Both the industry models, i.e., ASME B31G, modified B31G and DNV models, and the FEA model developed in this work predict that the failure pressure of a pipe with corrosion defects is reduced by the increasing corrosion depth and the decrease of the steel grade. The prediction by ASME B31G and the modified B31G models of the failure pressure of a defected pipe is higher than FEA result for low grade steels, and the conservatism decreases with the increases in corrosion depth and the steel grade. The prediction by DNV model shows close results to FEA model. The predictive reliability by ASME B31G and modified B31G models decreases with the corrosion depth and the grade of steel, while DNV model has a high reliability for the failure pressure prediction, compared to FEA model. The geometry of corrosion defects affects remarkably the local stress and strain distributions, and thus plays a critical role in the failure pressure prediction of pipelines. In the absence of corrosion defect, the von Mises stress of the inner surface of pipeline is higher than that of the outer surface. However, in the presence of corrosion defect, a stress concentration is developed at defect, resulting in the decrease of the internal pressure required to fail the pipe. When the corrosion depth is small, the von Mises stress in the inner surface of pipe is much lower than that at the defect base. With the increase of the corrosion depth, the stress concentration is enhanced, resulting in the further separation of von Mises stresses of the inner surface and that of the defect base. The applied strain in the longitudinal direction simulating the soil strain exerted on the pipeline, regardless of tensile or compressive one, would reduce the failure pressure of the defected pipe. In the presence of corrosion defects, the applied pre-strain increases the plastic deformation area, and thus the amount of internal energy absorbed. The predicted failure pressure of pipeline under the tensile pre-strain is smaller than that under a compressive pre-strain.
Reliability and failure pressure prediction of various grades of pipeline steel in the presence of corrosion defects and pre-strain
International Journal of Pressure Vessels and Piping ; 89 ; 75-84
2012
10 Seiten, 15 Bilder, 9 Tabellen, 18 Quellen
Article (Journal)
English
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