Exterior Steam Piping

[BronYrAur]

What is typically done to prevent freezing on exterior steam lines? I may need to run about 800' of 4" steam and 2" condensate across a flat roof. What do I need to do to prevent freezing, especially in the event of a power failure? Job is in Chicago.

 

[dtn6770]

A good insulation system and adequate trapping should get you there. The insulation thickness will depend on the operating and ambient temperatures as well as the type of insulation. Calcium silicate is fairly common. Metal jacketing should be applied, with sealant, to prevent water from getting into the insulation. Also along those lines, I'd suggest a 2 layer epoxy phenolic paint system be appiled to the piping if it's carbon steel and operates at or below 300F. That's probably not the case unless you've got very low pressure steam.

Make sure the lines have no (un-trapped) pockets and are sloped towards traps. The traps should be located at the bottom of "boots" where condensate can collect from the main flow of steam.

 

[STYMIEDPIPER]

dtn6770 has provided very good info.
I am not familiar with commercial projects, but if your project is heavy industry than you must select appropriate jacketing. If the environment is corrosive than a stainless stl jacket is warranted. If not corrosive than an aluminum jacket is suffice.

 

[unclesyd]

As mentioned good insulation, well maintained, is essential. I would use SS covering with SS tie wire for the insulation clamshells.
Based on my limited experience the biggest problem is keeping the steam traps from freezing. Hopefully someone from the cold country will jump in and offer a solution.

Here in NW Florida freezing traps bit us twice. Both incidents caused plant wide shutdowns that were quite expensive.

 

[Joesteam]

Proper trapping is essential, of course nothing will freeze unless there is a steam shut-down or no flow in the condensate line.
In this case the traps on the steam line must be piped correctly AND have gravity drainage (no vertical lift after trap)
For the condensate line, there is a 'freeze protection' valve that basically opens when the temperature reaches a lower limit. This must also be piped to a gravity drain.
Sarco makes this as well as Ogontz, for the latter look at:

http://www.ogontz.com/products/freezeprotection.htm

 

[Hipressure]

Try adding electrical heat tracing under the insulation.

 

[kenmac777]

We operate in Canadian winters with steam lines, some 600# and some 100#.

Slope steam mains to drain boots which are trapped to the condensate line. We use mineral wool on low pressure, cal sil on high pressure.

The condensate lines should be insulated and steam traced with stainless tubing. The steam tracing itself is trapped back into the condensate line.

The traps are capable of operating with some lift, dependent of course on the steam pressure. Our condensate main is 20' higher than the condensate trapping manifold.

We have removable insulation blankets on the thermodynamic traps. The Spirax TD42 trap has been a particularly good performer for me. We have hundreds of them, and it is a rarity to freeze one up, even at -30C.