Thermo-Mechanical Considerations for Flexible Joint Applications in Deepwater Production Risers

Abstract

Flexible joint technology is a common means of limiting motion-induced moments between coupled steel risers and production vessels. Production conditions in modern deepwater developments can include both high and low temperature conditions. The stiffness behavior of the elastomeric materials used in flexible joints is a function of temperature. For this reason, the engineering approach to this interface must account for flowline operating temperatures in order to ensure the mechanical integrity of the riser system. The analysis technique used to predict fatigue of the coupled structures should employ an accurate model of the stiffness behavior at the temperatures associated with various production cases. Examples of fatigue-critical applications in low and high temperature applications are presented, as well as design alternatives for reducing the influence of flowline temperature on flexible joint stiffness. One recent example was the design of the flexible joints for Independence Hub gas production steel catenary risers for which the gas arrival temperature was below freezing.