Flexible Joints have been an essential part of many steel catenary risers (SCRs) as one of the main means for connecting SCRs to the floating facilities in deep water. Since 1994 when the first Flexible Joints were installed on the Augur Tension Leg Platform (TLP), many Flexible Joints have been designed and installed for 6 inch to 24 inch SCRs on all kinds of floating production facilities and in a range of water depths. Woodside Energy Limited (Woodside), as operator of the Browse LNG Development on behalf of the Browse Joint Venture participants for their original Browse LNG Development concept (Browse to Kimberley subsea development and onshore processing concept), had contemplated using Flexible Joints as top termination units for the high temperature 24 inch Wet Gas Export SCRs. Woodside contracted Oil States Industries, Inc. (OSI) to design, manufacture and test a prototype 24 inch Flexible Joint that would meet the project’s stringent operational and fatigue requirements for 40 years design life. This high temperature 24 inch Flexible Joint was the largest Flexible Joint ever manufactured since its design required bellows and a thermal barrier. A state-of-the-art qualification program for the high temperature 24 inch Flexible Joint was undertaken to demonstrate its feasibility for use on the 24 inch wet gas export SCRs for the Browse project in approximately 600m water depth. The Flexible Joint prototype was subjected to a comprehensive test program, including axial and rotational tests, hydrotests and a fatigue test, which was developed to cover all aspects of the Flexible Joint design and its components. In this paper, the details of the high temperature 24 inch Flexible Joint qualification program will be presented with emphasis on the steps taken to successfully complete the program and the lessons learned from the challenges that were encountered. The paper will also provide a summary of the challenges and steps taken to complete the program which presented a unique opportunity to expand on the capability of the industry to go beyond what has been previously accomplished. The program was very challenging in all aspects but succeeded in achieving all of its goals.

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.