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Stainless Steel tubing PQE, CQE,CQ,CQM

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Prometheus21

Prometheus21

Mechanical
Apr 22, 2023
104
Hello everyone,

I am currently redesigning a H2 distribution and filling system (small diameter tubing (6-18 mm) - 250 bar working pressure) to reduce the chance of leakage.

In that regard I am looking at different SS tubing qualities and was wondering if any of you have experience with using PQE, CQE,CQ or CQM ? In combination with ferrule fittings I imagine CQ or CQE rating would be satisfactory as long as the specified surface roughness is appropriate, and the tubing is handled carefully during installation; any input?

I often see "Manufactured in accordance with SP3-007/SP6-064"; I am not familiar with these standards, does anyone know where these can be purchased?

 
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Are you doing this all in 304L?
Make sure that you are using annealed tubing (not cold worked for higher strength).
Welded tubing must have no external dimensional indication of the weld.
And welded or seamless requires good NDT.
Welded would be ECT and air-underwater while seamless should be UT and air-underwater.


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P.E. Metallurgy, consulting work welcomed
 
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Hi,

Thank you for the response;

Everything is in seamless, bright annealed, 316L; with an electropolished interior and exterior to a surface roughness of minimum
– Ra 0,25μm (10μinch).

 
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Seamless may be waste, just make sure that it is all Ultrasonic Tested.
There is no inherent performance difference compared to welded tube.
But then since you are going EP obviously cost is not an issue.
The only things that we used to EP were for pharmaceutical and high vacuum applications.
The reason for EP is not to lower the roughness.
Roughness is a macroscopic measure, after all the spec is called "Wave and Lay".
EP is to reduce the microscopic texture.
This reduces absorbed materials on the surface.

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P.E. Metallurgy, consulting work welcomed
 
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Cost is not an issue, no. The cost of leaking hydrogen and related downtime is too high in comparison to the cost of the tubing.
Yeah these are laboratory quality rated tubing, often used for high pressure gas applications or for high purity gases, or as you say pharma or vacuum applications as well(Europe).

"The reason for EP is not to lower the roughness." True, but it does help with the end result, no? In general much depends on the parts tolerance and general surface finish before EP, but it will help reduce the Ra if Im not mistaken (?) Then again with ferrule fittings I am as you say more interested in the reduction of absorbed material on the surface.

 
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EP may or may not change the measured surface roughness.
It depends on the prior mechanical finish.
Considering that profilometers don't work below about 24uinch because of the stylus radius.
We only had one customer that really understood this.
He would order pipe that was oxide annealed and pickled, so rather rough ID.
And then we would EP it.
It would still be >60uinch roughness but the internal surface area was reduced by 3-6 times.
It was very wavey, but it had no microscopic features.
I never saw EP used for gases outside of semiconductor.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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"Considering that profilometers don't work below about 24uinch because of the stylus radius." - Good point; now I've learned something new today too.

"I never saw EP used for gases outside of semiconductor." - Interesting; in Europe it is often used for Ultra high purity gases (oxygen for aerospace usage, Hydrogen 99,9999%, gases used for calibration of sensitive offshore well-instruments as well as for phosphine and phosgene usage in laboratories). Is it required in all those applications? Probably not. Then again the industrial gas industry is filled with weird customer requirements and the old adage of it ain't broke don't fix it.
 
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