Hydrogen Embrittlement of Steels for Hydrogen Gas Storage

Using hydrogen as an energy carrier is a key technology for transitioning our current fossil fuel-based industry and energy sector to renewable energy sources. As hydrogen is stable over the long term, it can easily be stored and transported to the consumer via pipelines. However, since hydrogen has a lower energy density by volume compared to natural gas, it must be compressed more than natural gas to achieve the same energy content. Increased hydrogen partial pressures increase the absorption of hydrogen in steels, exacerbating the conditions regarding hydrogen embrittlement. It is therefore crucial to know how much hydrogen different steel classes absorb as a function of pressure and temperature. In the course of this work, industrial steels with ferritic-perlitic and tempered martensitic microstructures, as well as quenched and tempered steels with different heat treatments and an austenitic stainless steel were analysed under pressures of up to 1000 bar and temperatures up to 200 °C. In order to be able to make statements about what the absorbed hydrogen contents mean with regard to the hydrogen embrittlement tendency of the materials, Constant Load and Slow Strain Rate Tensile tests were conducted. Furthermore, the determination of the critical hydrogen content was done combining experimental data and numerical simulations. In addition, the diffusion kinetics and the trapping behaviour of the different steel grades were investigated. At room temperature, no higher contents than 1.1 wt.-ppm were absorbed by carbon steels, regardless of microstructure. This content is in the range of or above the critical hydrogen content for higher-strength grades. Therefore, an increased tendency to embrittlement can be expected for these steels when they are applied under very high hydrogen partial pressures. A linear relationship between hydrogen content and the square root of the partial pressure was found even under high pressures, taking the measurement uncertainty into account. The hydrogen absorption of the tested austenitic material exceeds that of the ferritic/martensitic grades by a factor of about 100. Nevertheless, the material exhibits a very high resistance to hydrogen embrittlement, whereby hydrogen contents of around 100 wt.-ppm primarily affect the reduction of area, while the fracture elongation remains unaffected.