specified thickness? 2

[mengnr]

I am analyzing a component in accordance with the BPVC, which I am not very familiar with, and I'm stuck on practically the first paragraph. UG-4 says materials subject to pressure stress shall conform to Section II, Part D, Subpart 1, Tables 1A, 1B, and 3, which list material properties. In Section II, I find materials, strength properties, and a "specified thickness," which I couldn't find an explanation of. Does this mean materials which exceed the specified thickness are forbidden by the code? For example, 6061-T6 has a specified thickness of up to 0.249. Does this mean I can't use half-inch thick 6061-T6 in a pressure vessel? Why? I don't know why that would be more unsafe than 0.249-inch-thick 6061-T6.

 

[metengr]

In Section II, I find materials, strength properties, and a "specified thickness," which I couldn't find an explanation of.

Your post lacks information. After reading UG-4 in ASME Section VIII, Div 1, what I believe you are asking is in reference to the statement below;

(e) Materials outside the limits of size and/or thickness
given in the title or scope clause of the specifications given
in Section II, and permitted by the applicable part of Subsection
C, may be used if the material is in compliance
with the other requirements of the specification,(1) and no
size or thickness limitation is given in the stress tables.
In those specifications in which chemical composition or
mechanical properties vary with size or thickness, materials
outside the range shall be required to conform to the composition
and mechanical properties shown for the nearest
specified range.[/quote UG-4]

By the way (1) is a footote, please read it below
1 In some instances the limitations of the scope clause in the material
specifications are based on a very realistic maximum. It is recommended
that the designer and/or fabricator confer with the material manufacturer
or supplier before proceeding, thus assuring himself that except for size
or thickness, all requirements of the material specification will be met
and so certified.


I will let you read and digest the above. Now review one or more ASME Section II material specifications that provide mechanical property requirements based on thickness limits and/or size.

 

[mengnr]

Thanks for the detailed answer. You're right, I should clarify. I was confused by the "no size or thickness limitation is given in the stress table." The next sentence sounds like it's contradicting that by saying that there is no maximum thickness limit as long as the material meets the strength, elongation & bend diameter factor shown in the table? I found it somewhat unclear that there is a maximum specified thickness shown when the material I am looking at is readily available in thicker plates. If the material properties are what matters and not the thickness, then why give a maximum thickness in the table? Thanks for the answer.

 

[metengr]

mengnr;
ASME B&PV Code has escape clauses and exceptions. The thickness limitations in Tables 1A, 1B in Section II are there because during review and qualification of this material by Section II Subcommittee, the submitter for this material could not guarantee mechanical properties or chemical composition or both for thicker or larger diameter sections.

 

[mengnr]

Thanks for the explanation -- I appreciate the help.