Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Reexamination Certificate
2000-02-03
2001-09-18
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
C405S168100, C405S173000, C015S003500, C137S015010, C137S317000
Reexamination Certificate
active
06290431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diverless process for tapping a pressurized subsea pipeline without removing the pipeline from service. This diverless process utilizes specialty clamping equipment, tapping equipment and remote operating vehicles for operating at water depths beyond that accessible by divers.
2. Prior Art
Various kinds of underwater pipeline work have been carried out using divers equipped with various tools. Deep water conditions entail high subsea pressure and dangerous conditions. Manned or diver equipped operations are not suitable if the pipeline is at a depth which is inaccessible by divers.
Remote operating vehicles perform visual and operational functions that are more limited than those functions performed by divers. To compensate for this limitation, processes must be developed to adapt the available technology to the work requirements. These processes are typically referred to as “diverless”. Developed diverless processes are easily adapted for use using divers and/or control from the sea surface in diver accessible water depths.
It has been proposed in the past to utilize a diverless underwater pipe tap system. De Sivry et al. (U.S. Pat. No. 4,443,129) discloses an example of a diverless underwater pipe tap system including a lifting device to engage and displace the pipe, a working platform installed vertically above the tapping region and various tools used to carry out operations including concrete stripping, ovality or roundness measurement, and a tapping operation. De Sivry et al. contemplates cutting out a section of the pipeline. There is no disclosure or suggestion of a tap procedure while the pipeline is under pressure and de Sivry would not be suitable for such an operation.
Likewise, various hot tap machines for tapping into a pipeline while the pipeline is pressurized have been disclosed. Reneau et al. (U.S. Pat. No. 4,223,925) discloses one example of a hot tap machine for an underwater pipeline. It is advantageous to perform work on the pipeline without interrupting the flow of liquids or gases therethrough.
It is also known to provide a remote operated subsea vehicle (ROV) controlled from the surface which includes thrusters or other mechanisms for propelling it through the water in response to a source of power at or controlled from the surface.
Brooks et al. (Re27,745) illustrates an example of a submersible wireline robot unit that may be controlled remotely.
None of the foregoing would be suitable for deep water conditions where the external subsea pressure is extreme.
Given that the life spans of certain deep water oil and gas developments will be coming to an end in the near future, there will be an increasing number of existing pipelines which have excess transport capacity, thereby leaving excess pipeline infrastructure in deep water locations.
If production from new fields can be tied into existing pipelines, then the investment in the pipeline can be spread out over more than one development. A diverless hot tap capability would allow the extension of pipelines from new fields to be connected to existing pipelines. This will reduce the overall length of the pipeline required to support a new field.
It would also be possible to lay new trunk lines into areas in order to support multiple future field developments which would use lateral pipelines without having to pre-install connection facilities and valves at predetermined locations along the pipeline.
Additionally, in deep water oil and gas developments, the cost of the pipeline infrastructure is estimated to be the majority of the cost of all of the installed subsea equipment.
As an alternative to diverless hot tap systems, it would be possible to take an existing line out of service, cut a section of the pipeline and bring it to the surface, install a valve, lower the section back to the bottom and reconnect with a suitable jumper. Such an approach is not only time-consuming but requires the pipeline to be out of service. It would also be possible to pre-install blind branch connection facilities in the pipeline for future tie-ins. A disadvantage is that a great number of branch facilities would have to be installed to cover all possible future tie-in locations, a procedure that would be both time-consuming and expensive.
Notwithstanding the foregoing, there remains a need for a diverless process of tapping a deep water subsea pipeline under high pressure without removing the pipeline from service.
SUMMARY OF THE INVENTION
The invention described herein is a diverless process for tapping into a deep water, pressurized subsea pipeline without removing the pipeline from service. This invention provides a method to hot tap into an existing subsea pipeline and connect a second, or multiple, pipelines by means of a horizontal pull-in and connection process.
The initial phase will be locating a desired position of the hot tap along the pipeline and determining the in-situ conditions at that location. Various means such as subsea cameras, side-scan sonar, towed vehicles and remotely operated vehicles (ROV) may be used to locate and identify an area of interest. A preferred location on the pipeline will be indicated by the absence of any circumferential or longitudinal welds.
After the desired area of interest and pipe section have been located, it may be necessary to excavate soil, sand or silt from underneath the pipeline to provide access for the hot tap equipment. A work-class ROV may be used to blow away the soil, sand or silt or a suction dredge may be used to remove it, thereby creating an excavated area for installing the hot tap equipment. It may then be necessary for the ROV to clean the pipeline using a hydraulically operated brush or low pressure water jet.
In the next stage, two or more pipe lifting frames will be lowered from the surface and aligned by the ROV to straddle the pipeline during positioning. The lifting frames will be spaced at appropriate positions along the pipeline to effectively lift the pipeline without exceeding its plastic limit or otherwise damaging the pipeline. The distance between, and the number of lifting frames required, will be dependent upon the pipe size, wall thickness, internal pressure, soil conditions and other site-specific parameters.
Each of the lifting frames incorporates a pipe grip mechanism that can move transverse or perpendicular to the axis of the pipeline and lowered onto the pipeline using hydraulic supply and controls provided by the ROV. The pipe lifting frames are also fitted with mud mats that may be extended or retracted by the ROV to provide sea bed stability.
After the lifting frame is positioned over the pipeline at the desired location, the pipe grip mechanism is lowered onto the pipeline using the ROV hydraulic supply and controls. After the pipe grip is lowered and brought into contact with the pipeline, the grip mechanism is closed securely around it and hydraulically locked. The pipe grip mechanism, then supporting the pipeline, is raised to the desired height above the sea bed by the ROV using a mechanical jack screw device or hydraulic means. The second pipe lifting frame is landed and operated in a similar manner so that the pipeline is supported by at least two lifting frames.
When the pipeline has been raised to the desired height by the pipe lifting frames, a measurement tool will be lowered from the surface on to the pipeline to check pipe roundness, ovality and axial alignment or straightness. The measurement tool will be guided into position and then powered and controlled by the ROV.
After the pipeline has been checked for ovality and straightness, the measurement tool will inspect the pipeline condition at the desired hot tap area and note any anomalies or welds in the area. In the event that the pipeline contains a longitudinal weld that would affect the sealing area, a weld bead removal tool will be lowered from the surface and guided onto the pipeline by the ROV. The ROV will then operate the weld bead removal tool to machine the weld fl
Cross Donald W.
Decker Larry
Exley Gern D.
Hicks David J.
McCoy Richard W.
Bagnell David
Head Johnson & Kachigian
Mayo Tara L
Williams Field Services Gulf Coast Company, L.P.
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