Metal catenary riser
A metal catenary riser typically uses a free-hanging configuration and is constructed of steel or titanium. Metal catenary risers have a touchdown region in which the riser picks up and lays down on the seabed as the FPS moves up and down due to wave/tidal action. Special devices to suppress vortex-induced vibration and to accommodate the flexure at the top of the riser are usually required.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards