GB2229787A

GB2229787A - A mobile emergency shut off valve system

Info

Publication number: GB2229787A
Application number: GB8907017A
Authority: GB
Inventors: Derek William Frank Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-03-28
Filing date: 1989-03-28
Publication date: 1990-10-03
Also published as: GB8907017D0

Abstract

A Mobile Emergency Shut-off plug or Valve 6 is located in a branched stowage receptacle 9 above an isolation valve 7 and out of the path of the normal fluid flow, shown by arrow 10 in a pipeline riser 1 leading from an oil production platform sited in water. The plug or Valve 6 is temporarily fixed within the receptacle 9 preventing it moving down the riser 1. For whatever reason, if it is required to shut off the flow of fluid in the riser 1 then the Valve 6 is released into the path of the fluid where its presence would normally constitute an unacceptable restriction. The Mobile Emergency Shut-off Valve system has means of stopping the progress of the valve 6 down the riser 1, fixing if to the inside of the riser 1 and effecting a seal preventing fluid communicating across the Valve 6. Means are also provided to retrieve the valve 6 after use (e.g. by a tether (11, Fig 3) or by pigging). The branched stowage receptacle 9 is located above the water surface but the position for stopping and actuating the deployed Valve 6 is below the water surface. <IMAGE>

Description

A MOBILE EMERGENCY SHUT OFF VALVE SYSTEM This invention relates to a mobile emergency shut off valve, hereinafter refered to as an MESV, and the means of installation and use thereof.

An hydrocarbon fluid producing installation sited in water extracts hydrocarbon deposits from underneath the seabed, lake bed or riverbed.

The fluid is processed and then exported to a land based site, other installation or loading system via a pipeline. Thus an installation may have pipes bringing fluid in and other pipes taking fluid out from the installation. The section of pipeline from the seabed to the topsides facility is known as a "riser". The installation may be fixed to the seabed or floating.

Risers can connect to pipelines of considerable length thus containing large quantities of hydrocarbon fluids. It is not current practice to provide shut off valves on these risers at a position below the water surface such that in an emergency, the installation may be isolated from the pipelines going to or from it. Shut off valves are normally provided above the water surface but an incident, which may not be directly associated with the riser, may breach the integrity of the riser in such a way that a uncontrolled escape of hydrocarbon fluid may occur. Such an incident may be a fire or explosion elsewhere on the installation which subsequently affects the integrity of the riser.

Emergency shut off valves can be permanently installed in a section of the riser or in the pipeline at a suitable position below the water surface which is considered to be protected by virtue of the protective layer of water above it and its distance away from the installation.

However, such valves cannot be readily maintained and retrospective fitment to existing installations involves flooding of the pipeline and carrying out extensive underwater work to fit the emergency shut off valve.

To avoid these problems associated with retrospective fitment, previous inventions have been proposed that permanently fit a valve internally, by passing through the pipeline a special valve designed to fit within the bore. Such a valve would be fixed at a predetermined location. This concept however causes a major restriction to the full bore thus affecting the flow capability of the pipeline in normal operation. The special valves prevent routine "pigging" of the pipeline and they may not be retrievable for inspection and maintenance work. "Pigging" is a term used for the passing of a mechanical device (the pig) through the length of the riser and pipeline for the purpose of cleaning the internal surface and carrying out inspection.

According to the present invention there is provided a Mobile Emergency Shut Off Valve system comprising a branched stowage pipe or receptacle built off the riser above the water surface; an MESV which is normally stowed in the receptacle out of the path of the fluid; an isolation valve separating the receptacle from the riser; an access means on the receptacle which is able to withstand the maximum pressure that can exist within the riser; a means of releasing the MESV automatically or manually from the receptacle such that it may pass under the action of gravity or other motive power down the riser or pipeline.

Further according to the present invention there is provided an MESV system which has means of stopping, then fixing and sealing the MESV to the inside of the riser or pipeline at a desired position below the water surface such that it can close or significantly restrict any fluid communication across the MESV.

Further according to the present invention there is provided means of retrieving the MESV. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a typical offshore production platform, riser and pipeline.

Figure 2 shows a riser and branch receptacle with the MESV in its stowed position.

Figure 3 shows the MESV deployed to a position in the riser below sea level.

Refering to Figure 1, a gas riser 1, is used to convey hydrocarbon gas to a pipeline 2, which in turn conveys the gas to a land based process facility. The riser joins the pipeline at the sea bed and forms a continuous pipe. The riser is attached to an offshore production platform 4. The sea level is shown and would typically be between 20 metres and 400 metres above the seabed.

Refering to Figure 2, an in line branch pipe 3 is built onto the riser such that the flow of gas by-passes the branch as shown by arrow 10. The branch is fitted with a full bore isolation valve 7 and actuator 8.

Above the valve a receptacle 9, hold the MESV 6. The isolation valve 7, is shown in the closed position. In this way the receptacle can be vented to atmosphere and an access means 5 opened to enable the removal of the MESV for inspection and testing as required. In standby mode the receptacle would be under riser pressure with the isolation valve 7 in the open position (not shown).

Refering to Figure 3, whether for test purposes or in response to an emergency on the platform, the MESV is released from the receptacle enabling it to pass under gravity down the riser. At a desired position at depth D below sea level, the MESV is stopped and temporarily fixed to the inside wall of the riser. After fixing, a sealing system is sequentially actuated to contain the gas in the pipeline and riser section below the MESV allowing gas pressure above to be vented if necessary.

A tether 11, may connect the MESV to a device in the receptacle enabling the subsequent retrieval of the MESV after equalising pressure across it. Alternatively the MESV could be "pigged" through the pipeline to the other end.

Similarly, the MESV will operate within a gas import riser where the gas may be flowing up the riser during deployment of the MESV. It is important that the MESV does not cause an excessive pressure drop across it resulting in an upthrust force which may inhibit the passage of the MESV down the riser.

Claims

1. A Mobile Emergency Shut Off Valve (MESV) system which can be installed above water level within an hydrocarbon fluid riser of an hydrocarbon production installation sited in water comprising an MESV which is normally located in an isolated branched receptacle out of the path of the fluid flow and for which means are provided to move the MESV into (and out of) the path of the fluid flow to (and from) a position below water level where it is temporarily fixed and can seal off or significantly restrict any fluid communications across the MESV.

2. An MESV system as claimed in Claim 1, wherein the system can be retrospectively installed to an existing facility without the need to flood the pipeline or carry out extensive underwater work.

3. An MESV system as claimed in Claim 1 or 2 wherein means includes means for allowing fluid to freely pass through the MESV during its descent after deployment until such time as the sealing system is activated.

4. An MESV system as claimed in Claims 1,2 or 3 wherein means includes means for retrieving the MESV after deployment whether for the purpose of routinely testing the system or as a result of an emergency necessitating the deployment of the MESV.

5. An MESV system as claimed in any one of the preceeding Claims wherein the MESV can be deployed manually or automatically.

6. An MESV system as claimed in any one of the preceeding Claims wherein the branched receptacle used to stow the MESV prior to deployment is provided with means of isolation from the riser.

7. An MESV system as claimed in Claim 6 wherein means includes means to vent the receptacle and access it for the removal and replacement of the MESV.

8. An MESV system as claimed in any one of the preceeding Claims wherein the MESV system can be installed in risers having fluid flow in any direction.

9. An MESV system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.