NO340344B1

NO340344B1 - Shutter mechanism for a subsea basket

Info

Publication number: NO340344B1
Application number: NO20151542A
Authority: NO
Inventors: Morten Karlsen; Kim Halling Odden
Original assignee: Vetco Gray Scandinavia As
Priority date: 2015-11-05
Filing date: 2015-11-05
Publication date: 2017-04-03
Also published as: NO20151542A1

Description

Shutter mechanism for a subsea basket

TECHNICAL FIELD OF THE INVENTION

The present invention relates to improvements in lifting and lowering baskets used for deployment and recovery of process equipment and tools in subsea exploration and production operations.

BACKGROUND AND PRIOR ART

The devices referred to are generally named cages or baskets which are arranged to be lowered in wires from a crane that is installed on a surface vessel. These baskets for deployment and recovery of subsea process equipment can vary in shape and dimensions but typically they include a floor and four walls made as open steel framework through which water can pass during lifting and lowering of the basket through the sea.

While a free passage of water via the open framework is advantageous especially during lowering of the basket through the surface region or "splash zone", the design may cause problems with the basket sinking too far into the ground and with dirt filling the basket through its perforated floor as the basket is seated on a soft and muddy seabed.

Some of the methods previously applied in order to prevent a subsea basket from sinking into the mud include, inter alia, the installation of mud mats on the seabed, or forming a bed of gravel at the area where the basket is to land. Other methods include increasing the surface area of the basket by means of foldable flaps that are arranged pivotable at the sides of the basket, e.g., or by means of hydraulically or mechanically driven plates that provide a cover to the basket floor before landing on the seabed.

US 7908988 B1 discloses a subsea basket comprising trussed panels in walls that rise from a bottom including an open grating which is welded or otherwise attached to a framework of longitudinal and transverse beams. The openings through the grating are static, and US 7908988 Bl provides no other structural means to meet the objects of facilitating a lowering of the basket through the splash zone while simultaneously ensuring a safe landing on the sea floor without sinking into the mud.

GB 2511500 A discloses a mudmat for a pipeline accessory, and is thus not an example of the subsea baskets to which the present invention belongs. GB 2511500 A can still be seen as an example of a desire to expand the supporting surface upon landing, in this case achieved by rotating a supplementary bottom section from an inline position, in parallel with the mudmat in a lowering sequence, to a transverse position for laterally expanding the mudmat area upon landing on the seafloor.

WO 2015/147647 Al discloses a method for lowering a subsea structure through the splash zone. The structure of WO 2015/147647 Al has a flat and covered support base with subsea equipment arranged thereon, and is thus not an example of the subsea baskets to which the present invention belongs. Yet the method disclosed in WO 2015/147647 Al is mentioned as an example of addressing the problem of lowering a subsea structure through the splash zone. The lowering in WO 2015/147647 Al is facilitated by tilting the structure upon passage through the splash zone, and returning the structure to a horizontal mode before landing on the seafloor.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a subsea deployment and recovery basket which avoids the need for hydraulic or mechanical drives in order to cover the floor or other parts of the basket framework before landing on the seabed.

The object is met in a deployment and recovery basket for lowering or lifting subsea equipment from a surface vessel to the sea bottom, the subsea basket formed with walls rising from a floor by which the basket rests on the sea bottom in settled position, wherein the floor and walls are designed as framework through which water can pass in lowering and lifting operations. Swinging shutter blades are pivotally journalled in the basket and arranged to cover at least parts of the framework of the basket in a closing position of the shutter blades, wherein the shutter blades are actuated towards and away from the closing position by a water-depth depending, water-pressure driven mechanism.

In preferred embodiments of the invention the water-pressure driven mechanism includes a pressure sensitive actuator and a push- and/or pull rod (push/pull rod).

The pressure sensitive actuator is preferably realized in the form of a gas-filled piston and cylinder unit. The pressure sensitive actuator may alternatively include a mechanical spring, and may also alternatively be realized in the form of a gas-filled flexible bellows. The gas in the gas-filled piston and cylinder unit may be contained in a flexible and/or elastic balloon or a bellows.

In preferred embodiments a set of shutter blades are arranged interconnected via a push/pull rod for simultaneous actuation by a common actuator. In alternative embodiments two or more sets of shutter blades may be arranged interconnected via a common push/pull rod that is driven by two or more cooperating actuators.

The shutter blades may be arranged in parallel rows wherein each row comprises one or more water-pressure driven actuator mechanism(s).

The shutter blade may be shaped as an elongate blade which is pivotally journalled in the basket framework for swinging about a pivot in each end of the blade. The push/pull rod may be pivotally linked to the shutter blade via a hinge. The push/pull rod may be linked to the actuator or to an actuator piston via an intermediate link and hinges.

The shutter blade may be arranged to swing through 90° from the closing position. The shutter blade may be arranged pivotable so as to depend below the framework of the basket floor in the non-covering, open positon.

The push/pull rod is a force transferring means preferably realized as a rigid element, and may if appropriate alternatively be realized as a flexible wire.

The shutter blades may be realized as continuous sheets or alternatively be arranged with perforations or include meshes.

In preferred embodiments the internal pressure (bias) of the actuator is set for opening of the shutter blades at an external pressure of 5 bar or less acting on the piston, preferably at least at external pressures below 2 bar. In correspondence herewith the internal pressure (bias) of the actuator is set for closing the shutter blades at an external pressure of 2 bar or more acting on the piston, preferably at least at external pressures above 5 bar.

SHORT DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be further explained below with reference made to the drawings wherein

Figs. 1A-1C are schematic views illustrating the water-depth depending, water-pressure driven shutter mechanism at three stages between open/non-covering position (Fig. IA) and covering position (Fig. 1C), Fig. 2 is a side view of a subsea deployment and recovery basket including a shutter mechanism incorporated in the framework structure of the basket floor, the shutter blades being pivoted to the closing position, Fig. 3 is a cut-out portion of the drawing of Fig. 2 showing the shutter mechanism and shutter blades in a non-covering position, and Fig. 4 is a partial top view of the subsea deployment and recovery basket of Figs. 2 and 3, with shutter blades shown in covering position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figs. 1A-1C show the shutter mechanism 1 for covering at least parts of a subsea deployment and recovery basket. The subsea basket 2, visible in a side view in Fig. 2, generally comprises four walls rising from the periphery of a floor wherein the floor and walls are designed as framework including longitudinal and transverse beams and upright posts and intermediate stays in a welded steel structure, as is known per se. Figs. 1A-1C show the shutter mechanism 1 separated from the basket 2. More precisely, in Fig. IA the shutter mechanism is shown in an open and non-covering position, Fig. IB shows the shutter mechanism in movement towards the closing position, and Fig. 1C shows the shutter mechanism 1 in closed and covering position.

The shutter mechanism 1 comprises a number of plate shaped shutter blades 3 which are interlinked by means of a rod or wire 4 that is pivotally connected to the shutter blades 3 at pivot joints or hinges 5. Each shutter blade 3 is pivotally suspended in the framework 6 of the subsea basket, to swing about pivot axes 7 respectively. In the open position illustrated in Fig. 1 the shutter blades 3 may depend below the floor of the subsea basket.

The positions of the shutter blades 3 are adjusted through the operation of an actuator 8 in dependence on the depth of submersion of the subsea deployment and recovery basket. The actuator 8 comprises a body 9 movable in a housing 10 against the force of a mechanical spring or a compressible gas volume 11 which applies a bias to the movable body towards the open position shown in Fig. IA. The movable body may be realized as a piston 9 arranged for reciprocating motion in a housing realized as a cylinder 10, the cylinder and piston forming a piston and cylinder unit. When gas is applied as biasing spring 11 in the piston and cylinder unit, the gas may be contained in a flexible or elastic balloon or bellows in which case the requirement for sealing of the piston and cylinder unit can be greatly reduced.

The movable body or piston 9 is exposed to the seawater which enters into the housing via entry ports 12 formed in the end of the housing or cylinder 10. As the subsea basket with shutter mechanism is lowered into the sea to a depth wherein the pressure SP of the ambient water balances and overcomes the force of the compressed gas volume or spring, the movable body 9 is moved inwards in the housing thus pulling the rod or wire 4 in the closing direction as illustrated in Fig. IB. A link member 13 can be arranged as illustrated to transfer the motion of the piston 9 to the rod or wire 4.

The actuator 8 may be set to an initial pressure of about 1.2-2 bar to ensure that the shutter blades are open and the framework of the subsea basket is open and non-covered at sea level for free passage of water as the basket is lowered into the sea, through the splash zone. As seawater pressure SP rises with water depth to above the initial pressure, the actuator starts to retract thus pulling the shutter blades towards the closing position as shown in Fig. IB. At greater depth and corresponding pressure the actuator is fully retracted, and the basket floor, or other structural part of the basket framework if applicable, becomes covered as illustrated in Fig. 1C.

The actuator can be tuned and dimensioned by proper design and dimensioning of the biasing force (gas volume/spring) acting on the piston and the area of the piston that is subjected to the seawater pressure. Persons skilled in the art are familiar with these design parameters per se and they need not be further illustrated. As an example and general indication only a 2-5 bar closing pressure is a reasonable choice for many applications, although other closing pressures may be applicable and considered with respect to the water depth at the subject location.

Another realization and embodiment of the shutter mechanism is schematically illustrated in Figs. 2-4. The shutter mechanism 1' of Figs. 2-4 comprises two sets of shutter blades 3' pivotally hinged at 14 to a longitudinal beam 15 which is included in the floor frame of the subsea deployment and recovery basket 2. Each shutter blade 3' comprises a primary blade 3.1 and a secondary blade 3.2 adjoining each other under an angle a in a seam 3.3 that coincides with a pivot axis provided by the hinge 14. In the covering position shown in Figs. 2 and 4 the shutter blades 3' cover the gaps that are formed between beams 15 and 16 in the basket floor.

The shutter blades 3' are interlinked through a push/pull rod 4' that connects to each shutter blade 3' via a link 17 respectively. The link 17 is rigidly connected to a shutter blade 3' via a first journal pin 18 that passes the hinge 14 from a first end of the link 17 to be fixed to the shutter blade at the seam 3.3. From the other end of the link 17 a second journal pin 19 extends through a slot or long-hole 20 formed in the push/pull rod 4', thus providing a sliding/pivoting engagement that moves the shutter blades 3' in and out of the closing position when the push/pull rod 4' is actuated in the direction as is schematically illustrated in Fig. 3 by the arrow F.

The forces required to move the push/pull rod 4' in the arrow F direction is provided on one hand by a spring or gas volume 11' that is encapsulated in the actuator 8' and on the other hand by the pressure of the ambient seawater. More precisely, at sea level and in the uppermost region beneath the sea surface the spring or gas volume 11' pre-stresses the push/pull rod and shutter blades towards the open/non-covering position shown in Fig. 3 by acting towards a first side 9.1 of a piston 9' that is connected to the push/pull rod 4' and arranged for back and forth movement inside the actuator 8'. At greater depths the ambient seawater pressure SP, which acts upon the other side 9.2 of the piston 9', overcomes the biasing force of the spring/gas volume 11' to move the push/pull rod and shutter blades towards the closing position disclosed in Figs. 2 and 4, under compression of the spring/gas volume 11' as indicated by the compressed state of the spring/gas volume 11' which is shown in the drawing.

Figs. 2-4 illustrate an optional variant of the shutter mechanism wherein two sets of shutter blades 3' are interlinked through a common push/pull rod 4' which is powered by three actuators 8' in cooperation.

Other variants and embodiments include actuators arranged in opposite sides of the basket to operate shutter blades that reach transversely over the width of the basket floor. Still other variants include an arrangement of parallel rows of shutter blades in the length direction of the basket, each row of shutter blades associated with a dedicated actuator or set of actuators.

The shutter mechanism of the present invention is by no means limited to the use in the floor of a subsea basket as illustrated in the drawings. On the contrary, the shutter mechanism is likewise applicable for covering the framework of the basket walls if appropriate. The accompanying claims are therefore construed to encompass the general application of the shutter mechanism in subsea deployment and recovery baskets, as well as construed to cover the embodiments disclosed and other non-disclosed embodiments which can be derived from this disclosure.

Claims

1. A basket (2) for lowering or lifting subsea equipment from a surface vessel to the sea bottom, the basket formed with walls rising from a floor by which the basket rests on the sea bottom in settled position, wherein the floor and walls are designed as framework through which water can pass in lowering and lifting operations,characterized byshutter blades (3; 3<*>) pivotally journalled in the basket and arranged to cover at least portions of the framework of the basket in a closing position of the shutter blades, wherein the shutter blades are actuated towards and away from the closing position by a water-depth depending, water-pressure driven mechanism (1; I").

2. The basket according to claim 1, wherein the water-pressure driven mechanism includes a pressure sensitive actuator (8; 8^ and a push/pull rod (4; 40.

3. The basket according to claim 2, wherein the pressure sensitive actuator (8; 8<*>) is a gas-filled piston and cylinder unit (9, 10).

4. The basket according to claim 3, wherein the gas in the gas-filled piston and cylinder unit (9, 10) is contained in a flexible and/or elastic balloon or a bellows.

5. The basket according to claim 3, wherein the internal pressure of the actuator is set for opening of the shutter blades at an external pressure of 5 bar or less acting on the piston, preferably at least at external pressures below 2 bar.

6. The basket according to any of claims 2-4, wherein the internal pressure (bias) of the actuator is set for closing the shutter blades at an external pressure of 2 bar or more acting on the piston, preferably at least at external pressures above 5 bar.

7. The basket according to any previous claim, wherein a set of two or more shutter blades are interconnected via a push/pull rod (4; 4^ for simultaneous actuation by a common actuator (8; 8<*>).

8. The basket according to any previous claim, wherein two or more sets of shutter blades are arranged interconnected via a common push/pull rod (4^ that is driven by two or more cooperating actuators (8<*>).

9. The basket according to any previous claim, wherein shutter blades are arranged in parallel rows, each row comprising one or more water-pressure driven actuator mechanism (s).

10. The basket according to any previous claim, wherein the shutter blade (3; 3*) is a blade which is pivotally journalled (7; 14) in the framework, and the push/pull rod (4; 4^ is pivotally linked (5; 19, 20) to the blade.

1 l.The basket of claim 9, wherein the push/pull rod (4) is linked to the actuator or an actuator piston (9) via an intermediate link (13) and hinges.

12. The basket of claim 9 or 10, wherein the shutter blade is pivotable through 90° between closed and open positions.

13. The basket of any previous claim, wherein the shutter blades are pivoted to depend below the framework of the basket floor in the open position.

14. The basket of any previous claim, wherein the push/pull rod is a rigid element or a wire.