Submerged Turret Loading (STL) Buoys are typically used with floating storage and
offloading (FSO) vessels in deepwater oilfields, where pipelines are unavailable, to gather and temporarily store crude oil from underwater wells. Subsea flowlines are tied into manifolds on the seabed connected to the STL Buoy via flexible risers. The FSO pulls the STL buoy up through a moonpool, or opening, in the ship's hull to offload the buoy at the surface into the vessel's storage tanks. After loading the ship, the turret buoy is lowered to a safe depth of about 100' to 150' below the surface.
Some STL buoys are permanently anchored to a floating production storage and offloading (FPSO) vessel throughout the field life and only disconnected during marginal weather.
STL Buoys are also used for floating liquified natural gas (FLNG) storage and regasification facilities.