Flange leakage design continuation
Flange leakage design continuation
(OP)
Hi all,
The interesting post on flange load design got me thinking about the existing ASME/ANSI B16.4/B14.3 flanges and whether they would pass the rigidity factor test in Appendix 2. Has anyone done a project where they did a rigidity check of off-the-shelf ANSI flanges with piping loads, hydro, and bolting loads?
Also, I am writing up a standard right now and I wrote this requirement in for custom flange design.
"4.3.9 Custom designed flanges shall be checked for likely hood for in-service leakage by calculating the flange rigidity factor (J) per Appendix 2. Flange thickness shall be increased if J < 1.0. The applied moment (Mo) in the equation shall include the combination of all in-service loads including external piping loads."
What do some of you experts think about what I wrote? Critique is welcome to help me improve on this requirement.
The interesting post on flange load design got me thinking about the existing ASME/ANSI B16.4/B14.3 flanges and whether they would pass the rigidity factor test in Appendix 2. Has anyone done a project where they did a rigidity check of off-the-shelf ANSI flanges with piping loads, hydro, and bolting loads?
Also, I am writing up a standard right now and I wrote this requirement in for custom flange design.
"4.3.9 Custom designed flanges shall be checked for likely hood for in-service leakage by calculating the flange rigidity factor (J) per Appendix 2. Flange thickness shall be increased if J < 1.0. The applied moment (Mo) in the equation shall include the combination of all in-service loads including external piping loads."
What do some of you experts think about what I wrote? Critique is welcome to help me improve on this requirement.





RE: Flange leakage design continuation
I believe that your less than sign should be a greater than sign. If the calculated rigity exceeds 1 then the thickness must be increased. See 2-14(c)
EJL
RE: Flange leakage design continuation
Thanks for the sharp eye. You're right, it should be a > sign. I also typed the flange specs wrong, it should read ASME/ANSI B16.47/B16.5.
RE: Flange leakage design continuation
I don't know the purpose of the spec you are writing, but if I was a fabricator reading your para. I would say first "Its already mandatory for me to meet flange rigidty, why would anybody put that in a spec?", and second "I wonder if this customer has a favorite method to include the effect of external loads, or does he just want to second guess whatever method I choose?"
This is not intended as unfair criticism of what you are trying to accomplish, its just that my experience in the fabrication end of this business has exposed me to all kinds of unclear language in specs that cause no end of interpretation or misunderstanding. So, my point is, if you are going to put something like this in a spec, be as clear and unambiguous as possible, even to the extent of giving equations, etc.
Hope I haven't gone off an a tangent again... :)
Regards,
Mike
RE: Flange leakage design continuation
No worries about any "unfair criticism" coming my way. I'm used to it; I get'em at home all the time. LOL.
Yes, my intention for the paragraph is to be clear to the fabricator that paragraph 2-14 in a Mandatory Appendix is to be applied. Reason I say something about this is on one project, a fabricator argued that paragraph 2-14 is "optional" and they want cost extra to increase the flange thickness on many large diameter custom design flanges on a Vac Tower. This fabricator raised a stink and gave our vessel engineer a hard time. After that, the standard included this pargaraph to make sure this kind of c*&% don't happen again. What you and I sometime think is common sense and deemed part of the code, may not be the same with another person. Kinda like shoving democratic ideas to countries that don't want it.
Yes, in another paragraph I have defined the method to convert the external loads to equivalent pressure end load H. Just wanna make sure the guy considered external loads into his calc.
RE: Flange leakage design continuation
Good luck with it.
Mike
RE: Flange leakage design continuation
As far as how I would go about including a calculation methodology, I've personally used EN-1591-1, but I would consider that to be overly onerous on a manufacturer to perform. There is no commercial software that does the calc, and it took me weeks of Mathcad work to implement it myself. I would not recommend it to anyone...
RE: Flange leakage design continuation
Digging thru my folders full of paper I find "ASME Section III, 1977, NB-3647.1"
It's the old Peq = 16*M/Pi*G^3 + 4*F/Pi*G^2
Regards,
Mike
RE: Flange leakage design continuation
RE: Flange leakage design continuation
I missed out on some software training this week because of a field deal that got postponed probably till NEXT week, when the conference is.
Ah, the life of an engineer:)
Bring us back some good stuff, TGS4. And enjoy San Antonio. Never been there.
Mike
RE: Flange leakage design continuation
I use the same method as SnTMan mentioned above. Never seen teh EN-1591 either. Anyway to get a free copy of it for light reading before bed time?
Yeah, I thought about asking the boss if I can go the the conference next week. But 4 days is costly and too much. Is there a way to get a copy of that flange paper for a look see?
RE: Flange leakage design continuation
There are commercial softwares to performing calculations of flange connection according to EN 1591 (EN 13445-3 annex G). Here's links to few websites:
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We are using VVD-program (visual vessel desing by Ohmtech). The newest module includes flange calculations according to EN 1591.
Calculations according to EN 1591 are indeed very difficult to perform without any software because there are lots of iterations in this method. When I studied this method, I used MathCad. I got 40 pages of calculations for just one flange connection (I didn't know how to do loops in MathCad). Then I did Excel program with lots of VBA code. It worked quite nicely.
Nowadays we calculate our vessels with VVD. It uses formulas introduced in EN 13445-3 (Unfired pressure vessels). With VVD we can calculate almost every components in our vessels, eg. shell, ends, nozzles, flanges and so on.
Vesselguy,
Here's few links for more information about EN 1591:
http://www.sealeng.com/ase/index.html
http://www.unm.fr/en/general/en13445/
(look for Background to the rules in Part 3 Design. Click the acrobat icon to open the pdf-file. Then look for annex G.)
RE: Flange leakage design continuation
RE: Flange leakage design continuation
That code case is not acceptable in one jurisdiction as the rigidity calculation was mandatory for flanges 40" diameter and above. It was part of the 3.5 design factor code case but for some reason was not rolled into the code with the design factor change.
EJL
RE: Flange leakage design continuation
TGS4, any news from the conference?
Cheers,
gr2vessels
RE: Flange leakage design continuation
That said, I would be very comfortable (for initial design purposes) using a value of 1.5X rating pressure when using the equivalent pressure method.
Since the failure mechanism of flanges is leakage, I would certainly apply the rigidity check (or at least impose a limit of 0.3 degrees of flange rotation at the actual install bolt loads) to all flanges. It has been demonstrated numerous times that excessive rotation is a sure-fire way to ensure leakage. It is also very difficult to improve rigidity after the fact.
My 2 cents.
RE: Flange leakage design continuation
On a different note, while browsing the ASME PVP 2007 website, I noticed that the chairman of the executive commitee of publications is employed by the Dept. of Mechanical & Astronautical Engineering at the Naval Postgraduate School in California. Do they have a High Speed Railway Dept.?
Cheers,
gr2vessels
RE: Flange leakage design continuation
The flange design rules are due for a serious overhaul, but the Code Committee responsible for flange design (SWG-BFJ) did not get Div. 2 rewrite marching orders until too late. There was one presentation at PVP07 about this, but the development of rules are extremely complicated, so it may be a while...
Not a specific high-speed rail dept at NPS, but then again, when has the navy been interested in railways?
RE: Flange leakage design continuation
Cheers,
gr2vessels
RE: Flange leakage design continuation
RE: Flange leakage design continuation
I've been using Visual Vessel Design from OhmTech for more than 4 years now.My experience is that this is the best software for mechanical design of pressure vessels and shell & tube heat exchangers. I especially enjoy to use the new module for flange calculations according to EN 1591. It also support EN 13445,ASME VIII Div. 1 and PD5500. The calculations seems to be very reliable and I saved hours of work. Try out the demo version, it should be available from www.ohmtech.no.