end portion of a support arm 34 of rectangular section which extends longitudinally of the apparatus and the ends of the arms remote from the end assembly 14 support an annular collector member 36 to be described in detail hereinafter. Intermediate the lengths of the arms the support 10 or housing serves as the main load carrier and rests on a base 38 which is secured to appropriate foundations. The support 10 takes the form of a thick plate 1 3 with upper and lower transverse bars 15, and 1 7 which define, with the respective upper lower horizontal boundaries of the plate, two slots (not shown) which respectively, each slidably receive two of the arms 34.The upper bar 1 5 carries a further bar 1 9 extending parallel to the longitudinal axis of the apparatus and having apertures 23 at balance points of the apparatus to enable lifting. The pivotal mounting of the arms 34 at the hinge bracket 16 and the sliding relationship with the slots in the central support 10 enables mounting and demounting of parts of the apparatus to be described hereinafter. An end flange 46 of the hydraulic cylinder 22 is secured to the plate 1 3 by a plurality of bolts 47 screwed into tapped bores.

Inlet and outlet couplings 45, 48 of the cylinder 22 are indicated in the side wall of the cylinder. The cylinder serves to vary the effective location of the collector 36 relative to the support 10, so that couplings of differing lengths can be tested and also acts to restrain the forces generated by the search gas during testing.

In addition to carrying one end of the hydraulic cylinder 22, the support 10 also carries by means of countersunk bolts 51 (broken lines) a plate 50 with an inset ring 52. This plate is drilled with bores 56, 58 which serve to supply pressure fluid for activating the seal of the tool carrying the pipe coupling and further bores (not shown) fo.' the admission of a search gas which is used for carrying out the test on the coupling, the search gas being conducted into an annular space 54 lying inside the coupling.

The plate 50 carries a guide ring 64 with tapped bores having grub-screws 65 enabling securing to the periphery of the plate 50. The guide ring is internally stepped at 67 and its internal passage is bell-mouthed at 69 to assist engagement of couplings to be tested with the seal 52. The step 67 keeps the seal 52 in place. Recesses (not shown) enable the access of pipe connections to the pressure fluid and search gas passages in the plate 50.

The plate carries a central, cylindrical extension 68 having an internally screw-threaded bore 74 which receives a mandrel 76 extending, as illustrated, into the right-hand part 78 of the pipe coupling. An internally-stepped sleeve 80 surrounds the central extension 68 and a part of the mandrel 76 and an annular, stepped seal 82 (preferably of a material marketed under the Registered Trade Mark HAL LITE) acts between these two parts to prevent leakage of pressure fluid which is used to activate a main seal 84 of the tool.

The passages 56, 58 drilled in the plate 50 are continued as 59 along the axis of the mandrel 76; an outlet portion 86 leads to a chamber 88 defined by an end surface of the extension 68, an internal surface of the sleeve 80 and one part of a composite piston member 90, 92 slidable on the mandrel 76. The piston member 90, 92 is slidable in a bore 94 of the sleeve of slightly larger diameter than the main portion surrounding the body portion 72. The part 90 has a peripheral recess 96 accommodating an O-ring seal (not shown), an internal annular seal 98 (preferably of HALLITE) and an annular extension 100 which fits into a recess of the second part 92.

The second part 92 also has a peripheral recess 102 accommodating an O-ring seal (not shown) and an annular extension 104 extending away from the part 90. The end face of extension 104 abuts a ram 106 of hollow cylindrical form which has an antiextrusion ring 108 held by grub screws 110 in an annular peripheral recess. Internally the ram 106 has bronze bushes 109 cooperating with the mandrel 76. The ram 106 abuts at its right-hand end face the main seal 84 which has to withstand very high extrusion forces and is preferably made in accordance with our co-pending ( ) application ( ) ("CYCLING RUBBER"). At the right-hand end the main seal abuts a ring 111 which like the ram 106 has an anti-extrusion ring 112 secured by grub screws 114.

A nose piece 11 6 has an annular recess which accommodates an annular end member 118 of rubber which merely serves to avoid damage to a coupling as the coupling is placed in position. Both the ring 111 and the nose piece 11 6 are internally screw threaded onto a corresponding thread of the mandrel 76 and thus effectively act together as lock nuts to prevent in advertent loosening. The nose rubber 118 is held in position by washers 124 one of which is received in a groove on a reduced diameter end portion 1 26 of the nose piece.

A coupling 1 2 under test is illustrated in chain lines and as will be seen the annular section space 54 lies between the left-hand part 66 of the coupling and the sleeve 80 which has an outer diameter identical to that of the sealing rubber 84 in the non-compressed condition. A helium/air mixture or other search gas is admitted to the annular space 54 through the passages (not shown) in the left-hand end portion of the mandrel 76.

As already indicated, the support arms 34 carry at their right-hand end a collector assembly 36 part of which is also illustrated in Fig. 2. The collector assembly consists of a two part, split, housing 1 30 having a step 1 32 (broken lines) receiving a two-part, split, insert 1 33 having O-ring seals 1 34, 1 36 received in corresponding annular grooves, a passage 1 38 being formed in the insert intermediate the seal and opening at a step 1 39 of the insert. The outer circumference of the annulus 1 30 is recessed (Fig. 4) so that it receives the free ends of arms 34 and is welded thereto.The split housing 1 30 and the split insert 1 33 can be mounted on the apparatus as illustrated owing to the pivotal mounting of the arms 34 and to the slots (not shown) where the arms pass through the support structure 10. When located and secured together the annulus and insert are welded to the arms as indicated at 1 35. The split housing 1 30 is primarily held together when a coupling is in situ by two brackets 131 pivoted on one of the arms 34 and each carrying a screwed member 137 having a handle 141 by which the member can be conveniently tightened and released.By means of the seals 134,136 any leakage search gas is constrained to pass to the passage 1 38 and thence to a connection on the outer periphery of the housing 1 30. This connection (not shown) in turn leads to a sensitive detector capable of detecting very small amounts of helium. A suitable detector for this purpose is a mass spectrometer (not shown) preferably operated in the over-pressure viscous mode.

In operation, after a coupling 12 has been located in the position illustrated, pressure fluid is admitted to the space 88 immediately adjacent the composite piston 9Q. 92 and this pressure fluid acts on the piston and then on the ram 106 to compress the main seal 84 axially so that it expands radially and thus prevents any search gas, subsequently admitted, from passing down the interior of the coupling or pipe. The subsequently admitted air/helium mixture or search gas passes to the annulus 1 28 and is maintained at a pressure less than the pressure of the toolactivating fluid. More generally the force exerted on the seal must be in excess of the force acting in parts subjected to the search gas so that the risk of blowout is reduced.It is, of course, essential that outer coupling part 66 should be kept in sealing contact with the seal 52 and this is ensured by the restraining action of the step 1 39 of the collector insert 1 33 in conjunction with the arms 34 and the hydraulic actuator 22. On completion of a test the search gas is first released followed by the pressurizing fluid which de-activates the seal 84. An appropriate interlock will be included in the control circuit to ensure that this sequence is followed.

A further interlock is provided at the split housing 1 30 as illustrated in Fig. 4. Adjacent the upper split a small hydraulic cylinder 140 is mounted byt welding to the end surface of one arm 34 and to the adjacent part of the housing 1 30. A plunger 142 of the cylinder is mounted to engage in a recess 144 provided in a bar 146 welded to the left-hand, as shown, half of the split housing 1 30. The cylinder 140 is connected in the same circuit as the pressure fluid which operates the sealactivating ram 106 so that the latter can only be operated if the cylinder 140 is operative and the plunger engaged.

An interlock, now shown, is also provided in the lower half of the split housing in the form of a micro air valve having a plunger which co-operates with an apertured angle bracket. The valve is mounted on the end face of one half of the housing and the angle bracket on the other half. The valve is incorporated in the hydraulic circuit so that the ram can only operate if the plunger of the micro valve is operative.

Because of the very small size of the helium molecule and the sensitivity of available gasdetecting apparatus such as a mass spectrometer even a very small leak can be detected within about 30 seconds. If no leak is detected the air/helium mixture is withdrawn and subsequently the tool activating pressure fluid is released so that the coupling can be removed from the test facility. High pressures, in excess of 6000 Ib/sq.in. (422 Kg./sq.cm.) can be applied by the search gas.

The pressures of both activating fluid and search gas are high and it is therefore essential that these pressures should be balanced.

The pressurizing fluid (liquid or gas) admitted to the chamber 88 acts axially both on the left-hand face of portion 90 of the two-part piston and on the end face of the extension 68. The surfaces are identical in area and thus there is no net axial force. Similar remarks apply to the search gas which acts on an annular end face of one coupling part and on an annular surface of the plate 50.

In order to test a coupling of smaller axial length the hydraulic cylinder is activated so that end assembly 14 and the arms 34 move to the left, bringing with them the collector 36. When the desired spacing is achieved a fresh coupling is inserted and a fresh test carried out.

The apparatus hereinbefore described has advantages, such as high speed, safety, and the ability to detect extremely small leaks quantitatively.

The pipe coupling leakage detection apparatus hereinbefore particularly described enables bench testing of couplings of different lengths and although the external characteristics must be the same different diameter couplings can be accommodated by substitution of certain parts. The use of very dilute helium as the search gas (of the order of 1 %) is made possible by the high sensitivity of available mass spectrometers and preferably these instruments are operated in the over-pressure viscous mode. The small proportion (in air) of helium or other search gas results in economy in operation.

Claims (12)

1. Pipe coupling leakage detecting apparatus comprising an elongate tool adapted to support a coupling to be tested, a support structure carrying a fluid actuator and operative to carry a plurality of elongate members extending parallel to the tool and having collector means at the free ends and so located as to collect any leakage search gas from a coupling being tested, operation of the actuator serving to adjust the operating length of the tool to accommodate couplings of different lengths, the elongate tool supporting a compressible seal member and means to activate the seal by engagement in compression thereof, means for introducing a pressure fluid capable of actuating the compressible seal, means for introducing a search gas to a space defined by the tool whereby the coupling thread can be exposed to the search gas and the collector means serve to collect any leakage search gas, and detector means such as a mass spectrometer capable of measuring quantitatively any search gas which may leak through the coupling thread and which has been collected by the collector means.

2. Apparatus according to claim 1, wherein the tool has an internal passage for pressure fluid which serves to compress the seal member and thereby activate the seal by radial expansion thereof.

3. Apparatus according to claim 1 or claim 2, wherein the collector means includes an annular member with seals arranged to lie on a coupling to be tested and spanning a possible leakage zone thereof, passages being provided to collect any leakage search gas.

4. Apparatus according to any one of claims 1 to 3 wherein the fluid actuator serves to adjust the locations of the free ends of the elongate members whereby the apparatus can be readily adapted to the lengths of couplings to be tested and also serves during testing to resist forces generated by the search gas.

5. Apparatus according to any one of the preceding claims, wherein the plurality of elongate members extend axially of and surround the fluid actuator, the ends of the arms carried by the support structure being pivotally mounted on the structure.

6. Apparatus according to any one of the preceding claims, wherein the compressible seal is activated by a ram, itself driven by a two-part piston operated by the pressure fluid.

7. Apparatus according to any one of the preceding claims, comprising a nose piece at one end of the tool carrying a resilient member serving to protect a coupling as it is mounted on the tool.

8. Apparatus according to claim 7 wherein the nose piece is internally screw-threaded and cooperates with another internallyscrewed threaded member which acts as a lock nut and serves to retain the compressible seal on the tool.

9. Apparatus according to claim 1, wherein the collector means surrounds and is rigid with an annular member which provides an abutment for one end of one part of a coupling to be tested, the annular member having a passage for any leakage search fluid leading to the collector.

10. Pipe coupling leakage detecting apparatus comprising an elongate tool adapted to support a coupling to be tested, a support structure carrying a fluid actuator and operative to carry a plurality of elongate members extending parallel to the tool and having collector means at the free ends so located as to collect any leakage search gas from a coupling being tested, operation of the actuator serving to adjust the operating length of the tool to accommodate couplings of different lengths and to resist forces generated during tests, the elongate tool supporting a compressible seal member and means to activate the seal by engagement in compression thereof, to cause radial expansion and consequent sealing against the internal periphery of a coupling being tested, means for introducing a pressure fluid capable of actuating the compressible seal, means for introducing a search gas to an annular space defined by the tool and the coupling being tested whereby the coupling thread can be exposed to the search gas and the collector means serve to collect any leakage search gas, and a mass spectrometer or other detector means capable of measuring quantitatively any search gas which may leak through the coupling thread and which has been collected by the collector means.

11. A pipe coupling leakage detecting apparatus comprising an elongate tool assembly adapted to support a coupling to be tested, support means for the tool disposed at one end thereof, a plurality of arms extending parallel to the tool and pivotally mounted at an end remote from the tool on an end assembly, a hydraulic actuator mounted at one end on the end assembly and at the other end on the support means, the actuator being operable to move the arms axially relative to the support means whereby different coupling sizes can be accommodated, and collector means for any leakage search gas mounted at the ends of the arms remote from the support means, the collector means also serving to locate a part of the coupling under test, the arrangement being such that the tool, the coupling being tested and the collector means lie to one side of the support means and the actuator and end assembly lie on the other side of the support means.

12. Pipe coupling leakage detection apparatus substantially as hereinbefore described with reference to the accompanying drawings.