Factors that affect the accuracy of ullage measurements?
Basically, exactly the same things that affect dips, although no ullage could ever take place on a floating roof.
Requirements for Ullaging
The needs of tank dipping (See HCOTEG177700) mostly apply here. Ullaging could be used in Rail Tank Wagons where there is no automatic loading meter. This is rare.
The difference in our requirements for ‘ullaging’ are:
- The tank must be constructed so that the height from the top of the liquid to the ullaging point (marked at the top of the tank) can be converted to the volume of liquid within the tank, by using a calibration table compiled specifically for each tank, i.e. the tank must be designed and built specifically in order to allow ullaging.
- The ullaging rod should be graduated in 2mm gradations.
- The must be an absence of water where it is the total volume of oil which matters (as opposed to measuring the ‘opening’ and ‘closing’ volumes).