GB2281365A - A sealing device for sealing an elongate body - Google Patents

Abstract

A sealing device for sealing an elongate body (1) such as a cable, pipe or umbilical, at its entrance to an apparatus, such as an offshore J-tube (2) has a centralizer (5) arranged around the elongate body (1) inside a pull in flange (3) at the lower entrance of the J-tube (2). A seal (7) is arranged around the elongate body (1) next to the centralizer (5) and is formed as a conical one piece split annulus. The split is in a plane substantially parallel to the axis of the annulus (5) and to the axis of the elongate body (1). Pressure means (9 - 13) is provided for pressing the seal (7) into sealing contact against the elongate body (1), against a flange surface (8) and against the centralizing means (5). <IMAGE>

Description

A SEALING DEVICE FOR SEALING AN ELONGATE BODY The present invention relates to sealing off an elongate body, such as a cable, a pipe or an umbilical, at its entrance into an apparatus, in particular at the lower horizontal end of an offshore J-tube, leading from the sea floor to a platform structure. The sea floor may be several hundred meters below the sea level.

In some cases it is desirable, after an elongated body has been installed within a J-tube, that the sea water surrounding the body within the J-tube is deoxidized to prevent or reduce corrosion. In order to neutralize the sea water in the tube, inhibiting agents is added to the water, and the inside pressure is normally some 5-6 bar more than the pressure of the surrounding water. A problem arises, however, due to difficulties in obtaining a full seal between the body surface and the tube entrance. If the seal is poor the external sea water will be gradually exchanged with the inhibited sea water within the tube.

From British Patent No 2188999 there is known a sealing device comprising at least two elements which are arranged to be pressed against each other, against a circumference of the elongate body and against the aperture of said apparatus. At least one of the elements is hinged to the apparatus.

US Patent No 4,712,800 relates to a split elastomer ring for repairing potheads and to a process of repairing a pothead therewith. The ring has an elastomeric body and a central opening. A slit is provided in the body of the ring so that it may be opened and inserted around the cable at the base of the pothead. A silicone sealant is placed between the ring and the pothead and the ring holds the sealant against the cable and the base of the pothead body. The ring has in itself no sealing effect and cannot be used in connection with sealing of J-tubes.

The present invention to provide alternative efficient full seal at the entrance of a J-tube.

According to the invention there is provided a sealing device for sealing an elongate body, such as a cable, pipe or umbilical, at its entrance into an aperture of an apparatus, such as an offshore J-tube, characterised in that it comprises centralizing means which in use is arranged around the elongate body inside a pull-in-flange at the lower entrance of the J-tube, sealing means arranged around the elongate body next to the centralizing means, and formed as a one-piece split annulus, the split being in a plane substantially parallel to the axis of the annulus and to the axis of the elongate body, and pressure means for pressing the sealing means into sealing contact against the elongate body, against a flange surface and against the centralizing means.

With this invention there is obtained an efficient sealing device which may be installed by divers or with an ROV after installing the elongated body within the J-tube.

A further advantage is that pollution that might be caused by leaking inhibiting agents is effectively prevented.

In order that the invention and its various other preferred features may be understood more easily, some embodiments thereof will now be described, by way of example only, with reference to the drawings, in which: Figure 1 illustrates schematically a crossection of an installation including a sealing device and constructed in accordance with the invention, Figure 2 shows one example of sealing means that can be used in the installation of Figure 1, and Figures 3 and 4 show alternative installations incorporating sealing means and constructed in accordance with the invention.

Referring now to Figure 1 an elongated body 1, such as a cable, a pipe or an umbilical, is shown which is installed within a J-tube 2. The lower end of the J-tube indicated is normally provided with a blind flange (not shown) which has to be removed and replaced by a special pull-in-flange before installing the elongated body 1. The pull-in-flange 3 is designed to fit against the J-tube flange as shown. The interconnection is sealed with one or more O-rings. The entrance side (right side) of the pull-inflange is formed as a bellmouth to insure that the surface of the elongate body is not damaged when pulling it into the J-tube. Depending on how the J-tube entrance is designed, the pull-in-flange 3 may also have a bellmouth 4 facing into the J-tube. The J-tube entrance may also be designed as a combination of items 2 and 3. This is illustrated in Figure 3.

The pull-in-flange 3 is installed by divers (or an ROV) using a lifting device, such as a buoyancy device (not shown) while installing bolts and nuts. The next step is to insert the elongated body 1 through the pull-in-flange 3 and the J-tube 2, and install the end of the elongated body before assembling a split centralizer unit 5 around the body. The centralizer is a two-piece annulus which fits tightly around the body and rests against a shoulder 6 on the inner surface of the pull-in-flange. The centralizer is preferably made from a high-viscosity non-yielding material like polyamide (Nylon, PA6) or polyoxymetylene (POM). The two parts of the centralizer are interconnected by means of guiding pins.

Seal 7 is now placed around the body. The seal is formed as a one-piece split annulus as shown in Figure 2, the split 20 being in a plane substantially parallel to the axis of the annulus and to the axis of the elongated body.

The seal 7 is made of a low viscosity silicone rubber, such as that having the designation RTV-2 (tradename Powerseal 600 of Wacker-Chemie). The hardness is some 25 Shore A whereas the compression set is 2090 at 22h and 1500C. Its surface roughness is very low and it seals well against other body surfaces. The outer surface of the seal 7 is partially conical to fit against an inner conical surface 8 of the pull-in-flange and partially cylindrical to fit against a cylindrical inner surface of guiding means 9. The seal should be arranged such that the transition between the conical and cylindrical areas is at a small step on the inner surface of the flange 3. Conical surface 8 which has an angle of some 25 (15 -40 ) should also be very smooth.

As the seal 7 is to be replaceable, this means that a non-split seal cannot be used. Some advantages of using the single-split soft seal shown are: the one-piece seal is easier to handle than a twopiece seal, - and the special soft material facilitates easy snap-on and snap-off of the seal, the single split seals seal easier than the two splits of a two-piece seal, there are no bolt through-holes that have to be sealed as in the case of the previously mentioned British patent.

Pressure means are arranged to press the seal 7 against the elongated body 1, against the inside wall 8 of the pull-in-flange 3 and against the centralizer unit 5. The pressure means consists of a hinged steel pressure plate 10 which is closed around the elongated body 1. The pressure plate is fitted with a pressure plate 11 made of the same material as the centralizer unit 5. As shown the pressure plates 10/11 are pushed against the seal 7 in a controlled manner by means of Teflon coated bolts 12 arranged in a flange 13. The guiding means 9 may be a split tube which is fitted after arranging the components 10 and 11. A bending restrictor clamp indicated at 14 may be mounted on to the flange 13.

With the sealing device shown, the sealing process is simplified because there are only three sealing surfaces: 1) the single split of the seal 7 itself, - 2) the seal against the elongated body 1, and - 3) the seal against the smooth conical surface 8 of the flange 3. Tests have shown that under moderate pressure (10 bar) the very soft rubber fills all irregularities of contacting surfaces, such as surfaces of elongated bodies having polymer sheaths which for instance may have a rough surface due to careless handling.

Whereas the pull-in-flange 3 preferably is a onepiece structure, the components 9, 10, 11 and 13 are preferably individual two-piece hinged structures. Care should be taken to ensure that the hinges are displaced relatively to each other, and relatively to the split of the seal 7 and the meeting surfaces of the centralizer along the circumference of the structure. In the drawing sections are taken to show some of the hinges and some of the meeting surfaces, such as hinges of items 9 and 10, and a meeting surface of the centralizer unit 5 and of the plate 11.

Figure 2 illustrates one embodiment of the seal 7.

It is made of a low viscosity material enabling it to be snapped on and off an elongated body 1. The seal is made as a one-piece split annulus. The split 20 is designed such that it will be completely closed and sealed when pressed into position. The surfaces 21 and 22 are designed such as to fit snugly into the compartment defined by the pull-inflange 3 and the guiding means 9.

Figure 3 shows an alternative installation in the case that the J-tube entrance is designed as a combination of the items 2 and 3 shown in Figure 1. The J-tube 30 is provided with a bellmouth portion 31 having a conical inner surface 32 corresponding to the surface 8 in Figure 1. The bellmouth of the J-tube ends in a flange 33 which initially is provided with a blind flange (not shown). In the drawing the blind flange has been replaced with a flange 34 corresponding to the flange 13 in Figure 1. Components for arranging a bending restrictor are not shown. The components 35, 36 and 37 correspond to components 10, 11 and 12 in Figure 1. Guide means 38 corresponds to the guide 9 in Figure 1, but in this case the guide 38 is welded to the flange 34. The components 34 (with 38), 35 and 36 are preferably hinged to simplify underwater installation. Care should be taken to make sure that the inner surface of the J-tube bellmouth is not too rough to receive the sealing components As explained in connection with Figure 1, the sealing components are fitted after the elongated body 1 has been installed on the offshore platform. Sealing components 39 and 40 corresponding to items 5 and 7 in Figure 1 are installed as explained above. A centralizer 39 has a shoulder 42 preventing it from being pushed into the J-tube.

Finally a collar 41, which may be a three-piece hinged structure is locked around the sealing assembly and bolts 37 are tightened to obtain a desired pressure on the seal 40.

In some cases the elongate element is provided with a factory mounted hang-off-head (not shown) for simplifying installation of its the upper end on the platform. Due to difference in diameter between the elongated element and the inside of the J-tube and also due to the curvature of the Jtube, it will be difficult to predetermine the exact length of the element between the installed head and the sealing position. The exact position of the seal along the length of the element can therefore not be decided before the hangof head has been installed. In such cases the centralizer should be designed to allow slide-through of the element, and the sealing device should be installed on the J-tube so that the element can be slid to a desired position within the centralizer 5 (and 39) before compressing the seals 7 (and 40).

In order to simplify installation of the sealing device with an ROV, the centralizer and the sealing means can be arranged on the elongate element before lowering the element to the sea bed. Care should be taken to protect the surfaces of these sealing items during this process.

As an alternative to the embodiments illustrated in Figures 1 and 3, there may be used alternative pressure means 50 as illustrated in Figure 4. The pressure means 50 consists of a frame 51 with a Y-shaped clamp 52 which is hinged to the top 53 of the frame. The frame 51 is secured to a flange 54 on the J-tube. In the drawing a part of the J-tube wall is removed to show other details.

When the clamp 52 is swung upwards, the elongate element 1 with centralizer 55 and sealing means 56 can be entered through the J-tube flange 54. A shoulder 57 on the centralizer defines its penetration into the flange. Th- elongate element 1 may be slid through the centralizer 55 and the sealing means 56 until a desired position is reached.

The Y-clamp 52 is then swung downwards and locked to the frame by locking means 58. Finally the seal 56 is compressed by controlled tightening of bolts 59 corresponding to bolts 12 and 37 of the embodiments of Figures 1 and 3.

Figure 4 also shows slots 60 in the outer surface of the centralizer 55, for enabling circulation of inhibiting agents through a pipe 61 in the J-tube.

Whereas it is important to prevent sea water from entering the J-tube, care should be taken to make the elongate body itself sealed against longitudinal flow or migration of water in its outer layers, and also within the elongate body if it is not fitted with one or more impervious sheaths.

The centralizer unit 5, 39, 55 preferably consists of a two piece annulus made of a high viscosity material such as polyamide (Nylon, PA6) or polyoxymethylene (POM).

Claims (10)

CLAIMS:

1. A Sealing device for sealing an elongate body (1), such as a cable, pipe or umbilical, at its entrance into an aperture of an apparatus, such as an offshore J-tube (2,30), characterised in that it comprises centralizing means (5,39,55) which in use is arranged around the elongate body (1) inside a pull-in-flange (3,31,54) at the lower entrance of the J-tube (2,30), sealing means (7,40,56) arranged around the elongate body (1) next to the centralizing means, and formed as a one-piece split annulus, the split (20) being in a plane substantially parallel to the axis of the annulus and to the axis of the elongate body, and pressure means (9-13;34-38;50-53) for pressing the sealing means (7,40,56) into sealing contact against the elongate body (1), against a flange surface (8,32,54) and against the centralizing means (5,39,55).

2. A sealing device as claimed in claim 1, characterised in that the seal (7,40,56) is made of a low viscosity silicone rubber.

3. A sealing device as claimed in claim 1 or 2, characterised in that the outer surface of the seal (7,40,56) is partially conical (21) to fit against an inner conical surface (8,32) of the flange (3,31,54), and partially cylindrical (22) to fit against a cylindrical inner surface of guiding means (9,38).

4. A sealing device as claimed in claim 1, 2 or 3, characterised in that the centralizing means (5,39,55) consists of a two-piece annulus made of a high viscosity material.

5. A sealing device as claimed in any one of the preceding claims, characterised in that the centralizing means (5,39,55) is provided with a shoulder (6,42,57) which fits against a corresponding shoulder within the pull-inflange.

6. A sealing device as claimed in any one of the preceding claims, characterised in that the pull-in-flange (3) is a separate one-piece unit sealed to the J-tube entrance.

7. A sealing device as claimed in claim 6, characterised in that the pull-in-flange has a bellmouth (4) facing into the J-tube.

8. A sealing device as claimed in any one of the preceding claims, characterised in that the pressure means (50) comprises a frame (51) which is arranged to be secured to a J-tube flange and which is provided with a hinged clamp (52) which can be locked to the frame.

9. A sealing device as claimed in claim 8, characterised in that the clamp (52) is Y-shaped so as to allow closure and locking of the clamp after insertion of the elongate body (1) into the J-tube.

10. A sealing device for sealing an elongate body substantially as described herein with reference to the drawings.