External design pressure

[19750412]

Hello

I make design of pressure vessel with dimpled outside shell for which design pressure is specified in data sheet at 0.75 MPa. Design pressure for inner shell is 0.45MPa. Inner shell is partially covered by dimpled shell two times distance of 1000 mm. The length of inner shell is 3700 mm. My question is, should I make calculation for inner shell for external pressure amounts 0.3 MPa, as difference of both above pressure values. Or is possible to avoid calculation for external pressure for inner shell due to fact that pith for spot welds is 50 mm and therefore unsupported length of inner shell is inconsiderable.

Thank you in advance.
ARTI

 

[prex]

Yes you must check the inner shell to external pressure. The result of this check might be obvious, as you state, but the demonstration must be more factual, words like negligible or inconsiderable are out of place in a design report.
As codes generally do not provide rules for external pressure calculations of dimpled assemblies, you could need to revert to a proof test.

prex

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