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304 vs 304L vs Dual rated 304/L as it applies to ASME codeHelpful Member!(3) 

jcmech (Mechanical) (OP)
10 Mar 07 10:58
I have recently performed an ASME code calculation (using software) on a pressure vessel.  I thought that it was odd that the vessel would pass for 304 but not for 304L.  This of course raised the question of what the difference is between the two at say 1150 degrees F.  My question isn't really what the difference between them is, rather what are the properties of the dual rated version, and if there is such a clear dividing line of 0.03% carbon content, how can the material perform the function of both?  Also, my purchasing manager has stated that he cannot find pure 304 anywhere, that we must use 304/L or go to a different # stainless, is this true?
DSB123 (Mechanical)
10 Mar 07 11:37
Hi There jcmech,
                304/304L dual certified material is readily available if you go to the right stockists/manufacturers. 304 is stronger than 304L. The dual certified material meets the requirements of both material specifications.We have used dual certified plate and pipe material on a recent Project. We did not have much problem sourcing.
Helpful Member!(2)  metengr (Materials)
10 Mar 07 12:22
jcmech
Dual certified stainless has to be carefully evaluated for service. At low to moderate temperature service, no problem because corrosion resistance is the controlling factor in design application. Once you get above 1000 deg F, there are noticeable differences in creep strength that you must consider in your design (the maximum service temperature permitted for 304L is 1200 deg F, while for 304 is 1500 deg F).  

If you have access to ASME B&PV Code, review Section II, Part D. Evaluate the differences in allowable stress values between 304 and 304L.
Helpful Member!  EdStainless (Materials)
11 Mar 07 15:39
Remember that 304 has no minimum carbon level.  Any 304L that has enough room temp strength will be able to be dual certified.
The real issue is creep resistance.  The original creep limits for 304 were based on material with some C in it.  Even if you have high strength 304L with nitrogen it will not have as high of creep strength.
You need to look at the limitation on your design very carefully.

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unclesyd (Materials)
13 Mar 07 23:05
We don't allow dual certified 304/304L other than some specific applications on our site due to inherent corrosion problems with our process. We specifically call out the allowable Carbon, Sulphur, and Phosphorous on all 304L material used in site, none of the dual certifiable material can meet our chemistry requirements.

We also take into account both the High and Low allowable for design with both 304 and 304L, noting that the Low values for 304 and the High values for 304L overlap at the lower temperatures. I'm not sure how this is handled at the present with the dual certified materials.
rolledalloy (Materials)
3 Apr 07 13:10
Since you are operating at temperatures in the creep range there is the possibility of dual certified 304/304H (UNS 30400/30409).  This would ensure a minimum carbon content and a minimum grain size to provide adequate creep strength.  It is available in plate form.  Other product forms could have availability issues.

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