Finite Element Modeling And Experimental Validation Of Buckle Arrestors For Deepwater Pipelines.

Abstract

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.