Evaluating Fitness-for-Service of Corroded Metal Pipelines: Structural Reliability Bases

This paper presents a methodology for evaluating fitness-for-service (i.e., safety, serviceability, and reliability) of corroded metal pipelines. A model for predicting pipe failure pressure is developed from a series of nonlinear finite-element analyses of metal pipes of different diameters and wall thicknesses with corrosion defects of different sizes and depths. The strength limit state (burst) and service limit states (yield and leakage) both are investigated in the pipe fitness-for-service analyses. Uncertainties associated with in situ measurement of flaw size, pipe geometry, pipe material properties, operating pressures, and corrosion in exposure environments are considered in a time-dependent reliability analysis of pipe performance over a service life of 50 years. Engineering variables that have the most significant impact on the reliability of a corroded pipe are identified through Monte Carlo-based sensitivity studies. Finally, a set of simple reliability-based evaluation tools are presented for assessing pipeline safety. The procedure and the results presented in this paper can be used to support decisions related to continued safe operation of pipes, optimal pipe inspection intervals, and maintenance schedules.

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