The offshore oil industry is in the midst of an expansion phase into deep water production locations. Drilling and production at these extreme depths has caused a fundamental re-examination of current offshore structural technology. One of the structures being re-examined is production risers. High strength steel may be replaced by continuous fiber and polymer composite materials. The advantages of composites are their high specific strength and stiffness, corrosion resistance, and long life cycle. It is not structurally efficient to replace metal risers with composite risers that maintain the same inter coupling methods; the lack of material isotropy makes structural design significantly more complex. This study addresses the needs of a composite riser designer and uses this information to design composite riser couplings.
Critical loading, material properties, and design limitations needed for the composite riser design engineer were examined and found to be lacking. The complex environment of composites under a combination of environmental, constant and dynamic tension, and pressure loads have yet to be addressed in a published study. Filament winding was shown to be the most economically efficient manufacturing method currently available to this study. This method of manufacture has certain inherent limitations that are included in each analysis. The method chosen for connecting composite risers is to attach metal end- couplings to the riser ends. These metal ends are easily connected using conventional methods. The design challenge is then the efficient attachment of the metal end-coupling and composite tube structure.
The finite element method was used to analyze various solutions to the design problem. A sample joint was designed that uses two bulges at the composite-end-coupling interface to maximize the uniformity of the failure criteria values at the bond for the case of axial loading. Pressure loading was found to have an extremely uniform effect on the failure criteria values throughout the joint; uniformity is not a problem. Two aspects of the study, environmentally degraded material properties and the failure analysis method, appear to have a significant amount of inaccuracy. Material testing is needed to improve the accuracy in these critical areas.
