GB2295874A - Pipeline isolation apparatus and method - Google Patents

Abstract

The apparatus, for use on the ends of tee-pieces 5 or on elongate sections of pipeline, comprises a body 40 having a chamber 60, sealable means 45 for receiving a portion of a pipeline 10 within the chamber 60 and means for controlling the pressure of fluid within the chamber 60 such that, in use, the pressure of the fluid within the chamber 60 is at least equal to the pressure of the fluid within the pipeline 10. The apparatus may further be provided with an access hatch 50 to permit access to and from the chamber and an umbilical cord 55 for controlling the pressure. <IMAGE>

Description

Pipeline Isolation Apparatus and Method This invention relates to an apparatus and method for the isolation of pipelines and in particular, though not exclusively, to subsea pipelines used for the transport of oil and gas.

To cater for the increasing exploitation of subsea oil and gas reserves there is present upon the worlds seabeds a myriad of pipelines and associated piping networks. The installation of such pipework can, even in relatively shallow waters, be very expensive. There are, therefore, significant economic advantages to be gained from the adaption and expansion of existing pipework to meet product transport requirements.

When effecting a connection to an existing subsea pipeline it is of paramount importance to both provide a safe working environment for divers and diving equipment and to prevent or minimise the escape of oil or gas into the surrounding ocean. To this end many oil and gas pipelines, when initially installed, are provided with tee-pieces or connections to permit future expansion or tie-in with another pipeline. If foresight was exhibited in the installation of the original pipeline tee-pieces may be provided with isolation valves. However, it is frequently found that these isolation valves are incapable of providing an adequate barrier. Thus it is often found impossible to complete the tie-in whilst continuing to use the existing pipeline to transport fluid.In this event the pipeline has to be shut down or depressurised to a lower level, both of which are expensive, time consuming and lead to reduced production.

Further, isolation techniques exist which can be used to interrupt the flow of fluid within a pipeline and thus provide a safe area. These involve the introduction of a blocking element into the pipe or the freezing of fluid within the pipe. The first of these is accomplished by the introduction of a "pig" or "packer" into the pipeline by either pumping or manual insertion at an appropriate entry point. However manual insertion cannot be carried out when a safe area does not already exist. The pig/packer can be actuated by umbilical command, remote control, hydraulic pressure or any other appropriate method. A drawback with this technique is that it cannot be used where doubt exists regarding the integrity of the tee-piece or connection isolation valves.

The second technique is non-intrusive and involves the introduction of a suitable liquid media into the region of the relevant valves or pipework. This liquid is then frozen by the external application of a low temperature refrigerant or liquid nitrogen. This technique can be used where the former is unsuitable but it can be costly due, for example, to vessel time requirements.

The two techniques discussed above may also be used to isolate sections of pipelines which have not been installed with future connection points but need to be modified thus. They may also be used for repair or maintenance operations on lengths of pipe which require intervention. In either case the problemsldisadvantages hereinbefore discussed are present.

It is an object, therefore, of the present invention to obviate or mitigate at least some of the aforementioned problems/disadvantages.

According to a first aspect of the present invention there is provided an apparatus for isolating a portion of a pipeline comprising a body having a chamber, sealable means for receiving said portion of said pipeline within said chamber and means for controlling pressure of fluid within said chamber such that, in use, said pressure of said fluid is at least equal to pressure of fluid within the pipeline.

In this way if the portion of the pipe is opened or cut, and the fluids allowed into intimate contact, the fluid within the pipeline will be caused to remain substantially within the pipeline.

In a first embodiment of the present invention particularly adapted for isolating an end of a tee-piece of a pipeline, the sealable means comprises a first port provided with a seal.

In a second embodiment of the present invention particularly adapted for isolating a portion of an elongate pipeline, the sealable means comprise first and second ports at opposing ends of said body, said first and second parts being provided with respective seals.

Further in said second embodiment said body may comprise at least two portions which portions are sealably engageable one with the other around said pipeline so as to form said chamber.

Said means for controlling pressure of fluid within said chamber preferably comprises an umbilical connection.

Said body may be provided with an access hatch or the like.

The fluid within chamber may be a gas or a liquid.

According to a second aspect of the present invention there is provided a method of isolating a portion of a pipeline comprising: providing an apparatus comprising a body having a chamber; locating said apparatus on said portion, such that said portion is location within said chamber; sealing said chamber; and controlling pressure of fluid within said chamber such that said pressure of said fluid is at least equal to pressure of fluid within the pipeline.

Two embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures which are: Fig 1 a schematic representation of a pipeline incorporating a tee-piece; Fig 2 a cross-sectional representation of a pipeline isolation apparatus in accordance with a first embodiment of the present invention, adapted for use at a pipeline tee-piece; Fig 3 a partially cut-away perspective view of the apparatus of Fig 2; Fig 4 a schematic representation of a conventional intervention operation required to isolate a damaged pipe section; Fig 5 an exploded view of a pipeline isolation apparatus in accordance with a second embodiment of the present invention, adapted for use on a length of pipeline; and Fig 6 a partially cut away perspective view of the apparatus of Fig 5 installed on a length of pipeline.

Referring firstly to Fig 1, there is shown a schematic representation of a typical tee-piece 5 attached to a pipeline 10. The pipeline 10 may be a subsea pipeline. Isolation valves 15 are provided to prevent fluid within the pipeline 10 from escaping via extension points 20 and 25. Extension point 25 is provided with a flange 30 to facilitate the connection of further pipework. In the event of the isolation valves 15 being incapable of providing an adequate barrier while connecting further pipework alternative means of flow interruption need to be implemented.

Referring now to Figs 2 and 3 there is shown a first embodiment of an apparatus according to the present invention comprising a hyperbaric module 35 which serves to encapsulate the extension point 25 on tee-piece 5.

Said module 35 provides a substantially cylindrical main body 40, having a chamber 60 and sealable means in the form of an attachment device 45 on the body 40 for receiving the extension point 25 within the chamber 60.

The attachment device 45 thus anchors the module 35 to the tee-piece 5. The attachment device 45 includes means to hermetically seal the module 35 when in place on the tee-piece 5.

The module 35 further provides an access hatch 50 and communication means 55 between the module 35 and external control mechanisms (not shown). The communication means may take the form of an umbilical connection to a surface vessel for controlling the pressure of fluid within the module 35.

In use, the module 35 is positioned by suitable means upon the tee-piece 5. The positioning operation may be carried out by, for example, a manned submersible, a remotely operated vehicle, or via a crane situated on a diving support vessel. The actual method adapted will be governed by conditions such as the depth of the pipeline and the orientation of the tee-piece 5 relative to the surface.

To ease installation the module 35 may be assembled from a plurality of discrete segments or incorporate hinged sections to allow it to be fitted over awkward piping configurations. Once in place the module 35 is anchored to the tee-piece 5 by the attachment device 45.

Said device 45 may advantageously be able to accommodate a range of pipeline surface conditions such as a fusion bonded epoxy anti-corrosion layer or a concrete antibuoyancy coating.

Once in place the module 35 is sealed such that chamber 60 is hermetic in nature. Chamber 60 can then be pressurised to match or exceed the internal pressure of the pipeline itself.

If fluids within the chamber 60 and the pipeline 10 are brought into intimate contact, (for example by removing or opening valve 25 or by removing a portion of the pipeline 10 by cutting) fluid with the pipeline 10 will not flow into the chamber 60. As the pressures of fluids contained within pipelines can vary enormously a number of techniques for pressurising the chamber 60 are possible. These may typically encompass the use of pressurised fluids such as sea water or diving gas if human entry into the chamber 60 is sought. The pressurised environment contained within the chamber is regulated via the control means 55.

Entry into the chamber 60 can be conducted through the access hatch 50. It will be apparent that the hatch 50 will need to be equipped with a form of "airlock" if the chamber 60 is not to depressurise during entry.

Access may be granted to either human or mechanical resources and this choice will depend on a number of factors including the type of work to be carried out within the chamber 60, the depth at which operations are being conducted, the overall dimensions of the module 35 and work site, and the pressure and nature of the fluid contained within the chamber 60 to identify but a few.

For example, if operations are required to be conducted on a 50mm diameter pipe carrying a highly pressurised gas then the module 35 could be equipped with remotely operated actuation and manipulation devices within the chamber 60. On the other hand if the pipe diameter is large enough and the pipeline 10 carries liquid at a relatively low pressure then a manned module 35 could be employed. The chamber 60 could be pressurised with diving gas and an operator saturated to the same pressure installed via the access hatch 50. In this particular example the module 35 acts in much the same way as a hyperbaric diving habitat.

It will be apparent to one skilled in this particular art that the operation of such systems described hereinbefore will require the implementation of dedicated safety procedures and associated devices. This is required to counter the risks of such eventualities as a chamber 60 breach and consequent sudden decompression.

Fig 4 shows a schematic representation of a length of pipeline 65. In order to repair structural damage or to install a pipe junction at a point 70 it has in the past been necessary to interrupt the flow of fluid upstream and downstream of the work area. This has in the past been accomplished by the aformentioned freezing or packing operations by isolating the pipeline at points 75 and 80 on either side of the point 70.

Figs 5 and 6 illustrate a second embodiment of the present invention adapted to fit on to an uninterrupted length of pipe 10. In the second embodiment there is provided a hyperbaric module 35 composed of a substantially cylindrical main body 40, a pair of attachment devices 45, an access hatch 50 and communication means 55 between the module 35 and external control mechanisms (not shown) . As in the first embodiment the module 35 provides a hermetically sealed chamber 60 around the pipeline 10, and in this instance a work area 90.

It should be understood that the embodiments of the present invention described hereinbefore are given by way of example only, and are not meant to limit the scope of the invention in any way. Indeed it will be apparent to one skilled in this particular art that the invention can be configured to accommodate a wide range of operating parameters such as pipe diameter, operating depth, pipe orientation relative to the surface etc.

From the foregoing description it is apparent that the present invention seeks to alleviate the disadvantages associated with prior art isolation techniques by the use of externally mounted apparatus.

Said apparatus is used to provide a local balanced pressure environment thus allowing access to the inside of the pipeline without the need for freezing or the utilisation of an internal blocking device.

Claims (10)

Claims

1 An apparatus for isolating a portion of a pipeline comprising a body having a chamber, sealable means for receiving said portion of said pipeline within said chamber and means for controlling the pressure of fluid within said chamber such that, in use, said pressure of said fluid is at least equal to pressure of fluid within the pipeline.

2. An apparatus as claimed in claim 1, wherein the apparatus is adapted for isolating an end of a tee-piece of a pipeline, the sealable means comprising a first port provided with a seal.

3. An apparatus as claimed in claim 1, wherein the apparatus is adapted for isolating a portion of an elongate pipeline, the sealable means comprise first and second ports at opposing ends of said body, the first and second ports being provided with respective seals.

4. An apparatus as claimed in claim 3, wherein the body comprises at least two portions which portions are seal ably engageable one with the other around the pipeline so as to form the chamber.

5. An apparatus as claimed in any preceding claim, wherein the means for controlling pressure of fluid within the chamber comprises an umbilical connection.

6. An apparatus as claimed in any preceding claim, wherein the body is provided with an access hatch or the like.

7. An apparatus as claimed in any preceding claim, wherein the fluid within the chamber is a gas or a liquid.

8. A method of isolating a portion of a pipeline comprising: providing an apparatus comprising a body having a chamber; locating the apparatus on the portion, such that said portion is location within said chamber; sealing the chamber; and controlling pressure of fluid within the chamber such that the pressure of the fluid is at least equal to pressure of fluid within the pipeline.

9. A pipeline isolation apparatus as hereinbefore described with reference to Figs 2 and 3 or Figs 5 and 6.

10. A method of isolating a portion of a pipeline as hereinbefore described with reference to Figs 2 and 3 or Figs 5 and 6.