A 36/48 in. dual diameter pipeline needed to be inspected for wall thickness and axial cracking in a single run. Each pipeline segment differs in length, and has a different range in wall thickness. A challenging characteristic of the line was the 36 in. launcher and 48 in. receiver in 28 of the sections. Thus, the resulting outer diameter change is about 305 mm or 33%. From an intelligent inspection perspective, additional boundary conditions had to be taken into account, for example tight 15 D bends and a medium with high attenuation - which is especially important for the crack inspection technology. A tool utilising ultrasonic inspection technology was requested by the pipeline operator, because current conventional MFL technology was limited in detecting and identifying certain metal loss morphologies, such as narrow axial external corrosion (NAEC). Additionally, UT technology would provide direct measurement of features, compared to magnetic flux leakage technology (Kopp & Willems, 2013).
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