Development And Validation With Testing Of A High Strength Steel Fatigue Resistant Threaded & Coupled Premium Connectors Product Line For Outer Production Riser And Single Barrier Riser Applications in Deepwater And Ultra Deepwater
Authors: Sches Celine , Caron Olivier , Dekervel Antoine 
Published: October 2011

In the past decade, fatigue resistant threaded and coupled premium connectors have been developed and validated for outer production riser and single barrier riser applications. These connectors have been field proven through various projects in the Gulf of Mexico, on sizes like 9 5/8?? in 110ksi material, 10 ¾?? in 95ksi Sour Service material and 12 ¾?? in 95ksi High Collapse material. Compared to weld-on connectors, T&C risers lead to significant weight savings on the full riser system thanks to the use of high strength material (up to 125 ksi in yield). Moreover, this benefit can be achieved with superior gas sealing and fatigue performance.

Based on these successes, the need was identified to develop a whole product line, which would be qualified through a clear process.

Until then, no official standard was existing to include all needed requirements for the qualification of T&C riser premium connectors. This is why V&M has defined a generic testing qualification procedure which is based on existing standards like ISO 13679, on state of the art rules from the industry and on the experience of more than 10 years of R&D work on premium T&C riser connectors.

This process has been used as a guideline to test a T&C riser premium connectors product line from 9 5/8?? to 14" pipe OD with various wall thicknesses (from 0.4?? to 0.8??) and grades (from L80 to Q125). For this evaluation work, specific sizes have been identified and tested regarding their criticality on various aspects (galling resistance, tightness under internal and external pressure, fatigue resistance, etc.). In addition to this systematic evaluation, specific studies such as " mean tension influence on fatigue performance?? or " sealability after fatigue?? have significantly improved the knowledge on these T&C connectors.

This paper will prove the robustness of T&C riser premium connectors design for all sizes within the defined product line. It will therefore present this solution as a beneficial alternative to weld-on connectors for outer production riser applications, as well as a viable solution for single barrier riser applications, particularly for deep water and ultradeep water.

Introduction

The deepwater field developments of the last two decades (up to 8 000 ft water depth) have made apparent the need to revisit the standard design and testing methods of the riser strings. Offshore floating production systems designed for such depths introduced higher fatigue requirements for pipes and connector, by increasing load variability on the risers as well as sensitivity to currents (i.e. vortex induced vibrations VIV).

Therefore, TTR applications called for the development of premium threaded and coupled (T&C) connectors, implemented with proper fatigue enhancement techniques. These T&C connectors were developed as an alternative to other solutions for TTR applications involving welding processes and hence limiting the pipe material selection to 80ksi YS maximum.

With their unmatched ability to be threaded on virtually any material, premium T&C connector would allow the use of high strength grades (usually OCTG grades up to 125 ksi according to API 5CT) and therefore allow weight savings assuming that the main design parameter is internal pressure resistance.