On
bottom stability analysis is performed to ensure the stability of the pipeline
when exposed to wave and current forces and other internal or external loads
(e.g. buckling loads in curved pipe sections). The requirement to the pipeline
is that no lateral movements at all are accepted, or alternatively that certain
limited movements that do not cause interference with adjacent objects or over
stressing of the pipe are allowed.
Hydrodynamic stability is generally obtained by increasing the submerged weight of the pipe by concrete coating. There are other ways such as increasing the steel wall thickness, placing concrete blankets or bitumen mattresses across the pipeline, anchoring or covering it with gravel or rock. Alternatively, the hydrodynamic forces may be reduced by placing the pipeline in a trench on the seabed, prior or subsequent to installation. The natural backfilling of a pipeline depends on the environmental conditions and the seabed sediment at the location.
Hydrodynamic stability is generally obtained by increasing the submerged weight of the pipe by concrete coating. There are other ways such as increasing the steel wall thickness, placing concrete blankets or bitumen mattresses across the pipeline, anchoring or covering it with gravel or rock. Alternatively, the hydrodynamic forces may be reduced by placing the pipeline in a trench on the seabed, prior or subsequent to installation. The natural backfilling of a pipeline depends on the environmental conditions and the seabed sediment at the location.
Source: http://112.220.84.59:8080/PmcXml_WorkBench/upload/snak/E1JSE6/2013/v5n4/E1JSE6_2013_v5n4_598_f007.jpg
A pipeline on the seabed forms a structural unit where
displacement in one area is resisted by bending and tensile stresses. The real
situation most probably involves a great variety of pipeline-seabed interface
conditions. pipeline self lowering may result in some sections of a pipeline
being embedded to a larger degree than determined by touchdown forces, and
parts may even be fully buried. The embedment is influenced by soil
characteristics and phenomena such as scour, sediment transport and other
seabed instabilities. In other sections the pipe may be slightly elevated above
the seabed due to seabed undulations or scour processes. For both conditions,
the hydrodynamic forces are reduced relative to the idealized on bottom condition.
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