Sludge dispersal/inhibition in floating roof storage tanks

A fluid storage tank (2) comprising a chamber (4) having a roof (6) arranged to float upon a body of fluid contained in the chamber (4). A nozzle is (8) is suspended from the roof (6) and pumping means (18) are arranged to circulate a flow of oil through the chamber (4) via the nozzle (8), to inhibit or disperse a build-up of solid or semi-solid materials upon the floor of the chamber (4). Preferably the nozzle jets project parallel to the base of the tank, and below the distal ends of the support legs (4) of the roof. The nozzles are also preferably rotatable about a vertical axis. Provision may be made for heating the fluid circulated via the nozzle.