ASME SECTION VIII Sizing of bursting disc

[mingki]

Hi, I am trying to size the correct burst disc and calculate required discharge area according to ASME VIII.
Here's the specification.
-Burst design pressure(Po): 21.34PSIG
-Burst pressure(Pb) : 23.47PSIG
-Absolute bursting pressure(P1) : 38.17PSIA
-Flow required(W) : 92,395.72lb/hr

And I am wondering whether this calculation fomular is correct.

Required discharge area(A)= W / 51.5 x Kd x Kr x P1 x Kn
I don't know what is 51.5 is for..
Anyway, if I calculate the required discharge area,it is
92,395.72 / 51.5 x 0.62 x 0.88 x 38.17 x 1 = 86.15 Sq.in

The fomular for sizing the burst disc is I think..
Burst disc size = ?(root)4A / ?
And, if I size the burst disc according to this formular, it is,

?(root)4 x 86.15 Sq.in / ? = 10.47inch
So, the size of burst disc has to be 12inch.
Does my calculation correct?
Please help~!

 

[Duwe6]

At a glance, this looks to be a proper diameter. Very low pressure and very high slow rate gives a HUGE Rubture Disk diameter.

Try recalcing your system using a little thicker metal. If you can give the system a doubled Max Allowable Working Pressure, you cut the area of the Rupture Disk in half. Just because you only need a small pressure for the Operating Pressure, there is no reason that the system cannot be rated at a much higher pressure, and relieved based on that higher Design Pressure.

 

[mingki]

Thank you very much.
I appreciate your answer.
I just realized that there is another fomular to calculate required discharge area(A) as below.

A = W X ?(root)(T X Z)/M / C X Kd X Kr X P1

Where,
W = required flow
T = Absolute temperature in Degree. Rankine
Z = (I don't know)
M = Molecular weight
C = 326(Is this a coefficient?)
Kd = Coefficient of discharge(Where can I find coefficient chart?)
Kr = Measure of the flow resistance through the rupture disc and accounts for the holder and the bursting characteristics of the disc
P1 = Absolute bursting pressure

I tried to find the fomular I have in ASME code section VIII division 1, 2 to find out how these calculation formulars are used but I couldn't find them.
Where can I find the ASME fomulars related with bursting disc?
I'm desperate, please help me~!

 

[psafety]

If the disc is in piping and the inlet exceeds 8-pipe diameters and the discharge 5-pipe diameters you'll need to use the line loss method vs. a Ko of 0.62 you would use the Kr value.

 

[mingki]

Thank you for your reply.
Could you tell me more about the line loss method and what Ko does mean? Please help me. I am totally lost and I have no idea how to size my burst disc properly.

 

[psafety]

Ko is the orifice coefficient of 0.62 in your first post. The disc is sized more as an orifice.

As I stated the conditions previously depend on if the discharge is piped. Then a Kr value from the manufacturer will be used in your line loss (assume compressible) calculation.