Trays materials selection when the design temp. lower than -101C

[jiang1976]

I have a question on the trays materials selection for a tower. The minimum design Temperature of the tower is -101C. 304SS was selected for the construction of the shell and heads of the tower. Can I use 410SS for the trays materials, if only temperature is taken into account? What is the minimum service temperature for 410SS, as trays materials?

Thanks.

 

[metengr]

jiang1976;
410 stainless steel is not really suitable for low temperature service. This material exhibits a loss in toughness at -20 deg F (-29 deg C) and below. Also, ASME B&PV Code limits the use of this material at -20 deg F and warmer for thicknesses 1/4" and less. I would be concerned for the risk of brittle fracture in welded attachments inside the tower.

I would use an austenitic or Ni-base steel for the trays.

 

[vesselfab]

well, trays do not normally weld to anything, so brittle fracture at welded attachments would not be a problem.

but as metengr says an austenitic ss like 304 would most likely be the best. a ni based steel is not a normal tray manufacturer's material, so that may throw them into a tizzy, and it may be hard to get in the thicknesses used for trays and tray parts.

 

[jiang1976]

Thanks.

 

[jiang1976]

Since trays are removable internals, we do not need to think about the welding properties. Can we use 410SS for trays at a temperature warmer than -46C and below -29C? The limit of ASME B&PV Code at -29C (-20 deg F) is normally used for the weldment, not non-pressure part, right?

 

[metengr]

jiang1976;
Why are you considering 410 ss for this application (I am not a pressure vessel process expert)? If you have no structural or attachment welds for the trays that is fine, but this material has poor toughness. Can you risk having tray failures from fatigue crack propagation or some other damage mechanism? If so, go with 410 ss (quenched and tempered at or above 1200 to 1325 deg F). If not, you might need to re-think your material selection.

 

[jiang1976]

metengr:

thanks for your answer.

Acctually, the client want to use 410SS to save money. Personally, I'd like to use 304SS. I need evidence to support my point. I started my work two month ago. That's the reason I come here.

 

[metengr]

jiang1976;
I would go back to the Owner and tell them what I mentioned above - if they can tolerate potential brittle fracture of the trays from service induced fatigue cracks or from SCC (higher strength martensitic stainless steels can exhibit increased risk of stress corrosion cracking) or some other damage mechanism, then use 410 ss to save a buck.

 

[jiang1976]

Thanks for your help.