This paper deals with the buckling behavior of UOE pipes under bending moment, and proposes reliable evaluation methods for the compressive strain limit (εLimit). Full-scale bending tests were performed to evaluate the effect of change in the mechanical properties during the anti-corrosion coating and the geometric imperfection induced by the intentionally mismatched girth weld. During the numerical simulation, the pipe was modeled using the measured pipe profile and the material constitutive law newly developed to analyze the orthogonal anisotropy. The test results verified that εLimit was not degraded by aging, although it declined for pipes with girth welds. The numerical model gave a good prediction for εLimithence revealing that the mechanical property in circumference affects the buckling resistance of UOE pipes. To analyze the effects of material characteristics, simplified models were proposed and the results obtained from the validated models suggest that the conventional method using the isotropic work hardening law may overestimate εLimit under high internal pressure.
Design technique, or a so-called strain-based design (SBD), is applied for line pipes buried in discontinuous permafrost subject to ground movement such as frost heave and subsidence, while tensile and compressive strain limits are considered into SBD, represented by the joint integrity of the girth weld and the buckling resistance of the pipe body (Glover, 2004, Barbas, 2007). This paper describes the buckling resistance of UOE linepipes under a bending moment with internal pressure, which is the typical loading condition in discontinuous permafrost. Generally, bending deformation is allowable up to the peak moment, since local buckling leads to excessively high strain inducing pipe burst. The early local buckling increases the maintenance cost of pipelines. Many studies note that the major dominating factors for pipe buckling include the material characteristics and the pipe geometries (Suzuki, 2003, Tsuru, 2007).
