From:
Jeffrey Lewin <jclewin**At_Symbol_Here**MTU.EDU>
Subject:
Re: [DCHAS-L] Curious about Teflon tape
Date:
Sep 21, 2023 12:33 UTC
Reply-To:
ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID:
<CAEwQnqiJJN_jnU4gya=ohSQMCCYaYr6-Xes84cn72a5Ty1YTug**At_Symbol_Here**mail.gmail.com>
In-Reply-To:
<CAJug0Owgrij=pjNdNiG4MMKjHWxYRGUnHAmew_a_ef1_AGtS6g**At_Symbol_Here**mail.gmail.com>
From page 168 of "Prudent Practices"
"Do not use Teflon tape on straight thread (e.g.,
Swagelok) where the seal is formed through gaskets
or by other metal-to-metal contacts that are forced to-
gether when the fitting is tightened [e.g., Compressed
Gas Association (CGA) gas cylinder fittings or com-
pression fittings]. Metal-to-metal seals are machined to
tolerances that seal without the need of Teflon tape or
other gasketing materials. If used where not needed, as
on CGA fittings, Teflon tape only spreads and weakens
the threaded connections and can plug up lines that it
enters accidentally."
A job aid from Airgas was posted to CSHEMA, but I can't find the original online. One of the comments with an arrow pointing to the CGA fitting states:
"Do not use teflon tape on the CGA fitting. Some CGA fittings seal with a gasket [My note - CO2 incubator regulators are one of these] others are metal to metal. Never use teflon tape to seal a metal CGA connection as it will cause a leak."
Jeff
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.
Thank you very much,
Ben
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