Abstract: Apparatus for servicing a structure has a buoyancy arrangement comprising a series of buoyancy chambers and a gas supply connected to a first one of the chambers, the chambers being interconnected so that. as gas is supplied to the first one of the chambers and that chamber fills with gas. the gas then begins to escape into the next one of the chambers in the series until that chamber is full of gas, and so on until the series of chambers is full of gas. The supply of gas can be controlled so as to achieve the desired level of buoyancy. The gas may be supplied from an external gas supply, or from a cylinder carried by the apparatus.

Abstract: Apparatus for servicing a structure comprises a frame for assembly around the structure, the frame having least one pair of first and second arms pivotally attached at proximal ends thereof to the frame and carrying respective rotating members arranged to contact the structure and driveable to move the frame along the structure.