Method for replacing an outer annular ring of a fluid swivel and a fluid swivel

Abstract

A method for replacing an outer annular ring of a fluid swivel includes a swivel comprising an inner annular ring and an outer annular ring, the rings being located with their adjacent cylindrical surfaces in close proximity for defining a chamber, for receiving a fluid, between peripheral opposing faces of the inner annular ring and the outer annular ring, wherein the inner annular ring is adapted to be connected to an end of a fluid line and wherein the outer annular ring is adapted to be connected to a product piping on the vessel, wherein the method comprises the steps of: removing the outer annular ring, replacing the outer annular ring by means of a first semi-circular element and a second semi-circular element, and fixing the first semi-circular element to the second semi-circular element, by means of a fixing means, to form a replacement outer annular ring of the swivel.

Claims

1. A fluid swivel for allowing fluid transfer across a rotary interface between an end of a fluid line connected to a seabed and product piping on a vessel for gas and oil production, wherein the fluid swivel comprises: an inner annular ring; an outer annular ring; the inner annular ring and the outer annular ring being located with their adjacent cylindrical surfaces in close proximity for defining a toroidal-shaped chamber, for receiving a fluid, between peripheral opposing faces of the inner annular ring and the outer annular ring; wherein the inner annular ring is adapted to be connected to the end of the fluid line, which extends through the inner ring towards the toroidal-shaped chamber in order to allow fluid supply towards or from the toroidal-shaped chamber; wherein the outer annular ring is adapted to be connected to the product piping and is provided with a duct to allow the fluid to flow from or to the toroidal-shaped chamber towards the product piping; wherein the outer annular ring comprises at least a first circular segment and a second circular segment, wherein the first circular segment and the second circular segment together form a ring, and a fixing means for fixing the first circular segment and the second circular segment to form the outer annular ring of the fluid swivel; wherein the first and the second circular segments are connected via a weld line positioned at an inner annular surface between the first and second circular segments; and wherein a tension is applied to the first and second circular segments by the fixing means, such that the weld line is always under compression.

2. The fluid swivel according to claim 1, wherein there are two different seal barriers between the first circular segment and the second circular segment consisting of a permanent metal-to-metal contact and a continuous welding at the inner annular surface between the first circular segment and the second circular segment.

3. The fluid swivel according to claim 1, wherein the fixing means comprise at least a first bolt to fix the first circular segment and the second circular segment together at a first contact surface.

4. The fluid swivel according to claim 1, wherein the outer annular ring comprises a first semi-circular element and a second semi-circular element.

5. The fluid swivel according to claim 1, wherein the outer annular ring comprises super duplex stainless steel.

6. A turret structure for allowing a vessel for gas and oil production to be connected to an end of a geo-stationary fluid duct and for allowing product piping on the vessel to be connected to the end of said geo-stationary fluid duct via a rotary interface, wherein the turret structure comprises the fluid swivel according to claim 1.

7. A vessel comprising the turret structure according to claim 6.

8. A method for replacing the outer annular ring of the fluid swivel according to claim 1, the method comprising: removing the outer annular ring; replacing the outer annular ring with the at least a first circular segment and a second circular segment; and fixing the at least a first circular segment and a second circular segment to each other via a fixing means, to form a replacement outer annular ring of the fluid swivel.

9. The method according to claim 8, wherein the method comprises fixing the first circular segment to the second circular segment with at least a first bolt.

10. The method according to claim 8, wherein the method comprises connecting the inner annular surface between the at least a first circular segment and a second circular segment by forming the weld line.

11. The method according to claim 10, wherein the method comprises increasing, after the connecting, a contact force at a contact surface between the first circular segment and the second circular segment via the fixing means.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in detail with reference being made to the drawings, wherein:

(2) FIG. 1 shows a swivel comprising the replacement outer annular ring according to the invention;

(3) FIG. 2 shows a cross section of the swivel according to FIG. 1;

(4) FIG. 3 shows an alternative embodiment of the bottom part of the swivel according to FIGS. 1 and 2;

(5) FIG. 4 shows the outer annular ring for the swivel according to the present invention;

(6) And FIG. 5 shows a detail of the weld line area in order to connect a first semicircular element to a second semicircular element by means of a weld.

(7) FIG. 1 shows a possible embodiment of a swivel 1 according to the present invention, wherein the replacement outer annular ring comprises a first and a second semi-circular elements. It will be understood that the replacement outer annular ring could also comprise three or more circular segments, adapted to form the outer annular ring. These other embodiments are not shown in the accompanying drawings.

(8) The swivel 1 is adapted to provide a rotary fluid connection between a geo-stationary duct and product piping on a vessel for production, storage and offloading of hydrocarbons.

(9) The functioning of the swivel is similar to existing swivels and will briefly be discussed with reference to FIG. 2.

(10) The swivel according to FIG. 1 comprises an outer annular ring in order to define a fluid chamber in the interior of the swivel, which outer annular ring comprises a first semi-cylindrical element 10 and a second semi-cylindrical element 20. The two elements 10 and 20 are not identical but are essentially the same in their design and functioning. The semi-circular elements 10 and 20 are provided at their interior with a wall for defining the fluid chamber inside the swivel 1 (see FIG. 2) in order to be able to withstand the high pressure within this fluid chamber the elements 10 and 20 are relatively heavy and of rigid construction. In order to avoid excessive weight, the elements 10 and 20 have an interior box like construction in order to gain weight without losing the rigidity of the elements 10 and 20 (see FIG. 2). Both semi-circular elements 10 and 20 have two end faces with which they contact the other semi-circular element, the contact areas are schematically indicated with lines 30 and 31. In order to be able to withstand the high pressure within the fluid chamber it is important that the two semi-circular elements 10 and 20 are pressed together at the contact area 30 and 31 with sufficient pressure. According to the present invention the two elements 10 and 20 are bolted together by means of studbolts. According to FIG. 1 four studbolts 41, 42, 43 and 44 are shown. By means of the studbolts 41-44 the exact tension between the two elements 10 and 20 at the contact area 30-31 can be determined.

(11) In FIG. 2 a cross section is shown according to the line A-A of element 20 of the swivel 1 according to FIG. 1.

(12) The cross section of element 10 would have been similar. FIG. 2 shows a toroidal chamber 2 which is defined on the interior between peripheral opposing faces of an inner annular ring 3 and the interior wall 21 of the semi-circular element 20. The inner annular ring 3 is the part of the swivel 1 which is adapted to be connected to a geo-stationery duct. The outer annular ring comprising the elements 10 and 20 can rotate with respect to the inner annular ring 3 because of the presence of a roller bearing 4. The swivel 1 further comprises a top inner ring 5, a top outer ring 6, a bottom outer ring 7 and two bottom rings 8 and 9, wherein the rings 3, 4, 5, 6, 7, 8 and 9 in combination with the roller bearing 4 are all bolted together using bolts 51, 52, 53 and 54. Other elements as shown in FIG. 2 are standard elements of a swivel which will not be described in detail below.

(13) As shown in FIG. 2 the semi-circular element 20 has a box shaped construction and that part of the interior volume of the semi-circular element 20 is empty in order to save weight. Regarding the size of the semi-circular element 20 and the material used, the semi-circular elements 10 and 20 have a tendency to become relatively heavy.

(14) In FIG. 2 it is shown that with the construction of the swivel as shown in FIG. 2 it is possible to release for instance the bolts 53 and 54 in order to remove at least part of the rings 7, 8 and 9 in order to make space to move the semi-circular element 20 in a vertical direction. This movement in a vertical direction is necessary to allow the semi-circular elements 10 and 20 to be welded together as will be described with reference to FIGS. 4 and 5.

(15) In FIG. 3, an alternative embodiment is shown of the swivel 1 according to FIG. 2 wherein the form of the bottom rings 7 and 9 is amended. In FIG. 4 only the two semi-circular elements 10 and 20 are shown with the respective bolts 41, 42, 43 and 44. FIG. 4 shows the full length of the contact areas 30 and 31 that means the contact surfaces wherein the semi-circular elements 10 and 20 are in contact with each other. In practice, it will be very difficult to produce semi-circular elements 10 and 20 which, once connected to each other using the bolts 41-44, will have a contact area on the inner peripheral surface which is perfect in the sense that not a single micro opening will exist between the two semi-circular elements 10, 20 when pressed together. To make sure that the two semi-circular elements 10 and 20 are correctly connected to each other, according to the invention the semi-circular elements 10 and 20 will, in a first instance, be connected together by using the bolts 41-44. In this first instance, the bolts will only be tightened in order to keep the semi-circular elements 10 and 20 correctly positioned one with respect to the other. That means for instance that the bolts 41-44 are pre-tensioned at the level for instance of 5-30% of their maximum pre-tension. Once the two semi-circular elements 10, 20 are connected together with this limited pre-tension, they are moved eccentric to the axis of the inner annular ring to create the space required for welding. It is then possible to produce a continuous weld line over the contact line 33 which is shown in FIG. 5. The direction of the weld line 33 is perpendicular to the direction of the contact line 30 which is also visible in FIG. 5. Similarly, a second continuous weld line will be produced which will be perpendicular to the contact surface 31.

(16) Once the two weld lines are produced the interior surface of the now connected semi-circular elements 10 and 20 will be machined in order to obtain the required surface conditions needed for proper operation of the now combined semi-circular elements 10, 20 as the outer annular ring for the swivel 1 according to FIG. 1.

EXAMPLES

(17) According to an example the semi-circular elements 10, 20 are produced of super duplex stainless steel, for instance super duplex stainless steel Zeron 100. In order to fix the two elements together, carbon steel studbolts 41, 42, 43 and 44 are used, for instance class B24 studbolts.

(18) When positioning the first and second semi-circular elements in place in order to form a new outer annular ring for a swivel 1, in a first instance the studbolts 41-44 are used to fix the semi-circular elements 10,20 together having the studbolts pre-tensioned to 5-30% of their final pre-tension level. Preferably, this pre-tension is set to 25% of their final pre-tension level.

(19) Once the first and second semi-circular elements have been fixed together as described above, the weld connections between the internal phases of the first and second semi-circular elements are added.

(20) Thereafter, the pre-tension on the studbolts 41-44 is increased to their final pre-tension level. By increasing the tension on the bolts the weld will be put under compression.

(21) The now combined semi-circular elements 10, 20 are ready to operate as the new outer annular ring of the swivel.