A Client operates a 28km long, 24 pipeline with a wall thickness of 12.7mm.

The pipeline was inspected using ILI in 1998 and 2008. The Client required a run comparison of the two inspections to provide the following:

• Establish corrosion growth rates by either matching features between runs or identifying areas of new growth.
• Report differences between the ILI runs for identifying non-corrosion features, such as dents or girth weld anomalies.

The general approach adopted by AFAA for performing an ILI run comparison comprises two stages:

• Stage 1: Data Gathering
• Stage 2: Alignment of Data and Feature Comparison

Stage 1 involves collection and analysis of the ILIs that are to be compared and any additional data that may provide explanations for differences between the two ILIs.

Stage 2 involves firstly aligning the data between the two ILIs to allow a feature comparison to be made. It then involves looking at each aligned spool and detailing the features from the initial ILI to the most recent ILI to find features that match, features that do not match with the most recent ILI and also new features on the pipeline which did not appear in the initial ILI. This will allow the amount of growth between the two runs to be calculated.

AFAA were able to provide the Client with a detailed breakdown of the following:

• For metal-loss features
  • Number and growth of matched features
  • Number of un-matched features and a distribution of their size
  • Number and size of new features
• For dents
  • Number of matched dents
  • Number of new dents and their orientation on the pipeline
• Comparison of change in number of mill anomaly and weld anomaly features.