Internally Flanged Base (lFB) tanks are designed to be installed where there is sufficient access to the sides of the installation to allow the fixing of the panels from outside the tank but where a headroom restriction may exist. A clearance of 500mm is usually required on all sides.

The base panels are fastened together from within the tank and the tank assembled on a flat and level base capable of fully supporting the tank and without movement.

The fixings for the base are only accessible from the inside of the tank. This offers a saving in overall headroom requirements because the tank does not need to be raised to allow man access to the base panels. There is still the need for sufficient headroom above the tank for opening the manway cover we recommend 750mm Because the base panel flanges are facing into the tank, an IFB will have a residual depth of water (80mm) after draining which needs to be pumped out to thoroughly empty the vessel. The flat and level base must be 300mm longer and wider than the external dimensions of the tank. The final base support system must be flat and level and strong enough to support the weight of the tank when full without movement.
The base structure for lFB tanks must be to the following tolerances:

• 2mm in any metre
• 6mm in any 6 metres
• Maximum beam deflection 1:500

In cases where space restricts the access to the sides of a tank a TlF tank should be considered.