Appendix 2 Flange Rigidity calculation issue 3

[TLUB]

Hello,

I am creating a custom flange for a Horizontal Low Water Cut Out Switch. I am struggling to see how flanges can pass the rigidity factor calculation.
My question is how do any flanges pass this check or am I misunderstanding something?

The goal is to minimize the size and weight of this product and in doing so, eliminates the possibility of using B16.5 Flanges.
The maximum Operating Conditions for boiler service = 1000psi at 550F.
Design conditions = 1250psi at 570F.
I created an excel spreadsheet that calculates everything for ASME BPVC VIII App.2 and just went through and manually calculated to make sure it was functioning properly. The custom flange meets all of the design checks EXCEPT the flange rigidity factor calculation. I attached a screen shot of the inputs below.

The flange is designed in a way to be similar to a weld neck flange (integral flange). The chamber is a 3" Sch.80 SA-106 pipe, the Flange is made out of SA-105 and it is being butt-welded to the pipe.

The 0.300" is making the rigidity factor calculation solve very high since it is in the denominator and being squared. I even input a 1500# 3" Weld Neck Flange dimensions and it was still >1...somewhere around 38 or so if I remember correctly.
Equation = (52.14*V*Mo)/(L*E*go²*Kl*ho)
V = .1583
Mo = 22871
L = 2.6854
E = 27090
go = 0.300
KI = .3
ho = .8216

 

[Christine74]

I'm not sure where you went wrong in your calculation but there's just no way that the Rigidity Index of a 1500# flange could possibly be as high as 38. I would expect it to be well below 0.5.


-Christine

 

[SnTMan]

TLUB, I have not designed flanges under Div. 2, but many, many under Div. 1,. I assume they are similar as to flange rigidity.

My experience is that it is not difficult to meet rigidity, usually the most practical means is to increase flange thickness. Often a fairly small increase does the job.

I can't speak to details of your flange (you don't really think your image is legible, do you?), but first I'd confirm a 0.300 neck meets the design condition. BTW you should be using 1250 / 570 if you are not. You can play with hub dimensions g1 and h but I doubt it'll help much. You should try to minimize lever arms.

Beyond that, I'd say go with a B16.5 flange if the needed thickness is too great for you. Rigidity check is not required for them.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[cbPVme]

Your elastic modulus is off by a factor of 1000. It should probably by 27090000.

 

[SnTMan]

cbPVme, yes. Didn't notice. Thx

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TLUB]

thank you all for your help on this! The solution however is quite embarrassing that I did not catch it before (being off by a factor of 100 for the modulus). Getting that corrected fixed everything!

SnTMan, (not sure how to tag you), I am using the design pressure/temp of 1250psi and 570F but thank you for confirming I was doing it right! Also, I honestly thought the picture would be able to be opened and "blown up" larger, my bad. This is only my second post here.

anyway, thank you all again for the help!

 

[r6155]

Do you plan to acquire this custom design with SA 105 material (forging)? Did you think about all the tests and NDE?
Stud 1/2" is not a good idea for this pressure-temperature.
Gasket material?
I suggest ASME B16.5 CLASS 900.

Regards