Subsea risers

A buoy for a subsea riser, the buoy comprising an inner part for attachment to a riser pipe, an outer part that is movable relative to the inner part, and a buoyant body for applying buoyant upthrust force to the riser pipe, wherein:

• the buoyant body is spaced radially from the inner part;
• the inner part comprises a part-spherical inner ball formation and defines a longitudinal axis;
• and
• the outer part comprises a complementary socket formation engaged with the ball formation, and is pivotable about pivot axes that are orthogonal to each other and that intersect the longitudinal axis.

A method of supporting a rigid subsea riser pipe that is suspended from a surface support as a catenary extending from the surface support through a sagbend to a seabed touch-down point, the method comprising:

• applying buoyant upthrust force to the riser pipe from a subsea buoy that surrounds the riser pipe and is positioned between an upper end of the riser pipe and the sagbend;
• and
• in response to movement of the surface support, deflecting the riser pipe to vary inclination, relative to the buoy, of a portion of the riser pipe extending through the buoy;
• wherein the buoyant upthrust force is applied to the riser pipe via an attachment interface that attaches the buoy to the riser pipe and that allows rotation of the riser pipe relative to the buoy about at least two horizontal axes, and
• wherein the attachment interface comprises a part spherical inner ball formation fixed relative to the riser, the ball formation being engaged with a complementary socket formation fixed relative to the buoyant body.