The deployment of hydrogen pipelines as part of the energy transition introduces unique engineering challenges, amongst other regarding the use of field bends. While field bends are a common and effective solution in pipeline construction - offering flexibility in adapting to terrain and reducing the need for prefabricated components -their suitability for hydrogen service raises concerns.
Hydrogen’s molecular properties, including its small size and high diffusivity, make pipeline materials susceptible to hydrogen embrittlement and stress corrosion cracking. Field bends, typically formed on-site through cold bending, introduce localized plastic deformation, cold-work hardening, micro-cracks and residual stresses that may exacerbate these vulnerabilities. Unlike factory induction bends, field bends are subject to less controlled conditions, increasing the risk of microstructural damage and crack initiation. During the field bending process limits of the material are actually reached by purpose, which following the strategies for hydrogen however should be avoided, as cold bending can transform an otherwise acceptable pipe grade into locally high-risk component in hydrogen service.
ASME B31.12permits field bends under strict procedural and quality control measures, while explicitly noting that cold bending may make linepipe more susceptible to the effects of hydrogen embrittlement. However, it emphasizes the need for adherence to geometric tolerances, and verification of material integrity to mitigate hydrogen-related degradation. Chapters addressing design, fabrication, and inspection highlight the importance of minimizing stress concentrations and ensuring long-term reliability in hydrogen service.
Given these considerations, this paper argues that while field bends may remain a practical necessity in pipeline routing, their use in hydrogen pipelines should be critically evaluated. A risk-based approach is recommended, favouring factory bends where feasible and enforcing conservative parameters, rigorous inspection and testing protocols for any field bends applied. The paper will further explore design alternatives, construction strategies, and regulatory implications to support safe and sustainable hydrogen infrastructure development.