In-line inspection in lieu of hydrostatic testing for low frequency electric resistance welded pipe

Evaluation of ILI performance must go beyond the verification of the largest anomalies identified in the inspection report. Understanding the types and morphology of cracks that have the potential to grow and affect the integrity of the pipeline is an important process. The approach chosen for this pipeline was to remove pipe sections from service for technology calibration and assessment. The pipe sections were examined with ILI technology in a pump-through facility, inspected with many NDE methods, and destructively tested.

These results were communicated to ILI analysts and used to calibrate and improve the interpretation of the inspection results. The process for fully understanding the cracking threat is pipeline specific and other approaches that can rely more heavily on field NDE are possible. Emerging NDE imaging approaches that confirm crack dimensions can be a useful part of the process. Ultrasonic imaging techniques using FMC data such as TFM or IWEX are becoming commercially available and other imaging techniques are in the demonstration phase such as x-ray computed tomography (XCT). These imaging approaches can augment (and have the potential to replace) destructive examination.

For ILI to be accepted in lieu of hydrostatic testing, all significant anomalies must be found. For some anomalies, where interpretation can be difficult, the use of other ILI data sets and knowledge of the pipeline could help identify anomalies that have a higher potential for being undersized, thus increasing the confidence that all significant anomalies must be found.

In the 20th century, hydrostatic testing was the common method to ensure integrity of pipelines with corrosion, but metal loss ILI has superseded that approach in this century. This work shows the advances in crack ILI and field NDE that could make crack ILI inspection a viable alternative to hydrostatic testing for all pipelines in the near future.

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