Which design considerations do I have to take if for some reason I have to bury (in the ground) a steam line with no possibilities of a tunnel because of the long length of the buried section

Thanks for advise

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?

is a line to supply steam to a cluster, we are thinking to buried the pipe because we are installing this line from a cluster to other cluster 1.1 km away and crossing an electric power 800 Kv line, we think the steam trap can be located each 100m and in a sump. the is no possibility of freeze for wheathers conditions this is tropical place, and there is no ciclical use is permanent steam supply and is only to buried 300m the rest of the line is above ground

Go here and read about the product "Gilsulate".
http://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

I don't think, it is a good option to bury the steam line as the steam lines are always under stress & thermal load always acts on them resulting in line expansion. The best way to go below grade is to create a below grade tunnel where the line is still free & is not back-filled with soil.

A steam line can be buried for 500 feet or so in a sleeve but the stress must be calculated and handled within that sleeve. You may get uplift and require guides around the pipe. Stress should be in the loop on that one. Otherwise you are looking at a tunnel where the pipe can move freely and be anchored, guided, expansion loops, traps etc. Take into consideration by burying you have introduced a low point where you need to trap or else you can have serious water hammer issues if the condensate becomes airborne or starts to pond at a low point. You will then have to handle that Condensate. If you have a Condensate return then you are OK but if not you will have to convey that liquid back to a safe drain point. It depends on the size of line, temperature, pressure, saturated or superheated etc on the volume of Condensate expected and the required sizing for that Condensate line.
Handle that one carefully because Steam Piping accidents are not pretty and can be very dangerous for the operators in the plant. If a steam line is not designed properly you could have burst piping at possibly high temperatures and high pressure.
Safety should always be one of our main concerns when we design.