Dear Gents,

The flange leakage calculation report added in CAESAR II 5.1 is a very convenient function to make a simple report in a short time.

However, I have recently noticed that the calculation report does not include design pressure (Pmax - should be the maximum of P1, P2, P3, etc...) in the evaluation as follows:

Peq = F / (pi * G^2 /4) + M / (pi * G^3 / 16)
Peq <= Maximum Operating Pressure per ASME B16.5 (per CAESAR II 5.1)
Peq + Pmax <= Maximum Operating Pressure per ASME B16.5 (per Peq method)

Please advise if I am misunderstanding some factors in the calculation.

Regards,
Yung Lee

Lee, it is a method to check the further analysis is req or not? My question is if it is exceeds( normally for high temp cases), could we check flange leakage with caesar or go for the Modified routing..
Rams

Not exactly. In the "Peq Method" implemented in CAESAR II, the Equivalent Pressure (Peq) must be less than P_B16.5 as you say. However, Peq is determined as:

Peq = Pn + F / (pi * G^2 /4) + M / (pi * G^3 / 16)

where Pn is the user defined pressure of the load case in question. You can see this easily by setting up two load cases as follows:

1) W+T1+P1
2) W+T1+P2

where P2 is double P1. Then it should be easy to see in the output that the input pressures contribute to Peq.

Dear Richard,

I have an example showing the problem:

Design Pressure = 38 barg
Axial Force = 6355 N
Bending Moment = 15235 N.m.
G/C = 9.91 in

CAESAR II calculates the equivalent pressure as follows:

Peq = 49.87 (bars)
Allowable Pressure = 132.16 (bars)
Ratio % = 37.73%

=> Please refer to node 10 to 20 in the attached S7-002_S.out.

If I calculate the Peq induced from the external forces and moments,

Peq = F / (pi * G^2 / 4) + M / (pi * G^3 / 16)
= 6355 / (pi * (9.91 * 0.0254)^2 / 4) + 15235 / (pi * (9.91 * 0.0254)^3 / 16)
= 1277.06 + 48650.85 = 49927.91 (Pa)
= 49.93 (bars)

Therefore, if I calculate the summation with the maximum pressure:

Peq + Pmax = 49.93 + 38 = 87.93 (bars)
Allowable Pressure = 132.16 (bars)
Ratio % = 87.93 / 132.16 = 66.5%

In this calculation, I think CAESAR II Peq report does not include the design pressure of the piping system.

Could you please help me to figure out the reason?

What are the components (W, T1, etc) in the load case your looking at? In other words, what is in L50 and what is in L31?

I am working on an FPSO topsides job. The load case includes weight, pressure, temperature, combinations of accelerations, structural deflection due to sagging and hogging, module structure deflection due to accelerations, and extreme wind pressure.

Definition of the specific load cases are:

L31 = WIN1
L50 = max(L34 through L49)

L34 through L49 = W + T2 + P1 + H +/- U1 +/- U2 +/- U3 + D1 (+ D2) + D3 (+ D4) + D5 (+ D6)
(They are 16 combinations of accelerations and structural displacements)

(Where T2 = Maximum Design Temperature, P1 = Design Pressure)

L51 = absolute combination of L31 and L50

Of course, I have seleted T2 as the temperature required for flange Peq calculation.
Please let me know if you need any further information.

OK.

It's that maximum combination that's causing the commotion here, that is, your "L50 = max(L34 through L49)".

For this combination, we select the maximum value from your list of load cases (L34 ... L49) for every reported response (such as X,Y,Z displacements, forces, and moments, and stress). Unfortunately, pressure is not a reported response in these MAX/MIN combination cases. Since we have no pressure carried over to this report, there is no line pressure for this flange report. Does this make sense? (I am not asking you if our implementation makes sense; I'm asking if my explanation answers your question.)

I apologize. We will have to fix something here.

In the meantime, I suggest you avoid flange checks on MAX/MIN combinations. Pressures are carried forward for other combination types since the resulting pressure is used to recalculate stress. But I am skeptical of the value of these other combination types. For example, if I have P1 in LC5 and P2 in LC7 and if I look at LC7-LC5 as an algebraic combination, the line pressure will be (P2-P1). I don't think we should be evaluating pressure differentials. To avoid this, be sure pressures are only included in only one of those load cases you are combining.