Dear MoverZ, Dear CraigB,

I don’t know if I can convince this forum there is a serious problem in the Flange Calculator. Anyway this is what I’m thinking about and this is my (legit User!) feedback to Coade.
The Calculator applies the flange design equations as valid for every pressure load because CAESAR II computes flange stresses according to the ASME Code equations.
The only question would be if we really understand the ASME Code equations.

About the particular aspect of the bolts, we all know the ASME Code counts a "seating" bolts load and an "operational" bolts load. Caesar II Flange Calculator evaluates both.

I’d like to convince YOU that the ASME Code doesn’t really consider a variation in bolts load!
Please don’t say yet "you are a ……!" (even this is possible!), and PLEASE take a look to the pages 17- 19 of the Taylor Forge 502 Bulletin.
I’ve attached these pages.
You may observe that the figures 4, 5 and 6 of this reference show that, when a pressure is applied:
- the bolts load remains as W
and
- the flange is always under mechanical equilibrium.

The Taylor Forge’s work is assimilated by the ASME VIII Code, so for me, it makes sense to put the question "Really we understand what the ASME Code says?"

Let me explain my understanding.

The ASME Code (Rossheim- Marks- Taylor Forge) wants to assure for gasket two "magic" numbers "y" and "m":
- For the seating condition, at least the value "y";
- For the maximum pressure load (let’s say "design pressure", p_max) at least the value "m*p_max".
The bolts must assure the most conservative condition.
For this purpose, the ASME Code procedure is to calculate two required forces and two required bolts areas and to develop the calculation selecting the biggest value.
W_m2 is the bolts required force able to assure the value "y" on gasket, for the seating condition.
W_m1 is the bolts required force able to assure the value "m*p_max" on the gasket, for the p_max load.
The ASME Code equations lead to a value W that is greater than W_m1 and W_m2, so there is the certitude that the actual values "y" and "m" shall be greater than those tabulated.
The bolts are selected.

And that’s all about the bolts; here the Code finishes his intentions.

Did the ASME Code say that the actual bolts load is W for the seating condition and W_m1 for the operational condition? In my understanding, no.

If I want to understand more about "operational" loads, the Code equations are not really helping me.

In fact, when tightening the bolts, the bolts load is not W_m1, is not W_m2 and probably is not W. The actual value is done by the applied torque moment and consequently by the bolt tightening stress. And I can note this value as W0.

I may assume that W0 remains constant.
Is this real? Probably not, but this assumption has been conservatively taken for dimensioning case. This was the Taylor-Forge approach, their equation are ASME Code now.
If I want to know more, I need a "stress-strain" analysis of the flange and I’ll understand how the bolts are participating.
If I want to repeat the same assumption that has been made for flange dimensioning, I would consider W0 as constant.

I can now verify the flange. There is no need to check the gasket stress but I can do it.

For the seating condition: the gasket load and bolts load are under mechanical equilibrium. So the gasket load is W0 and the actual "y" value is greater than the value tabulated. I can calculate the flange stress, J index, etc. for the seating condition.

For any operational condition (a pressure load p<p_max), the gasket load, bolts load and pressure load give forces that are under mechanical equilibrium.
I can evaluate the gasket load as W0- Pi/4*G*G*p. This assures the mechanical equilibrium. The actual "m" value would be calculated and is greater than the value tabulated. I can calculate the flange stress, J index, etc. for the operational condition. Because the assumption made, the bolts load remains as W0, so the operational bolts load is assumed to be the same as seating bolts load.

What do you think about my interpretation?

My best regards,

NOTE. I've corrected few typing mistakes in text. Sorry!



Dear MoverZ,

You say "Div 2 includes external loads directly without need for the 'Kellogg' equivalent pressure method.".
Not exactly...I would say.
For the design case, it is perfectly true. For the operating case, another story....
The Code is not giving us an equation for the gasket load under the external loads, so how we are going to count this? I’ve propose two formulas, following the same interpretation… but, in my opinion, they are too conservative! Again, a "Stress- Strain" model would say much more about.


Best regards,