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stanrick (Mechanical)
14 Oct 08 8:34
Can anyone tell me what it means for a steel to be "dual rated" as "SA312-304/304L" or "SA240-304/304L"? Also, if this steel is used in ASME Sec. VIII Div 1 calculations, which properties should be used? 304? 304L? Average?

Thanks!

Rick
SnTMan (Mechanical)
14 Oct 08 9:12
stanrick, typically it means that the steel meets the mechanicals of straight grade and the chemistry of L grade.

It is fairly common to use straight grade mechanicals.

As I recall there was a pretty extensive discussion of this issue a whaile back, maybe in the metallurgy forum, I'm not sure. You may turn it up with a search.

Regards,

Mike
doct9960 (Mechanical)
14 Oct 08 10:44
stanrick,

You can use the allowable stress of either 304 or 304L, but the material that should be listed in the Manufacturer's Data Report must correspond to the material grade used in the design. For example, you used the allowable stress of SA-240-304 on the shell design,  the Manufacturer's Data Report should only list SA-240-304 on the shell material.
jte (Mechanical)
14 Oct 08 11:13
stanrick-

Some material spec's overlap, and as explained above, a "dual rated" material meets the requirements of both spec's. This is common for "straight" grade stainless and "L" grade stainless materials. Typically, the vessel designers want the "straight" grade for the higher allowable stress while the materials engineers often prefer an "L" grade. Thus, dual rated material can sometimes keep both the mechanical and materials engineers happy. However, the ASME code documents are, well, Mechanical. So for ASME document purposes, you would write in the material used to determine the allowable stress. But... to make sure the use of dual rated material doesn't get forgotten (to keep materials engineers happy 20 years from now), its a good idea to make a note of its use in the "remarks" section of the Data Report.

For a Code reference, see Interpretation VIII-1-92-166 on page 591 in Volume 34:

Quote (Int-VIII-1-92-166):

Question (1): May a dual stenciled material (e.g., SA-240 304/304L) be listed as SA-240 304, SA-240 304L, or SA-240 304/304L in the Manufacturer's Data Report Forms when using only one set of design allowables for the particular Grade designation?

Reply (1): No, the material shall be listed as the material grade chosen from the allowable stress tables.

Question (2): If the dual stenciled material is listed as SA-240 304, may the "Remarks" section of the Manufacturer's Data Report Form contain the phrase "The shell and bottom head material meet all the requirements of SA-240 304 and SA-240 304L,"?

Reply (2): Yes.

jt
 

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