View Full Version : Stainless Tubing

02-02-2011, 07:43 PM
Does anyone know where or if 400 series stainless tubing can be purchased? One of our engineers is trying to find some for it's thermal expansion properties but we can't find any tubing.

Is there someting about 400 series that would make it unsuitable for tubing?

By the way, preferably DOM tubing; no seam.


02-02-2011, 07:55 PM
409 is commonly used for automobile exhaust systems. Should be readily available but I would expect it to be rolled and welded. Maybe that's OK.

02-02-2011, 08:22 PM
It might be because that a is martensitic alloy, it does not like alot of cold work and has a touch of brittleness and lower facture toughness. DOM requires cold working and that might make that series real pain to make.

02-02-2011, 08:26 PM
Thanks Gentlemen, I found somebody that makes welded tubing looks like they may make specials as well. I'll give them a call tomorrow and see what they say.

By the way, I forgot to mention, this has to be relatively smalle diameter like .5" or so.

Thanks again.

02-02-2011, 08:55 PM
They might make brake line tubing in stainless.

02-02-2011, 09:24 PM
Is the thermal expansion of 400 series that significantly different from the 300 series? I'm surprised.

[Edit]: Yes it is. I just looked it up. 304 is about 17.5 um/m/deg C. 440 is about 10.5 um/m/deg C.

02-02-2011, 10:05 PM
" Yes it is. I just looked it up. 304 is about 17.5 um/m/deg C. 440 is about 10.5 um/m/deg C."

Is it really? If you have to go to 6 decimal places how significant could it be? Any long run of pipe or tubing must have an expansion joint so it would be irrelevant if this is to be a conduit of any kind. However as previously noted it would be subject to serious fatigue problems due to repeated pressurization cycles. I don't recall ever seeing any small diameter 400 series tubing, but 300 series is commonly used for control and instrumentation.
Many years ago I was in the scrap metal business. The first man I worked for told to always remember "there are no hard and fast rules in the scrap business except for one and that is there are no hard and fast rules in the scrap business". 409 is an example of this. To be considered a stainless steel the alloy must contain 10% Cr. Except for 409. It is however always welded, it rusts, although slowly, and has no application other than automotive exhaust systems. It will not fly for this application.

02-02-2011, 10:19 PM
It's for a tunable VHF (and UHF) filter using what we call a "push-pull" resonator design. When it's extended the resonator is about 10-12" long, I can't remember the exact dimensions.

This stainless part will be about half that length. It'll be part of the mechanism that extends and retracts the resonators.

A change of a few thousandth's of an inch in the resonator length will put the filter electrically out of spec. Typically they have to operate -55 to +85 degrees C.

So, any reduction in CTE is a good thing.

Generally we use invar for this type of application but we're trying to find another option.

Thanks again.

02-03-2011, 12:54 AM

02-03-2011, 08:40 AM
Maybe you should look into thermal expansion compensation then insted?

I seem to recall a cool demo of it for pushrods, Where you put a lever in the middle of the pushrod arrangement at half length (pivot in center of lever, rod attached to each end), the lever changes the push into a pull.
Meaning that if both rods expand at the same rate, The end result is no expansion along the total length.