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In this lecture, the safety assessment of hydrogen gas storage systems is presented using the example of composite pressure vessels. The main element is a probabilistic approval approach based on five steps. Firstly, the testing and evaluation of properties at the beginning of life are shown. Secondly, methods for artificial aging and the effect on the residual strength are presented. Thirdly, testing against dedicated accidents is introduced. Fourthly, effects on the surveillance of production quality are discussed. Finally, degradation and the end of life are estimated. Background information and examples are given for each step. The assessment presented is a method applicable for many safety-related systems.
Monte-Carlo-Analysis of Minimum Burst Requirements for Composite Cylinders for Hydrogen Service
(2021)
For achieving Net Zero-aims hydrogen is an indispensable component, probably the main component. For the usage of hydrogen, a wide acceptance is necessary, which requires trust in hydrogen based on absence of major incidents resulting from a high safety level. Burst tests stand for a type of testing that is used in every test standard and regulation as one of the key issues for ensuring safety in use. The central role of burst and proof test is grown to historical reasons for steam engines and steel vessels but - with respect for composite pressure vessels (CPVs) - not due an extraordinary depth of outcomes. Its importance results from the relatively simple test process with relatively low costs and gets its importance by running of the different test variations in parallel. In relevant test und production standards (as e. g. ECE R134) the burst test is used in at least 4 different meanings. There is the burst test on a) new CPVs and some others b) for determining the residual strength subsequent to various simulations of ageing effects. Both are performed during the approval process on a pre-series. Then there is c) the batch testing during the CPVs production and finally d) the 100% proof testing, which means to stop the burst test at a certain pressure level. These different aspects of burst tests are analysed and compared with respect to its importance for the resulting safety of the populations of CPVs in service based on experienced test results and Monte-Carlo simulations. As main criterial for this the expected failure rate in a probabilistic meaning is used. This finally ends up with recommendations for relevant RC&S especially with respect to GTR 13.
The introduction reflects the political background in Germany and worldwide concerning hydrogen as energy carrier. This leads to available hydrogen strategies and the reaction of BAM by launching the competence centre H2Safety@BAM. Fokus is set on the competence area TestCert, the special role of the division “Safety of Gas Storage Systems” there and its increasing success in research activities.
The main part explains the needs for a risk-controlled market ramp-up concerning hydrogen products and appropriate measures being under development in division 3.5: risk control, tools for consequence estimation and limitation, probabilistic assessment of end of safe life, the efficiency assessment and optimization of current regulations, the structural health monitoring (SHM) with necessary improvement of measures for quality management in the digital world of safety assessment. Last but not least, the wide range of full-scale testing and simulation of worst-case scenarios is explained.
This lecture shows an overview of cross-cutting topics whithin the dynamic sector of hydrogen technologies including European and other international strategies, legal and policy frameworks, networks and relevant stakeholders, research and demo-projects, regulations, codes & Standards as well as initiatives and associations concerning hydrogen safety and education.
Introduction of H2Safety@BAM
(2021)
This contribution for the Open Forum of the 8th HSN Symposium introduces the SensRef activities of the Competence Centre H2Safety@BAM.
The determination of the measurement uncertainty of quantitative and qualitative results is an important quality management tool, for example to describe measuring equipment, procedures, measurement results and the quality of products. The lecture presents the process description for the determination of the measurement uncertainty according to GUM, the determination of uncertainties in qualitative measurement results and the application of the measurement uncertainty for conformity assessment.
Sensor systems are widely used in hydrogen technologies. The lecture presents requirements and properties of sensor systems and shows application examples of these technologies for safety and process control for hydrogen technologies. The focus is on gas sensors as well as sensors for pressure, temperature and gas flow. These systems are applied, among other things, for monitoring and control of operating conditions, indication of hazardous conditions and triggering of alarms.
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. Limited data on room temperature diffusion coefficients reported in literature vary widely by several orders of magnitude (mostly attributed to variation in 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. From the results obtained, diffusion coefficients were calculated using to different methods, time-lag, and inflection point. Results show that, despite 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.
Ellipsometry-based approach for the characterization of mesoporous thin films for H2 technologies
(2021)
Porous thin layer materials are gaining importance in different fields of technology and pose a challenge to the accurate determination of materials properties important for their function. In this work, we demonstrate a hybrid measurement technique using ellipsometry together with other independent methods for validation. Ellipsometry provides information about the porosity of different mesoporous films (PtRuNP/OMC = 45%; IrOx = 46%) as well as about the pore size (pore radius of ca. 5 nm for PtRuNP/OMC). In addition, the electronic structure of a material, such as intraband transitions of a mesoporous IrOx film, can be identified, which can be used to better understand the mechanisms of chemical processes. In addition, we show that ellipsometry can be used as a scalable imaging and visualization method for quality assurance in production. These require accurate and traceable measurements, with reference materials playing an important role that include porosity and other related properties. We show that our novel analytical methods are useful for improving analytical work in this entire field.
Hydrogen production via water electrolysis will be an essential cornerstone in development of sustainable, fossil-free fuel and chemical production on a global scale. The activity and stability of each catalyst is highly dependent on the properties of the coating, i.e., phase composition, crystallinity, accessible surface area, and many other factors. The key to developing improved catalysts is a better understanding of the relationships between their performance, stability, and physicochemical properties. However, these relationships can be complex and are also strongly influenced by the reaction environment. Therefore, operando analysis of the catalyst material during catalysis at realistic potentials and current densities is highly desirable. However, many analytical techniques cannot be applied in liquid environments at realistic potentials and current densities.
We propose environmental ellipsometric analysis in a dedicated electrochemical flow cell as a method to evaluate gas evolution reactions operando under realistic working conditions. Figure 1 illustrates schematically the developed technique. Key factors to success are highly active model-type catalysts, a suitable sample environment, and a deep understanding of the appropriate model development, as well as concise cross validation with numerous other analytical techniques.
The method was developed and validated by analyzing a calcination series (300 – 600 °C) of mesoporous templated IrOx films ex-situ and operando under oxygen evolution reaction (OER) conditions. The employed environmental electrochemical spectroscopic ellipsometric (ECSE) analysis revealed during OER the change of optical and electronic properties, i.e. the dielectric functions, resistivity and band-to-band transitions (p-d band transitions). Film thickness and porosity were validated by means of scanning electron microscopy (SEM), X-ray reflectometry (XRR) or ellipsometric porosimetry (EP), electrical and electronic properties by means of conductivity measurements, X-ray photoelectron spectroscopy (XPS) or UV-Vis-NIR absorption spectroscopy. The electronic structures of the catalysts from valence electron energy loss spectra (VEELS) derived from ε1 and ε2 from SE measurements reveal a direct correlation with electrochemical activities in OER.
In the presentation reversible and irreversible potential-dependent changes of the catalyst properties during operation will be discussed along with the dynamics of gas formation, transport and dissolution at different potentials.