nozzle neck thickness output

[plantguyjj]

Tom,

Can you please comment on the methodology behind the output for the nozzle neck thickness calcs?

Ignore external pressure and area reinforcement calcs and just consider a small bore nozzle subject to internal pressure (in rating mode). It looks like to me that Compress is using the UG(45) thickness for the nozzle and solving for the allowable pressure in the cylinder that is connected to the nozzle (tr from UG-37(a). It then appears to set the nozzle design pressure to the allowable pressure determined from the cylinder and solve for a nozzle neck thickness.

Most of my work with Compress is evaluating existing vessels, not new design. I see cases where my nozzle neck is greater than the UG(45) but Compress appears to be limiting the allowable pressure of the nozzle. If the nozzle neck is greater than the UG-45 min, why not just use UG-27(c)(1)and determine an MAWP for the nozzle neck based on the available wall thickness?

Also, I have noticed that I do not get a deficiency message during cases where the MAWP for the nozzle neck is less than the design pressure of the cylinder that it is attached to. I can submit a file to demonstrate this if desired.

thanks

 

[TomBarsh]

COMPRESS performs all calculations for the nozzle report based on a consistent pressure; ie: the same pressure is used for reinforcing area calculations, calculations for UG-45, UW-16, Appendix 1-7, WRC-107, etc, etc.

The pressure used in the nozzle report depends on the nozzle mode is selected on the Nozzles 1 tab in the Set Mode Options dialog. COMPRESS provides several modes for design/reporting of nozzles, see

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

I assume you generally use the "Rating" calculation mode. In this mode you can have nozzle calculations produced based on the specified design pressure (plus static head, if any) or have COMPRESS determine the nozzle's MAWP.

Now we really get to your question, which I will restate as "How does COMPRESS determine the nozzle's MAWP?".

COMPRESS determines the highest pressure at which all applicable Code requirements are met. By definition, this is the MAWP. In other words, increasing this pressure by a fraction will result in some Code requirement being exceeded. How COMPRESS does this is discussed in this document

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

At this time ASME Section VIII is a Code for "new construction". Attempting to rerate existing vessels per this Code is sometimes difficult, as you find for the UG-45 requirements.

In COMPRESS you might wish to specify that the nozzle being analyzed is an "Opening" rather than a "Nozzle". In this case only the UG-45(a) requirements will be applied; requirements of UG-45(b) will not be applied. In any case, the nozzle wall thickness will be rated to withstand the specified loads, but no "artificial" requirements based on UG-45(b) will be imposed.

My understanding is that ASME is preparing a post-construction Code that will address some of these issues.

Hope this helps.

Tom Barsh
Codeware Technical Support

 

[plantguyjj]

As always, very helpful.

thanks