Technical Field

The invention relates to an electric crane for use on an unmanned wellhead platform. The invention relates in particular to an electric crane that at the same time has low overall height.

Background Art

A normally unmanned installation offshore is a type of automated oil or gas platform designed to be primarily remotely operated, without the constant presence of personnel. A typical unmanned platform is shown in figure 1 a.

These platforms are generally characterized by their small size. They are often a compromise between providing the convenience of surface wellheads, which are easier to build and maintain and avoiding the high operating cost of a full production platform.

The unmanned platforms are commonly serviced from a nearby larger platform. Regular visit may be made for routine maintenance and for smaller well work, by use of a Service operation vessel for transport of personnel and support for the operation. One example of such operations is well intervention by wireline. Even though the platforms are small and most of the time unmanned there is a requirement for equipment that fulfills the safety regulations when the platform is manned. The reduced space and height limitation during drilling periods also requires other solutions than normal platforms.

Due to the operation of these platforms, there are needs for new equipment that are adapted for these specific platform types.

There is a drive in the industry to change to full electric cranes, so also for UWP. There are many advantages to use electric cranes instead of other conventional types of cranes, such as hydraulic cranes.

The electric cranes are for instance environmentally friendly in that:

- There is no need for hydraulic oil. - Low noise level.

- Energy savings from low starting current and from not having to continuously run the crane machinery.

- Regenerated and consumed power are monitored.

- Control of power consumption/back power.

- Lower energy consumption (between 30 and 35 per cent).

- Less power consumption might affect the choice for smaller.

- Generator/transformer capacity. The electric cranes are also high cargo-handling efficiency, for instance:

- Improved operational performance.

- Short response times.

- Maximum speed based can be on actual load.

- Exact position of the load is maintained even with open brake.

- Short cycle times due to higher speeds.

- More precise operation ensuring easier control and load positioning.

There are also advantageous with service and maintenance of electrical crane:

- Extended lifetime of components.

- Maintenance friendly.

- Lower maintenance costs.

- Fewer consumables.

- Improved fault-finding.

- Easy access to data for trouble-shooting.

Improved load cycle performance can be summarised as:

-The ramp time for each motion will be based on the load; this will optimise the response time of the crane.

- Response times will be shorter with operators achieving an almost immediate reaction.

- Crane operation will be step-less with maximum speed based on the load and outreach only. - The electric crane can keep the load in an exact position even with the brake open, which makes it easy to handle the load.

When a jack up rig is used to perform operations on the unmanned platform, the jack up rig is arranged close to the platform and will during drilling also have a cantilevered drilling rig that protrudes from the jack up rig. The cantilevered drilling rig will then extend over the unmanned platform which makes it unsuitable to have high obstructions, like a tall crane, hindering the movement of the cantilevered rig. Figure 1 a shows an example of an unmanned platform 100.

Figure 1 b shows the unmanned platform 100 with a jack up rig 200 where the cantilevered drilling rig 201 are shown. This cantilevered drilling rig 201 could come into conflict with a crane that has a high tower.

An example of a prior art electric crane 150 is shown in figure 2a. These cranes 150 comprises a main mast 151 and a lifting part 152, 152', 152" (shown in different positions) and have an extended tower 153. The lifting operation of the crane 150 are perform by a rope or winch 154 connected between the tower 153 and the lifting part 152. These types of cranes 150 are however not suitable to use together with the jack up rig 200 on unmanned platforms 100 as described above.

An example of a low building crane 170 is shown in figure 2b. these cranes 170 are also known as luffing cranes 170. The jack up rig and the cantilevered drilling rig 201 as shown in figure 1 b may easily be used together with the luffing crane 170 without any conflict between the operations as the drilling cantilever can operate above the crane 170.

In the traditional low building crane as shown in figure 2b, the luffing operation, ie the movement of the crane boom in the vertical direction is performed by hydraulic mechanism.

The functionality such as the swing mechanism and the hoisting mechanism however could be done electrically. The prior art low building luffing cranes 170 have a crane boom 172 that is operated by a hydraulic lifting mechanism 173 as shown in the figure 2b. The hydraulic lifting mechanism or cylinder 173 is arranged between a vertical main mast 171 that is connected to the platform 100 and the underside of the cantilevered lifting part or crane boom 172 to move the lifting part 172 up and down to perform the lifting operation.

None of the prior art lifting cranes 150, 170 shown in figure 2a and 2b are both low building and at the same time electrical in the lifting operations with all the advantageous as described above. It is therefore an object of the invention to provide a crane for an unmanned platform that has both completely electrical operations and at the same time is low building so that it can be installed and potentially used during drilling phase with jack up rig.

Summary of invention

The invention relates to a crane for an unmanned platform comprising a vertical main mast for connection with the platform and a cantilevered swiveling crane boom configured to perform lifting operations. The invention is distinctive in that the crane further comprises a strut with fixed length having a first end pivotable connected to said main mast and a second end slidingly connected to the crane boom with a longitudinal glide path, said crane further comprises a lifting arrangement having an electrical driving device adapted to impose a force on the second end of the strut to move the second end back and forth along the longitudinal direction of the crane boom between the glide path ends. , The crane further comprising a sliding mechanism having a glide path formed as an elongated opening arranged along the longitudinal axis of the crane boom and a yoke pivotable connected to the second end of the strut, said yoke is adapted to move within the glide path between end points of the glide path.

The invention also relates to a crane for an unmanned platform comprising a vertical main mast and a cantilevered swiveling lifting part, such as a crane boom, said lifting part is pivotable connected to the main mast. The invention is distinctive in that the crane further comprising a strut having a first end pivotable connected to the main mast and a second end slidingly arranged within a longitudinal glide path on the lifting part and being movable between defined end positions of the glide path. Said crane further comprises a lifting

arrangement connected in one end to the second end of the strut. The lifting arrangement having an electrical driving device adapted to impose a force on the second end for movement of the second end of the strut along the glide path to perform the lifting operation of the crane. In a preferred embodiment of the crane is that the strut is attached to the main mast below the lifting part when the crane being installed at the platform.

In yet another embodiment of the invention, the glide path is formed as elongated opening along the longitudinal axis of the crane boom, said yoke is adapted to move within the glide path (13).

In yet another preferred embodiment of the invention, the lifting arrangement comprising a wire or rope operably arranged between the second end of the strut and the electrical device, said electrical device is arranged on the crane boom.

In another embodiment of the crane, the lifting arrangement further comprising a tackle system with a first snatch block fixedly attached to the crane boom and a second snatch block fixedly attached to the yoke, said wire or rope is extending around the first and second snatch block before extending towards the electrical device.

In another embodiment of the invention, the electrical device and the first snatch block are arranged on opposite longitudinal sides of the glide path of the crane boom. In a further embodiment of the crane, the electrical driving device is a winch.

In another embodiment of the invention, the lifting arrangement comprises a screw mechanism having a frame part fixedly attached to the crane boom and a rod with helical grooves adapted to rotate around its longitudinal axis within the frame, said second end of the strut is adapted to mate with the grooves in the rod so the second end of the strut is movable within end positions in the frame part when the rod is rotated.

In yet another embodiment of the invention the lifting arrangement comprises a rack and pinion mechanism, wherein the pinion is connected to the second end of the strut and is adapted to move along a rack arranged on the crane boom, said pinion is connected to an electrical device.

In another embodiment of the invention, the crane is provided with a working deck and handrails.

Brief description of drawings

Figure 1 a shows an example of an unmanned platform. Figure 1 b shows a jack up rig with a cantilevered drilling rig extending over the unmanned platform.

Figure 2a shows a prior art electric crane with a high tower for performing the lifting operations.

Figure 2b shows a prior art hydraulic luffing crane. Figure 3 shows a perspective view of a low building electric crane according to the present invention, with the lifting part or the crane boom in the resting position.

Figure 4 shows a perspective view of one embodiment of the lifting

arrangement of the low building crane according to the invention. Figure 5-6 shows the lifting arrangement according to the embodiment shown in figure 4, viewed from above.

Figure 7-8 shows the lifting mechanism according to the embodiment of the invention shown in figure 4, side viewed.

Figure 9 shows the low building crane with the lifting part or crane boom in the upper most position.

Figure 10-13 shows a detailed view of the embodiment of the lifting

arrangement in figure 4 of the low building crane viewed from different sides. The lifting part being in the uppermost position.

Figure 14 shows another embodiment of the lifting arrangement with a screw arrangement to displace the second strut end along the lifting part or crane boom.

Figure 15-16 shows another embodiment of the lifting mechanism with a rack and pinion arrangement to displace the second strut end along the lifting part or the crane boom. Figure 17 shows a crane according to another embodiment of an electrical lifting arrangement, viewed in the resting position.

Figure 18 shows a crane according to another embodiment of an electrical lifting arrangement, viewed in a lifting position.

Figure 19-21 shows a detail view of the crane according to the embodiment of figure 17-18.

Figure 22 shows a different arrangement of the electric drive according to the embodiment shown in figure 17-21 .

Detailed description of the invention The following describes a preferred embodiment of the present invention and some relevant prior art which are purely exemplary for the sake of

understanding the invention and non-limiting.

Figure 3 shows an embodiment of a low building electric crane 1 according to the present invention. The crane 1 comprises a vertical main mast 2 that is adapted to be fixedly attached to the platform 100. The crane 1 further comprises a lifting part or cantilevered, swivelling crane boom 3. The crane boom 3 is pivotably connected in one end 4a to the main mast 2. The other end 3b of the crane boom 3 is extending to a free end where the hoisting operations is performed. A strut 4 is in a first end 4a pivotably connected to the main mast 2 and at a second end 4b slidably or movable connected to the crane boom 3.

As shown in the figure 3 the first end 4a of the strut 4 could be connected between a pair of brackets 6 that is connected to the main mast 2 of the crane 1 .

The first strut end 4a is attached in the lower region of the main mast 2 as shown in the figure 1 . The first strut end 4a is attached to the main mast 2 below the crane boom 3.

The brackets 6 could preferable be arranged below the crane boom 3 so that the lifting operation is performed from the underside of the strut 4. There could be other connections between the main mast 2 and the strut 4 as long as the connection allows the strut 4 to rotate in relation to the main mast 2.

The strut 4 has a fixed length. The figure 4 also shows a sliding mechanism also called a lifting mechanism 5 according to one embodiment of the invention. The sliding mechanism 5 will be further described below. There is also arranged a lifting arrangement 20 with a tackle system to reduce the forces that is needed to perform the lifting operations. In addition, the lifting arrangement 20 according to the embodiment of figure 3-13 comprises an electrically driven device 12, such as a winch 12. A wire or rope 9 is arranged in operable contact with the electrically driven device 12, the tackle system and the second end of the strut 4b. A lifting arrangement 20 according to the embodiment shown in figure 3-13 comprises the electrically driven device 12, tackle system 10, 1 1 and the wire or rope 9.

There could also be one or more working decks 7a attached to the crane 1 for safe and easy access of personnel. The crane 1 could also be provided with hand rails 7b for safety measures. Figure 4 shows a perspective view of the lifting arrangement 20 and the sliding mechanism 5 shown in figure 3.

The sliding mechanism 5 comprises a yoke 8 that is connected to the second end of the strut 4b. The second end of the strut 4b is pivotably connected to the yoke 8. The yoke 8 is arranged within an elliptical or similar shaped opening 13 in the lifting arm. The opening is further called a glide path 13 (see figure 8).

The glide path 13 have end points 13a, 13b so that the yoke 8 with the strut 4 is forming a resting position of the crane boom 3 when being positioned at a first end point 13a. This position is shown in figure 4-8. The yoke 8 with the strut 4 is forming an uppermost position of the crane boom 3 when being positioning at a second end point 13b of the glide path13. This position is illustrated in the figures 9-13. The tackle system of the lifting arrangement 20 further comprises a first snatch block 10 and a second snatch block 1 1 . The wire or rope 9 is extending around both first and second snatch block 10, 1 1 a suitable number of times. The first snatch block 10 is fixedly attached to the crane boom 3. The first snatch block 10 could preferably be arranged near the end of the crane boom 3 connected to the main mast 2 of the crane 1 .

The second snatch block 1 1 is connected to the yoke 8 or forms a part of the yoke 8. The second snatch block 1 1 is adapted to glide along with the yoke 8 between the end positions 13a, 13b in the glide path 13. The wire or rope 9 is attached to either the first snatch block 10 or the second snatch block 1 1 and extending a number of times around and between the snatch blocks 10, 1 1 before the wire or rope 9 is extending towards a winch 12. The winch or electrical driving device 12 is preferably arranged at the upper side of the crane boom 3. The winch 12 is also preferably situated further away from the main mast 2 than the glide path 13, as shown especially in figure 8. The position of the winch 12 is not however limited to this position. The winch 12 could have other arrangements or positions on the crane boom 3.

The winch 12 and the first snatch block 10 are preferably arranged on opposite sides of the longitudinal direction of the glide path 13. It is important to have a little distance between the snatch block 10 because this makes it easier to spool the wire or rope 9 onto the snatch blocks 10, 1 1 . The forces that are required for moving the second strut end 4b by the electrical driven device, such as the winch 12 could therefore be reduced because of plurality of wire-lengths or rope-lengths 9 are extending between the first and second snatch 10, 1 1 . The lengths are extending in parallel flights between the first and second snatch blocks 10, 1 1 .

The tackle system thus reduces the forces that the electrical driven device of the winch 12 has to perform on the second strut end 4b to move the second strut end 4b in the glide path 13.

Figure 5 and 6 shows a detailed view of the lifting mechanism 5 according to the embodiment as described in relation to figure 4. These figures are perspective viewed. The yoke 8 has two yoke parts 8a, 8b arranged at both sides of the second snatch block 1 1 . The figure 5 shows the yoke parts 8a, 8b slidingly or movably arranged within the crane boom 3. In the figures there is arranged a top structure 14 elevated from the remaining crane boom 3. The top structure 14 and parts of the crane boom 3 forms a groove 15 on both sides of the second snatch block 1 1 where the yoke parts 8a, 8b could rest and slide within. The grooves 15 could have different designs. Figure 5 shows a sectional cut between the top structure 14 and the crane boom 3. For illustrations purposes figure 6 shows a continuously designed top structure 14 where the yoke 8 parts are covered completely within the crane boom 3. Figure 7 shows the crane from figure 6, viewed from the side. In this figure it is illustrated that the sliding mechanism 5 are arranged within the crane boom 3.

In this case the sliding mechanism 5 is arranged in the upper part of the crane boom 3 of geometric reasons to obtain a better force reaction. The winch 12 is situated on the upper surface of the crane boom 3.

Figure 8 shows a section inside the crane boom where a part of the crane boom is removed. The lifting mechanism with the glide path13, the first and second snatch block 10, 1 1 and yoke 8 are shown in detail in this figure.

A part of the strut 4 is extending at the inside of the crane boom 3. There is thus a crane boom cover 3c extending downwardly on each longitudinal side of the crane boom 3 covering a part of the strut 4. . A slit 3d is formed between the crane boom covers 3c where the strut 4 is adapted to move as shown in the figure 7-9.

Figure 9 shows a perspective view of the crane 1 where the crane boom 3 is in the uppermost position.

This position of the crane 1 is further shown in detail in figure 10-13, viewed from different sides of the crane 1 . The yoke 8 with the second snatch block 1 1 is positioned at the end second end position 13b in the glide path 13 close to the first snatch block 10.

The functioning of the low building crane according to the embodiment as shown in figure 3-13 shall be further described below:

In the resting position of the crane 1 as shown in Figure 3-8, the crane boom 3 is arranged substantially horizontal. The yoke 8 with the second end of the strut 4b is in this position situated in the first end position 13a of the glide path 13.

When lifting operation is to be perform by the crane 1 , the winch 12 will pull in the wire 9. This results in that the first and second snatch block 10, 1 1 that are in contact with the wire 9 will be pulled towards each other. Since the first snatch block is fixedly attached to the crane boom 3, it will be the second snatch block that moves towards the first snatch block 10. The second snatch block 1 1 is connected to the yoke 8 and second end of the strut 4b which means that the second end of the strut 4b moves accordingly towards the first snatch block 10.

The strut 4 has a fixed length which results in a compression force S along the longitudinal axis of the strut 4 when the force F from the lifting arrangement 20 acts on the yoke 8. The lifting forces are acting along the longitudinal axis, (shown as the axis C in fig 3 and 9) of the crane boom 3, along the glide path 13. The resulting force R is an upwardly directed lifting force on the upper side of the glide path 13. The lifting arrangement 20 and the strut 4 performs the lifting force on the crane boom 3 until the second snatch block 10 is moved to the second end point 13a of the glide path 13. The crane boom 3 is now in the uppermost position as shown in Figure 9-13.

The forces acting on the crane boom 3 are illustrated in Figure 4 as S, F and R.

Figure 14, 15 and shows further embodiments of the invention. Instead of the winch 12 and tackle mechanism 5 to perform the lifting operation, as shown in Figure 3-13, the lifting operation could be performed in other ways for instance with a screw mechanism 50 or a rack and pinion mechanism 70, 80. These arrangements 50, 70, 80 being the sliding mechanism.

The figures show principle sketches of the mechanism 50, 70, 80 that could replace the winch and wire arrangement 12, 9 for displacing the strut end 4b between two end positions in the crane boom 3.

The screw mechanism 50 could be arranged as a replacement of the tackle system as shown in figure 3-13 or in addition to the tackle system, only replacing the winch 12 and wire 9 of the previously described arrangement. The screw mechanism 50 shown in the figure 14 has a frame structure 51 which could be arranged in the crane boom 3. The screw mechanism 50 comprises further a rod 54 with helical grooves arranged within the frame 51 . The rod 54 is adapted to rotate around its longitudinal axis by an electrical driving device 53.

A movable device, for instance a beam 52, having an opening suitable to mate with the rod 54 so that the beam 52 moves along the rod 54 when the rod 54 rotates. The end of the strut 4b could be connected to the beam 52 so that the strut end 4b moves accordingly, when the rod 54 is rotated. The direction of the rotation defines in which direction the strut end 4b moves. The short sides 51 a, 51 b of the frame 51 defines in this embodiment, the end positions of the strut end 4b. The strut end 4b could also comprise an arrangement with an opening so that the strut end 4b could mate with the rod 54 and be moved along the rod 54 directly.

If the screw mechanism is arranged in connection with the tackle system 5 from figure 3-13, the movable rod 54 could be coupled to a wire or rope 9 in order to move the strut 4.

Figure 15 and 16 shows a typical rack and pinion arrangement 70, 80 that could be used instead of the winch 12, rope or wire 9 and the tackle and rope mechanism 5 with the first and second snatch blocks 10, 1 1 .

The strut end 4b is in this embodiment coupled to the rack or pinion and the crane boom is coupled to the other part of the rack or pinion. This results in that the strut end 4b moves in relation to the crane boom 3 along the longitudinal axis of the crane boom 3.

Figure 17-21 shows another embodiment of the low building electric crane according to the invention.

The parts that are similar in the embodiments have the same reference number in the drawing.

In this embodiment, the crane has a strut 1 1 1 that has a first strut part 1 12 and a second strut part 1 13 that are telescopically moveable in relation to each other.

Figure 17 shows the crane 1 10 in the resting position with the second strut part 1 13 retracted within the first strut part 1 12.

Figure 18 shows the crane in the lifting position where the second strut part 1 13 is protruding from the first strut part 1 12 so that the strut length of the strut 1 1 1 is prolonged.

An electric driving mechanism 1 15, such as an electric motor is attached to the strut 1 1 1 to perform the movement of the second strut part 1 13.

The embodiment with the strut extendable lifting arrangement is shown in detail in figure 19-21 .

Figure 19 shows a detail view of the crane 1 10 in the resting position with the second strut part 1 13 arranged within the first strut part 1 12. The first strut part 1 12 is in the embodiment pivotably attached to the vertical main mast in on end 1 12a. The attachment could for instance be through a bracket 6 that is fixedly attached to the main mast 2. This is similar to the embodiment as disclosed in figure 3-13. The second strut 1 13 is in one end pivotably connected to the crane boom 3. The attachment to the crane boom 3, could for instance be through a bracket 1 14 that is fixedly attached to the crane boom 3. The bracket 1 14 is arranged at the underside of the crane boom 3. The second strut part 1 13 and the pivotable connection to the crane boom 3 is shown in greater detail in figure 20-20. In these figures, the crane 1 10 is in the same position as shown in figure 18, where a part of the second strut part 1 13 is extending from of the first strut part 1 12. The crane boom 3 is then lifted in the vertical direction compared to the position shown in figure 17 and 19.

The opposite ends 1 12b, 1 13b than the pivotable connected ends 1 12a, 1 13a of the first and second strut part 1 12, 1 13 are telescopically connected to each other. This results in that the first and second strut part 1 12, 1 13 are adapted to move in relation to each other along the longitudinal axis. The longitudinal axis of the strut 1 1 1 is indicated with the line L in figure 20.

The second strut part 1 13 could have threads 1 16 arranged along the outer surface of the second strut part 1 13. The threads 1 16 could be arranged along the whole or partly around the outer surface of the second strut part 1 13.

The first strut part 1 12 could have a disc 1 17 with an opening that is adapted to mate with the threads 1 16 in the second strut part 1 13.

The electrical motor 1 15 is preferably connected to the first strut part 1 12 to rotate the disc 1 17 or the first strut part 1 12. This is similar to a linear actuator.

The threads 1 16 are arranged helically so that when the disc 1 17 or the first strut part 1 12 is rotated around the longitudinal axis L of the strut 1 1 1 , the second strut part 1 13 is forced out of or into the first strut part 1 12 resulting in either that the strut 1 1 1 is extended or shortened depending on the direction of rotation.

Other embodiments of the strut 1 1 and the lifting arrangement are also possible.

For instance, the second strut part 1 13 with the threads 1 16 could be pivotably attached to the vertical main mast 2. The first strut part 1 12 could then be pivotably connected to the crane boom 3.

It is also possible that the electrically driven device 1 15' is operable coupled to the second strut part 1 13 in order to rotate the second part 1 13 into or out of the first strut part 1 12. This is illustrated in figure 22. The present invention has been described with reference to a preferred embodiment and some drawings for the sake of understanding only and it should be clear to persons skilled in the art that the present invention includes all legitimate modifications within the ambit of what has been described hereinbefore and claimed in the appended claims.