Hydrogen-induced damage of materials: A review of testing and evaluation methods, and hydrogen mapping techniques

Hydrogen is expected to be one of the primary clean energy carriers of the future due to the depletion of fossil fuels and the resulting climate change. Hydrogen, however, drastically degrades the properties of metals, imposing a considerable barrier on structural materials used in the production, transportation, and storage of hydrogen. Due to the limited scope of reliable available testing methods, it is still challenging to effectively determine the hydrogen concentration and distribution in materials, evaluate hydrogen-induced damage and understand the respective degradation mechanism(s). Hydrogen-induce damage evaluation tests have been generally performed mechanically either ex-situ with hydrogen-pre-charged specimens or in-situ in hydrogen-containing environments. Hydrogen-induced damage is highly dependent on the distribution of hydrogen in a material; hence, mechanical evaluation tests should be supported with microstructure-sensitive hydrogen detection and mapping techniques. The various types of ex-situ and in-situ mechanical tests used to evaluate the hydrogen-induced damage of metals are explored in this study. The slow strain rate test is the widely used mechanical test for evaluating the vulnerability of metals to hydrogen-induced damage, where hydrogen diffusion is considered during testing. The three common types of hydrogen pre-charging techniques used for charging specimens with hydrogen are also included in the study. Immersion, electrochemical, and high-pressure/temperature gaseous charging methods are commonly used to charge metal-samples with hydrogen. The hydrogen detection and mapping techniques for examining the hydrogen distribution in metals at various length scales are also discussed.