摘要：Deepwater pipelines are designed to withstand, without collapsing, the
external pressure acting on them and the bending imposed on them, either by
the laying process or by the topology of the sea bottom. In previous
publications we have developed and experimentally validated finite element
models to predict collapse loads and collapse propagation loads. Even
tough a pipeline normally has enough strength to prevent collapse under
normal operation conditions, under some accidental conditions collapse may
occur at some section. Being the collapse propagation pressure much lower
than the collapse pressure, the collapse, once it occurs, may propagate
through large distances along the pipeline. To avoid the occurrence of this
propagation, collapse arrestors are normally welded to pipelines and, if the
cross-over pressure is higher than the external pressure, they prevent the
collapse propagation. The accurate and reliable determination, using
finite element models, of cross-over pressures, for different combinations
pipes / arrestors, is a key engineering capability. In this paper we discuss
the finite element models that we developed, using shell elements, for the
calculation of cross over pressures and their experimental validation for
seamless steel pipes. In the literature two cross-over mechanisms were
identified: the flattening and the flipping modes; their occurrence depends
on the ratio (arrestors stiffness/pipes stiffness). Numerical and
experimental results that we obtained for the two cases are compared and we show
that the agreement between them for both, cross-over pressure and cross-over
mechanism, is excellent.
