Behaviour of large-diameter line pipe under combined loads

Experimental testing of four full size pipes with diameter (762 mm) to thickness (8.3 mm) ratios of 92 was conducted to investigate the behaviour of pipelines deformed into the post-buckling range under combinations of internal pressure, axial compression and imposed curvature. The specimens were subjected to internal pressure causing hoop stresses of 0, 20, 40 and 80 percent of yield strength of the pipe material to determine the effect on the local buckling mode. The non-pressurized specimen failed in a "diamond shape" mode whereas the pressurized pipes failed in a single "outward bulge" mode. Increased internal pressure was found to lower the buckling moment but stabilize the post-buckling behaviour.;Non-linear finite element models of the tests were developed using ABAQUS software incorporating measured initial imperfections and material properties. Good correlation between the analytical and test results was observed. An analytical study of initial imperfections concluded that increased magnitude of imperfection causes a significant reduction in peak moment and buckling curvature.