Method for installing riser pipe

Abstract

To provide a method for installing a riser pipe with excellent workability.SOLUTION: A method for installing a riser pipe 1 comprises an exposure step of exposing an end part 2e of a subsea pipe 2 to the air, and a guide clamp attachment step of attaching, to the end part 2e of the subsea pipe 2, a guide clamp 3 that guides an end part of the riser pipe 1.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for constructing a riser pipe.

Background Art

[0002] Conventionally, there has been a pipe for passing liquids such as oil, which is composed of a subsea pipeline arranged on the seabed, a pipeline arranged in the air, and a riser pipe arranged therebetween and rising vertically. Among such pipes, particularly in the construction for newly installing or renewing the riser pipe, it is necessary to weld the existing subsea pipeline and the newly installed riser pipe in the air at sea.

[0003] However, at sea, due to the action of waves and winds, the relationship between the posture of the existing subsea pipeline and the posture of the newly installed riser pipe is unstable, making welding difficult. Therefore, there is room for improvement in the workability when installing the riser pipe.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the problems in the above background art, an object of the present invention is to provide a method for constructing a riser pipe with excellent workability.

Means for Solving the Problems

[0006] The gist of the present invention is as follows.

[0007] One aspect of the present disclosure is a method for constructing a riser pipe, including an exposure step of exposing an end portion of a subsea pipeline to the air, and a guide clamp attachment step of attaching a guide clamp for guiding an end portion of the riser pipe to the end portion of the subsea pipeline.

Advantages of the Invention

[0008] According to the present invention, a method for constructing a riser pipe with excellent workability can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] (Embodiment) FIG. 1 is an explanatory view of a subsea pipeline 2 immediately after removing an existing riser pipe. FIG. 2 is an explanatory view of an exposure process and a guide clamp attachment process. FIG. 3 is an explanatory view showing a situation where the riser pipe 1 is being lifted. FIG. 4 is an explanatory view of a centering process. FIG. 5 is an explanatory view of a lifting process, a centering process, and a welding process. FIG. 6 is an explanatory view of a lifting and lowering process.

[0011] The construction method of the riser pipe 1 according to the present embodiment can be applied to a construction work of removing an existing pipe for passing a liquid such as oil and replacing it with a new pipe, as shown in FIG. 1. Further, the construction method of the riser pipe 1 according to the present embodiment is particularly suitable for a construction work of removing the riser pipe 1 and replacing it with a new riser pipe 1 among existing pipes composed of, for example, a subsea pipeline 2 arranged in the sea, a land pipeline 4 arranged on land, and a riser pipe 1 that connects them and extends vertically along a length corresponding to their height difference. Note that the construction method of the riser pipe 1 is not limited to the construction work of updating the riser pipe 1, and may be applied to a construction work of newly installing the riser pipe 1. Hereinafter, the construction method of the riser pipe 1 according to the present embodiment will be described in chronological order using the construction work of updating the riser pipe 1 as an example.

[0012] (Riser Pipe) As shown in FIGS. 3 and 5, the riser pipe 1 has a vertical portion 11, a horizontal portion 12, and a curved portion 13 between the vertical portion 11 and the horizontal portion 12. The vertical portion 11 and the horizontal portion 12 each extend linearly. Note that the riser pipe 1 may have a horizontal portion 12 that is connected from the vertical portion 11 via the curved portion 13 and another horizontal portion 12 that is connected from the horizontal portion 12 via another curved portion 13. That is, the first horizontal portion and the second horizontal portion may have different directions. Note that the riser pipe 1 may not have a horizontal portion 12.

[0013] As shown in FIGS. 1 to 6, the construction method of the riser pipe 1 according to the present embodiment includes an exposure step (see FIG. 2) of exposing the end portion 2e of the subsea pipe 2 to the air in order to meet quality assurance or technical requirements for performing welding in the air. Further, the construction method of the riser pipe 1 according to the present embodiment includes a guide clamp attachment step (see FIG. 4) of attaching a guide clamp 3 for guiding the end portion 1e of the riser pipe 1 to the end portion 2e of the subsea pipe 2. Further, the construction method of the riser pipe 1 according to the present embodiment includes a hanging step (see FIGS. 3 and 5, etc.) of hanging the riser pipe 1 with the pipe axis 1a of the vertical portion 11 in the riser pipe 1 in a posture along the vertical direction. Here, along the vertical direction means substantially vertical, and it does not have to be exactly vertical, and includes, for example, a case where it is inclined within a range of about ±10 degrees. Further, the construction method of the riser pipe 1 according to the present embodiment includes a centering step of aligning the centers of the end portion 2e of the subsea pipe 2 and the end portion 1e of the riser pipe 1. Further, the construction method of the riser pipe 1 according to the present embodiment includes a welding step of welding the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipe 2 along the annular gap 31 formed in the guide clamp 3. Since the construction method of the riser pipe 1 according to the present embodiment includes such steps, even in a marine construction involving welding of unstable welding objects with unstable positions and postures on an unstable scaffold, such as welding the subsea pipe 2 exposed to the air on the floating structure F such as a barge and the riser pipe 1 suspended by a crane or the like supported by the floating structure F such as a barge, the centering of the subsea pipe 2 and the riser pipe 1 can be easily achieved and welding can be performed. Therefore, a construction method of the riser pipe 1 with excellent workability can be provided.

[0014] Specifically, as shown in FIG. 1, a floating structure F such as a barge equipped with a crane or the like is prepared on the sea where the end portion 2e of the subsea pipe 2 that becomes the joint (see the welded portion W in FIG. 14) with the riser pipe 1 (not shown) is located. The existing riser pipe to be updated is separated from the subsea pipe 2 and the onshore pipe 4 in advance.

[0015] (1) Exposure step Next, as shown in FIG. 2, the end 2e of the subsea pipe 2 is exposed to the air (exposure step). Specifically, for example, by providing a float on the subsea pipe 2, buoyancy is generated to lift the subsea pipe 2 until the end 2e is exposed to the air. Alternatively, for example, the subsea pipe 2 is lifted by a crane or the like supported by the floating structure F until the end 2e of the subsea pipe 2 is exposed to the air.

[0016] (2) Guide clamp attachment step Then, as shown in FIG. 2, a guide clamp 3 for guiding the end 1e of the riser pipe 1 is attached to the end 2e of the subsea pipe 2 (guide clamp attachment step). At this time, as shown in FIG. 14, the guide clamp 3 is attached to the end 2e of the subsea pipe 2 such that the welded portion W between the end 2e of the subsea pipe 2 and the end 1e of the riser pipe 1 is in a positional relationship of being exposed from the annular gap 31 provided in the guide clamp 3. That is, the end 2e of the subsea pipe 2 is sandwiched in a state of being received in the inner cavity 3v of the subsea pipe side attachment portion 36 of the guide clamp 3, and the guide clamp 3 is attached to the end 2e in a state where the end 2e is not interposed in the inner cavity 3v of the riser pipe side attachment portion 37 including the guide 32. Details of the guide clamp 3 will be described later.

[0017] (3) Lifting step In parallel with the above-described exposure step and guide clamp attachment step, as shown in FIGS. 3 and 5, etc., the riser pipe 1 is lifted by a crane or the like in a posture where the pipe axis 1a of the vertical portion 11 of the riser pipe 1 is along the vertical direction (lifting step). And in a state where the riser pipe 1 is lifted, the posture of the riser pipe 1 is appropriately changed by operating a rope or the like connected to the riser pipe 1, so that the end 1e of the riser pipe 1 facing the end 2e of the subsea pipe 2 is directed toward the end 2e of the subsea pipe 2. When the riser pipe 1 has a horizontal portion 12 as shown in FIGS. 3 to 5, the end 1e of the riser pipe 1 directed toward the end 2e of the subsea pipe 2 is the end 1e of the horizontal portion 12.

[0018] Also, as shown in FIGS. 3 and 5, the above-described hanging process includes an intermediate clamp mounting process of mounting an intermediate clamp 51 to the middle part of the riser pipe 1, an anchor clamp mounting process of mounting an anchor clamp 52 to the lower end part of the riser pipe 1, and a clamp connection process of connecting the intermediate clamp 51 and the anchor clamp 52 with a cable body 53. After these processes are executed, it includes a process of hanging the intermediate clamp 51. Here, the lower end part of the riser pipe 1 referred to herein is the part located at the lower end of the vertical part 11 in the riser pipe 1, and the middle part of the riser pipe 1 is the part located in the middle (between the upper end part and the lower end part) of the vertical part 11 in the riser pipe 1. The intermediate clamp 51 may be one, but two (see FIG. 3) or three or more may be used as long as they are mounted above the anchor clamp 52 in the vertical part 11. The cable body 53 is, for example, a wire rope, a chain, a sling, etc. made of steel or resin.

[0019] Specifically, after mounting the intermediate clamp 51 and the anchor clamp 52 on the riser pipe 1 and connecting both with the cable body 53, a lifting tool H such as a hook at the tip of a wire rope or the like suspended from a crane or the like is locked to the intermediate clamp 51. The cable body 53 may be attached to an eye plate provided on a suspension clamp 50 (intermediate clamp 51 or anchor clamp 52) via a shackle or the like.

[0020] Then, in that state, the riser pipe 1 is lifted by the lifting tool H. Then, as shown in FIG. 3, the vertical part 11 of the riser pipe 1 assumes a posture along the vertical direction. In such a posture, even if the frictional force (holding force) of the intermediate clamp 51 is insufficient, a part of the force acting along the pipe axis 1a on the intermediate clamp 51 is transmitted to the anchor clamp 52 via the cable body 53 and becomes a reaction force due to the frictional force of the anchor clamp 52. Therefore, the force acting along the pipe axis 1a on the intermediate clamp 51 can be reduced. Thus, even if the frictional force of the intermediate clamp 51 is small, the intermediate clamp 51 can be prevented from sliding along the pipe axis 1a of the riser pipe 1.

[0021] (Reinforcement process) Here, as shown in FIG. 3, when the riser pipe 1 has not only the vertical portion 11 but also a curved portion 13 that is continuous with the vertical portion 11 and continuously changes the direction of the pipe axis 1a, and a horizontal portion 12 that is continuous with the curved portion 13 and the pipe axis 1a extends along the horizontal direction, a reinforcing member 60 is appropriately attached between the vertical portion 11 and the horizontal portion 12 so as to straddle the curved portion 13 of the riser pipe 1 (reinforcing process). Further, when the horizontal portion 12 is curved via the curved portion 13, the reinforcing member 60 is attached between adjacent horizontal portions 12 so as to straddle the curved portion 13. The reinforcing member 60 is, for example, a hollow tubular shape made of steel. Both ends of the reinforcing member 60 are fixed to the riser pipe 1 by clamps having the same structure as the suspension clamp 50 described later. Thereby, the deformation of the curved portion 13 is suppressed, so that the stress of the curved portion 13 due to the dead weight acting on the riser pipe 1 during suspension can be reduced, and damage can be prevented. Further, the clamp for fixing the reinforcing member 60 can be used as the anchor clamp 52 of the suspension clamp 50.

[0022] (Suspension Clamp) As described above, in order to lift the riser pipe 1 by the lifting tool H, it is preferable to use the suspension clamp 50 (intermediate clamp 51, anchor clamp 52). The suspension clamp 50 can be used to lift the riser pipe 1 by the lifting tool H.

[0023] FIG. 7 is a side view of the suspension clamp 50. FIG. 8 is a rear view of the suspension clamp 50. FIG. 9 is a front view of the suspension clamp 50. FIG. 10 is a bottom view of the suspension clamp 50. FIG. 11 is a side view of the first divided body 61. FIG. 12 is a side view of the second divided body 62. Specifically, as shown in FIGS. 7 to 12, the suspension clamp 50 has a locking portion 66 for locking the lifting tool H, an intermediate clamp 51 that can be attached to the intermediate portion of the riser pipe 1, an anchor clamp 52 that can be attached to the lower end portion of the riser pipe 1, and a cord-like body 53 that connects the intermediate clamp 51 and the anchor clamp 52. The cord-like body 53 is preferably in a state of being stretched without slack. The locking portion 66 is a plate-like body provided with a hole and may be a so-called pad-eye.

[0024] The intermediate clamp 51 or the anchor clamp 52 has a structure shown in FIGS. 7 to 12, for example. The intermediate clamp 51 and the anchor clamp 52 may have a similar structure.

[0025] As shown in FIG. 7, the suspension clamp 50 includes a first divided body 61 and a second divided body 62. The first divided body 61 and the second divided body 62 are structured to swing closer to or away from each other about an axis 60a along the pipe axis 1a. Specifically, with the first divided body 61 and the second divided body 62 open in a direction perpendicular to the pipe axis 1a of the riser pipe 1, the riser pipe 1 can be received between the first divided body 61 and the second divided body 62. And when the first divided body 61 and the second divided body 62 are closed, the riser pipe 1 is clamped between the first divided body 61 and the second divided body 62.

[0026] The suspension clamp 50 includes a first fastening body 63 and a second fastening body 64. And by fastening the first fastening body 63 and the second fastening body 64 while clamping the riser pipe 1 between the first divided body 61 and the second divided body 62, the riser pipe 1 can be gripped.

[0027] Further, the suspension clamp 50 includes an eye plate 65.

[0028] As shown in FIGS. 3, 5, and 6, the eye plate 65 provided on the intermediate clamp 51 and the eye plate 65 provided on the anchor clamp 52 are connected by a cable body 53 via an appropriate connector such as a shackle. Thus, even if the gripping force of the intermediate clamp 51 is insufficient, a part of the force acting along the pipe axis 1a on the intermediate clamp 51 is transmitted to the anchor clamp 52 via the cable body 53 and becomes a reaction force due to the frictional force of the anchor clamp 52. Therefore, even if the frictional force of the intermediate clamp 51 is small, the intermediate clamp 51 can be prevented from sliding along the pipe axis 1a of the riser pipe 1. Therefore, even if the frictional force per suspension point in the suspension clamp 50 is small, the suspension clamp 50 can firmly grip the riser pipe 1 without shifting.

[0029] (4) Core alignment process Next, align the centers of the end 2e of the subsea pipeline 2 and the end 1e of the riser pipe 1 so as to change from the state shown in FIG. 4 to the state shown in FIG. 5 (core alignment process). Specifically, with the riser pipe 1 suspended, by operating a rope or the like appropriately connected to the riser pipe 1 so that the pipe axis 2a at the end 2e of the subsea pipeline 2 coincides with the pipe axis 1a at the end 1e of the riser pipe 1, the position and orientation of the riser pipe 1 are adjusted. At this time, a guide clamp 3 having a tapered guide 32 with a frustum-shaped inner cavity 3v expanding from the subsea pipeline 2 side toward the riser pipe 1 side is attached to the end 2e of the subsea pipeline 2, so that it is easier to insert the end 1e of the riser pipe 1 into the inner cavity 3v of the guide 32. Then, insert the end 1e of the riser pipe 1 into the inner cavity 3v of the guide 32, and then push the end 1e of the riser pipe 1 toward the end 2e of the subsea pipeline 2. For example, connect the eye plate provided on the guide 32 and the eye plate provided on the clamp of the riser pipe 1 with a rope or the like, and apply tension to the rope with a lever block (registered trademark) or the like to pull the end 1e of the riser pipe 1 closer to the end 2e of the subsea pipeline 2. Then, the end 1e of the riser pipe 1 reaches the inner cavity 3v of the riser pipe side attachment portion 37 (see FIG. 14). In this way, the end 1e of the riser pipe 1 is guided so that the end faces and the pipe axes of both the riser pipe 1 and the subsea pipeline 2 approach each other while being restricted from moving by the guide clamp 3. In this way, the core alignment can be easily achieved.

[0030] Here, the guide clamp 3 is a tubular body whose inner cavity 3v (see FIGS. 13 and 14) can be expanded and contracted by a fastening member 3S. And the core alignment process may include reducing the diameter of the inner cavity 3v. Specifically, the core alignment process may include reducing the diameter of the inner cavity 3v by, for example, screwing the fastening member 3S by the fastening member 3S. More specifically, with the fastening member 3S loosened and the inner cavity 3v in an expanded state, the end portion 1e of the riser pipe 1 is inserted, and by tightening the fastening member 3S to reduce the inner cavity 3v, the posture of the pipe axis 1a of the end portion 1e of the riser pipe 1 is corrected to match the posture of the pipe axis 2a of the end portion 2e of the subsea pipe 2. At this time, from the state where the fastening member 3S is loosened and the inner cavity 3v is expanded, a jack such as hydraulic pressure or pneumatic pressure may be used to reduce the inner cavity 3v, and then the fastening member 3S may be tightened. Thereby, fine adjustment can be performed so that the end faces of both the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipe 2 and both pipe axes 1a, 2a coincide with each other. Note that the inner cavity 3v may be expanded and contracted by expanding and contracting the distance between the first guide clamp split body 3A and the second guide clamp split body 3B using a jack such as hydraulic pressure or pneumatic pressure without using the fastening member 3S.

[0031] (Guide Clamp) FIG. 13 is a side view of the guide clamp 3. FIG. 14 is a view taken in the direction of arrow A in FIG. 13. As described above, the guide clamp 3 is suitably used for welding the subsea pipe 2 and the riser pipe 1. Specifically, as shown in FIGS. 13 and 14, the guide clamp 3 includes a first guide clamp split body 3A and a second guide clamp split body 3B that are split in a direction perpendicular to the pipe axes 1a, 2a of the pipes to which the subsea pipe 2 and the riser pipe 1 are connected, and a fastening member 3S that fastens the first guide clamp split body 3A and the second guide clamp split body 3B. Then, with the first guide clamp split body 3A and the second guide clamp split body 3B facing each other, the outer circumferences of the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipe 2 are covered and clamped, and by tightening the fastening member 3S, a vertical resistance force is generated between the riser pipe 1 and the subsea pipe 2 and the guide clamp 3, enabling both to be gripped.

[0032] Further, the guide clamp 3 is provided with a subsea pipeline side attachment portion 36 that can be attached to the end portion 2e of the subsea pipeline 2, a tapered guide 32 that guides the riser pipe 1, a riser pipe side attachment portion 37 that can be attached to the end portion 1e of the riser pipe 1, and a connecting portion 38 that connects the subsea pipeline side attachment portion 36 and the riser pipe side attachment portion 37. The subsea pipeline side attachment portion 36 is configured to cover and sandwich the outer periphery of the end portion 1e of the riser pipe 1, and by tightening the fastening member 3S, the end portion 2e of the subsea pipeline 2 can be gripped. The riser pipe side attachment portion 37 is configured to cover and sandwich the outer periphery of the end portion 1e of the riser pipe 1, and by tightening the fastening member 3S, the end portion 1e of the riser pipe 1 can be gripped.

[0033] Here, the guide clamp 3 is provided with an annular gap 31 that exposes the welding portion W between the subsea pipeline 2 and the riser pipe 1 between the subsea pipeline side attachment portion 36 and the riser pipe side attachment portion 37. The annular gap 31 is provided annularly. For this reason, the central portion of the connecting portion 38 is cut out so as to avoid the vicinity of the welding portion W. Since the guide clamp 3 has such a structure, the pipe axis 1a of the riser pipe 1 and the pipe axis 2a of the subsea pipeline 2 are aligned, and in a state where the end faces of both are butted against each other, the position and the posture relationship between the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipeline 2 can be maintained. And in that state, the welding portion W (the outer peripheral portion of the butted end faces) can be exposed so that an operator can easily perform a welding operation using a welding device.

[0034] (5) Welding process Next, the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipeline 2 are welded along the annular gap 31 formed in the guide clamp 3 (welding process). Thus, an annular gap 31 is formed in the guide clamp 3, and the guide clamp 3 is attached to the end 2e of the subsea pipe 2 with the welded part exposed from the annular gap 31. Therefore, even while the relative positions and postures of the end 1e of the riser pipe 1 and the end 2e of the subsea pipe 2 are maintained by the guide clamp 3, the end 1e of the riser pipe 1 and the end 2e of the subsea pipe 2 can be welded along the annular gap 31. Thus, even on an unstable scaffold in offshore construction, it is possible to perform a welded joint while stabilizing the relative positions and postures of the end 1e of the riser pipe 1 and the end 2e of the subsea pipe 2, improving the workability.

[0035] (5) Hoisting and lowering process Finally, as shown in FIG. 6, with the riser pipe 1 suspended by a hoist H, the welded and connected riser pipe 1 and subsea pipe 2 are lowered to a desired position in the sea. Specifically, the welded and connected riser pipe 1 and subsea pipe 2 are hoisted and lowered to the seabed (hoisting and lowering process). After this, the riser pipe 1 and the onshore pipe 4 are connected by welding or the like as appropriate. Through the above steps, the renewal of the riser pipe 1 is completed. Thus, according to each of the above steps, it is possible to provide a construction method for a riser pipe with excellent workability even in an operation on the sea, which is an unstable scaffold. Note that the above construction method for the riser pipe 1 is not limited to an operation on the sea, which is an unstable scaffold, and may include an operation on a stable scaffold such as a jacket-type temporary scaffold constructed together with piles supported on the seabed.

[0036] (Other embodiments) As described above, one embodiment has been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like are possible. For example, the construction method for the riser pipe 1 is not limited to a project for renewing the riser pipe 1, and may be applied to a project for newly installing the riser pipe 1.

[0037] For example, in order to move or change the posture of the newly installed riser pipe 1 lying on the stockyard, before suspending the intermediate clamp 51 with the lifting tool H and setting the vertical portion 11 in a posture along the vertical direction, as shown in FIG. 15, the vertical portion 11 may first be suspended in the air in a posture along the horizontal direction. Here, it is assumed that the riser pipe 1 does not have a horizontal portion 12. FIG. 15 is another embodiment of the suspension clamp 50. FIG. 16 is a detailed view of portion P in FIG. 15. FIG. 17 is a detailed view of portion Q in FIG. 15. FIG. 18 is a detailed view of portion R in FIG. 15. FIG. 19 is a detailed view of portion S in FIG. 15. FIG. 20 is a detailed view of portion T in FIG. 15.

[0038] As shown in FIG. 15, when lifting the riser pipe 1 with the vertical portion 11 lying horizontally by means of the lifting tool H via the upper end portion of the riser pipe 1 and the intermediate clamp 51 (51A) provided at portion Q in the vertical portion 11 of the riser pipe 1 and raising the vertical portion 11 to be along the vertical direction, support is also provided via the intermediate clamps 51 (51B, 51C) at two locations, namely portion R and portion S, which are different from the location where the lifting tool H lifts. Thereby, since the vertical portion 11 can be supported at multiple points, even if the vertical portion 11 is long, an excessive load can be prevented from acting on the vertical portion 11. And at this time, each of the intermediate clamps 51 (51A, 51B, 51C) is connected to an anchor clamp 52 fixed to the lower end of the riser pipe 1 via a cable body 53. Specifically, the intermediate clamp 51A is connected to the intermediate clamp 51C via the cable body 53C. The intermediate clamp 51B is connected to the intermediate clamp 51C via the cable body 53B, and the intermediate clamp 51C is connected to the anchor clamp 52 via the cable body 53A. The intermediate clamp 51C is connected to the anchor clamp 52 via the cable body 53A. The anchor clamp 52 is fixed to the lower end of the riser pipe 1 (the lower end in the state where the riser pipe 1 is lifted, which is the right end in FIG. 15). In this way, the intermediate clamp 51 is connected to the anchor clamp 52 via the cable body 53. Therefore, when the vertical portion 11 of the riser pipe 1 is suspended in a posture along the vertical direction by the lifting tool H, even if a force acts on the intermediate clamp 51 to shift the intermediate clamp 51 along the pipe axis 1a from the riser pipe 1, it can be prevented from shifting because the cable body 53 connected to the anchor clamp 52 resists.

[0039] The construction method of the riser pipe 1 of the present embodiment includes an exposure step of exposing the end 2e of the subsea pipeline 2 to the air, a guide clamp attachment step of attaching a guide clamp 3 for guiding the end 1e of the riser pipe 1 to the end 2e of the subsea pipeline 2, a suspension step of suspending the riser pipe 1 in a posture where the pipe axis 1a of the vertical portion 11 in the riser pipe 1 is along the vertical direction, an alignment step of aligning the axes of the end 2e of the subsea pipeline 2 and the end 1e of the riser pipe 1, and a welding step of welding the end 1e of the riser pipe 1 and the end 2e of the subsea pipeline 2 along the annular gap 31 formed in the guide clamp 3. Thereby, even on an unstable scaffold in offshore construction, the end 1e of the riser pipe 1 can be easily guided to the end 2e of the subsea pipeline 2, and the pipe axes of the two can be aligned with each other. Therefore, a construction method of a riser pipe with excellent workability can be provided.

[0040] The guide clamp 3 used for welding the subsea pipeline 2 and the riser pipe 1 in this embodiment includes a first guide clamp split body 3A and a second guide clamp split body 3B that are split in a direction perpendicular to the pipe axis of the pipeline, and a fastening member 3S that fastens the first guide clamp split body 3A and the second guide clamp split body 3B. The guide clamp 3 is provided with a subsea pipeline side attachment portion 36 that can be attached to the end portion 2e of the subsea pipeline 2, a tapered guide 32 that guides the riser pipe 1, a riser pipe side attachment portion 37 that can be attached to the end portion 1e of the riser pipe 1, and a connecting portion 38 that connects the subsea pipeline side attachment portion 36 and the riser pipe side attachment portion 37. And the guide clamp 3 is provided with an annular gap 31 that exposes the welding portion W between the subsea pipeline 2 and the riser pipe 1 between the subsea pipeline side attachment portion 36 and the riser pipe side attachment portion 37. Thereby, even on an unstable scaffold in offshore construction, welding can be performed in a state where the positional and postural relationship between the end portion 1e of the riser pipe 1 and the end portion 2e of the subsea pipeline 2 is stabilized, and the workability can be improved.

[0041] The suspension clamp 50 used for lifting the riser pipe 1 by the lifting tool H in this embodiment has a locking portion 66 for locking the lifting tool H, an intermediate clamp 51 that can be attached to the intermediate portion of the riser pipe 1, an anchor clamp 52 that can be attached to the lower end portion of the riser pipe 1, and a cable-like body 53 that connects the intermediate clamp 51 and the anchor clamp 52. Thereby, in offshore construction, the riser pipe 1 can be surely gripped by the suspension clamp 50 and can be suspended by the lifting tool H. Therefore, the workability of the riser pipe 1 in offshore construction can be improved.

Explanation of Signs

[0042] 1 Riser pipe 1a (of the riser pipe) pipe axis 1e (of the riser pipe) end 2 Subsea pipeline 2a (of the subsea pipeline) pipe axis 2e (of the subsea pipeline) end 3 Guide clamp 3A First guide clamp split body 3B Second guide clamp split body 3S fastening member 3v inner cavity 4 onshore piping 11 vertical part 12 horizontal part 13 bending part 31 annular gap 32 guide 36 subsea piping side attachment part 37 riser pipe side attachment part 38 connecting part 50 suspension clamp 51 intermediate clamp 51A intermediate clamp 51B intermediate clamp 51C intermediate clamp 52 anchor clamp 53,53A,53B,53C cable-like body 60 reinforcing member 60a shaft 61 first divided body 62 second divided body 63 first fastening body 64 second fastening body 65 eye plate 66 locking part F floating structure H lifting tool W welded part

Claims

**Claim 1** A method for installing a riser pipe, comprising: An exposure step of exposing the end of the subsea pipeline to the air; A guide clamp mounting step of mounting a guide clamp for guiding the end of the riser pipe on the end of the subsea pipeline. The method for installing a riser pipe includes these steps. **Claim 2** The guide clamp mounting step is to mount the guide clamp on the end of the subsea pipeline exposed to the air in the exposure step. The method for installing a riser pipe according to Claim 1. **Claim 3** The exposure step is to lift the subsea pipeline with a crane until the end of the subsea pipeline is exposed to the air. The method for installing a riser pipe according to Claim 1 or 2. **Claim 4** The exposure step is to float the subsea pipeline by providing floats on the subsea pipeline until the end of the subsea pipeline is exposed to the air. The method for installing a riser pipe according to any one of Claims 1 to 3. **Claim 5** The method for installing a riser pipe according to any one of Claims 1 to 4 includes a hanging step of hanging the riser pipe by a sling in a posture where the pipe axis of the vertical portion of the riser pipe is substantially along the vertical direction. **Claim 6** The method for installing a riser pipe according to any one of Claims 1 to 5 includes a core alignment step of aligning the cores of the end of the subsea pipeline and the end of the riser pipe. **Claim 7** The method for installing a riser pipe according to any one of Claims 1 to 6 includes a welding step of welding the end of the riser pipe and the end of the subsea pipeline along the guide clamp. **Claim 8** The method for installing a riser pipe according to any one of Claims 1 to 7 includes a hoisting and lowering step of hoisting and lowering the welded and connected riser pipe and subsea pipeline to the seabed.

Images