Gas connection - thread sealant on flare end?

[Hardt]

I am confused about instructions that came with a 4' long flexible stainless steel connector to be used to connect lpg tank to range. It gives strong warnings not to use thread sealant on the flare threads. Now I can understand that you would not want to put sealant on the flare end itself because it would interfere with the metal-to-metal mating with the flare seat but how would sealant on the threads somehow keep the flare joints from mating properly? After reading a few posts about the "best" sealant, I bought a tube of Rectorseal 5 and plan to use it instead of teflon tape for this project. I thought I would disregard this warning and apply sealant sparingly on the back half of the flare threads, far away from the flare end to not contaminate it but I don't want a leak so I thought I would check with the experts on this forum. Please offer your advice if you can. Thanks.

[Randyj]

The flared end, I assume, is copper which is a soft metal and should seal with no problem. The reason for the warning against using a sealant is, as you have surmised, to prevent the sealant from getting in the orifice and other places blocking the flow of the gas. Before you apply sealant you might want to do a soap bubble test. Go ahead and hook it up and turn the gas on, take a cup with a generous amount of dishwashing liquid, add warm water and mix it up really good then spray or use a small paint brush to really slop it on the fitting and threaded area really good. You will have some bubbles from the soapy water..but look for new bubbles forming... if you can get it on without any bubbles .. that's great..then look for bubbles. No bubbles = no leak..and you're in good shape.

[jadnashua]

Pipe threads are tapered, they get tighter the further you screw things together, but things can leak around the thread, so you need tape or dope to fill the gaps and make the seal.

The threads of the nut that holds a flare fitting or a union together are like those on a screw or bolt - the only reason they'd get tight is if they bottomed out - there are not intended or capable of making a seal except to compress some fitting or gasket material together so the mating surfaces are jammed together and make a seal. Sort of like the threads on your water hose...it is loose until you compress the washer. So, no joint compound or teflon tape is needed or wanted on those threads. A drop of oil might help you to tighten it enough to compress the mating surfaces, though, depending on what you are doing.

[Randyj]

Thanks Jad.. I knew that but didn't know how to put it in words... excellent comparison. My dead brain comes to life from time to time (brain farts)....

[Hardt]

Ah, Ok I think I understand the concept now!! Tapered screw connections use tightness to achieve water/gas intergrity but non-tapered screws connections are mainly to provice mechanical compression and the integrity is provided by a compression ring, flare joints, etc. But still, what would be wrong by using sealant on the threads since it would provide the lubricant that you mentioned and also allow a second line of defense should there be a leak at the flare matings, compression ring, etc?

[Randyj]

The reason for the warning against using a sealant is, as you have surmised, to prevent the sealant from getting in the orifice and other places blocking the flow of the gas.

This is the best answer I can come up with at this time.

[hj]

Maybe so, but I ALWAYS use joint compound on the flare ends to make sure any irregularities are filled. It also lubricates so things go together the way they are supposed to. An engineer put that warning on the connector, but he never tried to actually assemble one.

[kordts]

I was doing some repairs at our pastor's apt. I opened up the door to the utility room and smelled gas. I squirted bubble on the gas flexi. It bubbled at the flare adapter coming out of the gas cock. I pulled it apart and about puked. A teenager trying to be helpful, using the skills and know-how his dad taught him, installed the dryer for our pastor. He wrapped electrician's tape around the flare instead of thread sealant. A typical DIY brainstorm with possibly deadly consequences.

[Randyj]

Definitely true... I ALWAYS check for leaks after connecting a gas line. If I can't find soap bubbles or anything else I'll at least spit on it. Not worth taking chances.

[Hardt]

Ok, thanks for the lesson and all the opinions. I knew about tapered and non-tapered screw fittings but did not relate the two types to the use/non-use of sealants. I've operated under the principle of if the matings are metal-to-metal, use a sealant. If plastic-to-plastic or plastic-to-metal a sealant is redundant because the plastic is compliant enough to "fill-in" any irregularities in the machined surfaces. After reading Jim's explanation, I've gone back and re-read the instructions of my last plumbing experience: installing a kitchen faucet and there is NO mention of having to use a sealant for the supply fitting to faucet fitting connection!! However, HJ says he ALWAYS uses sealant at a flare connection so I plan to go with my initial inclination and use a sealant carefully and sparingly at the flare end. For other future water plumbing projects however, I will experiment and skip the teflon tape and rely on the flare ends, compression ring, rubber gasket, etc. to give me a leak-free connection. For gas connections I will use a sealant for the extra insurance it provides. Thanks again for all the inputs!

[Randyj]

The big trick on flared ends is to have good, smooth mating surfaces. Once it's torqued down your only danger is over/under torqued flare nuts.

[Bob NH]

I was doing some repairs at our pastor's apt. I opened up the door to the utility room and smelled gas. I squirted bubble on the gas flexi. It bubbled at the flare adapter coming out of the gas cock. I pulled it apart and about puked. A teenager trying to be helpful, using the skills and know-how his dad taught him, installed the dryer for our pastor. He wrapped electrician's tape around the flare instead of thread sealant. A typical DIY brainstorm with possibly deadly consequences.

New Hampshire lets people do plumbing and electrical work on their own houses, and had even allowed gas work by homeowners. However, a recent fatal explosion resulted in a state law that permits only licensed persons to do any gas work.

One possible consequence of using any kind of lubricant on the threads of a flare or compression fitting nut is that it increases the load resulting from a given torque. I saw one case where Loctite was slobbered onto the threads and face of a large nut and provided so much lubricating effect before it set up that it caused failure of the fastener when the specified torque was applied.

[Hardt]

"Over torquing" ouch, another fly in the ointment!! Yes, many years ago when I first started working on my cars I always wondered about the accuracy and consistancy of the torquing processing. If you are working on a new installation with brand new fasterners, I would expect that you can be confidant that you can torque all the fasterners precisely and accurately. If however, you are working on an old car that has been out in the elements, and the fasterners are rusty, greased, heated, banged up, etc. how can you expect to torque accurately. Maybe one of you mechanical engineers can enlighten me on what conditions need to be present to set an accurate torque. BTW, I do have torque wrenches but don't have an adapter to use for this application.

Getting back to this topic, I have the installation instructions for the gas range-to-gas supply and it says to apply teflon tape or an appropriate thread sealant to ALL male pipe threads. This is contrary to the instructions that came with the flexible connector. Go figure...

So to close this thread, if you all never hear from me again, I've blown myself up and I've instructed my wife to put on my headstone: " I shoulda stuck with the electric range!"".

[Gary Swart]

I'm not a pro, but I have 100% gas appliances in my home and they are all connected with a flex pipe. I used no sealant of any kind on any of them and have never had a leak. I always check every joint/connection with dishwashing detergent just to be sure. I have found some small leaks on my lines, but never on a flex connection. BTW, I use Oatey pipe compound on my joints, no tape.