ASME flange calculations design bolt load Vs. applied bolt load

[meatpuppet]

Hi,

I am trying to understand the main differences between ASME & another code which derives from it regarding flange calculations.

If I take a look at the ASME flange design calculations, I see that everything is focused on the design bolt load, which is the greater of Wm1 & Wm2 (operating & seating conditions).

Moment MG due to the reaction of the gasket is then calculated, for the operating condition, as MG = HG*hg, with HG = Wm1

If I take the code I am working on, what I read is the following:
The moment due to the reaction of the gasket is MG = HG*hg, where HG is the difference of the applied bolt load and the sum of other loads acting on the flange:
HG = W - HD - HT

Then, calculations go on with stresses SR, SH & ST... Exactly in the same way as for the ASME.

What I do not understand is:
- Where exactly is it said in the ASME that the design bolt load (max(Wm1,Wm2)) is NOT TO BE EXCEEDED?
- Is the assumption HG = W - HD - HT correct, knowing that W is the actually applied bolt-up load?

Thanks a lot for your support on this topic, I am definetly stuck...

 

[SnTMan]

meatpuppet, first, Sec VIII, Div 1, Apx 2:

W = H + Hp
Hg = W - H = H + Hp - H
Hg = Hp

Your Code:

Assuming W = H + Hp, and Ht = H - Hd, as per Apx 2,
Hg = W - Hd - Ht = W - Hd - (H - Hd)
Hg = W - H
then Hg = Hp, same as Apx 2. Why the different formulation, I don't know.

The above applies to operating case, W = Wm1

Calculations in Apx 2 are to be used for design only, and it is known and expected that actual service bolt loads will exceed design loads. See Apx S for a fuller discussion.

Regards,

Mike

 

[TGS4]

I completely agree with everything that SnTMan said, and I will only add to that list ASME PCC-1.

 

[meatpuppet]

Hi,

Thanks a lot for your answers.

As I am not familiar with ASME, can you please describe the terms H & Hp ?

Because in my code W = n*T*(...thread parameters), where T is the torque in lbs.ft applied to each bolt and n the number of bolts.

Actually what I do not understand in ASME is that the bolt load used for design seems different from the true bolt load (as the one I describe just above).

Thanks a lot for your clarifications.

 

[SnTMan]

meatpuppet, H is hydrostatic end force applied at gasket mean diameter (G), H = pi/4 * G^2 * P

Hp is contact load on the gasket, Hp = 2 * b * pi * G * m * P, b is effective gasket width, m is a gasket factor dependent on the type of gasket.

BTW, I hope your (...thread parameters) has the unit of feet.

Regards,

Mike

 

[meatpuppet]

So W = H + Hp according to the ASME code has nothing to do with the torque applied to the bolts?

Actually I am trying to show that the code I am using is far too conservative compared to the ASME. My customer claims the formulas are the same, but on this particular topic it seems I disagree...

Appendix 2 is the Taylor Forge method, correct?

Yes my formulas are always converted in metric units, including the applied torque (N.m).

Thanks a lot for your feedback, I appreciate.

 

[SnTMan]

meatpuppet, yes Apx 2 is basically the TF method, with some changes to accomodate the finer points, and yes actual bolt torque is not considered.

The closest you could say it gets is the optional provision that W = Ab * Sa (W = actual bolt area * allowable bolt stress), but again it is based on Sec II. Part D allowables, not applied stress.

Regards and good luck,

Mike

 

[ijzer]

I think that your question in more or less answered in ASME VIII-1 nonmandatory Appendix "S"