Analytical model for lateral instability of quasi-rectangular or circular armor wires in flexible pipes and umbilicals

摘要

The present paper addresses armor wire lateral instability in flexible pipes and umbilicals. Analytical models are formulated for the lateral instability of armor wires with quasi-rectangular or circular cross-sections considering the armor wire axial rotation constrained by the adjacent layers or free, respectively. The axial rotational effects on the lateral instability of quasi-rectangular and circular armor wires are discussed. The present analytical model for quasi-rectangular armor wire lateral instability is verified with availabe test data from literature, indicating that it is reasonable to consider the quasi-rectangular armor wire normal direction coinciding with the toroid normal direction even if a gap is formed in axial compression. Parametric studies are performed to investigate the effect of armor wire layer properties on the lateral stability limit. This is followed by some useful suggestions for improving the design of armor wire layers against the lateral instability.