Allowable Stresses on FEA of ASME VIII DIV I Pressure Vessel 1

[victorluna]

Hello,

I'm perfoming a FEA on a ASME SEC VIII DIV I Pressure Vessel, since this division is basically a cookbook and rule of thumb based, I'm not sure if the results I obtained from ansys are allowable for this vessel, on UG-23 I became on doubt if these stresses are limited by 1.5 S or 3S, can someone please help me? The images are attached. The allowable stress of my material for the given temperature is S = 138MPa

The first case is the surroundings of an opening.

http://files.engineering.com/getfil...-bfad-4bcc-a85c-69ee703e6722&file=stress1.jpg

And the second is probably a bending stress caused by discontinuity.

http://files.engineering.com/getfil...-16ab-4682-a549-0b26fed6ff01&file=stress2.jpg

Thanks for the attention.

 

[corus]

1.5Sm is generally for primary stresses whereas 3Sm is for primary plus secondary stresses. Secondary stresses are generally strain dependent and can arise from thermal loads or can occur at structural discontinuities. Have a look at the code or other pressure vessel codes as they're all based upon the same principles. It's a little more complicated than a cookbook.

 

[victorluna]

Yes, I understand that, what is confusing to me is the definition of of primary and secondary stresses. I confess I still haven't looked any codes other than the SEC VIII div I, but I haven't found the definition for these stresses on that part of the code. Is the opening considered a discontinuity?

 

[TGS4]

I wrote a blog post on this topic. Please read and come back here if you have questions.

http://becht.com/blog/performing-an...ision-1-to-qualify-an-article-u-2-g-component

 

[victorluna]

TSG4 , Thanks for the reply. So, what you say in your post is that I should analyse using the parameters set by division II, In that case, my allowable stresses won't be the ones declared in UG-23, but those stated on the division II even though the vessel was designed by division I, is that correct?

 

[TGS4]

Not quite. What method are you using to demonstrate Protection Against Plastic Collapse? Can you exempt the components from evaluation of Protection Against Local Failure? How will you demonstrate Protection Against Ratcheting? (Elastic, elastic-plastic?)

 

[victorluna]

I was hoping that the sec VIII div I code, would stablish that for me, based on the stresses. Anyway, I will have a further look at this issue. Can you please tell me where this U-2(g) article was published? I didn't found it.

 

[TGS4]

Division 1 does not provide any guidance. And since you are not at all familiar with either Division 1 or Division 2, I would highly recommend that you find an experienced engineer to act as your mentor, or hire an experienced consultant. This is not something that you will be able to do on your own without help.

U-2(g) is in the very front of Division 1.

 

[Riansyah]

Very unsafe design,
even use welding pad. Check solution for Nozzle load.