Flange rating mismatch 1

[AnEngineer]

I have a situation where instrument nozzle on vessel is CS 600#. But specification dictates that level guage flanges should be 316 SS. I can not use 600# SS flange because of lower strength of SS. Is there any duel certified material (or other solution) that I can use instead of upgrading to 900# rating.

Help will be appreciated.

 

[TD2K]

What are the design conditions for the tower? It might help someone identify what options you have, if any.

 

[AnEngineer]

TD2K,

It's a separator, DIV-2 design with DP 1350 psi @ DT 170 F

 

[pve5]

ANEngineer ( Mechanical)

I suggest use 600# CS with SS 316 weld overlay. I have used this optionin past for separator to Div.2

 

[TD2K]

Can you reduce the design temperature for the trim? Some companies take the design temperature for the column as the maximum operating temp plus 50F to allow for uncertainities between design and actual operating conditions.

If you have a good idea of the range of operating conditions/cases and don't need that 50F margin for the trim, that would give you the 1350 psig design pressure you need (you wouldn't have to give up all of the 50F margin looking at the B16.5 tables).

 

[alexafkh]

I sugget to use a thicker 316SS flange. You can calculate the thickness you need by B16.5 for the blind flanges or UG-34 and UG-39 for the flanges with openenings.

Good luck

 

[jte]

TD2K's idea of evaluating the design temp is a good one.

Presumably the instrumentation is B31.3. If so you could invoke the 90% design temp rule in 301.3.2(b)(2) which states (read the Code yourself for exceptions!) that the design temp for uninsulated flanges may be taken as 90% of the fluid, or 153°F. Not quite the 145°F you're looking for, but much closer. Now verify that you meet 302.2.4 (especially the "owners approval" part!) and you're probably home free.

If you can upgrade to a 321 material (Group 2.4) then the 90% design temp rule gets you there (1363 psi at 153°F) without going to 302.2.4. I still recommend getting the owners approval on this approach.

Another option for you to consider may be to upgrade the flange to a 347 flavor (Group 2.5) which, if I did my interpolation correctly, has a DP of 1359 psi.

jt

 

[jte]

Alex-

Welcome to the forum! Thanks for taking the time to fill out the "personal profile". Sometimes checking the profiles helps me to understand a particular poster's perspective so I think its a valuable tool for the group.

jt

 

[JimCasey]

Perhaps even simpler: you could use lap-joint flanges with 316 wetted parts and a CS unwetted flange. Or, pragmatically, since CS is apparently compatible with the process fluid, just get the spec changed to allow CS level instrument.