non linear buckling analysis using ansys on a pipe

Hi,

I am doing buckling analysis of a pipe with liner inside it. I did eigen buckling on the problem. buckling pressure from my calculation is 15.83Mpa  and from ansys it is 15.19Mpa, so I am pretty happy with that. But i would like to do nonlinear buckling analysis on the same problem as a part of my project.

can anyone suggest how to do it using ansys 12,mechanical apdl

Thanks