Nonlinear buckling failure of an FGM subsea lined pipeline with an oval defect

The present investigation focuses on rehabilitating cracked subsea pipelines by incorporating a functionally graded material (FGM) liner. Seawater sweeps into the cracked area of the pipeline, generating water pressure at the outer surface of a liner, which leads to "single-lobe" or "double-lobe" deflections because of the constraints of the pipeline. In addition, in practical engineering, issues including inadequate expansion and deflection of the pipeline may cause the liner to become oval. Accordingly, a systematic theoretical scheme is developed to elucidate the buckling characteristics of an encased oval FGM liner under uniform pressure. The critical buckling pressure is computed explicitly from the thin-walled shell principle and energy method. A two-dimensional (2D) simulated model obtains the buckling pressure and pressure-displacement equilibrium path. Theoretical solutions are in close alignment with the other closed-form solutions, simulated results, and experimental results. Finally, the influence of volume fraction exponent and ovality on the critical buckling pressure and critical circumferential force is discussed comprehensively. The conclusions illustrate that the increasing volume fraction exponent and ovality significantly decrease the pressure capacity. As the double-lobe deflection occurs, the liner exhibits the higher pressure capacity than the single-lobe case.