Auto-Refrigeration

[jtseng123]

All,

For a new CS vessel that will have auto-refrigeration, do I just use UCS-66, 67, 68 and 160 to specify the thickness, or shall I go by API 579 and ASME FFS-1 fitness-for-service and develop a minimum allowable temperature ? I do not think I need to go by API 579/ASME FFS-1 for new vessel. What is your opinion ?

 

[metengr]

I think any reference standard to allow the designer to better evaluate design conditions either in or pre-service to avoid brittle fracture is worth it. In this case, you can use the methodology in Part 3 of API 579 to determine a minimum allowable temperature curve.

As a minimum, you can run a sanity check against initial vessel design to evaluate risk.

 

[Ehzin]

I may just be overly cautious with some wording used but UCS-66, 67,... wouldn't specify thickness. I'd say the order of logic would be as follows:

1) Determine tmin from UG-27 and specify thickness.
2) Define the MDMT (May be using this term inappropriately. I believe I've seen MDMT used as both the stamped minimum temperature the vessel can physically handle and also the minimum temperature that can be encountered during operation/transient conditions. I consider it as more of the former although that could easily be argued.)
3) Use UCS-66, Fig. UCS-66, and relevant sections to determine if the MDMT is acceptable without requiring impact testing.
4) Take any credit from UCS-66.1 as necessary and appropriate.

There's a lot of other steps but here's a very brief overview. Actually Fig. UCS-66.2 has the overview of the logic for this process regarding the MDMT, I'd recommend referring to that.

Thanks,
Ehzin

Was assuming this is a coded vessel given that UCS sections were mentioned. If it's not coded then I suppose using any relevant guidelines regarding MDMT could be acceptable. ASME Section VIII does provide somewhat thorough guidelines.