From:
Tammy M. Lutz-Rechtin <tlutzrec**At_Symbol_Here**UARK.EDU>
Subject:
Re: [DCHAS-L] Curious about Teflon tape
Date:
Sep 21, 2023 23:27 UTC
Reply-To:
ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID:
<SA0PR04MB7449DBE9B2A27B1488686BFEBAF8A**At_Symbol_Here**SA0PR04MB7449.namprd04.prod.outlook.com>
In-Reply-To:
<409722077.1073617.1695318067453**At_Symbol_Here**mail.yahoo.com>
Ben,
The threads on the regulator to cylinder connection are parallel threads. Our machinist and fabricator says “Teflon should only be used on NPT fittings because these are tapered threads. Teflon prevents “seizing” in the tapered metal-metal
connections.” Besides, Teflon can expand the thread opening, lead to over-tightening by users to prevent leaks and eventual mis-threading damage to both the regulator and cylinder connections.
From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
On Behalf Of Michael McCutcheon
Sent: Thursday, September 21, 2023 12:41 PM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: Re: [DCHAS-L] Curious about Teflon tape
The connections (fittings) on a compressed gas cylinder are CGA fittings and are designed such that the metallic mating surfaces create the mechanical, gas tight, seal; different
than tapered thread type fittings, such as NPT, that require some sort of sealing compound such as Teflon tape to create a gas tight seal at the threads as opposed some sort of mating surface. With CGA, flare, or other "compression type" fittings, the use
of Teflon tape can actually create leaks because it prevents the mating surfaces from creating a mechanical seal. There are very few fittings that require the addition of tape or compound to create a seal. If you are getting leaks from a "compression type"
fitting, it is because there is debris or some sort of damage to the mating surfaces and tape or compound will not fix it; must be replaced.
See the following article from Airgas on the
The “Do’s and Don’ts” of CGA Cylinder Connections
Hello,
This is nothing to get excited about, just a matter of curiosity.
At our annual safety training we were told not to use Teflon tape when attaching regulators to gas cylinders. The ultimate reason given was that the tape would
not allow the regulator's ball to fit tightly to the gas cylinder's socket.
I find this a bit difficult to believe. This would only apply if the threads on the regulator and the cylinder were tapered. Because a tapered thread connection
stops going in once the male and female diameters are the same, using tapered threaded parts would require highly precise machining so that the male would stop going in at the precise distance to firmly seat the ball in the socket. Such precision would be
prohibitively expensive. (I think.)
Rather I think the reason is because white Teflon tape is not 100% Teflon and the other component is combustible. There is a green Teflon tape for use with
oxidizers that is 100% Teflon. To avoid the use of the more common tape on an oxygen cylinder, the easiest way is to say "No Teflon tape on gas cylinders."
When appropriately used, the Teflon tape acts as a lubricant, so that a regulator can be put on (and taken off) without the use of an enormous wrench.
I know that I may be entirely wrong about this, so I am seeking the expert opinion of L-CHASers.
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