As the energy sector transitions toward low-carbon solutions, hydrogen is emerging as a critical source of energy. However, the unique properties of hydrogen introduce significant challenges. Hydrogen molecules are small and prone to causing material embrittlement and cracking—especially in steel pipelines originally designed for oil or natural gas. Moreover, the explosive potential of hydrogen demands rigorous inspection protocols to minimize risks to infrastructure and public safety.

For operators repurposing existing pipelines to carry hydrogen, adaptations such as internal protective coatings, strengthened welds, and reinforced seals are essential. Refurbished pipelines require reassessment prior to operation due to the new operating parameters and risks. In particular, these lines remain prone to cracking. A pressing concern is the early and accurate detection of cracks, especially non-volumetric cracks, which are harder to identify but can lead to catastrophic failure.

This paper examines the comparative effectiveness of current in-line inspection (ILI) technologies for crack detection in repurposed hydrogen pipelines. Magnetic flux leakage (MFL) tools, while effective for volumetric defects, fall short when detecting crack openings with small widths. Ultrasonic testing (UT) methods, particularly crack-tip diffraction, offer superior resolution but are limited to liquid mediums. Alternatives such as electromagnetic acoustic transducers (EMAT) and acoustic resonance technology (ART) can operate in gas but lose accuracy with insulated or coated lines.  

The paper presents a comparative framework outlining the strengths, weaknesses, and operational requirements of each method, helping operators determine the best solution based on pipeline characteristics, inspection environment, and risk tolerance. Special attention will be given to emerging adaptations of UT designed to bridge these limitations.

As operators transition global infrastructure to accommodate new energies, understanding the limits and potential of current ILI technologies is critical to maintain safety, reliability, and public trust—and ensure that the change happens as painlessly as possible.