Numerical Simulation of the Buckling of the Steel Pipes with Helicoidally Weld under Combined Actions

摘要

The national oil industry requires the evaluation of the existing infrastructure, as soon as better designs of the pipes and risers capable to assuring an optimal level of security, for that, the evaluation and retrofit of the existing pipelines is necessary, as well to create new pipelines or risers for transportation and distribution of oil products. Then, it is common to get situations, in the performance of fixed offshore platforms, in which risers might be found with lowly internal pressure or empty due to maintenance or repairing, this condition could represent an unfavorable situation that might become highly critical. Consequently, this research is focused to study the buckling of the steel pipes with helicoidally weld under combined load. In particular, for safety prediction, the failure modes and uncertainties involved in each loading condition need to be incorporated in the analysis in order to specify the pipelines use thresholds that keep them over acceptable safety levels within their operating lifetimes. The study is carried out through two types of analysis; buckling shell theory and numerical analysis by finite element method using techniques of bifurcation numerical analysis or EULER, where the shell wall and weld line are modeled with solid elements. The numerical models of the steel pipes included non-linear analysis with the mechanical models of the steel material such as Ramberg-Osgood law. The pipes are modeled as circular cylindrical thin structures, the combining action considered are, external pressure p_e, axial compression N and bending moment M; the critical external pressure is obtained by stability analysis.