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Paradigm busted – Pinhole detection utilising UHR Axial MFL and Caliper ILI, By: Mark Olson

With the advent of ultra-high resolution (UHR) MFL/caliper combination tools, the detection, characterisation, and sizing of true pinhole anomalies is a new frontier for axial magnetic flux leakage (MFL) inline inspection (ILI). This paper will discuss seven years of experience with UHR MFL inline inspection, challenging conventional wisdom on MFL technology.

Shifting paradigms is difficult. With the advent of ultra-high resolution (UHR) MFL/caliper combination tools, the detection, characterisation, and sizing of true pinhole anomalies is a new frontier for axial magnetic flux leakage (MFL) inline inspection (ILI).

The conventional wisdom to be challenged is that: 1) MFL technology isn’t capable of sufficient detection/accuracy for true pinholes, and 2) in-the-ditch NDE techniques are more reliable than MFL In-line inspection results for (primarily internal) pinhole metal loss.

This white paper will discuss the past seven years of experience with UHR MFL inline inspection. Pull testing on machined defects demonstrated that 3 mm (~0.125 in.) defects could be reliably detected, characterised, and sized to depths of 10% internally and 20% externally at lower ILI speeds (20% and 25% at full tool specification speeds). Subsequently, field correlation on hundreds of internal and external pinhole corrosion features qualified the API 1163 POD, POI, and sizing specifications. Regrettably, this exposed the real-world challenges facing in-the-ditch NDE techniques, and NDE technician experience locating the pits and reliably measuring the true pit depths in-the-ditch. Further laboratory testing compared the effectiveness of various in-the-ditch NDE techniques and identified recommended best practices.

 
 

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