Snap behaviour in the upheaval buckling of subsea
pipelines under topographic step imperfection
Z.K. Wang & G.H.M. van der Heijden
Pipelines exposed to high temperature and high pressure with a
topographic step imperfection are susceptible to the phenomenon of upheaval
buckling potentially leading to a hazard for the structural integrity of the
pipeline. To analyse this problem we derive analytical upheaval buckling
solutions and obtain the locations of maximum displacement and maximum axial
compressive stress. We also analyse the typical post-buckling behaviour and
its dependence on step height, axial soil resistance and wall thickness. The
difference in behaviour between a pipeline with step imperfection and one
with a symmetric prop imperfection is discussed. Our results show that a
pipeline with a step imperfection is more prone to upheaval buckling than a
perfect pipeline. For sufficiently small step heights the pipeline may suffer
a snap-back instability under decreasing thermal loading, raising the
possibility of hysteretic snap behaviour under cyclic thermal loading (for
instance caused by periodic start-ups and shut-downs). The snap-back buckling
disappears for large enough step height and the minimum critical temperature
difference decreases with increasing step height and wall thickness or with
decreasing axial soil resistance. The maximum compressive stress decreases
with increasing step height and axial soil resistance or with decreasing
wall thickness. A pipeline with step imperfection is safer than one with a
symmetric prop imperfection.
keywords: subsea pipeline, upheaval buckling, step imperfection
Marine Structures 69, 102674 (2020)