An Alternative Top Termination for a Steel Catenary Riser

Flexible joints and tapered stress joints are the commonly used top terminations for deepwater steel catenary risers (SCR). A flexible joint, by design, can accommodate large angular motions between the floating host and the SCR. A tapered stress joint, on the other hand, is a more rigid termination for the SCR and cannot easily accommodate large host angular motion. Recent activities in potentially hot and sour fields, however, have posed new challenges and requirements on the ability of a flexible joint to sustain long-term operations. A tapered stress joint can be an attractive alternative to a flexible joint for hot and sour operations. However, excessive large bending moments could be induced by the tapered stress joint onto the host structure. In this paper, an alternative approach to SCR top termination is proposed, which utilizes a combination of riser guide and stress joint to provide the required top termination flexibility. The SCR is connected to the host at the riser top, and is allowed to slide along and rotate about a riser guide fixed onto the host at some distance below the top support. The flexibility of the proposed top termination is realized by the riser pipe deflection between the top support and the riser guide. A stress joint is used to alleviate the high riser stress at the riser guide, without increasing the lateral load on the guide. The proposed top termination thus provides a flexible connection as well as a continuous conduit for the fluid stream. It is an attractive option for high temperature and pressure operations, especially in the presence of higher concentrations of sour elements. For applications that are not driven by hot and sour conditions, the new approach to SCR top termination seems to have the potential to be more cost effective, especially for application to larger diameter deepwater SCRs. Numerical simulations were used to demonstrate the feasibility of the proposed top termination for deepwater SCRs.