Brass to Brass Pipe Thread Connections
‘Round here, as most places I presume, SOP is to use Teflon tape or pipe dope to seal pipe thread connections for water. But lately I heard that brass is somewhat peculiar and will “seal” to itself better without the addition of Teflon.
Love to learn, so enlighten me!
NPT threads, regardless of what material they're made out of, are NOT designed to seal without the use of a thread sealant. Think of them as a spiral path between what's inside your pipe and the outside world- without a sealant in there, eventually you're going to get a leak.
Brass has a few things going for it. It has an extreme resistance to "galling" (i.e. seizing by welding of the rubbing parts together under the pressure and heat generated while the parts are being threaded up). This property makes brass more "forgiving" than stainless etc. when you use an inadequate quantity or quality of thread sealant. It's also relatively soft and deformable. Combine these two qualities and you can see that you might just be able to deform the two pieces during installation enough that you get a seal- for now.
Use teflon tape, pipe dope or both, on all NPT threads. Full density teflon tape by itself is fine for plumbing applications. So is a good quality anaerobic pipethread sealant ("pipe dope")- and it's a better choice for large pipe fittings.
You wouldn't want to use teflon of pipe joint compound on a compression fitting as one or both could easily impede a proper seal. Otherwise, for threaded fittings, use whichever one you prefer.
Rare to do any brass to brass these days.
I recently pulled apart a bunch of brass pipe. Was popular at one point, and seemed to have plenty of life left in it. Anyways, there was nothing on the threads, from what I could tell, and no leaks either.
I think the idea is that brass will 'squish' to conform itself to seal with the mating part, sort of like brass or copper washers do. Less likely to leak than steel to steel.
I would still use the tape or paste for insurance, however. No big cost.