ASME U1 STAMP

[LupusLupis]

Hope somebody can help me:
I need to know if it's possible to perform the ASME U1 STAMP on a vessel with some parts design as per ASME VIII division 1 other parts ASME VIII division 2.

 

[jamesl]

For a Div 1 stamped vessel, Div 2 formula or equations can be used under U-2(g), however Div.1 allowable stresses have to be used.

If some pressure containing parts on the vessel are designed per Div.2 with Div.2 allowable stressed, then the vessel cannot be stamped as Div.1.

 

[LupusLupis]

Thank you james, so for example:
If I disegn my vessel as per Div.1 except the thickness of a dished cover where I use a beam bending/shear formula (NOT UG34 Div.1) and I verify the ideal vonmises stress with the division 2 intensity factor * allowable stress ASME II-D Tab.1A, I cannot perform the U1 STAMP?

 

[jamesl]

Two problems with your approach:

1. I am not sure why you need to use Div.2 on dished heads. Div.2 equations can only be used under U-2(g) when Div.1 code does not provide design rules for the part. If Div.1 covers the parts, you cannot use Div.2 to bypass Div.1.

2. You do have to use Div.1 allowables even if you use Div.2 equations under U-2(g).

In my opinion, the vessel cannot have Div.1 stamp as described.

 

[TGS4]

I concur with jamesl - U-2(g) is ONLY applicable if there are no rules available in Division 1. In your example where there are rules for dished heads in UG-34, then you are required to follow those rules, in order to call it a Division 1 vessel (and apply the U-stamp).

On the other hand, if the geometry of your head were sufficiently unique that you could argue that it doesn't fall under any of the mandatory rules, then you could apply U-2(g). Please note, however, that validating something to Division 2, Part 5 is much much more complex than comparing some stress to an allowable. I would argue that you have to satisfy ALL of the requirements of Part 5 (all of the failure modes) in their entirety. I appreciate that this sounds like overkill, but the Code authors, in generating the rules that exist in Division 1 (and the design-by-rules in Division 2, Part 4) have considered all of these failure modes (and then some) in the development of the rules. Furthermore, a thorough understanding of all of these failure modes should be a prerequisite for applying Part 5.

<gets off his soap-box>