Liquid Nitrogen Piping

Zman

A friend of mine is working on a project that requires a 40' underground delivery pipe for a liquid nitrogen.
They are hearing conflicting information on the type of pipe required. One party is saying Type K hard or soft copper, the other is saying braided stainless steel. The pipe will be exposed to -321 F temp.
Has anyone had experience with this?
@Jamie Hall ?

ChrisJ

Zman said:

A friend of mine is working on a project that requires a 40' underground delivery pipe for a liquid nitrogen.
They are hearing conflicting information on the type of pipe required. One party is saying Type K hard or soft copper, the other is saying braided stainless steel. The pipe will be exposed to -321 F temp.
Has anyone had experience with this?
@Jamie Hall ?

A quick Google search yielded specialized vacuum insulated stainless steel piping.

I highly recommend whoever does it finds out for sure what they need to do. Something actually documented.

SlamDunk

I would contact the provider of the liquid nitrogen and ask them how distribution is typically piped.

ScottSecor

We did a project back in the late 1980's with nitrogen. The manufacturer/nitrogen supplier supplied all of the piping. It was copper type K rigid with factory applied 3" rigid foam pipe insulation, covered with a white plastic coating (it was installed mostly outside the building). If I remember correctly, we brazed with silver brazing rod (very expensive) and had to run nitrogen (or was it some other inert gas) through the piping when we brazed it. Fittings were heavy wall if I recall. Special long stem "cryogenic" valves were used, if not user's hand would get instant "freezer burn" when someone touched a valve handle.

Again it was thirty years ago, but I think it was Union Carbide and/or Linde that supplied the roughly sixteen feet tall vertical tank ( I guess about 1000 gallons) and most of the materials mentioned above. I believe they made money off the nitrogen and the tank rental fees. Insulated piping and fittings were a lost leader I guess.

Really nothing tricky, except a twenty foot length of 1" copper type K weighed about 100 pounds (with the insulation) compared to around 10 pounds for plain copper. Pipe was placed on 6x6 treated wood blocks on the roof, with nothing more than galvanized 6" straps to hold the insulated pipe in place. The copper elbows were covered with the 6" plastic shell and then triple expanding foam (or something similar) was injected and left to cure.

I don't recall any special tools or licenses were required, but again that was a long time ago. For the record, the system was in place and used for about ten years without any problems. For the life of me I cannot recall if there was a regulator on the outlet of the tank or was it placed inside near where they "flash froze" the pizza bites. By the way, the were the best pizza bites I've ever eaten!

Jamie Hall

@ScottSecor 's played with the stuff more recently than I have. Underground or not, you have to have insulation on it and use the correct fittings and braze. Solder won't take it.

You also have to make provision for expansion and contraction -- one end of your 40 foot section can and probably should be fixed, but the other end absolutely has to be free to move, and not just a little. There I would make the connections to whatever this thing is going to with the braided stainless -- either that or cryogenic rated expansion joints. The movement will be on the order of several inches.

pecmsg

Stainless Steel Double pipe with a vacuum between to prevent heat transfer.

Copper can be used but will turn into a snow ball! Used at the fill point of the tank.


Braded Stainless is used where flex is needed, tank to building, building to appliance etc

ScottSecor

@Jamie Hall has a god point, we put a "U" in the middle of the roughly sixty foot run on the roof for expansion.

Solid_Fuel_Man

I have piped liquid nitrogen from the vacuum jacketed tank to a mixing station for a welding gas supplier.

Did it with regular ACR type L and refrigeration fittings. Sil-Fos 15% with standard nitrogen purge. It should be insulated, if not it ends up with 3" of solid ice on it in about an hour. Any voids in the braze joints show up as its cryogenically frozen and will leak.

Keep in mind wherever the shutoff valve is that any liquid in the lines will boil off and have tramendous pressure. We braze in little bell shaped relief valves between every potential trap point.

The stuff is wicked cold!