Just read the "316L high purity sea

[rickfischer51]

Just read the "316L high purity seamless tubing SF" post, and its got me thinking. I'm analyzing something that is already built (yeah, I know, don't say it). Material is dual certified 304/304L. We wanted 304/304L elbows from McMaster-Carr, but when I took the catalog number from the drawing to the catalog to check the dimensions, I found the catalog number was for dual certified 316L. Fabrication was done off site, don't know yet what they actually used. Any potential problems I should know about?

 

[MagBen]

304L Vs 316L: mechanicals are almost identical, especially in annealed condition. 316L can be a little stronger than 304L if in cold worked condition (same CW%), but could be negligible. corrosion of 316L is superior to 304L, especially pitting corrosion.

 

[EdStainless]

In most service the corrosion resistance is similar enough to not cause any issues.
Welds can be a different story. Often when doing the welds you get very different penetration and asymmetric welds.
I would run a borescope inside and look at the ID of the welds. Make sure that they are what you expect.

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P.E. Metallurgy, Plymouth Tube

 

[rickfischer51]

Thanks. Im not so worried about mechanicals as the pressure is low. More concerned about the weld problems described in the previous post. Both 304L and 316L are base metal group A, which gets filler metal group A filler, all of which are E316L..., so my guess is Im ok. Just wanted to check.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[mk3223]

May not see any problem for the 316/316L in your system since both 304/L and 316/L dual grade material are the 300 series austenitic stainless steel with similar corrosion resistance property. In general, 316/L is more expensive material. It's possible that the system was paid extra cost to build because of the material.

 

[rickfischer51]

Thanks for the input.
1. Borescope is on the agenda as soon as we can locate it.
2. Corrosion is not an issue. This thing will be in contact with nothing(vacuum) and liquid helium. It gets cleaned and scrubbed, then assembled in a clean room, then stuffed inside a cryostat with a couple tons of other stainless thingies and assorted bits.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[EdStainless]

Weren't these welds made without filler? That is typical for high purity systems.

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P.E. Metallurgy, Plymouth Tube

 

The dual certification question is quite different from the variable penetration problem.

The straight and L grade compositions overlap, and it is possible to meet the higher strength requirements of the straight grade with carbon content at the upper end of the L grade range. Dual certification of these grades is mainly driven by commercial imperative; i.e., reducing stock for jobbers. Usually it is not a problem; with normal welding practices, risk of sensitization with the dual certified grades is minimal. However for high temperature applications you normally would want to specify 304H.

As far as weldability is concerned, you can mix and match 304/304L, 316/316L and their respective matching filler metals without consequence (although I don't recommended doing that). Your welders won't notice a difference.

Corrosion-wise, 316/316L offers improved chloride pitting resistance over 304/304L, and is typically the first step up the alloy ladder when 304/304L is inadequate. However 316/316L offers no improvement in chloride SCC resistance.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."