Bending stiffeners constrain the dynamic radius of flexible risers at offshore platform and subsea interfaces. The extreme bending and fatigue hotspots of a flexible riser occur near these interfaces. Conventional design of bending stiffeners first account for the extreme metocoean environment to ensure the riser does not bend below the minimum allowable bending radius (MBR). The stiffener design for extreme loading normally proves acceptable for less onerous fatigue loading provided the steel armour in riser annulus stays dry. Flexible riser operations have shown that there are several mechanisms for the annulus to loose its dry-state. A flexible riser that is not fatigue tolerant to a non-dry annulus often needs to be replaced at short notice or shut-down due to the rapid onset of corrosion fatigue of the steel armour wires. This paper demonstrates recent advances in designing bending stiffeners so that a flexible riser can sustain life of field operation with a non-dry annulus. These advances are accomplished by optimising the tapered profile of the bending stiffener and accounting for additional stiffening due to bending hysteresis in a flexible riser. A case study is presented to demonstrate the improvement in fatigue performance of a flexible riser.

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