Hello, This is a real simple question but I am having a hard time to answer it. We have cylinder with outer Radius Ro, Inner Radius Ri. Internal pressure = 0. External pressure = to be find. Material is Nylon. I would like to know: External pressure Po at which the tube/cylinder will go under deformation given Yield strength. How do i find the external pressure on a rod- Given it is not a pressure vessel? Should i use the collapse pressure formula OR Radil stress formula assuming Internal pressure Pi to be zero?