14 Oct 08 11:13
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:
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.