Corrosion of the Metal on the Floating Roof and Fixed Roof Storage Tank causes the Stored Hydrocarbon to leak on the surface of the roof. The Hydrocarbon collected on the Roof can be dangerous and a potential Fire Hazard. Leaking Holes can also cause water to seep in the tank and contaminate the fluid in the tank.
No need for decommissioning of the tank or decanting the tank. The entire job is done while the tank roof is leaking (that is the hydrocarbon is flowing out). No need to lower the level of the stored fluid in the tank.