Ullage/sizing

[scorcher]

Is there a consistent definition of ullage? E.g., if a tank is quoted as 100m3, is this the absolute volume, the mechanical design volume to a level, or the maximum liquid in normal operation. Which of these figures does ullage relate to.
Similarly for reactors, if it is quoted as 10,000l, would the normal operating be at 9,000l for a non-foaming /boiling reaction?

 

[25362]

From what I could gather, ullage has different meanings depending on the user.

For example, an engineering definition would identify it as that amount (volume) the container -such as a fuel tank- lacks of being full.

In a vertical bottle of wine it would be the volume from the surface of the wine up to the cork or stopper or cap.

In naval architecture it is the distance from the surface of the oil in a cargo tank of an oil tanker to the top of the hatch, or to the top of the inspection cover in the hatch or to any other reference point designated beforehand.

 

[JoeTank]

In the API storage tank world, the tank volume definitions have been very owner specific. However, some uniformity may come about due to a revision of API-650, Appendix L. This appendix was revised to include a set of uniform definitions for the various tank capacities (Low level alarm, high level alarm, etc. Take a look, it may help answer your question.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[Nosey]

On many occasions I have seen tank datasheets stating Total Volume and Maximum Operating Volume.

The ullage is generally taken as the difference between these two values (as the other contributors have stated).

As far as I know there is no set requirement for the volume of ullage. Some companies set them as part of their design manuals, but it depends very much on
- the fluid in the tank,
- the duty of the tank,
- whether or not the tank is in a standard size
- the consequences of any upstream or downstream instrument failures (as part of a HAZOP).

(to name but a few issues).

You'll have to make an educated judgement based upon these factors (and the others that are specific to your application).

Regards

Nosey.