[time-nuts] Swagelok and metric tubing question

[Chuck Harris]

Compression fittings work by crushing the surface
of the tubing, and the surface of the compression
insert together to make a gas tight seal.

Stainless is very tenacious stuff, and as a result,
when it is drawn through a die when sizing it as
tubing, it gets axial ridges formed by galling, and
damage to the dies.

If you are planning on welding the tubing, the ridges
won't matter, but if you are planning on using a
compression fitting, the ridges must be eliminated,
which is done by more expensive machining processes.

You can sometimes use tubing with ridges with
compression fittings if the fittings have a highly
compliant insert made of plastic, rubber, or copper.

Usually, though, when stainless is specified for the
tubing, you are going to want an all stainless solution
for the fittings too... which means ponying up for
the more expensive polished stainless steel tubing.

Don't even think of using compression fittings meant
for copper, or plastic tubing on stainless.  It won't
go well if you do.

-Chuck Harris


cdelect at juno.com wrote:
> Bob,
> 
> That's the cheapest I have been able to find it.
> 
> I'll probably go that route with the expensive version as it's specified
> for compression.
> 
> I know the original setup mixes copper and stainless but I have read that
> is not recommended???
> 
> Cheers,
> 
> Corby
> 
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