GB2041110A - Seals - Google Patents

Abstract

The invention relates to toroidal, elastomeric seals suitable for use in underwater installations where a pipeline passes through a duct. The seal is designed to accommodate both longitudinal and radial relative movement between pipe (36) and duct. It has the form of a double-walled elastomeric tube (37), the walls defining a hollow toroid, the seal being able to roll longitudinally by translation of part of outer wall (37B) into inner wall (37A) and vice-versa, the distance between the innermost diameter and outermost diameter of the seal being greater than the radial distance to be sealed and the seal having a sealable, circumferentially- extending split (defined by ends 38 and 39) in its outer wall. The seal, by virtue of its split, can be manufactured on a toroidal former rather than a cylindrical mandrel as would be required for an unsplit construction. <IMAGE>

Description

SPECIFICATION Seals This invention relates to seals and particularly to seals for sealing and protecting pipes within, for example, an outer duct. It is particularly relevant to underwater pipes and ducts but is not limited to such application.

However, for convenience the invention will be described below with particular reference to underwater usage.

In the offshore oil and gas extraction industry, considerable quantities of rigid, submaring pipelines are employed. Such lines may be used for example to connect one offshore platform with another platform or with a shore installation. In the latter case, a pipeline may extend for several hundred kilometres.

To accommodate eventual pipe installation it is known to incorporate ducting in the structure of a platform. The inside diameter of the ducting is greater than the outside diameter of the pipe to be accommodated. The difference in diameters may be, for example, in the region of 300 mm and the ducting may have an internal diameter, for example, approaching 1 m.

It is desirable that the contained piping should be free to move -longitudinally within the ducting so as to accommodate thermal expansion and contraction without buckling and it may also be desirable to accommodate a certain amount of relative movement in the radial direction. It is also desirable that the annular space between the pipe and duct should be sealed, preferably at both extremities, against the entry of sea water. A further requirement is that the inner surface of the duct and the outer surface of the pipe should be protected against corrosion.

It will be apparent that once installed, a pipe within a duct is only accessible with difficulty. Failure of the pipe would necessitate a costly shutdown of operations and the application of extensive repair procedures. In the case of a main flow line to shore from an offshore platform, shut down and repair procedures can involve very considerable daily costs.

An inflatable one-piece seal capable of accommodating some relative movement between a pipe and a duct has been proposed but is thought to be of limited application as discussed below.

It is an objective of the present invention to provide a sealing system having the desirable features enumerated above, in particular the accommodation of relative movement between pipe and ducting, and which by its efficient operation considerably reduces the risk of pipe failure.

Accordingly the invention provides a toroidal seal in the form of a double-walled tube, the walls being of a flexible elastomeric composition and capable of defining between them a hollow toroid, whereby the seal can roll in a longitudinal direction by translation of part of the outer wall of the tube into the inner wall and vice-versa without loss of sealing effect, the distance between the innermost diameter and the outermost diameter of the seal being greater than the radial distance to be sealed and the seal having a sealable, circumferentially-extending split in its outer wall. By "circumferentially-extending" is meant extending around the surface of the seal in a plane perpendicular to its longitudinal axis.

In yet a further embodiment the invention provides a sealed system in which a pipe passing through a duct is sealingly engaged with the walls of the duct by means of one or more seals of the invention as previously described.

The radial distance to be sealed will be the difference between the inner diameter of a duct, for example, and the outer diameter of a pipe passing through the duct.

Moreover, by forming the seal with a circumferential split, manufacture can be carried out around a toroidal former, whereas if a continuous, unsplit seal were to be made, this would have to be done around a cylindrical mandrel. This latter technique would involve making the inner and outer walls of the double-walled tube "flat" against the surface of the mandrel with film or other separating means between them to prevent their bonding together. This flat method of manufacture imposes limitations on the radial distance that can be sealed since clearly, there will be a relatively low limit to the amount of expansion that can take place without weakening the structure when this flat type of seal is inflated to separate the inner and outer walls.

The seal of the invention is therefore designed to accept in sealing engagement a pipe through the central bore defined by the inner wall of its tube and to seal against the inner surface of, say, a duct by virtue of the outer wall of its tube. The means provided to seal the circumferential split in the tube can be accommodated in suitably provided engaging means set in the inner surface of the duct.

Preferably the engaging means will contain the seal and the whole unit will be accommodatable in the duct.

Sealing between pipe and duct is thereby achieved and the flexibility and geometry of the double-walled tube enable relative longitudinal movement between pipe and duct since the seal will roll with such movement. During such rolling part of the inner wall of the flexible tube will be translated into the outer wall and vice-versa - up to the limit imposed by the sealing means. Where an equal or approximately equal rolling distance is required in each direction it will be appropriate to form the sealable split at or near the midpoint of the seal. Where an unequal rolling distance is required, the split may be placed closer to one of the ends.

It is possible that a non-textile reinforced, elastomeric seal, having the shape of the subject seal would accommodate the abovedescribed rolling movements and maintain the required sealing engagement. It is, however, preferred to include reinforcing means in the body of a seal to ensure adequate pressure retention particularly in deeper waters.

It is well known to employ textile, yarns, cords and fabrics for the reinforcement of polymeric products. It is equally well known that such inclusions tend to exert a relatively permanent shape-retaining effect of a product.

Such effect is in fact employed in many products where a relatively stable shape is required under differing operation conditions.

In instances where a change of shape is required under e.g. varying pressure or tensile conditions, it is usual to introduce pleats or folds into the construction. In the present case, a system of reinforcement is employed which permits substantial changes of shape to occur in a seal without loss of reinforcing capacity. A system of textile cord reinforcement is employed in which the layers of cords in a cord/elastomer laminate are substantially free to move relative to one another.

The cords will normally be laid at an angle to the longitudinal axis of the seal and it is preferred that at least two layers of cords are employed, the cords in one layer being inclined in the opposite sense to those in the other layer. It is preferred that the angles employed in the final product are from 20 to 40'. As the seal is made on a former of the required final toroidal shape, the wrapping angle employed will be the same as the final angle. As indicated above, use of a former is possible since it is desired to form the seal as a split toroid, which of course enables removal of the former from the formed product. The split can be sealed by the incorporation of bead wires or flanges which can then be clamped together. If desired a clamp may be inserted inside a split seal to clamp its inner wall firmly to the pipe to be sealed.

The seal may conveniently be contained concentrically within a rigid tube which may readily be attached to the wall of the duct to be sealed. The tube may be, for example, of plastics material but it is preferred to use metal, especially steel. The tube should be of sufficient length to accommodate the seal in all its sealing positions.

The rigid tubes containing the seals may be bolted or welded to the inner wall of the duct and in another embodiment a tube may form a casing into which two or more seals can be fixed. Thus a sealing unit containing two or more seals may be clamped or otherwise attached in position in the duct to provide a convenient sealing means with the minimum of attachment and installation work.

In another embodiment the seal of the invention is provided with a skirt attached around one of its walls, usually the inner wall.

The skirt is conveniently of rubberised fabric and its length is such that it extends beyond one end of the seal. The skirt can then be clamped to the pipe passing through the seal to provide additional sealing protection. The skirt may be bonded to the outside face of the inner wall of the seal over a portion of the length of the latter so that the ability to roll is still retained. The skirt is preferably clamped adjacent where is emerges from the seal.

The invention is further described with reference to the accompanying drawings in which: Figure 1 is a representation of a platform located in the sea bed; Figure 2 is a sectional view of a duct in the platform; Figure 3 is a diagrammatic representation in sectional view showing rolling movement of a seal; Figure 4 is a similar view of Fig. 3 with the seal in collapsed condition; Figure 5 is a sectional view showing a pipe passing through a seal of the invention; Figure 6 is a similar view showing a pipe passing through a seal of the invention in which an internal clamp is used; Figure 7 is an elevation, part sectioned showing a stage in the manufacture of a seal of the invention on a toroidal former;; Figure 8 is an enlarged sectional view of the flange area of Fig. 7, and Figure 9 is an elevation with part cut away of the seal of Fig. 7 when finished and in assembly with a rigid tube.

Fig. 1 represents part of a concrete platform located on a sea bed. A number of identical, hollow concrete chambers 1 are commonly employed in part as buoyancy aids to assist in towing a platform to the required site. On arrival above a sea bed site, the chambers are flooded, causing the platform to sink to the sea bed. After installation, the chambers 1 may remain water-filled to enhance the stability of the platform.

A number of hollow concrete legs 2 support a a superstructure of working deck 2A above sea-level. Such legs are commonly used also to house many of the vertical pipes (risers) which extend from the sea bed to the working platform. As described in relation to chambers 1, the legs 2 may be adapted to provide buoyancy en route to site and may then be flooded. After the platform has been installed, the legs are usually evacuated of water so as to provide a safe working environment for the installation of pipes and machinery. Following such installation, the legs may again be flooded or may remain air-filled. In the former case, it is usual to evacuate the water periodically to facilitate inspection and maintenance of the installation.

A duct 3, typically 1 m in diameter, communicates between leg 2 and the outside environment. In so doing, it passes through chamber 1. To prevent ingress of water during towing and installation, one or both ends of the duct may be fitted with temporary covers or seals.

A riser pipe 4 is installed inside leg 2. An underwater pipeline 5 communicates at its distant end, with a shore installation. It is required to make a connection between pipes 4 and 5 utilising duct 3. Previously, such connection was commonly made by introducing a separate length of pipe into duct 3 and joining ends of the said pipe to the riser and pipeline ends respectively. The aforesaid method requires a considerable amount of work to be carried out underwater. To utilise the construction of one joint only between the underwater pipeline and the riser pipe avoids much of this underwater work and the present invention is particularly applicable to the latter system.

Fig. 2 is an enlarged and simplified sectional view of the duct 3 in Fig. 1 prior to the installation of the platform on a sea bed. Seals 9, 10, 11 and 12 are seals of the invention constructed as later described. They are shown in the deflated condition. Items 13 and 14 are guiding and supporting elements.

(Seal 15 is a flexible, rolling diaphragm seal, within a housing, for subsequent attachment).

To assist in an appliciation of the construction and function of the subject sealing system, a brief description of usage is given: A platform containing the above-described duct is installed on a sea bed site. Chambers 1 and legs 2 are water-filled. Temporary covers are removed from duct 3 and the near end of pipeline 5 is hauled through the duct to emerge inside leg 2 at a position suitable for attachment to riser pipe 4. Seals 9, 10, 1 1 and 12, have been fixed in their desired positions prior to hauling pipeline 5 through the duct. The seals have valve inlets (not shown) and are then connected to a soure of pressure at the surface at least equal to the ambient water pressure and the seals thereby assume their fully-sealing configuration between duct and pipeline. The legs 2 may then be emptied of water, and the rolling diaphragm seal 15 attached to the pipeline 5.

Seals 11 and 12 are then deflated by removal of the pressure applied from the surface and are maintained in that condition.

Water contained in the toroidal space between the duct and the pipe is evacuated. It is replaced by anti-corrosive fluid. Seals 9 and 10 are capable, by virtue of their construction, of maintaining a sealing engagement regardless of thermal movement of the pipe.

Thus, the above described arrangement provides an effective sealing and corrosion preventing system.

It will be apparent that the efficiency of the system depends largely upon the ability of a toroidal seal to enter into the maintain a sealing arrangement. Fig. 3 shows diagrammatically the magnitude of typical movements which must be accommodated by a seal without loss of sealing engagement. For a seal of length 1 m, dimension 'X' may be of the order 0.75 m. Fig. 5 indicates the size difference between the collapsed and sealing condition of a seal. In both drawings, constructional details are omitted.

Fig. 5 illustrates a pipe 36 passing through a seal 37 of the invention. Inner wall 37A of the seal contacts the pipe and outer wall 37B is in contact with rigid tube or outer sleeve 42. The outer wall 37B has a circumferentially-extending split defined by ends 38 and 39 in which have been positioned reinforcing bead wires 40 and 41. Ends 38 and 39 are clamped together and to tube 42 by circumferential clamping means 43 whereby the effect of a closed seal in achieved.

Fig. 6 shows a similar system to that of Fig.

5 but in which an internal clamp 44 is used.

Clamp 44 holds inner wall 37A of the seal tightly against pipe 36. It is of course inserted prior to closure of ends 38 and 39 by clamping means 43.

Referring to Figs. 7, 8 and 9, there is shown the assembly of a seal on a toroidal former and a finished seal contained within a rigid tube.

In Fig. 7 a sectional, toroidal former 51 has releasably attached to it a metal ring 52.

Ring 52 is provided with bolt holes 53 and is fitted to former 51 at a position coincident with that of the split in the eventual seal. It is also provided with an airway as indicated in Fig. 8.

A A single ply 54 of unvulcanised elastomeric sheet has been positioned to cover the former 51 as indicated and to extend up the vertical faces of ring 52.

Plies 55 and 56 of weftless, nylon cord fabric have then been applied at opposite angles one to the other over ply 54. In practice, 4 plies of cord are used. Two plies only are shown here for ease of description.

A covering ply 57 of unvulcanised, elastomeric sheet has been wrapped over ply 56.

Plies 54 to 57 inclusive are assembled onto the former 51 in known manner and consolidated to form a homogeneous structure.

Figure 8 is an enlarged fragment of a section through the vertical components (flanges) and ring of Fig. 9.

Ring 52 contains a right-angled channel 58, which will form the airway of the eventual seal. Item 60 is a temporaty extension of channel 58. Item 59 is a threaded bush, embedded in former 51.

To locate and retain the ring on the former, extension 60 is first aligned with bush 59 and then bolted firmly in position. (After manufacture of the seal, extension 60 is plugged and welded).

Annular reinforcing plates 61 and 62 are embedded in both flanges.

Construction of the flanges is carried out concurrently with building the seal on the former and embodies the following stages: Elastomeric sheet 54 and the first cord ply 55 are positioned, as shown, against the vertical faces of ring 52. Holes are cut through 54 and 55, corresponding to the holes in ring 52. Steel plates 61 and 62, drilled to correspond with ring 52, suitably prepared for bonding are placed in position as shown. Note that the outside diameters of plates 61 and 62 are slightly smaller than that of ring 52.

Second cord ply 56 and covering ply 57 are similarly positioned and perforated. The edges of the cord and elastomeric plies are then trimmed flush with the outer edge of plates 61 and 62. The trimmed edges are covered with unvulcanised elastomeric strip 63 and 64.

After fabrication of the seal as described above, the assembly is bound with textile wrappers in known manner and is vulcanised in an autoclave. After vulcanisation, the wrapping cloths are removed and the product, including ring 52, is removed from the former.

The seal is now ready for installation in a rigid tube assembly. Fig. 9 shows a representative seal and tube assembly. Item 64 is a connector, communicating with channel 58 and adapted for attachment to inflation means not shown. Items 65 and 66 are lengths of rigid, steel tube having flanges 67 and 68 respectively between which the flanges of the split seal are clamped. Flanges 67 and 68 are suitably drilled to accommodate retaining bolts.

It will be apparent that the retaining bolts pass through the flanges of the seal and through ring 52, to be secured by nuts in a conventional manner.

Tubes 65 and 66 are also provided with larger diameter flanges or spacers 69 and 70 suitable for attachment by welding to the inside of a duct.

Claims (22)

1. A toroidal seal in the form of a doublewalled tube, the walls being of a flexible elastomeric composition and capable of defining between them a hollow toroid, whereby the seal can roll in a longitudinal direction by translation of part of the outer wall of the tube into the inner wall and viceversa without loss of sealing effect, the distance between the innermost diameter and the outermost diameter of the seal being greater than the radial distance to be sealed and the seal having a sealable, circumferentially-extending split in its outer wall.

2. A toroidal seal according to Claim 1, in which the elastomeric composition is reinforced with textile cords lying at an angle to the longitudinal axis of the seal.

3. A toroidal seal according to Claim 2, in which two layers of cords are utilised, the cords in one layer being inclined in the opposite sense to those in the other layer.

4. A toroidal seal according to Claim 2 or 3, in which the cords are inclined from 20 to 40 to the longitudinal axis of the seal.

5. A toroidal seal according to any one of the preceding claims, in which the seal is accommodated concentrically within a rigid tube, the tube being attachable to the wall of the duct to be sealed.

6. A toroidal seal according to Claim 5, in which the tube is of sufficient length to accommodate the seal in all its sealing positions.

7. A toroidal seal according to any one of the preceding claims, in which a skirt is attached around one wall of the seal and is of sufficient length to extend beyond one end of the seal.

8. A toroidal seal according to Claim 7, in which the skirt is attached to the inner wall of the seal.

9. A toroidal seal according to Claim 6 or 7, in which the skirt is of rubberised fabric.

10. A toroidal seal according to any one of the preceding claims, in which the split is sealable by the incorporation of bead wires or flanges which are clampable together.

11. A toroidal seal according to any one of the preceding claims, in which the seal has a valve inlet connected to a source of pressure.

12. A toroidal seal substantially as hereinbefore described with reference to and as shown in Fig. 3, 4 and 5 of the accompanying drawings.

13. A toroidal seal substantially as hereinbefore described with reference to and as shown in Figs. 3, 4 and 6 of the accompanying drawings.

14. A sealed system in which a pipe passing through a duct is sealingly engaged with the walls of the duct by a toroidaal seal in the form of a double-walled tube, the walls being of a flexible elastomeric composition and capable of defining between them a hollow toroid, whereby the seal can roll in a longitudinal direction by translation of part of the outer wall of the tube into the inner wall and vice-versa without loss of sealing effect, the distance between the innermost diameter and the outermost diameter of the seal being greater than the radial distance to be sealed and the seal having a sealed, circumferentially-extending split in the outer wall, the pipe passing through and being in sealing engagement with the bore of the seal.

15. A sealed system according to Claim 14, in which the seal is contained concentrically within a rigid tube which is bolted or welded to the walls of the duct.

16. A sealed system according to Claim 15, in which the tube is of sufficient length to accommodate the seal in all its sealing positions.

17. A sealed system according to Claim 15 or 16, in which the tube contains two or more seals.

18. A sealed system according to any one of Claims 14 to 17, in which the seal has a skirt attached around one of its walls, the skirt extending beyond one end of the seal where it is attached around the pipe passing through the seal.

1 9. A sealed system according to Claim 18, in which the skirt is attached to the inner wall of the seal.

20. A sealed system according to any one of claims 14 to 19, in which a clamp is positioned inside the hollow toroid to clamp the inner wall of the seal to the pipe.

21. A sealed system substantially as hereinbefore described with reference to and as shown in Figs. 2, 3, 4 and 5 of the accompanying drawings.

22. A sealed system substantially as herein before described with reference to and as shown in Figs. 2, 3, 4 and 6 of the accompanying drawings.