Assessment of corrosion defects in pipelines.

摘要

The focus of this thesis is the assessment of corrosion defects in pipelines with the goal of providing a more complete understanding of the failure of these defects and addressing the conservatism in the currently accepted assessment procedures.; Two forms of simply shaped defects, long grooves and single pits, were investigated in detail to develop a fundamental understanding of corrosion defect failure. A solution to predict the failure pressure of a long groove was developed and agrees with Finite Element analyses and experimental test results. In addition, a solution to predict the failure pressure of uncorroded pipe was developed since this is an upper bound for the failure pressure of a corrosion defect. The effect of element mesh density, defect circumferential dimension, varying material properties and defect interaction on the defect failure pressure were considered. In addition, the validity of the Folias factor used in RSTRENG was investigated and found to be inconsistent with the Finite Element results.; Burst test results of 40 pipe sections removed from operating pipelines due to the presence of corrosion defects are presented in an experimental database. This database was used to investigate the accuracy of the currently accepted assessment procedures. The RSTRENG procedure was found to be the most accurate due to the consideration of the actual corrosion geometry. Twenty-five of the defects in the experimental database were analyzed using three-dimensional elastic-plastic Finite Element analysis. When accurate material properties and defect measurements are available this is the most accurate method of assessment.; A new model for predicting the failure pressure of corrosion defects is proposed. This model uses the elastic-plastic material properties, as determined from uniaxial tensile tests, and corrosion measurements in the same form as the currently accepted RSTRENG procedure to predict the defect failure pressure.; A statistical model, based on the experimental database, is presented for the various assessment procedures considered and a three-level assessment procedure is proposed when detailed material properties are available. This procedure consists of the solution for a long groove, the Weighted Depth Difference model and three-dimensional Finite Element analysis. (Abstract shortened by UMI.)