GB2528664A

GB2528664A - A subsea cutting tool and a blade therefor

Info

Publication number: GB2528664A
Application number: GB1413217.9A
Authority: GB
Inventors: Keith Elliott; Rory Mcgarry; Christopher James Bond
Original assignee: Allspeeds Holdings Ltd
Current assignee: Allspeeds Holdings Ltd
Priority date: 2014-07-25
Filing date: 2014-07-25
Publication date: 2016-02-03
Also published as: GB201413217D0

Abstract

A subsea cutting tool 1 and a blade (11, figure 2) therefor are provided primarily but not exclusively for use in severing umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like in emergency situations. The tool comprises a body 2 defining a cutting aperture 5 and at least one guide channel (7, figure 2) for the blade. An anvil 6 is retained by the body and the blade is moveable along the guide channel to contact the anvil. The blade is comprised of stainless steel with a carbon-based coating. The coating is preferably a layer of diamond-like carbon (DLC) and the stainless steel is preferably a plastic mould steel that is alloyed with nitrogen.

Description

A SUIBSEA CUTTING TOOL

AND A BLADE THERIEFOR

The present invention relates to a subsea cutting tool and to a blade therefor that is primarily but not exclusively for use in severing umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like in emergency situations.

In offshore industries, for example in oil and gas drilling industries, surface vessels are often connected to seabed installations and to the seabed itself by lines such as umbilicals, hydraulic hoses, tethers, moorings, towing lines and the like. Should an emergency situation arise, for example in heavy seas, it is sometimes necessary to sever these lines to disconnect the vessel from the installation or the seabed. Conventionally, hydraulic tools that are used in an installation at the seabed are fed with hydraulic fluid through hoses that are connected to the surface vessel. In the past, the severing of the hydraulic hose took place on or close to the vessel but this had the unfortunate consequence that the severed hose fell to the seabed and the hydraulic fluid it contained spilt into the sea. The heavy, severed end of the hose could also cause considerable damage to the installation itself as it fell to the seabed. Thereafter, the hose had to be recovered by divers for reconnection. The same applied to other umbilicals and lines connected to the vessel. More recently, hydraulic hose cutting tools have been deployed as part of a subsea rig so that the hose can be severed close to the rig and then reeled back into the vessel. This permits the hydraulic fluid to be contained and divers do not need to recover the hose prior to reconnection. However, the consequence of using a subsea hydraulic hose cutting tool is that it has to be submerged ready for emergency use for a considerable period of time, possibly for a number of years.

A conventional hydraulically actuated subsea cutting tool has a guillotine blade that is driven through the item to be cut and impacts against an anvil. Often such cutting tools are remotely operated, for example by attachment to a manipulator arm of a remotely operated vehicle (ROV) but in all cases they are deployed and then returned to a surface vessel. Hence, such a cutting tool is never submerged in seawater for a lengthy period of time. In order to withstand the forces involved and to enable the blade to cut through tough items such as armoured telecommunications and power cables, hydraulic lines and the like, the blade has to have a considerable compressive strength. Typically, therefore it is made from steel with a high mechanical strength. Also, as it is going to be deployed in a corrosive environment, it is usually protected from such corrosion by being given a coating of a titanium alloy or compound. One such coating is TiN (titanium nitride). Such a coating also increases the blade's hardness and lubricity, which is advantageous because generally the cutting edge of the blade tends to be blunt and becomes progressively blunted through use. This is rarely a problem as the hydraulic forces that power the blade are sufficient to drive it through most items to be cut. However, if the subsea cutting tool is to be employed as an emergency cutting tool it has to remain on stand-by in a submerged condition for a considerable period of time. In these circumstances protection of the blade by titanium alloy or a titanium compound is insufficient as seawater will eventually corrode or degrade the titanium coating.

In order to overcome the aforementioned problem, emergency-use subsea cutting tools have been proposed in which the blade is potted in wax or similar potting compound. This protects the blade from the corrosive effects of seawater but has the unfortunate consequence that operation of the cutting tool cannot be readily tested in situ as cycling the blade between its retracted and extended positions for testing breaks the wax seal. This means that the testing and maintenance of such cutting tools has to involve removal of the cutting tool from the seabed installation back to the surface vessel as the blade of the cutting tool has to be repotted before it can be redeployed.

One object of the present invention is to overcome or substantially mitigate the aforementioned disadvantages and to provide an emergency use subsea cutting tool that can be tested in situ while it is submerged without any need for it to be removed from a seabed rig.

According to a first aspect of the present invention there is provided a subsea cutting tool comprising a body defining a cutting aperture and at least one guide channel; an anvil retained by the body; and a blade moveable along said guide channel to contact the anvil, characterized in that the blade is comprised of stainless steel with a carbon-based coating.

In a conventional subsea cutting tool, a stainless steel blade would be impractical as its mechanical properties would be insufficient for the cutting operations that it has to perform so that it would quickly fail. However, it is has been found that if used in a subsea cutting tool for emergency use then the blade has sufficient mechanical strength for a one-cut use, which is all that is required. Also, the carbon-based coating provides a long-term corrosion resistance that enables the cutting tool to be maintained on stand-by in a submerged condition for many months.

Preferably, the coating is comprised of a layer of diamond-like carbon (DLC).

Preferably also, the coating has a thickness of at least 2 jim and is preferably in excess of 4 pm.

Preferably also, the blade has a sharp cutting edge.

According to a second aspect of the present invention there is provided a blade for a subsea cutting tool characterized in that it is comprised of stainless steel with a carbon-based coating.

It will be appreciated that while such a blade may only be capable of a single emergency cut, the rest of the tool may be re-used once re-fitted with a new blade.

The present invention will now be described by way of example with reference to the accompanying drawings in which;-Fig. 1 is a side elevation of a first embodiment of subsea cutting tool in accordance with the present invention, a blade thereof being shown in a retracted position; and Figs. 2 and 3 are longitudinal cross-sectional views of the tool along the lines Il-TI and Ill-Ill in Fig. irespectively but with the blade being shown in an extended position in Fig. 2; Fig. 4 is a side elevation of a second embodiment of subsea cutting tool in accordance with the present invention; and Fig. 5 is a longitudinal cross-sectional view along the line V-V in Fig. 4.

A first embodiment of subsea cutting tool 1 shown in Figs. 1 to 3 of the drawings comprises a bifurcate body 2 with first and second arms 3 and 4 between which is a substantially U-shaped, cutting aperture 5. An anvil 6 is detachably located through guide channels 7 formed in the arms 3, 4 so that in an operative position that it extends between the arms 3, 4 as shown in the drawings. The anvil 6 is secured in this position by securing screws 8 that screw into channels 9 formed in the arms 3, 4 and that carry locking washers which retain the anvil 6 in position. In this operative position the anvil 6 bridges the arms 3 and 4 and thereby traps any item it is desired to sever between the arms 3 and 4 within the aperture 5 defined by the body 2. It will be appreciated that for use in severing umbilicals and hydraulic hoses in emergency subsea situations, the hydraulic hose or umbilical to be severed is permanently located in such a trapped position ready to be severed by operation of the tool 1 at a moment's notice, the tool 1 being solely deployed for this purpose.

A guillotine blade 11 is mounted within the body 2 so that it can slide between the arms 3, 4 to contact the anvil 6. In this way the blade ii can be driven down the body 2, through any item trapped in the aperture 5, until it impacts the anvil 6, thereby severing the item. The blade ii is hydraulically actuated, being driven by a hydraulic piston 12 located within a housing 13 attached to the body 2. Located at the top and bottom of the housing 13 on opposite sides of the piston 12 are inlet/outlet ports 14 and 15 respectively through which pressurizing fluid can flow into or out of the housing 2 to reciprocate the piston 12 and thereby the blade 11 up and down. In use, the ports 14 and 15 are connected to hydraulic hoses that are linked to an appropriate self-contained hydraulic fluid control system that is controllable from a surface vessel.

A second embodiment of subsea cutting tool 20 is shown in Figs.4 and . This tool 20 is of cantilever design and in place of a bifurcate body has a hook-shaped body 21 that defines an interior cutting aperture 22 with a guide channel 23 along its inner side. At the base of the "hook" is seated an anvil 24. The anvil 24 in this embodiment does not need to be removed to locate the item to be cut in the cutting aperture 22 but is detachable from the tool 20 so that it can be replaced if necessary should it become damaged or removed during testing or servicing of the tool 20. A blade 25 is mounted in the upper part of the body 21 so that it can slide down the guide channel 23 to contact the anvil 24. As with the first embodiment, the blade 25 is hydraulically actuated by a hydraulic piston arrangement located within a housing 26 attached to the body 21. The details of this arrangement are identical to those described above with reference to Figs. 1 to 4 and have therefore been labelled with the same reference numerals.

In both embodiments of cutting tool 1, 20, the blade 11, 25 is comprised of stainless steel that has been coated with a carbon-based coating, in particular and preferably a layer of diamond-like carbon (DLC). It has been found that such a coating protects the blade 11, 25 from corrosion by seawater, is chemically inert and can withstand a harsh, subsea environment at considerable depths where the external pressure is high and the temperature is low. Unlike conventional steel blades with titanium-based corrosion-resistant coatings, a blade 11, 25 in accordance with the present invention is capable of remaining submerged yet still effective for many months.

Preferably, the stainless steel of the blade is a plastic mould steel that is alloyed with nitrogen and has been quenched and tempered to provide a hardness of between and 58 inclusive on the Rockwell scale. Nitrogen improves the corrosion resistance and also the wear resistance of the steel owing to a homogeneous distribution of fine precipitates. The fine, homogeneous, crystalline structure is the reason for its performance characteristics. The hardness of the steel would be impractical for a conventional subsea cutting tool but is sufficient for use in an emergency cutting tool as in the present application.

DLC coatings are abrasion resistant, which is important when they are deployed at depth in subsea conditions where grit contamination is a hazard, and exhibit lubricity so that the coated blade 11, 25 can travel smoothly up and do-i the guide channel or channel 7, 23. They also exhibit high hardness so that even the sharp tip of the blade 11, 25 is protected. In this regard, the anvil 6, 24 is preferably made of a softer material than the blade 11, 25, for example aluminium bronze. This means that in use the blade ii, penetrates the anvil 6, 24 to some extent to ensure a clean and swift cut.

Also, aluminium bronze is corrosion resistant, in particular by seawater.

DLC coatings are formed using knoi plasma enhanced chemical vapour deposition techniques when ionized and decomposed carbon or hydrocarbon species land on the surface of a substrate, in this case the stainless steel blade 11, 25 with an energy that is typically between 10 eV and 300eV. Tn particular, the uncoated blade 11, 25 is treated in a process chamber into which precursor gases are introduced. These gases are broken down within an ionized plasma into various species of carbon, hydrogen and other dopants that subsequently condense as a solid coating on the blade's surface. As the coating can be deposited at a low substrate temperature (<200°C) the structure of the blade 11, 25 is not damaged nor is cutting edge blunted. Once deposited, the DLC coating is amorphous and consists of carbon chains in an amorphous structure with a mixture of sp2 (triagonal graphite) & 53 (tetrahedral diamond) bondings. In the present invention, the coating is preferably deposited with a thickness of at least 2 am and advantageously is in excess of 4 pm.

is In use, the cutting tool 1, 20 is deployed with the blade 11, 25 retracted, as shown in Figs. 1, and 3 or Fig. , and the hose or umbilical to be cut already located in a within the cutting aperture 5, 22. In the first embodiment, therefore, the anvil 6 is secured between the arms 3, 4. The inlet/outlet ports housing 14 and 15 are connected to hydraulic hoses linked to the self-contained hydraulic fluid control system. The tool 1 is then in a stand-by condition ready for emergency deployment. On a signal from a surface vessel, hydraulic fluid is pumped into the inlet/outlet port 14 with the inlet/outlet port 15 unpressurized to force the piston 12 and thereby the blade 11, 25 downwards along the guide channel 7 or channels 23 so that the blade 11, 25 cuts through the trapped item, such as a hose or umbilical, as it impacts the anvil 6, 24. The cutting blade 11, 25 is primarily designed to be a single-use blade as the tool 1, 20 is for emergency use only. Hence, it does not matter if the cutting edge of the blade 11, 25 is damaged after use.

When it is desired to service the tool 1, 20 it is not necessary to return it to the surface vessel. Instead, the tool 1, 20 can be detached from the hose, umbilical or other line that it is intended to cut and the blade 11, 25 can then be reciprocated up and down for testing before the hose, umbilical or line is again located in the cutting aperture 5, 22 and, if necessary the anvil 6 replaced. In the second embodiment, as the anvil 24 is made of a softer material than the blade 25, the blade is not blunted by the anvil 24 during this testing procedure but the anvil 24 may be removed for testing if necessary.

Alter use of either of the cutting tools 1, 20 described above, the blade 11, 25 5 likely to be unserviceable. However, it is expected that in many cases the tool 1, 20 may be reusable once it has been fitted with a new blade 11, 25.

Claims

CLAIMS1. A subsea cutting tool comprising a body defining a cutting apertures and at least one guide channel; an anvil retained by the body; and a blade moveable along said guide channel to contact the anvil, characterized in that the blade is comprised of stainless steel with a carbon-based coating.
2. A tool as claimed in Claim 1, wherein the coating is comprised of a layer of diamond-like carbon (DLC).
3. A tool as claimed in Claim 1 or 2, characterized in that the coating has a thickness of at least 2 km.
4. A tool as claimed in any of Claims 1 to 3, characterized in that the coating has a thickness in excess of 4 pm.
5. A tool as claimed in any of Claims 1 to 4, characterized in that the blade is comprised of a plastic mould steel that is alloyed with nitrogen.
6. A tool as claimed in any of Claims 1 to 5, characterized in that the blade has a sharp cutting edge.
7. A tool as claimed in any of Claims 1 to 6, characterized in that the anvil is comprised of aluminium bronze.
8. A tool as claimed in any of Claims 1 to 7, characterized in that the anvil is detachably secured between the first and second arms of the body that respectively define one or a pair of guide channels.

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9. A tool as claimed in any of Claims 1 to 7, characterized in that is of a cantilever type.
10. A tool as claimed in any of Claims 1 to 9, characterized in that the blade is hydraulically actuated.
ii. A tool as claimed in Claim 10, characterized in that the blade is driven by a hydraulic piston located within a housing attached to the body.
12. A blade for a subsea cutting tool, characterized in that it is comprised of stainless steel with a carbon-based coating.
13. A blade as claimed in Claim 12, characterized in that wherein the coating is comprised of a layer of diamond-like carbon (DLC).
14. A blade as claimed in Claim 12 or 13, characterized in that the coating has a thickness of at least 2 pm.
15. A blade as claimed in any of Claims 12 to 14, characterized in that the coating has a thickness in excess of 4 jim.
16. A blade as claimed in any of Claims 12 to 15, characterized in that the blade is comprised of a plastic mould steel that is alloyed with nitrogen.
17. A blade as claimed in any of Claims 12 to i6, characterized in that it has been quenched and tempered to provide a hardness of between 53 and 8 inclusive on the Rockwell scale.
i8. A blade as claimed in any of Claims 12 to i6, wherein the blade has a sharp cutting edge.-11 -
19. A subsea cutting tool substantially as described herein with reference to any of Figs. 1 to 3 or either of Figs. 4 and 5 of the accompanying drawings.
20. A blade for a subsea cutting tool substantially as described herein with reference to any of the accompanying drawings.