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This study gives an overview on the important field of joining processes for component fabrication in hydrogen technologies. The current main issues and future perspectives are highlighted for the different technological field of hydrogen generation, storage, transport and use. In addition, the emerging field of additive manufacturing is included. Some remarks are given for standardization and regulations.
Offshore wind turbines (OWT) are a major goal of the energy strategy of Germany encompassing the increase of the installed wind power. OWT components are manufactured from welded steel plates with thicknesses up to 200 mm. The underlying standards and technical recommendations for construction of OWTs encompass specifications of so-called minimum waiting time (MWT) before non-destructive testing of the weld joints is allowed. Reason is the increased risk of time-delayed hydrogen assisted cold cracking as hydrogen diffusion is very slow due to the very thick plates. The strict consideration of those long MWT up to 48 h during the construction of OWTs leads to significant financial burden (like disproportionately high costs for installer ships as well as storage problems (onshore)). In this study, weld joints made of S355 ML were examined in comparison with the offshore steel grade S460 G2+M. The aim was to optimize, i.e., reduce, the MWT before NDT considering varied heat input, hydrogen concentration and using self-restraint weld tests. This would significantly reduce the manufacturing time and costs of OWT construction. To quantify the necessary delay time until hydrogen-assisted cold cracks appear, acoustic emission analysis was applied directly after welding for at least 48 h.
As the world shifts to a decarbonized economy, the demand for hydrogen-based technologies is rapidly increasing. In order to make optimal use of hydrogen as an energy carrier, the infrastructure for hydrogen storage and transport in particular, must meet high technical safety standards. The indispensable basis for such safety assessments are the material properties, which must be evaluated under operating conditions that are as real as possible.
The conventional method for the assessment of the material properties in gaseous hydrogen is conducted by testing materials in high-pressure hydrogen gas in a pressure vessel (autoclave). It is an established method that allows to perform common standardized tests such as tensile, fatigue and crack growth tests under varying hydrogen conditions. However, this method is complex and entails high costs due to extensive safety regulations.
The hollow specimen technique is a more efficient test method, which can be used to assess the mechanical properties of materials under high-pressure hydrogen gas. The procedure is conducted by enclosing high-pressure gas into a hole along the axis of the tensile test specimen. Recently, this method has been successfully performed at pressures up to 1000 bar and over a wide range of temperatures. Due to the low hydrogen volume needed, this method requires minimal safety regulation; therefore, the costs are reduced when compared to the conventional autoclave technique. This method is now in a standardization process, which has been initiated by Japan as a new working package in ISO (TC 164/SC 1/WG 9).
The following contribution presents preliminary results obtained testing common grades of metastable austenitic stainless steel. For this purpose, the mechanical properties and fracture surface of solid and tubular specimens were assessed and compared using slow strain rate tensile (SSRT) test as part of the preliminary work at the Fraunhofer IWM. In a similar way, pipeline steels evaluated under hydrogen atmospheres using the geometry adapted by BAM will be presented. Within the framework of the TransHyDE flagship project, more results with the goal of supporting the standardization of the hollow specimen technique are expected to be obtained.
During the energy transformation from fossil fuels to renewable energy sources, the use of hydrogen as fuel and energy storage can play a key role. This presents new challenges to industry and the scientific community alike. The storage and transport of hydrogen, which is nowadays mainly realized by austenitic stainless steels, remains problematic, which is due to the degradation of mechanical properties and the possibility of phase transformation by hydrogen diffusion and accumulation. The development of materials and technologies requires a fundamental understanding of these degradation processes. Therefore, studying the behavior of hydrogen in austenitic steel contributes to an understanding of the damage processes, which is crucial for both life assessment and safe use of components in industry and transportation. As one of the few tools that is capable of depicting the distribution of hydrogen in steels, time-of-flight secondary ion mass spectrometry was conducted after electrochemical charging. To obtain further information about the structural composition and cracking behavior, electron-backscattered diffraction and scanning electron microscopy were performed. Gathered data of chemical composition and topography were treated employing data fusion, thus creating a comprehensive portrait of hydrogen-induced effects in the austenite grade AISI 304L. Specimens were electrochemically charged with deuterium instead of hydrogen. This arises from the difficulties to distinguish between artificially charged hydrogen and traces existing in the material or the rest gas in the analysis chamber. Similar diffusion and permeation behavior, as well as solubility, allow nonetheless to draw conclusions from the experiments.
The development of hydrogen technologies is a key strategy to reduce greenhouse gas emission worldwide. Power-to-Gas is a challenging solution, in which hydrogen and methane can be used in mobility, industry, heat supply and electriity generation applications. This presentation deals with the tribological behaviour of polymer materials in hydrogen and methane, both in gas and in liquid form.
Martensitic 9 %-Cr steels like P91 and P92 show susceptibility to delayed hydrogen assisted cracking depending on their microstructure. In that connection, effective hydrogen diffusion coefficients are used to assess the possible time-delay. The small number of available diffusion coefficients varies already at room temperature by several orders of magnitude (mostly regarded as result of present microstructure). Especially P91 weld metal diffusion coefficients are rare so far. For that reason, electrochemical permeation experiments had been conducted using P92 base metal and P91 weld metal (in as-welded and heat-treated condition) with different thicknesses. The diffusion coefficients are calculated by two methods (time-lag and inflection point method) were performed. The results show that, despite of microstructural effects, the sample thickness must be considered as it influences the calculated diffusion coefficients. Finally, the comparison of calculated and measured hydrogen concentrations (determined by carrier gas hot extraction) enables the identification of realistic diffusion coefficients.
Martensitic 9 %-Cr steels like P91 and P92 show susceptibility to delayed hydrogen assisted cracking depending on their microstructure. In that connection, effective hydrogen diffusion coefficients are used to assess the possible time-delay. The small number of available diffusion coefficients varies already at room temperature by several orders of magnitude (mostly regarded as result of present microstructure). Especially P91 weld metal diffusion coefficients are rare so far. For that reason, electrochemical permeation experiments had been conducted using P92 base metal and P91 weld metal (in as-welded and heat-treated condition) with different thicknesses. The diffusion coefficients are calculated by two methods (time-lag and inflection point method) were performed. The results show that, despite of microstructural effects, the sample thickness must be considered as it influences the calculated diffusion coefficients. Finally, the comparison of calculated and measured hydrogen concentrations (determined by carrier gas hot extraction) enables the identification of realistic diffusion coefficients.
As more industrial interests focusing on using salt caverns and repurposed gas or petroleum reservoirs for alternative fuel storage, i.e. CO2/H2, the question raises whether microorganisms may impact the infrastructure, gas purity and storage condition over time.
Environments with high salinity (> 1.5 Meq of NaCl) are resided by halophiles (salt-loving microorganisms). To compensate for the intensive osmotic stress, they have resorted to two main adaptation strategies: 1) production of compatible solutes and 2) accumulation of intracellular KCl. Microbial community analysis of several high salinity environments revealed a number of recurring genera, including Halomonas and Halanaerobium. However, the impact of halophiles on the overall integrity and stability of the storage facilities remain largely unknown.
To evaluate the suitability and stability of saline storage facilities, several model halophilic microorganisms, such as members of Halomonas, will be selected as testing subjects. First, the impact of halophiles on the infrastructure will be determined using an integrative approach by combining a number of techniques, including electrochemistry, TOF-SIMS, SEM/FIB/EDS and FIB-TEM. Second, the abilities of halophiles to alter the fuel composition (i.e. increase/decrease the fractions of H2) will be monitored using gas chromatography by growing them under high pressure.
As a result of climate change and the accompanying mandatory shift to renewable energy resources, microorganisms will continue to play an important role in the energy sector, both to their benefit and detriment. Thus, it is important to achieve a certain level of understanding regarding the activities and mechanisms of halophiles prior to large-scaled excursions.
Eight commercial austenitic stainless steels were tensile tested in reference atmosphere, in gaseous high-pressure hydrogen and in gaseous hydrogen precharged condition using conventional (CS) and tubular specimens (TS). For all configurations, 0.2 yield strength and ultimate tensile strength were comparable. In reference atmosphere, reduction of area of CS was higher compared to TS, whereas in gaseous high pressure hydrogen reduction of area of CS was lower compared to TS. In gaseous hydrogen precharged condition reduction of area of CS and TS were comparable for the severely affected grades. The differences in necking behavior between CS and TS are explained by different competitions between necking and hydrogen assisted crack initiation and growth especially for the tests in high pressure hydrogen gas.