Zhe Wang

Helical or sinusoidal buckling of the inner pipe usually occurs in the unbonded pipe-in-pipe systems. Helical or sinusoidal buckling of the inner pipeline creates enough lateral loads on the outer pipe to cause a global lateral buckle in the PIP. 

 

Usually, this buckling phenomenon is a chotic buckling. Dynamic method is used in this kind of analysis. Beam element and ITT element are used.