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I also dope the threads of a union. Not for the sealant, but to lubricate the threads. I to at one time laughed at the plumber that doped threads untill I realized that those are the ones that I didn't need a hammer to loosen.

dope on the threads is acceptable if not adviseable. dope on the faces never, unless maybe it's 4:59 AND ONLY if all else has failed and is failing. Even then, I would not use it, but I've seen it done.
A bit of oil on the faces of flares and unions never hurt.

Some utility companies recommend a non-teflon dope. I'm not a utility, but because of that non-teflon rumor, I got attached to the NT variety of a brand name pipe dope.
But it doesn't come out of your clothing...EVER!

I remember back in the late 1960's working in a high pressure ammonia freezer plant. All the pipe threads of the various sized steel pipe were doped with a two part sealant, the first component was a yellow powder known as litharge, this was mixed with glycerine until it became a thick paste which was then applied to the pipe threads. When it dried it became rock hard. When you had to dismantle pipe put together with this dope you had better remember where the 36 or even 48" pipe wrenches were. Any other older guys remember working with this?

I use dope on my union threads, more on the bigger pipes. when im getting into 2" and larger i will switch from dope to permatex, but use alot less.

I myself never use dope on unions, flair or compression fittings but I sure find a lot out there that have goop all over them.

Originally Posted by beachtech

wonder if he is putting pipe dope on flare fitting too lmao

a couple of drops of oil (or a tiny bit of never seize) on the male face works wonders. ran across one where some knuckle head used loctite reefer sealant on all servicable flares on a machine.
(i also thin out a fresh can of never sieze with oil)

wonder if he is putting pipe dope on flare fitting too lmao

Originally Posted by Lurch77

I put dope on the union THREADS only, not on the union mating surfaces. I wasn't taught this, it is just something that works well. As some others in this thread have mentioned, I use it this way to facilitate dis-assembly at a later date, not to create a better seal. Why don't I use something like anti seize? Because I already have the dope right next to me and it works fine.

As already stated I always used anti-seize on the threads, but I guess some types of dope will work as well, but I would use the Teflon (white) type not something like Permatex.


Kevin

I put dope on the union THREADS only, not on the union mating surfaces. I wasn't taught this, it is just something that works well. As some others in this thread have mentioned, I use it this way to facilitate dis-assembly at a later date, not to create a better seal. Why don't I use something like anti seize? Because I already have the dope right next to me and it works fine.

Well, I'd say this argument could go on for a long time, BUT pipe dope or never seize definately help to get unions apart in many cases. Example...for almost twelve years I had the service contract on a pro football stadium that used 350 degree hot water for heating. All piping was socket weld. Had over two hundred reheats, plus preheat coils in the 68 AHU's, some of which were face/bypass. Once a year for two weeks while the team was away at camp, we did a shutdown to rework things like control valves, coil replacements, thattype of thing. If you didn't use either dope or never seize, you were not getting the onions apart, period. with it, no problem. We also liked to hit the faces a bit, in the event of misalignment of the piping, it seemed to allow for easier movement of the ground joint when tightening, without scarring the face. For me, 1/2" gas line no, but for any sort of process piping, hot water etc, its on there. We do a lot of bigger equipment that most would consider industrial, and it just makes life easier.

Originally Posted by heavymetaldad

hey old timer!

that's me: I maybe used, but I ain't used up

Originally Posted by heavymetaldad

glycol dissolves teflon pastes. should use that black goo called grip. think hercules makes it. and don't get it on your clothes

I learned that the hard way on a York YCIV while changing out the coolant pump. Does not matter which glycol either. They both do it!. It even did it with Locktite 567 . That glycol is something else!

Have only ever saw one union with pipe dope on the threads. Was on the valve train on a 105 boiler horsepower 2 1/2 inch union. This needed to come apart on a regular basis for maintenance. Made it easier to come apart so I was told.

Apart from that one time never put dope on any threads on unions for steam, hot water, fuel oil or heavy process oils.

Using Masters Metallic on the male threads makes a difference.

http://www.gfthompson.com/pipes.html

I am sure there is a similar product in the USA.

Come across the odd union with pinholes that leaks...usually stamped China on the fitting but thats another story

Using a bit of dope on the threads as a means to keep things from seizing up is a good idea, and if you're like me, open the bottle and you'll have dope all over yourself almost immediately.

Using anti-seize instead of dope, well it accomplishes the same purpose and probably works as good or better... but when you become covered with this silver (or copper) colored substance... it's nearly impossible to wipe off and often just keeps smearing until you give up even trying and are mostly silver...

Back when I did steam piping I was taught:
Pipe dope on the Pipe threads
Never-seize on the union threads and the shoulder the nut half sits on.

Never had any leakage problems, and you could undo the union years later.

Kevin

Originally Posted by jmac00

aaah, the guy that told me that was "old school", and it was 20-25 years ago but it did work?

hey old timer!

Originally Posted by heavymetaldad

glycol dissolves teflon pastes. should use that black goo called grip. think hercules makes it. and don't get it on your clothes

aaah, the guy that told me that was "old school", and it was 20-25 years ago but it did work?

Originally Posted by jmac00

there is ONE guaranteed way to "seal" NPT threads.

Use Teflon tape and then put pipe dope over the Teflon tape. This is about the only way you can run anti-freeze through screwed pipe without leaks. An old pipe fitter told me that trick. Just use caution because you can screw fittings together so far that you will crack the fitting.

glycol dissolves teflon pastes. should use that black goo called grip. think hercules makes it. and don't get it on your clothes

Here in san jose ca. flex conn. is requierd. But then i`ve gone through a 7.3 earthquake that the w/h & furnace danced a jig on the platform.

Originally Posted by ACFIXR

I learned how to make up pipe joints 32 years ago while working on drilling rigs---
1. clean your joint
2. swab with dope
3. apply some twine at the base
4. make up the fitting
5. quit tightening when the twine squeezes out.

that what she said