An Improved Methodology for the Design of Marine Drilling Riser Couplings

Abstract

The current trend in offshore drilling is a significant increase in water depth in the specification of drilling risers, associated with high density muds. This situation presents a real challenge for the design of the drilling riser which depends to a large extent on these parameters, as well as other related to operational and environmental conditions. In particular, improved design methodologies are required to better assess the margins of riser couplings regarding their static performance and fatigue life. As recommended by API Spec 16R, the stress linearization and classification in one of the key steps to design a riser connector. The designers are encountering some difficulties in the application of this methodology to 3D finite element results. IFP has then proposed a simple approach that applies to non-axisymmetric geometries of connectors. It consists in calculating the membrane and bending stresses in a given plane by averaging over a suitable portion of a cross-section the results of the linearization in the stress classification lines (SCLs) located in the selected plane. A short presentation of a breech-block type riser connector, on which the methodology has been applied, is given at the beginning of this paper. The API specification 16R requirements regarding the design criteria are then discussed. A simple approach to extend the stress linearization and classification methods to three-dimensional FEA is proposed. The proposed methodology is applied to the design of the Clip connector. At last, the R&D work aiming at improving the fatigue analysis of riser connectors is introduced at the end of the paper.