Cyclic-Bend-Over-Sheave Fatigue Testing of an Umbilical for Oil Production in Ultra-Deep Waters

Abstract

Floating systems are an attractive concept for oil and natural gas production from deep water or marginal fields. That kind of system will, in general, require flexible pipes for production and control from wellheads to the surface.Umbilicals are a type of flexible lines, composite products made of several steel and plastic concentric layers which, working together, provide strength and leakproofness. Their primary functions are transmitting hydraulic, electric and optical signals from the surface. The structure of an umbilical can resist severe loads, which act in the usual operational conditions of an offshore production platform, in the particular case of Brazil, for ultra-deep waters (beyond 2,000 m). Besides, these structures, as permanent risers on floating production units, will be exposed to dynamic loads from waves and from movements of the vessel during their operational life or even during the installation process. Hence, certain regions of a pipe may be limiting with regard to fatigue life. Therefore, this work deals with fatigue testing, stress analysis and numerical modeling of 6 specimens of one type of 2-inch electro-optical flexible pipe (umbilical). The experimental tests were carried out in two test rigs assembled to simulate the umbilical lifetime (operation) and the installation process, both combining axial and bending loads. Good correlation was found between the experimental and the theoretical behavior.