Numerical study on critical axial forces of upheaval buckling for initially stressed submarine pipelines on uneven seabed

For pipelines on uneven seabed, upheaval buckling may occur if the axial compressive force reaches the critical force of upheaval buckling. The critical axial force is sensitive to the seabed undulation, However, the effect of the seabed undulation on the critical force has not been completely discussed. Moreover, effect of the initial stress which accumulates in the pipe wall when the pipeline conforms to the seabed undulation under self-weight has been rarely examined. This paper mainly focuses on the effect of the initial stress. Using numerical tools developed with the Vector Form Intrinsic Finite Element (VFIFE) method, effect of the initial stress is proved significant. Subsequently with the theory of dimensional analysis, a formula of the critical axial force is derived. This formula covers the dimensionless undulation length and the Out-of-Straight (OOS) of the seabed undulation. Considering three seabed undulation shapes, coefficients in the formulas are determined with numerical results from the VFIFE simulations. Finally, the proposed formulas are proved applicable for pipes with different properties and within the error range of ±10% for pipelines in continuous contact with the seabed in a large dimensionless scope.