Literature Review on Reinspection for Pipelines Carrying Hydrogen or Hydrogen/Natural Gas Blends
This literature review critically examined the methodologies currently employed in the U.S., Europe, and other countries, to determine in-line inspection (ILI) reinspection intervals for transmission pipelines containing hydrogen gas or natural gas/hydrogen blends. An in-depth comparison and discussion about Codes and Standards was also provided.
The scope of this literature review included:
- Identification and sizing of ILI features,
- Commentary on reinspection intervals in relevant Codes and Standards,
- Discussion on accelerated fatigue and stress corrosion cracking (SCC) crack growth rates (CGRs) due to the presence of hydrogen,
- Discussion on the effects of the pressure regime in gas pipelines,
- Experiences with converting existing pipelines, experiences from hydrogen-blending, pipeline conversions to hydrogen, and new hydrogen pipeline construction, in the U.S. and internationally,
- Status on joint industry projects (JIPs),
- Crack-related failure causes, pre-existing defects, and hydrogen embrittlement mechanisms, and
- A review of pertinent Standards from Germany and the United Kingdom.
Several ILI technologies exist with the capability to detect cracks that are suitable for gas (hydrogen/natural gas) pipelines. This includes the latest in circumferential magnetic flux leakage (MFL) and helical MFL tools and considerations for ultrasonics. A summary of ILI technologies is provided here:
- Traditional Ultrasonics ILI
Ultrasonics have taken the lead in crack detection, but they can be limited in the detection of certain crack morphologies due to the physics required. In a liquid system, the industry has seen enormous improvement and maturation of ultrasonic technology crack detection (UTCD) tools in detecting and sizing crack‑like defects. However, this technology is typically not practical for use in gas lines due to the requirement of a liquid couplant medium, nor is it typically available or reliable in smaller-diameter pipelines.
- Circumferential MFL ILI
Although circumferential tools have traditionally been used to screen for axial pipeline cracks, only recently have new developments occurred using multiple technologies on a singular platform to significantly advance the understanding of the capabilities of MFL combination technologies to provide detection and sizing of crack-like anomalies both on the axial and off-axis angles. Additionally, certain technologies are beginning to show reliable detection of circumferential cracks and off-axis cracks.