JPS63111392A - Flexible joint of riser pipe including large number of tube - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the use of risers in the offshore oil and gas industry.

Risers are structural pipes that connect equipment on the ocean floor to ships on the surface. As a floating ship at sea is moved by surrounding forces while at anchor, the riser also moves, resulting in an angular shift.

Therefore, a flexible joint is usually used at the base of the riser to allow this angular movement. Ball fittings, universal fittings, and layered elastomer/steel fittings (
A variety of flexible joints have been used, such as Murdoch joints. These fittings were satisfactory when using a single pipe. However, there are problems when using several pipes. This is commonly applied when several tubes are housed within a larger pipe, such as when risers are used in offshore well workovers and production.

Access to the wellbore is via an inner tube and the structural loads are carried by the outer pipe.The present invention relates in particular to the flexibilization of risers with inner tubes.

One solution is to use a variant of the Murdoch fitting with multiple holes. However, this is more complex in that additional moving parts are required to hold the elastomer in compression. It also creates kinks, which limits movement of the device through the tube. Since the tubes are arranged so that they are confined closer to each other as the angle increases, the device will be confined to small angles.

Another solution is to make the pipes and tubes deformable without using flexible joints. In this case, the outer pipe is gradually strengthened towards its base in order to obtain high bending moments.

This is called a stress joint. A significant drawback of this is that the structure beneath the stress joint has high bending moments (see FIG. 2).

High bending moments can be reduced by arranging the flexible unit within the outer case. The radius of curvature of the curvature can therefore be reduced to allow for smaller diameter inner tubes. This can be achieved in two ways. First, a multi-flex joint can be used to approximate several straight sections, the curves of the inner tube. How this is done is the subject matter of Canadian Patent Application No. 421-909. Second
The method of At the lowest position there is no deflection and therefore no bending moments are induced, but there are problems with the relative length changes of the inner tube and outer pipe.

This is shown in Figure 4. When the riser is positioned vertically, the tube and pipe lengths are the same. It is important that the inner tube is maintained within its permissible stress levels when the riser is tilted. Therefore, there is a minimum radius of curvature at which the tube can be bent. - An example is illustrated in FIG. In this view, the inner tube bends from a vertical position toward the centerline of the outer pipe at an angle, bends in the opposite direction with the same minimum radius, and approaches and becomes parallel to the centerline of the outer pipe. The centerline distance of the inner tube is longer than the centerline distance of the outer pipe, so that the top of the tube is lower than the top of the pipe. A direct way to overcome this is to provide the tube with a flexible joint (which does not serve the purpose) or to provide a slide joint with the tube (although this is generally problematic).

Alternatively, the relative length changes can be accommodated by shortening the outer case. This needs to be done while the riser is still able to carry the structural loads. Figure 5 illustrates how this can be achieved. Instead of a central pivot, a disk is attached to the bottom of the outer pipe of the riser. As the riser moves angularly, the end of the disc becomes the pivot point. As the riser tilts, point E on the outer pipe moves below point A on the inner tube, effectively shortening the length of the outer pipe relative to the inner tube.

The diameter of the disk determines the amount of relative length change. therefore,
It is possible to accurately compensate for the difference in travel length between a curved tube and a straight riser pipe. This is true for the shape shown in FIG. 5 for only one selected angular position.

Although we have discussed a certain radius of the pivot disk at the bottom of the riser to accommodate a certain angle, other angles cannot accurately compensate for relative length changes, but the main purpose is to It is to keep it. This is achieved by making the above geometry the maximum expected angle of the riser. This is the case when the inner tube is tilted at the highest preset stress level. At smaller angles the opposite phenomenon occurs and the inner tube has a longer length. The geometry of the inner tube is varied by creating additional opposing curves at both ends of the inner tube. Various shapes of the inner tube have been proposed, but they do not necessarily arise by themselves, limiting the bending so that a minimum radius of curvature is not exceeded and the deflection is not concentrated in one part of the length. It is also possible to additionally provide a stiffening member or a stiffening member.

Hereinafter, the present invention will be explained based on examples.

A preferred embodiment of the invention is shown in FIG. 1, in which a riser outer pipe 1 covers an inner tube bundle 2. The ends of the tube bundle 2 are connected to a connector assembly 3 at the bottom. These are connected to the riser base 4 by the connector 3.
It is shown attached to. The guide member is
It consists of a guide cone and -time fixing member 5, and a slide guide member 6. The riser outer pipe l is attached to the connector assembly 3 via bearing pads 7.8. Pad 7 is attached to outer pipe l and pad 8 is attached to connector assembly 3. Bearing pads 7.8 are used to avoid point contacts that create high local stresses. The bearing pads 7.8 therefore distribute the load over a wide area and reduce contact stresses. They are made of suitable bearing materials.

At certain angles of the riser, only one bearing pad is subject to the tensile load of the riser. - When the riser is tilted in the plane, it pivots around the radial center of one of said bearing pads. As the slope plane changes, the contact location changes to the next bearing pad. To achieve this effect, the bearing pad has a spherical contact surface. In this way the riser can be tilted in any direction and the load is automatically supported by the appropriate pad within the ring of bearing pads. Since the bearing pad is offset from the centerline of the riser, it serves to shorten the length of the outer pipe as described above to compensate for the difference in length between the outer pipe and the inner tube.

To avoid problems with length differences between the individual inner tubes, they can also be twisted at least 180 degrees and rotated all together as an assembly.

To avoid torque problems, the tubes may be divided into groups, with one set twisted in one direction and the other set twisted in the other direction, and to ensure that all of the tubes move together. In order to prevent the tubes from bending tighter than the minimum radius of curvature mentioned above, a funnel-shaped guide member 10 is provided, in which all the tubes may be joined together by a plate such as the one indicated at 9. has been done.

The guide assembly consisting of parts 5.6 shows how the flexible joint assembly can be used with the riser guide and positioning members described in Canadian Patent Application No. 421-909.

Riser base 11 is a typical riser base for floating production equipment where flow lines from individual surrounding wells converge to raise the riser.

Figure 1 shows the application of a floating manufacturing device to a riser for flexible joints that require an inclination of 30 degrees or more.
It may also be used as a test riser for workover or expansion wells. In this case, a smaller angle is required,
The diameter of the joint will be very small, but more importantly, it will allow woody access through the hole.

The angled inner tube of the present invention is ideal for this use.

[Brief explanation of the drawing]

FIG. 1 is a cutaway perspective view of a riser flexible joint illustrating an embodiment of the present invention, FIG. 2 is a diagram illustrating a large bending moment generated at the base of an inclined riser, and FIG. 3 is a diagram showing a riser base with no bending moment. FIG. 4 is a diagram showing the relative length change of the outer case and inner tube at the base of the riser, and FIG. 5 is a diagram showing compensation for the relative length change by the deflection pivot point. 1...Outer pipe, 2...Inner tube, 7.8.
...Bearing pad. 82 Figure 3

Claims (3)

[Claims] (1) The pivot point of the flexible joint is offset from the centerline of the riser to compensate for the difference in length between the bent inner tube and the inclined outer pipe when the riser is tilted at a certain angle. A flexible joint for riser pipes containing multiple tubes. (2) A flexible joint according to claim 1, wherein an annular eccentric pivot point is formed to transfer the load so that the riser can be tilted in any direction. 3. A flexible joint according to claim 2, in which the load is transferred by spherical bearing pads that reduce local contact stresses and position the components in their proper relationship.