Beginning in 1991, methods to determine corrosion rates from multiple in-line inspections of pipelines have been developed and successfully implemented on a large transmission pipeline system. In 2000, investigations were performed to understand the characteristics of corrosion rates on a particular 500 km long pipeline that had been inspected three times over an 8 year period. The object of the study was to determine the variability of corrosion rates along the pipeline. With that data, authors applied the distribution of corrosion rates observed on the
pipeline with multiple inspections to other similar pipelines that had been inspected only once. The results of the analyses are of great benefit in determining the appropriate re-inspection interval when compared to other methods which use a single assumed corrosion rate.