High strength tape layer modeling for analysis of flexible pipe axisymmetric behavior and birdcaging limit

Abstract

Flexible pipes are critical elements for offshore oil and gas development and determining its response in axisymmetric loadings is of paramount importance. Often the anti-birdcage tape layer is represented by a tubular structure with either isotropic or orthotropic material properties. However, it is recognized that a tubular structure cannot fully replicate the stiffness and strength and deformation mechanisms of helically wound tape layers. This paper presents a mathematical model for the local analysis of unbonded flexible pipes subjected to axisymmetric loadings where three anti-birdcage tape layer modeling strategies are presented including helical tape, orthotropic and isotropic tubes. This model is then verified against existing test data. The deviations caused by the orthotropic and isotropic tube modeling strategies in different loading conditions are discussed. This is followed by parametric studies on the effects of anti-birdcage tape tensile stiffness, laying angle and direction on the flexible pipe mechanical behaviors in tension, axial rotation in both directions, axial compression, as well as birdcaging limit loads. The importance of considering non-uniform tensions in the filaments that constitute the tape is discussed.