AU3256399A - Protective device for pipe partially laid on the seafloor - Google Patents

Description

Protective device for pipe partially laid on the seafloor The present invention relates to a protection device 5 for a pipe deposited partly on a seabed, and more particularly to a pipe connecting a surface unit to equipment on the seabed such as a wellhead or a manifold. 10 The pipes connecting a surface unit to equipment on the seabed are in diverse and varied configurations, such as those called free-hanging, lazy-S, lazy-wave, etc. These configurations are described and illustrated in the document American Petroleum Institute (API) , first 15 Edition, June 1, 1988 and entitled "API Recommended Practice 17B". When the rigid or flexible pipe, connecting a surface unit to equipment on the seabed, comprises a part 20 resting on the seabed, this bearing part may be forced to move against the seabed according to the variations in the position of the surface unit. As long as the surface unit moves in directions which 25 are approximately parallel to the direction of the bearing part of the pipe, the very slight rubbing of the said part over the seabed causes virtually no damage to the outer sheath of the pipe because of the fact that the length of the pipe is designed to take 30 these movements of the surface unit into account. On the other hand, when the same surface unit moves in directions not parallel to the bearing part, the latter follows the movements of the said surface unit and 35 consequently deform. These movements of the bearing part cause erosion or hollow out the seabed to a certain depth which may be as much as one metre or more when the first layer of the seabed is sand. CD LUj

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-2 As a result of the repeated movements of the bearing part, the layer underlying the said first, sand layer is bared. Now, in certain regions of oil production, such as in the sea off Brazil, the underlying layer 5 consists of coral or any other abrasive-type terrain. The rubbing of the protective covering of the pipe on the coral rapidly destroys, at least partially, the said covering, with the consequences well known to the experts such as, for example, deformation of the armour 10 plies into a birdcage; since this deformation is irreversible, it means that the pipe is out of use and that it has to be replaced. Such pipe replacements are extremely expensive, not 15 only because of the cost of the actual pipe but also because of the cost of the production shutdown, the equipment necessary for replacements, etc. In Patent Applications GB-A-2,260,590 and 20 GB-A-2,276,694, devices are described, and illustrated, for protecting flexible pipes which rest on a seabed or are buried. These devices consist of several identical sections connected together to form a continuous protection over a predetermined length of the said 25 flexible pipe. The connection means between the half shells forming the sections are provided in such a way that a gap is left in the mortice so as to allow a degree of longitudinal flexibility of the devices. 30 However, these devices are fixed with respect to the pipe which is to be protected and because of the material used - polyurethane - they would not withstand for a long time the abrasion caused by the rubbing over a hard surface, such as coral or an abrasive-type 35 surface. In addition, they are designed to protect the pipe from any external attack, particularly that which might arise from digging or excavating machines, such as the burying machines which are generally used in shallow waters. W u 4 <n_ -3 In the following text, reference will be made to a flexible pipe but it should be understood that the present invention can be employed for any type of 5 immersed pipe, such as a rigid riser whose protective covering consists of an anticorrosion paint. In general, the present invention relates to pipes having an external covering liable to be damaged by rubbing on a hard and/or abrasive-type surface. 10 The object of the present invention is to propose a protection device for a flexible pipe connecting a surface unit to a seabed apparatus and having a bearing part liable to move over the seabed. 15 A subject of the present invention is a protection device which is characterized in that it consists of at least one protection element placed around at least one portion of that part of the flexible pipe which is to 20 be protected, the said protection element being mounted so as to rotate freely about the said portion. One advantage of the present invention is the fact that that part of the pipe normally in contact with the 25 seabed is protected by the protection element, the latter being subjected to the rubbing of the seabed or of the underlying layer which may consist of coral. Another advantage is that the protection element is 30 free to rotate, thereby allowing it to roll over the sand on the seabed or over the underlying coral, so that the rubbing is greatly reduced. According to another characteristic, the protection 35 element consists of several two-part olives, each part resting freely via its ends on shoulders of collars interposed between two consecutive olives.

-4 Consequently, changing one or more olives after they have become worn is very easy to accomplish. Further advantages and characteristics will become more 5 apparent on reading the description of one embodiment of the present invention, as well as on examining the appended drawings in which: - Figure 1 is a schematic view of a flexible pipe 10 connecting a surface unit to equipment on the seabed; - Figure 2 is a partial sectional view of the protection device according to the invention. 15 A surface unit consisting, for example, of a production platform 1, is connected to equipment on the seabed, such as a wellhead 2, via a flexible pipe 3. In the example illustrated, the flexible pipe 3 has a so called free-hanging configuration, but it could have 20 another configuration in which a part 4 of the said flexible pipe 3 rests on the seabed 5. In certain production regions, such as for example in the sea off Brazil, the first layers of the seabed consist of a surface layer of sand and at least one hard underlying 25 layer such as a layer of coral. When the surface unit 1 moves in directions X approximately parallel to the part 4 of the pipe, the latter rubs little against the seabed 5 since the total 30 length of the flexible pipe between the fastening ends 6 and 7 is designed to absorb these movements. On the other hand, when the same surface unit 1 moves in other directions, for example in directions Y 35 perpendicular to the directions X, the part 4 of the pipe is moved along paths some of which are circular arcs centred on the fastening end 7. Each time the part 4 of the pipe moves, part of the seabed is removed as a -1- -5 result of the rubbing of the said part 4 of the pipe against the seabed 5. The device according to the invention is intended to 5 protect at least one portion of the said part 4 of the pipe and, preferably, the entire part 4 of the pipe and even beyond that, for example as far as the start 8 of the curvature of the pipe which, in principle, is not resting on the seabed. 10 The device partially illustrated in Figure 2 comprises at least one protection element which, in a preferred embodiment, consists of an olive 9 which is free to rotate about that part of the pipe 4 which is to be 15 protected. Preferably, each olive 9 consists of two half-olives 10, 11. Each half-olive 10, 11 comprises, at the ends 12', 13', regions 12, 13 which rest on shoulders 14, 15 of support collars 16 which are fastened to the pipe and which are interposed between 20 two consecutive olives 9. The regions 12, 13 rest freely on the shoulders 14, 15 or leave a small gap between them and the said shoulders. The gap which may be left opposite the bearing regions 12, 13 and the shoulders 14, 15 is, for example, between 3 and 5% of 25 the internal diameter of the olive, measured perpendicular to the said bearing regions 12, 13. Apart from allowing the olive to rotate, the gap between the bearing regions and the shoulders allows water to flow between the olive and the flexible pipe in order to 30 flush out the air that might be trapped and the water when the flexible pipe is being raised. In order to fulfil these air- and water-flushing functions, small holes may also be provided in each of the half-olives. The length of each shoulder 14, 15 is sufficient for 35 the maximum curvature that the part 4 of the pipe can adopt not to allow the ends 12', 13' to become detached from the shoulders 14, 15. In the example in Figure 2, it may be seen that the bearing regions 12 of the half olive 10 are pressed against the rims 17 of the 7___ -6 collars, whereas the bearing regions 13 of the half olive 11 press against the free edge of the shoulders 15, but without becoming detached from the collars 16, this being so despite the curvature of the part 4 of 5 the pipe, it being possible for the said curvature to achieve a radius as small as 3 m for pipes ranging in internal diameter from 2 to 16 inches. Tests carried out have shown that a length of the shoulders 14, 15 of between 80 and 100 mm is sufficient to keep the ends of 10 the olives on the corresponding shoulders of the support collars. Preferably, each support collar 16 also consists of two parts, which are connected together by suitable means such as bolts 18, it being understood that each collar is firmly attached to the 15 pipe so that it can neither slide nor rotate with respect to the flexible pipe. The number of olives 9 essentially depends on the length of that part 4 of the pipe which is to be 20 protected and the length of each olive may vary or be constant in the same device. A length of 1 m for each olive is suitable. The connection between the half-olives 10, 11 of an 25 olive 9 may be made by any suitable means, such as a mortice and tenon, which would be provided on the opposing faces of the half-olives to be assembled. In order to avoid any relative movement between the 30 protection device and the flexible pipe, it is preferable to provide a support collar 16 firmly attached to a component which is normally fitted on the end 7 of the flexible pipe 3, for the purpose of connecting it to the wellhead 2. The last support 35 collar located on the end of the device, on the same side as the region 8, may be tightly clamped against the flexible pipe 3 so as to prevent relative movement, although this is not necessary as long as the collar located on the same side as the end 7 is fixed. Ct -7 The half-olives 10, 11 may optionally include reinforcement regions 19, such as those illustrated in Figure 2. 5 When the device according to the invention is fitted onto that part 4 of the pipe which is to be protected, the latter is no longer in contact with the seabed. This is because it is the olives 9 which rest on the 10 seabed since their external diameter is greater than the external diameter of the support collars which remain fixed, the olives 9 rotating freely on the shoulders 14, 15 each time that part 4 of the pipe is moved as a result of the lateral movements of the 15 surface unit 1 in directions cutting the directions X. Finally, each olive is made of a relatively strong material, such as, for example, a glass-epoxy composite or a light but strong metal. 20 In the above description, reference was made to substantially continuous protection of the portion of that part 4 of the pipe which is to be protected, it being possible for the latter to be of the flexible or 25 rigid type. It goes without saying that it would be possible, without departing from the scope of the present invention, to provide protection which is not continuous. For example, it would be possible to leave a free space between two consecutive fixed collars, 30 which free space would not be protected by an olive. Of course, the free space would have a shorter length than that of each olive in order to prevent, as far as possible, significant rubbing caused by the first layer of the seabed getting in between the said consecutive 35 collars during movement of the pipe. Because of the diameter difference existing between the olives and the support collars, it is guaranteed that the spaces without any protection will not be in contact with the ard sublayer.

Claims (12)

1. Protection device for a pipe (3), of the type 5 comprising at least one protection element (9) placed around at least one portion of that part (4) of the pipe (3) which is to be protected, characterized in that the said protection element (9) is mounted so as to rotate freely about the 10 said portion.

2. Device according to Claim 1, characterized in that it comprises several protection elements (9) placed along the length of that part (4) of the 15 pipe which is to be protected.

3. Device according to Claim 1 or 2, characterized in that each protection element (9) consists of an olive, the ends (12, 13) of which bear freely 20 against shoulders (14, 15) of a support collar (16) fastened around that part (4) of the pipe (3) which is to be protected.

4. Device according to Claim 3, characterized in that 25 each olive (9) consists of two half-olives (10, 11), each half-olive (10, 11) having, at each end (12, 13), a region which rests freely on a shoulder of the said support collar. 30

5. Device according to either of Claims 3 and 4, characterized in that the maximum external diameter of the olive (9) is greater than the maximum external diameter of the said support collar (16). 35

6. Device according to one of Claims 3 to 5, characterized in that the length of each shoulder (14, 15) of the support collar (16) is determined so that the corresponding bearing region of the -9 olive remains in contact on the said shoulder whatever the curvature imposed on the said part of the pipe which is to be protected. 5

7. Device according to one of Claims 3 to 6, characterized in that the total length of each olive is approximately equal to one metre.

8. Device according to one of Claims 3 to 7, 10 characterized in that the length of each shoulder (14, 15) of the support collar (16) is between 80 and 100 mm.

9. Device according to one of Claims 3 to 8, 15 characterized in that a small gap is left between the opposing faces of the bearing regions and the shoulders, the said gap being between 3 and 5% of the internal diameter of the said olive, measured perpendicular to the end bearing regions. 20

10. Device according to one of Claims 3 to 9, characterized in that each support collar (16) is made in two parts which can be fixed together. 25

11. Device according to Claim 1, characterized in that the protection element consists of at least one hollow cylinder placed around that part of the pipe which is to be protected. 30

12. Device according to one of Claims 1 to 11, characterized in that the pipe is protected over a length which is greater than the length of that part of the said pipe which is to be protected. -01 -7