High Strength Tapes Layer Design and Qualification, Reinforcement Solution Against Armor Buckling of Flexible Pipe

Abstract

Unbonded flexible pipelines for deep water field applications are subject to elevated hydrostatic constraints; bore pressure being dropped brings high compressive stresses due to reverse end cap effect. If the external sheath is unsealed, the axial compression loads transmitted to the tensile armors induce their radial expansion, which can lead to their buckling. Specific layers shall be added in order to maintain armors in place: anti-buckling tapes. These layers, designed with high performance fibers, have been introduced in the early 1990's when the use of flexible pipe has grown in deep water. Various failure modes are expected and observed depending on the fiber characteristics, tape construction, tensile armors properties and annulus environment. For each pipe design, an optimum has to be found between the anti-buckling tapes loads and the compressive stress in the armor layers in order to ensure sufficient safety margins against both tapes breakage and different buckling modes of the armors. Anti-buckling tape interaction with the tensile armors and annulus environment main influencing parameters will be explained in the light of full scale tests performed on flexible pipes in hyperbaric tank. Specific laboratory devices have also been developed to be representative of the operating behavior of both armors and high strength tapes. In parallel, this paper will present qualification tests performed in compliance with the requirements of 2014 editions of API standards 17J and 17B. The tests showing tape resistance and flexible pipe behavior have enabled to establish a robust design rule. This process is being scrutinized by an Independent Verification Agent and aims at leading to Type Approval Certification according to the latest edition of API 17J.