Effect of high-pressure hydrogen charging environment on stress distribution in metals: (a) laboratory environment: charging of coupons from outside in autoclave causing compressive stresses vs. (b) real application: charging of pipeline material via inner pressure causing tensile stresses
Source: BAM
Green hydrogen the energy carrier in future. In order to distribute large volumes of hydrogen, compression or liquification of the gas is required. Hydrogen partial pressures up to 200 bar are common in industry (e.g., for gas bottles), while pressures up to 1000 bar will be considered in future. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals is crucial for avoiding hydrogen embrittlement. In that connection, the hydrogen solubility in steels with ferritic or martensitic microstructure is significantly affected by the hydrostatic stress, the pressure, and the temperature. When qualifying materials for high‐pressure hydrogen applications (e.g., for pipelines or tanks) typically autoclave systems are used for the hydrogen charging. In general, compressive stresses decrease the hydrogen solubility while tensile stresses increase the solubility. From that point of view, a simply “lookalike” question arises:
Is a sample pressurized from the inside (experiencing tensile stresses like in a pipeline) comparable to a model-like sample pressurized from the outside (e.g., material coupons in autoclave experiencing pure compressive stresses)?
For that purpose, a pressure equivalent to compensate the effect of compressive stresses on the hydrogen solubility inside of closed autoclaves was proposed in this study. The aim was to achieve hydrogen solubilities that are equivalent to those reported in pipelines and high-pressure hydrogen storage tanks subjected to tensile stresses. Moreover, it is shown that the temperature has a certain effect especially at very low temperatures, in other words: under cryogenic conditions for storing liquid hydrogen. From that point of view, hydrogen trapping in the microstructure can increase the virtual hydrogen solubility with decreasing temperature. That means that the material has a hydrogen solubility minimum close to room temperature (what is more or less in contradiction to the expected behavior). To describe this effect, the generalized law for gas solubility was parameterized using available hydrogen solubility data for different steel grades charged in gaseous high-pressure hydrogen. Different parameter sets were obtained in accordance with the respective material, verified and critically discussed. The study was conducted within the ongoing research collaboration on materials for hydrogen technologies between BAM and Technical University Graz, Austria.
Effect of Tensile Loading and Temperature on the Hydrogen Solubility of Steels at High Gas Pressure
A.-K. Drexler, Florian Konert, Jonathan Nietzke, E. Hodžić, S. Pastore, J. Domitner, Michael Rhode, C. Sommitsch, Thomas Böllinghaus
published in Steel Research International, essay number 202300493.
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