flange fea 4

[hari sankar]

i need to analyze 4 inch 1500# wnrtj flange. when i modelled cad according to pipe data, i am getting a clearance of 6mm between the flange faces. when i referred ASME B16.5 ,a 3mm gap between flange face is mentioned. In real time, will the gap between flange faces be zero after applying the bolt preload?

 

[TGS4]

Unlikely.

How are you modeling your gasket?

 

[hari sankar]

modelled octagonal ring type gasket according to pipe data. RTJ soft iron ring type R39.

 

[TGS4]

The ring will set the distance between the flanges. There will not be contact between the flanges other than the ring.

 

[hari sankar]

i got a clearance of 5-6mm when i modelled according to the pipe data. But in asme b16.5, they provide approximate clearance between flange faces as 3mm. When i asked some professionals, they even suggested to make the gap between flange faces 0.
I have one more doubt. while applying bolt preload, should we apply gasket seating load (wm2) or the operating condition preload (wm1) ? I am of the opinion that in high pressure rated flanges and non self energizing type gaskets, wm1 must be applied.

 

[TGS4]

The assembly bolt load should be used - see ASME PCC-1, Appendix O. It will be neither of the two quantities that you listed.

If I may ask - what is the purpose of this analysis?

 

[hari sankar]

in the pv elite report from our client, the flange fails due to less bolt area. it is a standard 4inch 1500 pound welded neck rtj flange. we need to show that its safe for operation acc to asme sec viii div 2.

 

[hari sankar]

in the pv elite software also, wm1 and wm2 are calculated. let me go through the document which u suggested. can you just go through page number 376 of asme sec viii div 1 ? thanks in advance.

 

[TGS4]

Wait wait wait! This is a STANDARD flange, and you're trying to evaluate it using VIII-1 App 2? And it fails? Well, of course it does! This is a well known phenomenon. Why would you do that? Use the pressure-temperature rating for the standard flange.

 

[hari sankar]

sorry to bother you again. can you please elaborate?
the operating temp is 43.33 deg celsius and 3670 psig. according to its pressure temp rating it can withstand a pressure of 3634 psig at 50 deg celsius. so its very much at the brim of its limit. so we need to perform fea, and find out whether its safe for operation or not.

 

[curtis2004]

Why not chose 4"x2500# RTJ instead of all these discussions?
Do you have nothing else to do?

Curtis

 

[hari sankar]

Actually, our scope is to use fea to find out whether the flange is safe for operation or not. since the code requirements are conservative, by using fea we can be confident whether to use it or not. The flange rating was provided by our client. And dont know why you are getting offended. Am not disturbing you in any manner. If people are willing to help, then why do you bother? curtis2004

 

[TGS4]

Speaking from experience, your activity is doomed to fail.

Either fix the design pressure to fit inside the P-T limits of the standard, or go up a Class, as suggested by curtis2004. Unless you are working for free, the cost of going from Class 1500 to Class 2500 is minor compared to the engineering costs that are attempting to embark upon.

There have been dozens of papers written on this topic - search for flange design papers presented at the ASME PVP Conference. However, from the basis of your questions, I am going to flat out state that you are not competent to perform this work. And the cost of you finding someone competent (see paragraph above) will be much more than the cost to replace hundreds of these flanges.

Please make sure to show this free advice to your boss.

 

[hari sankar]

Thanks tgs4

 

[curtis2004]

hari sankar,

I am not offended, but also just asked questions. I am very sorry, I didn't realized that my short questions will be sounding that harsh...
TGS4 already explained all you need to know now.

 

[LittleInch]

Why don't you just use a group 1.2 material for your flange?

50 C rating is 3750 psig

Not much spare, but some.

As many other more competent than me have said - a flange FEA to ASME VIII will fail, especially this close to the limits in B 16.5. Everyone know that but B 16.5 has stood the test of time so it is globally accepted that it is good for the pressures and temperatures stated in that standard.

Also next time say FEA (capitals), not fea (lower case). FEA stands for three words, fea I thought was a typo.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hari sankar]

Thanks littleinch, will keep it in mind.