Interesting topic. Went searching around a bit, because I was curious
myself. This is what I found from various trade sites and such.
Bare threaded pipe fittings typically have about a 20% surface contact, with
the other 80% allowing leaks because there is no metal to metal contact.
Teflon tape was originally meant to be used as a thread lubricant on
tapered fittings. It wasn't to increase torque values, but to prevent the
thread surfaces from galling on each other, which would increase leaks.
It slow flows or cold flows (deforms) in the process of threading the
fittings together, incidentally creating a mechanical seal. The sealing
effect is a byproduct. Teflon tape comes in many different colors, all of
which are apparently the same. White simply being the most popular
color. Teflon tape has a propensity for being cut while the fitting is screwed
together, allowing threads of teflon tape to contaminate the product in the
pipe. This renders it rather unsutable for things like natural gas, where
perfect
closure of a valve is critical.
Pipe dope is a solid sealant that relies on solvent action to flow into
the thread voids. The solvent evaporates, leaving the solids as a
sealant, or glued joint. It is rigid and brittle. Pipe dope tends to
break up under vibration, and depending on the formulation it can be
disolved by different fluids and gasses. It also tends to make disassembly
difficult and requires complete thread cleaning to reassemble.
The anaerobic sealers are apparently the best, in that they do not
evaporate, stay flexible, and are far more resistive to solvents or
corrosive actions.
The cost factors of teflon tape vs pipe dope is minute, with both
being typically less than a penny a use. Teflon tape coming up
slightly cheaper then pipe dope. I do not know about the cost
of the anaerobic sealers.
>>> "Keith Kaplan" <keithka@microsoft.com> 08/16 8:22 PM >>>
Basic plumbing question -- what are the relative advantages of pipe dope
versus Teflon tape? Is one good for water and the other for natural
gas, or maybe one for PVC and one for black pipe? What would be best
for compressed air lines? I've always used tape for the nipples on air
tools and hoses, but is dope better? Is dope cheaper but tape is less
messy? Everywhere I've read seems to refer to them as if they're
interchangeable, but surely there's a difference.
///
/// shop-talk@autox.team.net mailing list
/// To unsubscribe send a plain text message to majordomo@autox.team.net
/// with nothing in it but
///
/// unsubscribe shop-talk
///
///
|