The Evolving Importance of Axial Crack Detection in Hydrogen and CO₂ Pipelines

As hydrogen and carbon dioxide pipeline networks are expected to expand to support energy transition objectives, axial crack detection is emerging as one of the most critical aspects of pipeline integrity management. The shift from transporting conventional natural gas to transporting future fuels introduces new material behaviors, operating regimes, and risk profiles. Recent industry research and field experience reveal a clear pattern: accurate, early, and sensitive detection of axial cracks is essential for enabling the safe, large‑scale transport of hydrogen and carbon dioxide.

Because of these changing conditions, inspection technologies must detect increasingly small and subtle axial crack-like anomalies. Technologies, such as Ultrasonic Testing (UT) and Electromagnetic Acoustic Transducer (EMAT), will play central roles in this. Each technology has distinct advantages based on its physical principles, application environment, and sensitivity characteristics. 

Technology overview: Why sensitivity matters

UT and EMAT technologies are recognized methods for inspecting gas pipelines, yet their operational principles lead to differences that become especially relevant when considering the evolving demands placed on pipeline infrastructure. UT relies on transmitting ultrasonic sound waves through a liquid coupling medium to enable precise wall‑thickness measurements and detailed crack characterization, making it an important and widely trusted method for crack detection. However, the reliance on a coupling medium introduces limitations for hydrogen and CO₂ pipelines which cannot easily be fully or partially filled with a  liquid. This greatly increases the operational complexity of a UT inspection in a gas pipeline. 

EMAT, on the other hand, induces ultrasonic sound waves directly within the pipe wall, without requiring liquid coupling. This allows it to operate reliably in gas pipelines, regardless if natural gas, hydrogen or CO₂. EMAT can also detect coating disbondment providing a broader view of pipeline health. Recent developments in EMAT technology have improved sensitivity, increased sensor coverage, and strengthened detection probabilities, making EMAT particularly well aligned with the emerging requirements of hydrogen and CO₂ pipelines.

Hydrogen pipelines: Increased sensitivity requirements

Hydrogen fundamentally alters the structural reliability landscape of steel pipelines. Its embrittling effect reduces ductility, lowers fracture toughness, and accelerates fatigue crack growth. This means that small, shallow cracks that would not be a major concern in natural gas service may become critical under hydrogen service, particularly if there is pressure cycling.

The recent development of EMAT-C Ultra includes higher sensor coverage, dual clockwise–counterclockwise sound paths, and refinements in signal quality when compared with existing EMAT systems. These improvement collectively support higher detection reliability for axial cracking, including the capability to detect comparatively small features in the pipe body.

This level of sensitivity directly supports hydrogen‑specific engineering critical assessments (ECAs), where acceptable defect dimensions are typically smaller than in natural gas operations. Consequently, repurposing to hydrogen demands more precise anomaly characterization and a better understanding of how material behaves under hydrogen exposure.

Across the industry , a consistent conclusion emerges: hydrogen service requires the detection of smaller axial defects than previous pipeline applications, making advanced EMAT‑based inspection increasingly important.

CO₂ Pipelines: Managing rapid crack propagation risks

Transporting CO₂ via pipelines introduces a different set of fracture‑mechanics challenges, particularly when operating in the dense phase. Unlike hydrogen, which raises concerns around embrittlement, CO₂’s decompression characteristics can promote rapid crack propagation from axial flaws, if not properly mitigated.

High‑pressure CO₂ transport requires proactive, high‑resolution inspection programs. Safe network expansion depends on thorough in-line inspection (ILI) processes that can identify axial cracks before they grow into critical cracks,  particularly given CO₂’s sensitivity to containment breaches and the associated public‑safety and environmental considerations.
In this context, axial crack detection is not just an engineering concern – it is a foundational element of public confidence and regulatory compliance in future CCUS networks.

Inspection strategy in repurposed pipelines

The transition to future fuels is expected to rely heavily on repurposed natural gas infrastructure. This significantly increases the relevance of legacy material properties, weld conditions, and recorded anomaly populations.

Repurposing frameworks emphasize that:

• Planar (axial) anomalies become critical assessment drivers when pipelines transition from natural gas to hydrogen.
• Hydrogen material property verification (MPV) and updated toughness testing are necessary to assess and cracks detected appropriately.

These points reinforces the idea that axial crack detection involves more than just identifying features; it also enables more accurate, data‑driven integrity decisions throughout repurposing projects.

Toward a multi‑fuel crack detection paradigm

Across hydrogen and CO₂ pipeline applications, three themes consistently appear in recent technical work:

1. Axial cracks pose a common threat to the integrity of future fuel pipelines.
   Hydrogen increases the sensitivity of materials to small cracks, while CO₂ increases the consequences of crack propagation. Both require tailored crack inspection strategies.
2. Advanced EMAT technologies are becoming central to managing planar anomalies.
   EMAT‑C Ultra developments demonstrate improved sensitivity, reliability, and compatibility with dry‑gas inspection – critical attributes for both hydrogen and CO₂ pipeline operations.
3. Data quality and verification frameworks are increasingly important.
   Field‑verified anomaly databases, updated material property verification methodologies, and hydrogen‑specific testing protocols ensure accurate assessments based on crack detection results.

These advancements suggest that axial crack detection will be one of the defining capabilities enabling the safe expansion of hydrogen and CO₂ pipeline networks.