Pressure Swing Vessel, U1 or U2 1

[GK Miller]

I am currently designing a pressure swing vessel. The pressure will swing from +85 psig to near full vacuum every 2 minutes, 24/7, for a 30 year lifespan. In the past, we have had these evaluated and stamped as U1 vessels. In speaking with my previous AI, the code may have changed for non standard vessels. Doing a keyword in Section VII, most hits for cyclic loading fall under bellows.

So my questions, can anyone give guidance on how I would design and qualify this loading condition as a U1? or should I pass this to a U2 shop and stop thinking about it.

 

[marty007]

I don't believe that anything has changed in this regard. A U1 shop could still design and build this vessel if they have the knowledge and expertise to perform the fatigue and ratcheting analyses.

The new edition of VIII-1(2019) has simply clarified how the rules of ASME VIII-2 can be used for the design of U1 vessels.

 

[DriveMeNuts]

Div 1 is allowed for fatigue. See UG-22(e).
However there are no rules for fatigue. You will need to use U-2(g) to in turn use a fatigue method such as ASMe VIII Div 2 or PD5500 Appendix C or others to conduct your fatigue assessment.
Some workshops are competent enough to complete basic design by rules calculations for static pressure. However, I have never come across a workshop that has the remotest clue how to design for fatigue. You may need to find someone else to do the fatigue analysis in advance and then advise the fabricator of minimum thicknesses to use in their static calculations. This may become an iterative process when designing for partial vacuum fatigue. It may be just better to do the entire fatigue and static design yourself.

 

[XL83NL]

However, I have never come across a workshop that has the remotest clue how to design for fatigue

Same experience here.