I'm checking some calculations of my software for the minimum thickness of a cylindrical shell. I do not understand why I get different results if I use the formula UG-27 (1) from the one that uses the Mandatory Appendix 1 (1).

The condition "P does not exceed 0.385SE" is satisfied but I get the same results only if in the formula UG-27 (1) I consider R as the outer radius of the cylindrical shell and not the internal one as defined in UG-27(b) and specified in note 19: “For pipe, the inside radius R is determined by the nominal outside radius minus the nominal wall thickness.”

Where am I doing wrong?

Any help will be appreciate

Best Regards

AMinati

## Cylindrical shell thickness

- Frohnert
**Posts:**54**Joined:**Tue 19. Feb 2013, 17:18

### Re: Cylindrical shell thickness

Hi,

As you have already noted: UG-27 uses the inside radius and Appendix 1 the outside - two different formulas. The results of both formulas are only the same, if the required thickness and the actual thickness are the same. If the actual thickness is larger than required, you are calculating two different cylinders.

I made a slide regarding this topic some years ago:

This means: for a thick cylinder using the formula with the outside diameter is conservative, simply since the cylinder is larger, that´s it. Just try it out with our calculation form for cylinders (https://www.cis-inspector.com/asme-code-calculation-cylinder.html), here you can compare the results for a thick and a "just OK" cylinder with all four formulas available.

Have fun

Michael

As you have already noted: UG-27 uses the inside radius and Appendix 1 the outside - two different formulas. The results of both formulas are only the same, if the required thickness and the actual thickness are the same. If the actual thickness is larger than required, you are calculating two different cylinders.

I made a slide regarding this topic some years ago:

This means: for a thick cylinder using the formula with the outside diameter is conservative, simply since the cylinder is larger, that´s it. Just try it out with our calculation form for cylinders (https://www.cis-inspector.com/asme-code-calculation-cylinder.html), here you can compare the results for a thick and a "just OK" cylinder with all four formulas available.

Have fun

Michael

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Best regards,

Michael Frohnert

Michael Frohnert