PV Support lug baseplate bending allowable? 3

[jlcochran1]

What bending allowable is typically being used for design of support lug baseplates on an ASME section VIII, Div 1 pressure vessel. Example would be 316L SS lug. Design t= 400 deg F, Oper t = 212 deg F. Assume dual certified material. Is it typical to use .6*316SS yield@ design temp (or operating temp) for a baseplate? Or is some other allowable typically used? This is only for the lug structure itself, the vessel program is using code allowables to check shell induced stresses at design temp in fully loaded seismic condition.

Thanks,
John

 

[jte]

jlcochran1-

Since the baseplate of the lug is clearly a structural component, I'd use an approach based on the AISC ASD book (or LRFD if you have it). In the Allowable Stress Design ninth ed. ("the green steel book") chapter on columns you'll find a baseplate design procedure on page 3-106. For what it's worth, Blodgett in "Design of Welded Structures" from the Lincoln Arc Welding Foundation (a great book for general structural design)

https://ssl.lincolnelectric.com/foundation/item.asp?prodnum=DWS

refers back to the AISC approach. The ASD uses an allowable bending stress, Fb, of 3/4 yield.

You should, of course keep in mind that the steel book does not consider the softer nature of stainless steel.

As a client, I would not accept a design which used a temperature less than the vessel design temperature unless you could provide a rational, quantitative argument which backs up the temperature which you are using for the design.

jt

 

[JoeTank]

I generally agree with jte's post; however, I'd modify it just slightly. I'd use S = 0.75 x Yield at the max design temperature of the SS material too. But, even though material may be dual certified, you should use the yield value of the shell material to be consistent in your design. It's a minor point, but you also have to show the client something he can accept.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jlcochran1]

Thanks for all the prompt helpful input. After surveying different consulting Mechanical and (1) Structural P.E.'s with approx. 15+ years experience in vessel design I got the following feedback:

AGREE: Use design temp, base on AISC
DISAGREE: Acceptable to use higher yield in dual-certified material and whether the design allowable should be .6, .66, or .75 yield.

For now we will use 2/3 yield at design temp based on the straight grade yield for dual certified SS.

JLC

 

[waskillywabbit]

A very useful program for designing PVs and their supports is CodeCalc or PVElite found at

http://www.coade.com.

It fully analyzes leg/supports/lugs required based on loading.

I hope this helps some.

Brian