Objective This study aims to deeply investigate the influence of different initial circumferential surface crack shapes (elliptical and sectoral) on pipeline crack propagation behavior under axial forces, thereby providing theoretical support for the structural integrity safety of offshore structures.

Methods The crack propagation process is simulated and analyzed using the phase field method, and cracks are represented in a diffused manner through a continuous field function. Relying on the Francfort−Marigo variational principle, fracture energy is integrated into the total potential energy of the system. A degradation function is introduced to quantify the reduction of strain energy caused by damage. Secondary development is conducted in finite element software ABAQUS, and the staggered solution strategy is used to solve the problem of pipe crack propagation.

Results The results show that when the depth of an elliptical circumferential surface crack is less than half the wall thickness, the crack first propagates circumferentially, then extends through the wall thickness until penetration occurs. When the extent of the elliptical crack penetration is larger, the crack first extends through the wall thickness until penetration, then propagates circumferentially. Sectoral cracks tend to penetrate through the wall thickness first, followed by circumferential expansion.

Conclusions The results of this study indicate that the fracture phase-field method can accurately simulate the local evolution process of cracks in pipes and highlights the impact of the initial crack shape and the extent of crack penetration on the structural integrity of pipes under the action of axial forces. This has significant implications for enhancing the safety and reliability of pipeline structures.