The collapse pressure of the pipe must exceed the net external pressure everywhere along the pipeline in accordance with API-1111 as follows:
Where:
P_{i} = Internal Pressure
P_{o}= External hydrostatic pressure
P_{e} = elastic collapse pressure of the pipe, in psi
P_{y} = yield pressure at collapse, in psi
f_{0}= Collapse factor (A 0.70 Collapse factor is required for seamless or ERW pipe)
E = modulus of elasticity, in psi
v = Poisson’s ratio (0.3 for steel)
t = Pipe thickness
D = Pipe outside diameter