GB2293429A - Pipe plug - Google Patents

Abstract

A high pressure access fitting assembly for connection to a high pressure conduit comprising a body (2) with a bore (9) therethrough into which a removable plug (10) is screwed. The plug has a primary sealing member (16) adapted to make a high pressure seal with a sealing surface (9b) provided on the body when the plug (10) is screwed into it. The plug (10) also includes a secondary sealing member (27) axially spaced from the primary seal (16) and plug orientating means operable to ensure that the plug can be screwed into the body in only one direction which is preferably an outwardly radially extending flange (14) which can optionally include a sealing surface (14a) adapted to make metal-to-metal contact with a correspondingly shaped sealing surface (7) on the plug (10) to provide a tertiary seal thereon. <IMAGE>

Description

IMPROVED HIGH PRESSURE ACCESS FITTING The present invention relates to an access fitting assembly for providing access to the interior of conduit systems which operate at pressures up to 6000psi.

Conduit systems such as pipelines suffer from corrosion which needs to be monitored on a regular basis for safety reasons and this is normally done by attaching an access fitting to the conduit which contains a plug that can be removed to allow a probe to be inserted physically into the conduit (or other measuring equipment to be attached to the access fitting) without the need to shut down the system of which the pressurised conduit is a part. The body of the access fitting is normally permanently attached to the conduit by welding, screwing or a flange connection, a removable plug being screwed into the access fitting body to make a pressure seal therewith. The plug can either be hollow or solid depending on the type of access that the fitting needs to provide.

One of the problems with known access fittings of the aforementioned type is that, in exceptional circumstances, the plug which is screwed into the fitting body to make the required high pressure seal can be screwed into the fitting body the wrong way round. This is because the plug is generally cylindrical and is provided with a thread along part of its length by means of which it is screwed into the body. The nose of the plug is generally frusto-conical and includes a primary seal which engages with a primary sealing surface on the body. A secondary seal is axially displaced from the primary seal and bleed apertures are normally located between the primary and secondary seals.The threaded body section is generally located rearwardly of the primary and secondary seals and its end remote from the frusto-conical nose portion is provided with a nut which can be engaged by a suitable tool to screw the plug into the access fitting body.

Unfortunately, the threads on the plug body and its general shape are such that there is nothing on the plug to prevent it from being inadvertently screwed into the body the wrong way round. Although it is extremely unlikely that this would happen, it has been known to occur and the consequences could have been catastrophic as no high pressure seal was made.

It is an object of the present invention therefore to provide an improved high pressure access fitting in which the plug can only be inserted into the plug body in one direction and thus the correct way round whereby its primary sealing member makes the required high pressure seal with the sealing surface on the plug body.

According to the invention there is provided a high pressure access fitting assembly for connection to a high pressure conduit such as a pipeline comprising a body with a bore therethrough into which a removable plug having proximal and distal ends is screwed, the plug including a sealing member adapted to make a pressure seal with a sealing surface provided on the body when the plug is screwed into the body, the plug including plug orientating means operable to ensure that the plug can be screwed into the body in only one direction.

Preferably the sealing member is located adjacent the distal end of the plug and provides a primary seal, a secondary seal being provided adjacent the proximal end of the plug.

In a preferred embodiment, the plug has screw threads on its outer surface located between the primary and secondary sealing members which cooperate with corresponding screw threads on the body.

Preferably the plug orientating means extend radially outwardly from the plug by a distance which is greater than the internal diameter of the threaded bore which receives the plug so that when the plug is screwed into the body, the plug orientating means engage with the body to prevent further axial movement of the plug into the body.

Preferably, the plug orientating means is a flange which engages with the body to prevent said further axial movement of the plug therein. The flange is preferably located on the plug intermediate the screw threads and the distal end thereof so that if an operator attempts to put the plug into the access fitting body the wrong way round, the flange will prevent the threads on the plug body coming into contact with the threads formed in the plug body so the plug cannot be screwed into it. The operator will therefore immediately realise his mistake and reverse the orientation of the plug as a result of which he will find that the nose fits correctly into the plug body and the plug can then be screwed into it.

In a preferred embodiment, the part of the plug orientating means which contacts the fitting body is bevelled to provide a sealing surface which engages with a correspondingly shaped bevelled sealing surface formed on the body in its proximal end, said bevelled sealing surfaces engaging when the plug is screwed fully into the body into its sealing position thereby providing a tertiary seal therebetween.

Preferably the tertiary seal is a metal to metal seal but an auxiliary resilient sealing member can be incorporated into the tertiary seal if necessary.

In the preferred embodiment, the secondary seal is axially located between the primary and tertiary seals, preferably between the plug threads and the tertiary seal.

The plug can either be solid or have a bore therethrough closed at its distal end by suitable means such as a bore seal nut.

Preferably the primary seal includes an inclined face which cooperates with a correspondingly shaped face on the body to make the high pressure seal therewith.

In the preferred embodiment, the secondary seal is a resilient O-ring which can be made of any suitable flexible resilient material such as natural or synthetic rubber, silicon, Viton or EPDM. The primary seal is preferably made from glass-reinforced Teflon but other materials such as VESPEL or KHEMRAZ could be used. If the fitting is to operate at high temperatures, the primary seal can be made from a stainless steel material such as NITRONIC 60 so that a metal to metal seal is provided.

Instead of providing the plug with bleed holes which extend through the interior of the plug of the type employed in the access fittings of the prior art, the threads on the plug preferably include a V-shaped cut therein extending axially of the plug across the threads thereon to allow pressure to bleed off, for instance, when a retreival tool is attached to the fitting and it is required to equalise the pressure in the tool with the pressure in the pipeline at a controlled rate when the primary seal is intentionally released. With the prior art fittings, the bleed holes are normally located between the primary and secondary seals, which means that if the primary seal should fail for any reason, pressure can escape through the bleed holes in the plug thereby by-passing the secondary seal and this is a serious safety hazard.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIGURE 1 shows various different ways of attaching an access fitting of the present invention to a pressurised conduit; FIGURE 2 is a cross sectional view through a high pressure access fitting of the present invention with a hollow plug assembly installed therein; and FIGURE 3 is a cross sectional view of the high pressure access assembly of Figure 2 but with a solid plug assembly installed therein.

Referring to the drawings there is shown in Figure 1 three different ways of attaching access fittings to a high pressure conduit or pipeline 1. The access fitting 2 is attached to the pipeline 1 by a flareweld. The access fitting 2a is attached to the pipeline 1 by means of a flange whereas the access fitting 2b is attached to the pipeline 1 by means of a buttweld. The access fitting 2 can however be attached to the pipeline 1 in other ways not illustrated, for instance, by welding a socket to the pipeline 1 and mounting the access fitting 2 therein or welding an NPT union to the pipeline and screwing an access fitting 2 therein.

Referring now to the access fitting shown in Figure 2, this comprises a body 2 having a proximal end 2d and a distal end 2c. The body 2 has a bore 9 extending through it which has a section 9a at its proximal end of a larger internal diameter than section 9c adjacent the proximal end of the body. The bore 9a is connected to the bore 9c by a bevelled sealing surface 9b, the purpose of which will be explained more fully hereafter. Threads 3 are provided on the outer surface of the body 2 adjacent the proximal end 2d to permit the attachment thereto of other apparatus such as retraction tools and the like.

The distal end 2c of the body 2 is tapered at 4 and includes an annular collar 5 and the body is welded to the pipe 1 in this region. The proximal end 2d of the body is formed with an annular bevelled rebate 7, the purpose of which will also be described shortly. Screw threads 8a are formed along part of the length of the larger diameter portion 9a of the bore 9 as illustrated.

A plug 10 with threads 8b thereon is screwed into the bore 9 in the body 2. In the illustrated arrangement, the plug 10 has a bore 13 extending through it, the proximal end of the bore 13 including threads 11 adapted to threadingly receive a pipe plug 12 therein. The proximal end of the plug 10 is also formed with plug orientating means in the form of an annular flange 14 having a bevelled surface 14a which contacts with the annular bevelled rebate or seat 7 on the body 2 when the plug 10 is fully screwed into the body 2. An annular rebate 26 is formed in the plug 10 immediately adjacent the flange 14 and an O-ring 27 is located therein, the outside diameter of the O-ring 27 being slightly greater than the internal diameter of the bore 9a in the body 2.

The plug 10 is provided with an annular rebate 15 near its distal end which mounts a primary deformable sealing member 16 which is frusto-conical in shape so that its outer surface can engage with the bevelled surface 9b on the fitting body 2. The primary sealing member 16 is retained on the plug 10 by means of a primary seal retaining member 17 which is screwed onto an externally threaded collar 18 provided at the distal end portion of the plug 10. The retaining member 17 has an annular flange 23 which engages the sealing member 16 to retain it in position on the plug 2.

The distal end of the bore 13 through the plug 2 is also internally threaded at 20 to receive a bore sealing nut 19 therein, the free end of the nut engaging with a bore seal 25 to provide a fluid tight seal at the distal end of the bore 13. The nut 19 is locked in position by means of retaining screws 22.

The way in which the access fitting 2 shown in Figure 2 operates will now be described. In order to assemble the fitting 2, the plug 10 is screwed into the fitting body 2 by means of the threads 8a,8b until the frusto-conical surface of the primary sealing member 16 engages with the sealing surface 9b provided in the bore 9 and makes a high pressure seal therewith. When the plug 10 is completely screwed into the body, the bevelled surface 14a on the orientation flange 14 contacts and seats against the corresponding annular bevelled surface 7 on the fitting body 2 and makes metal to metal contact therewith. This provides a high pressure tertiary seal between the plug 10 and the body 2. At the same time, O-ring 27 contacts the wall of the bore 9a and makes a secondary seal therewith.

Although not illustrated, the threads 8b on the plug 10 have a V-shaped groove cut in them to allow pressure to bleed past them when the seal between the primary sealing member 16 and the sealing surface 9b on the fitting body 2 is released, for instance, when a retreival tool (not shown) is used.

When a retreival tool or assembly is attached to the access fitting by means of the threads 3, it allows the plug 10 to be removed and replaced with a probe or some other measuring or inspection device without releasing the high pressure in the conduit to which the fitting 2 is attached. When the retreival tool is secured on the fitting 2 in known manner, the plug 10 is unscrewed to allow the pressure in the retreival tool (atmospheric) to be increased to equal that in the pressurised conduit to which the fitting 2 is attached. This is done by unscrewing the plug 10 thereby releasing the primary and tertiary seals 16 and 7.When the plug 10 has been unscrewed sufficiently to move the secondary seal 27 axially out of the bore 9, high pressure in the conduit can flow past the primary seal 16, through the V-cut in the threads 8b and out of the bore 9 into the interior of the retreival tool until the pressures upstream and downstream of the plug 10 equalise. The plug 10 can then be replaced by another suitable measuring device or probe in known manner.

Another important advantage of the preferred illustrated access fitting is that it has 3 high pressure seals 16, 27 and 7 thus rendering it much safer than known fittings.

Should the primary seal 16 fail for any reason, then the pressure will gradually weep through the bore 9 via the Vshaped bleed cut out (not shown) in the threads 8b until it reaches the secondary seal provided by the O-ring 27 where it will be contained. Should for any reason this secondary seal fail then there is the preferred further tertiary seal provided by the cooperation between the bevelled face 14a on the orientating flange 14 and the sealing surface 7 on the fitting body 2. The illustrated access fitting is thus extremely safe.

Another important advantage of the illustrated access fitting is that it is impossible to insert the plug 10 into the fitting body 2 the wrong way round because the plug orientating flange 14 precludes this from happening. It will be appreciated that should an operator inadvertently think that the pipe plug 12 is the front nose of the plug 10 and try to insert it into the bore 9 in the fitting body 2, he would find that the flange 14 stops the threads 8a,8b from engaging so he would immediately reverse the plug 10 and the threads 8a,8b would then mesh allowing the plug 10 to be screwed into the body 2.

The embodiment shown in Figure 3 is identical to that illustrated in Figure 2 except that there is no throughbore 13 in the plug 10. Instead, the distal end of the plug 10 is formed with an externally threaded spigot 30 on which the primary seal retaining nut 17 is screwed and retained in position by means of the retaining screws 22. In all other respects the assemblies are identical.

The two embodiments just described are given by way of example only and it should be noted that the tertiary seal described is a preferred optional feature of the access fitting of the invention. The main feature which characterises the present invention over the prior art is the provision of the laterally extending orientation flange 14 which prevents the plug 10 being screwed into the fitting body 2 the wrong way round. Rather than provide a tertiary seal as a result of the cooperation between the bevelled surfaces 14a and 7, the flange 14 could simply engage with the end face 2d of the fitting body 2 or a rebate therein or some other part of the body 2 to limit axial movement of the plug 10 into the body 2 in the correct direction or prevent insertion of the plug 10 in the body 2 in the wrong direction.

Claims (18)

1. A high pressure access fitting assembly for connection to a high pressure conduit comprising a body with a bore therethrough into which a removable plug having a proximal and distal end is screwed, the plug including a sealing member adapted to make a high pressure seal with a sealing surface provided on the body when the plug is screwed into the body, the plug including plug orientating means operable to ensure that the plug can be screwed into the body in only one direction.

2. A fitting as claimed in claim 1 wherein the sealing member is located adjacent the distal end of the plug and provides a primary seal.

3. A fitting as claimed in claim 2 wherein a secondary seal is provided adjacent the proximal end of the plug.

4. A fitting as claimed in claim 3 wherein the plug has screw threads on its outer surface located between the primary and secondary sealing members which cooperate with corresponding screw threads on the body.

5. A fitting as claimed in any preceding claim wherein the plug orientating means extend radially outwardly from the plug by a distance which is greater than the internal diameter of the threaded bore which receives the plug so that when the plug is screwed into the body, the plug orientating means engage the body to prevent further axial movement of the plug into the body.

6. A fitting as claimed in claim 5 wherein the plug orientating means is a flange.

7. A fitting as claimed in claim 6 wherein the flange is located on the plug intermediate the screw threads and the distal end thereof.

8. A fitting as claimed in any preceding claim wherein the face of the plug orientating means which contacts the fitting body is bevelled to provide a sealing surface which engages with a correspondingly shaped bevelled sealing surface formed on the body in its proximal end, said sealing surfaces engaging when the plug is screwed fully into the body into its sealing position thereby providing a tertiary seal therebetween.

9. A fitting as claimed in claim 8 wherein the tertiary seal is provided by the metal to metal contact between the bevelled surface on the plug orientating means and the bevelled surface on the fitting body.

10. A fitting as claimed in claim 8 or claim 9 wherein the tertiary seal incorporates an auxiliary resilient sealing member.

11. A fitting as claimed in any of claims 8 to 10 wherein the secondary seal is located between the primary and tertiary seals.

12. A fitting as claimed in claim 11 wherein the secondary seal is located between the plug threads and the tertiary seal.

13. A fitting as claimed in any preceding claim wherein the plug is solid.

14. A fitting as claimed in any one of claims 1 to 12 wherein the plug has a bore formed therethrough closed at its distal end by bore closure means.

15. A fitting as claimed in any preceding claim wherein the sealing member has an inclined face which cooperates with a correspondingly shaped face on the body to make the high pressure seal therewith.

16. A fitting as claimed in any of claims 2-15 wherein the secondary seal is a resilient O-ring.

17. A fitting as claimed in any preceding claim wherein the threads on the plug have a V-shaped cut therein extending axially of the plug across the threads thereon.

18. A high pressure access fitting substantially as herein described with reference to the accompanying drawings.