WO2003106877A1

WO2003106877A1 - Method of reinforcement of marine buoyancy unit

Info

Publication number: WO2003106877A1
Application number: PCT/GB2003/002496
Authority: WO
Inventors: Gary Lee Brown; Ronald Northcutt; Jeffrey Peck
Original assignee: Balmoral Group Limited
Priority date: 2002-06-12
Filing date: 2003-06-11
Publication date: 2003-12-24
Also published as: GB2389563A; GB0213472D0; GB2389563B; AU2003244792A1; BR0311140A

Abstract

A marine buoyancy unit (10, 9) which fits at least partly around a marine object such as a riser with auxiliary conduits is composed of a main body (15) of syntactic foam with an external layer or skin (11) of harder polymeric composite. To reinforce the unit, slots or channels (13) are cut in the exterior of the unit or borings are created which extend within the unit and reinforcement in the form of webs or strips (20) are placed into the slots or channels or borings. The reinforcement is embedded into the slots, channels or borings by introducing a curable resin.

Description

DESCRIPTION

METHOD OF REINFORCEMENT OF MARINE BUOYANCY UNITS

The present invention is concerned with a method of reinforcing a marine

buoyancy unit.

Known buoyancy units and modules are made of low-density syntactic

foam with a skin or layer of harder polymeric composite. They serve primarily to

impart buoyancy to marine objects and secondarily to protect such objects. In

harsh marine environments such units and modules tend to become damaged or to

fracture from time to time.

An object of the invention is to provide a method of renovation upgrading

and/or reinforcement for such units and modules

According to one aspect of the invention there is provided a method of

reinforcing a marine buoyancy unit designed to fit at least partially around a

marine object; said method comprising cutting slots or channels in an exterior

surface of the unit, placing reinforcement materials in the channels and filling the

channels with a curable resin to embed the reinforcement material into the

channels.

In another aspect the invention provides a method of reinforcing a marine

buoyancy unit designed to fit at least partially around a marine object; said

method comprising producing borings extending within the unit, placing

reinforcement in the borings and filling the borings with a curable resin to embed

the reinforcement into the borings. The unit may be of part-cylindrical, e.g. semi-cylindrical, shape with an

exterior skin or layer of high strength polymeric composite and an interior formed of syntactic foam. The channels penetrate the skin and extend into the syntactic

foam interior whereas the borings would extend through the syntactic foam

closely adjacent the skin. A number of such units would be united to form a

module surrounding part of the marine object. The channels or borings extend

longitudinally of the unit. A glass fibre mat may be laminated onto the exterior after the channels or borings are filled.

The invention may be understood more readily, and various other features

of the invention may become apparent, from consideration of the following

description.

An embodiment of the invention will now be described, by way of

example only, with reference to the accompanying drawing in which Figure 1 is a

cross-section of a buoyancy module at a preliminary stage in carrying out a

method of reinforcement in accordance with the invention, and Figure 2 depicts part of a strip of reinforcement used in the method.

As shown in Figure 1, a buoyancy module 10 is composed of two

complementary units 9 each of semi-cylindrical form with a continuous outer layer 11. This is merely illustrative and there can be more than two units 9

making up the module 10. The interior main bodies 15 of the units 9 within the

layers 11 are composed of syntactic foam. The units 9 are designed to fit around a

marine object and part of the layers 11 define an internal cavity 5 shaped to conform with the marine object. By way of example the marine object can be a

riser or pipeline with auxiliary conduits. Semi-circular recesses 12 in the

diametric plane 14 separating the units 9 are designed to fit around a pair of such

conduits. The units 9 can be held on the marine object by means of flexible bands

or bolts but it is possible to provide an interlocking connection between the units

9. Normally a series of modules 10 each composed of a pair of the units 9 would

be arranged end-to-end along the marine object and the ends of the modules 10.

At any time during their service life in a marine environment, the modules

10 and the units 9 may need to be renovated, upgraded and/or at least reinforced to

prevent fracture or separation into parts following fracture. A method of such

reinforcement, in accordance with the invention, will now be described. As

shown in Figure 1, a number of channels, here three, are made in the exterior of

each of the units 9. Typically, the channels 13 are positioned at 10°, 90° and

170° from the diametric plane 14 in the anti-clockwise sense. Typically the width

of each channel 13 is around 2.5cm (one inch) and the depth of each channel 13 is

around 5 to 6 cm (two to two and a half inches). The depth of each channel 13 is

such that the outer layer 11 is penetrated and the channel extends into the interior

foam 15. Each channel 13 extends along the length of the unit 9 but terminates

inwardly of the ends. Typically around 2.5cm (one inch) separates the ends of the

units 9 from the ends of the channels 13. After the channels 13 have been

produced any paint on the exterior peripheral surface 16 is removed in the vicinity

of each channel 13 and the regions 17 of the surface 16 at the juncture with the channels 13 are buffed to provide a mechanical key. Any debris left from the

cutting of the channels 13 and the other treatments is removed by broshing or by

vacuum cleaning. The channels 13 are then filled with reinforcement such as

strips 20 made of a polymeric fibre mesh.

Part of one of the strips 20 is shown in Figure 2. The strip 20 has warp

bands 21 extending along its length and thinner weft bands 22 running in the

transverse direction. As shown there are ten to twelve warp bands 21 over the

width of the strip 20. The overall width of the strip 20 is greater than the width of

the channels 13. For convenience, each strip 20 is bent and rolled into a tight

cylinder held with tie wraps. After placing the rolled strips 20 in the channels 13,

the tie wraps are released and removed. The next stage in the preferred method is

to apply a glass fibre mat over the filled channels 13 and to introduce a resin mix

which fills the channels 13 to embed the strips 20. Vents in the mat allow air to

escape. The mat itself can be held in place with a pre-formed semi-rigid sheet

which is removed once the resin has cured. After curing the exterior of the

reinforced unit 9 is buffed or sanded and then painted.

The reinforcement need not be in the form of a mesh. Instead continuous

webs or strips of reinforcement material can be used or individual polymeric

fibres or strands can be used. In all cases the reinforcement is made from

polymeric fibres or strands either separate or joined together. The number of

channels 13 and their dimensions discussed above are suitable for the strips 20 of

polymeric mesh fibre and the channels 13 may be adapted to suit other reinforcement materials. For example, single fibres or strands would need a

channel depth of at least 15mm. The most important characteristic is the tensile

strength of the mesh reinforcement material. Ideally once the strips or other

reinforcement 20 have been embedded in the channels 13 and the glass fibre mat

has been bonded onto the exterior surface of the unit 9 the additional or

supplementary tensile strength of the reinforced unit 9 or module 10 is between 25

and 200 kilo Newtons per metre circumference. The number of channels, the

width or diameter of the reinforcement and the characteristics of the reinforcement

can be adjusted to produce this tensile strength.

The fibres making up the reinforcement are made of tough rather than

brittle material and have significant elongation at break (minimum 5%, ideally over 20%). This elongation performance may be inherent in the nature of the fibre

itself, e.g. PE.PP Nylon, polycarbonate PET PE/PP, copolymers or imparted by twisting the fibres, e.g. "Kelvar" (RTM).

A material suitable for the reinforcement is the mesh system in the

"Sympaforce" range made by Synteen Technical Fibres Inc of Lancaster, South

Carolina, USA and Synteen GmbH of Klettgau-Erzingen, Germany. This is a

high tenacity PET mesh bonded and encapsulated in PNC "plastisol" paste. Meshes with weight and tensile strength biased in the axial direction are preferred,

with grades of axial strength of 50 to 200 kΝ/m and transverse/circumferential

strength of 25-100 kΝ/m being particularly suitable. The mesh nature achieves

the advantageous intermittent mechanical locking, whilst plastic surface finish gives the desired, only poor adhesive bonding to the epoxy resin encapsulating

mix.

It is advantageous if the reinforcement is intermittently locked into the

resin mix rather than continuously bonded, to allow the essential elongation of the

reinforcement at the fracture location to be accommodated over a greater length of

reinforcement. Reinforcement in the form of mesh systems provide the

intermittent locking whilst the surface finish on the reinforcement can be selected

to limit continuous bonding.

In an alternative method instead of creating the open channels 13

longitudinal borings can be made in the units 9 near the exterior surface. The

reinforcements 20 are inserted into the borings which need to penetrate at least

one end face of the unit 9 and the borings are filled with resin as before.

Claims

1. A method of reinforcing a marine buoyancy unit designed to fit at least

partially around a marine object, said method comprising cutting one or more slots

or channels in an exterior surface of the unit or producing borings extending

within the unit, placing reinforcement material in the slots, channels or borings

and filling the slots, channels or borings with a curable resin to embed the reinforcement material therein.

2. A marine buoyancy unit shaped to fit at least partially around a marine

object, the unit comprising a syntactic foam body with an exterior composite skin

and comprising one or more slots, channels or borings formed in the material of the buoyancy unit and containing reinforcement material embedded in cured resin.

3. A marine buoyancy unit, or a method of producing a marine buoyancy unit, as claimed in claim 1 or claim 2, wherein the unit is of part-cylindrical shape

such that a number of such units can be united to form a module surrounding part of the object, wherein the slots, channels or borings extend longitudinally of the

unit.

4. A marine buoyancy unit, or a method of producing a marine buoyancy

unit, as claimed in claim 1, 2 or 3, wherein there are from 2 to 5 slots, channels or

borings in the unit.

5. A marine buoyancy unit, or a method of producing a marine buoyancy

unit, as claimed in any preceding claim, wherein the reinforcement is in the form

of a web or strip of polymer.

6. A marine buoyancy unit, or a method of producing a marine buoyancy

of individual strands of polymer.

7. A marine buoyancy unit, or a method of producing a marine buoyancy

unit, as claimed in claim 5, wherein the web or strip is composed of mesh with a

plurality of longitudinal bands and a plurality of transverse bands.

8. A marine buoyancy unit, or a method of producing a marine buoyancy

unit, as claimed in claim 7, wherein the longitudinal bands are wider than the

transverse bands.

9. A method of reinforcing a marine buoyancy unit as claimed in claim 1

or in any of claims 3 to 8 when appended to claim 1, wherein a glass fibre mat is

laid onto at least part of the exterior surface to overlie one or more of the channels prior to the application of the resin and the mat is bonded onto the surface with the resin.

10. A marine buoyancy unit as claimed in claim 2 or in any of claims 3 to

8 when appended to claim 2, wherein glass fibre mat is provided at the unit's

exterior surface over the slots, channels or fillings, the mat being bonded to the

surface by the cured resin.

11. A method of reinforcing a marine buoyancy unit, or a marine

buoyancy unit, according to any preceding claim, wherein the unit has an exterior

layer of high strength polymer and an interior made of syntactic foam.

12. A method of reinforcing a marine buoyancy unit, or a marine buoyancy unit, according to claim 11, wherein the slots, channels or borings

penetrate the external layer and extend into the syntactic foam.

13. A method according to any preceding claim, wherein the additional

tensile strength contributed to the unit by the reinforcement is in the range 25-200

k Newtons per metre circumference.

14. A method substantially as hereinbefore described with reference to, a

and as illustrated in, the accompanying drawings.

15. A marine buoyancy unit substantially as herein described with

reference to, and as illustrated in, the accompanying drawings.