An analysis describing the benefits of an accurate in-line inspection (ILI) system performance is presented in this paper. A good ILI performance is characterized as an accurate description of the condition of an inspected pipeline. Information from a better ILI performance, as compared to a poorer one, can be used to reduce the number of required digs and/or extend the re-inspection interval without compromising the pipeline’s integrity. As a result, these parameters can be used to assess the benefits of the improved inspection performance.
For this analysis, the ILI performance was represented by the depth sizing accuracy as the depth of a feature is one of the most critical parameters in assessing the pressure containment capacity at the feature location. This work utilized a sensitivity analysis in which the impact of various levels of ILI performance on a pipeline integrity program in terms of the number of required repairs for a given reliability threshold was examined. The number of required repairs associated with each inspection performance was calculated using a reliability based assessment method. This method was selected because it fully accounts for the statistical characteristic of the ILI performance.
The sensitivity analysis considered two pipeline condition scenarios for two pipeline systems. The first pipeline condition scenario was characterized as having a high number of features, many of which were severe in size, while the second condition scenario consisted of fewer features that were less significant in size. The analysis was carried out for both axial stress corrosion cracking and metal loss corrosion features.
The results of the analysis show that a more accurate ILI depth measurement leads to a more accurate pipeline reliability estimate, and therefore, a reduction in the number of required repairs. However, the benefit associated with continued ILI measurement accuracy improvement exhibits a diminishing trend.