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Influence of Hydrogen Uptake and Diffusion in Structural Components in the Field of Renewable Energy
(2021)
Great efforts are invested worldwide in the development of efficient electrolysis processes, fuel cells technologies and hydrogen transport and storage infrastructures. This includes the exploitation of existing gas-grid infrastructure for the injection of hydrogen. Considering transport and storage facilities, the utilization of gaseous hydrogen can be divided into two main groups which are differentiating in the pressure regime. Fueling stations are operating in high pressure (>800 bar) and high purity and therefore use austenitic stainless steels in their compression systems. On the other hand, existing gas infrastructure where the natural gas is transported across long distances is usually operating with up to 300 bar. In this case the pipe-systems consist of several steel classes, mainly low alloyed steels in which the surface quality and the gas mixture are strongly varying.
Even though ingress of hydrogen can lead to catastrophic failures in all steels, its exact impact on the mechanical properties, as well as its interaction with the surface, microstructure and lattice and the underlying mechanisms remain unclear. Therefore, research on the impact of gaseous hydrogen in pressure vessels and pipes has clearly an integral part on the path to safe and sustainable use of the different components along the different chains. This becomes even more relevant considering the influence of impurities in the gas, e.g. sulfur and with the introduction of new production technologies, such as additive manufacturing, into the market.
Determination of these interactions and impact that might lead to the degradation of the properties can allow a safe use of steels in present and future hydrogen-based energy applications.
The following contribution gives an overview of the problem and introduction to the conventional and innovative tools used and developed nowadays to analyze it. For this purpose, materials were loaded with hydrogen by electrochemical means and under high pressure and elevated temperatures. The results presented provide an invaluable insight into the impact of hydrogen on the integrity of selected steels used in the two mentioned above applications. This work is part of an ongoing research in which mechanical, chemical, structural, and microstructural analyses tools are combined in-situ and ex-situ.
Um die Absorption von Wasserstoff und dessen Verhalten in den Werkstoffen beim Einsatz unter Druck-H2 sowie die H- abhängigen Materialeigenschaften zu definieren, entwickelt die BAM mit ihrer langjährigen Erfahrung adäquate Prüfkonzepte, die einsatzrelevante Bedingungen und reale Beanspruchungen (Temperatur, Wasserstoff und mech. Beanspruchung) hierarchisch berücksichtigen. Der Vortrag gibt eine Einführung in das Thema von wasserstoffunterstützen Materialschäden durch die Problematik der Einspeisung von Wasserstoff in bestehende Erdgasnetze. Ferner wird auf die Hochdruck-Infrastruktur (sowie H2-Tankstellen) und die Entwicklung von Prüfkonzepten für die Gasinfrastruktur unter Druckwasserstoffbeaufschlagung eingegangen.
Increasing environmental problems with conventional energy technology are stimulating the demand for alternative energy solutions. With air quality reaching catastrophic levels in large cities worldwide, Fuel Cell Electric Vehicles offer the ideal combination of clean power with the amenities of electric drives. Hydrogen use on vehicles, nevertheless, also raises some issues about safe handling. As fuel cells and hydrogen applications, including vehicles, approach technological maturity, developing their business cases becomes crucial in introducing them to the consumer markets.
The Joint European Summer School JESS 2021 addresses these issues by offering high quality graduate level courses on selected topics of vehicle technology, innovation & business development, safe handling of hydrogen, and modelling. This series of summer schools has been ongoing since 2004 and targets an audience of university students (MSc and PhD levels) and post-doctoral researchers. We also welcome more experienced researchers and engineers wishing to expand their general knowledge, for instance, to suit a newly acquired position or collect credits for Continuous Professional Development (CPD). The course content is tailored to the needs of a diverse audience: newcomers to the field, experienced students, and young professionals working at the forefront of fuel cell and hydrogen applications.
Duplex (DSS) and austenitic stainless steels (ASS) are frequently used in many energy related applications. The duplex grade is considered to have outstanding mechanical properties as well as good corrosion resistance. The austenitic phase combines high ductility, even at low temperatures, with sufficient strength, and therefore such materials are applied in storage and transport of high-pressure hydrogen. During service in acidic environments large amounts of hydrogen can ingress into the microstructure and induce many changes in the mechanical properties of the steel. Embrittlement of steels by hydrogen remains unclear even though this topic has been intensively studied for several decades. The reason for that lies in the inability to validate the proposed theoretical models in the sub-micron scale. Among the very few available methods nowadays, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) enables a highly accurate mapping of hydrogen in the microstructure in a spatial resolution below 100 nm. In the present work ToF-SIMS was used as a main tool in order to investigate the effect of deuterium on a duplex microstructure of lean and standard DSSs during and after the electrochemical charging process. Electrochemical charging simulates the service of a component in acidic environments under conditions of cathodic protection that are commonly applied to prevent corrosion reactions. ToF-SIMS after multivariate data analysis (MVA) was combined with high resolution topographic images and electron back-scattered diffraction (EBSD) data to characterize the structural changes. It was observed that the ferritic phase was affected almost identical in all steels whereas in the austenitic phase significant differences were obtained in the lean duplex in comparison to the standard DSS. The obtained results have been compared to similar investigations on a AISI 304L austenitic stainless steel. The advantage of the combined techniques is reflected by the ability to correlate the hydrogen distribution in the microstructure and the resulted phase transformation.
The use of duplex stainless steels (DSS) in energy related applications is well known. Nowadays, DSSs become more favorable than austenitic steels due to the outstanding mechanical properties, the good corrosion resistance and the lower nickel content.However, the use of the duplex grade in acidic environments such as seawater can lead to a severe degradation in the structural integrity of the steel by hydrogen-induced/assisted cracking mechanisms, which can eventually result in premature failure. Hydrogen assisted degradation and cracking of steels remains unclear even though this topic is intensively studied for more than a century. The main gap lies in the validation of the proposed theoretical models at the sub-micron scale. Industrial and the research communities define a need for an accurate method by which it is possible to image the distribution of hydrogen in the microstructure. Among the very few available methods nowadays, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) provides precise mapping of hydrogen in the microstructure. Moreover, the powerful combination of ToF-SIMS with multivariate data analysis (MVA), electron backscattered diffraction (EBSD) for providing a the structural information and the use of data fusion techniques can contribute to a better understanding of the hydrogen induced degradation processes in the material.
In the present work two types of duplex grades were chosen as a case study (standard and lean DSS). The duplex class, consist of equivalent amounts of ferrite and austenite, was investigated by ToF-SIMS and EBSD during and after electrochemical deuterium charging in order to simulate the service of a component in acidic environments. Deuterium is known to act on the steel similarly to hydrogen and therefore was used as a tracer for hydrogen. The results show that the ferrite was affected almost identical in both steels whereas in the austenitic phase significant differences were observed in the lean duplex in comparison to the standard duplex. The advantage of the combined techniques is reflected by the ability to correlate the hydrogen distribution in the microstructure to the resulted structural changes.
In the presented research, the high potential and abilities of secondary ion mass spectrometry (ToF-SIMS) to detect and locally map the hydrogen distribution in two types of duplex stainless steels are shown. The research validates certain proposed mechanisms by combining ToF-SIMS with high-resolution scanning electron microscopy and electron-backscattered diffraction. The combination of data from several techniques on the same region was conducted in this field for the first time by applying data treatment of the ToF-SIMS raw data and data fusion approach. This powerful combination of methods allows reviewing of the occurring processes related to hydrogen assisted cracking. The step beyond the state of the art in this field was gained here by developing permeation and mechanical loading experiments within the ToF-SIMS during chemometric imaging of the hydrogen distribution in the microstructure. The research presents the necessary correlation between the hydrogen distribution and the resulted structural changes, the diffusion behavior in a duplex microstructure and stress induced diffusion of hydrogen by applying external load at the microscale.
Due to its low mass and high diffusivity in presence of compositional, thermal and mechanical gradients, hydrogen within a metallic microstructure can result in severe loss in ductility even at low concentrations and might lead eventually to a catastrophic and unpredictable failure of structural components during service. In this context, hydrogen mapping at the microscale is still considered among the most important challenges on the pathway towards a better understanding of the hydrogen transport and assisted cracking phenomena in metals, specifically in structural components, e.g. steels.
Among the very few available techniques to localize hydrogen at the microscale, Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was proven to be a reliable tool. Based on the assumption that deuterium influence the microstructure similarly to hydrogen, in the following contribution ToF-SIMS was applied as the main technique to detect and locally map the deuterium distribution in several alloys: lean 2101 and standard 2205 duplex stainless steel (DSS), AISI 304L austenitic stainless steel and titanium 6Al-4V alloy. These alloys were selected as case studies in this work due to the wide use of them in many applications and environments which frequently provide critical conditions for hydrogen absorption and assisted degradation.
The innovative design of in-situ and ex-situ experiments enabled us to elucidate the permeation, transport and trapping of deuterium in the microstructure in sub-micron resolution for the first time. In addition to the novel experimental setups, further progress was gained by applying computational multivariate data analysis (MVA) on the raw data and data fusion with high resolution structural characterization methods (scanning electron microscopy and electron back-scattered diffraction – SEM/EBSD). This combination allowed us to correlate the deuterium distribution and the influence on the microstructure.
The following presentation provides an overview on some of the challenges with metallic materials used as structural materials in the energy sector for the transport and storage of hydrogen. The presentation contains explanations about the methodologies utilized to characterize the susceptibility of these materials for hydrogen.