Accurate corrosion modeling improves reliability estimations

Researchers derived five corrosion rate distributions from different pit growth models and used them to perform reliability analyses of underground pipelines from synthetic and real-life data. The probabilistic distribution of defect corrosion growth rate, or simply corrosion rate (CR), must be estimated to predict future dimensions of corrosion defects. CR distribution used in reliability estimations of underground pipelines often is based on the operator's knowledge of soil. Five CR models helped evolve the initial empirical pit-depth distribution of the defects in the 1996-ILI set. The analysis interval or evolution time was 10 years. Corrosion growth modeling design excluded evolution of the corrosion defect lengths. Changes in the defect length have little or no influence on the estimation of the failure probability associated with individual corrosion defects. The initial and final pit-depth distributions from 1996-ILI and 2006-ILI inspections provided the basis for estimating the exponent v instead of using the value previously recommended by the authors.