Run Comparisons: Using in-line Inspection Data for the Assessment of Pipelines

In the past In-line Inspection (ILI) was mainly done for the purpose of quickly finding defects that had to be repaired in order to restore the pipeline integrity. Currently this task shifts to a continuous monitoring of the pipeline's condition, which allows to derive new conclusions like the assessment of corrosion growth. The paper will discuss how defect growth can be estimated from continuous inspections and what implications the advancement in inspection technology has. Several models of corrosion growth assessment are discussed. Their applicability depends on the condition of the pipeline, i.e. the density of defects and the available data. A stepwise process can be defined in which more detailed information will allow to use more accurate methods of corrosion growth assessment. In a final stage the data of high-resolution ultrasonic inspection tools can be used to compare defects on a basis of wall thickness C-Scans. This will generate more precise conclusions about corrosion growth on single defects, which was not possible with the traditional statistical approach. In particular it is possible to assess corrosion growth on selected sites even in an early stage of corrosion or if the number of corrosion sites is small.