Nozzle load affects on MAWP

[Bobfromoh]

I did an analysis of a vessel with nozzle loads.
On one nozzle, the local stresses were acceptable but when I checked the Pressury Summary, The mawp of that nozzle was lower than thw MAWP of the vessel.

I couldn't follow how the calculation was done. Can you expain it or is there some reference to look at that would help?

Thanks.

 

[TomBarsh]

COMPRESS provides several nozzle design/reporting options. See this FAQ:

http://www.codeware.com/faq/1013.html.

I assume that you have left the nozzle option at the default, which is to design nozzles for "Design P, Find MAWP and MAP". In this mode, COMPRESS enforces that the nozzle has sufficient reinforcing area, weld size, etc, for the design pressure (plus static head, if any); then when calculations are run the reports are based on the nozzle MAWP and MAP. See this document for discussion of how COMPRESS determines the nozzle MAWP and MAP:

http://www.codeware.com/faq/1015.html.

COMPRESS does not perform any "stress" calculations until the ASME Code calculations are run. Thus stresses due to external loads on nozzle (analyzed using WRC-107) or found for large openings under Appendix 1-7(b), if required, are not calculated until the ASME Code calculations are run. This means that nozzles whose design is governed by a stress analysis, rather than area, weld size, etc, will not be revealed until the calculations are run. In this case, the designer must adjust the design as necessary and re-run the Code calculations.


Tom Barsh
Codeware Technical Support