NL2004843C2 - Vessel and process for installing an underwater pipeline. - Google Patents

Description

VESSEL AND PROCESS FOR INSTALLING AN UNDERWATER PIPELINE

The present invention relates to a vessel and to a process for installing an underwater pipeline.

5 A known process for installing an underwater pipeline is the so-called 'S-lay' . This process comprises of pipe sections being welded to each other on a ship or barge. Support vessel bring new pipe sections to the ship which lifts the pipe sections by crane to 10 the storage area on deck of the pipe lay ship. The pipe sections are then welded together in a string of welding stations. Before the pipe is launched from the ship, the pipe is held by a tensioner and to assure the pipe is not damaged while being launched, a support structure, 15 such as a 'stinger' is connected to the stern of the ship. The welding of the pipe sections and the associated weld control onboard the ship is a relatively time consuming effort.

The present invention aims to provide a more 20 simple S-lay process and vessel for installing an underwater pipeline.

This aim is achieved by the following vessel and process .

Vessel comprising means to facilitate the 25 connection of pipes to form a string of connected pipes by means of a screw connection and a means to support the string as the string, when in use, is launched from the vessel.

A process for installing an underwater pipeline 30 by connecting pipe sections to form a string of connected pipe sections by means of a screw connection 2 on board of a vessel and launching the string of connected pipe sections from said vessel.

Applicants found that a pipe string having screw connections can be launched from a vessel having the 5 claimed support means in a S-lay process. This is advantageous because by using such support means the height of the construction on board of the vessel can be minimized. This in contrast to some prior art pipelaying vessel having very high constructions as for 10 example illustrated in US-A-2003/0138297. The process according to the invention has the additional advantage that the connection of the pipe sections can be performed quicker than by the prior art welding process. An additional advantage is that existing pipe sections 15 can be used which are known for many years in the drilling industry as 'casing pipe'. Each drilled well contains casing pipe, there is a widely spread knowledge on fabrication, assembly and quality assurance of casing pipe and specifically the threads used to connect the 20 pipe. A further advantage is that the equipment required on the vessel according to the invention can be same as the existing drilling equipment which is known to the skilled person in the field of drilling for many years. Thus very little development and engineering will be 25 required to manufacture the vessel and/or perform the invented process. Further advantages will be discussed when describing the below preferred embodiments.

The process can be applied to install pipelines underwater in sea, rivers and lakes. The pipeline will 30 be installed on the sea, river or lake bottom. Any reference in this application to bottom shall have the meaning of sea, river or lake bottom. Optionally a 3 trench is made in which the pipeline can be positioned when performing this process. The pipeline can be covered after installation.

The pipe sections are preferably steel pipe 5 sections. Optionally the pipe sections can be coated with an anti-corrosion coating, for example an epoxy resin coating. Suitably the outer diameter of the pipe section is between 5 and 50 cm and more preferably smaller than 40 cm. The threadform of the screw 10 connection at both ends of the pipe section provide mechanical and/or structural strength, the casing thread must be compatible with the pressures and fluids associated with the application. Some known advanced thread forms incorporate a gas seal. By applying the 15 right torque when rotating the pipe section the selected metal will slightly deform to obtain such liquid, and sometimes also gas, tight connection. In a preferred embodiment a torque wrench is used, which results in that the quality of the resulting connections will not 20 vary within any large margins. This results in that no or very minor inspection of these connections is required when performing the process according to the invention, thereby making the process much faster than the prior art welding process.

25 The vessel has means to support the string of connected pipes as the string, when in use, is launched from the vessel. This support aims at avoiding damaging the string of pipes during said launch. Such a support is especially advantageous when the pipe, as it is 30 connected to the string, is positioned substantially horizontal. If such a substantially horizontal positioned string of pipes is launched from the vessel 4 without sufficient support the string of pipes may buckle or damage due to the resulting bending of the string of pipes. The means to support is preferably a metal framework attached to one end of the vessel or 5 alongside the vessel. Such means are known and sometimes referred to as stingers. The stinger like extension controls the deflection of the pipe in the over-bend region above the pipeline inflection point in order to return the angle of the pipeline at the sea surface to 10 the horizontal. The preferred curvature radius of the stinger corresponds to at least the maximum bending stress. To avoid a bending moment peak at the last roller, the pipe suitably lift off smoothly from the stinger well ahead of the lower end of the stinger.

15 Designing a suitable stinger will thus depend on the depth of the bottom and the properties of the pipe sections used. An example of a stinger is described in US-A-49 92001 and in US-A-4112698.

Preferably the process comprises the following 20 steps, wherein, the pipe sections are connected by (i) fixing the string of connected pipe sections, (ii) connecting a pipe section to the string of connected pipe sections by rotating the pipe section resulting in a screw connection between said pipe 25 section, wherein a prolonged string of pipe sections is obtained, (iii) releasing said string and (iv) launching the string with the prolonged string of pipe sections from the vessel and repeating steps (i)- 30 (iv) .

Fixing in step (i) is suitably holding the string of connected pipe sections such that a new pipe section 5 can be connected in step (ii) by rotation of the new pipe section relative to the string of connected pipe sections .

Step (ii) is suitably performed such that the 5 pipe section is positioned substantially horizontal when being rotated. By substantially horizontal is meant that the angle between the horizon and the pipe section is not more than 20°, preferably less than 10°. The advantage of such a horizontal positioning is that the 10 height of the construction on board of the vessel can be minimized. This in contrast to for example the pipelaying vessel disclosed in WO-A-96/27751.

The pipe string is suitably launched from the vessel in a S-lay process. The average angle of the 15 string of connected pipe sections as present between the vessel and the bottom and the bottom itself is preferably between 5° and 60°, wherein the bottom is the sea, lake or river bottom on to which the pipeline is installed. The process according to the present 20 invention is preferably applied in relatively shallow water, more preferably wherein the vertical distance between the bottom and the water surface is less than 100 m and preferably less than 60 m.

During Step (iv) the vessel is suitably moved 25 forward along the length of the pipe section as attached in step (ii). When the pipe string is launched from the vessel in one direction, the vessel will suitably be moved in the opposite direction. The vessel may be moved using a propulsion system which is an integral part of 30 the vessel. In such case it is preferred to move the vessel using a dynamic positioning system. In case the vessel is used in shallow waters as discussed above the 6 positioning and movement of the vessel is preferably performed through the use of anchors, associated anchor chains, and/or cables and the re-location of the anchors is performed by using additional ships, like tugs and 5 the like.

The pipe section may comprise of a single pipe section. Alternatively the pipe section used in the process may be pre-connected sections of two, three or four individual pipe sections. These pre-connected 10 sections may be pre-connected on shore or aboard the vessel in a separate process.

The invention is also directed to a process to install two or more parallel pipes on the sea-bottom simultaneously by performing the above process in 15 parallel on the same vessel.

The invention will be illustrated by means of Figures 1-4. Figure 1 shows a top view of a possible vessel according to the invention. Figure 1 shows a vessel (la) having means to facilitate the connection of 20 pipe sections (2) to form a string (3) of connected pipes by means of a screw connection. Preferably the means for facilitating the connection of pipes comprises tensioner means (4) to fix the string of pipes (3) and means to rotate the pipe section, preferably a torque 25 wrench (5), which in use, is connected to the string (3). The vessel (1) is further provided with a stinger like extension (6) at one end (7) of the vessel (la), suited to provide additional support for the string (3) as the string (3), when in use, is launched from the 30 vessel (la).

The vessel (la) preferably has a storage area (9) for carrying pipe sections (2) and lifting means, such 7 as a crane (10), suited to transport a pipe from a storage area (9) to the means to facilitate the connection of pipes. Figure 1 also shows a pipe handling section (11) which may have rollers to move the pipe 5 sections to the torque wrench (5). As shown in Figure 1 the means to facilitate the connection of pipes to form a string are arranged such that in use the pipe as it is connected to the string is positioned substantially horizontal.

10 Figure 2 is a side view of the vessel (la) of

Figure 1.

Figure 3 is a top view of another possible vessel (lb) according to the invention. Figure 4 is a side view of vessel (lb). The references in Figures 3 and 4 have 15 the same meaning as in Figures 1 and 2. The string of pipes is not shown in this Figure. Vessel (lb) has a stinger like support (6) positioned alongside of the vessel (lb). The advantage of such a vessel is that the vessel itself can support the stinger like extension (6) 20 more easily than when the stinger like extension is positioned at the end of the vessel as shown in Figure 1. This embodiment is also preferred when two parallel pipelines are installed. The vessel (lb) will then have a similar tensioner means (4), torque wrench (5) and 25 stinger like extension (6) at both sides of vessel (lb).

The vessel (1) may be a ship having its own propulsion system, a barge or any other type of floating structure. The vessel may have a dynamic positioning system or anchors to position and move the vessel when 30 installing an underwater pipeline.

8

Preferably the above vessel is used in the process for installing an underwater pipeline according to the present invention.

Claims (17)

1. Vessel comprising means for facilitating pipe joining so as to form a connection or line of connected pipes by using screw connections, as well as means for supporting the connection or line of pipes when in use , is laid from the vessel. 2. Vessel according to claim 1, wherein the means for facilitating the connection of the tubes comprise tensioning means intended to hold the tube line, as well as means for rotating the tube which, during use, is connected to the line. 3. Vessel as claimed in claim 2, wherein the means for rotating the tube are formed by a torque wrench. 4. Vessel as claimed in any of the claims 1-3, wherein the vessel is provided with a storage space in which tubes can be stored. 20 5. Vessel as claimed in any of the claims 1-4, wherein the vessel is provided with hoisting means that are suitable for transporting a tube from a storage space in which tubes are stored, to the means that facilitate the connection of the tubes. 25 Vessel according to any of claims 2-4, wherein the means for facilitating the connection of the tubes to achieve a connection or line of tubes are arranged in such a way that, during use, the tube is connected to the line or connection of pipes, is positioned virtually horizontally. 7. Vessel as claimed in any of the claims 1-6, wherein the vessel is equipped with a dynamic positioning system or anchors. 8. Vessel as claimed in any of the claims 1-7, wherein the means intended to support the line or the connection of pipes is a metal frame which is connected to one end of the vessel, or along the side of the vessel. vessel. 9. Method for laying a pipeline under water, by interconnecting pipe sections in order to arrive at a connection or line of connected pipe sections, by making use of a screw connection on board a vessel, and lowering it of the connection or line of connected pipe sections from the vessel. 10. Method as claimed in claim 9, wherein the tube sections are connected by (i) immobilizing the connecting line or line of connected tube sections, (ii) connecting a tube section to the line or connection of connected tube sections by rotating the tube section, resulting in a screw connection between the tube sections, whereby an extension of the line or connecting of pipe sections is realized, (iii) releasing the line or connecting, (iv) lowering the line or connecting with the extended line or connecting of tube sections from the vessel, and repeating steps (i) - (iv). 11. A method according to claim 10, wherein step (ii) is carried out in such a way that the tube section is positioned substantially horizontally when it is rotated. A method according to any one of claims 9-11, wherein the average angle of the line or connection of connected pipe sections as present between the vessel and the bottom, and the bottom itself is between 5 ° and 60 °, the bottom the bottom is from the sea, from the river, or from the lake on which the pipeline is laid. A method according to any of claims 9-12, wherein the vertical distance between the bottom and the water surface is less than 100 m, the bottom being the bottom of the sea, the river, or the lake on which the pipeline is laid . The method of claim 13, wherein the vertical distance between the bottom and the water surface is less than 60 m. The method of any one of claims 9-14, wherein the outer diameter of the tube section is between 5 and 50 cm. 10 Method for laying two or more parallel tubes on the seabed, by performing the method according to claims 9-15 in parallel on the same vessel. 17. Method as claimed in any of the claims 9-16, wherein use is made of the vessel according to any of the claims 1-8. 20