Introduction: Upheaval Buckling

Upheaval buckling occurs in pipelines operating at high temperature and high pressure, HTHP. The driving force is due to axial compressive force in the fully constrained pipeline when the increase of temperature or pressure. Residual lay tension and partially constrained pipeline on the other hand reduces the axial compressive force.
For partially constrained pipeline, the elbow connecting the riser and pipeline is free to expand towards platform. The value of residual lay tension is normally between 0 to 20% of lay barge laying tension.

Introduction: Global Buckling

Global Buckling ( Pipe buckles due to compressive force in a fully restrained pipeline )

There are two types of Global Buckling:

1. Lateral Buckling: pipe buckles horizontally
2. Upheaval Buckling: pipe bucles vertically

Fig 1: Lateral Buckling

Fig 2: Upheaval Buckling

Global Buckling is a load response mode due to compressive effective axial force but NOT a failure mode. Ultimate failure mode of Global buckling includes:

Fatigue.
Fracture.
Local Buckling.

In general, effective axial force, S exists in pipelines (OMAE 2005). If pipeline is fully restrained (especially for HP/HT), this will contribute to restrained effective force, S0 (compressive). As long as effective axial force needed to trigger buckle, Seff is greater than S0 , the pipe is safe from buckle globally. The level of axial force depends on soil resistance, environmental and trawling effects, cross section and out of straightness of pipe.