Numerical Research To Residual Strength Assessment Of The Corroded Inside Steel Pipeline

Pipeline transportation is the important way of petroleum transportation all long. Most of pipelines are embedded in the underground; they are damaged by factors of inner and outer. With the increase of service year of long transportation underground pipeline, pipelines corrosion has become more and more serious. However, the prime reason in failure factors of pipeline is the internal corrosion which reaches to 30%~50% in the pipeline failure. So the study for the pipelines residual strength of corroded pipelines has important significance for the decision-making of the function, servicing and replacing of the pipelines.Firstly, this paper sets forth in brief the background and development of the residual strength assessment technology and the theory of corroded pipeline, summarizes various assessment methods of corroded pipeline as well as their advantages and disadvantages.Secondly, the Finite Element was performed on the assessment and study of residual strength of corroded pipeline. Liner-elastic finite element is adopted. Geometrical nonlinearity and material nonlinearity is considered by using linear elastic-linearity hardening mode and Bin Fu failure criterion. The influences of the limit load of pipeline which various corrosion sizes and stress distribution status at the defect of pipeline is obtained. The figure of strain and stress with the inner-pressure is obtained. At the same time, the largest inner-pressure is analyzed with the non-liner least square estimation method by MATLAB and SPSS software. And a fitted multiple regression equation on the limit load of pipeline with axial internal corrosion is deduced. The result of Finite Element Analysis and that of existed criteria are compared. The study indicate that the results of the limit load of the pipeline corroded inside in one axes that are calculated by the fitted multiple regression equation are almost equal to the results by the finite element method. And the conservative of the criterion B31G is conquered in a certain extent. Forecasted results are parallel with the results of finite element method and are accurate.Finally, taking the maximum allowing operation pressure (MAOP) as assessment rule the new method of the residual strength assessment of various inside corrosion is put forward .The multilevel assessment system of corrosion defects is established. Taking local corroded pipeline for example, evaluate the corrosion defects by classification.