GB2168406A - Removable layback pile guide - Google Patents

Abstract

A removable layback guide assembly, for use in piling offshore structures, has a support arm (14) and an open pile guide (17). The support arm is pivotal on top of a leg (10) of the offshore structure which is to be piled, and the guide (17) is pivotal on the end offshore structure which is to be piled, of the support arm (14). The guide (17) and support arm (14) can be fixed relative to each other at different angular displacements, so that a series of piles can be laid back into the pile guide (17), and then moved to appropriate angular positions relative to the leg (10) of the structure, where they can be driven into the seabed beneath the structure to secure the structure. <IMAGE>

Description

SPECIFICATION Removable layback pile guide The invention relates to the piling of offshore structures, and particularly but not exclusively to the piling of platform for the drilling for and production of oil and/or gas.

Such structures are frequently formed of lattice steel framework towers, secured to the seabed by elongate tubular steel piles, which are driven through pile guides attached to legs at the corners of the towers, and pile sleeves around the bases of the towers.

The insertion of the elongate piles into the pile guides can be a difficult operation, since in the interests of avoiding offshore welding the piles are made up in the maximum lengths that can be handled by available cranage.

To illustrate the problems which have to be faced, piles may be of the order of 100 metres long, and of 86" outside diameter.

In the past piles have been treaded through a series of fixed pile guides extending down the depth of the tower; or have been inserted in rotatable pile guides mounted on the tops of the legs for rotation about the axes of the legs; or have been laid back into fixed pile guides, which have closure members or gates to secure the piles into the guides, as was done for Woodside Petroleum's North Rankin 'A' platform offshore Australia.

With the development of platforms in deeper water depths than heretofor, the constraints of piling operations can be a limiting factor in the platform installation operations which are needed to bring an offshore oil or gas field into operation.

The invention provides removable layback guide assembly capable of providing lateral support for foundation piles to be driven parallel to a leg of an offshore tower structure during installation, which assembly comprises a support arm mountable at or near the top of the leg for limited rotational movement about an axis generally parallel to the axis of the leg, and an open guide mounted on the support arm at a position away from the leg for limited rotational movement relative to the support arm about another axis generally parallel to the axis of the leg, such that the open guide is capable of supporting a pile laterally with its opening facing away from the leg.

It is preferred that the support arm and the open guide are adapted to be locked against rotation in a number of predetermined positions, at least some of such positions being suitable for the installation of piles to be driven parallel to that leg.

It is further preferred that the predetermined positions of the support arm and the open guide are such that any offset of the axis of the support arm from the axis of the leg can be accounted for by locking the support arm and the open guide at slightly different angles with respect to the leg and the support arm respectively.

It is also preferred that there are attachment points on or near a periphery of an outer surface of the open guide, such attachment points being arranged to move the open guide through an angle appropriate to the angular displacement of each pile from a pile handling position at which the piles are layed back into the open guide.

If is further preferred that movement may be effected by the action of winches or jacks on the attachment points.

In one preferred form the support arm is made up of three parts, namely a pivot for rotation of the support arm relative to the platform, a distance piece, and a pivot for rotation of the open guide relative to the support arm, whereby the assembly can readily be adapted to suit the configurations of a plurality of different platforms by the insertion of different distance pieces to represent the different pile configurations of those platforms.

The invention also provides a platform having an assembly as described above.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial side elevational view on the top of one leg of an offshore platform, showing a removeable layback guide assembly, and Figure 2 is a plan view looking down on that leg, showing two possible operating positions of the layback guide assembly.

As shown in Figure 1, a leg 10 of an offshore platform is supported by a brace 11 and is surmounted by a cranked extension 12. A removeable layback guide assembly 14 is mounted on top of the extension 12.

The removeable layback guide assembly 14 comprises a support arm 15, having at one end a mounting 16 rotatable on the leg extension 12, and at the other end an open pile guide 17 rotatable on the support arm. The axis of rotation of the support arm on the leg extension, and the axis of rotation of the open guide on the support arm, are both generally parallel to the axis of the leg 10.

Because of the batter of the leg 10 (slightly exaggerated in Figure 1) the arm 15 and the open guide 17 are biased by gravity to one position. In order to move them from this position, it is necessary for winches or jacks (not shown) to be used to change the configuration of the assembly.

The arm 15 can be secured to the leg extension 12 by a pin 18 slotted through one of several holes 19. Similarly the open guide 17 can be secured to the arm 15 by a pin slotted through one of several holes 21.

In use a pile (not shown in the drawings) can be laid back into the open guide 17 at a first position, and then the arm 15 can be rotated with the open guide rotated correspondingly, to take the pile to the particular radial position (relative to the leg) at which it is required. Due to the batter of the leg it is a feature of the invention that the angles of rotation of the arm 15 relative to the leg 10, and the open guide 17 relative to the arm 15, are not the same. The respective angles are designed to bring the pile to the required position allowing for the batter, and the pin holes 19 and 21 are disposed accordingly.

With the pile guide 17 in its correct position, the pile can be driven through its lower guides and pile sleeve (not shown), and thereafter secured to the pile sleeve by grouting. Subsequent piles can be installed at other positions around the leg by moving the assembly 14 to the required radial positions relative to the leg.

According to a feature of the invention the support arm 15 may be made up of three parts, namely the mounting 16 for a pivot portion rotatable on leg extension 12, a distance piece 22, and a pivot for rotation of the open guide 17. The pivot portions can be joined by distance pieces 22 of different lengths to suit the leg configurations of different platforms. As shown in Figure 1, joints may be made at positions 23 and 24 on the arm 15.

Claims (8)

1. A removable layback guide assembly capable of providing lateral support for foundation piles to be driven parallel to a leg of an offshore tower structure during installation, which assembly comprises a support arm mountable at or near the top of the leg for limited rotational movement about an axis generally parallel to the axis of the leg, and an open guide mounted on the support arm at a position away from the leg for limited rotational movement relative to the support arm about another axis generally parallel to the axis of the leg, such that the open guide is capable of supporting a pile laterally with its opening facing away from the leg.

2. Assembly as claimed in Claim 1 in which the support arm and the open guide are adapted to be locked against rotation in a number of predetermined positions, at least some of such positions being suitable for the installation of piles to be driven parallel to that leg.

3. Assembly as claimed in Claim 2 in which the predetermined positions of the support arm and the open guide arm are such that any offset of the axis of the support arm from the axis of the leg can be accounted for by locking the support arm and the open guide at slightly different angles with respect to the leg and the support arm respectively.

4. Assembly as claimed in any are of the preceeding claims in which there are attachment points on or near a periphery of an outer surface of the open guide, such attachment points being arranged to move the open guide through an angle appropriate to the angular displacement of each pile from a pile handling position at which the piles are layed back into the open guide.

5. Assembly as claimed in Claim 4 in which movement may be effected by the action of winches or jacks on the attachment points.

6. Assembly as claimed in any one of the preceeding claims in which the support arm is made up of three parts, namely a pivot for rotation of the support arm relative to the platform, a distance piece, and a pivot for rotation of the open guide relative to the support arm, whereby the assembly can readily be adapted to suit the configurations of a plurality of different platforms by the insertion of different distance pieces to represent the different pile configurations of those platforms.

7. Assembly substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

8. A platform having an assembly as claimed in any one of the preceding claims.