A Comparative Study Into the Fatigue Capacity of the Pressure and Tensile Armor Layers in Unbonded Flexible Pipes

Over the years, extensive full-scale fatigue testing has shown the C-profiled pressure armor (PA) layer to be so robust that the tensile armor (TA) layers have become the main design driver in fatigue. This trend applies even when considering the development of high-spec flexible pipe structures, which are suited to increasingly higher operating bore pressures. Furthermore, the modeling work reflects these observations, consistently showing low damage to the PA layer when subjected to service loads. Efforts have been made to design fatigue test setups targeting the PA layer specifically. These tests have further shown that the PA layer can suffer much harsher conditions than experienced in service. This study aims to theoretically compare the fatigue properties of the TA and PA layers and compare the most severe load forms for the PA layer to service conditions. The study supports the observations that the PA layer is robust in dynamic loading, which makes the TA layers the design driver in fatigue.