The present invention relates to a method and apparatus for cutting underwater structures.
Currently, submerged structures are cut employing different methods and using apparatuses of different nature with the purpose of removing and/or replacing the same.
Some of the known cutting devices make use of fixed blades, such as that described in document U.S. Pat. No. 3,056,267, while others are provided with several rotary blades coordinated in their action, such as that described in document U.S. Pat. No. 4,180,047. However, both apparatuses have the drawback of operating only on the emerging, free end of the submerged structure.
In document EP-B-0540834 there are disclosed a method and device for cutting underwater structures which make use of a diamond cable as a cutting means; the device allows the underwater structure to be cut at any level between the seabed and the surface.
Nowadays, the in-force provisions governing the field and applied worldwide, which are extremely more strict as for what concerns the environmental protection, require that submerged structures are cut below the level of the seabed, without leaving potentially dangerous stumps of the cut structure emerging from the seabed. Under these conditions and employing the presently available means, it is required to remove a considerable amount of seabed around the base of the structure to be cut. This additional operation is cost- and time-consuming, and it often damages the environment which should be safeguarded instead.
From document GB-A-409754, an apparatus is known to demolish an underwater structure. Said apparatus comprises a boring tool, namely an auger, which is guided with a guiding tube; the boring tool creates a series of holes diagonally into the structure, even below the level of the seabed, in order to weaken the structure as well as to allow the removal thereof. Alternatively, the hole created by the boring tool can be used for positioning a charge of explosive. However, such a method does not appear neither safe nor easy to be used.
Document EP-B-1373645 (hereinafter referred to as “document '645”) discloses a method and apparatus for cutting an underwater structure below the level of the seabed on which it is installed. The method of document '645 includes the sequential steps of determining the ideal plane of cutting having taken in account characteristic features of the structure such as its morphology and positioning on the seabed, the shape and consistency of the seabed, and the depth below the level of the seabed at which the cutting has to be performed; positioning and anchoring cutting means in the proximity of the cutting area; boring at least one hole through the seabed in the proximity of the structure, at least up to the depth at which the cutting has to be performed, along a direction parallel to the cutting direction and lying on the cutting plane; introducing said cutting means into said hole, and cutting the structure, said cutting being performed outside of said hole. In document '645, the apparatus adapted for carrying out the method of the same patent includes boring means to bore the hole; cutting means comprising a cutting frame and a movable cutting unit which, in use, at least partially radially projects from said hole, means for positioning said boring means and said cutting means; and anchoring means.
However, while the method and apparatus as disclosed in document '645 achieve the intended goal of performing the cutting below the seabed, they still have certain drawbacks. Indeed, since the practice has shown that cutting is performed substantially obliquely to the structure to be cut, cutting is more difficult to be initiated and it takes more time than if it were possible to cut substantially perpendicularly to the structure. Finally, the on-field practice has shown that the movable cutting unit often suffers from clogging problems with the debris of the seabed which limit the performance thereof.
Therefore, an object of the present invention is to provide a method for cutting an underwater structure which allows to obtain said cutting below the level of the seabed with a minimum expenditure of means and of energies, with the least impact as possible on the surrounding marine environment, and with an increased efficiency and easiness when compared to the methods of the prior art.
A further object of the present invention is to provide an apparatus adapted for carrying out the above-described cutting method.
Therefore, an object of the present invention is a method for cutting an underwater structure, typically a support pier of an offshore production platform, below the level of the seabed on which it is installed, comprising the following steps: a step of positioning cutting means and penetrating means associated with said cutting means in close proximity to the underwater structure to be cut, at the intersection region between said structure and the seabed; a step of causing both said penetrating means and said cutting means associated therewith to penetrate into said seabed in a substantially longitudinal direction to a portion of said structure which is embedded in the seabed; and a cutting step which includes actuating and driving said cutting means and said penetrating means in a substantially perpendicular direction to said embedded portion so as to cut said structure below the level of the seabed.
In a preferred embodiment of the method of the present invention, said penetrating step includes causing said penetrating means and said cutting means to penetrate into the seabed in a substantially longitudinal direction to said embedded portion of said structure and, simultaneously or sequentially, moving said penetrating means and said cutting means towards said embedded portion so as to partially wind said cutting means around said embedded portion, said cutting means being of a flexible type.
In a further preferred embodiment of the method of the present invention, said cutting step includes exerting a stretching action on said flexible cutting means while they are actuated and driven, along with the penetrating means associated therewith, in a substantially perpendicular direction to said embedded portion so to obtain a substantially perpendicular transversal cut of said structure below the level of the seabed.
In another preferred embodiment of the method of the present invention, said cutting step includes applying a swinging movement to both said penetrating means and said cutting means while they are actuated and driven in a substantially perpendicular direction to said embedded portion so to obtain a substantially perpendicular transversal cut of said structure below the level of the seabed.
In yet another preferred embodiment of the method of the present invention, said penetrating step includes causing said penetrating means and said cutting means to penetrate into the seabed in a longitudinal direction to said embedded portion of said structure and, simultaneously or sequentially, moving said penetrating means and said cutting means towards said embedded portion so as to partially wind said cutting means around said embedded portion, said cutting means being of a flexible type, and wherein said cutting step includes first exerting a stretching action on said flexible cutting means and then applying a swinging movement to both said penetrating means and said cutting means while they are actuated and driven in a substantially perpendicular direction to said embedded portion so to obtain a substantially perpendicular transversal cut of said structure below the level of the seabed.
In a further variant embodiment, while the cut is being performed, the cutting means can be moved along the effective direction of penetration and in the way opposite to the way of penetration so as to cut the structure with a non-coplanar cut geometry in order to prevent a potential slipping of the portion of the structure being cut.
Another object of the present invention is an apparatus adapted for carrying out the method of the present invention, said apparatus being characterized as comprising a penetrating/cutting frame, an anchoring frame, and a swinging frame which connects the penetrating/cutting frame to the anchoring frame.
Preferably, the penetrating/cutting frame of the apparatus according to the present invention comprises a diamond-edged cable driven along a closed circuit by a series of pulleys between two parallel, mutually spaced tubular columns which, at one end, are transversally connected by a rigid back plate in such a manner that the penetrating/cutting frame has a fork shape, and which, at the free end, carry respective perforating devices each preferably comprising a cutting head and a respective motor drive unit.
More preferably, said series of pulleys, which are accommodated within the columns, comprises an aligned pair of swivel pulleys which are positioned in the proximity of the free ends of the respective columns so as to subtend a cutting portion of the diamond-edged cable, and a pulley which is provided with a motor drive unit for moving the diamond-edged cable along the closed circuit at a certain speed.
Even more preferably, the apparatus according to the present invention comprises a compensating device for changing the geometry of said cutting portion of the diamond-edged cable from a rectilinear configuration to a curved or angled configuration, and vice versa.
In a preferred embodiment of the apparatus according to the present invention, the apparatus further comprises auxiliary ejecting nozzles to assist the swinging frame in its swinging movement to drive the active portion of the penetrating/cutting frame towards the underwater structure to be cut, said auxiliary ejecting nozzles preferably comprising ejecting nozzles arranged on the penetrating/cutting frame and supplied with a pressurized fluid from supply lines.
Referring now to the present invention in greater detail,
Also referring to
For reasons that will appear clear hereinafter, said cutting portion 51 can take on two alternate configurations, i.e. a rectilinear configuration (
In order to allow the diamond-edged cable 5 to pass from one column 21 to the other, there are provided passage windows 210, 210 at the free ends of the columns and passage windows 220, 221 at the connected ends thereof. Obviously, the window 221 has such a length to allow the cable to extend longitudinally while the configuration of its cutting portion 51 is changed from the rectilinear configuration to the curved configuration, and vice versa. Each of the perforating devices 23 includes a cutting head 230 and a relevant motor drive unit 231.
Referring now to
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Alternatively, as it can be seen from
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Furthermore,
The application and the operation of the preferred embodiment of the cutting apparatus according to the present invention will be described hereinbelow. As already stated above, the cutting apparatus 1 is used to cut an underwater structure, typically a support pier P of an offshore production platform, below the level of a seabed F, in order to avoid that a potentially dangerous stump of the pier can emerge. In a preparative step and specifically referring to
At this point, turning to
When the three frames of the cutting apparatus 1 according to this preferred embodiment of the present invention are positioned appropriately, the perforating devices 23 at the ends of the columns 21 of the penetrating/cutting frame 2 are activated, and the entire penetrating/cutting frame 2 is lowered into the seabed by switching on its linear actuator 10. During this lowering step, the two columns 21, due to their initial angle of inclination, partially fork the pier P, thus causing the cutting portion 51 to partially wind around the pier in a perpendicular direction to the same, and to take on the curved configuration as already previously described and illustrated in
At this point, the diamond-edged cable 5 is activated at the desired work speed and, simultaneously, the compensating device 64 is lifted (
As it can be inferred from the above description, the cutting apparatus according to the present invention can perform a substantially perpendicular cut of the underwater structure below the level of the seabed without removing a considerable amount of soil at the base of the structure, and without clogging the cutting means with debris which could compromise its action. Furthermore, if it is required to cut more structures in the same area, for example more piers of an offshore production platform, the modular nature of the present apparatus allows, for example, to install an anchoring chassis for every pier to be cut, and to re-use the same penetrating/cutting frame—swinging frame assembly by mounting and removing it to/from the respective anchoring frame every time. Alternatively, the operation of assembling the three frames can be performed before the whole apparatus is lowered into water, either in factory or extemporaneously on the support boat.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IT2012/000028 | 1/31/2012 | WO | 00 | 7/23/2014 |