EP0436605A1

EP0436605A1 - Subsea flowline connection

Info

Publication number: EP0436605A1
Application number: EP19890910892
Authority: EP
Inventors: Richard Curtis Torgersen; John Ernest Petrarch House Horsell Park Lawson; Stephen Anthony Hatton
Original assignee: FSSL Ltd; Cameron Offshore Engineering Ltd; Mobil Oil Corp
Current assignee: FSSL Ltd; OneSubsea Offshore Engineering Ltd; ExxonMobil Oil Corp
Priority date: 1988-09-22
Filing date: 1989-09-21
Publication date: 1991-07-17
Also published as: GB8822268D0; BR8907670A; WO1990003492A1

Abstract

On relie (Fig. 1) un appareil sous-marin (11) et une canalisation d'alimentation dont la terminaison se trouve éloignée de l'appareil au moyen d'un élément d'accouplement vertical (17). On monte sur l'appareil (11) avant l'immersion un joint de canalisation composé d'une paire d'éléments en forme de U (19, 20) ayant des branches parallèles (19', 19'', 20', 20''), l'une des branches de chaque élément étant reliée à l'autre par une pièce de raccordement rotative (21), l'autre branche (19'') de l'élément (19) soutenant le joint sur l'appareil pour pivoter autour de l'axe de la branche, éventuellement par une autre pièce de raccordement (22), et l'autre branche (20'') de l'élément (20) ayant un dispositif d'accouplement (23) qui peut coopérer avec la canalisation, les éléments en forme de U (19, 20) de la canalisation étant replié contre l'appareil au moment de son immersion. Lorsque l'appareil est immergé un véhicule télécommandé (15) tire et déplie l'élément de canalisation et aligne les éléments d'accouplement (23, 17). La pièce de raccordement (21 et 22) est de préférence un joint à fluide du type qui permet un certain mouvement de pivotement dans toutes les directions, lorsque une pression liquide provenant du véhicule télécommandé ou de l'appareil (11), l'active.We connect (Fig. 1) an underwater device (11) and a supply line whose termination is remote from the device by means of a vertical coupling element (17). A pipe joint composed of a pair of U-shaped elements (19, 20) having parallel branches (19 ', 19' ', 20', 20) is mounted on the device (11) before immersion. ''), one branch of each element being connected to the other by a rotary connecting piece (21), the other branch (19 '') of the element (19) supporting the seal on the apparatus for pivoting about the axis of the branch, possibly by another connecting piece (22), and the other branch (20 '') of the element (20) having a coupling device (23) which can cooperate with the pipe, the U-shaped elements (19, 20) of the pipe being folded against the device at the time of its immersion. When the device is submerged a remote-controlled vehicle (15) pulls and unfolds the pipe element and aligns the coupling elements (23, 17). The connecting piece (21 and 22) is preferably a fluid seal of the type which allows a certain pivoting movement in all directions, when a liquid pressure coming from the remote-controlled vehicle or from the device (11) activates it. .

Description

SUBSEA FLOWLINE CONNECTION

This invention relates to the connection of a hydrocarbon flowline to subsea production apparatus and particularly to a method of making such a connection suitable for performance by remotely operated submersible vessels. It is known to pass hydrocarbons from a subsea well through various control and safety valves arranged in a so-called Christmas tree structure at the well head and into a flowline at, or embedded in, the sea bed for transport to some other location. The valve tree is usually lowered onto, and if necessary removable from, a support bed and the connection of a flowline thereto is not without difficulty.

It is known to use flexibility of the flowline, or rather an over-length end portion, by drawing it into engagement with an outlet port on the valve tree. Such an approach presents difficulties in terms of alignment and exerting mating forces on and between the flowline and valve tree.

Another approach uses techniques employed also in replacing damaged sections of flowlines and comprises lowering the flowline so that it terminates some distance apart from the support bed and upon lowering of the production apparatus valve tree inserting a flowline spool or link between and connecting the respective parts.

It will be appreciated that in the subsea operating environment it is difficult to ensure a precise disposition of flowline termination with respect to the production apparatus and it is generally impracticable to fabricate such a connecting link of precisely predetermined length or assumed axial alignment of the flowline and production apparatus outlet port. Connecting links or spools are in practice provided with joints which permit axial extension and angular offset, or swivel, of different sections or end coupling parts, examples of such being given by patent specification EP 210714A and EP 207582A respectively. Connecting links incorporating such joints in the dimensions used as hydrocarbon flowlines are also

SUBSTITUTE SHEET usually configured and installed with the help of lifting machinery by divers who ensure the configurations each connecting link is tailored to the particular disposition of valve tree structure and flowline. It will be understood that even when the end of the flowline is brought a nominally predetermined position with respect to production apparatus the accumulation of dimensional and positional tolerances with structures of this size and nature still requires individually tailored connecting pieces. It will be further understood that in wells which are too deep for direct diver action such a connecting piece has to be assembled by the use of submersible vehicles with the limitations imposed by their lack of dexterity and size. This latter factor may be a matter for consideration where the production apparatus and flowline termination is contained within a protective framework and the protective framework constrains the manoeuvrability and access of such a submersible vehicle.

It is an object of the present invention to provide a linkage arrangement between an outlet of a subsea hydrocarbon production apparatus and a subsea flowline, and method of making such a connection by the linkage arrangement, which is simpler than known connections and performable by, but not limited to, remotely operated submersible vehicles with limited manoeuvrability.

According to a first aspect of the present invention a method of making a flowline connection between an outlet of subsea hydrocarbon production apparatus lowered onto a subsea support bed and a subsea flowline comprises assembling on the apparatus prior to submerging and lowering to the support bed a flowline link comprising first and second U-shaped flowline pieces, each having limbs extending from a bight portion and terminating substantially parallel to each other, with one limb of each flowline piece joined end-to-end to the other piece by way of an axially rotatable connecting piece, the other limb of the first flowline piece pivotally mounted on said apparatus with the limb axis in a predetermined attitude with respect to operational disposition of the apparatus for rotation about the limb axis and the other limb of the second flowline piece fitted with a first part of a two part termination coupling cooperable with that of a second part, disposing the flowline pieces of the link with respect to each other and the apparatus so that the flowline pieces are folded against the apparatus, providing said second part of the termination coupling at a terminal portion of the flowline, in either order lowering the flowline onto the sea bed with the coupling part displaced apart from the support bed and directed in said predetermined attitude and lowering the apparatus carrying the flowline link onto the support bed, and thereafter rotating the flowline pieces with respect to the production apparatus and each other to unfold the flowline link and displace the first part of the termination coupling into axial alignment with the cooperable second part on the flowline and joining the two parts of the termination coupling.

According to a second aspect of the present invention a linkage arrangement between an outlet of a subsea hydrocarbon production apparatus lowered onto a support bed and a subsea flowline comprises

(i) a flowline link arranged to be lowered as a unitary structure with apparatus to the support bed, said flowline link comprising first and second U-shaped flowline pieces each having limbs extending from a bight portion and terminating substantially parallel to each other, one limb of each piece being joined end-to-end to the other piece by way of an axially rotatable connecting piece, the other limb of the first flowline piece being pivotally mounted on said lowered apparatus with the limb axis in a predetermined attitude for rotation about the limb axis and the other limb of the second flowline piece carrying at its end a first part of a two part termination coupling,

(ii) a second part of the two part termination coupling attached at the end of the flowline and extending substantially in said predetermined attitude, and

(iii) means operable to rotate the flowline pieces with respect to each other and the submerged apparatus to align the two parts of the termination coupling and effect coupling thereof.

The invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a first form of subsea hydrocarbon production apparatus and a flowline with a flowline link between them made of pivotally connected flowline pieces in accordance with the present invention,

Figure 2 is a side elevation of a portion of the hydrocarbon production apparatus of Figure 1 showing the flowline pieces connection assembled thereon for deployment with the production apparatus,

Figure 3 is a plan view of the production apparatus of Figure 1 and flowline piece assembled thereon after submerging the apparatus, the relative disposition of the flowline and the attachment of a submersible vehicle to the flowline pieces to perform the connection method,

Figure 4 is a plan view similar to Figure 3 showing relative rotation between the flowline pieces by the submersible vehicle,

Figure 5 is a plan view similar to Figure 4 but showing relative rotation between the flowline pieces and production apparatus displacing the remote end of the flowline pieces towards the flowline termination for connection thereto, and Figure 6 is a perspective view of a second form of subsea hydrocarbon production apparatus in which the flowline link is carried by and deployed from apparatus submerged before a valve tree having a production outlet to the flowline link. Referring to Figure 1 a subsea hydrocarbon production apparatus 11 comprises a series of control and safety valves which deliver liquid or gaseous hydrocarbon products to an outlet port 12 which, as shown, extends downwardly at the side of the apparatus. Because of the stacked nature of the valves comprising a large part of the apparatus it is often referred to as a Christmas tree or valve tree. In one form the production apparatus including the valve tree 11 and outlet 12 is a unitary structure assembled and lowered from the surface to rest on a submerged support bed 13, the tree furthermore being susceptible to hauling back to the surface for maintenance or replacement.

As shown the support bed 13 is surrounded by a substantial framework 14, into which the apparatus is lowered, which serves to protect it from damage by large objects moving through the water and permits limited access by a remotely operated submersible vehicle (ROV) 15.

At least one flowline 16 by which well products are removed is laid on, or buried in, the sea bed and terminates at the framework 14 in an upstanding portion 16' and displaced from the operational position of the production apparatus, that is, from the support bed 13.

A flowline link 18 extends between the tree outlet port 12 and flowline 16 comprising first and second U-shaped flowline pieces 19, 20. The flowline pieces 19 and 20 have limbs 19', 19" and 20', 20" respectively extending from bight portions 19'" and 20"' respectively, which limbs terminate substantially parallel to each other. As shown the limbs are straight and the axis of the limb where it terminates thus extends for the whole limb, making it convenient to refer to the limb axes as being parallel. One limb of each piece, say 19' and 20' , is joined end-to-end to the other piece by way of an axially rotatable connecting piece 21.

The connecting piece permits the limbs 19' and 20' to rotate relative to each other about a common limb axis and may be of the type shown in the aforementioned EP 207582 which permits such relative rotation when supplied with a pressurised fluid and also permits limbs 19' and 20' to axially misalign or swivel to a limited extent about an axis transversely to the axis of the limb to which fitted.

The other limb 19" of the first flowline piece is connected by way of a further connecting piece 22 of similar form to the downwardly extending outlet port 12. Such connecting piece provides a mounting for the flowline link on the apparatus by which the limb 19", and the remainder of the link 18, is able to pivot about the axis of the limb. The outlet port 12 and connected limb are arranged such that the limb axis extends in a predetermined direction when the apparatus is operationally disposed on the support bed and conveniently this predetermined operational attitude is vertical, defining also the axis attitudes for the other limbs. The other limb 20" of the second flowline piece is connected to a first part 23 of a two part termination coupling which is adapted to co-operate with a second part 17 carried on the upstanding flowline portion 16' which also extends substantially in the .predetermined vertical direction and is likewise vertically directed. The limb 20" of the flowline link is thereby securable to the upstanding portion 16' to provide a flow path between the outlet 12 and flowline 16 by way of the flowline pieces.

A guidance funnel 24 in the form of a tapered wall, vertically inclined ramp adjacent the second part 17 of the termination coupling facilitates alignment of the two termination coupling parts 17 and 23 as will become clear.

The flowline link is thus composed of flowline pieces connected by the known adjustable joints but it will be appreciated that the formation and coupling of the link in situ is difficult if not impossible to effect using normal assembly techniques without the aid of divers.

In accordance with the present invention the flowline connection shown in Figure 1 is made by assembling on the production apparatus before submerging to the support bed the flowline link 18, comprising flowline pieces 19, 20, connecting pieces 21 and 22, and termination coupling part 23, and orientating the flowline pieces of the link with respect to each other and the apparatus so that the pieces are folded flat against the apparatus, as shown in the elevation and plan views of Figures 2 and 3 respectively.

The two flowline pieces 19, 20 conveniently have limbs which extend orthogonally to straight bight portions and are assembled so that with all the limbs extending in a vertical direction the bight portions are horizontal, permitting the termination coupling part 23 to move to and from the apparatus by relative rotation between the flowline pieces and/or apparatus about a vertical axis common to the limbs and connecting pieces 21 and 22. Formation of the connecting piece 21 and/or 22, as a swivel joint pivotable about an axis in a horizontal plane transversely to the nominally vertical connecting axes of the flowline pieces permits the limb 20" and the first part 23 of the termination coupling to be movable substantially in the direction of the limb 20" axis, that is, vertically, by a limited amount.

The flowline_. link is maintained in the shown disposition folded flat against the apparatus by the clamping property of the connecting pieces 21 and 22 whilst they are not energised with pressurised fluid, but pins or clips 25 may be inserted in addition to ensure no unwanted rotation can take place at the connecting pieces. The flowline 16 with its terminal portion 16' and termination coupling part is disposed conveniently adjacent the framework 14, and protected thereby, with the flow axis of the portion 16 substantially vertical to agree with the predetermined nominally vertical direction of the limb 20" of the second flowline piece.

Either before or after the flowline is lowered the apparatus 11 is submerged and lowered onto the structure bed when both are in place the ROV 15 approaches the production apparatus, removes any rotation inhibiting pins or clips from the connecting piece, attaches itself to the second flowline piece 20 at a convenient docking point 26, as shown in Figure 3, and connects a fluid pressure supply to the connecting piece 21 and, possibly, connecting piece 22 by hose 27. Having energised the connecting pieces to permit axial rotation the ROV retracts from the apparatus structure 11 and moves the first part 23 of termination coupling horizontally as illustrated by Figures 3 and 4 until it is disposed in axial alignment with the cooperable second part 17 at which time the parts are brought together to cooperate and are secured to each other in suitable form, automatically or with the aid of the ROV.

It will be appreciated that the first part 23 of the termination coupling is directed into axial alignment with the second part 17 by the taper of the guidance funnel 24 whereas, by virtue of the limited vertical swivel of the second flow piece permitted by one or both connecting pieces, abutment between the first part 23 of the coupling and the vertically inclined ramp of the funnel permits the first coupling part 23 to be raised in the vertical axial direction with respect to the flowline to clear and align with the part 17 as a result of the ROV guiding the flowline pieces only in a horizontal direction. When the coupling is made between parts 17 and 23 the ROV removes fluid pressure from connecting piece 21 and/or 22 thereby fixing the relative dispositions of the flowline pieces with respect to each other, that is fixing the configuration of the flowline link, before unlocking from the point 26 and withdrawing from the apparatus. It will be appreciated that the precise positional relationship between the submerged production apparatus 11 and flowline termination 16' , both in a horizontal and vertical direction, is immaterial as the variable length and height provided by the two rotatable U-shaped flowline pieces and the connecting pieces permits the required link to be assembled with the aid only of simple manoeuvres and operations on the part of a ROV.

To ease the ROV control burden imposed by having two flowline pieces to rotate relative to each other and to the apparatus, rotation of the first flowline piece with respect to the apparatus may be performed by a ram 28 extending between the first flowline piece and the apparatus. The ram may also be powered by fluid pressure from the ROV or from the apparatus or some equivalent form of motor may be incorporated. Also to ease the burden on the ROV the flowline piece

20 and/or piece 19 which has vertical swivel motion about an energised connecting piece may be provided with a buoyancy collar, for example, of syntactic foam, as shown at 29 to ease vertical manoeuvrability and support by the ROV. The connection method although described above with reference to a ROV is not dependent upon the use of such a vehicle or indeed any vehicle and the flowline pieces may be moved manually in shallow seas providing suitable arrangements are made to energise, that is, pressurise, the connecting piece 21 and/or 22 to permit rotation. Also as indicated hereinbefore the connecting pieces need not be of a form which requires pressurised fluid from an external source to permit rotation. Such connecting pieces are preferred but the energising fluid may be obtained from sources other than the attendant mover of the flowline pieces and may, for instance, be provided by a line extending from a source in the production apparatus or from the surface.

The connection method described hereinbefore is in relation to apparatus in which the flowline link is carried by a single-piece production apparatus with the arm 19" of the first flowline piece connected prior to submerging to the production outlet 12 by means of a connecting piece 22 which permits rotation of the link about the predetermined vertical axis with respect to the apparatus.

It will be appreciated that it is only the supporting of the flowline link and apparatus to be submerged and its ability to subsequently pivot about the predetermined axis which is important in respect of deploying the flowline link and this may be provided in a different form of production apparatus without departing from the scope of the invention.

Referring to Figure 6 this shows another form of production apparatus in which apparatus 30 carrying the flowline link 18 is assembled above water and lowered to the submerged support bed 13 separately from the part of the production apparatus comprising the valve tree 31 and production outlet 12. The flowline link 18 is mounted on the apparatus 30 by means of a support 32 which permits the limb 19" to pivot with respect to the apparatus about the predetermined (vertical) axis, the end of the limb not being connected, and the flowline pieces of the link to be folded flat against the apparatus.

The apparatus 30 carrying the flowline link assembly is lowered to the support bed with the flowline pieces folded flat against its side and thereafter drawn out by ROV or other means, including a ram if desired, to couple with the flowline 16. The valve tree 31 is then lowered onto the apparatus 30 so as to mate with the well and with the production outlet 12 aligned with and into coupling engagement with the end of limb 19". It will be appreciated that rotation of the flowline pieces relative to the apparatus may be completed before the outlet 12 is coupled to the first flowline piece so that the coupling therebetween need not be axially rotatable as described above for connecting piece 22.

As a further example of variations of structural detail which may be employed it will be seen that all swivel motion about a horizontal axis, that is, to permit movement of the termination coupling part 23 in a vertical direction may be provided by the pivot support between limb 19" and the apparatus rather than connecting piece 21. Alternatively such vertical motion of the termination coupling 23 may be provided by axial telescoping of one of the limbs rather than rotation at one of the connecting pieces or mounts.

It will be understood that the guidance funnel 24 is not essential but provides a convenient way of ensuring axial alignment between flowline piece limb 20" and flowline 16' for the parts of the termination coupling. Similarly the ramp function which enables a vertical axial separation of the coupling parts as they are brought into alignment is not essential, the separation being effected by lifting of the flowline piece 20 by the ROV or attached buoyancy with the ROV thereafter forcing the aligned coupling parts into engagement. Furthermore the vertical motion of the limb 20" may not be necessary to clear the flowline termination for alignment of coupling parts if arrangements are made for the first coupling part 23 to move only in a horizontal plane above that of part 17 which is mounted on a subsequently raisable portion of flowline to effect coupling.

Although the relative rotation between the flowline pieces 19 and 20 in order to unfold the limb is performed conveniently by pulling on at least the second flowline piece by ROV or equivalent it will be understood that such rotation could be effected by a motor permanently or temporarily disposed to operate between the first and second flowline pieces, such as a rectilinear ram, similar to that 28, or a rotatable fluid or electrical rotor carried on one limb 19' or 20' and driving against an abutment or the like carried by the other limb. It will be understood that the predetermined direction in which the limbs extend and about which they pivot need not be vertical provided the terminal portion 16' of the flowline has a corresponding attitude but such a non-vertical direction may place a greater burden on the ROV or equivalent in moving the flowline pieces in other than horizontal, and possibly vertical, directions.

It will be seen that in general apparatus lowered to a rectangular subsea support bed and has four sides enabling such a flowline link to be carried on any or all sides and possibly more than one link on any one side.

Claims

- 12 -

Claims: 1. A method of making a flowline connection between an outlet of subsea hydrocarbon production apparatus lowered onto a subsea support bed and a subsea flowline, comprising assembling on the apparatus prior to submerging and lowering to the support bed a flowline link comprising first and second U-shaped flowline pieces, each having limbs extending from a bight portion and terminating substantially parallel to each other, with one limb of each flowline piece joined end-to-end to the other piece by way of an axially rotatable connecting piece, the other limb of the first flowline piece pivotally mounted on said apparatus with the limb axis in a predetermined attitude with respect to operational disposition of the apparatus for rotation about the limb axis and the other limb of the second flowline piece fitted with a first part of a two part termination coupling cooperable with that of a second part, disposing the flowline pieces of the link with respect to each other and the apparatus so that the flowline pieces are folded against the apparatus, providing said second part of the termination coupling at a terminal portion of the flowline, in either order lowering the flowline onto the sea bed with the coupling part displaced from the support bed and directed in said predetermined attitude and lowering the apparatus carrying the flowline link onto the support bed, and thereafter rotating the flowline pieces with respect to the production apparatus and each other to unfold the flowline link and displace the first part of the termination coupling into axial alignment with the cooperable second part on the flowline and joining the two parts of the termination coupling.

2. A method as claimed in claim 1 comprising carrying the flowline link on apparatus including the production apparatus outlet and mounting said first flowline piece on the apparatus by a further rotatable connecting piece extending between said other limb of the first piece and the outlet.

3. A method as claimed in claim 1 or claim 2 comprising rotating the first flowline piece with respect to the production apparatus by a ram acting between the production apparatus and the first flowline piece.

4. A method as claimed in any one of claims 1 to 3 comprising rotating the flowline pieces with respect to each other and/or the production apparatus by a submersible vehicle.

5. A method as claimed in claim 4 comprising restraining the flowline pieces folded for lowering of the apparatus and releasing them for rotation by submersible vehicle.

6. A method as claimed in claim 4 or claim 5 comprising forming the rotatable connecting piece between the first and second flowline pieces from a connecting piece releasable for axial rotation under fluid pressure and releasing the flowline pieces for axially rotation in response to fluid pressure applied to the connecting piece by a submersible vehicle.

7. A method as claimed in any one of the preceding claims including providing adjacent the second part of the termination coupling a guidance funnel and moving the first part of the termination coupling on the second flowline piece into the funnel to guide it into axial alignment with the second part of the termination coupling on the flowline.

8. A method of making a flowline connection as claimed in any one of the preceding claims comprising forming at least one rotatable connecting piece as a swivel joint pivotable about axes in a plane transversely to a limb axis to which connected and permitting the first part of the termination coupling and the second flowline piece to be moved substantially in the direction of said predetermined attitude and into cooperation with the second part of the termination coupling part.

9. A method as claimed in claim 8 including arranging the guidance funnel as a ramp inclined in the direction of the predetermined attitude and by motion of the second flowline piece transversely thereto moving the first part of the termination coupling across the ramp and displacing it axially with respect to the second part of the termination coupling vertically to effect axial alignment by way of said transverse motion.

SUBSTITUTE SHEET

10. A method as claimed in any one of the preceding claims including providing on at least one of the flowline pieces buoyancy means.

11. A method as claimed in any one of the preceding claims comprising causing said predetermined attitude of rotation axes and flowline termination to extend in a substantially vertical direction and orientating the flowline pieces by motion in a horizontal direction to dispose the termination coupling part of the second flowline piece in vertical alignment with the termination coupling part of the flowline.

12. A method of making a flowline connection substantially as herein described with reference to the accompanying drawings.

13. A linkage arrangement between an outlet of a subsea hydrocarbon production apparatus lowered onto a support bed and a subsea flowline comprising

(ii) a second part of the two part termination coupling attached at the end of the flowline and directed substantially in said predetermined attitude, and

14. An arrangement as claimed in claim 13 in which said other limb of the first flowline piece is mounted on said lowered apparatus by way of a further axially rotatable connecting piece to a production outlet thereof.

15. An arrangement as claimed in claim 13 or claim 14 in which at least one connecting piece comprises a swivel joint pivotable also about axes in a plane transversely to the connecting axes and permitting motion of the first part of the termination coupling in the direction of the coupling axis.

16. An arrangement as claimed in any one of the preceding claims in which each connecting piece is rotatable only in response to fluid pressure applied thereto.

17. An arrangement as claimed in any one of the preceding claims in which the means operable to rotate the first flowline piece with respect to the apparatus comprises an extensible ram extending between the apparatus and said first flowline piece.

18. An arrangement as claimed in any one of the preceding claims in which the means operable to rotate the second flowline piece with respect to the first comprises a submersible vehicle.

19. An arrangement as claimed in claim 18 in which the second flowline piece is provided with a docking point for the submersible vehicle.

20. An arrangement as claimed in claim 18 when dependent on claim 16 in which the submersible vehicle comprises the source of fluid pressure.

21. An arrangement as claimed in any one of the preceding claims including a guidance funnel adjacent the second part of the termination coupling operable to guide the first part of the termination coupling into alignment with said second part.

22. An arrangement as claimed in claim 21 in which the guide funnel comprises a ramp inclined in the direction of the predetermined attitude and disposed with respect to the second part of the termination coupling to separate the two coupling parts axially by motion of the flowline pieces transverse to said direction of predetermined attitude.

23. .An arrangement as claimed in any one of the preceding claims including buoyancy means attached to at least one of the flowline pieces pivotable in the direction of said predetermined attitude.

24. An arrangement as claimed in any one of the preceding claims in which said predetermined attitude is substantially vertical.

25. A linkage arrangement between an outlet of a subsea hydrocarbon production apparatus lowered onto a support bed and a subsea flowline, substantially as herein described with reference to, and as shown by, Figures 1 to 5 or Figure 6 of the accompanying drawings.