# Pipe dope on unions.



## raylo32 (Nov 25, 2006)

Interesting topic... I am a DIY and I just replaced my furnace and gas range in the last couple of months. I read here not to put dope on the union surfaces but some said it was OK to put dope on the threaded part of the unions. Imagine my surprise when everything I took apart had dope all over the place including the union surfaces. It even looked like some could have gotten into the gas lines. Oh well, I never had any trouble with anything... but when I put it all back together I did not use dope on the unions and they do not leak.


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## hvactech126 (Nov 11, 2010)

I dont put dope on the unions, that is not acceptable practice.


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## REP (Jul 24, 2011)

You use dope on the pipe connections but not the union surfaces.I have seen dope used on the tightening nut .It dosen't hurt anything but usually not needed..The reason you don't put dope on the union surfaces is because it will get in the way of the machined surfaces and possibly cause a leak.


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## beenthere (Oct 11, 2008)

No dope needed on unions.


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## how (Feb 26, 2011)

Don't know any professionals who would waste their time doping the mating surfaces of a union. The smallest bit of pipe dope that gets into a gas valve can ruin it. A union that won't seal without pipe dope on the mating surfaces should just be replaced or the two piping sections should be redone to line up correctly with the union(if they aren't already).


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## COLDIRON (Mar 15, 2009)

" just say no to dope"


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## biggles (Jan 1, 2008)

aren't there still GAS unions for natural gas pipe ups only.there is nothing running even in a commercial install that a fitter would use dope on them


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## VIPlumber (Aug 2, 2010)

I'm a no dope advocate on unions & flared fittings.


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## Doc Holliday (Mar 12, 2011)

In Texas a job will fail if you do not use pipe dope on gas lines or at least I think it will. It is very abundant and mandatory on all jobs concerning gas furnaces. I'd suspect it the same for all gas appliances.

Better safe than sorry, I guess.


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## how (Feb 26, 2011)

Hey Doc
Boy this is a subject with legs. It's right up there with "Should gas lines within a residence be electrically grounded or not?"

I don't think anyone is saying that they wouldn't use dope or tape on gas connections except for this thread on the mating/threaded cinching parts of a union?
Or have I got that wrong?


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## hvac benny (Dec 29, 2009)

Doc, there are certain types of gas fittings that work without dope, such as unions and flare fittings. Dope is required, however, where ever you have an MIP-FIP connection.


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## COLDIRON (Mar 15, 2009)

Doc Holliday said:


> In Texas a job will fail if you do not use pipe dope on gas lines or at least I think it will. It is very abundant and mandatory on all jobs concerning gas furnaces. I'd suspect it the same for all gas appliances.
> 
> Better safe than sorry, I guess.


Doc, were're only talking about the mating surfaces of unions, everthing else gets doped.


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