WO1993021392A1

WO1993021392A1 - Improvements relating to the protection of corrosion-susceptible members

Info

Publication number: WO1993021392A1
Application number: PCT/GB1993/000739
Authority: WO
Inventors: Anthony Edward John Strange
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-08
Filing date: 1993-04-07
Publication date: 1993-10-28
Anticipated expiration: 1994-10-08
Also published as: UY23566A1; GB9207624D0; ZA932547B; AU3959393A; MX9302058A

Abstract

A wrapping (2) for a conductor, riser or pile (1) on an offshore rig is a composite sheet with an outer skin (3) of impermeable resilient flexible material and an inner layer (4) of felt impregnated with a thixotropic gel. The edges of the wrapping which are to meet are provided with loops (5), conveniently formed by the outer layer being doubled back and apertured, which interdigitate to receive a flat locking bar (12). The wrapping (2) is stretched to make the loops (5) overlap using temporary abutments (7, 19) secured nearby to the outside of the wrapping. In one form the abutments (7) are beams attached to flexible panels (8) with fibres that interlock with fibre panels (6) on the outside of the wrapping. In another form, the outer skin (3) is doubled near each looped edge with a panel (16) having apertures (17) for anchorage members (21) to be inserted and become captive to the panel. These members (21) remain exposed at the windows (17) for coupling to respective beams (19), preferably via a parallel rod (20) that allows hinging.

Description

"Improvements relating to the Protection of Corrosion-Susceptible Members" This invention relates to the protection of corrosion-susceptible members such as conductors, risers or piles as used on or forming part of oil rigs, piers or jetties. For convenience, this specification will mostly refer to conductors, although the invention is applicable to the protection of any elongate member which may be subject to corrosion. There has been described in WO 87/05066 a pile protection system where a wrapping comprises a flexible sheet with substantially rigid outwardly extending flanges along opposed edges which are adjacent when the wrapping is positioned around a pile. These flanges afford counter abutments for the application of tools by which hoop stresses may be imposed on the wrapping. When the flanges are squeezed together, they are fastened, usually by bolts, and then the tools can be removed.

The wrapping generally comprises an outer skin of water impermeable flexible material, such as reinforced plastics sheet, and in particular nylon reinforced Neoprene, and an inner layer of liquid permeable material such as felted or porous plastics material bonded to the outer skin. Polypropylene felt is suitable and this is impregnated with a thixotropic gel which will be water resistant and may have various other properties such as corrosion inhibition and/or biocide. This impregnated sealant does not form a permanent bond to the pile surface and so the wrapping can be removed and replaced if necessary.

This has proved extremely effective and it will continue to be used. However, it does have one drawback in the projecting flanges. There are some applications where these are obstructive. For example, drill pipes may have to pass through guide tubes. There is clearance, but not sufficient to accommodate the flanges of the existing wrapping. Therefore, a wrapping is needed which has a profile only marginally larger than the pipe itself. Also conductors have to be built up length by length, and while most of the outer surface can be pre- sheathed or coated, at the ends where they are joined they have to be left bare and protection applied after connection on the rig. There are various forms of joint, but most stand proud of the main conductor lengths. A close fitting rigid sleeve, or one with rigid lengthwise components such as in WO 87/05066, cannot be used over such joints.

The existing solution to these problems is most unsatisfactory. It requires the portion of the workpiece to be protected to have all oils and grease removed, which normally requires the use of solvents. The area should then be shot blasted or power brushed, and this is not always practical to carry out, particularly on a drilling floor. Then the workpiece has to be pre-heated to a minimum of 60°C, and an epoxy primer applied. Finally, a shrink sleeve is installed and the shrinking is carried out using a large propane fuelled naked flame torch. On a rig, this requires a Hot Work Permit and a full time fire watch in attendance. It is highly dangerous, and the whole installation time can take half an hour or more. It has been found that short cuts are taken in this process, and in particular the priming and pre-heating are often omitted. It is the aim of this invention to provide a much safer system based on that described in WO 87/05066 but with the elimination of the projecting flanges. The wrapping can be installed cold, without undue preparatory work on the workpiece. Interdigitating loops with a bar threaded through offer a low profile, and they have been proposed in GB- 1439214 for closing up a sleeve around the column of an offshore structure. But the approach to protection is otherwise totally different. GB-1439214 describes a net- like sleeve to which marine growth will cling, and when the sleeve is removed, it will tear away most of that growth as well. No hoop tension is applied to the sleeve (it is not necessary) , and therefore threading the locking bar is not a problem. Our wrappings are intended to embrace the protected member so tightly that there is no possible access for water to the surface of the member, and that means stretching the wrapping to generate substantial hoop tension. The loop connecting technique cannot then be used without overcoming the stretching problem, and this the present invention aims to do.

According to the present invention there is provided a wrapping for a corrosion-susceptible member such as a conductor, riser or pile comprising a resilient PC /GB93/00739

flexible sheet with opposed edges which are adjacent when the wrapping is positioned around said member, these edges having interdigitating loops to receive a common locking element threaded through them in the manner of a hinge pin, and means adjacent said edges on the external side of the wrapping for the temporary fixing of abutments, whereby the wrapping can be stretched around said member for the generation of hoop stresses and for the loops to overlap sufficiently or the insertion of the locking element by the urging together of the temporary abutments.

Generally, the structure of the wrapping will follow that of the protection system of WO 87/05066 and comprise an outer layer, usually of nylon reinforced Neoprene, and a felted inner layer impregnated with a thixotropic gel.

Conveniently, the loops are formed by apertured edge portions of the outer layer of the sheet being folded back and secured to the exterior of the sheet. Alternative¬ ly, just one set of loops may be formed in this manner, while the other set of loops is formed by a separate, folded strip of sheet material secured to the outside of the wrapping and set back from the associated edge to leave a flap to bridge the inside of the joint. The locking element is preferably a flat bar of corrosion-resistant metal such as Inconel, Monel or stainless steel that will be tangential to the wrapping and bendable radially to the wrapping to conform to the contours of the wrapped member. As the wrapping shrinks after stretching, it will force the bar to wuκ» ^ij<u PCT/GB93/00739

bend as necessary. The loops will be pulled flat around the bar and the joint will thus be only marginally proud of the rest of the wrapping.

In order to perfect the seal over the zone covered 5 by the loops and a little to either side, there may be a strip spanning the joint on the inside. This may be a separate band of polypropylene for example, or the loops along one edge may be formed by a separate folded strip of the outer layer material secured to the outer layer to leave

10 a marginal flap to span the gap and tuck under the opposite edge.

The temporary abutments may each comprise a beam along the edge of a flexible panel which, when in position, follows the contour of the wrapping around the member away

15 from the looped edges. On the inside of each panel there are barbed fibres such as those sold under the Registered Trade Mark 'Velcro', and the exterior of the wrapping in this region is also provided with such fibres. When the abutment panel is applied and pressed firmly against the

20 wrapping the interlocking fibres hold it there securely and, although it can be peeled away later, there is immense resistance to shearing in the direction tangential to the wrapping. Thus, the temporary abutments can be squeezed together and pull the wrapping tight, imposing the required

25 hoop stresses. This squeezing can be carried out by various means, such as by hydraulic rams or by tightening nuts on drawbolts, both extending through the abutments at intervals along their length. The temporary abutments may alternatively each comprise a beam linked at intervals along its length to anchorages on the exterior of the sheet. These anchorages may each be provided by a panel doubling the thickness of the outer layer of the sheet adjacent the looped edges, for example by extending the edge portions or the separate strip turned back to form the loops. Each panel of this doubling is apertured along a central band and firmly secured to the outside of the wrapping along the marginal bands parallel to the adjacent looped edge. This allows elements to be inserted through the windows between the two layers and to leave ends exposed at the apertures to be attached to the beam. Conveniently the insertable elements are of U-for , ^" the web of each U being trapped by the doubling and the limbs of the U projecting from the apertures and being adapted for attachment to the beam. Preferably the attach¬ ment of said elements to the beam is through an intermediate removable hinge pin parallel to the beam.

For a better understanding of the invention, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a cross section of part of a conductor showing the closure of a protective wrapping,

Figure 2 is a perspective view of part of the conductor showing the wrapping installed,

Figure 3 is a face view of another wrapping showing the joint before completion, and

Figure 4 is a perspective view of the wrapping of Figure 3 in position on a conductor.

In Figures 1 and 2, the conductor 1 is a cylindri¬ cal steel tube and a wrapping 2 consists primarily of an outer layer 3 of Neoprene and an inner layer 4 of felt impregnated with a thixotropic gel. Before installation, when laid flat, it will be rectangular and along the edges which are to meet there are formed loops 5. They give a castellated effect, and they are arranged, as best seen in Figure 2, to interdigitate closely. They are formed from the outer layer 3 being folded back, cut and secured by stitching and adhesive.

Set back from the edges with the loops 5 there are two flexible panels 6 secured to the outer face of the layer 3. Each panel 6 is of a material with barbed fibres, such as that sold under the Registered Trade Mark 'Velcro¹. The panels extend over the full height of the wrapping (assuming it is in place around a vertical conductor) and over a substantial portion of the circumference. They serve as anchorages for temporary abutments 7 which are secured to the edges of complementary flexible panels 8. Each abutment 7 is a rigid beam with a series of apertures 9, and is of a length matching the height of the wrapping.

For installation, as best seen in Figure 1, the abutments 7 are placed either side of the looped edges, with the panels 8 extending away from those edges and pressed against the panels 6 so that the fibres interlock. The wrapping is placed around the conductor and through the apertures 9 there are inserted draw bolts 10. By tightening nuts 11 on these bolts, the abutments 7 are drawn together, causing the sets of loops 5 to overlap. The resistance to shear between the panels 6 and 8 is very substantial, and so large hoop stresses can be generated in the wrapping. Once the loops 5 overlap to a sufficient degree, a flat locking bar 12 with a permanent cap 13 at its upper end and a temporary guide cap 14 at its lower end is inserted down through them in the manner of a hinge pin. When fully through, the cap 14 is removed. Then the nuts 11 are gradually relaxed, leaving the locking bar 12 to take the strain. The loops 5 flatten out as shown, leaving only a very small hump at the join.

^"Previous to this operation, a polypropylene backing strip 15 may be positioned over the zone of the intended join to assist completing the seal. Alternatively, the wrapping itself may be extended to form a sealing slap, and one set of loops will then be formed by a separate strip of outer layer material attached to the outside of the wrapping and set back from the edge which provides the flap. It will be understood that means other than the bolts 10 and nuts 11 can be used to squeeze the abutments 7 together. For example, hydraulic rams could be employed. In all cases, care will be taken to ensure that the squeez¬ ing is kept substantially uniform along the length of the abutments, and likewise when they are being eased off they will be kept in parallel.

Once the locking bar 12 is holding the wrapping, the bolts 10 can be removed, and then the abutments 7 by peeling the panels 8 away from the panels 6.

The wrapping can be removed by reversing this procedure. In some circumstances, it can be done more rapidly, simply by pulling out the bar 12. For the attach- ment of a powered winch line, which would normally be necessary, the bar could have a hole (not shown) just below the cap 13, and this would be left clear of the wrapping.

In Figures 3 and 4 parts similar to those of Figures 1 and 2 are similarly referenced. But the panels 6 are replaced by panels 16 of the same material as the outer layer 3 and these are conveniently extensions of the edge portions or the separate strip that are turned back to form the loops^'5. Each panel 16 is stitched and adhered to the outer layer 3 along its edge portions parallel to the looped edges, leaving the central band free but flat against the layer 3. Windows 17 are pre-cut in this central band and the land portions 18 between them serve as anchorages for temporary abutments. These each comprise a beam 19, apertured at intervals to receive bolts or hydraulic rams, with a hinged linkage through a removable parallel rod 20 to square U-shaped members 21 engaged with the panels 16. The rod 20 is set away from the beam 19 by lugs 22 and will be close to the wrapping on the side of the beam remote from the loops. Each member 21 is worked through a window 17 and under a land portion 18 so that its free ends, which are screw threaded, project from adjacent windows. Yokes 23 are then screwed onto these ends and present aligned holes to receive the rod 20, which also passes through the lugs 22. This wrapping, with the abutments fitted, is applied around a zone to be protected and drawn taut and secured in the manner described. Once the locking bar 12 is in place, the tensioning means are removed and then the rods 20, freeing the beams 19. The yokes 23 are unscrewed and the members 21 eased clear of the panels 16.

Again, the wrapping can be removed by reversing this process.

Figure 2 shows a wrapping around a uniform cylinder. Figure 4 shows that such wrappings can accommo¬ date to non-uniform sections, such as at joints. The locking bar 12 is inserted when the wrapping is slightly over-stretched and the loops aligned. When the tensioning means are relaxed, the wrapping shrinks and moulds itself to the joint, and the locking bar, which is thin in the radial direction, also bends to conform to the contours.

Claims

1. A wrapping for a corrosion-susceptible member such as a conductor, riser or pile comprising a resilient flexible sheet with opposed edges which are adjacent when the wrapping is positioned around said member, these edges having interdigitating loops to receive a common locking element threaded through them in the manner of a hinge pin, and means adjacent said edges on the external side of the wrapping for the temporary fixing of abutments, whereby the wrapping can be stretched around said member for the generation of hoop stresses and for the loops to overlap sufficiently for the insertion of the locking element by the urging together of the temporary abutments.

2. A wrapping as claimed in claim 1, wherein the loops are formed by apertured edge portions of the sheet being folded back and secured to the exterior of the sheet.

3. A wrapping as claimed in claim 1, wherein one set of loops is formed by an apertured edge portion of the sheet being folded back and secured to the exterior of the sheet and another set of loops is formed by a separate apertured, folded strip of sheet material secured to the outside of the wrapping and set back from the associated edge to leave a flap to bridge the inside of the joint.

4. A wrapping as claimed in claim 1, 2 or 3, wherein the locking element is a flat bar that will lie tangential to the wrapping.

5. A wrapping as claimed in claim 4, wherein the bar is bendable radially to the wrapping to conform to contours of the wrapped member.

6. A wrapping as claimed in any preceding claim, wherein the temporary abutments each comprise a beam along the edge of a flexible panel which, when in position, follows the contour of the wrapping around the member away from the looped edges, on the inside of each panel there being barbed fibres which interlock with barbed fibres on the exterior of the sheet.

7. A wrapping as claimed in any one of claims 1 to 5, wherein the temporary abutments each comprise a beam linked at intervals along its length to anchorages on the exterior of the sheet.

^"8. A wrapping as claimed in claim 7, wherein the anchorages each comprise a panel doubling an outer layer of the sheet adjacent the looped edges, each panel being apertured along a central band and being firmly secured to the outside of the wrapping along its marginal bands parallel to the adjacent looped edge, this allowing inser¬ tion of elements through the windows between the two layers while leaving their ends exposed at the apertures to be attached to the beam.

9. A wrapping as claimed in claim 8 as appendant to claim 2 or 3, wherein the panels are extensions of the folded edge portions or the folded edge portion and the separate strip which form the loops.

10. A wrapping as claimed in claim 8 or 9, wherein the insertable elements are of U-form, the web of each U being trapped by the doubling and the limbs of the U projecting from the apertures and being adapted for attach¬ ment to the beam.

11. A wrapping as claimed in claim 8, 9 or 10, wherein the attachment of said elements to the beam is through an intermediate removable hinge pin parallel to the beam.