Thanks Dave.

I got some more info about how to calculate it. Its based on the mass momentum theory.
Fh=1.414 x Da x Qa x Ro(((P1-P2)/Ro)+(Qa^2/2 x Ap^2))^0.5

Where Qa=Qr(A2/A1)
Ap=0.785((Do-2t) x 0.0254)^2

Da= Dynamic Load Factor
P1=Inlet Pressure(barg)
P2=Outlet Pressure(barg)
Do=Inlet Pipe diameter(inch)
t=pipe wall thickness(inch)
Ro=Liquid density(Kg/m^3)
A1=Required orifice area(inch^2)
A2=Actual Orifice Area(inch^2)
Qr=Required flow rate(m^3/sec)


Regards,
Kumar