What's The best material for buried wet returns.

The Steam Whisperer

We are essentially repiping all the steam mains in a large home to gain ceiling height and buried wet returns will made things much easier. Looking for the best materials.

Fred

@The Steam Whisperer (Formerly Boilerpro) Have you seen this approach, used by Gerry gill?
http://www.gwgillplumbingandheating.com/webapp/p/669/wet-return-pipe-technique

EzzyT

I'd go the approach that Fred has mentioned, that's exactly how we repipe buried wet returns.

ChrisJ

I'd do Gerry Gill's idea but in copper.

I'd also include hose connections and shut offs on both sides so you can flush it out.

The Steam Whisperer

Thanks, I hadn't seen that yet. However, These are going to be finished spaces, so direct burial is probably going to be needed. I still may try to just keep it above grade in the furred out walls. The owners are trenching the wall in order to put in footer drains, so we have a convenient trench to run the piping. I suspect the drain line will be back filled with limestone.

Danny Scully

PVC works best lol sorry I had to. If you direct bury I would use black iron or copper but insulate completely.

SWEI

If it's truly buried (no easy access) I'd probably use Aquatherm. On a commercial job, I'd spec a temperature sensor with an alarm set for ~200°F just upstream of it.

JUGHNE

Just an idea that I've never seen applied for this situation is plastic/pvc coated UG steel gas pipe. It has cathode protection applied to the pipe. This system protects the pipe from corrosion from the outside in........don't know about corrosion from the inside out which is probably of more concern with condensate. Maybe someone has actual experience of doing this. This system has protected NG UG piping for more than 50 years in my area. FWIW

The Steam Whisperer

I was also looking at CPVC. Most plastics have a temp limit of 200F. However that limit is for fairly high pressures, not 15 PSI. Anybody seen pressures specs for piping at say 220F? Fortunately, this is two pipe with orifices so nearly all of the return water will be near room temp, except the drips off the mains. Also, what do you insulate with? I think there are some high temp. foam insulations that could be used.

Coated black pipe makes a lot of sense ( maybe Schd 80)

ChrisJ

Stupid question, maybe.
How would normal PVC tolerate 200-212 liquid at 1PSI or less? I know Danny Skully made a joke above, but seriously.

Somehow PVC drains seem to tolerate people dumping boiling water down them all of the time, no? Of course that's only momentary and at zero pressure.


From Wiki : PVC starts to decompose when the temperature reaches 140 °C, with melting temperature starting around 160 °C

Using it for a wet return below the water line on a steam system certainly sounds smarter and less deadly than using it for venting flue gasses so if you're gonna make fun of this question I certainly hope you've never used it on a power vent or direct vent system.

Pumpguy

Aquatherm is a PP-R (Polypropylene - Random) plastic pipe for use in most applications up to 200 degrees F. This according to their website. This max temperature might be a concern.

You might take a look at poured-in-place insulating products like GILSULATE or DRITHERM. These are offered as having the advantage of being hydrophobic. This means they don't "wet", thus repel ground moisture in addition to being an insulating product.

Do some research on these products. What you find might be interesting and a good choice for this application.

Jamie Hall

Myself I'd go with ductile iron. Not steel. Not copper. Not plastic. Ductile iron. The idea of the plastic coated flavour is a good one, though -- the corrosion to worry about it from the outside in, from lime and concrete and so on attacking the metal, and DI is amazingly tough stuff.

Of course, one does have to thread it...

nicholas bonham-carter

If you use the Gerry Gill method, the pipes would be easy to change in 20 years when the rust takes hold!--NBC

SWEI

Aquatherm is specified for a 60 years of continuous service at 30-45 PSI (depending on wall thickness) of 200°F water. Depending on the chain length, polypropylene melts somewhere between 266°F and 340°F. They make boiler HX bottoms out of it.

They do make coated copper tube...

Bio

Why not use 316 SS pipe, resist up to 1500 * F

ChrisJ

Bio said:

Why not use 316 SS pipe, resist up to 1500 * F

Sounds affordable?

SWEI

Class 150 (industrial) 304 SS pipe and fittings are much less expensive than brass these days. They're imported, but from Taiwan -- where some of the best machinery in the world is made. I'm growing to like them.

SWEI

Ja, there's also a certain friction thing that feels quite different. Respect the fear of work hardening.