I'm making a contraption out of black iron pipe, that needs to be gas tight at a low PSI yet pretty high temp. Maybe 500 to 600 degrees.

 

Will pipe dopes withstand this? I see stuff on grainger listed to 1000 degrees, although I don't know if they will work.

 

I also see caulk listed as high heat,although I think it's used for cementing chimney pipes.

 

I'm running a series of iron pipe connections moving room temperature air fed by a fan through a fire. Hence low PSI yet high temp. Should be arc welded but I don't have one

McMaster has some stuff that is 1175 and other that goes up to 1500...expensive though.

 

Can you just get the parts that run through the fire bent into shape? This way no joints are exposed directly to flames.   Once a joint is not directly in the fire, the air in the pipes won't that hot.  The combustion gasses in a wood fire typically don't exceed 800 but heated air through a pipe will be much lower than that and a typical high temp pipe dope will be fine.

If you are making a "Heat a lator" for your fireplace PM me.

 

BTW I have a 115v welder you can borrow.

Plumbing fittings are cut with a taper die.  This means that as you fit the pipes tighter, they will eventually bind, and in actuality, you may not need dope at all.  http://en.wikipedia.org/wiki/National_pipe_thread

 

In any case, the clean air inside the pipe will be at a higher pressure than the dirty air in the fire, therefore, the failure method (if the joints failed) would be that the clean air IN your pipe leaks OUT and not that the dirty air from the fire leaks IN to your clean air.

Under pressure service with hot air/gas under an atmosphere gauge the amount of leak would be so small I don't think it would mater a bit if you used nothing. But I would use something like you.

 

You could brush on a castable refractory or use a fine grout from a tube gun.

I'm back on this subject because winter is coming.

 

I made a template out of cardboard, and I realize that one of my angles is not 45 or 90 degrees. Perhaps 25 degrees or so using an eyeball protractor. I was planning on using black iron pipe, yet I am having second thoughts. I can use two 90 degree fittings and one nipple between them to achieve the angle I need, but it will flow like crap. 

 

Suggestions? Cutting the pipe and welding it isn't an option since I'm not a metal fabricator by any means. 

bend the pipe

You can get 22.5 degree elbows.  I'm not sure what you're trying to keep from leaking out but if you're just blowing room air through a pipe, pipe threads will be more than air tight enough.  If you really need absolutely no leakage, you can get high temp sealants that will work.  Somebody mentioned mcmaster.com, I order from them several times a week. they have everything and will have what you need. Keep in mind that high temp and direct exposure to flame are different things.

I live on the border of Morris and Sussex county's. Don't you live close to me. I have a threading machine and all the dies from 3/8" to 2" I also have a 220v mig that will weld back iron. But you can just use blue permatex instead. What we normally use for steam pipe that gets pretty hot. When I measure take offs I usually use a folding stick ruler it works best to get your angles right. Could also use a swing joint if you had to. Ive never seen a 22-1/2" black fitting but they probably make one. Broad industrial in Denville would be the place to find that fitting. I highly doubt you would find anything other than 90's or 45's at a supply house. Unless your looking for PVC then they would have it in stock. What size black iron are you working with?

If you need fire caulk I can bring it home. I work in a refinery.

Every plumbing supply sells fire caulk. We have to use it around pipes wherever we penetrate a sill, top plate, or wall with pipe. The electricians use it as well, Its code. I never thought of using it for thread sealant though. We do use the red high heat RTV silicon to seal boiler and furnace flue pipe and vent hoods though. That may also work. Most oil fired appliances have flue temperatures from 400 to 600 deg, and it holds up great at that range. Furnace cement would be another option they make that in caulk tubes as well, but it hardens and becomes brittle pretty quick.

 

I know your probably buying pre cut and threaded nipples, so your limited to what length pipes you can get. The threading machine gives you the options to make your pipe whatever length you need so you can get exactly the angle you need.

 

I've steered away from the pipe dope.

 

My current plan is to build it out of whatever the largest pipe is I can find. Likely 1 1/2". For the weird angles I'm probably going to use two 90 fittings and a nipple since I know whatever I use won't be perfect.

 

I wanted to find some 2" steel tubing and have it bent at an exhaust shop, but I would be concerned about it degrading after too many heat cycles. Plus anything on the shelf is probably galvanized.

I can get 2" schedule 40 black pipe from the supply house with one phone call delivered to your door. They come in 21' or 10' lengths. Or you could pick it up yourself at Hanover supply in Randolph at the beginning of Sussex tpk. Behind the old motor vehicle building. I'll even call it in for you on my cash account if you want, so you get my price structure.

 

What does the 10'run?

What does the 10'run?

Probably around $25-$30 I can call for a price Monday morning if you want. Give me a list of fittings you need as well and I'll get a quote for everything in one shot.

Will PM you.

Cool