Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – With protection or indication of pipe or trench
Patent
1991-07-18
1993-03-16
Corbin, David H.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
With protection or indication of pipe or trench
405158, 405172, F16L 112
Patent
active
051939371
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to seabed mattresses for the protection and stabilisation of seabed installations such as pipelines.
The use of mattresses, especially articulated mattresses, in offshore, coastal and marine engineering is well known for stabilisation, protection and scour prevention of pipelines, flowline umbilicals, seabed templates, steel and concrete platforms and the like. These mattresses are particularly useful in areas of high bottom current where hydrodynamic forces are considerable. Thus, for example, a seabed pipeline can be covered with such a mattress so that the pipeline is stabilised by the weight of the blanket thereon and also the adjacent seabed is protected against erosion. Examples of articulated mattresses and their use are given for example in European patent specification 152232A to which reference should be made for further details. Generally, these mattresses comprise concrete or similar elements joined together to allow relative articulation.
Subsea stabilisation mattresses can be relatively massive, eg. a mat of 5 m.times.2 m would weigh (in air) over 2.5 tonnes. However, even so, when they are laid over a seabed pipeline, for example, they can still be prone to movement during a storm or tidal surge. Whilst, in theory, greater stability could be obtained by increasing the mat weight, we have found another way of dealing with this problem.
Further, in addition to stability in extreme storm conditions, a stabilisation mattress should desirably also be capable of withstanding the impact thereon of anchors or trawlboards travelling laterally, or dropped objects travelling largely vertically.
We have shown an improved mattress design in our PCT application GB 890091 from which U.S. Pat. No. 5,052,859 issued to the present inventor and was assigned to the same assignee, whereby an articulated mattress is formed from elements characterised in that the mattress has a relatively thick region from which its thickness tapers to at least one side edge.
A highly preferred feature of that invention is the provision of a recessed "tunnel" region in which a seabed pipeline is received and thus protected by the mattress. The tunnel is preferably dimensioned to allow lateral movement of the pipeline (but not upward buckling) to accommodate thermal expansion. In a further preferred feature of that invention, a heat insulation material can be introduced into the tunnel inside a container. The container is generally positioned within the tunnel recess prior to placement of the mattress, and the container is filled from an external source.
We have now found, in accordance with one aspect of the present invention, a new way of providing heat insulant material in a recessed tunnel region of a mattress (such as those mattresses of our above PCT application, or others). According to the present invention, the heat insulant is provided in the tunnel prior to deployment of the mattress, eg. it is provided during manufacture of the mattress or at some stage prior to emplacement of the mattress on a seabed pipeline or the like.
In one aspect, therefore, the invention provides a seabed stabilisation mattress which comprises at least one concrete or like member including a tunnel-like recess to receive a subsea pipeline or the like, wherein the mattress includes a heat-insulation material in the tunnel to insulate the said pipeline or the like when the mattress is laid thereover. Preferably, the mattress comprises a plurality of concrete or like members articulated together.
In a highly preferred embodiment of the invention, the insulant material is such that, when the mattress has been laid over a pipeline (or the like), it will soften or liquefy as it warms to the pipeline temperature. Materials such as waxes or bitumen are very suitable in that they will soften or liquefy close to the wall of the pipeline as it heats up due to the passage of contained hot fluids. This softening or liquefaction will minimise lateral resistance to any movement of the pipeline in the tunnel and allow the pipeline
REFERENCES:
patent: 4166710 (1979-09-01), Spiridonov
patent: 4469469 (1984-09-01), Kennedy
Corbin David H.
SeaMark Systems Limited
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