My guess is that you have a fitting where the threads weren't tapered properly or similar issue. Use pipe dope and move on. If you run into it again, consider using a different brand of fitting.

It is possible the the problem can be traced to the fittings but based upon the description in Orouke's original post I suspect he has one of two problems, and more likely both.

1. Wrong tape- Teflon was first created by Dupont Chemical Corp. and the word "Teflon" is a registered proprietary trade name for PTFE (Polytetrafluoroethylene). It was originally package on white spools with a white cover ring. Due to copyright restrictions as other companies began producing PTFE tape they were not permitted to use the name Teflon so they simply labeled it PTFE Thread Tape. Dupont then argued that the white container was also a registered trade mark, so the other manufacturers were required to change the packaging slightly, thus we see blue spools with a white ring, red spools with a white ring, and recently I have seen white spools with a blue ring. All of these are single density PTFE tape. (The first clue is if you can buy the roll for $1 or less it is almost a certainty that it is single density tape. The triple density tape generally sells for about $3 or more, depending on the size of the tape and the length of the roll).

Note-The PTFE tape commonly found in the hardware store is 1/2" wide whereas most plumbers prefer to use 3/4" or 1" wide tape, which is generally only available a plumbing or HVAC supply store.

When double density PTFE tape first came on the scene it was also white, packed on a white spool and primarily only marketed to professional tradesmen through the plumbing or HVAC supply houses. Most plumbers quickly adopted it because it was quicker and easier to apply and made a much more reliable joint. Shortly thereafter many gas codes were amended to require the use of double density tape on gas joints. Once the codes were changed they began making the double density tape yellow so that the inspectors would have a visual indicator that the correct tape had been used, thus to this day the yellow double density tape is often labeled as "Gas Tape".

As the PTFE tape industry evolved into more products they adopted a standardized color code.

WHITE- Single density tape to be used as a thread sealant on NPT (National Pipe Taper) threads which are equal to or less than 3/8".

YELLOW-Double density "Gas tape" suitable for NPT threads equal to or greater than 1/2" but not more than 2"

Red- Triple density tape suitable for NPT threads equal to or greater than 1/2" but not more than 2". (NOTE-The package is a red spool with a red cover ring and plainly labeled 'triple density", but the tape itself appears as a pale pink color).

GREEN TAPE- Listed as "OXY/MED tape"-certified oil free to be used on lines conveying oxygen and some specified medical gasses.

COPPER TAPE- Contains copper granules and is certified as a mechanical thread lubricant but is not certified as a thread sealant.

I suspect that even though orouke meant well by selecting a red roll, none the less, he mistakenly got a roll of single density tape on a red roll with a white cover ring.

The second problem I suspect is that the joint is not tight enough. When tightening any NPT thread it requires the use of two wrenches. One wrench is used to hold the fixed fitting steady while the second wrench is used to screw the fittings together. When an NPT joint is properly tightened there should not be any more than 1-1/2 threads visible.

I realize that many homeowners and novices are afraid that they will over torque the joint, but with more than 30 years experience I have only seen one copper female fitting fail from over tightening but i have seen hundreds leak because the installer was afraid to crank it up.

Well, lazypup, once again, you were right. I was using the wrong Teflon tape, apparently it was the single density. I bought some pink tape and it is much thicker indeed.

HOWEVER the tape was probably not the only problembecause I redid now the joint using #5 Rector Seal pipe dope (yellow color) and it still leaks, actually it leaks more now. It leaked slowly in the beginning but now it is up to one drop / 5sec (perhaps the water is now gradually washing off the dope).

I will try once more with the pink tape. If that does not work I would not know what to do. See I cannot take out the female adaptor and re-sweat a new one without at least undoing the other PEX connection (and find an extra 1" of slack in the PEX pipe, already secured to joists) which would be a real pain.

{{gwi:2027536}}

I sugget you may have put the female slightly out of round.

Well, I made one fifth try with the pink (triple density) tape and IT WORKED! No leak !!

I was meticulous to wrap the tape in the spiral fashion described by lazypup. Ended up going 5 times around.

I noticed that, in the previous attempts the last ½ turn had a bit of a "gritty" feeling - as in metal against metal. But with the pink triple density tape the feeling on the wrenches was smooth all the way to the final maximum torque I could apply. Not sure if this has any significance.

Unfortunately, I did not attempt to thoroughly clean the pipe dope embedded deep in the threads (did not read lazypups last comment in time) so I hope the #5 Rector Seal is chemically long term compatible with Teflon.

In all my attempts, I tightened that joint as much as I could. I was using two wrenches in opposite directions and applied as much force as I could with each hand (my guess 60 lb of force and given the fact that the wrenches were about 1ft long that would be about 60 lb*ft). There was no space for extensions.

Although now it does not leak, the fact that dope alone did not work makes me think that something else besides using the wrong tape was going on. The theory that I may have somewhat squashed the female out of round seems plausible to me. I have not made many threaded connections, but this one seems to have been particularly troublesome.

Is it my impression or does Teflon permanently deform with time? What I mean is that, seems to me, that I would tighten the joint as much as I could, but then if I waited, say, 10 minutes I could give it another 1/8 turn applying the same maximum torque. So I hope the Teflon does not deform/decompress with time to the point that it starts leaking again.

This thread pretty much answers all my questions in a thread I just started, "RE-use of 1/2" copper nips (MIPS) w/ brass supply stops?"

For YEARS I've been bumbling along, ig-nernt, thinking single-density PTFE tape is OK for 1/2" IPS fittings, and leaving several threads exposed, happy to have maybe 4 turns total, with only the last 1-1/2 turns needing the wrench's torque!... OTOH, I've made many long-lasting, leak-free joints this way.

HOWEVER... yesterday I went to put some new supply stops on some previously used/torqued copper nipples, and I guess I totally "wimped" it! I'm talking a measly 4 wraps of lame-o no-name single-density PTFE tape, and a mere 1-2 wrenched turns, with many threads remaining... result: LEAKS.

Still, kinda weird that the one I torqued one complete extra turn more than the other is the one which leaked more. Oh well, OFF TO GET SOME PINK TAPE, and try, try AGAIN!

For whatever it's worth, this is what my final successful wrapping looked like,
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