ASME VIII - Div. 1 App. 2, 2004 ed. "Flange factors in formula form"

[carnevalibus]

Hi everybody!
I need to carry out a very accurate verification about flange leakage.
Instead of using tables 2-7.2. 2-7.3, 2-7.6 to find flange factors F, V, f it is possible to use formulas in table 2-7.1.
The problem is that I obtain right values of factor f, but unreasonable values of F and V comparing them with figures above mantioned. Has anyone experienced the same? Is there an error comprised within constant C37 and E6?
My calculation has been executed by means of a calc worksheet.
Thanks,

Marco

 

[TGS4]

Please do NOT use Appendix 2 for anything to do with flange leakage or flanges in-service. Appendix 2 is a DESIGN methodology that is set up to help you DESIGN a flange that should have a low probability of leakage. Never, ever, take the bolt loads from these calculations as even an indication of what you should be using in-service.

Refer to ASME PCC-1 (the new version just came out) for guidance on how you should be handling flange in the field.

If you are still convinced that you need to do a

a very accurate verification about flange leakage

then I would recommend that you either someone who has extensive experience in troubleshooting flanges, extremely experienced in FEA of bolted flange joints (very very rare, BTW), or both. The complex interaction between initial bolt-up, the initial bolt-up method (hammer wrench, torque wrench, hydraulic tensioners, etc) the gasket (especially if you use compound gaskets like spiral-wound gaskets), operating conditions (high temperature, gasket creep, bolt creep, bolt thread embedment, vibration, etc), operating fluid properties all make for a very difficult "calculation" for those who lack experience and expertise. You may spend a lot of time getting a complicated calculation sheet, but you'll end up with a very good looking wrong answer.

 

[carnevalibus]

Thanks for the fast reply TGS4!
The verification I have to carry out still belongs to a design step, I'm not dealing with in-service equipment. I'm trying to make the calculation more automated, so I verified the possibility to use those formulas. Since the graphs I obtained for factors F and V don't correspond with tables 2-7.3, 2-7.6 I was wondering if anybody had the same problem. Anyway I really appreciated the suggestion "..but you'll end up with a very good looking wrong answer." , bacouse in the end this is the risk!

 

[TGS4]

I appreciate what you're saying, but I hope that you understand that at some point this flange that you are designing has to go into service. If you're worried about leakage, focus on PCC-1. The assembly bolt load and proper selection of the gasket has a much better influence on the performance of the flange as opposed to the design of the flange itself (although adherence to the rigidity factors are good practice). Flanges that leak are almost always not over-stressed...

 

[tetraz]

The problem is that I obtain right values of factor f, but unreasonable values of F and V comparing them with figures above mantioned. Has anyone experienced the same? Is there an error comprised within constant C37 and E6?

I rememeber something about a problem with these constant, they should have been corrected in one of the subsequent Addenda. If possible, procure 2007 edition and compare the constants.

Regarding the methodology itself, I concur with TGS4; moreover, if you would like to accurately check flange behaviour, I suggest you to rely on EN 13445 Appendix G, wich details a completely different approach to flange desing.
In case of metal-to-metal flange, examine EN 1591-3.
Hope this helps..
Regards

 

[carnevalibus]

...you would like to accurately check flange behaviour, I suggest you to rely on EN 13445 Appendix G, wich details a completely different approach to flange desing.

Ok I will check it, I didn't know it! Thank you!