In-Line Inspection Performance III: Effect of In-Ditch Errors in Determining ILI Performance

The performance of in-line inspection tools employed for pipeline integrity assessments has significant impact on the reliability of assessment results and subsequent remediation program. Previous papers by the lead authors established criteria for determining the number of “successful” field validation measurements for establishing whether a tool’s performance should be accepted or rejected and how to assess the tool performance when a claimed performance can be neither rejected nor accepted. This “apparent” validated performance contains both the ILI tool measurement error and the in-ditch measurement error. Determination of the true tool error can have significant impact on the response to ILI feature characterization relating to timing for repairs and justification of re-assessment intervals. Measurement errors, associated with the currently available technologies employed in the field for in-line inspection metal loss validation measurements, are discussed in this paper. The relative effect of variations in validated tool error due to field measurement error on pipeline integrity is discussed within the context of actual in-line assessment case studies.