Originally Posted By: George7941
On my roll of yellow PTFE tape for gas lines, it says to use it for lines no larger than 1 1/2in.
I assume larger threads have larger gaps that the tape cannot fill. So, the question that arises is - what do you use on large dia threads?
I don't know why your roll of tape says that it's only good up to 1-1/2" pipe. It may be that the manufacturer offers a wider tape, and wants you to use that. Teflon tape is commonly available in 1/2", 3/4", and 1" widths. Having said that, as pipe gets bigger, it is harder to seal. A few years ago, I did a gas piping job that involved several hundred feet of galvanized pipe from 4" down to 1/2" diameter, all threaded. We used mostly X-Pando, which is an industrial thread sealant that expands as it dries. It worked well. On at least a couple of 4" threads, we used a combination of Key-Tite and teflon tape, which also worked well. We were required to use a 24-hour recording gauge to test this pipe, and we passed.
Another factor to consider is the contents of the pipe. There are different sealants for different liquids and gases. If it's water or compressed air, pretty much any pipe dope will be OK, although on the big sizes some are better than others.