WO2007064224A1

WO2007064224A1 - Cutting tool and method for cutting an umbilical

Info

Publication number: WO2007064224A1
Application number: PCT/NO2006/000444
Authority: WO
Inventors: Harald Arnt Friisk; Karl Olav Haram
Original assignee: Norsk Hydro Produksjon A.S.
Priority date: 2005-12-02
Filing date: 2006-11-29
Publication date: 2007-06-07
Also published as: NO20055698L; NO20055698D0; NO324062B1

Abstract

A cutting tool (10, 20) and a method for cutting an umbilical (1 ) between preferably a subsea production and processing plant and a control room on shore or on a platform in connection with repair of a subsea umbilical (1 ). The cutting tool (10, 20) is arranged on and operated by a remote-controlled subsea vessel or another tool carrier (6). The cutting tool (10, 20) comprises: a fixing device (8) for connection to the remote-controlled subsea vessel or tool carrier, a hydraulic unit (11 , 21), comprising a hydraulic motor, and a diamond wire (12, 22) that is connected to and continuously driven by the hydraulic motor, whereby the diamond wire (12, 22) will successively cut through all the layers and components of the umbilical (1 ) until it has been completely cut off.

Description

"Cutting tool and method for cutting an umbilical"

The present invention concerns a cutting tool for cutting an umbilical between preferably a subsea production and processing plant and a control room on shore or on a platform in connection with repair of an umbilical underwater. The cutting tool is arranged on and operated by a remote-controlled underwater vessel or arranged in a repair frame.

The present invention also concerns a method for cutting an umbilical between preferably a subsea production and processing plant and a control room on shore or on a platform using the above cutting tool.

An umbilical between a subsea production and processing plant and a control room on shore or on a platform is normally the only connection that makes it possible to check necessary functions and to supply power to electric motors in the subsea plant. The length of the umbilical may, for example, be 120 km, and it will often be installed in several sections from the reel-in area on land down to, for example, 850 metres' depth in the field. The installation routes often pass over areas that are heavily exposed to fisheries activities such as trawling, and the umbilical will often be installed in very "hilly terrain".

The umbilical will normally be protected against possible damage, for example by fishing activities, and will normally, along its full length, be buried in the seabed or be protected by stones placed over it in a controlled manner.

However, burying and covering with stones provide no guarantee that external damage or other faults will not occur throughout the entire field's life. It is, therefore, important that any potential damage to the umbilical can be repaired in the best possible technical manner and the financially most favourable manner. Damage has previously occurred on umbilicals and repairs have been implemented with good results. However, the umbilicals in question have only included hydraulic, optical and electrical functions, not the supply of a barrier gas to high-power electric motors, which is a necessary function in connection with umbilicals that are to operate the plant in the future.

The purity of the supply gas that will surround the motor's windings as an insulating barrier and contribute to cooling the motors in the subsea plant is extremely critical for avoiding electric flashovers and subsequent motor breakdown.

Just small quantities of water in critical umbilical guides can lead to the breakdown of equipment located in production and processing plants. Very considerable repair costs may be incurred. It is, therefore, important for water or other contaminants to be prevented from penetrating.

A fault in an umbilical may occur, in principle, at any location along its length. Depending on the nature of the damage or fault, alternative methods for restoring control will be assessed.

A normal method for repairing an umbilical is to cut it underwater near the damaged area with a hydraulic cutting machine. The end is then pulled up to a service vessel for further processing and for a new section to be spliced in before the umbilical can be relaid on the seabed in a controlled manner.

However, it should be noted that a cutting operation underwater is critical with regard to water penetration in pipes containing media other than the environment with a pressure other than the ambient pressure.

New technology in connection with underwater compression plants, where an umbilical connects a subsea production and processing plant and a control room on shore or on a platform, means that such an umbilical has dimensions that make it difficult to cut it in an operation with existing tools. Existing tools have to be repositioned several times to be able to cut through such an umbilical.

US patent 4,304,505 describes a method for repairing a damaged pipe laid on deep seabeds. The method substantially comprises the step of joining a central pipe stub between the ends of the two adjoining pipe portions. Such operation is performed directly on the seabed rather than on the pipe-laying barge. Special coupling sleeves are provided at both ends of the central pipe stub, said sleeves being received in a watertight manner on the two pipe terminal portions, by clamping said sleeves thereon. Apparatus and tools for carrying out said method are also described in this publication.

GB patent 2 276 431 describes an improved method for automatically repairing underwater pipelines, particularly suitable for great depths. The method is performed in situ and without the use of divers or other personnel operating at depth. The damaged pipe piece is cut away. The weighting concrete is removed by a cutter automatically centred about the pipeline axis by an expansion-centring head. The end connectors are guidedly installed by means of an alignment apparatus and the replacement piece is installed with the aid of an appropriate reference and guide apparatus, all effected by a single working module. The method permits a repair to be performed in situ on a pipeline regardless of its length, even if it lies at great depth. The invention also relates to certain specific apparatus for implementing said method.

The present invention aims to solve the problems associated with cutting an umbilical that has relatively large dimensions, i.e. a large cross-section in relation to traditional umbilicals.

One object of the present invention is for the umbilical to be cut using an optimal, effective method in one operation.

Another object of the invention is to produce a clean cut surface. The object of the present invention is achieved by means of a cutting tool for cutting an umbilical between preferably a subsea production and processing plant and a control room on shore or on a platform in connection with repair of a subsea umbilical. The cutting tool is arranged on and operated by a remote-controlled underwater vessel or another tool carrier, where the cutting tool comprises:

- a fixing device for connection to the remote-controlled underwater vessel or other tool carrier;

- a hydraulic unit comprising a hydraulic motor and

- a diamond wire that is connected to and continuously driven by the hydraulic motor, whereby the diamond wire will successively cut through all the layers and components of the umbilical until it has been completely cut off.

Preferred embodiments of the cutting tool are further elaborated on in claims 2 and 3.

The objects of the present invention are also achieved by means of a method for cutting an umbilical between preferably a subsea production and processing plant and a control room on shore or on a platform using the cutting tool specified above. The method comprises the following steps: - the umbilical's damage site is identified;

- the umbilical is lifted up from the seabed and placed preferably in one or more frames of a type known in the art;

- the cutting tool is arranged in position, preferably at the umbilical's damage site/cutting site, and - the cutting tool is activated and all layers and components in the umbilical are cut successively, thus producing a cut with a clean cut surface.

Moreover, preferred embodiments of the method are elaborated on in claims 5, 6, 7 and 8.

The present invention will be described in the following with reference to the attached figures, where: Fig. 1 shows a damaged umbilical cord that is lifted up from the seabed, Fig. 2 shows the cross-section of an umbilical cord, Fig. 3 shows a perspective image of a truncated umbilical cord, Fig. 4 shows a first embodiment of a cutting tool in accordance with the present invention, and

Fig. 5 shows a second embodiment of a cutting tool in accordance with the present invention.

First with reference to Figures 2 and 3, the umbilical 1 is shown built up of several internal elements such as umbilical guides or pipes 4, where all the elements are necessary for the control and operation of a subsea gas compression plant. The elements are "packed" in a manner that produces the minimum external dimensions, and the individual elements are well protected and the strength and integrity of the umbilical in connection with installation are optimised. The above figures also show that the umbilical 1 is surrounded by an external casing 2 and, within this casing, support elements 3.

In connection with damage to the umbilical 1 , the damage site 25 must be identified and a sufficient part of the umbilical 1 must be lifted up from the seabed and, for example, arranged on one or more working frames or frames 6 so that the umbilical can be prepared for cutting and pulling up to a service vessel. Reference is made to Figure 1 in this connection.

Preparation of the umbilical before cutting may involve the umbilical 1 being exposed on each side of the damage site 25, and the outer casing and support element 3 of the umbilical being removed so that the individual pipes 4 in the umbilical are exposed. A tool may subsequently be used to seal the pipe 4 by an area(s) 5 being flat-clamped and the pipe 4 being sealed in at least two places on both sides of the damage site 25. The umbilical 1 , which is supported in frames 6 in this case, can now be cut at the damage site 25. A hydraulically operated cutting tool 10, 20, comprising a hydraulic unit 11 , 21 and diamond wire 12, 22, can now be used to cut the umbilical 1 in one operation, producing a clean cut surface. The cutting tool 11 , 21 is attached to the underwater vessel's manipulator and is placed in position above the umbilical 1 by this manipulator or another tool carrier.

The cut performed will be straight through, i.e. a clean cut without elements cracking in many directions. The clean cut means that it is possible to thread alternative lifting or securing equipment onto the umbilical 1 from the cut side. For example, installation of a "Chinese finger" or a ready-mounted clamp that is only finally tightened after installation. The clean cut thus prepares the way for the fixing devices stated to be fixed to the cut section in a simple, effective manner, after which the pipe ends can be lifted up to the service vessel.

With reference to Figure 4, a first embodiment of a cutting tool 10 in accordance with the present invention is shown. The cutting tool 10 is designed as a bow saw comprising a brace 15 with a guide track for the diamond wire 12. The diamond wire 12 is driven by the hydraulic unit 11 , comprising a hydraulic motor. During cutting, the bow saw is moved in a continuous downward movement until the umbilical 1 has been completely cut off.

Figure 5 shows a second embodiment of the cutting tool 20 that comprises a hydraulic unit 21 , which pulls the diamond wire 22 around the umbilical 1 in a continuous operation. The diamond wire 22 will successively cut through all layers and components of the umbilical 1 until the umbilical has been cut all the way through.

The cutting tools 10, 20 will both have a fixing device 8 for connection to the remote-controlled underwater vessel or other tool carrier/repair frame 6.

Claims

1. A cutting tool (10, 20) for cutting an umbilical (1) between preferably a subsea production and processing plant and a control room on shore or on a platform in connection with repair of a subsea umbilical (1), where said cutting tool (10, 20) is arranged on and operated by a remote-controlled underwater vessel or another tool carrier (6), characterised in that said cutting tool (10, 20) comprises: a fixing device (8) for connection to the remote-controlled subsea vessel or other tool carrier (6); a hydraulic unit (11 , 21), comprising a hydraulic motor, and a diamond wire (12, 22) that is connected to and continuously driven by the hydraulic motor, whereby the diamond wire (12, 22) will successively cut through all the layers and components of the umbilical (1) until it , has been completely cut off.

2. A cutting tool (20) in accordance with claim 1 , characterised in that said diamond wire (22) is designed to be mounted around a mainly peripheral area of the umbilical (1) and, moreover, is moved, by means of the hydraulic motor, in a continuous rotational movement around the umbilical (1) until it has been completely cut off.

3. A cutting tool (10) in accordance with claim 1 , characterised in that said cutting tool (10) is designed as a bow saw comprising a brace (15) with a guide track for said diamond wire (12), which is driven by the hydraulic motor, whereby the bow saw is moved in a continuous downward movement until the umbilical (1) has been completely cut off.

4. A method for cutting an umbilical (1) between preferably a subsea production and processing plant and a control room on shore or on a platform, using a cutting tool (10, 20) in accordance with claim 1 , characterised in that said method comprises the following steps: said umbilicaPs damage site (25) is identified; said umbilical (1) is lifted up from the seabed and placed preferably in one or more frames (6) of a type known in the art; said cutting tool (10, 20) is arranged in position, preferably at the umbilical's damage site/cutting site (25), and said cutting tool (10, 20) is activated and all layers and components in the umbilical (1) are cut successively, thus producing a cut with a clean cut surface.

5. A method in accordance with claim 4, characterised in that said cutting tool (10, 20) is arranged in position at the cutting site (25) and is handled by a remote-controlled subsea vessel or another tool carrier (6).

6. A method in accordance with claim 4, characterised in that said cutting tool (10, 20) is mounted separately in a repair frame (6) and is operated by means of said frame.

7. A method in accordance with claim 4, 5 or 6, characterised in that said cutting tool (10, 20) is arranged in position above said umbilical (1) and said cutting tool's diamond wire (12) is put into continuous motion and said cutting tool (10) is moved downwards until the umbilical (1) has been cut off. A method in accordance with claim 4, 5 or 6, characterised in that said cutting tool (20) is arranged in position beside the umbilical (1) and a diamond wire (22) is pulled around the umbilical (1) in a continuous operation until the umbilical (1) has been cut off.