Pipeline Global Buckling
06.23
Global buckling of pipelines may be treated as the
buckling of a bar (pipe) in compression. The global buckling may occur either
downwards (free span), horizontally (lateral buckling on sea bed) or vertically
(as upheaval buckling of buried pipelines or on a crest of exposed pipelines
followed by a lateral turn-down). Local buckling is a gross deformation of the
pipe cross section. Global buckling is a response to compressive force
generated by high temperature and high pressure (HP/HT), which will generally
reduce the axial capacity of the pipeline. Pipelines exposed to high
temperature and high pressure or pipeline with a low buckling capacity will be
governed by global buckling. In DNV’s RP-F110 [19], three global buckling
scenarios resulted from HT/HP are introduced: · Exposed pipelines on even seabed.
Global buckling occurs in the horizontal plane, post buckling configuration may
be allowed. · Exposed pipelines in uneven seabed. Global buckling occurs
first in the vertical plane (cause feed-in and uplift) and subsequently in the
horizontal plane, or combined scenarios with scenario I, post buckling
configuration may be allowed. · Buried/covered pipelines, global buckling in the
vertical plane, so called upheaval buckling. Global buckling is a load
response, not a failure mode. However, global buckling will imply some failure
modes [20] such as: · Local buckling, for pipeline subjected to combined pressure.
Longitudinal force and bending, local buckling may occur. The failure mode may
be yielding of the cross section or buckling on the compressive side of the
pipe. · Fracture, which is caused by tensile
strain, generally includes brittle fracture and plastic collapse. · Fatigue, pipeline components such as
riser, unsupported free spans, welding should be assessed for fatigue.
Potential cyclic loading fatigue damages, which may include
vortexinduced-vibrations (VIV), wave induced hydrodynamic loads, cyclic
pressure and thermal expansion loads. · Ratcheting, ratcheting generally describes the
accumulated plastic deformations under cyclic loads in pipelines that exposed
to high temperature and high pressure. · Bursting, it is governed by tensile hoop stress,
which may occur in the tensile part of pipeline.
Sumber
(http://www.diva-portal.org/smash/get/diva2:648750/FULLTEXT01.pdf)
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