MOUSEHOLE APPARATUS

Abstract

An arrangement to dampen an impact of a pipe or a set of pipes falling down from a deck includes a first set of bars each of which is bent and a bottom plate configured to form a receptacle for the pipe or the set of pipes falling down from the deck. The arrangement is configured to be connectable to the deck.

Description

CROSS REFERENCE TO PRIOR APPLICATIONS

[0001] This application is a U.S. National Phase application under 35 U.S.C. .sctn.371 of International Application No. PCT/EP2014/066133, filed on Jul. 28, 2014 and which claims benefit to Norwegian Patent Application No. 20131103, filed on Aug. 12, 2013. The International Application was published in English on Feb. 19, 2015 as WO 2015/022175 A2 under PCT Article 21(2).

FIELD

[0002] The present invention relates to an apparatus for dampening the impact of falling pipes or sets of pipes in a mousehole.

BACKGROUND

[0003] Mouseholes are used as temporary holes on drilling decks to connect lengths of pipes before they are introduced into a well, and for breaking out the same set of pipes after usage in the well. The mousehole is normally arranged in the proximity of the well center on the drilling deck, and extends vertically down from the drilling deck towards the surface of the sea. A mousehole is in principle a hollow tube to help the making and breaking of stands with or without an elevating system inside, usually denoted as a "rabbit". Mouseholes have developed from one single hole in the ground on rigs arranged onshore, to more technically advanced solutions on offshore installations such as drilling or intervention vessels or rigs. Challenges have been experienced with these offshore solutions from the very beginning. These challenges relate to pipes arranged in the mousehole sometimes being dropped down into the hole, either as a result of an accident and/or an incautious operator. If a pipe or set of pipes is dropped down the hole, the pipe will go straight through the mousehole, and possibly through anything lying underneath the mousehole. This could cause severe damage to, for example, a floating installation, or even to a wellhead arranged on the seabed. This can again lead to a release of well fluid, and consequently serious discharge damages, and/or be dangerous for personnel on the rig.

[0004] Various types of dampening devices to dampen the impact of falling pipes or sets of pipes have therefore been developed, some of which are described in NO 330793 B1, WO 2010/050821, WO 2007043891, U.S. Pat. No. 3,689,060, U.S. Pat. No. 5,468,121 and U.S. Pat. No. 3,966,054.

[0005] NO 330793 B1 describes a device to dampen the impact when a pipe or a stand of pipes falls down in a mousehole device, the mousehole device comprising at least one tube with a bottom that is set up to receive a pipe or a pipe stand. The at least one tube is connected to a first end of at least one stretch element which, at its other end, is connected to a deck or a structure which has a fixed connection to the deck. The at least one stretch element is set up to undergo a plastic deformation without breaking when subjected to a falling pipe or pipe stand that exceeds a certain kinetic energy.

[0006] Some systems exist which in principle have the same function, i.e., to absorb a falling pipe inside a mousehole. However, in these systems, either the effective drop height is too small, so that they are only able to absorb low energies, or, as is described in NO 330793 B1, the systems can only be used for new mousehole installations which do not incorporate elevating systems (winch and wire, external hydraulic cylinders, etc.) and which are sensitive to fatigue loading by reacting on operational loads.

SUMMARY

[0007] An aspect of the present invention is to solve at least one of the drawbacks related to the prior art.

[0008] An aspect of the present invention is to provide an alternative solution for absorbing and/or releasing the energy of a falling pipe or set of pipes from an accidental drop having high kinetic energy.

[0009] An aspect of the present invention is to provide an arrangement which can be adapted for use on every type of mousehole, with and without elevating systems.

[0010] An aspect of the present invention is to provide an arrangement that can be used on mouseholes that have already been installed, as well as on those mouseholes that are to be installed on a rig.

[0011] In an embodiment, the present invention provides an arrangement to dampen an impact of a pipe or a set of pipes falling down from a deck which includes a first set of bars each of which is bent and a bottom plate configured to form a receptacle for the pipe or the set of pipes falling down from the deck. The arrangement is configured to be connectable to the deck.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is described in greater detail below on the basis of embodiments and of the drawings in which:

[0013] FIG. 1 shows an overview of the present invention as part of an offshore arrangement;

[0014] FIG. 2 shows an enlarged view of the marked section in FIG. 1, showing an embodiment of the present invention;

[0015] FIG. 3 discloses, A) an example of a bar having 7 bends, and, B) an example of a bar having 5 bends;

[0016] FIG. 4 discloses a detailed top-view of the connection frame for connection between the bars and the main deck;

[0017] FIG. 5 shows a view along section A-A in FIG. 4;

[0018] FIG. 6 shows a side-view of the present invention; and

[0019] FIG. 7 shows a view along section C-C in FIG. 6 disclosing details of a bottom plate of the present invention.

DETAILED DESCRIPTION

[0020] The present invention relates to an arrangement for dampening the impact of a pipe or set of pipes falling down from a deck, the arrangement comprising at least a first set of bars and a bottom plate forming a receptacle for the falling pipe or set of pipes, wherein the bars in the at least first set of bars are bent. The term "receptacle" should be understood as any device of basket or container shape, which device is applicable to receive and hold a falling object.

[0021] In an embodiment of the present invention, the arrangement can, for example, comprise at least a second set of bars. The bars in the at least first and/or second set of bars, or any successive additional set of bars, may be bent or straight, dependent on the required dampening effect.

[0022] In an embodiment of the present invention, each set of bars can, for example, comprise at least one bar, two bars, or a plurality of bars, for example, four bars. In order to have as low a reaction as possible on the main deck, a ductile steel can, for example, be used to provide a high degree of elongation, i.e., a plastic deformation, before rupturing. In order to avoid shock load on the main deck, which could be very harmful due to the high speed of the falling object, the current arrangement comprises at least two sets of bended bars, wherein each set of bended bars has a different number of bends. The inventive arrangement absorbs the energy of the impact while unfolding the bends in the first set of bars, taking advantage of bending stiffness, as well as when some of the bars are already in axial stretch, i.e., unfolded, while the bars in the second set of bars are still bent, thereby creating a much "softer" absorption and a step-wise dampening effect.

[0023] The number of bends in each bar may vary and the bends may follow successively along the length of the bar with or without any straight portions between each bend.

[0024] In an embodiment of the present invention, the first set of bars can, for example, be adapted for elastic deformation before plastic deformation.

[0025] In an embodiment of the present invention, the second set of bars can, for example, be adapted for elastic deformation before plastic deformation.

[0026] The first set of bars may be adapted for a two-step deformation; it may first be subject to elastic deformation, and secondly be subject to plastic deformation.

[0027] The second set of bars may be adapted for elastic deformation after which the first set of bars is subject to elastic deformation.

[0028] In an embodiment of the present invention, the bars in the different set of bars can, for example, be arranged in a spaced-apart relationship around a circumference forming the receptacle, e.g., every other set of bars being from different sets of bars or, alternatively, being grouped.

[0029] In an embodiment of the present invention, each set of bars can, for example, comprise an equal number of bars.

[0030] The arrangement may comprise a wave protection device for the at least first set of bars. In an embodiment, the wave protection device comprises a structure surrounding the at least first set of bars to reduce the impact of waves on the arrangement.

[0031] In an embodiment of the present invention, the bars can, for example, be made of steel, for example, an austenite composition, in order to have as low a reaction as possible on the main deck while allowing for a high elongation before rupture.

[0032] From tests, very good results on the austenitic steel in the annealed condition type X2CrNiMo17-12-3 (Number 1.4432) have been achieved. This material has proven to allow a very high elongation (around 45%) with an ultimate tensile strength of minimum 520 MPa.

TABLE-US-00001 Minimum Guaranteed Values Typical Values (10 mm plates) Y.S. 0.2% Y.S. 1% UTS Y.S. 0.2% Y.S. 1% UTS .degree. C. .degree. F. MPa Ksi MPa Ksi MPa Ksi MPa Ksi MPa Ksi MPa Ksi El % 20 68 220 32 260 38 520/670 76/98 310 44 350 51 580 85 45

[0033] This material can be welded to carbon steel by using a high nickel type of austenitic metal, such as type 309 or Inconel.RTM. 625. The filler metal can be mixed with about 30% of the carbon steel, but still have enough nickel to remain austenitic. For large weld grooves, the carbon steel side is buttered with high nickel, and the remaining weld groove can be completed with ordinary type 316L filler. Welding can, for example, be performed in non-elongated areas of the material.

[0034] The arrangement may further comprise a frame for connection to a deck.

[0035] In an embodiment of the present invention, the frame can, for example, be connected to the deck and to the at least first set of bars. The frame may be used as a connection between the bended bars and the deck in order to spread the reaction forces over a larger area of the deck. The connection between the bars and the frame and main deck can be as welded connections as set forth below:

[0036] 1. Weld material should be with the same austenitic material as the bars so that the elasticity is similar and no high stress point appears in the bar-weld interface.

[0037] 2. The welded bar ends should be wider and the transition should be smooth, as a test bar, in order to provide that the connection is not the weak point, and the elongation is on the bar's free length.

[0038] Although the present invention has been described in different aspects and embodiments, it should be clear that any aspect or embodiment of the present invention may be combined with any of the other aspects or embodiment(s). It is, for example, possible to arrange a third, fourth, fifth, sixth etc. number of sets, to provide an even more step-wise dampening effect of the falling object.

[0039] These and other characteristics of the inventive arrangement for dampening the impact of falling pipes or sets of pipes falling into a mousehole will be clear from the following description of an embodiment, which is provided as a non-restrictive example, with reference to the attached drawings.

[0040] FIG. 1 shows an overview of the present invention as part of an offshore arrangement where the inventive damping arrangement 5 for dampening the impact of a falling pipe or set pipes is highlighted in the rectangle. The upper part of the mousehole is connected to a drill floor 8 (shown as a plate in FIG. 1). The total length of the shown mousehole has a size of approximately 21 m, the dampening arrangement 5 making up approximately 4 m of the total length. A frame 4, forming an upper part of the dampening arrangement 5, is further connectable to a deck (not shown) on a platform. In the disclosed embodiment, the damping arrangement 5 is provided with a wave protection device 9 for the bended bars 2, 3, which is shown as a hollow structure 9 surrounding the bended bars 2, 3. The hollow structure 9 may be of a rectangular or a cylindrical shape. A bottom plate 1 closes off the bottom of the mousehole.

[0041] FIG. 2 shows an embodiment of the inventive damping arrangement 5. The arrangement 5 comprises a stiff bottom plate 1 connected to two or more bended bars 2, 3. The bended bars 2, 3 are connected to a deck (not shown) by a frame 4. Each bended bar 2, 3 forms part of a set of bars having the same number of bends 6 and or the same length in a folded state and in an unfolded state, i.e., after elastic deformation (and possibly plastic deformation) has taken place. The bended bars 2, 3 can be custom designed in order to achieve the requested energy absorption, depending on the accidental drop height and stand weight.

[0042] In order to connect the present invention to existing decks or platforms, a rigid frame 4 is provided which allows for the dissipation of the reaction force on the deck (not shown). The frame 4 can be designed to lower the compression stress on the deck as low as is needed depending on the number of bended bars 2, 3 and the dimensions of the bottom plate 1.

[0043] The bended bars 2, 3 may vary in its geometry and section. The disclosed embodiment shows an arrangement having two sets of bended bars 2, 3 (the first set of bended bars 3 has five bends, and the second set of bended bars 2 has seven bends) in a symmetrical arrangement. Every bended bar 2, 3 is paired across from a similar bended bar 2, 3 to avoid a tilting of the bottom plate 1.

[0044] FIG. 3 A discloses an example of a bended bar 2 having seven bends 6, while FIG. 3 B discloses an example of a bended bar 3 having five bends 6. As is clear from the drawings, the bended bars 2, 3 have the same lengths when in the folded/bended position, but, due to the different number of bends 6, the bended bars 2, 3 may have a different length in the unfolded position. If a damping arrangement 5 comprises two different sets of bended bars 2, 3 having two different number of bends 6, e.g., five and seven bends 6, the set of bars comprising the bended bars 3 having five bends 6 will elastically deform so that, when the five bends 6 are in an unfolded/non-bended position, the bended bars 2 having seven bends 6 will be in bending deformation.

[0045] The lower parts of the bended bars 2, 3 may be reinforced, e.g., have a thicker material i.e., larger cross-section, for connection with the bottom plate 1 (compare element 1 FIG. 1). The upper parts of the bended bars 2, 3 may similarly also be reinforced for connection with the frame 4 (compare element 4, FIG. 1) or the deck.

[0046] FIG. 4 discloses a detailed top-view of the frame 4 for the connection between the bended bars 2, 3 and the deck. The frame 4 is typically a solid frame of rectangular or circular shape, fabricated with normal carbon steel. A number of connection holes 7 are arranged in a spaced apart relationship around the circumference of the frame 4. The connection holes 7 are adapted to connect with the deck (not shown in FIG. 4). The connections between the spaced-apart bended bars 2, 3 and the frame 4 are similarly illustrated. The frame 4 is provided with a central through-going opening.

[0047] FIG. 5 shows a view along section A-A in FIG. 4 disclosing a side-view of the frame 4.

[0048] FIG. 6 shows a side-view of the inventive damping arrangement 5 disclosing a first and a second set of bended bars 2, 3 where only two of the bended bars 2, 3 in each set are shown.

[0049] FIG. 7 shows a view along section C-C in FIG. 6 disclosing details of a bottom receiving part, e.g., a bottom plate 1, of the inventive damping arrangement 5. The connection points between the bended bars 2, 3 and the bottom plate 1 is also illustrated. The connections may be any connections known to the person skilled in the art.

[0050] The embodiment of the present invention as shown in the drawings dampens falling objects, such as pipes or sets of pipes, when falling into a mousehole. The embodiment is also adaptable to every type of mousehole, with or without elevating systems, for both existing and for new installations.

[0051] In the preceding description, various aspects of the arrangement according to the present invention have been described with reference to the shown embodiment. For purposes of explanation, specific numbers, systems and configurations are set forth in order to provide a thorough understanding of the arrangement and its workings. This description is not, however, intended to be construed as limiting. Various modifications and variations of the shown embodiment, as well as other embodiments of the arrangement, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention as set forth in the claims.

Claims

1-12. (canceled)

13. An arrangement to dampen an impact of a pipe or a set of pipes falling down from a deck, the arrangement comprising: a first set of bars each of which is bent; and a bottom plate configured to form a receptacle for the pipe or the set of pipes falling down from the deck, the arrangement being configured to be connectable to the deck.

14. The arrangement as recited in claim 13, wherein the arrangement further comprises a second set of bars.

15. The arrangement as recited in claim 14, wherein each of the second set of bars is bent.

16. The arrangement as recited in claim 14, wherein the first set of bars and the second set of bars together create a step-wise dampening effect.

17. The arrangement as recited in claim 14, wherein, the receptacle is formed around a circumference, and the first set of bars and the second set of bars are arranged so as to have a spaced-apart relationship around the circumference.

18. The arrangement as recited in claim 14, wherein each of the first set of bars and the second set of bars comprises at least one bar.

19. The arrangement as recited in claim 14, wherein each of the first set of bars and the second set of bars comprises four bars.

20. The arrangement as recited in claim 14, wherein each of the first set of bars and the second set of bars comprises a plurality of bars.

21. The arrangement as recited in claim 20, wherein each of the first set of bars and the second set of bars comprises an equal number of bars.

22. The arrangement as recited in claim 13, further comprising a frame configured to be connected to the deck.

23. The arrangement as recited in claim 22, wherein the frame is connected to the deck and to the first set of bars.

24. The arrangement as recited in claim 13, further comprising a wave protection device for the first set of bars.

25. The arrangement as recited in claim 22, wherein the wave protection device comprises a structure configured to surround the first set of bars.

26. The arrangement as recited in claim 13, wherein the first set of bars are made of steel.

27. The arrangement as recited in claim 26, wherein the steel is an austenite composition.