Sec VIII Div 1,Appendix.2 Flange thickness

[c8829]

Hi Everyone

Whatever i understand and concluded from Appendix 2 flange thikness is Correct??
Conclusion="You need thinner flange for weak(In term of Fastner design Strength)fastners and thicker flange for strong fastner"

If i am right, i cant understand that Logic !!!!!!

 

[c8829]

any thought ......

 

[prex]

Where did you get that statement?
It may simply mean that by overbolting you'll need a thicker flange, as the bolting up condition could govern.

prex
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[sathikn87]

Its an iterative method. The bolt size should be optimum for required cross-sectional area.In simple, If the bolt is too thin, it will not meet the required cross-sectional area of bolt & if it is too thick, Flange moment for Gasket seating condition may increase and you will get a thicker flange

 

[JStephen]

For the cases I've worked through, that is correct, I wound up using weaker bolts to make the flange design work. Which doesn't seem backwards, just odd.

 

[marty007]

Generally that's true, it comes from eq.(5) of the 2013 code edition: W=(Am+Ab)Sa/2.

So if you provide significant excess bolting in your design, you need to consider a higher bending moment on the flange resulting in a thicker flange. With experience, you can normally keep Ab very close to Am, resulting in a thinner flange.

I've never read a detailed description of the background to the above formula, but would imagine that it is intended to provide some margin for the actual in-field bolting that the flange will see. If the flange only needs 1" bolts, but you have oversized the bolts to 1.5" (same quantity), then the installation crew will likely provide a typical torque for a 1.5" bolt, putting significantly higher compressive force on the flange. This formula will provide some extra strength/thickness in the flange to resist the higher loads provided by the overbolting.

Just my 2-cents.

Cheers,

 

[c8829]

Thanks to prex,sathikn87,Jstephen.marty007.
prex: i didn't found that statement from nowhere its just my conclusion, as i have done so many varieties of flange calculation.
I agree with all of you....
Now logically if anything goes wrong fastners suppose to break first...but by making that flange so thick (which is stronger than nozzle neck and stubend) i think fastners dont go off first. !!!! but nozzle stubend or nozzle neck will damage first.Am i on right direction?????