GB2388169A

GB2388169A - Pipe joint

Info

Publication number: GB2388169A
Application number: GB0209930A
Authority: GB
Inventors: Stephen Hatton
Original assignee: 2H Offshore Engineering Ltd
Current assignee: 2H Offshore Engineering Ltd
Priority date: 2002-05-01
Filing date: 2002-05-01
Publication date: 2003-11-05
Also published as: GB0209930D0

Abstract

A pipe joint between two oil or gas well pipes 12,14 has a male/female threaded connection, with an elastomeric seal 22 on the external side of the threads. The external seal is bonded to an outer pipe diameter so as to straddle the corrosion resistant coating on the pipe. As a result, there is no place where either of the pipes is exposed to seawater without being protected by the seal and/or the corrosion resistant coating. The seal can have outward facing ribs 26 to make contact with the female part of the joint. Generally two pipes 12,14, each with a male threaded end, will be connected by a short coupling sleeve 10 which has two internal, female threaded portions.

Description

- 1 238816

Pipe Joint This invention relates to a pipe joint for joining two pipes, by means of a threaded connection and is intended 5 particularly, but not exclusively, for connecting steel pipes used for offshore riser and flowline systems constructed for transportation of hydrocarbons between the seabed and a floating vessel.

10 Risers are long tubular structures assembled from shorter lengths of steel pipe typically 12m long. In service they are subjected to high dynamic loads and since service lives in excess of 20 years are often required fatigue is an important design issue. High strength joints are 15 required between pipes and these must exhibit a low stress concentration factor in order to achieve the required design life.

Known threaded and coupled joints are shown in Figure 1.

20 Such joints consist of a machined tapered thread on the end of each pipe 1. These are then connected using a coupling sleeve 2. This method is cost effective since it does not require welding or local thickening of the pipe wall, and joints of this type are manufactured in large 25 quantities for application in wellbore casing programs.

However, these conventional casing connection designs do not normally provide an external seal to prevent water ingress into the thread. Water ingress can cause corrosion 30 and this can affect fatigue performance leading to

l - 2 premature failure.

Other known joints incorporate a rubber 'O. ring or lip seal. These designs require the body of the pipe to be 5 locally machined to provide a good sealing surface to interface with the seal which is located in a pocket machined on the internal diameter of the coupling sleeve.

Such joints have two design features that are not desirable. Firstly, the machined surface reduces the wall 10 thickness of the pipe locally, which increases its stresses when the pipe is under load. Secondly, a portion of the machined seal surface is directly exposed to the external seawater, which can result in corrosion pitting.

15 According to the present invention, there is provided a pipe joint between two pipes for use in offshore oil and gas exploration and production, the joint comprising male threaded portions on two pipe ends, a coupling sleeve with two internal female threaded portions for engagement 20 with the male threads and elastomeric seals for preventing water penetration from the exterior of the pipe to the engaged threads and to the interior of the pipes.

The seals are preferably located between, and seal between, surfaces of the pipe and coupling sleeve in a manner which prevents exposure of bare metal on the pipe body. The joint does not require the pipe body to be machined to achieve a reliable seal. As a result, the only parts of the pipes which are exposed to seawater are parts 30 which have their corrosion resistant coating intact.

- 3 The elastomeric seals are preferably located (after assembly of the joint) in seal pockets formed in the internal diameter of the coupling sleeve. The seal pockets will be machined, to provide a surface against which the 5 seal can be seated. The machined surfaces of these pockets will be exposed to seawater outside of the joint, but this region is not a critical portion of the joint and some corrosion here can be tolerated. The seals are landed and preloaded during normal make-up of the joint.

The seals are preferably annular in form and are permanently bonded, using a suitable adhesive, to the pipe ends. Nitrile rubber is a suitable seal material. The seals do not have to be bonded to the pipes. If the seals 15 are elastic annular rings, they may be stretched over the pipe ends and friction may be sufficient to ensure that the seals go into the pockets on the sleeve on make-up, with the preload exerted through being confined in the pocket ensuring an adequate seal both against the pipe 20 surface and against the sleeve.

Each seal can have one flat face, which is adhesively bonded to one pipe, and one ribbed face arranged so that the crests of the ribs make sealing contact with a surface 25 of a machined pocket in the sleeve. The ribs preferably have a saw-tooth profile, with the steep flank of each tooth facing out of the joint and being exposed to external water pressure. In an alternative form, the seal may have a simple wedge shape that locates in a tapered 30 pocket.

- 4 - The height of the ribs may vary along the axial dimension of the seal, with the highest ribs being at the outer edge of the seal exposed to water pressure. The crests of the 5 ribs may be rounded off.

The material of the seal should be soft enough to enable the joint to be assembled without risking displacing the bonding between the seal and the component to which it is 10 bonded, but hard enough to function as an effective seal under the conditions likely to be encountered in service.

A suitable seal has a hardness between 80 and 90 Shore.

It is also within the scope of the invention for the joint 15 may be made between two pipes without the interposition of a coupling sleeve. In this case, one of the pipes will have a male threaded portion and the other will have an end with a female threaded portion (for example by having a larger diameter collar with an internal thread welded to 20 the pipe end), and there will be just a single elastomeric seal. The invention will now be further described, by way of example, with reference to the accompanying drawings, in 25 which: Figure 1 shows a threaded and coupled joint according to the prior art;

30 Figure 2 shows a threaded and coupled joint according

- 5 to the invention; Figure 3 shows an enlarged details taken within the circle A from Figure 2; and Figure 4 is an enlarged view of part of an alternative seal ring form.

Figure 2 shows a coupling sleeve 10 joining two pipe ends 10 12 and 14. In the areas 16, the coupling sleeve and the pipe ends have mutually engaging threads to provide a mechanical connection between the three component=.

The joint configuration includes main high pressure metal 15 nose seals at 13.

The coupling sleeve length is longer than in the prior art

joint shown in Figure 1, and annular pockets 20 (see Figure 3) are machined on the internal diameter to 20 accommodate annular seals 22 that are mounted on the pipe bodies 12,14.

Typically the seals 22 are manufactured from a nitrite rubber with a low friction coating or lubricant such as 25 PTFE on the face contacting the coupling sleeve so as to minimise friction during make-up. As the seal is drawn into the pocket it is compressed by interference with the coupling sleeve pocket. This generates high compressive forces on both faces of the seals.

- 6 - Each seal 22 has a flat base 24 that allows it to be bonded to the pipe body using an adhesive. The upper face has a saw tooth profile 26, which provides a number of features: À Compliance of the tips 28 of the seal accommodates a wide range of seal pocket dimensional tolerances resulting from pipe diameter manufacturing fluctuations. 10À allows insertion of the seal into the coupling sleeve pocket with minimum force À generates point contact pressure at the tips of each tooth to initiate a positive seal; À provides increased contact pressure and hence 15improved sealing due to application of external over pressure; À allows excess thread dope and grease to be extruded out past the seal during coupling sleeve make-up; 20 The seals 22 are fitted circumferentially around the pipe bodies 12,14 using an adhesive. Each seal may either be a continuous ring or a strip with a scarf joint. The axial position of each seal on the pipe body is accurately determined using a gauge referenced from the machined pipe 25 end (at 18. The pipe body may be coated using an epoxy paint or a thermally sprayed aluminium to provide corrosion resistance. The coating extends up to, but stops short of the machined pipe thread. The seals are positioned on the pipe such that they straddle the 30 corrosion coating ensuring that no bare steel is exposed

on the pipe side of the seal once the connection is fully made-up. The threaded connection is made up conventionally. Each 5 pipe section has a sleeve lo threaded onto one end before that pipe section is deployed. When the pipe sections are to be connected, for example as a riser pipe, the sections are put into a vertical orientation with the sleeve end uppermost. The connection process is initiated by stabbing 10 the pipe into the coupling sleeve ensuring that the threads are not crossed. A taper thread profile allows the pipe and coupling sleeve to be deeply stabbed without rotation. The connection is then rotated to engage the threads using a torque tool to apply a controlled torque.

As the pipe 14 is rotated the seal 22 is drawn into the sleeve 10 until the final seal position is reached when the joint is fully made up. As the seal is drawn into its pocket it is compressed and preloaded to ensure a positive 20 seal. When fully engaged in the pocket, the leading face of the seal contacts the bottom of the tapered seal pocket 20 with a predefined compression.

Any excess thread dope that is trapped in the threads by-

25 passes the seal in the opposite direction to the saw tooth profile. This ensures that the seal is correctly seated and is not extruded out of the pocket due to hydraulic lock. 30 This seal arrangement where the seal is mounted on the

- 8 pipe ensures that pipe stabbing into the coupling sleeve and the initial critical make-up of the connection is not effected by the presence of the seal, which is initially kept clear of the pocket. This simplifies stabbing and 5 ensures that the seal is not damaged.

The seal configuration and method of attachment to the pipe body ensures that if the main high pressure metal nose seal leaks during a high load condition the 10 environmental seal (ie the seal 22) will allow the pressure to be released past the environmental seal. This ensures that trapped pressure in the threads does not effect the joint performance and does not simply blow the environmental seal out of its pocket.

Claims

( - 9 - Claims

1. A pipe joint between two pipes for use in offshore oil and gas exploration and production, the joint 5 comprising male threaded portions on two pipe ends, a coupling sleeve with two internal female threaded portions for engagement with the male threads and elastomeric seals for preventing water penetration from the exterior of the pipe to the engaged threads and to the interior of the 10 pipes.

2. A pipe joint as claimed in Claim 1, wherein the pipes are provided with a corrosion resistant coating, and the seals are mounted on the pipes at positions where the 15 coatings are intact, without damaging the effectiveness of the coating.

3. A pipe joint as claimed in Claim l or Claim 2, wherein the threaded portions carry tapered threads.

4. A pipe joint as claimed in Claim 1, wherein the seals are located on surfaces of the pipes which do not have a machined finish.

25 5. A pipe joint as claimed in any preceding claim, wherein the seals are landed into seal pockets formed in the body of the coupling sleeve and positively preloaded through the action of making-up the threaded connection.

30 6. A pipe joint as claimed in any preceding claim,

- 10 wherein the seals are initially located away from the coupling sleeve during stabbing of the pipe into the coupling sleeve to prevent damage to the seals.

5 7. A pipe joint as claimed in any preceding claim, wherein the seals are annular in form and are permanently bonded, using a suitable adhesive, to the respective pipe ends. lo 8. A pipe joint as claimed in any preceding claim, wherein the seals are made of nitrite rubber.

9. A pipe joint as claimed in any preceding claim, wherein the seals have one flat face, which is adhesively 15 bonded to one pipe, and one ribbed face arranged so that the crests of the ribs make sealing contact with the coupling sleeve.

lo. A pipe joint as claimed in Claim 9, wherein the ribs 20 have a sawtooth profile, with the steep flank of each tooth facing out of the joint and being exposed to external water pressure.

11 A pipe joint as claimed in Claim 10, wherein the 25 height of the ribs varies along the axial dimension of the seal, with the highest ribs being at the outer edge of the seal exposed to water pressure.

12. A pipe joint as claimed in any one of Claims 10 or 30 11, wherein the crests of the ribs are rounded off.

/ 13. A pipe joint between two pipes for use in offshore oil and gas exploration and production, the joint comprising a male threaded portions on one pipe end, a 5 female threaded portion on the other pipe end and an elastomeric seal between the pipe end" for preventing water penetration from the exterior of the pipe to the engaged threads and to the interior of the pipes.

10 14. A pipe joint substantially as herein described with reference to Figures 2 to 4 of the accompanying drawings.