I have the same questions as you. I am trying to estimate engineering hours for a job that includes a 2" steam line running underground for a short distance.
All I have is a write up from the client. I don't know why it needs to run underground. I'm asking if anyone has had a steam line running underground and if so, how they handled it. There are a few options, I'm looking for someone that has done it successfully.
I'm sorry that I can't help too much further because the only steam systems I've designed where all designed to be free of pockets and included drip legs every so often to catch condensate. Which, as far as I am aware, is the standard piping design for steam systems.
I am curious though, what type of process steam is this? Wet steam? Superheated steam? What is the purpose of this steam line? Perhaps that would make a difference. Hopefully more experienced individuals will be along soon.
Putting a steam header below ground is not impossible. The 2 main questions are WHY do you need to (bottom line how much money are you prepared to spend on this)?
And ...For how long a run (there are other ways to routing lines that are normally buried, but routed above grade ...40, 60 foot + or -, but it starts to get impractical after that )?
Perhaps this is a line with waste steam (that has completed its duty) with considerable condensate and has to be drained out. In such a case, It cannot be routed to a higher level as there shall be a build up of condensate in the vertical leg and thereby hamper the performance of the upstream equipment.
Thereby, the client may want to route the line to a lower level to facilitate condensate draining. In such a case, the heat content of the steam might be utilised as a tracer line to liquefy the waxy fluids deposited in the " low point" drain drum located underground.
underground steam lines have to be routed in hollow concrete trenches covered on grade with slab cover (either light for human traffic or heavy for vehicle traffic).
Routing in such trenches gives the steam line freedom for it to expand whenever steam flows in it.