The goals of integrity management programs are to reduce risk posed by pipelines to the public and environment as well as reliably deliver energy according to; on-time, on-volume and on-specification contractual terms. Operators must necessarily consider how to achieve these goals in a cost effective and sustainable manner and simultaneously provide the necessary assurances to stakeholders.
Knowledge of the ILI measurement uncertainties plays an important role in determining acceptance of an in-line inspection and performing integrity assessment of reported defects, and for establishment of longer term integrity strategy by using deterministic or probabilistic assessment methods.
For metal loss (corrosion), sizing tolerance relates to errors in the reported corrosion feature size as compared to its actual size, which can then be quantified statistically with standard deviation, or an error band at a certain confidence level. Sizing errors associated with ILI tools are quoted uniquely as a two sided confidence interval for a given confidence level. The depth-sizing variability of high-resolution MFL tools, for corrosion metal loss, is typically considered to be ±10 % wt (wall thickness) with 80% certainty (confidence level).
Due to many factors the actual accuracy of defect size and locations may not be consistent with the stated ILI specifications. Therefore, as part of any detailed integrity assessment, it is important the effects of sizing and discrimination errors be considered and accounted for in the integrity strategy.
How to address ILI measurement uncertainty will be presented in this presentation.