When installing a black pipe union, what do I dope in the center?

Question

Obviously I dope both ends, but what about the center? Do I dope the bevel or the center threads or neither or both or what?

I normally use TFE paste.

Answer 1

Gas fitters dope the threads of each fitting.

Answer 2

No dope on the sealing surface, absolutely none. I would wipe the surfaces to ensure they were clean but that's it. Some may disagree but I always put a bit of dope on the threads that join the two parts of the union. Not to seal anything, just for lubrication. I suppose a bit of stiff grease would work as well. It also retards corrosion to a degree and, in doing so, makes future disassembly a bit easier. Oh yeah, the guy talking about gas and the tape to use is for it is spot on. Don't use standard plumbers pipe dope on gas lines. That stuff is designed for water lines, not gas and some of it will react chemically with the gas. Same holds true of Galvanized pipe, it will react with the gas and cause heat. Not a good thing for a gas line.

Hey, Good Luck, I hope this helps.

Answer 3

From what you have discribed you need to have a crimped end to go into the chimney and a chrimped end into your stove. Most Heating and plumbing suppliers can crimp stovepipe for you or expand a standard size pipe so it will fit around your stove's exhaust Haveing this done will alow you to have your pipe fit around the outside on the stove and fit inside the chimney.

Answer 4

No. That is a machined surface that form a tight seal when you screw it together. Pipe dope will only mess it up.

Answer 5

Leave it as is as the union will for the seal. If it's for gas you would be wise to use PTFE tape on the threads.

Answer 6

put stuff on any part of any piece of pipe that will touch another. then that way it will be airtight