Collapse Strength of Thick-walled Steel Pipe Considering Post-Buckling Behavior

Abstract

In this research, failure modes of thick-walled and thin-walled pipes were compared based on mechanics of buckling theory and were verified using Finite Element Analysis (FEA). Also, the prediction equation which was used for the design of thick-walled pipe was suggested. The offshore steel pipe is vulnerable to external pressure, particularly during the construction phase. Therefore, the local buckling and collapse should be considered when designing a offshore steel pipe. The collapse is governed by the material and geometric properties of the steel pipe. The collapse strength of thin-walled pipe which has the failure mode relevant to linear elastic properties can be evaluated using analytic approach. However, the failure mode of thick-walled pipe with diameter to wall thickness (D/t) ratios below 15 is influenced by nonlinear inelastic properties. There is limitations to involve these properties when analytic method is used. A total of 360 cases were carried out, 3-Dimensional FEA considering material and geometric nonlinear properties, for accurate prediction of the collapse strength of thick-walled pipe. The results demonstrated that the failure mode of thick-walled pipe was influenced by post-buckling behavior. This behavior was relevant to material and geometric nonlinear properties, and brought the effect that the collapse strength was increased. A prediction equation for evaluating the collapse strength of thick-walled pipe was proposed. It was shown that the collapse strength of thick-walled pipe was more influenced by material properties than initial imperfections. This research suggests that parameters of material model are accurately considered when designing a thick-walled pipe.