Steel Pipe for underground?? good or bad idea?

[BoilerBob]

We are planning a large chip boiler install, to heat multiple buildings at my work. We have plenty of steel pipes on site, and were thinking of welding together (no fittings underground) and allowing for expansion at entry points and long runs.

Any ideas on what to use for insulation, I don't think we can use (closed cell) spray foam because of expansion issue? (or is it OK to use)

Maybe just the steel pipe and sand, any thoughts on this. Yes we would stay above the water table.

 

[maple1]

I would think steel pipe & sand would = huge heat loss.

Steel & closed cell foam - maybe?

The biggest issue I see with steel pipe though is corrosion.

 

[mikefrommaine]

I do some work for a company that owns several city blocks and heats 15-20 multi tenant buildings with two central oil fired steam boilers. Almost all of the piping is the original steel pipes. They go under the streets in culverts. Most of the pipes are wrapped in asbestos insulation. I'm sure they have losses but the pipes have held up.

 

[goosegunner]

Wouldn't pex expand more than steel?

gg

 

[BoilerBob]

Thanks for reply guys
maple - I think the expansion will crack the closed cell foam.

Mike - yeah, maybe fiberglass pipe insulation, then slide in culverts to protect insulation and room for expansion.

We sell culverts and have digging equipment, will have to price it up.
Thanks again PC

 

[BoilerBob]

gg

Dunno, I thought steel would expand more.

 

[maple1]

I've seen some pretty wild expansion rates quoted on here before re. Pex - and it's being used in foamed applications underground. Of course, Pex can usually give a bit without breaking, steel not quite so forgiving if its at all brittle.

 

[BoilerBob]

I did some reading, I guess pex does expand more than steel.
PC

 

[Bob Rohr]

We are planning a large chip boiler install, to heat multiple buildings at my work. We have plenty of steel pipes on site, and were thinking of welding together (no fittings underground) and allowing for expansion at entry points and long runs.

Any ideas on what to use for insulation, I don't think we can use (closed cell) spray foam because of expansion issue? (or is it OK to use)

Maybe just the steel pipe and sand, any thoughts on this. Yes we would stay above the water table.

You can buy pre insulated steel pipe like this 2" steel. It was used to pipe a large ground mount thermal array. It is encase in foam with a protective layer around the outside. The main goal is to protect the insulation and keep it dry. I think the standard Armaflex pipe insulation 220F with a sleeve over it would work.

The InsualSeal PVC I have used has foam and blast hole liner over it to protect and keep it dry.

 

[Tennman]

CTE foam 26x10-6; Steel 6x10-6. Polyurethane expands about 4 times faster per deg F than steel. Looks like you could foam in trench if supported and corrosion is controlled. Much like Bob's pic. I'd use pex because after welding, etc it might end up cheaper or the same. But I see no reason it wouldn't work.

 

[Tennman]

BTW steel in sand very bad idea.... Very. Enormous conduction energy losses. Unless u want warm dirt.