Buried steam line

It is possible you are not getting any feedback because no one has done this. I have worked on two projects with below grade steam headers.

One project was a modification to an existing plant but did not effect the existing tunnels or steam headers so I was never in the tunnels to see how the piping was done.

The other project was a proposal that was never built.

The key item that would seem to eliminate the possibility of successful design and operation of a direct bury Steam system includes:
1. The expansion and contraction of the piping due to the temperature cycles (operation vs. shutdown). This could tear off the insulation.
2. You would also have the condensate to contend with. Would the condensate be collected or dumped?
3. How do you handle the Steam Trap installation? Will they be buried or above ground? Remember Steam Traps require a lot of maintenance. If above ground they could be ripped off by the expansion of the steam header growth and the soil resistance on the small trap piping.
4. If the condensate is not collected and the steam traps are not underground how do you prevent the condensate from freezing during extreme cold weather or causing a swampy mess during the warm weather?

Why are you (or the project) considering buried Steam Headers?

Go here and read about the product "Gilsulate".
www.gilsulate.com/Gilsulate_International,_Inc./Home.html
I have used it before for buried hot lines (but not Steam).
I think it might be the answer to your situation.

Regards.
Jop