WO1990000491A1

WO1990000491A1 - Anchoring device

Info

Publication number: WO1990000491A1
Application number: PCT/NO1989/000072
Authority: WO
Inventors: Olav Bruset; Ronald W. Imrie
Original assignee: Wepco A/S
Priority date: 1988-07-14
Filing date: 1989-07-13
Publication date: 1990-01-25
Also published as: NO164729C; NO164729B; AU3980589A; NO883133L; NO883133D0

Abstract

An anchoring device (1) for a guideline having the form of an elongated body with a bottom anchoring assembly (1a) furnished with spring-loaded retractable (5) locking arms (4) and a top, line-attachment assembly (1b) for the guideline, arranged so as to provide for anchoring to a guidepost, wherein the anchoring assembly (1a) and line-attachment assembly (1b) are held together in anchoring mode by a shear pin (12). The anchoring assembly comprises a barrel piece (7) which is telescopically displaceable relative to a central core (9) fastened to the guideline-attachment assembly (1b), whereby the barrel piece (7) upon shearing of the shear pin (12) is telescopically displaced downward relative to the central core (9) of the anchoring assembly (1a), and wherein said central core (9) and locking arms (4) are furnished with adjacent and collaborating guide surfaces (9b, 4a) which upon downward displacement of the barrel piece (7) are caused to interact with each other and bring about the retraction of the locking arms into their non-locking position.

Description

ANCHORING DEVICE

BACKGROUND OF THE INVENTION

1) Field of the invention

This invention relates to an anchoring device for a guideline between a surface vessel and a subsea installation intended for the guided lowering of tools etc. The anchoring device is otherwise of the type disclosed more fully in the introductory section of the claim no. 1 herein.

2) Description of the prior art

In connection with subsea installations it is imperative to be able to lower tools etc. For this purpose, a sort of "guide wire" is usually strung between the surface vessel and the subsea installations, being materialised in the form of two or several, often four, guidelines of wire, one end of which is furnished with an anchoring device for fastening to the subsea installation. The subsea installation is provided with attachment points for the anchoring devices in the shape of guide posts, which typically contain a cylindrical guide funnel and, at the bottom, a radial shoulder. The anchoring device is arranged so that it may be guided home on the guide post of the subsea installation with the aid of an unmanned submersible craft (remotely operated vessel, ROV); the mating of the anchoring device and the guide post being made by means of spring-loaded, retractably hinged locking arms on the anchoring device, so designed that they move into . ?

the retracted, inactive position during passage through the bore of the guidepost by virtue of the close proximity of the guidepost bore wall, but subsequently by virtue of spring force extend to the outward, active position as soon as passage through the guidepost has been completed, thereby engaging with the lower shoulder of the guidepost. The guideline, the wire, can then be rendered taut by an upward pulling force, after which tools etc may be lowered down the guideline. When the time comes to recover the guideline onto the surface vessel after work is completed, the. locking function between the anchoring device and the associated guidepost must be released. For this purpose the anchoring devices of the prior art are devised in two main assemblies; the one being, in operation, the "top" assembly, to which the guideline is fastened; and the other being, in operation, the "bottom" assembly into which the locking arms are retractably hinged; the two assemblies being releasably fastened to each other by the aid of a transverse shear pin. When firm upward force is applied through the guideline, the shear limit of the shear pin is exceeded, whereupon the pin shears, allowing the top assembly of the anchoring device to be hauled up to the surface, while the bottom assembly of the anchoring device lands on the seabed and is thereby lost.

The bottom assembly of the anchoring device is a relatively costly piece of equipment and considering that on each subsea installation ^• frequent connections are made over a long period of time, the non-recovered bottom assembly of such anchoring devices represents a considerable sum. OBJECTIVE OF THE PRESENT INVENTION

One purpose of the novel equipments disclosed herein is to provide an anchoring device of the type considered for which the entire anchoring device is recoverable upon completion of the work operation. This purpose is accomplished in the equipment of the disclosure by designing the anchoring device in accordance with the characteristics set out in the claims hereinafter stated. BRIEF DESCRIPTION OF THE DRAWINGS The novel equipment is disclosed more fully hereinafter with reference to the exemplary embodiment of the invention shown in the figures, which, while serving to illustrate the invention, is not intended to limit its scope, where:

Figure 1 shows in side elevation/ axial section an anchoring device of the invention in the starting position before effecting engagement with the subsea guidepost, which position is identical with the locked position of the anchoring device once the engagement with said guidepost has been effected;

Figure 2 shows a side elevation/ axial section corresponding to Figure 1 in which the locking arms of the anchoring device have been retracted into the closed position in order to release the locking engagement with the shoulder of the guidepost.

Figure 3 shows a side elevation of a guide post. DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS

The novel anchoring device 1 of the invention is shown in the figures in generally vertical operational position and is generally of the form of an elongated body comprising a "bottom" assembly la, being the bottom assembly in the operating position; and a "top" assembly l , being the top assembly in the operating position.

The top assembly lb of the anchoring device is designed to accommodate fastening of the end of a guideline (not shown) in a manner generally as is known in the prior art. This guideline which typically is a wire, is inserted for the purpose through an axial bore 2 in the top assembly lb until the free end of the wire extends into the wider bore cavity 2a, whereupon locking of the guideline may be effected by flooding the cavity with molten alloy or epoxy resin (not shown). This is done before mating of the top assembly lb of the anchoring device with the other (bottom) assembly of the anchoring device and is known from traditional engineering practices.

The bottom assembly la of the anchoring device 1 is formed and arranged so as to achieve a releasable locking engagement with a subsea guidepost 3, which typically is permanently fixed to a subsea installation (not shown). The nose of the bottom assembly la preferably takes the form of a truncated cone in order to facilitate insertion in the guidepost 3.

One embodiment of the guidepost is shown in detail in Figure 3 which comprises a cylindrical portion 3a and an underlying shoulder 3b.

Serving as locking devices for the anchoring device 1 are two or more, preferably four, locking arms 4 which are retractably hinged on crosspms 5 in axially oriented recesses 6 in a barrel piece (sleeve) 7, a fuller account of which will be given in the ensuing.

The locking arms 4 are normally held in the extended position by means of the leaf springs 8, the one end of which is retained in said barrel piece 7, and the other, free end of which serves to press the associated locking arm 4 radially outward.

The bore of the guidepost 3 for the length of its cylindrical portion 3a is of marginally larger diameter than the diameter of the bottom assembly la of the anchoring device. The spread between the radial extremities of the coincidentally extended locking arms 4 is greater than said bore diameter, though the extension force exerted by the leaf springs 8 outward on the locking arms 4 is not so large as to prevent their being forced shut - thereby assuming their retracted, inactive position - during the passage of the bottom (and therefore foremost) assembly la of the anchoring device through the bore 3a of the guidepost 3. Immediately the locking arms 4 have cleared the lower edge of the guidepost 3, said lower edge being the shoulder 3b, the locking arms 4 snap out again, assuming their extended, active locking position in which they will rest against the shoulder 3b.

The operation of the guideline anchoring device 1 to provide locking engagement with the guidepost 3 may be effected as is known from the prior art by means of a remotely-operated submersible craft (ROV).

When after conclusion of the work task the guideline and anchoring device are required to be recovered to the surface and taken onboard the surface vessel while keeping the anchoring device substantially intact, the locking engagement of the locking arms 4 and guidepost 3 must be amenable to release without loss of any major components.

The bottom assembly la of the anchoring device comprises within the locking arms 4 an elongated central core 9 which in the exemplary embodiment shown in the figures is attached by screw thread at its rear end to an adaptor subassembly 10. This adaptor sub 10 is attached at its rear end to the top assembly b of the anchoring device 1 by means of a crosspin 11. The barrel piece 7 in which the locking arms 4 are retractably hinged, and the adaptor sub 10 and central core 9 screwed together, are releasably connected to each other by means of a transverse shear pin 12. Between said barrel piece 7 and the adaptor sub 10 a compression spring is confined, being in the form of a coil spring 13 which in its inactive, standby position, Figure 1, is compressed. When the shear limit of the shear pin 12 is exceeded, the barrel piece 7 which serves as storage receptacle for the locking arms 4 will be pushed telescopically relative to the central core 9 in the downward direction, as this forward pushing movement upon shearing of the shear pin 12 will be effected partially as a result of the weight of the barrel piece 7 and partially as a result of the pressure of the compressed (energised) coil spring 13.

The shear limit of the shear pin 12 is caused to be exceeded by means of an upward jerk in the grideline anchored in the anchoring device, whereupon the barrel piece 7 is pushed downward as already mentioned relative to the central core 9 of the bottom (foremost) assembly la. while being guided along it. The stroke of this telescopic displacement is limited by the impact of the foremost end 7a of the barrel piece 7 against the engagement shoulder 9a of said central core 9.

In order to achieve a retraction of the locking arms 4 into the inactive position, out of engagement with the guidepost 3, during the telescopic downward displacement of the barrel piece 7 along the central core 9, the front portion of the locking arms 4 and the touching portion of the central core 9 are furnished with mutually interacting guide surfaces, respectively 4a and 9b. Guide surface 9b is formed in the exemplary embodiment of the figures of an upwardly tapering conical section of the central core 9, while the guide surface 4a of the locking arms 4 has an appropriately contoured opposing face. As the barrel piece 7 is axially displaced the touching and interacting guide surfaces 9b, 4a cause the locking arms 4 to rotate about their hinge pins 5 in such manner as to assume their retracted, inactive position upon full displacement, see Figure 2. In this retracted, inactive position the locking engagement of the anchoring device 1 and the guidepost 3 is released, and the anchoring device may be withdrawn through the guidepost 3 and recovered to the surface by hauling in the guideline.

Once the anchoring device 1 has been recovered to the surface it only remains to operate the barrel piece 7 in reverse, reinstating its Figure 1 position, whereupon a new shear pin 12 may be inserted between the barrel piece 7 and the adaptor sub 10.

The normal procedure when releasing the anchor function of the guideline will be to tension up the guideline until the shear pin 12 shears. The guideline is then allowed to slacken off in order to allow the locking arms 4 to be pressed into their recesses 6, whereupon the anchoring device may be hauled to the surface. Practical tests have shown that the shock and attendant recoil resulting from the shearing of the shear pin 12 will in most cases serve to disengage the locking arms 4 from the shoulder without further ado.

It will be noted that a preferably fully penetrating bore through the subsea installation will serve the same purpose as the guidepost 3 shown by way of illustration, provided that suitable locking faces are furnished for the locking arms 4. In another alternative the locking arms 4 may be brought into engagement with axial slots in the cylindrical wall 3a, the upper limits of which slots then serve as the engagement faces for the locking arms 4.

Claims

1. An anchoring device (1) for a guideline having the form of an elongated body with a bottom, anchoring assembly (la) furnished with spring-loaded retractable (5) locking arms (4), and a top, line-attachment assembly (lb) for the guideline, arranged so as to permit anchoring to a guidepost, wherein said anchoring assembly (la) and said line-attachment assembly (lb) are held together in anchoring position by a shear pin (12). characterised in that said anchoring assembly (la) comprises a barrel piece (7) which is telescopically displaceable relative to said guideline-attachment assembly (lb) to which is fastened a central core (9), wherein said barrel piece (7) upon shearing of said shear pin (12) will be displaced telescopically downward^' relative to said central core (9) of said anchoring assembly (la), and wherein said central core (9) and said locking arms (4) are furnished with adjacent and interacting guide surfaces (9b, 4a) which upon downward displacement of the barrel piece (7) are caused to coUaboratively effect the retraction of said locking arms (4) into their non¬ locking position.

2. The anchoring device of claim 1 characterised in that the guide surface (9b) of said central core (9) of said anchoring assembly (la) has the form of an upwardly tapering conical section, and the adjacent interacting guide surface (4a) of said locking arms (4) has an appropriately contoured opposing face.

3. The anchoring device of claim 1 characterised in that there, between said barrel piece (7) and said central core (9), or adaptor subassembly (10), is confined an energised compressive spring (13).

4. The anchoring device of any of the claims aforesaid characterised in that the diameter of the bore of said barrel piece (7) only marginally exceeds the cross-sectional diameter of said central core (9), whereby said central core (9) constitutes a guide for said barrel piece (7) during the latter's said telescopic displacement action, and wherein said central core (9) is provided with an engagement shoulder (9a) which will accept the foremost end (7a) of said barrel piece (7), thereby limiting the displacement stroke of said barrel piece (7).