Drill Riser Buoyancy Modules
The drill riser provides a conduit for the drill string and drilling fluids from the ocean floor to the rig. This has significant weight which must be supported by its own structure and ultimately by the drilling vessel. In order to reduce this weight in water to a more manageable amount, discrete buoyancy units in the form of Drill Riser Buoyancy Modules (DRBMs) are fitted along the length of the riser.
Each buoyancy module consists of elongate cylinders which are supplied in two or three discrete elements which surround the drill riser and ancillary lines. These elements are attached together using either an internal fastener or by external circumferential straps.
The internal fastener system consists of four threaded stainless steel (or titanium) studs or bolts that pass through the elements, held together by a washer/locknut arrangement. Recesses are provided to accommodate the stud/bolt system. Strengthening plates are provided to support and distribute the loads.
The external fastening system consists of Kevlar straps and tensioning assemblies which are placed around the outside of the elements. Recesses are provided to guide the straps around the outside surface of the elements as well as to minimise their exposure and possible damage during handling operations.
Circumferential raised support pads (or flexure lugs) are provided to ensure adequate clearance between the external surface of the riser and the internal surface of the modules when the riser pipe flexes during handling or installation. Additional axial recesses allow the ancillary lines to be accommodated.
Transverse recesses are provided to accommodate clamping and guidance equipment. For ease of stacking a flat surface typically 12" wide is provided on the outside surface of the buoyancy elements.