sleeper height calculation

I checked through five different technical books about Piping Design. I found only one (by Terrence M Shumaker) that had anything in print about the height for "Sleepers".

Shumaker cited a range of from 12" (.3meters) to 24" (.6 meters) with a minimum of 12". There was no specific discussion about factors or conditions that should be considered.

So I will fall back on my own experiences for some guidelines. You have already commented on two issues, low point drains and Drip-legs for Steam Lines. Both of these are valid points that need to be considered. Others may also be present and should be considered.
These are:
- The geographic location of the plant may have natural plant life that will need to be cut from time to time. This may require extra space.
- All of the piping on the sleepers will need to be inspected, painted or the insulation may need to be repaired. Space under the lines needs to be provided.

I would start with a Sleeper height of 3'-0" (1 meter) as a minimum