WO2007064223A1

WO2007064223A1 - Method and device for preventing water ingress to critical lines in umbilical

Info

Publication number: WO2007064223A1
Application number: PCT/NO2006/000443
Authority: WO
Inventors: Harald Arnt Friisk; Geir Aalvik; 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: NO20055697L; NO20055697D0; NO325701B1

Abstract

A method and a clamping tool (10) for preventing water penetration in critical umbilical guides (4) 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 (1) underwater. The method comprises the following steps, which are performed by means of a remote-controlled underwater vessel or another tool carrier: the damage site (25) on the umbilical is identified and a sufficient part of the umbilical (1) is exposed on each side of the damage site (25); the umbilical (1) is lifted up from the seabed and placed preferably in one or more frames (6) of a type known in the art, after which the outer casing (2) and support elements (3) of the umbilical are removed and the individual umbilical guides or pipes (4) are revealed and identified; a clamping tool (10) is placed in position above the pipe (4) to be protected or sealed against water penetration; the clamping tool (10) is activated and the pipe is clamped flat, whereby the internal open area/cavity of the pipe decreases to approximately zero, and a pulsating movement is applied to the flat-clamped area (5) by means of the clamping tool (10), whereby material flow and internal mechanical fusion cold- weld and seal the pipe's flat-clamped area (5).

Description

"Method and device for preventing water ingress to critical lines in umbilical"

The present invention concerns a method and a clamping tool for preventing water penetration in critical umbilical guides between preferably an underwater production and processing plant and a control room on shore or on a platform in connection with repair of a subsea umbilical.

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 shore 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 on the seabed and pull the end up to a service vessel for further processing. The damaged section and a sufficient additional length of the umbilical are removed to ensure that as small a quantity of particles and seawater as possible mixed into the hydraulic fluid exists in the supply line when the umbilical is reinstalled after repair. Compressibility and the resistance of the hydraulic fluid to being mixed with water mean that only a limited length of a traditionally structured umbilical from the damaged area must be removed to splice in a new section.

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.

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 problems associated with the repair of umbilicals that include supply pipes for barrier gas. If the gas pipe is cut under pressure, the pressure in the lines will be reduced to the ambient pressure and water will penetrate into the gas pipe more easily than when it is mixed with a hydraulic fluid. The location of the damage along the route will also affect how far the seawater will be able to penetrate on each side of the cut site. Traditional underwater cutting will involve a considerable section of the umbilical being removed to ensure purity in the line. The traditional solution will, therefore, involve considerable uncertainty about how far back it is necessary to cut and what additional length has to be spliced in. The geometric shape of the umbilical during the repair and the fact that water will flow away from the cut site, while the umbilical is being pulled up to the service vessel, and further into the umbilical will further increase how far back a final cut has to be made. Technical uncertainties and costs involved with a repair, as well as requirements for backup umbilical length, mean that a traditional repair method is not considered to be a good solution for a repair of an umbilical as mentioned above.

One object of the present invention is, therefore, to prevent penetration of seawater into the umbilicaPs barrier gas line during all phases of a repair.

Another object of the present invention is to prevent seawater from becoming mixed with all hydraulic lines or pipes in the umbilical to reduce requirements for necessary cutting back of the umbilical before a new section is.spliced in.

The objects of the present invention are achieved by means of a method for preventing water penetration in critical umbilical guides between preferably a subsea production and processing plant and a control room on shore or on a platform in connection with a repair of an umbilical subsea. The method comprises the following steps, which are performed by means of a remote- controlled underwater vessel or another tool carrier:

- the damage site on the umbilical is identified and a sufficient part of the umbilical is exposed on each side of the damage site;

- the umbilical is lifted up from the seabed and placed preferably in one or more frames of a type known in the art, after which the outer casing and support elements of the umbilical are removed and the individual umbilical guides or pipes are revealed and identified; - a clamping tool is placed in position above the pipe to be protected or sealed against water penetration;

- the clamping tool is activated and the pipe is clamped flat, whereby the internal open area/cavity of the pipe decreases to approximately zero, and

- a pulsating movement is applied to the flat-clamped area by means of the clamping tool, whereby material flow and internal mechanical fusion cold- weld and seal the pipe's flat-clamped area. Preferred embodiments of the method are further elaborated on in claims 2, 3 and 4.

Moreover, the objects of the present invention are achieved by means of a clamping tool for preventing water penetration in critical umbilical guides between preferably an underwater production and processing plant and a control room on shore or on a platform in connection with the operation of an umbilical underwater, where the tool is designed as a U-shaped claw with an internal, movable clamping piston for compressing and flat-clamping a pipe arranged inside the claw between one leg of the claw and the clamping piston.

Preferred embodiments of the clamping tool are further elaborated on in claims 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 that is lifted up from the seabed, Fig. 2 shows the cross-section of an umbilical, Fig. 3 shows a perspective image of a truncated umbilical,

Fig. 4 shows a clamping tool in accordance with the present invention, and Fig. 5 shows the internal pipes of the umbilical exposed after removal of the outer casing and support elements.

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 an underwater 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. s A sufficient part of the umbilical 1 must then be exposed on each side of the damage site 25. The umbilical 1 will thus be placed in the frames 6 to ensure controlled removal of the outer casing 2 and support elements 3 of the umbilical so that the exposure of the individual pipes 4 in the umbilical 1 makes it possible to mount a clamping tool 10, which is shown in Figure 4. The clamping o tool 10 is designed as a U-shaped claw 11 with an internal, movable clamping piston 15 for compressing and clamping a pipe 4 arranged inside the claw 11 between one leg 12 of the claw and the clamping piston 15. The clamping tool 10 is also arranged with a pulsating device. The leg 12 of the U-shaped claw is also arranged with an internal press surface 18 and the opposite surface of the s clamping piston is arranged with an internal press surface 20. The press surface 18 and the press surface 20 are designed with approximately flat press surfaces that are adapted to one or more specific sets of pipe dimensions. The opposing press surfaces 18, 20 of the clamping tool are also arranged with upper and lower complementary projections 19, 21 for limited compression of 0 the pipe 4.

The method for preventing water penetration involves the critical pipe(s) 4 in the umbilical 1 being clamped flat mechanically in areas 5 using the clamping tool 10 and then being cold-welded or sealed by means of the clamping tool's s pulsating device. This sealing is performed at a minimum of two sites on each side of the damaged area. Reference is made to Figure 5 in this connection. The method and the clamping tool 10 in accordance with the present invention are intended to be used to prevent water penetration and to seal critical umbilical guides before the final cut is performed underwater, and the umbilical 0 is finally pulled up for further processing and repair. The clamping tool 10 for clamping and cold-welding the pipes in question is hydraulically operated and is placed in position above the pipe using a remote- controlled underwater vessel or another tool carrier. The clamping tool 10 is arranged with a fixing device 8 for connection to the remote-controlled underwater vessel or repair frame 6. The pipe in question 4 is first clamped as flat as possible so that the pipe's internal open area/cavity is reduced to approximately zero. The operation is performed by means of constant pressurisation of a hydraulic cylinder 14 that transfers the forces in a clamping function around the pipe 4.

After the initial clamping of the pipe 4, the tool 10 will pulsate further to achieve material flow and internal mechanical "fusion" to prevent water from penetrating past the clamped/cold-welded area of the pipe 4 when final cutting is performed underwater before the umbilical is pulled up to the service vessel. As mentioned above, the clamping tool 10 will have a design that allows one or more specific sets of pipe dimensions to be compressed and cold-welded. The press surfaces 18, 20 of the clamping tool are arranged with upper and lower complementary projections 19, 21 to hold the pipe 4 in place and limit its compression, thus preventing possible cracking of the pipe material.

The critical pipes 4 in an umbilical 1 of the type stated are sealed in an effective manner by means of the method and the clamping tool 10 in accordance with the present invention. The final cutting and pull-up of the umbilical 1 can thus be performed without any risk of water penetration in critical pipes 4.

Claims

Claims:

1. A method for preventing water penetration in critical umbilical guides (4) between preferably a subsea production and processing plant and a

5 control room on shore or on a platform in connection with repair of a subsea umbilical (1), characterised in that it comprises the following steps, which are performed by means of a remote-controlled subsea vessel or another tool carrier: o the damage site (25) on said umbilical is identified and a sufficient part of the umbilical (1) is exposed on each side of the damage site (25); 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, after which the outer casing (2) and support elements (3) of the umbilical are removed and the s individual umbilical guides or pipes (4) are revealed and identified; a clamping tool (10) is placed in position above the pipe (4) to be protected or sealed against water penetration; the clamping tool (10) is activated and the pipe is clamped flat, whereby the internal open area/cavity of the pipe decreases to approximately 0 zero, and a pulsating movement is applied to the flat-clamped area (5) by means of the clamping tool (10), whereby material flow and internal mechanical fusion cold-weld and seal the pipe's flat-clamped area (5).

s

2. A method in accordance with claim 1 , characterised in that said pipe (4) is sealed in at least two places on both sides of the damage site (25).

0 3. A method in accordance with claim 1 or 2, characterised in that said pipe (4) to be sealed is a hydraulic supply or return pipe.

4. A method in accordance with claim 1 , 2 or 3, characterised in that said pipe (4) to be sealed is a protective gas pipe.

5. A clamping tool (10) for preventing water penetration in critical umbilical guides (4) between preferably an underwater production and processing plant and a control room on shore or on a platform in connection with an operation of an umbilical (1) underwater, characterised in that the clamping tool (10) is designed as a U-shaped claw (11) with an internal, movable clamping piston (15) for compressing and flat-clamping a pipe (4) arranged inside the claw (11) between one leg (12) of the claw and the clamping piston (15).

6. A clamping tool (10) in accordance with claim 5, characterised in that the clamping tool (10) is arranged with a pulsating device, which causes the flat-clamped area (5) of the pipe to fuse mechanically and be cold- welded.

7. A clamping tool (10) in accordance with claim 5 or 6, characterised in that one internal press surface (18) of the claw and the opposite press surface (20) of the clamping piston are designed with approximately flat press surfaces that are adapted to one or more specific sets of pipe dimensions.

8. A clamping tool (10) in accordance with claim 5, 6 or 7, characterised in that the opposing press surfaces (18, 20) of the claw and the clamping piston are arranged with upper and lower complementary projections (19, 21) for limited compression of the pipe (4).