Multiscale Experimental Techniques for Evaluating Hydrogen Resistance in Structural Alloys for Energy Systems

Abstract

The reliable qualification of structural alloys for hydrogen energy applications demands experimental frameworks capable of resolving hydrogen-induced degradation across multiple length scales, from atomic hydrogen-lattice interactions to macroscopic fracture. This review provides a critical assessment of experimental techniques for evaluating hydrogen resistance in structural alloys, examining their capabilities, limitations, and relevance to hydrogen energy infrastructure. The principal degradation mechanisms, hydrogen-enhanced localized plasticity, hydrogen-enhanced decohesion, and hydride-induced embrittlement, are examined alongside their experimental signatures, with attention to unresolved discrepancies between permeation- and desorption-derived transport data. Macroscale mechanical testing, transport characterization, microstructural and nanoscale methods, and operando approaches are evaluated against recently codified fatigue design curves and qualification standards, revealing that fragmented, single-technique application continues to limit translation into reliable material selection criteria. A multiscale experimental framework is proposed, linking degradation mechanisms to technique selection, cross-scale data integration, and machine-learning-assisted qualification across four hydrogen energy contexts: pipelines, pressure vessels, turbines, and fuel cell systems. Infrastructure gaps, unharmonized transport-testing protocols, and characterization challenges posed by emerging systems, including high-entropy alloys and engineered barrier coatings, are identified as principal barriers, and a shared, structured hydrogen-materials data repository is argued as a prerequisite for accelerated, responsible deployment of hydrogen energy technologies.