NO342752B1 - Remote operation of subsea protection structures - Google Patents

Abstract

The present invention relates to a protective structure for subsea installations located on a seabed, where the protective structure com prises a plurality of structural elements connected to each other to form a frame structure in the protective structure, where a plurality of protection covers are pivotally connected to the structural elements of the frame structure, and where the protective structure further prices a torque transfer and / or lockdown arrangement for the protective covers.

Description

The present invention relates to a protective structure for subsea installations and more particularly the present invention relates to a protection cover for the protective structure.

WO 2010/103002 A2 regards a subsea well template, where the well temp late comprises a plurality of well slots arranged adjacent to a manifold reception space, and a plurality of template hatches for protection of well components, including a Christmas tree. Said hatches comprise at least a top protection cover and a side protection panel. The hatches are arranged to pivot between a closed and an open position, about a pivot axis arranged at a lower end of the hatch. When in open position, the well template exhibits absence of a framework extending up towards the top of the template.

WO 2012/138230 Al regards a device for operations in proximity of an underwater installation, where the underwater installation comprises processing equipment and is provided with at least one guide way and at least one manipulator device, where a base of the manipulator device is movably attached to the at least one guide way. The underwater installation further comprises a frame extending over the processing equipment.

NO 177647 B relates to a subsea protection structure for protection of components such as valve and control units incorporated in a subsea production plant for hydrocarbons, where the protective structure is adapted to rest on a seabed and is provided with a number of openings, through which openings modules can be lowered and lifted, where the openings are covered with hatches. The hatches are pivotally connected to the protection structure and can be opened and closed through wires and bollards.

US 2016/0290097 Al relates to a subsea wellbore protection (SWP) system, where the SWP system includes a wellbore penetrating a subterranean formation beneath a sea floor and a SWP structure positioned below grade with respect to the sea floor. The SWP structure comprises a caisson that encloses a first wellbore equipment component. The first wellbore equipment component is in fluid communication with the wellbore.

It has therefore become desirable, if not mandatory, to provide some form of protective coverage for exposed subsea well installations.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art, or at least to provide a useful alternative to prior art.

This object is achieved with a protective structure for subsea installations according to the present invention as defined in the enclosed independent claim, where embodiments of the invention are given in independent claims.

The present invention is in line with the development of more automation and remote operation of subsea fields. The present invention will make it possible to reduce time for operation of covers and/or hatches thus reducing costly operations with surface wire(s) from a surface vessel. Furthermore, the invention will make it possible to remotely open a cover or hatch from onshore while a stationary ROV can perform inspection, thus avoiding a costly surface vessel.

In accordance with the present invention, there is provided a protective structure for subsea installations arranged on and fixed to a seabed, where the protective structure comprises a plurality of structural elements connected to each other in appropriate ways in order to form a frame structure in the protective structure and such that the subsea installation is at least partly covered by the protective structure, a single or a plurality of protective covers being pivotally connected to the protective structure, where the protective structure further comprises a torque transfer and/or lockdown arrangement for the protective covers, the torque transfer and/or lockdown arrangement further comprising a first mode of operation where the at least one protective cover is free to rotate relative the at least one actuator and a second mode where the at least one protective cover is locked to the at least one actuator.

In one embodiment the torque transfer and/or lockdown arrangement for the protection covers comprises connection brackets, support elements and bolt(s), where each connection bracket may be provided with a first hole and a second hole and an opening for reception of a shaft journal or an actuator output shaft. The torque transfer and/or lockdown arrangement may further comprise a torsion element, where the torsion element may comprise a freestanding element formed as a closed hollow profile and being capable of transferring a torque over at least a part of a length of the torsion element.

According to one embodiment the torque transfer and/or lockdown arrangement may comprise a lever arm system, where the system may comprise a number of lever arms pivotally connected to each other and connected to at least one linear actuator in the form of a hydraulic, electric or the like cylinder.

According to an alternative embodiment of the torque transfer and/or lockdown arrangement, the arrangement may comprise a first element in the form of a toothed or cogged shaft, a second element in the form of a toothed or cogged sleeve and an element with a cogged area, where the first element, the second element and the cogged area will cooperate to bring the torque transfer and/or lockdown arrangement between the different states, i.e. the free state, the locked state and the "torque transfer" state. However, a person skilled in the art would know that the different elements also could be provided otherwise than with teeth, for instance a square form, a polygonal form or the like, and where the arrangement also may comprise a device to move the different part relative each other in order to bring the different parts in or out of contact with each other.

At least one actuator may be used to operate the torque transfer and/or lockdown arrangement, where the actuator may be in the form of a power transmission unit driven by an ROV operated torque tool or other motor, linear actuators or the like. Furthermore, a power supply interface may be connected to the at least one actuator through at least one hydraulic, electric or other cable, such that the actuator can be operated by a ROV and/or a power and/or control unit without interfering in opening motion of the protection cover.

In one embodiment of the present invention one or more actuators, where the actuator, for instance, may be a motor including a gearbox, can be connected to each protection cover of the protective structure, such that the protection cover together with the one or more actuators can be removed from the protective structure and transported to the surface for servicing, replacement etc, on a vessel or the like. Each actuator of the one or more actuators may then be connected directly to the protection cover through a connection bracket, or indirectly through a torsion element, where the torsion elements in order is connected to the protection cover through the connection brackets. The protection cover is then connected and disconnected to a structural element(s) of the protective structure through the torque transfer and/or lockdown arrangement, i.e. the one or more actuators or the torsion element, and support elements being connected to the structural element(s) of the protective structure.

In the following, preferred embodiments of the invention will be described in detail, by way of example only, with reference to the accompanying figures, where: Figure 1 is a perspective view of a protective structure for subsea installations according to the present invention, where some protection covers and/or hatches are shown in an open position, Figure 2 is a perspective view of an alternative protective structure for subsea installations according to the present invention, where the protection covers and/or hatches are shown in a closed position, Figures 3A-3B show a part of a protective structure and a part of a protection cover of the protective structure according to figures 1 or 2, where figure 3 A shows the protection structure and protective cover in an exploded view and figure 3B shows the protective cover connected to the protection structure, Figures 4A-4D show a power supply interface connected to an actuator and how the actuator can be arranged in the protective structure for subsea installations according to the present invention, where the actuator is used to open and close the protective covers and/or hatches, Figures 5A-5B show a torque transfer and/or a lockdown arrangement for the protection covers and/or hatches according to the present invention, Figures 6A-6B show an alternative embodiment of an arrangement of the power supply interface and an actuator according to figures 4A-4D, Figure 7 shows yet an alternative arrangement of the power supply interface and an actuator for the operation of the protection covers and/or hatches according to the present invention, where the actuator and power supply interface are permanently installed to the protective structure, Figure 8 shows an alternative source of power and/or control unit for remote operation of the actuator and the protection covers and/or hatches according to figures 3A-7, Figures 9A-9B show an alternative actuator for opening and closing arrangement for the operation of the protection covers and/or hatches, Figures 10A-10B show in greater detail the alternative opening and closing arrangement according to figures 9A-9B, Figure 11 shows an alternative source of power and/or control unit for remote operation of the actuator and the protection covers and/or hatches according to figures 9A-10B, Figures 12A-12B show an alternative embodiment of an actuator according to figures 4A-4D, Figures 13A-13B show yet an alternative embodiment of an actuator according to figures 4A-4D, and Figures 14A-14C show an alternative torque transfer and/or a lockdown arrangement for the protection covers and/or hatches according to figures 5A-5B, where figure 14A shows the arrangement in a none connection state, figure 14B shows the arrangement in a lock down state and figure 14C shows the arrangement in a torque transfer state. Figure 1 shows a protective structure 1 for a subsea installation 2 according to the present invention, where the subsea installation 2 is anchored to a seabed B. The protective structure 1 comprises a plurality of structural elements 3, 4, 5, 6, 7 connected to each other to form a frame structure in the protective structure 1. Furthermore, a deflector device 11 in the form of a structural element is connected to each upper corner of the frame structure, and slope downwards, from a top of the frame structure, to the seabed B.

A plurality of protection covers and/or hatches 12 are pivotally connected to the frame structure. The protective covers and/or hatches 12 can be brought between a fully closed position, where the protective covers and/or hatches 12 will protect equipment of the subsea installation 2, and to a fully open position, where the protection covers and/or hatches 12 provide an "opening" in the frame structure, such that maintenance, repair and/or replacement of equipment of the subsea installation 2 can be performed. The protection covers and/or hatches 12 are shown in a partly open or closed position in figure 1.

The protective covers and/or hatches 12 can be operated by a ROV (not shown), by remote control and/or by wires or the like. How this can be achieved is explained in the following.

Although figure 1 show that the protective structure 1 for subsea installations 2 comprises a plurality of protection covers and/or hatches 12, it should be understood that the protective structure 1 according to the present invention could be designed or constructed with only one protection cover or hatch 12.

Figure 2 shows an alternative design or construction of a protective structure 1 according to the present invention, where also this protective structure 1 comprises a plurality of structural elements 3, 4, 5 connected to each other to form a frame structure in the protective structure 1.

Furthermore, a deflector device 11 in the form of a structural element is connected to each lower corner of the frame structure, where the deflector devices 11 will slope downwardly away from the protective structure 1, to the seabed B.

The design or construction of the protective structures 1 shown in figures 1 and 2 are only shown as examples on how such a protective structure 1 could be and a person skilled in the art would know that such protective structures 1 could be designed or constructed in many other ways.

In figures 3A-3B is shown how a protection cover and/or hatch 12 can be releasably connected to a structural element 3, 4, 5, 6, 7 of the frame structure of the protective structure 1 for a subsea installation 2. A torsion element 13 in the form of a pipe or tube is connected to each protection cover and/or hatch 12 through two connection brackets 14. One end of such a connection bracket 14 is then designed or formed to be connected to the torsion element 13 and an opposite end of the connection bracket 14 is designed or formed to be connected to the protection cover 12.

Each end of the torsion element 13 and the connection brackets 14 is/are designed or formed to receive and accommodate a shaft journal 17 or an actuator output shaft 18 of an actuator 191, the actuator 191 in this embodiment being in the form of a power transmission unit, when the protection cover 12 is connected to one or more of the structural element 3, 4, 5, 6, 7 forming the frame structure of the protective structure 1.

Furthermore, the actuator 191, being a power transmission unit, is connected to a torque tool 19 or a motor (not shown).

The torsion element 13 is a construction with the ability to transfer torsion load, typically a freestanding element formed as a "closed" hollow profile, whereby the torsion element 13 is capable of transferring a torque from the actuator 191 to each of the connection brackets 14. A person skilled in the art would know how such a torsion element 13 should be constructed, whereby this is not described further herein.

Each end of the torsion element 13 is then connected to a connection bracket 14 and each connection bracket 14 is connected to the protection cover and/or hatch 12 towards an end of the protection cover 12.

The connection brackets 14 can be connected to the protection cover and/or hatch 12 and the torsion element 13 through bolts, welding, bonding or the like.

The structural element 3, 4, 5, 6, 7 of the frame structure is provided with two support elements 15 for the protection cover and/or hatch 12, such that the protection cover and/or hatch 12 can be connected to the structural element 3, 4, 5, 6,7.

Each of the support elements 15 is provided with an opening 16, where the opening 16 is provided to receive a shaft journal 17 or an actuator output shaft 18 of the power transmission unit 191.

As shown in figure 3 A, the left support element 15 is provided with a shaft journal 17, while the right support element 15 is provided with an actuator output shaft 18 of the power transmission unit 191, where the power transmission unit 191 can be connected to a torque tool 19. An actuator input shaft of the power transmission unit 191 is arranged in a receptacle 20 connected to the power transmission unit 191. The receptacle 20 is furthermore provided to receive and accommodate a torque tool 19, whereby the torque tool 19 in appropriate ways, through an output shaft 181, can be connected to or disconnected from the actuator input shaft (not shown) of the power transmission unit 191.

The shaft journal 17 is fixedly connected to the left support element 15, and will therefore not rotate relative the support element 15.

Through the above arrangement of the torsion element 13, the connection brackets 14 and the support elements 15, a protection cover and/or hatch 12 can be connected to the structural element 3, 4, 5, 6, 7 of the frame structure of the protective structure 1.

When the protection cover and/or hatch 12 is connected to the frame structure of the protective structure 1, as shown in figure 3B, a ROV can be used to operate the protection cover and/or hatch 12 between an open and a closed position. A ROV is equipped with a set of connectors that can connect to the a power supply interface 22, or a torque tool can connect directly to the ROV. The ROV arranges the torque tool 19 in the receptacle 20, where the torque tool 19 in turn, through the output shaft 181 is connected to the actuator input shaft of the power transmission unit 191. In either of these arrangements the ROV can supply power to the power transmission unit 191 through the torque tool 19 in order to operate the protection cover and/or hatch 12.

The protective structure 1 according to the present invention further comprises a torque transfer and/or a lockdown arrangement for the protection covers 12. The output shaft 18 of the power transmission unit 191 is then provided with a throughgoing hole 23, where the throughgoing hole 23 is aligned with a first and complementary hole 24 provided in each of the connection brackets 14. At the right support element 15, a bolt 25, where the bolt 25 in this case is used as a "lockdown and torque transfer bolt" is then used to lock the actuator output shaft 18 of the power transmission unit 191 to the torsion element 13 and also to "transfer" torque through the torsion element 13, such that the protection cover and/or hatch 12 can be operated when the protection cover and/or hatch 12 is to be opened or closed.

Each of the connection brackets 14 is also provided with a second hole 26, where the second hole 26 is provided at a vertical distance from the first and complementary hole 24. The bolt 25 at the right support element, when arranged in this alternative position (i.e. in the second hole 26) is then used only as a "lockdown bolt" for the protection cover and/or hatch 12.

At the left support element 15, the bolt 25 is always arranged in the second hole 26, such that the bolt will act as a "lockdown bolt".

If, for instance, the ROV is not able to connect to the power supply interface 22 and/or the power supply interface 22, the power transmission unit 191 and/or the torque tool 19 is/are damaged and/or not functioning properly, the ROV can release the connection between the output shaft 18 of the power transmission unit 191 and the torsion element 13 by removing the bolt 25, which in this case acts as a "lockdown and torque transfer bolt", and insert the bolt 25 again in the second hole 26, whereby the bolt 25 in this case will only act as "lockdown bolt". The protection cover and/or hatch 12 can now be operated by ROV and/or by a crane and wires or the like in order to open or close.

Figures 4A-4D show an arrangement where the torque tool 19 is not connected directly to the ROV, but where the power supply interface 22 for the ROV is connected to the torque tool 19, and how the power supply interface 22 can be arranged in the protective structure 1 such that the ROV can be connected to the power supply interface 22 without interfering the opening and closing area of the protection cover and/or hatch 12.

As can be seen in figure 4A, the power supply interface 22 is connected to the torque tool 19 through a cable 27, where such a cable 27 can be hydraulic, electric or other or a combination.

A torque tool 19 is installed into the receptacle 20 by the ROV and the power supply interface 22 is arranged on the outside of the protective structure 1 in order to ease the access to the power supply interface 22 and the operation of the torque tool 19.

In figure 4B the power transmission unit 191 is in the form of a gearbox, whereby the power transferred from the torque tool 19 to the torsion element 13 via the gearbox, can be geared up or down. A person skilled in the art would know how such a gearbox is designed or constructed, whereby this is not further described herein. Figures 4C and 4D show how the power supply interface 22 can be arranged in the protective structure 1 such that the ROV can be connected to the power supply interface 22 without interfering the opening and closing area of the protection cover and/or hatch 12. Figures 5A-5B show the torque transfer and/or lockdown arrangement according to the present invention in greater detail, where the arrangement is shown in a lockdown and torque transfer state in figure 5A and in a lockdown state in figure 5B.

In figure 5 A each of the connection brackets 14, which are connected to the torsion element 13, are provided with two holes, a first hole 24 and a second hole 26, where the holes 24, 26 are arranged vertically below each other and spaced apart a distance from each other. When the protection cover and/or hatch 12 is to be connected to the structural element 3-10, the torsion element 13 is brought into abutment with the shaft journal 17 and the actuator output shaft 18 of the torque tool 19 arranged in the openings 16 of the support elements 15. The throughgoing hole 23 provided in the actuator output shaft 18 of the power transmission unit 191 will then be levelled or aligned with the first hole 24 provided in the right connection bracket 14. Two bolts 25, one on each side of the torsion element 13 can then be used to lockdown the torsion element 13 and the actuator output shaft 18 of the power transmission unit 191, and the torsion element 13 and the journal shaft 17, such that a torque can be transferred through the torsion element 13, from a side where the power transmission unit 191 is arranged and to an opposite side of the torsion element 13.

In figure 5B the torque transfer and/or lockdown arrangement is used only as a lockdown arrangement, as the bolts 25 instead are installed in the second holes 26 provided in the connection brackets 14, whereby the power transmission unit 191 is "released" from the torsion element 13. The torque transfer and/or lockdown arrangement can, for instance, be used in this state if the power transmission unit 191 and/or the torque tool 19 is/are damaged, does not function properly or if it the power transmission unit 191 and/or torque tool 19 should be maintained or replaced, whereby the protection cover 12 still could be operated to be opened or closed.

Figures 6A-6B show an alternative arrangement of the receptacle 20 seen from a side (figure 6A) and from a front side (figure 6B), where the power transmission unit 191 in this embodiment is equipped with a bevel gear drive, and where the ROV (not shown) carrying the torque tool 19 can access the receptacle 20 from a side of the protective structure 1, such that the ROV will not interfere with the opening and closing area of the protection cover 12. Through this arrangement the ROV can use the torque tool 19 without the use of the power supply interface 22 and the cable 27.

Figure 7 shows an alternative embodiment of the opening and closing system for the protective covers 12, where only a part of the protective structure 1 is shown. In this embodiment, a permanently installed actuator in the form of a motor and gearbox 30 is connected to the support element 15, where the permanently installed motor and

gearbox 30 is connected to a power supply interface 22 through a cable 27, where also the power supply interface 22 is permanently connected to the protective structure 1. Through this embodiment the need for the ROV to carry with it the torque tool 19 and to connect to the power transmission unit 191 according to figures 4A-4B is eliminated, as these elements are permanently installed in the protective structure 1.

The cable 27 can be a hydraulic cable, an electric cable, other cable or a combination. Figure 8 shows an alternative embodiment of the opening and closing system for the protective covers and/or hatches 12, where it can be seen that a motor and gearbox 30 is connected to the support element 15, where the motor and gearbox 30 through power and/or signal cables 32 is connected to a power and/or control unit 33 arranged on a X-mas tree 34 of the underwater installation, whereby the power and/or controlling signals for operation of the protection covers and/or hatches 12 can be obtained from an X-mas tree 34 (or other subsea unit, not shown) and operated remotely, without use of, and independently of, a ROV. Figures 9A-9B show an alternative opening and closing arrangement for the operation of the protective covers and/or hatches 12, where figure 9 A shows the protection structure 1 and the protective cover and/or hatch 12 in an exploded view and where figure 9B shows the protective cover and/or hatch 12 connected to the protection structure 1.

Two connection brackets 14 are connected to the protective cover 12 through one end of the connection bracket 14. The other end of each connection bracket 14 is designed or formed to receive a journal shaft 17 connected to a support element 15, where the support element 15 is formed with an opening 16 for the reception for the journal shaft 17.

The end of the connection bracket 14 that is to receive and accommodate the journal shaft 17 is provided with a first hole 24 and a second hole 26 and the journal shaft 17 is provided with a throughgoing hole 23.

In this embodiment, a lever arm system connected to linear actuators are used to operate the protection covers 12. The lever arm system comprises a first lever arm 35, where one end of the first lever arm 35 is pivotally connected to the support element 15 through a pivot connection 38. An opposite end of the first lever arm 35 is pivotally connected to a first end of a second lever arm 36 through a pivot connection 39. The first lever arm 35 is also pivotally connected to a linear actuator 40 in the form of a hydraulic or electric cylinder through a pivot connection 41. The pivot connection 41 is arranged to be "off-center" of the first lever arm 35, i.e. the pivot connection 41 is located closer to an end of the first lever arm 35 than to a middle of a length of the first lever arm 35.

However, a person skilled in the art would know that the pivot connection 41 could be arranged anywhere on the first lever arm 35, where the location of the pivot connection 41 is decided in relation to the distribution between the length of stroke and the force of the chosen cylinder(s).

A second end of the second lever arm 36 is pivotally connected to a first end of a third lever arm 37 through a pivot connection 42. A second end of the third lever arm 37 is fixedly connected to the journal shaft 17 connected to the support element 15.

Furthermore, the linear actuator 40 is pivotally connected to the support element 15 through a pivot connection 43.

Through the above described lever arm system, the protection covers 12 can be connected to the protection structure 1 according to the present invention, whereby the torque transfer and/or lockdown arrangement as described according to figures 3A-3B can be used to determine if the protection covers 12 are to be operated through the actuator(s) 19, 30, 40, or if these should be "released" from the protection covers 12, such that the protection covers 12 could be operated "manually". Figures 10A-10B show in greater detail the embodiment according to figures 9A-9B, where figure 10A only show the lever arm system and figure 10B show, from a side, how the lever arm system is arranged in a closed and open state of the protection cover 12. Figure 11 shows how the embodiment according to figures 9A-9B can be operated remotely, where reference is made to the description according to figure 8.

Although figures 9A-11 show an embodiment where two linear actuators are used to operate the protection covers and/or hatches 12, it could be envisaged that only one linear actuator could be used with a torsion element 13, as described according to figures 3A-6B. Furthermore, it could also be an actuator, which act or work in a plane through a centre of gravity and perpendicular on the pivot line.

Figures 12A-12B show an alternative embodiment of an actuator according to figures 4A-4D, where it can be seen that the actuator in the form of the motor and gearbox 30 is mounted inside the torsion element 13, where the actuator output shaft 18 will extend out from the torsion element 13 on one side of the torsion element 13. Similarly, the shaft journal 17 is also mounted inside the torsion element 13, such that a part of the shaft journal 17 will extend out from the torsion element 13 on an opposite side of the actuator output shaft 18. Furthermore, the torsion element 13 is connected to the protection cover and/or hatch 12 through two connection brackets 14.

The support elements 15 are provided to receive and accommodate the actuator output shaft 18 and the shaft journal 17, such that the protection cover/hatch 12 can be connected to the protective structure 1.

Also in this embodiment, the protective structure 1 according to the present invention comprises a torque transfer and/or lockdown arrangement as described according to figures 3A-3B and 5A-5B, whereby reference is made to these figures for the explanation of the torque transfer and/or lockdown arrangement.

Figures 13A-13B show yet an alternative embodiment of an actuator device according to figures 4A-4D, where it can be seen that two actuators in the form of the motor and gearbox 30 are used, whereby the use of the torsion element 13 can be omitted.

The support elements 15 in this embodiment are provided to receive and accommodate the actuator output shafts 18 of the motor and gearbox 30, such that the protective cover and/or hatch 12 can be connected to the protective structure 1.

Also in this embodiment, the protective structure 1 according to the present invention comprises a torque transfer and/or lockdown arrangement as described according to figures 3A-3B, 5A-5B or figures 14A-14C, whereby reference is made to these figures for the explanation of the torque transfer and/or lockdown arrangement.

Through the embodiments shown in figures 12A-13B the actuator or actuators 30 are connected and fixed to the protection cover 12 through the torsion element 13 and connection brackets 14 or only through connection brackets 14, whereby this allow the protection cover(s) 12 together with the actuator(s) to be removed from the protective structure 1, whereby the protection cover 12 and the actuator(s) can be transported to a vessel (not shown) or the like for servicing, replacement etc. of the actuator(s) and/or protection cover(s).

In figures 14A-14C is shown an alternative torque transfer and/or a lockdown arrangement, where the arrangement comprises a first element 50 in the form of a toothed or cogged shaft, a second element 51 in the form of a toothed or cogged sleeve and a toothed or cogged area 52 arranged over at least a part of an inner length of the torsion element 13, where the first element 50, the second element 51 and the cogged area 52 will cooperate in order to bring the torque transfer and/or lockdown arrangement between the different states. The first element 50 is connected to a power transmission unit 191, whereby the power transmission unit 191 is used to transfer the torque to the torque transfer and/or lockdown arrangement in order to operate the protective cover and/or hatch 12 between the open and closed state. As this is described above, this will not be described any further here.

The second element 51 is provided with longitudinal grooves or slots (i.e. toothed or cogged) along its outer periphery, where the longitudinal grooves or slots will extend over the hole length of the second element 51 and longitudinal grooves or slots along its inner periphery over a part of the length of the second element 51. The cogged area 52 of the torsion element 13 will at least have the same extent as the length of the longitudinal grooves or slots along the outer periphery of the second element 51.

If the second element 51 is moved axially in the torsion element 13 and away from the first element 50, such that the first and second elements 50, 51 are in no contact with each other, then the torque transfer and/or lockdown arrangement is in a none connected state, whereby the protection cover and/or hatch 12 can be removed from the protective structure 1. This state is shown in figure 14A.

If the second element 51 is moved in an axial direction of the torsion element 13, but where the internal grooves or slots of the second element 51 are not in contact with the external grooves or slots (i.e. toothed or cogged) of the first element 50, the torque transfer and/or lockdown arrangement is in a locked state and the protection cover and/or hatch 12 can be operated manually. This state is shown in figure 14B.

If the second element 51 is moved in an axial direction of the torsion element 13 towards the first element 50, such that the internal grooves or slots of the second element 51 are brought into contact with the external grooves or slots of the first element 50, then the transfer and/or lockdown arrangement is in a torque transfer state and the protection cover and/or hatch 12 can be operated through the power transmission unit 191. This state is shown in figure 14C.

The second element 51 may in appropriate ways be connected to a device (not shown) which will be able to move the second element 51 in an axial direction of the torsion element 13 in order to bring the second element 51 into and out of abutment with the first element. As person skilled in the art would know how this can be done, whereby this is not described further herein.

The present invention has now been explained with reference to exemplary embodiments, but a person of skill in the art will appreciate that changes and modifications may be made to these exemplary embodiments that are within the scope of the invention as defined in the following claims.

Claims (13)

1. A protective structure (1) for subsea installations (2) located on a seabed (B), the protective structure (1) comprising a plurality of structural elements (3-7) connected to form a frame structure, and at least one protection cover (12) pivotally connected to the structural element (3-7) and connected to at least one actuator,characterizedin that the protective structure (1) further comprises a torque transfer and/or lockdown arrangement for the protection covers (12), the torque transfer and/or lockdown arrangement further comprising a first mode of operation where the at least one protective cover (12) is free to rotate relative the at least one actuator and a second mode of operation where the at least one protective cover (12) is locked to the at least one actuator.

2. Protective structure (1) according to claim 1,characterized in thatthe torque transfer and/or lockdown arrangement for the protection covers (12) comprises connection brackets (14), support elements (15) and bolts (25), each connection bracket (14) being provided with a first hole (24) and a second hole (26) and each support element (15) being provided with an opening (16) for reception of a shaft journal (17) or an actuator output shaft (18).

3. Protective structure (1) according to claim 2,characterized in thatthe torque transfer and/or lockdown arrangement for the protection covers (12) further comprises a torsion element (13).

4. Protective structure (1) according to claim 2,characterized in thatthe torque transfer and/or lockdown arrangement for the protection covers (12) further comprises a lever arm system (35, 35, 37).

5. Protective structure (1) according to any one of the proceeding claims,characterized in thatthe protective structure further comprises at least one actuator (19, 30, 40) for the operation of the protective covers (12).

6. Protective structure (1) according to claim 5,characterized in thata power supply interface (22) is connected to each of the at least one actuator (19, 30, 40) through at least one hydraulic, electric or other power cable (27, 32).

7. Protective structure (1) according to claim 5,characterized in thatthe at least one actuator is connected to each protective cover (12).

8. Protective structure (1) according to claim 7,characterized in thatthe at least one actuator is arranged inside a torsion element (13) connected to connection brackets (14) or connected to connection brackets (14).

9. Protective structure (1) according to anyone of proceeding claims 7-8,characterized in thatthe at least one actuator is in the form of a motor and gearbox (30).

10. Protective structure (1) according to claim 5,characterized in thateach of the at least one actuators (19, 30, 40) is connected to a power supply and/or control unit (33).

11. Protective structure (1) according to claim 3,characterized in thatthe torsion element (13) comprises a freestanding element formed as a "closed" hollow pro file, the torsion element 13 being capable of transferring a torque over a length of the torsion element (13).

12. Protective structure (1) according to claim 4,characterized in thatthe lever arm system (35, 36, 37) comprises a first lever arm (35), a second lever arm (36) and a third lever arm (37), the first and second lever arms (35, 36) being pivotally connected to each other through a pivot connection (39), the second and third lever arms (36, 37) being pivotally connected to each other through a pivot connection (42), and the third lever arm (37) being fixedly connected to a shaft journal (17) through a connection.

13. Protective structure (1) according to claim 2,characterized in thatthe journal shaft (17) or the actuator output shaft (18) is provided with a throughgoing hole (23).