Table of Contents
The development of hydrogen pipelines constitutes a critical component in the energy transition, particularly under schemes involving the reuse of existing infrastructure. Converting pipelines originally designed for hydrocarbon transport to carry gaseous hydrogen (GH₂) represents a cost-efficient alternative; however, it introduces technical uncertainties associated with hydrogen–steel interaction, hydrogen embrittlement, and the progressive degradation of service life.
Within the framework of the 21st Pipeline Technology Conference (ptc 2026), these challenges have been addressed from an integrity perspective, highlighting the Repurposing for Hydrogen track, where pipeline integrity management plays a central role in the viability of such systems.
Pipeline reuse: Engineering criteria
The reuse of pipelines in the energy transition requires evaluating the suitability of materials originally designed for natural gas under new service conditions. These systems are predominantly composed of API 5L carbon steels joined by welding, introducing critical metallurgical heterogeneities, particularly in heat-affected zones (HAZ).
From a regulatory standpoint, standards such as ASME B31.12 establish specific requirements for hydrogen transport, incorporating variables such as hydrogen partial pressure, reduced design factors, and stricter material selection criteria. Techniques such as hardness mapping enable the identification of crack-susceptible regions, particularly in welded areas.
In this context, companies such as ROSEN Group provide added value through specialized technical consulting in integrity assessment, defect analysis, and mitigation strategies for hydrogen pipeline reuse processes.
Hydrogen embrittlement: Mechanisms and technical evidence
Hydrogen embrittlement is the primary phenomenon affecting the integrity of hydrogen pipelines. This process is not directly associated with the transported molecular hydrogen (H₂), but rather with atomic hydrogen (H) that diffuses into the steel crystal lattice.
Thermodynamically, spontaneous dissociation of H₂ under typical pipeline operating conditions is not favored; however, surface adsorption mechanisms allow dissociation at the steel–gas interface, particularly in the presence of surface roughness, defects, or inclusions. This facilitates the absorption of atomic hydrogen, which concentrates in microstructural discontinuities and high triaxial stress regions.
The immediate effect is a reduction in ductility and plastic deformation capacity, with reported decreases in elongation at fracture ranging from 20% to 50%. While properties such as yield strength may not be significantly affected under static conditions, performance under cyclic loading shows substantial degradation.
Crack growth and fatigue behavior
One of the most critical aspects in pipeline reuse is the impact of hydrogen on fatigue resistance. The presence of hydrogen lowers the crack initiation threshold and accelerates crack propagation, significantly increasing the crack growth rate.
Experimental studies show that crack growth rates may increase by one to two orders of magnitude in the presence of gaseous hydrogen. This behavior is explained by mechanisms such as hydrogen-assisted decohesion, localized plasticity at the crack tip, and hydrogen recombination within internal cavities.
Consequently, fatigue life assessment becomes an essential requirement within pipeline integrity management, particularly considering that these systems operate under fluctuating pressure conditions.
Inspection and integrity control
The safe reuse of hydrogen pipelines requires the implementation of robust inspection programs. In-line inspection (ILI) technologies enable the detection of wall loss, longitudinal cracks, weld defects, and areas susceptible to phenomena such as Sulfide Stress Cracking (SSC).
These tools are essential to address key industry questions: What ILI inspections are required for hydrogen reuse? What is the actual leakage risk?
Due to the small molecular size of hydrogen, the likelihood of leakage through microscopic discontinuities is significantly higher, requiring stricter criteria in sealing, welding, and defect control.
Mitigation strategies for hydrogen embrittlement
From a materials engineering and integrity management perspective, mitigating hydrogen embrittlement requires a multifactorial approach based on controlling metallurgical, operational, and surface variables. Primary strategies include selecting materials with lower susceptibility to hydrogen damage (e.g., lower hardness steels with controlled microstructures), limiting hardness in critical regions through hardness mapping, and optimizing welding procedures to minimize residual stresses and microstructural heterogeneities in the heat-affected zone (HAZ).
From a physicochemical standpoint, it has been observed that the presence of certain gaseous species at low concentrations can influence hydrogen adsorption and dissociation processes on the steel surface. In particular, controlled incorporation of impurities such as oxygen or carbon monoxide may reduce the dissociation kinetics of molecular hydrogen, limiting the generation of atomic hydrogen and consequently decreasing its absorption and diffusion into the material.
In this context, the use of coatings as diffusion barriers has been widely investigated as a complementary mitigation strategy. Several studies have demonstrated that polymeric coatings, high-performance epoxies, and multilayer systems can significantly reduce hydrogen permeability, acting as effective barriers against surface adsorption mechanisms. Likewise, metallic and ceramic coatings have been evaluated for their ability to limit hydrogen diffusion under severe operating conditions.
The performance of these systems is directly related to critical parameters such as adhesion, continuity, defect resistance, and stability under pressure and temperature conditions. The presence of discontinuities, porosity, or coating degradation may create preferential sites for hydrogen adsorption and dissociation, significantly reducing their effectiveness as barriers.
Therefore, industry standards emphasize the need to integrate coating selection and specification within a comprehensive pipeline integrity management approach, including strict controls for surface preparation, application, inspection, and in-service monitoring. The combination of appropriate coatings with metallurgical and operational control strategies currently represents one of the most promising approaches to mitigate hydrogen embrittlement in hydrogen transport systems.
Strategic decision: Pipeline reuse in the energy transition
The reuse of existing infrastructure for hydrogen pipeline development represents one of the most relevant pillars for enabling the transition toward low-carbon energy systems. Compared to the high costs and timelines associated with building new networks, adapting existing pipelines accelerates the deployment of hydrogen as a key energy vector.
However, this strategy cannot be addressed solely from an economic perspective. Converting pipelines for hydrogen transport requires understanding and managing complex phenomena such as hydrogen embrittlement, fatigue behavior, and defect evolution under variable operating conditions. In this sense, reuse becomes an advanced engineering challenge, where system reliability depends directly on the quality of the technical analysis applied.
Pipeline integrity management thus assumes a strategic role, integrating in-line inspection, service life evaluation, crack growth analysis, and operational control variables. This approach enables the transformation of existing assets into infrastructure compatible with new energy demands, reducing risks and optimizing investments.
In the global context, where hydrogen is emerging as a key energy carrier for the decarbonization of industrial and transportation sectors, pipeline reuse stands out as a technically viable and scalable solution. However, its success will depend on the ability of engineering disciplines to integrate scientific knowledge, specific regulations, and advanced monitoring technologies.
Ultimately, the development of hydrogen pipelines through reuse not only responds to a technical necessity but also represents a strategic decision that connects legacy infrastructure with future energy demands.
Conclusions
The implementation of hydrogen pipelines through reuse schemes represents a strategic solution to accelerate the energy transition; however, its feasibility depends on a deep understanding of hydrogen embrittlement mechanisms and robust pipeline integrity management.
Compliance with standards such as ASME B31.12, combined with the application of advanced inspection technologies and structural analysis, enables effective risk management. In this context, the involvement of specialized companies such as ROSEN Group is essential to ensure sound technical decision-making.
Ultimately, the reliability and safety of hydrogen pipelines depend not only on the material itself but also on the quality of the engineering analysis applied in their reuse, ensuring long-term performance under demanding operating conditions.
References
- American Society of Mechanical Engineers. (2020). ASME B31.12: Hydrogen piping and pipelines. ASME.
- API. (2018). API Specification 5L: Specification for line pipe. American Petroleum Institute.
- San Marchi, C., Somerday, B. P., & Robinson, S. L. (2007). Permeability, solubility and diffusivity of hydrogen isotopes in stainless steels at high gas pressures. International Journal of Hydrogen Energy, 32(1), 100–116.
- Melaina, M. W., Antonia, O., & Penev, M. (2013). Blending hydrogen into natural gas pipeline networks: A review of key issues. National Renewable Energy Laboratory (NREL).