GB2176858A - Pipeline safety joint - Google Patents

Abstract

The invention relates to a pipeline safety joint comprising two pipe sections (11 and 12) slidably arranged relative to each other so as to form a fluid passage (13), a compensating bellows (18) of which the interior (19) is in fluid communication with the fluid passage (13) for exerting a compensating force to counteract the force caused by the pressure of the fluid present in the passage (13) during normal operation, a sleeve (26) of which one end (30) is in contact with a split key ring (24) arranged in an annular groove (25) in the second pipe section (12) and of which the other end (32) is in contact with the compensating bellows (18), the other end of the compensating bellows (18) cooperating with the first pipe section (11), and means for releasing the split key ring (24) if the pipe sections (11 and 12) are separated by an axial force in excess of a predetermined value. Such a pipeline safety joint is included in a pipeline to avoid damage to the pipeline when the pipeline is dragged away, for example by a dragging anchor. <IMAGE>

Description

SPECIFICATION Pipeline safety joint The invention relates to a pipeline safety joint which will be included in a pipeline or flowline when it is expected that there is a chance of loading the pipeline with such an axial force that the pipeline might be damaged. Subject to such a load is for example an underwater pipeline laying on the water bottom which may be picked up by a dragging anchor or by a trawl board pertaining to a fishing net dragged along the water bottom. In addition to damage to the pipeline also the installations to which the pipeline is connected may be damaged. The pipeline safety joint will be released if the axial force exceeds a predetermined value. The predetermined value of the axial force is so selected that the pipeline or the installation to which the pipeline is connected remains undamaged.

In a suitable embodiment two pipeline safety joints are included in the pipeline, one at or near each end of the pipeline.

Known in the art is a pipeline safety joint comprising two pipe sections slidably arranged in relation to each other so as to form a fluid passage, and an annular compensating chamber which is in fluid communication with the fluid passage and which is provided with an annular piston which is so arranged that the force exerted by the piston compensates the force separating the two pipe sections caused by the pressure of the fluid in the fluid passage during normal operation. To avoid leakage, the annular piston is provided with elastomer sealing rings.

The condition of the elastomer sealing rings will deteriorate with time. Consequently, the service life of the pipeline safety joint is dependent on the service life of the elastomer sealing ring which is strongly influenced by the fluids which are transported through the pipeline in which the pipeline safety joint is included. Because a variety of fluids can be transported through the pipeline the service life of the elastomer sealing rings, and consequently, the service life of the pipeline safety joint, cannot be predicted, and the pipeline safety joint must be often inspected, which can only be done after replacement.

It is an object of the invention to increase the service life of a pipeline safety joint, so as to reduce the amount of inspections considerably.

To this end the pipeline safety joint according to the invention comprises two pipe sections slidably arranged in relation to each other so as to form a fluid passage, a compensating bellows of which the interior is in communication with the fluid passage, means for transferring a compensating force exerted by the compensating bellows from one of the pipe sections (the first pipe section) via releasable holding means to the other pipe section (the second pipe section), and means for releasing the releasable holding means if the pipe sections are separated by an axial force in excess of a predetermined value.

The compensating force exerted by the compensating bellows during normal operation will substantially compensate the force separating the two pipe sections caused by the pressure of the fluid in the fluid passage.

Therefore, this force will not release the releasable holding means.

The invention will be described by way of example in more detail with reference to the drawings, wherein Figure 1 shows a partial longitudinal section of a pipeline safety joint according to the invention; and Figure 2 shows a partial longitudinal section of an alternative to the pipeline safety joint shown in Figure 1.

The pipeline safety joint shown in Figure 1 comprises a first pipe section 11 and a second pipe section 12 slidably arranged in relation to each other so as to form a fluid passage 13, which pipe sections preferably are circle cylindrical. The pipeline safety joint can be included in a pipeline or flowline with the use of flanges 14 and 15 arranged at the free ends of the pipe sections 11 and 12.

In order to compensate during normal operation the force caused by the pressure of the fluid in the fluid passage 13 acting on the end surfaces 16 and 17 to separate the pipe sections 11 and 12, the pipeline safety joint is provided with a compensating bellows 18.

The interior 19 of the compensating bellows 18 is in fluid communication with the fluid passage 13 by means of a conduit 20, and the central longitudinal axis 21 of the compensating bellows 18 is substantially parallel to the central longitudinal axis 22 of the pipeline safety joint.

A compensating force exerted by the compensating bellows 18 is transferred from a radially extending rim 23 pertaining to the first pipe section 11 to the second pipe section 12 via releasable holding means in the form of a split key ring 24 having two or more parts arranged in an annular groove 25 in the second pipe section 12. The means for transferring this compensating force comprise a sleeve 26, consisting of two parts 27 and 28 joined by screw bolts 29, of which the output side in the form of radially extending rim 30 is in contact with radial face 31 of the split key ring 24, and of which the input side in the form of radially extending rim 32 is in contact with one end of the compensating bellows 18, the other end of the compensating bellows 18 being in contact with the radially extending rim 23 pertaining to the first pipe section 11.From the split key ring 24 the compensating force is transferred to the second pipe section 12 via oblique face 34, located opposite to the radial face 31, to oblique face 35 pertaining to the annular groove 25.

The pipeline safety joint further comprises means for releasing the releasable holding means. The means include a shear pin 36 arranged so as to interconnect the pipe sections 11 and 12. To this end the radially extending rim 23 pertaining to the first pipe section 11 is provided with an annular groove 37 wherein a connecting ring 38 is slidably arranged, the connecting ring 38 being joined to the second pipe section 12 by means of stud-bolts 39 and nuts 40. The shear pin 36 is arranged in a radial hole 41 extending through the radially extending rim 23 as well as in radial hole 43 extending through the connecting ring 38 and being in a line with radial hole 41. The shear pin 36 may be pre-stressed by tightening the nuts 40.

The split key ring 24 is kept in position by a removable locking element 44, provided with a groove 45 cooperating with the outer surface 46 of the split key ring 24. The removable locking element 44 is connected to the radially extending rim 23 pertaining to the first pipe section 11 by means of connecting means in the form of connecting bolt 47.

The connecting bolt 47 is not fully tight so that there is a predetermined clearance between the head 48 of the connecting bolt 47 and the radial surface 49 of the radially extending rim 23 pertaining to the first pipe section 11. In this way the locking element 44 will be forced to follow the movement of the first pipe section 11 after this pipe section 11 is moved in axial direction relative to the second pipe section 12 over a distance equal to the clearance.

The interior 50 of the pipeline safety joint can be filled with grease, and to avoid spilling of the grease the pipeline safety joint is provided with an elastic cover 51 attached thereto by means of strips 52 and 53. In addition the elastic cover 51 enables the internal pressure to balance the external water pressure.

The interior 50 of the pipeline safety joint is separated from the fluid passage 13 by a metal seal 54. Moreover, where seawater ingress might occur, the pipeline safety joint can be provided with seals (not shown).

To avoid undesired separation of the pipe sections 11 and 12 during installation of the pipeline safety joint, the pipe sections are joined by means of installation bolts 55, of which in Figure 1 only the heads are shown.

When the pipeline safety joint is installed the installation bolts 55 are removed. In an alternative embodiment the installation bolts 55 are made of a material that easily corrodes in sea water, such as magnesium.

During normal operation the pipeline safety joint is included in an underwater pipeline (not shown) through which fluid under pressure is transported, and the installation bolts 55 have been removed. The compensating bellows 18 will exert a compensating force that will counteract the force caused by the internal pressure acting on the surfaces 16 and 17. The compensating force is transferred from the first pipe section 11 to the second pipe section 12, via the input side of the sleeve 26 in the form of radially extending rim 32, the connected sleeve parts 27 and 28, the output side in the form of radial extending rim 30 and the split key ring 24.

Because the force caused by the pressure of the fluid in the fluid passage 13 is compensated by the compensating bellows 18 the shear pin 36 is not loaded by this force.

If the underwater pipeline in which the pipeline safety joint is included is stressed by an axial force, for example an axial force resulting from lateral movements of the pipeline when it is pulled away by a dragging anchor or a trawl board, this axial force will not be compensated by the action of the compensating bellows 18, but this axial force will be transferred between the pipe sections 11 and 12 via the shear pin 36.

If the axial force exceeds the predetermined value at which the shear pin 36 fails, the first pipe section 11 will be allowed to move in axial direction away from the second pipe section 12. When this relative movement is greater than the clearance between the head 48 of the connecting bolt 47 and the radial surface 49, the locking element 44 will be forced to follow the movement of the first pipe section 11 relative to the second pipe section 12.

When the locking element 44 is moved away, the parts of the split key ring 24 slide along the oblique face 35 out of the annular groove 25 and into the space left by the locking element 44. Consequently, the two pipe sections 11 and 12 are separated.

The axial load at which separation occurs is so selected that it is below the failure load of the pipeline and below the failure load of the connections between the pipeline and underwater installations to which the pipeline is connected.

It will be appreciated that once the shear pin 36 has failed, further separation can take place when the axial force is lower than the aixial force required to cause failure of the shear pin 36.

Instead of one connecting bolt 47 the connecting means interconnecting the removable locking element 44 and the first pipe section 11 may comprise two or more connecting bolts, for example four or eight.

Instead of annular groove 37 in which connecting ring 38 is arranged, the radially extending rim 23 can be provided with a plurality of holes, for example eight holes, in which connecting pins are arranged connected by means of stud bolts and nuts to the second pipe section. An advantage of this embodi ment is an increased resistance to torque.

Reference is now made to Figure 2 showing an alternative embodiment of the invention.

The pipeline safety joint comprises a first pipe section 61 and a second pipe section 62 slidably arranged relative to each other so as to form a passage 63. The pipe sections can be provided with flanges (not shown) with which the pipeline safety joint can be included in a pipeline or flowline. The pipeline safety joint further comprises a compensating bellows 64 of which the interior 65 is in fluid communication with the fluid passage 63 by means of a conduit 66. The central longitudinal axis 67 of the compensating bellows 64 is substantially parallel to the central longitudinal axis 68 of the pipeline safety joint.

A compensating force exerted by the compensating bellows 64 is transferred from a radially extending rim 69 pertaining to the first pipe section 61 to the second pipe section 62 via releasable holding means in the form of a split key ring 70 comprising two or more parts arranged in an annular groove 71 in the second pipe section 62.

The compensating force is transferred by a sleeve 72 of which the output side in the form of radial face 73 cooperates with radial face 74 pertaining to the split key ring 70, and of which the input side in the form of radial face 75 is in contact with one end of the compensating bellows 64. The other end of the compensating bellows 64 cooperates with the radially extending rim 69 of the first pipe section 61 via radially extending rim 76 pertaining to a secondary sleeve 77 connected to the radially extending rim 69 by means of screw bolts 78.

The compensating force exerted on the split key ring 70 is transferred to the second pipe section 62 via corresponding oblique faces 79 and 80 pertaining to the split key ring 70 and the annular groove 71 respectively.

The pipeline safety joint further comprises means for releasing the releasable holding means. The releasing means comprise a shear pin 81 interconnecting the first pipe section 61 and the second pipe section 62. The shear pin 81 connects the first pipe section 61 to the sleeve 72 with the use of annular connecting element 82 which is connected to the radially extending rim 69 pertaining to the first pipe section 61 by connecting bolts 83, and the shear pin 81 is arranged in a radial hole 84 extending through the sleeve 72 and in a corresponding hole 85 extending through the annular connecting element 82.

The parts of the split key ring 70 are kept in the position as shown in Figure 2 by means of a removable locking element 86, which can be in the form of a split ring comprising two or more parts to facilitate installing the locking element 86. The locking element 86 is connected to the annular connecting element 82 by means of a rim 87 cooperating with a groove 88 in the annular connecting element 82 in such a manner that there is a predetermined axial clearance between the locking element 86 and the annular connecting element 82.

In order to avoid undesired separation of the pipe sections 61 and 62 during installation, the pipe sections 61 and 62 are joined with the use of locking ring 89 arranged against a stop 90 pertaining the the second pipe section 62, which locking ring 89 is joined to the secondary sleeve 77 by means of locking bolts 91.

In order to allow pre-stressing of the shear pin 81, the connecting bolts 83 are arranged in flanged bushings 92 arranged in holes 93 in the radially extending rim 69 pertaining to the first pipe section 61. Between the flange of the flanged bushing 92 and the radially extending rim 69 there is arranged a resilient element 95, as well as an annular stop 96.

In addition the pipeline safety joint is provided with a pin 97 interconnecting the two pipe sections 61 and 62 so as to avoid rotation about the central longitudinal axis 68 of one pipe section relative to the other.

In order to avoid leakage of fluid from the fluid passage during normal operation, the pipeline safety joint is provided with a metal seal 98.

During normal operation the pipeline safety joint is included in an underwater pipeline (not shown), and the locking bolts 91 have been removed. The force caused by the pressure of the fluid in the passage is compensated by the compensating force exerted by the compensating bellows 64 pressing the pipe sections 61 and 62 towards each other.

If the underwater pipeline is stressed by an axial force, for example an axial force resulting from lateral movements of the pipeline when it is pulled away by a dragging anchor, this axial force will not be compensated by the action of the compensating bellows 64. This axial force will be transferred from the first pipe section 61 to the second pipe section 62 via the resilient elements 95 or the annular stops 96, the flanged bushing 92, the connecting bolts 83 and the annular connecting element 82 to the shear pin 81. From the shear pin 81 the axial force is transferred via the sleeve 72, the radial face 73 and the split key ring 70 to the second pipe section 62. If the axial force exceeds the predetermined value at which the shear pin 81 fails, the first pipe section 61 will be allowed to move in axial direction away from the second pipe section 62.When this relative movement is greater than the predetermined axial clearance between rim 87 pertaining to the removable locking element 86 and the groove 88 pertaining the the annular connecting element 82, the locking element 86 will be forced to follow the movement of the first pipe section 61 relative to the second pipe section 62.

When the locking element 86 is moved away, the parts of the split key ring 70 slide along the oblique face 80 out of the annular groove 71 into the space left by the locking element 86. Consequently, the two pipe sections 61 and 62 are separated.

The force required to separate the pipe sections is so low that no damage is done to the pipeline itself or to elements connecting the pipeline to underwater facilities or adjacent structures.

During normal operation of the pipeline safety joint as described with reference to Figure 1, the compensating force exerted by the compensating bellows stresses the sleeve 26, whereas the compensating force exerted by the compensating bellows pertaining to the pipeline safety joint as described with reference to Figure 2 compresses the sleeve 72.

The pipeline safety joint as described with reference to the Figures 1 and 2 is provided with one compensating bellows having a circular cross-section, instead thereof the pipeline safety joint may be provided with an annular compensating bellows of which the central longitudinal axis substantially coincides with the central longitudinal axis of the safety joint.

In an alternative embodiment of the invention the pipeline safety joint may be provided with two or more compensating bellows of which the central longitudinal axes are substantially parallel to the central longitudinal axis of the pipeline safety joint. In a suitable embodiment the compensating bellows are arranged on a circular cylinder having a common longitudinal axis with the central longitudinal axis of the pipeline safety joint. In a further suitable embodiment the angles between adjacent compensating bellows are equal to each other. The number of compensating bellows is for example five to ten.

The magnitude of the compensating force exerted by a compensating bellows equals the fluid pressure times the effective cross-sectional area of the bellows. If the pipeline safety joint is provided with one compensating bellows, this force should be about equal to the force caused by the pressure of the fluid in the fluid passage. If the pipeline safety joint is provided with more than one compensating bellows the sum of the compensating forces exerted by the compensating bellows should be about equal to the force caused by the fluid pressure.

In the embodiments of the invention as described with reference to Figures 1 and 2, the pipeline safety joint is provided with one shear pin. In a suitable embodiment, there can be applied more than one shear pin, for example four to ten.

The connecting bolt 47 (see Figure 1) can be replaced by a rimmed ring cooperating with a groove in the removable locking element 44.

The rimmed ring is connected with a predetermined clearance to the removable locking element 44 so that the locking element 44 will be forced to follow the movement of the first pipe section 11 after this pipe section is moved in axial direction relative to the second pipe section 12 over a distance equal to the clearance. To facilitate installation of the rimmed ring, this ring can comprise two or more parts.

As described with reference to the Figures, the pipeline safety joint is included in a pipeline or flowline with the use of the flanges arranged at the free ends of the pipe sections, as an alternative the pipeline safety joint may be included in the pipeline or flowline by means of welds connecting the free ends of the pipe sections to the ends of the pipeline sections.

Claims (10)

1. Pipeline safety joint comprising two pipe sections slidably arranged in relation to each other so as to form a fluid passage, a compensating bellows of which the interior is in communication with the fluid passage, means for transferring a compensating force exerted by the compensating bellows from one of the pipe sections (the first pipe section) via releasable holding means to the other pipe section (the second pipe section), and means for releasing the releasable holding means if the pipe sections are separated by an axial force in excess of a predetermined value.

2. Pipeline safety joint as claimed in claim 1, wherein the compensating bellows have a circular cross-section.

3. Pipeline safety joint as claimed in claim 2, wherein the pipeline safety joint comprises two or more compensating bellows of which the central longitudinal axes are arranged on a circular cylinder having a common longitudinal axis with the central longitudinal axis of the pipeline safety joint.

4. Pipeline safety joint as claimed in claim 3, wherein the angles between adjacent compensating bellows are equal to each other.

5. pipeline safety joint as claimed in 3 or 4, wherein the pipeline safety joint comprises five to ten compensating bellows.

6. Pipeline safety joint as claimed in any one of the claims 1-5, wherein the means for transferring a force exerted by the compensating bellows comprise a sleeve of which one end is in contact with the releasable holding means and of which the other end is in contact with one end of the compensating bellows.

7. pipeline safety joint as claimed in any one of the claims 1-6, wherein the means for releasing the releasable holding means comprise a shear pin arranged so as to interconnect the pipe sections.

8. Pipeline safety joint as claimed in any one of the claims 1-7, wherein the means for releasing the releasable holding means comprise a removable locking element for keeping the holding means in a position wherein they cooperate with the second pipe section, and connecting elements interconnecting the locking element and the first pipe section in such a manner that the locking element is forced to follow the first pipe section after this pipe section is displaced in axial direction relative to the second pipe section over a predetermined distance in order to release the holding means.

9. Pipeline safety joint as claimed in any one of the claims 1-6, wherein the releasable holding means comprise a split key ring arranged in an annular groove in the second pipe section.

10. Pipeline safety joint substantially as described in the specification with reference to the accompanying drawings.