1. Teflon and PTFE are the same thing. The only difference between yellow and white Teflon tape is the thickness and color.

2. Natural gas is mostly methane. It is not reactive with Teflon at all.

3. Tapered pipe threads need to be sealed with Teflon tape or a pipe dope because there will always be a leak path — the threads can’t be machined perfectly so that they’ll interfere perfectly.

4. Theoretically, the Teflon tape would also help avoid galling, but since pipe threads are cut with lubricants, this is almost never a problem. (But watch out if you’re using degreased stainless steel! :^)

5. I use Teflon tape for the majority of pipe threads I connect, both on PVC and galvanized pipe. But when I really want a good seal that can’t leak, I use Titeseal #3.

Yep, I use teflon tape for just about everything. For galvanized water pipe though I like “real-tuff” teflon impregnated pipe dope from the same company that makes Megaloc. Great stuff!

Raised by plumbers. It’s kinda like being raised by wolves, ‘cept I’m handy around the house…

In my area (union shops) steamfitters do most of the commercial steam work. For the really HP work it all welded construction - with some flanged work on old construction. Out in the burbs - where we do remodel work - we deal with some old steam heat systems - with threaded pipe. Breaking free old work is always a challenge - but our old Ridgid Compound Leverage wrenches help. Nothing like that chain to help hold the pipe in the offset jaws.

For compressed air work - I need to let the steam fitters and the operating engineers sort out who does what.

I second the use of Hercules megaloc - and in general we seem to use more Hercules compounds (including their teflon tape) than other brands (e.g. Rectorseal). We generally take what our supplier hands us across the counter - unless we have had some experience to say no.

That said, for air compressor fittings, teflon tape is all I use. It lubes the thread, keeps my pipes from being fouled with liquid dope, and does a great job of sealing the joint if applied properly and the joint is properly torqued.

For low pressure gas service (15 in wc or less) under one inch, I use straight tape. For larger pipe, I add megaloc. It’s great stuff, that cleans up with just a rag. Very nice.

For steam service I use teflon tape with some dark gray stuff, I can’t remember the name, but it’s a real pain to clean up. Most white pipe dope just boils out of the joint when you exceed 90lb so it doesn’t work very well. If you’ve got the big wrenches out, you’re almost always better off with just teflon tape for steam, it keeps the threads lubed enough so you can get the joint tight enough and it doesn’t boil when heated.

For the record, compression fittings won’t hold 90lb steam (at least not the brass ones). A brass NPT joint will. Compression fittings are significantly weaker, flare fittings are much harder to make, but much more durable. Hardly anybody uses it anymore.

Natural gas will break down regular white teflon tape. I’m sure someone else in this post who’s better versed on natural gases properties can tell you exactly why, all I know is it does break down.

I see that there is special tape for gas, but what is the difference?

Do not use white teflon tape on gas lines…..use only the yellow tape for gas.”

He beat me too it, so ditto. http://www.coasttape.com/html/yellow_gas_line_ptfe_thread_se.html

Use it on everything threaded that you want to seal against fluids and might want to get off some day. EVERYTHING. You will regret it. When I was working with a lot of hot low viscosity waxes running through lines that had to come off about once a week, it was the only thing standing between third degree burns, insanity, and me.

hot or not even seems like a silly question when it comes to this. whenever i’m in the plumbing aisle buying pretty well anything to do with water and connections, i will pick up a roll.

it costs $0.59 per roll, there’s no reason not to keep buying it just to make sure you have one handy. Advice for DIY newbie amateur plumbers: get in the habit of always always using it, never question if you should or shouldn’t use it, just do it.

Side Note: I have no idea how much “Teflon” tape is out there as opposed to the generic PolyTetraFluoroEthylene (PTFE). PTFE tape doesn’t quite roll off the tongue but I digress.

The tapered pipe threads we all wrap them around are “supposed” to seal. That’s why they’re tapered.

In practice, we all know this is crap. Pipe threads never seal and without wrapping 3-4 layers of teflon, it leaks. Whenever possible, I’ll swap out NPTs for compression fittings. They may cost more but if it’s something hard to get to, it’s totally worth it.

I prefer tape over “pipe goop” for a couple reasons.
1. It doesn’t need to dry.
2. It’s easy to remove.
3. Messy factor.

I have found pipe goop does a better job of sealing so for those problem threads, I keep a tube around just in case.

Remember to read the MSDS and safety precautions on all liquid sealants. Unlike the more universal tape, goop has more specific application requirements.