Load-sharing marine drilling riser pipe tension slope

Marine drilling riser using a load sharing flange design as the coupling connector is getting popular as people venture into the ultra deep water, 10,000 ft and more. The advantage and goal is the reduction in riser pipe wall thickness; hence, the riser system weight saving. The float (gap) value between the auxiliary lines' coupling and the flange cut-out pocket is diligently designed in the engineering phase and carefully maintained in the manufacturing phase so that auxiliary lines start sharing the load at the desired tension magnitude. Two slopes of riser pipe tension curve, riser pipe carrying the full load then sharing with auxiliary lines, is well accepted and used in the design. However, it is found by finite element analysis that the riser pipe tension has a third slope when the auxiliary lines are pressurized. This paper presents the works done in deriving this finding and the associated fatigue problem needs to be considered in the load sharing flange design.