GB2209322A

GB2209322A - Folding boom

Info

Publication number: GB2209322A
Application number: GB8820686A
Authority: GB
Inventors: Victor Cyril Sessin
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1987-09-02
Filing date: 1988-09-01
Publication date: 1989-05-10
Also published as: GB8720596D0; GB8820686D0

Abstract

A folding boom comprises a first section (35) adapted for connection to a supporting structure (32) and a second section (36) adapted for the reception of a tip mechanism. The first and second sections are pivotally connected to one another and comprise bearings (41, 42) above the pivot for a boom hoist rope (39), so that in use the first and second sections form a rigid linear structure and at rest the second section pivots away from the first to form an angular structure. The boom is particularly suitable for use on a pedestal crane on an offshore platform or similar structure where it releases space for other equipment. The tip mechanism may be a hoisting pulley or a flare tip. <IMAGE>

Description

FOLDING BOOM This invention relates to a folding boom which is especially suitable for use as projecting equipment on offshore oil production and/or drilling platforms or vessels, such as crane booms and flare tips.

Offshore platforms require to be fitted with cranes for hoisting material onto the platform from supply vessels. Slewing boom pedestal jib cranes are generally employed for this work because of their positioning versatility. However, they suffer from certain disadvantages, particularly in their space requirements. When the crane is not in use, the boom is stowed across the deck. This effectively "sterilises" a considerable area of valuable deck space since nothing can be positioned there which would interfere with the subsequent deployment of the crane. The boom sometimes projects beyond the deck which denies vessels access to the platform in the vicinity of the overhang.

These problems are compounded when, as is often the case, more than one crane is present on the same platform, or, in the case of a single crane, a spare boom is positioned for instant deployment if the original boom requires replacement.

In recent years there has been a trend to optimise the space volume occupied by various packages on offshore platforms. As a result, platforms have become smaller and lighter and the available weatherdeck area used for storing containers and for stowing and changing-out crane booms is now at a premium.

A further disadvantage of offshore pedestal cranes is that access to the boom tip is difficult. Sheaves and control equipment which need to be serviced are situated at or near the tip.

The flare system on an offshore platform or vessel must be dimensioned such that the burners are situated a considerable distance away from other equipment on the platform or vessel. This can be done on large structures by situating the burners at the top of tall vertical towers. On small structures, however, this configuration is not feasible because it makes helicopter access difficult, if not impossible, and hence the burners must be supported by a boom projecting away from the platform. The boom may be horizontal, or, more usually, sloping upwards. These booms suffer from a similar problem of lack of access to the tip for burner maintenance and replacement.

We have now devised an improved folding boom which overcomes the above disadvantages.

Thus according to the present invention there is provided a folding boom comprising (a) a first section adapted for connection to a supporting structure and (b) a second section adapted for the reception of tip mechanism, the first and second sections being pivotally connected to one another and comprising bearings above the pivot for a boom hoist rope, so that in use the first and second sections form a rigid linear structure and at rest the second section pivots away from the first to form an angular structure.

In order to save even more space at rest the first section can itself be made of two pivoted sections.

The boom will generally be constructed with a mid-section in the form of a rectangular box girder structure and with end portions, at least one and possibly both of which are pivoted, in the form of pyramidal or wedge shaped structures. The pivot(s) will generally be situated on the underside of the boom. When the boom is extended, the topsides of the folding section(s) may be linked to the top side of the mid-section by clasp or socket joints.

The boom is particularly suitable for use with a pedestal crane.

Thus according to a further aspect of the present invention there is provided a pedestal crane comprising (a) a pedestal, (b) a boom support above the pedestal, (c) a folding boom, (d) boom hoist mechanism and (e) load hoist mechanism; the boom comprising (f) a first section pivotally connected to the boom support and (g) a second section comprising crane boom tip mechanism, the first and second sections being pivotally connected to one another, so that in use, as the boom hoist mechanism is actuated, the boom section comprising the boom tip mechanism is first raised to a position, preferably a horizontal position, coaxial with the section connected to the boom support and locked thereto and both sections are, if required, subsequently raised to a higher operating position.

The above sequence of actions, is, of course, reversible.

If the first section (f) itself contains another pivoted section (for reason of saving storage space as previously explained) these sections should be rigidly connected when the boom is fitted to the crane and should remain rigidly connected during all operations of the crane and while the crane is at rest.

A pedestal crane according to the present invention is particularly suitable for use on an offshore platform, as previously stated, and in this case the boom tip section in its resting position can be dropped towards a deck of the platform or even over a side. In either case, a lay down area immediately beneath can be provided to reach the boom tip for servicing.

Suitable cranes to which the folding boom concept may be applied include slewing boom jib cranes and ram luffing cranes. In the former, a boom hoist rope is used initially to raise the boom tip section and subsequently to raise the entire boom. In the latter, the load hoist rope used initially to raise the boom tip section and subsequently the ram is employed to raise the boom.

The boom of a slewing jib crane is preferably supported at rest by a conventional boom rest positioned adjacent to the pivot on the pedestal side.

As previously stated, the boom is also very suitable for use in supporting an extended flare.

Thus according to another aspect of the present invention there is provided a flare system comprising a folding boom comprising (a) a first section rigidly connected to a supporting structure, (b) a second section connected to the flare tip, the first and second sections being pivotally connected to one another and comprising bearings above the pivot for a boom hoist rope, (c) a boom hoist rope and (d) actuating mechanism for the boom hoist rope, so that, in use, as the boom hoist rope is wound in, the boom section connected to the flare tip is raised to a position coaxial with the section connected to the supporting structure and locked in position.

As with the crane, the flare system is particularly suitable for use offshore whether on a platform or a vessel. As before, at rest, the folding section can be dropped over the side of the platform or the vessel. In this case, however, because the boom has to project considerably beyond the platform or vessel, simply allowing the folding section to pivot freely may still leave the tip suspended in space and inaccessible. In order to reach the tip it may be necessary to continue the pivoting action so that the folding section folds back towards the other and the tip is brought to an accessible position on the platform or vessel. This can easily be done by attaching a pull-in rope at or near the tip.

The invention is illustrated with reference to Figs 1 - 7 of the accompanying drawings wherein: Fig 1 is a schematic elevation of a conventional crane, Figs 2 and 3 are schematic elevations of a crane according to the present invention, Fig 4 is a schematic elevation showing a folding spare boom according to the invention, Fig 5 is a schematic plan of a folding spare boom according to the invention and by way of comparison a conventional spare boom, and Fig 6 is a schematic elevation of a ram luffing crane showing a folding boom in both the folded and unfolded positions.

Fig 7 is a schematic diagram of a flare system incorporating a folding boom.

With reference to Fig 1, a conventional pedestal crane 1 is mounted on the weather deck 2 of an offshore platform. The crane comprises a pedestal 3, a boom support 4, a boom 5, and a boom hoist rope support 6. The boom is supported in the resting position by a boom rest 7. The boom is pivoted at end 8 to the boom support. The boom tip 9 at the other end carries sheaves 10 of the boom hoist rope 11 and sheaves 12 for a load hoist rope (not shown).

With reference to Fig 2, elements other than the boom 5 are as described in Fig 1. The boom in this embodiment is divided into two sections 13 and 14 by fitting a pivot 15 at the bottom chords 16 and 17 of each section. Rollers 18 and 19 are fitted across the top chords 20 and 21 to permit the boom top section to droop progressively as the boom hoist rope 11 is payed out beyond the "normal" boom rest limit. Sterilisation of platform working areas is therefore reduced and important access to the boom head for maintenance is readily gained from the platform weatherdeck level.

Fig 3 shows an alternative arrangement whereby the top section of the boom is drooped over the side of the platform 2 and where access to the boom head can be gained via a local working platform 22.

In the embodiment of Fig 4, the boom section 13 of Fig 2 is itself further divided into two pivoted sections 23 and 24 by means of a further pivot joint 25.

A rough comparison of occupied plan area of the folded boom against a conventional boom is shown in Fig 5.

The ram luffing crane illustrated in Fig 6 comprises a pedestal 31, a boom support 32, a folding boom 33 and a ram 34 mounted between the support and the boom.

The boom is composed of two sections 35 and 36 lockable by a pivot joint 37. Section 35 is pivotally mounted on support 32 and section 36 contains the boom tip mechanism 38.

A load hoist rope 39 is actuated by a winch 40 mounted on section 35 and passes over rollers 41 and 42, mounted on sections 35 and 36 respectively, to the boom tip 38 and hook 43.

In order to raise the boom, the dropped section 36 is first raised to the horizontal position by reeling in the load hoist rope 39 and locked in position. The boom 33, now a rigid structure, is then raised by actuating the ram 34.

With reference to Fig 7, a flare boom 51 is mounted on the edge of an offshore platform 52. The boom is divided into two sections 53 and 54 pivotally connected at 55. Section 54 carries the flare tip 56 at its furthest extremity. A gantry mast 57 supporting a roller 58 is mounted on section 53. A hoist rope 59 controlled by a winch 60 mounted on the platform 52 passes over the roller 58 and is attached to section 54 near the tip.

In normal use, sections 53 and 54 are locked together to form a rigid coaxial structure. When the flare tip requires maintenance, however, the sections are unlocked and the hoist rope 59 is paid out.

This allows the tip section 54 to pivot and drop downwards to assume a vertical position. A pull-in rope 61 is then actuated by winch 62 to continue the pivoting action and draw the tip towards the side of the platform 52 where it can be reached from a lay-down area 63 for maintenance.

After maintenance, the above procedure is reversed to erect the structure.

Claims

Claims:

1. A folding boom comprising (a) a first section adapted for connection to a supporting structure and (b) a second section for the reception of tip mechanism, the first and second sections being pivotally connected to one another and comprising bearings above the pivot for a boom hoist rope, so that in use the first and second sections form a rigid linear structure and at rest the second section pivots away from the first to form an angular structure.

2. A folding boom according to claim 1 wherein the first section is itself made of two pivoted sections.

3. A folding boom according to either of the preceding claims wherein the boom is constructed with a mid-section in the form of a rectangular box girder structure and with end portions, at least one of which is pivoted, in the form of pyramidal or wedge shaped structures.

4. A folding boom according to any of the preceding claims wherein the pivot(s) are situated on the underside of the boom.

5. A pedestal crane comprising (a) a pedestal, (b) a boom support above the pedestal, (c) a folding boom according to any of the preceding claims, (d) boom hoist mechanism and (e) load hoist mechanism; the boom comprising (f) a first section pivotally connected to the boom support and (g) a second section comprising crane boom tip mechanism, the first and second sections being pivotally connected to one another, so that in use, as the boom hoist mechanism is actuated, the boom section comprising the boom tip mechanism is first raised to a position coaxial with the section connected to the boom support and locked thereto.

6. A flare system comprising a folding boom according to any of claims 1 to 4 comprising (a) a first section rigidly connected to a supporting structure, (b) a second section connected to the flare tip, the first and second sections being pivotally connected to one another and comprising bearings above the pivot for a boom hoist rope, (c) a boom hoist rope and (d) actuating mechanism for the boom hoist rope, so that, in use, as the boom hoist rope is wound in, the boom section connected to the flare tip is raised to a position coaxial with the section connected to the supporting structure and locked in position.

7. A folding boom as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.