Gas Piping - teflon tape

ChrisJ

hot_rod said:

If you hold the teflon tape back two threads there will be no pieces inside the pipe.

The problem is when you tape off the end.

When you take the joint apart and reassemble there is a big risk for contamination.

JohnNY

I'll repeat this...
When I took my Master Plumber's license test in 1998, we had to assemble an 8-sided figure with ¾" black threaded nipples and fittings. Nothing was allowed to be put on the threads. They had to be clean and dry. Once assembled, we had to pump up the assembly with 100 PSI of air from a waiting compressor and dunk the whole thing into a 55-gallon drum filled with water. If any bubbles formed, you were free to leave and try again in a couple years when the test was given again.
Off topic, but that year the city received 2,500 applications for Master Plumber's licenses. 28 were awarded including mine.
We put way too much thought into the crap we put on pipe threads. Most are simply lubricants to allow the installer to make them tighter. Tapered threads seal themselves. Things like Permatex and Blue Block are sealants and if those are your go-to products you're doing something wrong.

ChrisJ

JohnNY said:

I'll repeat this... When I took my Master Plumber's license test in 1998, we had to assemble an 8-sided figure with ¾" black threaded nipples and fittings. Nothing was allowed to be put on the threads. They had to be clean and dry. Once assembled, we had to pump up the assembly with 100 PSI of air from a waiting compressor and dunk the whole thing into a 55-gallon drum filled with water. If any bubbles formed, you were free to leave and try again in a couple years when the test was given again. Off topic, but that year the city received 2,500 applications for Master Plumber's licenses. 28 were awarded including mine. We put way too much thought into the crap we put on pipe threads. Most are simply lubricants to allow the installer to make them tighter. Tapered threads seal themselves. Things like Permatex and Blue Block are sealants and if those are your go-to products you're doing something wrong.

It's my understanding npt needs thread sealer due to how the threads are cut and that's why nptf also called dry seal was created.


I suppose the biggest issue I have is that's what I've read but I've also never known you to lie neither can I imagine why you would on this.

So I don't know what to think now.

ethicalpaul

This post comes from an outside observer, so errors may exist, feel free to let me know LOL

Good job @JohnNY making through that gauntlet, but let's not pretend that particular test had much to do with proper plumbing. Its purpose was to filter out a bunch of people to keep a labor shortage in place that boosts wages of those who get through. Lots of industries have this.

Look at police physical entrance exams and then look at the physical condition of so many senior officers. Same thing.

I can understand an argument that the ability to pass that kind of test might ensure that someone can make a good series of joints, but it also helped to create the labor shortage in the industry that you have suffered from for over 30 years, right? I'm pretty sure more than 1% of those applicants would have been fine master plumbers, and very likely some of those who passed made crappy ones.

If you saw an apprentice of yours putting together a joint like that would you be happy with them? It's a weird test in my stupid opinion.

JohnNY

ChrisJ said:

It's my understanding npt needs thread sealer due to how the threads are cut and that's why nptf also called dry seal was created.


I suppose the biggest issue I have is that's what I've read but I've also never known you to lie neither can I imagine why you would on this.

So I don't know what to think now.

I don't know why that would be considering the point of a tapered thread is that it gets tighter as it gets deeper assembled. But you may be right. I really don't know. I don't assemble threaded pipe very much anymore but when I did it was very simple: wick on water pipe covered with pipe dope, and just dope alone on gas (never wick). When teflon tape came along we used it on lots of joints whether gas or water. Most of my guys have no idea what to do with a spool of wick and I think it's a shame. They love that Blue Monster crap and we go through tons of it. I'd have the same spool of wick for a month back then.
Alright, I'm officially rambling.

ethicalpaul

No disrespect John, we're the same age and I do the same thing in my field

ChrisJ

JohnNY said:

ChrisJ said:

JohnNY said:

I'll repeat this...

It's my understanding npt needs thread sealer due to how the threads are cut and that's why nptf also called dry seal was created.


I suppose the biggest issue I have is that's what I've read but I've also never known you to lie neither can I imagine why you would on this.

So I don't know what to think now.

I don't know why that would be considering the point of a tapered thread is that it gets tighter as it gets deeper assembled. But you may be right. I really don't know. I don't assemble threaded pipe very much anymore but when I did it was very simple: wick on water pipe covered with pipe dope, and just dope alone on gas (never wick). When teflon tape came along we used it on lots of joints whether gas or water. Most of my guys have no idea what to do with a spool of wick and I think it's a shame. They love that Blue Monster crap and we go through tons of it. I'd have the same spool of wick for a month back then.
Alright, I'm officially rambling.

Have a look at this John.

https://www.machiningdoctor.com/charts/nptf/

JohnNY

@ChrisJ I feel like that article and I are saying the same thing. A face to face mating makes the seal without the help of an additional sealant compound.

ChrisJ

JohnNY said:

@ChrisJ I feel like that article and I are saying the same thing. A face to face mating makes the seal without the help of an additional sealant compound.

The article says NPT does not make a seal without help but NPTF does.

Normal NPT does not due to larger tolerances because the root of the thread isn't tight, there's a small gap at the very peak / valley of the threads.

Any pipe threaded on a job site does not meet NPTF requirements, neither do Chinese nipples and fittings at the supply house.

If you look at Mcmaster you can buy both NPT, and NPTF fittings.

hot_rod

ChrisJ said:

hot_rod said:

If you hold the teflon tape back two threads there will be no pieces inside the pipe.

The problem is when you tape off the end.

When you take the joint apart and reassemble there is a big risk for contamination.

How often do you do that?

hot_rod

ChrisJ said:

JohnNY said:

@ChrisJ I feel like that article and I are saying the same thing. A face to face mating makes the seal without the help of an additional sealant compound.

The article says NPT does not make a seal without help but NPTF does.

Normal NPT does not due to larger tolerances because the root of the thread isn't tight, there's a small gap at the very peak / valley of the threads.

Any pipe threaded on a job site does not meet NPTF requirements, neither do Chinese nipples and fittings at the supply house.

If you look at Mcmaster you can buy both NPT, and NPTF fittings.

Back in the day, all threads were top quality. Look at the threads on store bought nipples and fittings now a days. SAD!
The tape helps mask these imperfections, IMO.

Even threading pipe on the job with new dies and the best cutting oils can still produce torn threads. Makers it hard to cut the thread off and start over when the pipe needs to be X length.

Properly done, joint tapes work well, and saves a redo in many cases.

To each his own, whatever method produces the best results, go with it Plenty of choices out there.

ChrisJ

hot_rod said:

ChrisJ said:

hot_rod said:

If you hold the teflon tape back two threads there will be no pieces inside the pipe.

The problem is when you tape off the end.

When you take the joint apart and reassemble there is a big risk for contamination.

How often do you do that?

I suppose code is written around all conditions.
All it takes is a guy replacing a bad gas valve on a furnace and now there's a small piece of PTFE tape in the new valve or the pilot light.

Changing water heaters, changing furnaces etc. All of these often require things to be pulled apart to change to different size nipples etc.



How often do I personally do it?
I think 3 times in the past 10 years due to changes.

I didn't write the code..... It's not my fault.

hot_rod

ChrisJ said:

hot_rod said:

ChrisJ said:

hot_rod said:

If you hold the teflon tape back two threads there will be no pieces inside the pipe.

The problem is when you tape off the end.

When you take the joint apart and reassemble there is a big risk for contamination.

How often do you do that?

I suppose code is written around all conditions.
All it takes is a guy replacing a bad gas valve on a furnace and now there's a small piece of PTFE tape in the new valve or the pilot light.

Changing water heaters, changing furnaces etc. All of these often require things to be pulled apart to change to different size nipples etc.



How often do I personally do it?
I think 3 times in the past 10 years due to changes.

I didn't write the code..... It's not my fault.

More of a workmanship issue. Takes seconds to clean off any shards of tape.

It's rare to find a gas valve without a screen. Plenty of rust and contaminates in gas piping from suppliers, regardless of teflon on the jobsite. Hence the use of drip or dirt legs.
There is always some crap in those legs when you remove old WH or boiler piping.

In 40 years of piping I've yet to have an inspector fail a gas piping system due to tape use? Have you?

JohnNY

@ChrisJ following the link on the page you sent me to the definition of NPT:

ChrisJ

hot_rod said:

ChrisJ said:

hot_rod said:

ChrisJ said:

hot_rod said:

If you hold the teflon tape back two threads there will be no pieces inside the pipe.

The problem is when you tape off the end.

When you take the joint apart and reassemble there is a big risk for contamination.

How often do you do that?

I suppose code is written around all conditions.
All it takes is a guy replacing a bad gas valve on a furnace and now there's a small piece of PTFE tape in the new valve or the pilot light.

Changing water heaters, changing furnaces etc. All of these often require things to be pulled apart to change to different size nipples etc.



How often do I personally do it?
I think 3 times in the past 10 years due to changes.

I didn't write the code..... It's not my fault.

More of a workmanship issue. Takes seconds to clean off any shards of tape.

It's rare to find a gas valve without a screen. Plenty of rust and contaminates in gas piping from suppliers, regardless of teflon on the jobsite. Hence the use of drip or dirt legs.
There is always some crap in those legs when you remove old WH or boiler piping.

In 40 years of piping I've yet to have an inspector fail a gas piping system due to tape use? Have you?

Isn't that the case with a whole lot of things required, or not allowed by code? In fact, isn't it the entire reason code was created in the first place?

You're posting as if I'm the one that made PTFE tape not allowed in some areas. I'm not. I didn't do it, I swear.

ethicalpaul

It also says this, though:

Sealants for NPT fittings and connections
NPT pipe thread design allows slight clearance between the thread crests and mating roots. This clearance creates a spiral leak path along the male thread crests. The spiral leak path is why NPT connections require a thread sealant to be leakproof.

How NPTF Threads Work

Crests of the threads are crushed against the mating thread roots when assembling NPTF threaded components. This crushing is in addition to the interference fit provided by the thread taper wedging the thread flanks together. Like NPT connections, tapered threads hold NPTF connections together. And these connections are solid and tight. Crushing the thread crests fills the potential spiral leak path in NPT connections. Filling this leak path is why NPTF connections do not generally need thread sealants and why NPTF is considered a dryseal connection.

JohnNY

Ok. I'm done with this.

hot_rod

In all places that have enforced codes, many AHJs write addendums, then you have the actual inspector that shows up and what they look for, or miss 🧐

Also the experience of the fitter and their preference.
Rectum-seal #5 was my go to for years. I got sick of the smell, now I buy the one with the most attractive label. Like I buy wine.

I haven’t found thread sealant to be a life threatening or a health hazard like maybe a missed or misapplied BFD, nothing to fret about, as long as you have a leak proof joint with an approved sealant.