EP3425119B1

EP3425119B1 - Demolishing an offshore jacket

Info

Publication number: EP3425119B1
Application number: EP18182076.2A
Authority: EP
Inventors: Joannes Simon Gerardus Hoondert
Original assignee: Hoondert Beheer BV
Current assignee: Hoondert Beheer BV
Priority date: 2017-07-05
Filing date: 2018-07-05
Publication date: 2022-03-02
Anticipated expiration: 2038-07-05
Also published as: EP4019701A1; NL2019190B1; EP3425119A1

Description

This invention relates to a method for demolishing a large spatial framework construction of steel tubes as used in the offshore industry, for example a jacket for carrying a platform or a windmill.
Document JP 2016 176271 discloses a method for demolishing a large spatial structure, suspending a centre tube and cutting a top inclination unit and a parallel unit after cutting lower portion of the centre tube and lower portion of the top inclination unit and the parallel unit, respectively. A first jack is progressively relocated with a second jack, and the lower portion of the centre tube is cut. The centre tube is suspended down with a top portion. The top portion is suspended down and removed on the ground.
The invention is defined by appended claim 1. Preferred embodiments of the invention are defined by the dependent claims.
The construction preferably has one or more of: at least three or four upright legs of steel, preferably thin-walled, tube; horizontal and/or diagonal cross braces or braces of steel, preferably thin-walled, tube fixed with the legs for stiffening the legs, in particular the kinking strength thereof and/or increasing the dimensional stability of the entire structure; an open truss construction; a tube construction; the areas bounded by the pipes are open; the loads are carried in the tubes by tensile and compressive forces.
Traditionally, a jacket is demolished vertically from above, usually on the mainland. For this reason, it is initially necessary to work at great heights, for example 50 or 100 meters. Large equipment such as cranes are needed. Working at a high altitude involves personnel risks.
The invention proposes to demolish from below, so that work can be carried out on or just above the ground and large equipment can be made superfluous.
To this end it is proposed to, every time, remove a part located at low level, e.g. the lower part, of the structure and subsequently to lower the structure and subsequently to remove the part located at low level at that time, e.g. the lower part. Thus, the height decreases stepwise, with a lower part being removed at an earlier time than a higher part. This allows working at a lower level, well below the initial level of the top of the jacket.
During the demolition, the jacket is usually on a surface above the local water level, for example on shore.
For example, one or more of the following is used: the structure is grasped at a level above the piece to be removed; the construction is lifted and then the piece is loosened and/or removed; loosening is, for example, due to severing such as sawing or cutting or milling or burning/melting, for example with cutting torches; after loosening and/or removing the piece the level of grasping is moved upwards along the construction, preferably after the construction has an alternative support, for instance is placed on the subsurface.
In a presently preferred application, a lifting system is used with an engaging provision for force fit engagement with the structure to provide, during operation, an upward force to the structure opposite to the direction of gravity. Preferably, the engaging provision is arranged for upwardly force fit engagement with a grip edge to the structure. Preferably, the engaging edge of the structure is provided by a recess or hole that is preferably made for the purpose of demolition, for example in a pipe wall, preferably of a leg. The engaging provision comprises, for example, a hook member, for example for gripping in the recess or hole.
The lifting system preferably comprises one or more of the following: a lifting element, for example hydraulic jack; a transmission means, for example a flexible pulling element such as a cable or chain, which is coupled to transmit force to the engaging provision; a loop means arranged to surround a tube on both radial sides; a control unit for controlling the lifting and lowering; an energy source, such as a hydraulic pump, for lifting; a support means for engaging with the structure, for instance for lateral support.
Preferably, a lifting element is placed on the one side of a tube and the engaging provision on the diametrically opposite side and these two are coupled to each other by the transmission means. Optionally, the lifting means is coupled to the support means which engages the construction. In operation, the engaging provision and support means are diametrically opposite each other and the tube is confined between them.
Instead of force fit engagement, friction fit engagement is conceivable, for example by using a noose means which can be laid radially in a loop around a smooth-walled tube and can clamp therewith.
Lowering step by step for example takes place in at least 3 or 5 or 10 steps and/or in steps of minimal or exactly 50 or 75 or 100 cm and/or maximum or exactly 2 or 5 or 10 meters wherein each time, with every step, a piece, as of this mentioned height is separated and removed.
The construction, for example one or all of its legs, is preferably provided with a row of holes above each other, with a pitch corresponding to the step size. After removing a piece, the lifting system is brought into engagement with the next hole, viewed in the upward direction.
The combination of hook, flexible pulling element (transmission means) and support ensures the force fitting engagement between lifting system and construction with simple means.
The drawing of a non-limiting embodiment shows in:

FIG. 1 a jacket to be demolished;
FIG. 2-5 detail A of fig. 1 during successive phases during demolition.

FIG. 1 shows a jacket 1 with four upright legs 2.
FIG. 2 shows a first step. The lifting system comprises a jack 5, support 6, the loop 8 (transmission means) and hook 7. The hook 7 is inserted into the bottom hole 3. The leg 2 stands on the floor 4. The loop 8 surrounds the leg 2 on both sides and is coupled to the hook 7 and the support 6. The support 6 abuting against the tube wall gives the lateral reaction force coming from the hook 7.
By extending/expanding the jack 5 further, the leg 2 is lifted off the floor 4, hanging on the hook 7 (fig. 3). Subsequently, the leg 2 is separated along the line 10. The line 10 is below the level of the hook 7.
The leg part 11 under line 10 falls on the floor 4 and is discharged (represented by the arrow in fig. 4 ).
Subsequently, the jack 5 is retracted/contracted until the leg 2 shortened at the bottom rests on the floor 4 (fig. 5) .
Subsequently, the hook 7 is hooked in the next hole 3, viewed in the upward direction, and the process starts again with the step shown in Fig. 2.
This procedure is repeated as often as desired, whereby the leg 2 is shortened from below and therefore the height of the jacket decreases stepwise.
This process could alternatively be carried out at a level above the floor and at a distance below the top of the jacket, for instance so that a lower part of the structure 1 remains in place during the demolition while above that pieces of construction are removed from below, as a result of which the height of the construction decreases.
Instead of a hole 3, a projection can be used, for example welded to the tube wall for this purpose.

Claims

Method for demolishing an offshore jacket structure wherein from the jacket each time a piece at low level, for example the bottom part, is removed and then the jacket is lowered and subsequently the then piece at a low level, for instance the lower piece, is removed, wherein
the method provides
the upright on shore demolition of the jacket, being a large spatial, open lattice construction of steel pipes, which has been applied as a jacket resting on the seabed, with which a platform above the sea level was carried, whereby the jacket is removed from the seabed and landed and which jacket comprises at least three or four upright legs of thin-walled steel tube and horizontal and diagonal braces of thin-walled steel tube fixed with the legs for stiffening the legs, so that the loads are carried by tensile and compressive forces in the tubes, with the jacket standing upright on shore, or on the mainland, or not on the water, or on the mainland on a dry surface above the local water level, and being demolished from below, so that work is done on or just above the ground, whereby the bottom part of the jacket is removed and then the remainder of the jacket is lowered and then the bottom piece of the remainder of the jacket is removed and then the remainder of the jacket is lowered, so that the height of the jacket decreases step by step, the lower part being removed at an earlier point in time than a higher part and the highest part being removed last, and during the entire process of demolishing the jacket, or the remainder thereof, is upright.
Method according to claim 1, wherein the jacket is gripped by a holding means of a lifting system at a level above the lower part to be removed, then, by operation of the lifting system, the jacket is by the holding means lifted from the subsurface at the location where it is gripped and in this lifted condition subsequently the bottom jacket part is removed by cutting it loose, then the remainder of the jacket is put back on the ground after which the holding means is released and then by the holding means the remainder of the jacket is gripped at a higher level, above the next to be removed lower part, and is then, by operation of the lifting system, by the holding means lifted at the location where it is gripped and in this lifted state the next lower part is then removed by cutting it loose and then the remainder of the jacket is put back on the ground after which the holding means is released.
Method according to any of claims 1 - 2, wherein stepwise lowering takes place in at least 3 or 5 or 10 steps where each time, at each step, a piece is separated from the height and removed.
Method according to any of claims 1-3, wherein the stepwise lowering takes place in steps of at least 25 or 50 or 75 or 100 centimetre and/or at most or exactly 2 or 5 or 10 meters, each time, with each step, a piece from this mentioned height is separated and removed.