The Challenge:
During pipeline dig validations, it’s common for NDE findings to be treated as the final word. But in many cases, there is more to the story than what the NDE company finds.
Without involving the ILI vendor, critical context can be lost. What appears to be a missed call may be the result of growth, feature evolution, or something unexpected.
The Difference NDE/ILI Integration Makes:
Operators who include the ILI vendor gain a far clearer picture. By cutting out and shipping pipe samples for comprehensive evaluation, deeper insights emerge through:
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Advanced NDE (pit gauging, laser scanning, granular correlation)
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Independent verification using additional ILI pull testing
For nearly 20 years, MISTRAS member-company Onstream Pipeline Inspection has supported pipeline operators with an industry-leading, ready-to-deploy ILI tool fleet, high-quality inspection reporting, and comprehensive Post-ILI validation services. Our validation capabilities include pipe sample assessment, such as pit gauging, ultrasonic wall thickness measurements, laser scanning, feature correlation, outlier analysis, pull testing, and detailed ILI Validation Results Reporting.
Read on to see how integration doesn’t just streamline the process—it strengthens confidence in the data, improves correlation accuracy, and enhances integrity decision-making across the asset lifecycle.
Case Study: Onstream ILI validation reveals previously-unknown 50% external corrosion missed even by NDE!
Onstream MFL reported through-wall internal corrosion features. The joint was removed and verified by an NDE company. The through-wall features were obvious, and internal/external discrimination was generally accurate; however, some nearby internal corrosion indications reported by MFL could not be confirmed during field validation.
What conclusions would you draw?
The NDE report assumed the “missing” features were simply MFL false positives. The case would have been closed, but Onstream requested the pipe for pull testing and independent verification. The same “false positive” features were again visible in the pull test.
Onstream then stripped and sandblasted the external pipe surface. This had not been done by the NDE company, assuming all the corrosion was internal. A series of external pinholes were revealed with depths up to 50%!
This independent validation completely changed the game for corrosion mitigation. The through-wall features themselves, initially assumed to be internal in origin, may in fact have been external.
Case Study: Extremely Fast Corrosion Growth Rates Confirmed by Pull Testing of Cutout Joint
A leak occurred when three through-wall holes appeared on a single joint. This pipeline had been inspected only a year prior, and the three deepest features reported on this joint were 47, 35 and 34 percent deep. Did these three features grow into leaks in only a year? Or did the inspection miss major features?
The joint was removed. Before being split and laser scanned, it was pull tested with the same MFL tool used during the inspection a year prior. The results were surprising. Dozens of large new features were detected, including all three holes. The pull test showed that all three through-wall features had not grown from features that existed a year ago – all three were brand new and had grown from zero to 100% in only a year!
Note the band of shallow internal corrosion at 6:00 visible in both inspection and pull test, which appears unchanged. The identical detection of these shallow features demonstrates the repeatability of the ILI tool. Meanwhile, several large pits at 4:00 and 8:00 have appeared in the year between inspection and pull test. Three of these reached 100% depth!
After pull testing, the joint was split and laser scanned. Many of the new internal features had depths exceeding 70%.
A review of the rest of the pipeline identified several other joints with deep features that appeared between 2018 and 2024 MFL inspections with depths up to 63%. Surprisingly, none of these leaked before the even newer features on the cutout joint. But they did serve as a warning that rapid growth was a possibility.
With 6 years between inspections, the growth rate is highly uncertain. Did these features appear 6 years ago, or less than 1 year ago? It’s impossible to know for sure. The pull test performed after the leak proved the growth rate was at the highest end of the possible range.
Lessons Learned
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Corrosion can grow extremely rapidly – from zero to 100% in less than a year!
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Growth rates vary widely from feature to feature. Even on the same joint of pipe, some features didn’t change in 6 years, while others grew very quickly. It’s the fastest-growing feature, not the average growth rate, that matters most.
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The longer the span between inspections, the more uncertainty around growth rate. Don’t assume the features started growing immediately after the last inspection. They may be much newer and much faster growing!
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Pull testing before splitting the pipe is very useful for determining the true growth rate.
Bottom Line
Dig validation is not the end of the investigation; it’s an opportunity to better understand asset condition and active threats. Integrating the ILI vendor into the validation process brings inspection data, field findings, and independent verification together for a more complete assessment, improving ILI / NDE correlation confidence and supporting integrity decisions. At Onstream, these validation services are a standard part of our offering.
To learn more, please reach out to our Onstream team: Contact - ONSTREAM | Pipeline Inspection Services