Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Patent
1997-07-02
1999-09-07
Taylor, Dennis L.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
226168, 254407, 405158, F16L 104
Patent
active
059476419
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to improvements in marine pipelaying methods and apparatus of the type in which a rigid pipeline is bent around an arcuate path at some stage in the pipelaying process. It is particularly concerned with avoiding damage to the pipe caused by zones of differing stiffness within the pipeline being bent around such an arcuate path.
Certain types of marine pipelaying operations involve the pipe being bent around an arcuate path, the pipeline often being subject to plastic deformation during such bending and subsequent straightening in the course of the laying operation. Such bending occurs both in pipeline systems where a continuous length of pipeline is assembled onshore and is spooled onto a reel, the pipe being unspooled from the reel and straightened as it is laid from the lay vessel, and in a variation of "stovepipe" operations in which joints of pipe are assembled into a continuous pipe on board the vessel and in which the assembled pipe is plastically bent around an arcuate path and subsequently straightened in order to achieve a desired launch angle of the pipe from the vessel.
The pipeline may include zones of differing stiffness. For example, the pipeline may include "buckle arresters" at periodic intervals. Buckle arresters comprise short lengths of pipe having greater wall thickness and greater outside diameter than the main body of the pipeline, and are incorporated into the pipeline at intervals to arrest the propagation of buckles in the pipeline which may occur if the pipeline tension is not correctly controlled during laying. Such buckle arresters constitute zones of increased stiffness in the length of the pipeline.
It has not hitherto been possible to pass buckle arresters around arcuate paths in the types of pipelaying system referred to above. When the pipe is bent around an arcuate pipe bearing surface defining an arcuate path, such as a reel or an arcuate diverter structure, the pipe will tend to hinge on either side of the zone of increased stiffness. This situation is worsened when the zone of increased stiffness also has an increased outside diameter.
It is an object of the present invention to provide a method and apparatus whereby a pipeline incorporating zones of differing stiffness can be bent around an arcuate path without damage to the pipeline adjacent such zones.
In accordance with a first aspect of the invention there is provided a method of bending a pipeline around an arcuate pipeline bearing surface defining an arcuate pipeline path, said pipeline having a main body of substantially uniform longitudinal stiffness and including one or more localised zones wherein the longitudinal stiffness is greater than that of the main body of the pipeline comprising varying the radius of curvature of the pipeline as it passes around said arcuate path over a predetermined distance along the pipeline on either side of said localised zone of increased stiffness, said radius of curvature being varied between a first value adjacent said zone which is greater than the radius of curvature of the arcuate path and a second value at the end of said predetermined distance which is substantially equal to the radius of curvature of the arcuate path, so as to prevent hinging of the pipeline on either side of said localised zone of increased stiffness.
Preferably, said first value of said radius of curvature and said predetermined distance are dependent upon the relative stiffnesses of the main body of the pipeline and of said localised zone and on the radius of curvature of the arcuate path.
Preferably, said radius of curvature is varied by the introduction of packing elements between the pipeline and the arcuate pipe bearing surface on either side of said zone.
Preferably also, said packing elements are attached to the pipeline prior to the pipeline passing around said arcuate path.
Most preferably, said packing elements each comprise a graded series of discrete elements adapted to be attached to the pipeline at intervals along said predetermined distances on either side
REFERENCES:
patent: 5348423 (1994-09-01), Maloberti et al.
patent: 5692859 (1997-12-01), Dickson et al.
Coflexip Stena Offshore Limited
Taylor Dennis L.
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