ASME VIII Div1 App2 2007 1

[Unleash]

Hi,

Im trying to automate a design step using the ASME code mentioned in the title. The thing is, I want to verify if im using the right class flange on the right place.

Ive almost finished the tool that would automate the calculations in appendix 2. The one problem I have is that I get unreasonable outcome from the formulas for "V, Vl, F, Fl".

I found a previous thread on this forum with the same problem, the sollution was a two way one: 1. Don't! 2. check the newer code.

I still want to do this, but ive checked the "newer" version...
So my question is:
Has anyone had experience with this problem, and if so how was it solved?

 

[Unleash]

No one? Hmm, thats a shame!

 

[vpl]

Did you read the first step in the two part solution presented previousl?

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[SnTMan]

Unleash, I find your statement of the problem a little unclear. Are you trying to verify ASME B16.5 flanges ("right class flange") with Section VIII, Div. 1 Appendix 2 calculations?

If so, the advice 1 you got (Don't) is good advice, it doesn't work out well. This has been discussed a number of times in the forum, a search will find further info.

Not sure what you mean by "unreasonable outcome", but without comparing expression by expression and variable by variable between 2007 and 2010 Codes, I feel pretty certain these equations have not changed in years and years.

That being the case I doubt your advice 2 is useful.

Can you provide further specific information?

Regards,

Mike

 

[Unleash]

The only previous post I found was this one:
http://www.eng-tips.com/viewthread.cfm?qid=281877&page=10

As far as I can tell there are two answers; The first one tells the inquirer to stop doing what he (or she) is doing and find someone with the right background. The second one states that teh newer edition holds the sollution.

The first answer is unacceptable, I cant do that. And since I am using the 2007 version, I should be able to find the sollution, but I cant.

So I hope I am overlooking something here, but what steps are we talking about? Or is there another post with more information?

 

[Unleash]

@ SnTMan:
Well, I think that is what I am trying to do. I am trying to calculate if a certain flange is the right flange for a certain situation. These certain flanges are ASME B16.5 flanges.

If this is not the way, what is? About searching the forum... I cant really find anything usefull. Do you have keywords/ links anything to point me in the right direction?

I get a different output when using the formulas compared to the corresponding figure. That is what I mean with "unreasonable".

 

[SnTMan]

Unleash, use the Google custom search box at the top of the page. Search ASME B16.5

Here's a sample:
thread292-283726
thread292-142360
thread794-246979

BTW, all B16.5 flanges have published T-P ratings. You could possibly just look it up.

Regards,

Mike

 

[Unleash]

Thanks for the quick replies!

Those links are really helpful, so Thanks for that!

Just one last question and then ill stop bothering you.
Norske veritas uses that calculation to verify flanges. Their instructions specify that first a common method may be used. In case that test is failed one can use the ASME VIII to verify. And in case even that fails a FEA can be applied. If all three tests fail, the flanges should be upgraded.

This is why I want to speed up said process. So if this is not the way, what is?
Or is there no way?

Thanks in advance!

 

[TGS4]

You may have misunderstood the intent of my response in the first thread that you referenced. The OP in that post was asking about flange leakage. My advice was that flange leakage is not addressed in Appendix 2.

The second thing that you misunderstood is that the newer Code that I was discussing was ASME PCC-1, NOT ASME Section VIII, Division 1.

If you are using ASME B16.5 flanges, just use the Pressure-Temperature rating in B16.5, and the bolting recommendations in PCC-1.

You say that Norske Veritas uses "that" calculation. Which calculation is that? What's wrong with the Pressure-Temperature charts?

 

[Jmoore1]

TGS4....one problem with just using the tables (especially if you are near the limits of the flanges at the P-T tables) is that these do not take into account any external loading...whatsoever... where using the appendix 2 calculations you can calculate a Peq based on the external loadings.

Unleash you could buy codecalc which would do this for you, but based on what youve done so far it might be a waste of money if all you need it for is flange calculations

On the other hand I have done these calculations and not run into a problem...check your units to make sure they work if you are getting eroneous results, these numbers should correspond to the tables.

Unless you are doing hundreds of these and you can not get the correct answers you could just use the tables 2-7.2, 2-7.3, 2-7.6, and not bother with those equations, although you would not be able to automate that part it would not take more than 2-3 minutes per flange.

 

[SnTMan]

A minor point...

Appendix 2 does not calculate an equivalent pressure due to external loadings, although there are ways to do so.

Given a calculated Peq, how about go back to the P-T rating tables?

Regards,

Mike

 

[TGS4]

Jmoore1, where does it say in B16.5 that you must include external loads, via some type of equivalent pressure calculation, in the pressure-temperature charts?

 

[Unleash]

@TGS4: That clarifies things! I was wondering why using the App 2 calculations was so explicitly discouraged.

@Jmoore: I have looked into that software, and indeed it isnt cost effective for the amount of usage and the calculations that would be run with it. So I hoped to make a small tool using VB and MS office to achieve the same kind of result with lower costs.

I'm almost finished, the tool works for the most part. But I get strange unmatching results in the "C" and "E" factors... negative values and very low values (nearing 0,001).

I will check my units, and try to run some more tests. Thanks for all the replies. I think I have my answers!

 

[Jmoore1]

TGS4, it does not, but as a responsible engineer, when at the pressure limits of these tables and with excessive external loadings additional analysis should be done to take into account these external loads.

Reading everything to the T often ends in a safety concerns...If you were 5 psi from the limits of b16.5 tables with 10000 lbf on the flange would you just go with the design conditions? absolutely not.

 

[TGS4]

...when at the pressure limits of these tables and with excessive external loadings additional analysis should be done to take into account these external loads.

First things first, what constitutes "excessive"? If I have a flange on a system with a design pressure equal to the rated pressure of the flange, would a 1ft*lb moment be excessive? Inferring from your previous posts, the answer is "yes".

Perhaps you have not had the time to do the research, but there have been many papers in the literature out there that discuss this issue. The ones that I am familiar with actually perform the "additional analysis" and show that limiting the design pressure + equivalent pressure of external loading to the flange rating pressure is incredibly conservative and not justifiable by any engineering method (other than ignorance).

Here's one of these paper to get you started:

http://asmedl.aip.org/getabs/servle...2819000059000001&idtype=cvips&gifs=Yes&ref=no

 

[Jmoore1]

TGS4 we might as well throw the codes out, there conservative anyways right? people clearly pay for all these asme codes just so they can ignore them since they have a safety factor. I pray I never find myself around a piping system you designed and fear for the lives of those that have.

The safety factors are there for a reason and the calculations we have fall short of being even moderately accurate.

 

[Jmoore1]

Additionally if you had read my post before posting a rude reply, I gave a vage number of 10000 lbf, not 1 lb*ft moment. But then again so many engineers just like to tell someone their wrong.

 

[TGS4]

Jmoore1, I have far more experience with Codes and Standards (on the writing and using and research sides) than you realize.

I am not advocating "throwing out the Codes". Just that (and you agreed), B16.5 does not state anything about external loads. So, now we are beyond the Codes, and into the realm of engineering judgment. Have you researched the published literature to see what constitutes good engineering judgment of those engineers that have been reviewed and vetted and published by their peers? Or are you substituting ignorance and a hunch for good engineering judgment? Have you done any of the advanced bolted flange joint calculations like those in EN-1591? Have you ever performed an FEA into a bolted joint under an external load?

To answer your question in your 4 Apr 11 14:44 post, I would perform the calculations recommended by the paper that I referenced, potentially modify the bolt preload (a bigger effect than even you can imagine - something that is NOT addressed in B16.5), and if the calculation says "yes", then yes. If the calculation says "no", then no. No hunches, no assumptions, no suppositions, just cold, hard numbers and math.

But then again so many engineers just like to tell someone their (sic) wrong.

Only when they're wrong.

 

[Unleash]

So... it has been a while, but I still need your help.

Ive been trying to unwrong my mistakes, but I cant really find them.

And still I get "wrong" values for Fl/ Vl etc. Ive attached a sheet with all the variables. Could you guys look it over for me, and tell me where I got it wrong?

Thanks in advance!

PS: Most of it is in english. Los met hub = Loose hub, imperiaal = imperial. And thats it I believe.

 

[Unleash]

Ow I see I have neglected to rename the variables F and V to Fl and Vl. This since the calculation is a calculation done for a loose hub flange.

So they are not F and V but Fl and Vl.