AU2013348479A1

AU2013348479A1 - Anchor, method of installing a mid water arch with an anchor, use of an anchor, and a mid water arch system for flexible risers comprising an anchor

Info

Publication number: AU2013348479A1
Application number: AU2013348479A
Authority: AU
Inventors: Geir GRIMSRUD; Jorgen Hogmoe
Original assignee: RISER SUPPORT SYSTEMS
Current assignee: RISER SUPPORT SYSTEMS
Priority date: 2012-11-23
Filing date: 2013-11-21
Publication date: 2015-06-04
Also published as: WO2014081317A1; NO337954B1; GB201509616D0; BR112015011868A2; NO20121408A1; GB2523497A

Abstract

The invention meets the demand by providing an anchor for a mid water arch or other use, distinctive in that the anchor (1) comprises an anchor beam (2), a number of slabs (3) arranged onto the anchor beam (2), and anchoring lugs (4, 5, 6) or equivalent means for fastening the lifting or anchoring line, slings or tether. The invention also concerns a method of installing a mid water arch with an anchor, use of an anchor, and a mid water arch system for flexible risers comprising an anchor.

Description

WO 2014/081317 PCT/N02013/050207 Anchor, method of installing a mid water arch with an anchor, use of an anchor, and a mid water arch system for flexible risers comprising an anchor Field of the invention The present invention relates to anchors, particularly anchors for midwater 5 arches. Background of the invention and prior art A traditional anchor for a mid water arch (MWA) is a fixed weight permanent anchor unit. A typical embodiment is a container or bucket that has been filled 10 with concrete, after which the concrete has solidified and the anchor works as a dead weight anchor. Alternative embodiments can be different anchor design, typically with one or more arms that hook or hold into the seabed, providing holding power in addition to the mass. A large number of anchor designs exist, some require intervention on the seabed in order to function properly and most 15 are direction dependent and depend on the seabed condition. A modern anchor embodiment is a suction anchor, which can be lighter but requires means for suction and is relative expensive and complicated in order to function properly. The anchor is connected with an anchoring line to a vessel or a surface or immersed buoy. Other terms for the anchor or anchoring line are rode, tether, 20 chain, cable, rope or line. Since the force is more or less vertical for a mid water arch buoy anchoring line, the anchor should not depend on direction of force or feasible seabed soil conditions, and preferably the anchor should not require any intervention or 25 periodic inspection on the seabed in order to work properly. Anchors relying on their mass are therefore most feasible for mid water arches. If an anchor relying on mass or weight is used, it will typically have a weight of about 250 metric tons. This means that the anchor can not be lifted or 30 transported easily, since solidified concrete not can be removed easily or a traditional two arm anchor can not be disassembled easily. This is a disadvantage, since cranes having sufficient lifting power are expensive. In some situations, an anchor, or the problems for transporting it, can delay a large development project. Due to the weight and size of traditional anchor designs, WO 2014/081317 2 PCT/N02013/050207 they are dependent upon being fabricated within reach of the installation vessel making it necessary to fabricate them close to the waterfront, which limits the options for fabrication places to yards or ports with quay access. Furthermore since the anchors are made from large amounts of massive concrete, they are 5 dependent upon long curing times (minimum 2 weeks) This is a problem since it occupies the quayside which is the most attractive and exclusive part of the fabrication facility. A demand exists for an anchor that is favorable with respect to fabrication, 10 transportation, installation, retrieval and re-use, and the objective of the invention is to meet the demand. Summary of the invention The invention meets the demand by providing an anchor for a mid water arch or 15 other use, distinctive in that the anchor comprises an anchor beam, a number of slabs arranged onto the anchor beam, and anchoring lugs or equivalent means for fastening the lifting or anchoring line, slings or tether. 20 The anchor beam, with or without one or more slabs fastened to the beam, preferably weights 60 metric tons or less in air, together with additional slabs to be installed subsequently the anchor preferably weights about 250 metric tons in air, such that each of the slabs and beam has a weight feasible for lifting in 25 air with a typical yard or vessel crane. This assumes a safe working load of 60 tons for the crane, at feasible extension or reach-out, however, if other loads are safe for lifting, the weights can be adjusted accordingly. Thus substantial savings can be made since the anchors can be made such that the anchor or the parts thereof is possible to transport on road. The anchors can be fabricated 30 on any yard or workshop with road access, which increases the numbers of fabrication opportunities, thus reducing cost and makes it possible to fabricate anchor and buoy simultaneously and thereby accelerating the fabrication schedule.

WO 2014/081317 3 PCT/N02013/050207 Transport and handling is made simpler and more cost effective since all parts of the anchor can be handled and transported separately by road. Dispensation for road transport of parts weighting up to 60 metric tons is likely to achieve, if not the part weights must be adapted to the maximum allowable weight for 5 transport by separating each 60 ton part into lighter parts that can easily be assembled. Weight of each part can be 80 ton or higher, 60 ton, 40, ton, 20 ton or whatever weight is safe and allowable for transport and handling at the actual sites. 10 The load bearing function is concentrated to the beam, which is made predominantly in steel to resist tension forces. This design ensure that the steel properties is utilized in a more optimum way which give the benefit of reduced steel weight compared to traditional anchor design, which yields reduced material cost 15 Preferably the slabs are arranged transverse to the beam, in one layer, preferably each slab weights 60 metric tons or less in air. Preferably the slabs have a recession or cut out adapted to rest over and along the top surface and side surfaces of the beam, preferably the slabs and beam have matching 20 conical cross section shape or recession or cut out, so as to fit by landing the slabs on the beam, and preferably the slabs or beam or both comprises means for releasable and/or permanent fastening. The anchor beam preferably comprises lifting lugs or equivalent and anchoring 25 lugs or equivalent, and slabs for subsequent installation comprises lifting lugs, ears or equivalent means for attaching a lifting sling or line. With the anchor beam comprising both lifting lugs, for the crane lifting sling, and anchoring lugs for the tether, both of which can be used at the same time, it is possible to deploy a complete mid water arch using a smaller capacity crane, which will be 30 clear from the description below. Preferably the beam has slab landing recessions or cut outs, allowing the slabs to land in correct position so as to land for example 3 slabs side by side on the beam, in intended positions.

WO 2014/081317 PCT/N02013/050207 The invention also provides a method of installing a mid water arch with an anchor according to the invention, distinctive in that: an anchor beam, including a number of slabs fastened to the beam up to 5 a total weight to be lifted safely by an available crane, and with a tether or anchoring line attached, is lifted in air and deployed into the sea, after which the tether is arranged to a mid water arch buoy, starting with the anchor immersed and the buoy in the air or on deck of an installation vessel, the mid water arch is deployed down to the seabed at the 10 intended position, optionally facilitated by additional means such as positioning devices and remotely operated vehicles, whereby the anchor firstly is in the water whilst the buoy is in the air, after which both the anchor and the buoy are submerged and deployed, and the anchor is landed on the intended position on the seabed, and 15 slabs are optionally added to the beam until the intended weight as immersed is reached. If required due to crane lifting capacity, slabs are added to the beam whilst the beam is submerged but before the beam is deployed down to the seabed, the 20 submerged beam hanging in the tether. The beam is initially lifted, with a number of slabs from nil to the number to reach but not exceed the safe working load for the required reach out of the crane. Any slabs preinstalled to the beam before lifting are preferably permanently fastened to the beam, whilst subsequently added slabs are preferably releasably fastened if they are added 25 when the beam hangs submerged from the vessel. Post-installed slabs can of course as an alternative be landed in intended positions on the beam when the beam is on the seabed. However, a step distinguishing the anchor and method from all prior art anchors and installation methods known to the applicant, is the adaptations for and the step to land slabs when the anchor is submerged but 30 before the anchor is landed on the seabed. This allows a simpler installation procedure for several reasons, such as adding beams when the anchor is near the vessel and crane compared to on the seabed, and to use the crane and vessel capabilities in an optimal way by using the full crane and vessel capacities by adapting the weights, reach outs and deployment distances WO 2014/081317 5 PCT/N02013/050207 better. The savings in time and money are significant. The slabs installed when the anchor is submerged but not landed on the seabed, are preferably fastened safely to the beam upon landing into spring loaded lockers, such as conical locking dogs or similar, on the beam and/or the slab. 5 Preferably the anchor, as lifted from the crane initially or with added weight by adding slabs with the anchor submerged but before lifting and submerging both the anchor and buoy for deployment, have a weight sufficient for holding the buoy when the anchor is landed on the seabed. Accordingly, the mid water arch 10 with an anchor of the invention can be safely submerged and deployed before flexible risers are landed on and fastened to the mid water arch buoy. The invention also provides a mid water arch for flexible risers, comprising a mid water arch buoy, an anchor and a tether connecting the anchor and buoy, 15 distinctive in that the anchor comprises an anchor beam, a number of slabs arranged onto the anchor beam, and anchoring lugs or equivalent means for fastening the lifting or anchoring line, slings or tether. The mid water arch can be transported and deployed easier 20 and at lower cost than other known mid water arches, using the method of the invention. The invention also provides use of an anchor according to the invention, for a mid water arch for flexible risers. 25 The anchor and mid water arch of the invention may comprise any feature as here described or illustrated, in any operative combination, and each such operative combination is an embodiment of the invention. The method of the invention may comprise any feature or step as here described or illustrated, in 30 any operative combination, and each such operative combination is an embodiment of the invention. Figure The invention is illustrated with one figure, namely WO 2014/081317 6 PCT/N02013/050207 Figure 1, illustrating an embodiment of an anchor of the invention. Detailed description Reference is made to Fig. 1, illustrating an embodiment of an anchor 1 of the 5 invention, comprising an anchor beam 2, two slabs 3 arranged on the anchor beam, and anchoring lugs 4, 5 and lifting lugs 5, 4. The anchor preferably comprises separate anchoring and lifting lugs or equivalent, since this is preferable for allowing the use of a lighter crane, however it is not obligatory since the same lugs or equivalent can be used for both the lifting slings and the 10 tether. The slabs comprise separate lifting lugs 6. Preferably the slabs are releasably fastened to the beam if it is a possibility for lifting up the mid water arch anchor using a small capacity crane, by lifting the anchor in pieces. The releasable fastening can preferably be unlocked by an ROV (Remotely Operable Vehicle), for example by grabbing and pressing together handles in 15 order to unlock a connected locking dog or similar with the ROV manipulator. For the illustrated anchor, a vacant space for an additional slab 3b is provided between two slabs 3 to be pre-fastened or fastened during installation or subsequently, as described. The two pre installed slabs illustrated, have been bolted to the beam before installation commences.

Claims

1. Anchor for a mid water arch or other use, c h a r a c t e r i s e d i n that the anchor comprises 5 an anchor beam, a number of slabs arranged onto the anchor beam, and anchoring lugs or equivalent means for fastening the lifting or anchoring line, slings or tether. 10

2. Anchor according to claim 1, wherein the anchor beam, with or without one or more slabs fastened to the beam, weights 60 metric tons or less in air, together with additional slabs to be installed subsequently the anchor weights about 250 metric tons in air, such that each of the slabs and beam has a weight feasible 15 for lifting in air with a typical yard or vessel crane.

3. Anchor according to claim 1 or 2, wherein slabs are arranged transverse to the beam, in one layer, preferably each slab weights 60 metric tons or less in air. 20

4. Anchor according to any one of claim 1 - 3, wherein the slabs have a recession or cut out adapted to rest over and along the top surface and side surfaces of the beam, preferably the slabs and beam have matching conical cross section 25 shape or recession or cut out, so as to fit by landing the slabs on the beam, and preferably the slabs or beam or both comprises means for releasable and/or permanent fastening.

5. 30 Anchor according to any one of claim 1-4, wherein the anchor beam comprises lifting lugs or equivalent and anchoring lugs or equivalent, and slabs for subsequent installation comprises lifting lugs, ears or equivalent means for attaching a lifting sling or line. WO 2014/081317 8 PCT/N02013/050207

6. Anchor according to claim 1-5, wherein the beam has a slab landing recessions or cut outs, allowing the slabs to land in correct position so as to land for example 3 slabs side by side on the beam, in intended positions. 5

7. Method of installing a mid water arch with an anchor according to any one of claim 1-6, characterised in that an anchor beam, including a number of slabs fastened to the beam up to 10 a total weight to be lifted safely by an available crane, and with a tether or anchoring line attached, is lifted in air and deployed into the sea, after which the tether is arranged to a mid water arch buoy, starting with the anchor immersed and the buoy in the air or on deck of an installation vessel, the mid water arch is deployed down to the seabed at the 15 intended position, optionally facilitated by additional means such as positioning devices and remotely operated vehicles, whereby the anchor firstly is in the water whilst the buoy is in the air, after which both the anchor and the buoy are submerged and deployed, and the anchor is landed on the intended position on the seabed, and 20 slabs are optionally added to the beam until the intended weight as immersed is reached.

8. Method according to claim 7, whereby slabs are added to the beam whilst the 25 beam is submerged but before the beam is deployed down to the seabed, the submerged beam hanging in the tether.

9. Method according to claim 7 or 8, whereby the anchor, as lifted from the crane 30 initially or with added weight by adding slabs with the anchor submerged but before lifting and submerging both the anchor and buoy for deployment, have a weight sufficient for holding the buoy when the anchor is landed on the seabed.

10 WO 2014/081317 PCT/N02013/050207 Use of an anchor according to any one of claim 1-6, for a mid water arch for flexible risers.

11. 5 Mid water arch for flexible risers, comprising a mid water arch buoy, an anchor and a tether connecting the anchor and buoy, c h a r a c t e r i s e d i n that the anchor comprises an anchor beam, a number of slabs arranged onto the anchor beam, and 10 anchoring lugs or equivalent means for fastening the lifting or anchoring line, slings or tether.