Abstract
The transportation of hydrogen-blended natural gas through existing natural gas pipelines is recognized as one pathway for decarbonization of the natural gas grid.
However, hydrogen introduces unique challenges due to its potential to impact mechanical properties of pipeline steels. Fracture toughness, a critical parameter for crack initiation and growth, is central to fitness-for-service assessments and defect tolerance evaluations. However, assessing fracture toughness in thin-wall carbon steel pipes (~0.2 in.) typical in natural gas distribution networks is challenging due to geometry limitations.
This study examined eight distribution network pipeline steels—two modern and six vintage—installed between 1956 and 1997 to evaluate hydrogen’s effect on fracture toughness. Tests were conducted in air and 30% hydrogen–70% methane blends at pressures of 500 psi on pipe body material, weld metal (including girth and seam welds), and heat-affected zones.
To address the limitations imposed by the small pipe wall thickness, a custom clip-on displacement gauge incorporating hydrogen-resistant strain gauges was developed to accurately measure crack mouth opening displacement (CMOD) in small-scale specimens while ensuring reliable performance under hydrogen exposure.
The test results demonstrate a consistent reduction in fracture toughness for all specimens tested in hydrogen compared with those tested in air, confirming the effect of hydrogen during testing. Hardness measurements were also conducted at three locations for each pipe—pipe body, weld metal, and heat-affected zone—and no clear correlation was observed between hardness and fracture toughness, either in air or in hydrogen-containing environments.
Microstructural characterization using optical microscopy revealed that steels with different microstructures exhibit distinct fracture toughness degradation behaviors in hydrogen, underscoring the role of hydrogen–microstructure interactions and offer insight into the variation in fracture toughness properties of modern and vintage pipeline materials.
These findings advance understanding of hydrogen embrittlement mechanisms in existing pipeline steels and provide a basis for predicting fracture toughness performance based on microstructural characteristics.
Author:
Sun, Lu
Publisher:
ASME The American Society of Mechanical Engineers
2026 International Pipeline Conference
Year Published:
2026
Purchase Link:
Coming Soon.
