Which feature characterizes a floating roof tank?

• A. Legless top with fixed cap
• B. Dome-shaped roof
• C. Legs on the roof
• D. Fixed floating outside

Answer: (C)

Floating roof tanks feature a roof that rides on the surface of the liquid rather than being fixed to the top of the tank. The roof is supported by legs, allowing it to rise and fall with the liquid level while staying above the tank bottom when levels are low. Those legs provide stability and keep the roof from contacting the shell as the level changes, which helps minimize vapor space and emissions. This is why the defining feature is legs on the roof. The other descriptions describe fixed-roof designs, such as a dome-shaped or legless top, which do not float on the liquid.