GB2313889A

GB2313889A - Connection between riser pipe and pipe system on a platform or ship

Info

Publication number: GB2313889A
Application number: GB9711215A
Authority: GB
Inventors: Finn Roeed
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 1996-06-05
Filing date: 1997-05-30
Publication date: 1997-12-10
Anticipated expiration: 2017-05-30
Also published as: NO962353D0; NO962353L; MX9704135A; GB2313889B; BR9703470A; ZA974803B; GB9711215D0

Abstract

The connection between a flexible or semi-flexible riser pipe 12 and the pipe system 3 comprises a connection housing 5, with an upper gasket 6 and lower bearing ring ,7 and a connection coupled to the riser pipe, provided with a continuous bore and with upper 9 and lower 10 part spherical surfaces to lie against the corresponding surfaces on the upper gasket 6 and lower bearing ring 7. The gasket 6 is present against the surface 9 by circumferently arranged springs and the process fluid from above. The upper surface 9 may be concave.

Description

TITLE: A DEVICE FOR CONNECTING A RISER PIPE TO A PIPE SYSTEM ON A FLOATING PLATFORM OR SHIP The present invention concerns a device for connection or suspension between a detachable flexible or semi-flexible riser pipe and a pipe system on a fixed or floating platform or ship, which riser pipe is designed to transfer oil andlor gas and extends from a well head on the sea bed to the platform or ship.

As oil and gas fields at great depths of the sea are developed, the installations will increasingly be floating structures such as plafforms which move under the influence of waves, wind and currents. This means that the pipes which are linked to production and injection wells on the sea bed must be sufficiently flexible and strong to be able to move with the platform on the surface. For this purpose, special flexible riser pipes have been developed which withstand high pressure and have relatively high bending flexibility. As the movements and wave forces are greatest at the surface, the pipe is also exposed to the greatest bending stresses in this area. In particular, the stress will be great where the flexible pipe is connected to the platform as this point is very stiff in relation to the pipe. Various principles have been elaborated to limit the bending stresses at the suspension point of the pipe. One method which is widely used involves the use of a stiff guide pipe through the wave zone through which the flexible pipe passes. In order to limit the bending stress on the flexible pipe at the entrance to the guide pipe, the latter is provided with a trumpet-shaped end piece which controls the bending radius of the flexible pipe when it lies against the wall on the inside. In this way, the bending stress on the flexible pipe can be reduced by means of the shape of the trumpet-shaped end piece. A more simple arrangement involves suspending the pipes freely from the deck. This produces high wave stresses on the pipes and it is particularly important to limit the resulting bending moments where the pipe is fastened to the deck. In such arrangements, it is common to use so-cailed bending limiters. These are specially manufactured flexible pipe sections which are placed outside the flexible pipe and which limit the bending radius of the flexible pipes with a precisely stepped bending stiffness. However, neither of these solutions provide satisfactory security against overstressing and thus the risk of breaking in the bending area of the pipes.

Today, there are thus solutions for suspending "standard" flexible pipes from floating platform. However, standard flexible pipes also have limitations regarding pressure and temperature so that for some oil and gas fields it is very unfavourable or impossible to use this type of pipe. One possible solution is to use semi-flexible pipes. This means pipes which are made of metals with a low Young's modulus and a high tensile strength such as titanium. These pipes will have acceptable stress tolerance in the area between the sea bed and the platform under the influence of waves and movement, but on account of the relatively high bending stiffness, it will be difficult or impossible to achieve an acceptable level of stress tolerance in the connection to the platform with the solutions described for standard flexible pipes.

With the present invention, a device for suspending detached flexible or semi-flexible riser pipes from fixed and floating plafforms has been arrived at which does not absorb bending stresses and which is thus not exposed to the risk of breaking or has a significantly reduced risk of breaking as a consequence of damaging bending stresses. The solution is thus much safer than the solutions known previously. Furthermore, it is easy and cheap and takes up little space.

The present invention is characterised in that the suspension system comprises a ball joint or a connection similar to a ball joint, comprising a connection housing with upper and lower bearing rings and a connection body or ball body which is provided with a continuous bore and upper and lower spherical parts which are designed to lie against the corresponding bearing parts on the upper and lower bearing ring as stated in the attached claim 1. The dependent claims 24 state advantageous features of the present invention.

Preferred embodiments of a connection or suspension device in accordance with this invention will now be described with reference to the acccr yin drawings, in which: Fig. 1 shows a drawing of a platform with a riser pipe which is connected to the platform by means of a suspension system according to the present embodiment, Fig. 2 shows an elevation of the suspension system according to the present embodiment, Fig. 3 shows, in larger scale, a detail of the system shown in Fig. 2, and Fig. 4 shows an alternative design of the system shown in Fig. 2.

As stated, Fig. 1 shows a drawing of a platform 1 with a riser pipe 2 which is connected to the platform, and a pipe system 3 mounted on the platform (see Fig. 2), by means of a suspension system 4 according to an embodiment of the present invention.

As particularly seen in Fig. 2, the suspension system or connection 4 comprises a ball joint or connection similar to a ball joint which comprises a connection housing 5, with an upper gasket 6 and a lower bearing ring 7, and a connection body 8 with upper 9 and lower 10 spherical parts which are designed to lie against the corresponding parts on the upper gasket 6 and lower ring 7. The connection body 8 is provided with a continuous bore 11 and is directly connected to the riser pipe, preferably by means of a welding connection.

The connection housing 5 is in two parts and comprises an upper part 12 and a lower part 13 which are connected by means of a nut and bolt connection 14. The upper housing part 12 is, in turn, connected to the pipe system 3 on the platform via a flange connection 15 while the lower housing part 13 is fastened to the platform structure (not shown in detail) via a funnel-shaped structural part 16 with a flange connection 29.

Regarding the structural part 16, a rubber ring 18 may appropriately be arranged on the inside to prevent the riser pipe coming into direct contact with the metal in this part 16 in order thus to avoid damage to the riser pipe.

Regarding the gasket 6 and bearing ring 7, these parts are arranged in cavities in each of their respective housing parts just inside the openings 19, 20 in the housing parts 12, 13. The lower bearing ring 7 is connected to housing part 13 while the upper gasket 6 is arranged to be movable and is pressed against the partially spherical bearing surface 9 of the connection body 8 by means of springs 23, arranged along the circumference of the ring 6, and internal process pressure in the ring 6, as shown in further detail in fig. 3. In the example shown here, the process pressure is thus utilised to achieve sufficient surface pressure between the spherical surfaces in the ring 6 and the connection body in order to achieve a sufficient metal-to-metal seal between these surfaces.

A retaining ring 24 with an inward-facing fixing hook 25 which is screwed, by means of a screw connection 26, to the upper housing part 12 is designed to keep the upper ring in place during mounting and possible demounting of the suspension system according to the present invention. Both the upper gasket and the lower bearing ring are provided with channels and grooves 21, 22 for the application of lubricant to the bearing surfaces between the rings and the connection body 8.

Furthermore, the gasket 6 and bearing ring 7 are, where necessary, provided with seals 27, 28 between the gasket 6 and bearing ring 7 and the housing parts 12, 13 and between the bearing surfaces of the gasket 6 and bearing ring 7 and the connection part 8.

The connection part 8 is, as shown in figs. 2 and 3, provided with convex spherical parts 9, 10 with a common centre. In order to prevent it collecting sand and other contaminants in the area between the upper bearing ring 6 and the spherical bearing surface 9, which damage this upper bearing support, the bearing surface 9 may be concave as shown in fig. 4.

In the example shown in fig. 4, the connection housing 5 is electrically insulated from the platform and pipe system by means of an electrically insulating material 17. This is done to prevent the formation of hydrogen on the riser pipe 12, which is made of titanium here. In this connection, please note that the present invention as it is defined in the claims is not limited to the use of a riser pipe of titanium but can be used for any type of riser pipe of flexible or semi-flexible type for which it may not be necessary to have electrical insulation between the riser pipe and the platform.

In particular, the upper gasket 6 is based on a metal-to-metal seal as a back-up seal for seal 28, as explained in a previous paragraph.

Claims

CLAIMS:

1. A device for connection or suspension between a detachable flexible or semi-flexible riser pipe (2) and a pipe system (3) on a fixed or floating platform or ship, characterised in that the device comprises a ball joint or a connection similar to a ball joint which comprises a connection housing (5), with an upper gasket (6) and lower bearing ring (7), and a connection body which is provided with a continuous bore and with upper (9) and lower (10) spherical parts which are designed to lie against the corresponding parts on the upper gasket 6 and lower bearing ring 7.

2. A device according to Claim 1, characterised in that the connection housing comprises an upper part (12) and a lower part (13) which are connected by means of a screw connection (14).

3. A device according to Claims l and 2, characterised in that the upper housing part (12) is connected to the pipe system (3) on the platform via a flange connection (15) or similar, that the lower housing part (13) is fastened to the platform structure via a structural part (16) and the riser pipe is connected directly to the connection part (8) by means of welding or similar.

4. A device according to Claims 1 and 2, c h a r a c t e r i s e d i n t h a t the structural part (16) has a funnel-shaped opening facing downwards.

5. A device according to Claims 3 and 4, characterised in that the housing (5) with the riser pipe (2) is electrically insulated from the pipe system (3) and the platform (1).

6. A device according to Claims 1-3, characterised in that the upper gasket (6) is arranged to be movable in the upper housing part (12) and is designed to be pressed against the upper spherical part (9) of the connection part (8) by means of a spring arrangement (23) and establish the process pressure in the pipe system (2, 3).

7. A device for connecting a detachable flexible or semi-flexible riser pipe to a pipe system on a fixed or floating platform or ship substantially as hereinbefore described with reference to Figs. 1-3 or Figs. 1 and 4 of the accompanying drawings.