Transmission, Distribution & Storage
Evaluation Techniques of Hydrogen Permeation in Sealing Rubber Materials
Dec 2020
Publication
Three techniques for determining the hydrogen permeation properties of rubber samples were developed based on the volumetric and gravimetric measurements of released H2 gas after sample decompression. These methods include gas chromatography (GC) by thermal desorption analysis (TDA) volumetric collection (VC) measurement of hydrogen by graduated cylinder and gravimetric (GM) measurement by electronic balance. By measuring the released hydrogen against elapsed time after the decompression of pressure the charging amount (C0) and diffusivity (D) were obtained with the developed diffusion analysis program. From these values the solubility (S) and permeability (P) of polymers were evaluated through the relations of Henry's law and P=SD respectively. The developed techniques were applied to three kinds of spherically shaped sealing rubber materials. D S and P were analyzed as a function of pressure. The transport behaviors obtained in the three methods are discussed and compared with the characteristics of each measuring technique. The correlations between transport parameters and carbon black filler or density are discussed.
Current Research Trends and Perspectives on Solid-State Nanomaterials in Hydrogen Storage
Jan 2021
Publication
Hydrogen energy with environment amicable renewable efficiency and cost-effective advantages is the future mainstream substitution of fossil-based fuel. However the extremely low volumetric density gives rise to the main challenge in hydrogen storage and therefore exploring effective storage techniques is key hurdles that need to be crossed to accomplish the sustainable hydrogen economy. Hydrogen physically or chemically stored into nanomaterials in the solid-state is a desirable prospect for effective large-scale hydrogen storage which has exhibited great potentials for applications in both reversible onboard storage and regenerable off-board storage applications. Its attractive points include safe compact light reversibility and efficiently produce sufficient pure hydrogen fuel under the mild condition. This review comprehensively gathers the state-of-art solid-state hydrogen storage technologies using nanostructured materials involving nanoporous carbon materials metal-organic frameworks covalent organic frameworks porous aromatic frameworks nanoporous organic polymers and nanoscale hydrides. It describes significant advances achieved so far and main barriers need to be surmounted to approach practical applications as well as offers a perspective for sustainable energy research.
Micro-grid Design and Life-cycle Assessment of a Mountain Hut's Stand-alone Energy System with Hydrogen Used for Seasonal Storage
Dec 2020
Publication
Mountain huts as special stand-alone micro-grid systems are not connected to a power grid and represent a burden on the environment. The micro-grid has to be flexible to cover daily and seasonal fluctuations. Heat and electricity are usually generated with fossil fuels due to the simple on-off operation. By introducing renewable energy sources (RESs) the generation of energy could be more sustainable but the generation and consumption must be balanced. The paper describes the integration of a hydrogen-storage system (HSS) and a battery-storage system (BattS) in a mountain hut. The HSS involves a proton-exchange-membrane water electrolyser (PEMWE) a hydrogen storage tank (H2 tank) a PEM fuel cell (PEMFC) and a BattS consisting of lead-acid batteries. Eight micro-grid configurations were modelled using HOMER and evaluated from the technical environmental and economic points of view. A life-cycle assessment analysis was made from the cradle to the gate. The micro-grid configurations with the HSS achieve on average a more than 70% decrease in the environmental impacts in comparison to the state of play at the beginning but require a larger investment. Comparing the HSS with the BattS as a seasonal energy storage the hydrogen-based technology had advantages for all of the assessed criteria.
H21- Leeds City Gate Project Report
Jul 2016
Publication
The H21 Leeds City Gate project is a study with the aim of determining the feasibility from both a technical and economic viewpoint of converting the existing natural gas network in Leeds one of the largest UK cities to 100% hydrogen. The project has been designed to minimise disruption for existing customers and to deliver heat at the same cost as current natural gas to customers. The project has shown that:
The project has provided costs for the scheme and has modelled these costs in a regulatory finance model. In addition the availability of low-cost bulk hydrogen in a gas network could revolutionise the potential for hydrogen vehicles and via fuel cells support a decentralised model of combined heat and power and localised power generation.
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
- The gas network has the correct capacity for such a conversion
- It can be converted incrementally with minimal disruption to customers
- Minimal new energy infrastructure will be required compared to alternatives
- The existing heat demand for Leeds can be met via steam methane reforming and salt cavern storage using technology in use around the world today
The project has provided costs for the scheme and has modelled these costs in a regulatory finance model. In addition the availability of low-cost bulk hydrogen in a gas network could revolutionise the potential for hydrogen vehicles and via fuel cells support a decentralised model of combined heat and power and localised power generation.
This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.
Metallurgical Model of Diffusible Hydrogen and Non-Metallic Slag Inclusions in Underwater Wet Welding of High-Strength Steel
Nov 2020
Publication
High susceptibility to cold cracking induced by diffusible hydrogen and hydrogen embrittlement are major obstacles to greater utilization of underwater wet welding for high-strength steels. The aim of the research was to develop gas–slag systems for flux-cored wires that have high metallurgical activity in removal of hydrogen and hydroxyl groups. Thermodynamic modeling and experimental research confirmed that a decrease in the concentration of diffusible hydrogen can be achieved by reducing the partial pressure of hydrogen and water vapor in the vapor–gas bubble and by increasing the hydroxyl capacity of the slag system in metallurgical reactions leading to hydrogen fluoride formation and ionic dissolution of hydroxyl groups in the basic fluorine-containing slag of a TiO2–CaF2–Na3AlF6 system.
Cohesive Zone Modelling of Hydrogen Assisted Fatigue Crack Growth: The Role of Trapping
Apr 2022
Publication
We investigate the influence of microstructural traps in hydrogen-assisted fatigue crack growth. To this end a new formulation combining multi-trap stress-assisted diffusion mechanism-based strain gradient plasticity and a hydrogen- and fatigue-dependent cohesive zone model is presented and numerically implemented. The results show that the ratio of loading frequency to effective diffusivity governs fatigue crack growth behaviour. Increasing the density of beneficial traps not involved in the fracture process results in lower fatigue crack growth rates. The combinations of loading frequency and carbide trap densities that minimise embrittlement susceptibility are identified providing the foundation for a rational design of hydrogen-resistant alloys.
Wood Cellulose as a Hydrogen Storage Material
Apr 2020
Publication
Hydrogen has become a strong candidate to be a future energy storage medium but there are technological challenges both in its production and storage. For storage a search for lightweight abundant and non-toxic materials is on the way. An abundant natural material such as wood cellulose would make an ideal storage medium from a sustainability perspective. Here using a combination of static DFT calculations and ab initio molecular dynamics simulations at different temperatures it is shown that wood cellulose has the ability to uptake H2 via a physisorption mechanism based on dispersion interactions of the van der Waals type involving the O-atoms of the d-glucose rings. The absorption causes little to no disturbances on the cellulose structure and H2 is highly mobile in the material. At an external pressure of H2(g) of 0.09 atm and T = 25 °C cellulose has a theoretical gravimetric density of hydrogen storage of ≈1%.
Hydrogen Embrittlement: The Game Changing Factor in the Applicability of Nickel Alloys in Oilfield Technology
Jun 2017
Publication
Precipitation hardenable (PH) nickel (Ni) alloys are often the most reliable engineering materials for demanding oilfield upstream and subsea applications especially in deep sour wells. Despite their superior corrosion resistance and mechanical properties over a broad range of temperatures the applicability of PH Ni alloys has been questioned due to their susceptibility to hydrogen embrittlement (HE) as confirmed in documented failures of components in upstream applications. While extensive work has been done in recent years to develop testing methodologies for benchmarking PH Ni alloys in terms of their HE susceptibility limited scientific research has been conducted to achieve improved foundational knowledge about the role of microstructural particularities in these alloys on their mechanical behaviour in environments promoting hydrogen uptake. Precipitates such as the γ′ γ′′ and δ-phase are well known for defining the mechanical and chemical properties of these alloys. To elucidate the effect of precipitates in the microstructure of the oil-patch PH Ni alloy 718 on its HE susceptibility slow strain rate tests under continuous hydrogen charging were conducted on material after several different age-hardening treatments. By correlating the obtained results with those from the microstructural and fractographic characterization it was concluded that HE susceptibility of oil-patch alloy 718 is strongly influenced by the amount and size of precipitates such as the γ′ and γ′′ as well as the δ-phase rather than by the strength level only. In addition several HE mechanisms including hydrogen-enhanced decohesion and hydrogen-enhanced local plasticity were observed taking place on oil-patch alloy 718 depending upon the characteristics of these phases when present in the microstructure.
Link to document download on Royal Society Website
Link to document download on Royal Society Website
Nonlinear Model Predictive Control of an Autonomous Power System Based on Hydrocarbon Reforming and High Temperature Fuel Cell
Mar 2021
Publication
The integration and control of energy systems for power generation consists of multiple heterogeneous subsystems such as chemical electrochemical and thermal and contains challenges that arise from the multi-way interactions due to complex dynamic responses among the involved subsystems. The main motivation of this work is to design the control system for an autonomous automated and sustainable system that meets a certain power demand profile. A systematic methodology for the integration and control of a hybrid system that converts liquefied petroleum gas (LPG) to hydrogen which is subsequently used to generate electrical power in a high-temperature fuel cell that charges a Li-Ion battery unit is presented. An advanced nonlinear model predictive control (NMPC) framework is implemented to achieve this goal. The operational objective is the satisfaction of power demand while maintaining operation within a safe region and ensuring thermal and chemical balance. The proposed NMPC framework based on experimentally validated models is evaluated through simulation for realistic operation scenarios that involve static and dynamic variations of the power load.
A Hybrid Energy Storage System Using Compressed Air and Hydrogen as the Energy Carrier
Feb 2020
Publication
In this paper an innovative concept of an energy storage system that combines the idea of energy storage through the use of compressed air and the idea of energy storage through the use of hydrogen (with its further conversion to synthetic natural gas) has been proposed. The thermal integration of two sub-systems allows for efficient storage of large amounts of energy based on the use of pressure tanks with limited volumes. A thermodynamic assessment of the integrated hybrid system was carried out. For the assumed operation parameters an energy storage efficiency value of 38.15% was obtained which means the technology is competitive with intensively developed pure hydrogen energy storage technologies. The results obtained for the hybrid system were compared to the results obtained for three reference systems each of which uses hydrogen generators. The first is a typical Power-to-H2-to-Power system which integrates hydrogen generators with a fuel cell system. The other two additionally use a compressed air energy storage installation. In the first case the compressed air energy storage system consists of a diabatic system. In the second case the compressed air energy storage system is adiabatic. The article has discussed the disadvantages and advantages of all the analyzed systems.
Freeze-dried Ammonia Borane-polyethylene Oxide Composites: Phase Behaviour and Hydrogen Release
Feb 2018
Publication
A solid-state hydrogen storage material comprising ammonia borane (AB) and polyethylene oxide (PEO) has been produced by freeze-drying from aqueous solutions from 0% to 100% AB by mass. The phase mixing behaviour of AB and PEO has been investigated using X-ray diffraction which shows that a new ‘intermediate’ crystalline phase exists different from both AB and PEO as observed in our previous work (Nathanson et al. 2015). It is suggested that hydrogen bonding interactions between the ethereal oxygen atom (–O–) in the PEO backbone and the protic hydrogen atoms attached to the nitrogen atom (N–H) of AB molecules promote the formation of a reaction intermediate leading to lowered hydrogen release temperatures in the composites compared to neat AB. PEO also acts to significantly reduce the foaming of AB during hydrogen release. A temperature-composition phase diagram has been produced for the AB-PEO system to show the relationship between phase mixing and hydrogen release.
Analysis of Environmentally Assisted Cracking Processes in Notched Steels Using the Point Method
Sep 2019
Publication
This paper proposes the use of the Point Method (PM) to analyse Environmentally Assisted Cracking (EAC) processes in steels containing U-shaped notches. The PM a methodology included within the Theory of Critical Distances (TCD) has been extensively validated by many authors for the analysis of fracture and fatigue phenomena of different types of materials containing notches. However it has never been applied to other critical or subcritical cracking processes such as EAC or creep crack propagation.<br/>This work provides a PM-based analysis of EAC emanating from notches which is validated by testing CT notched specimens of X80 and S420 steels subjected to aggressive environments under hydrogen embrittlement conditions.<br/>The results reveal that the PM accurately predicts the crack propagation onset condition as well as the evolution of the material’s apparent EAC resistance.
The Role of Hydrogen in Hydrogen Embrittlement of Metals: The Case of Stainless Steel
Apr 2019
Publication
Hydrogen embrittlement (HE) of metals has remained a mystery in materials science for more than a century. To try to clarify this mystery tensile tests were conducted at room temperature (RT) on a 316 stainless steel (SS) in air and hydrogen of 70 MPa. With an aim to directly observe the effect of hydrogen on ordering of 316 SS during deformation electron diffraction patterns and images were obtained from thin foils made by a focused ion beam from the fracture surfaces of the tensile specimens. To prove lattice contraction by ordering a 40% CW 316 SS specimen was thermally aged at 400 °C to incur ordering and its lattice contraction by ordering was determined using neutron diffraction by measuring its lattice parameters before and after aging. We demonstrate that atomic ordering is promoted by hydrogen leading to formation of short-range order and a high number of planar dislocations in the 316 SS and causing its anisotropic lattice contraction. Hence hydrogen embrittlement of metals is controlled by hydrogen-enhanced ordering during RT deformation in hydrogen. Hydrogen-enhanced ordering will cause the ordered metals to be more resistant to HE than the disordered ones which is evidenced by the previous observations where furnace-cooled metals with order are more resistant to HE than water-quenched or cold worked metals with disorder. This finding strongly supports our proposal that strain-induced martensite is a disordered phase.
Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging
Aug 2019
Publication
Herein the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2 leading to a fracture in the elastic deformation stage.
Investigation of the Multi-Point Injection of Green Hydrogen from Curtailed Renewable Power into a Gas Network
Nov 2020
Publication
Renewable electricity can be converted into hydrogen via electrolysis also known as power-to-H2 (P2H) which when injected in the gas network pipelines provides a potential solution for the storage and transport of this green energy. Because of the variable renewable electricity production the electricity end-user’s demand for “power when required” distribution and transmission power grid constrains the availability of renewable energy for P2H can be difficult to predict. The evaluation of any potential P2H investment while taking into account this consideration should also examine the effects of incorporating the produced green hydrogen in the gas network. Parameters including pipeline pressure drop flowrate velocity and most importantly composition and calorific content are crucial for gas network management. A simplified representation of the Irish gas transmission network is created and used as a case study to investigate the impact on gas network operation of hydrogen generated from curtailed wind power. The variability in wind speed and gas network demands that occur over a 24 h period and with network location are all incorporated into a case study to determine how the inclusion of green hydrogen will affect gas network parameters. This work demonstrates that when using only curtailed renewable electricity during a period with excess renewable power generation despite using multiple injection points significant variation in gas quality can occur in the gas network. Hydrogen concentrations of up to 15.8% occur which exceed the recommended permitted limits for the blending of hydrogen in a natural gas network. These results highlight the importance of modelling both the gas and electricity systems when investigating any potential P2H installation. It is concluded that for gas networks that decarbonise through the inclusion of blended hydrogen active management of gas quality is required for all but the smallest of installations.
A Review of Cohesive Zone Modelling as an Approach for Numerically Assessing Hydrogen Embrittlement of Steel Structures
Jun 2014
Publication
Simulation of hydrogen embrittlement (HE) requires a coupled approach; on one side the models describing hydrogen transport must account for local mechanical fields while on the other side the effect of hydrogen on the accelerated material damage must be implemented into the model describing crack initiation and growth. This study presents a review of coupled diffusion and cohesive zone modelling as a method for numerically assessing HE of a steel structure. While the model is able to reproduce single experimental results by appropriate fitting of the cohesive parameters there appears to be limitations in transferring these results to other hydrogen systems. Agreement may be improved by appropriately identifying the required input parameters for the particular system under study.
Link to document download on Royal Society Website
Link to document download on Royal Society Website
Technologies and Infrastructures Underpinning Future CO2 Value Chains: A Comprehensive Review and Comparative Analysis
Feb 2018
Publication
In addition to carbon capture and storage efforts are also being focussed on using captured CO2 both directly as a working fluid and in chemical conversion processes as a key strategy for mitigating climate change and achieving resource efficiency. These processes require large amounts of energy which should come from sustainable and ideally renewable sources. A strong value chain is required to support the production of valuable products from CO2 . A value chain is a network of technologies and infrastructures (such as conversion transportation storage) along with its associated activities (such as sourcing raw materials processing logistics inventory management waste management) required to convert low-value resources to high-value products and energy services and deliver them to customers. A CO2 value chain involves production of CO2 (involving capture and purification) technologies that convert CO2 and other materials into valuable products sourcing of low-carbon energy to drive all of the transformation processes required to convert CO2 to products (including production of hydrogen syngas methane etc.) transport of energy and materials to where they are needed managing inventory levels of resources and delivering the products to customers all in order to create value (economic environmental social etc.).
Technologies underpinning future CO2 value chains were examined. CO2 conversion technologies such as urea production Sabatier synthesis Fischer-Tropsch synthesis hydrogenation to methanol dry reforming hydrogenation to formic acid and electrochemical reduction were assessed and compared based on key performance indicators such as: CAPEX OPEX electricity consumption TRL product price net CO2 consumption etc. Technologies for transport and storage of key resources are also discussed. This work lays the foundation for a comprehensive whole-system value chain analysis modelling and optimisation.
Technologies underpinning future CO2 value chains were examined. CO2 conversion technologies such as urea production Sabatier synthesis Fischer-Tropsch synthesis hydrogenation to methanol dry reforming hydrogenation to formic acid and electrochemical reduction were assessed and compared based on key performance indicators such as: CAPEX OPEX electricity consumption TRL product price net CO2 consumption etc. Technologies for transport and storage of key resources are also discussed. This work lays the foundation for a comprehensive whole-system value chain analysis modelling and optimisation.
Alloy Optimization for Reducing Delayed Fracture Sensitivity of 2000 MPa Press Hardening Steel
Jun 2020
Publication
Press hardening steel (PHS) is widely applied in current automotive body design. The trend of using PHS grades with strengths above 1500 MPa raises concerns about sensitivity to hydrogen embrittlement. This study investigates the hydrogen delayed fracture sensitivity of steel alloy 32MnB5 with a 2000 MPa tensile strength and that of several alloy variants involving molybdenum and niobium. It is shown that the delayed cracking resistance can be largely enhanced by using a combination of these alloying elements. The observed improvement appears to mainly originate from the obstruction of hydrogen-induced damage incubation mechanisms by the solutes as well as the precipitates of these alloying elements.
Dynamic Operation of Fischer-Tropsch Reactors for Power-to-liquid Concepts: A Review
Apr 2022
Publication
The Fischer-Tropsch synthesis (FTS) is considered as a power-to-X (PtX) storage concept for converting temporally available excess energy to fuels or chemical compounds without the need of fossil resources. Fluctuating energy supplies demand a load-flexible energy system and a dynamically operating FTS reactor might be beneficial compared to traditional steady-state operations which rely on expensive upstream buffer capacities. This review provides an overview of recent experimental and simulation studies dealing with dynamic FTS operation and summarizes the main findings. The results are presented the two categories process intensification and PtX application. The review further discusses the experimentally difficult task of wide-ranging product characterization with a high temporal resolution. While dynamic reactor operation is often related to a complicated process control which challenges a save and efficient reactor performance the literature findings indicate that for dynamic FTS operation such concerns might not be as critical as assumed at least within well-known boundaries. Researchers further agree that dynamic operation might be a tool for process intensification. Especially hydrogen pulsing seems to be a potentially beneficial operating technique to remove accumulated liquid products restore initial catalyst activity and increase diesel-range productivity. The main challenge in this context is the prevention of high methane selectivity. A lucid future engineering goal seems to be the combination of the two applications: a robust and reliable FTS reactor in a PtX scenario that not only handles a fluctuating feed but uses such variations for process enhancement.
Stress–Corrosion Cracking of AISI 316L Stainless Steel in Seawater Environments: Effect of Surface Machining
Oct 2020
Publication
To understand the effect of surface machining on the resistance of AISI 316L to SCC (stress–corrosion cracking) in marine environments we tested nuts surface-machined by different methods in a seawater-spraying chamber. Two forms of cracks were observed: on the machined surface and underneath it. On the surface cracks connected with the pitting sites were observed to propagate perpendicular to the hoop-stress direction identifying them as stress–corrosion cracks. Under the surface catastrophic transgranular cracks developed likely driven by hydrogen embrittlement caused by the chloride-concentrating level of humidity in the testing environment. Under constant testing conditions significantly different SCC resistance was observed depending on how the nuts had been machined. Statistical evaluation of the nut surface-crack density indicates that machining by a “form” tool yields a crack density one order of magnitude lower than machining by a “single-point” tool. Microstructural analysis of form-tool-machined nuts revealed a homogeneous deformed subsurface zone with nanosized grains leading to enhanced surface hardness. Apparently the reduced grain size and/or the associated mechanical hardening improve resistance to SCC. The nanograin subsurface zone was not observed on nuts machined by a single-point tool. Surface roughness measurements indicate that single-point-tool-machined nuts have a rougher surface than form-tool machined nuts. Apparently surface roughness reduces SCC resistance by increasing the susceptibility to etch attack in Cl--rich solutions. The results of X-ray diffractometry and transmission electron microscopy diffractometry indicate that machining with either tool generates a small volume fraction (< 0.01) of strain-induced martensite. However considering the small volume fraction and absence of martensite in regions of cracking martensite is not primarily responsible for SCC in marine environments.
Impact of Chemical Inhomogeneities on Local Material Properties and Hydrogen Environment Embrittlement in AISI 304L Steels
Feb 2018
Publication
This study investigated the influence of segregations on hydrogen environment embrittlement (HEE) of AISI 304L type austenitic stainless steels. The microstructure of tensile specimens that were fabricated from commercially available AISI 304L steels and tested by means of small strain-rate tensile tests in air as well as hydrogen gas at room temperature was investigated by means of combined EDS and EBSD measurements. It was shown that two different austenitic stainless steels having the same nominal alloy composition can exhibit different susceptibilities to HEE due to segregation effects resulting from different production routes (continuous casting/electroslag remelting). Local segregation-related variations of the austenite stability were evaluated by thermodynamic and empirical calculations. The alloying element Ni exhibits pronounced segregation bands parallel to the rolling direction of the material which strongly influences the local austenite stability. The latter was revealed by generating and evaluating two-dimensional distribution maps for the austenite stability. The formation of deformation-induced martensite was shown to be restricted to segregation bands with a low Ni content. Furthermore it was shown that the formation of hydrogen induced surface cracks is strongly coupled with the existence of surface regions of low Ni content and accordingly low austenite stability. In addition the growth behavior of hydrogen-induced cracks was linked to the segregation-related local austenite stability.
Concept of Hydrogen Fired Gas Turbine Cycle with Exhaust Gas Recirculation: Assessment of Process Performance
Nov 2019
Publication
High hydrogen content fuels can be used in gas turbine for power generation with CO2 capture IGCC plants or with hydrogen from renewables. The challenge for the engine is the high reactive combustion properties making dilution necessary to mitigate NOx emissions at the expense of a significant energy cost. In the concept analysed in this study high Exhaust Gas Recirculation (EGR) rate is applied to the gas turbine to generate oxygen depleted air. As a result combustion temperature is inherently limited keeping NOx emissions low without the need for dilution or unsafe premixing. The concept is analysed by process simulation based on a reference IGCC plant with CO2 Capture. Results with dry and wet EGR options are presented as a function EGR rate. Efficiency performance is assessed against the reference power cycle with nitrogen dilution. All EGR options are shown to represent an efficiency improvement. Nitrogen dilution is found to have a 1.3% efficiency cost. Although all EGR options investigated offer an improvement dry EGR is considered as the preferred option despite the need for higher EGR rate as compared with the wet EGR. The efficiency gain is calculated to be of 1% compared with the reference case.
Pressurized Hydrogen from Charged Liquid Organic Hydrogen Carrier Systems by Electrochemical Hydrogen Compression
Feb 2021
Publication
We demonstrate that the combination of hydrogen release from a Liquid Organic Hydrogen Carrier (LOHC) system with electrochemical hydrogen compression (EHC) provides three decisive advantages over the state-of-the-art hydrogen provision from such storage system: a) The EHC device produces reduced hydrogen pressure on its suction side connected to the LOHC dehydrogenation unit thus shifting the thermodynamic equilibrium towards dehydrogenation and accelerating the hydrogen release; b) the EHC device compresses the hydrogen released from the carrier system thus producing high value compressed hydrogen; c) the EHC process is selective for proton transport and thus the process purifies hydrogen from impurities such as traces of methane. We demonstrate this combination for the production of compressed hydrogen (absolute pressure of 6 bar) from perhydro dibenzyltoluene at dehydrogenation temperatures down to 240 °C in a quality suitable for fuel cell operation e.g. in a fuel cell vehicle. The presented technology may be highly attractive for providing compressed hydrogen at future hydrogen filling stations that receive and store hydrogen in a LOHC-bound manner.
Baking Effect on Desorption of Diffusible Hydrogen and Hydrogen Embrittlement on Hot-Stamped Boron Martensitic Steel
Jun 2019
Publication
Recently hot stamping technology has been increasingly used in automotive structural parts with ultrahigh strength to meet the standards of both high fuel efficiency and crashworthiness. However one issue of concern regarding these martensitic steels which are fabricated using a hot stamping procedure is that the steel is highly vulnerable to hydrogen delayed cracking caused by the diffusible hydrogen flow through the surface reaction of the coating in a furnace atmosphere. One way to make progress in understanding hydrogen delayed fractures is to elucidate an interaction for desorption with diffusible hydrogen behavior. The role of diffusible hydrogen on delayed fractures was studied for different baking times and temperatures in a range of automotive processes for hot-stamped martensitic steel with aluminum- and silicon-coated surfaces. It was clear that the release of diffusible hydrogen is effective at higher temperatures and longer times making the steel less susceptible to hydrogen delayed fractures. Using thermal desorption spectroscopy the phenomenon of the hydrogen delayed fracture was attributed to reversible hydrogen in microstructure sites with low trapping energy.
Influence of Microstructural Anisotropy on the Hydrogen-assisted Fracture of Notched Samples of Progressively Drawn Pearlitic Steel
Dec 2020
Publication
In this study fracture surfaces of notched specimens of pearlitic steels subjected to constant extension rate tests (CERTs) are analyzed in an environment causing hydrogen assisted fracture. In order to obtain general results both different notched geometries (to generate quite distinct stress triaxiality distributions in the vicinity of the notch tip) and diverse loading rates were used. The fracture surfaces were classified in relation to four micromechanical models of hydrogen-assisted micro-damage. To this end fractographic analysis in each fracture surface was carried out with a scanning electron microscopy. Generated results increase the number of micromechanical models found in the scientific literature.
Assessment of the Contribution of Internal Pressure to the Structural Damage in a Hydrogen-charged Type 316L Austenitic Stainless Steel During Slow Strain Rate Tensile Test
Dec 2018
Publication
The aim of this study is to provide a quantification of the internal pressure contribution to the SSRT properties of H-charged Type-316L steel tested in air at room temperature. Considering pre-existing penny-shaped voids the transient pressure build-up has been simulated as well as its impact on the void growth by preforming JIc calculations. Several void distributions (size and spacing) have been considered. Simulations have concluded that there was no impact of the internal pressure on the void growth regardless the void distribution since the effective pressure was on the order of 1 MPa during the SSRT test. Even if fast hydrogen diffusion related to dislocation pipe-diffusion has been assessed as a conservative case the impact on void growth was barely imperceptible (or significantly low). The effect of internal pressure has been experimentally verified via the following conditions: (I) non-charged in vacuum; (II) H-charged in vacuum; (III) H-charged in 115-MPa nitrogen gas; (IV) non-charged in 115-MPa nitrogen gas. As a result the relative reduction in area (RRA) was 0.84 for (II) 0.88 for (III) and 1.01 for (IV) respectively. The difference in void morphology of the H-charged specimens did not depend on the presence of external pressure. These experimental results demonstrate that the internal pressure had no effect on the tensile ductility and void morphology of the H-charged specimen.
UV Assisted on Titanium Doped Electrode for Hydrogen Evolution from Artificial Wastewater
Jul 2018
Publication
Formaldehyde (H2CO) is the harmful chemical that used in variety of industries. However there are many difficulties to treat discharged H2CO in the wastewater. Hydrogen energy is arising as a one of the renewable energy that can replace fossil fuel. Many researches have been conducted on hydrogen production from electrolysis using expensive metal electrodes and catalysts such as platinum (Pt) and palladium (Pd). However they are expensive and have obstacles to directly use from the production. We used copper (Cu) as an electrode substrate because it has a good current density. To avoid corrosion issue of Cu substrate we used commercially available carbon (C) coated Cu substrate and synthesized titanium (Ti) on C/Cu substrate. We found that Ti was well synthesized and stayed on substrate after hydrogen evolution reaction (HER) in artificial wastewater. Moreover we quantified hydrogen production from the wastewater and compared it to pure water. Hydrogen production was enhanced in wastewater and H2CO was decomposed after reaction. We expected to use Ti-C/Cu electrode for hydrogen production of wastewater by electrolysis.
Highly Porous Organic Polymers for Hydrogen Fuel Storage
Apr 2019
Publication
Hydrogen (H2) is one of the best candidates to replace current petroleum energy resources due to its rich abundance and clean combustion. However the storage of H2presents a major challenge. There are two methods for storing H2 fuel chemical and physical both of which have some advantages and disadvantages. In physical storage highly porous organic polymers are of particular interest since they are low cost easy to scale up metal-free and environmentally friendly.
In this review highly porous polymers for H2 fuel storage are examined from five perspectives:
(a) brief comparison of H2 storage in highly porous polymers and other storage media;
(b) theoretical considerations of the physical storage of H2 molecules in porous polymers;
(c) H2 storage in different classes of highly porous organic polymers;
(d) characterization of microporosity in these polymers; and
(e) future developments for highly porous organic polymers for H2 fuel storage. These topics will provide an introductory overview of highly porous organic polymers in H2 fuel storage.
In this review highly porous polymers for H2 fuel storage are examined from five perspectives:
(a) brief comparison of H2 storage in highly porous polymers and other storage media;
(b) theoretical considerations of the physical storage of H2 molecules in porous polymers;
(c) H2 storage in different classes of highly porous organic polymers;
(d) characterization of microporosity in these polymers; and
(e) future developments for highly porous organic polymers for H2 fuel storage. These topics will provide an introductory overview of highly porous organic polymers in H2 fuel storage.
Internal and Surface Damage after Electrochemical Hydrogen Charging for Ultra Low Carbon Steel with Various Degrees of Recrystallization
Jul 2016
Publication
An ultra low carbon (ULC) steel was subjected to electrochemical hydrogen charging to provoke hydrogen induced damage in the material. The damage characteristics were analyzed for recrystallized partially recrystallized and cold deformed material. The goal of the study is to understand the effect of cold deformation on the hydrogen induced cracking behavior of a material which is subjected to cathodic hydrogen charging. Additionally charging conditions i.e. charging time and current density were varied in order to identify correlations between on the one hand crack initiation and propagation and on the other hand the charging conditions. The obtained hydrogen induced cracks were studied by optical microscopy scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Hydrogen induced cracks were observed to propagate transgranularly independently of the state of the material. Deformed samples were considerably more sensitive to hydrogen induced cracking which implies the important role of dislocations in hydrogen induced damage mechanisms.
Chemical Utilization of Hydrogen from Fluctuating Energy Sources- Catalytic Transfer Hydrogenation from Charged Liquid Organic Hydrogen Carrier Systems
Nov 2015
Publication
Liquid Organic Hydrogen Carrier (LOHC) systems offer a very attractive way for storing and distributing hydrogen from electrolysis using excess energies from solar or wind power plants. In this contribution an alternative high-value utilization of such hydrogen is proposed namely its use in steady-state chemical hydrogenation processes. We here demonstrate that the hydrogen-rich form of the LOHC system dibenzyltoluene/perhydro-dibenzyltoluene can be directly applied as sole source of hydrogen in the hydrogenation of toluene a model reaction for large-scale technical hydrogenations. Equilibrium experiments using perhydro-dibenzyltoluene and toluene in a ratio of 1:3 (thus in a stoichiometric ratio with respect to H2) yield conversions above 60% corresponding to an equilibrium constant significantly higher than 1 under the applied conditions (270 °C).
Paving the Way to the Fuel of the Future—Nanostructured Complex Hydrides
Dec 2022
Publication
Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However several drawbacks have detracted this material from going mainstream and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies either in the pristine or nanoconfined state coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H2 which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.
Hydrogen Embrittlement Susceptibility of Prestressing Steel Wires: The Role of the Cold-drawing Conditions
Jul 2016
Publication
Prestressing steel wires are highly susceptible to hydrogen embrittlement (HE). Residual stress-strain state produced after wire drawing plays an essential role since hydrogen damage at certain places of the material is directly affected by stress and strain fields. Changes in wire drawing conditions modify the stress and strain fields and consequently the HE susceptibility and life in service of these structural components in the presence of a hydrogenating environment. This paper analyzes the distributions of residual stress and plastic strain obtained after diverse drawing conditions (inlet die angle die bearing length varying die angle and straining path) and their influence on HE susceptibility of the wires. The conditions for industrial cold drawing can thus be optimized thereby producing commercial prestressing steel wires with improved performance against HE phenomena.
Effect of Corrosion-induced Hydrogen Embrittlement and its Degradation Impact on Tensile Properties and Fracture Toughness of (Al-Cu-Mg) 2024 Alloy
Jul 2016
Publication
In the present work the effect of artificial ageing of AA2024-T3 on the tensile mechanical properties and fracture toughness degradation due to corrosion exposure will be investigated. Tensile and fracture toughness specimens were artificially aged to tempers that correspond to Under-Ageing (UA) Peak-Ageing (PA) and Over-Ageing (OA) conditions and then were subsequently exposed to exfoliation corrosion environment. The corrosion exposure time was selected to be the least possible according to the experimental work of Alexopoulos et al. (2016) so as to avoid the formation of large surface pits trying to simulate the hydrogen embrittlement degradation only. The mechanical test results show that minimum corrosion-induced decrease in elongation at fracture was achieved for the peak-ageing condition while maximum was noticed at the under-ageing and over-ageing conditions. Yield stress decrease due to corrosion is less sensitive to tempering; fracture toughness decrease was sensitive to ageing heat treatment thus proving that the S΄ particles play a significant role on the corrosion-induced degradation.
Critical Assessment of the Effect of Atmospheric Corrosion Induced Hydrogen on Mechanical Properties of Advanced High Strength Steel
Dec 2020
Publication
Hydrogen absorption into steel during atmospheric corrosion has been of a strong concern during last decades. It is technically important to investigate if hydrogen absorbed under atmospheric exposure conditions can significantly affect mechanical properties of steels. The present work studies changes of mechanical properties of dual phase (DP) advanced high strength steel specimens with sodium chloride deposits during corrosion in humid air using Slow Strain Rate Test (SSRT). Additional annealed specimens were used as reference in order to separate the possible effect of absorbed hydrogen from that of corrosion deterioration. Hydrogen entry was monitored in parallel experiments using hydrogen electric resistance sensor (HERS) and thermal desorption mass spectrometry (TDMS). SSRT results showed a drop in elongation and tensile strength by 42% and 6% respectively in 27 days of atmospheric exposure. However this decrease cannot be attributed to the effect of absorbed hydrogen despite the increase in hydrogen content with time of exposure. Cross-cut analysis revealed considerable pitting which was suggested to be the main reason for the degradation of mechanical properties
Hydrogen Permeation Under High Pressure Conditions and the Destruction of Exposed Polyethylene-property of Polymeric Materials for High-pressure Hydrogen Devices (2)-
Feb 2021
Publication
Aiming to elucidate physical property affecting to hydrogen gas permeability of polymer materials used for liner materials of storage tanks or hoses and sealants under high-pressure environment as model materials with different free volume fraction five types of polyethylene were evaluated using two methods. A convenient non-steady state measurement of thermal desorption analysis (TDA) and steady-state high-pressure hydrogen gas permeation test (HPHP) were used both under up to 90 MPa of practical pressure. The limit of TDA method of evaluation for the specimens suffering fracture during decompression process after hydrogen exposure was found. Permeability coefficient decreased with the decrease of diffusion coefficient under higher pressure condition. Specific volume and degree of crystallinity under hydrostatic environment were measured. The results showed that the shrinkage in free volume caused by hydrostatic effects of the applied hydrogen gas pressure decreases diffusion coefficient resulting in the decrease of permeability coefficient with the pressure rise.
The Impact of Hydrogen on Mechanical Properties; A New In Situ Nanoindentation Testing Method
Feb 2019
Publication
We have designed a new method for electrochemical hydrogen charging which allows us to charge very thin coarse-grained specimens from the bottom and perform nanomechanical testing on the top. As the average grain diameter is larger than the thickness of the sample this setup allows us to efficiently evaluate the mechanical properties of multiple single crystals with similar electrochemical conditions. Another important advantage is that the top surface is not affected by corrosion by the electrolyte. The nanoindentation results show that hydrogen reduces the activation energy for homogenous dislocation nucleation by approximately 15–20% in a (001) grain. The elastic modulus also was observed to be reduced by the same amount. The hardness increased by approximately 4% as determined by load-displacement curves and residual imprint analysis.
Efficient Hydrogen Storage in Defective Graphene and its Mechanical Stability: A Combined Density Functional Theory and Molecular Dynamics Simulation Study
Dec 2020
Publication
A combined density functional theory and molecular dynamics approach is employed to study modifications of graphene at atomistic level for better H2 storage. The study reveals H2 desorption from hydrogenated defective graphene structure V222 to be exothermic. H2 adsorption and desorption processes are found to be more reversible for V222 as compared to pristine graphene. Our study shows that V222 undergoes brittle fracture under tensile loading similar to the case of pristine graphene. The tensile strength of V222 shows slight reduction with respect to their pristine counterpart which is attributed to the transition of sp2 to sp3-like hybridization. The study also shows that the V222 structure is mechanically more stable than the defective graphene structure without chemically adsorbed hydrogen atoms. The current fundamental study thus reveals the efficient recovery mechanism of adsorbed hydrogen from V222 and paves the way for the engineering of structural defects in graphene for H2 storage.
A Multi‐input and Single‐output Voltage Control for a Polymer Electrolyte Fuel Cell System Using Model Predictive Control Method
Mar 2021
Publication
Efficient and robust control strategies can greatly contribute to the reliability of fuel cell systems and a stable output voltage is a key criterion for evaluating a fuel cell system's reliability as a power source. In this study a polymer electrolyte fuel cell (PEFC) system model is developed and its performances under different operating conditions are studied. Then two different novel controllers—a proportional integral derivative (PID) controller and a model predictive control (MPC) controller—are proposed and applied in the PEFC system to control its output voltage at a desired value by regulating the hydrogen and air flow rates at the same time which features a multi‐input and single‐output control problem. Simulation results demonstrate that the developed PEFC system model is qualified to capture the system's behaviour. And both the developed PID and MPC controllers are effective at controlling the PEFC system's output voltage. While the MPC controller presents superior performance with faster response and smaller overshoot. The proposed MPC controller can be easily employed in various control applications for fuel cell systems.
Detection, Characterization and Sizing of Hydrogen Induced Cracking in Pressure Vessels Using Phased Array Ultrasonic Data Processing
Jul 2016
Publication
Pressure vessels operating in sour service conditions in refinery environments can be subject to the risk of H₂S cracking resulting from the hydrogen entering into the material. This risk which is related to the specific working conditions and to the quality of the steel used shall be properly managed in order to maintain the highest safety at a cost-effective level.<br/>Nowadays the typical management strategy is based on a risk based inspection (RBI) evaluation to define the inspection plan used in conjunction with a fitness for service (FFS) approach in defining if the vessel although presenting dangerous defects such as cracks can still be considered “fit for purpose” for a given time window based on specific fracture mechanics analysis.<br/>These vessels are periodically subject to non-destructive evaluation typically ultrasonic testing. Phased Array (PA) ultrasonic is the latest technology more and more used for this type of application.<br/>This paper presents the design and development of an optimized Phased Array ultrasonic inspection technique for the detection and sizing of hydrogen induced cracking (HIC) type flaws used as reference for comparison. Materials used containing natural operational defects were inspected in “as-service” conditions.<br/>Samples have then been inspected by means of a “full matrix capture” (FMC) acquisition process followed by “total focusing method” (TFM) data post processing. FCM-TFM data have been further post-processed and then used to create a 3D geometrical reconstruction of the volume inspected. Results obtained show the significant improvement that FMC/TFM has over traditional PA inspection techniques both in terms of sensitivity and resolution for this specific type of defect. Moreover since the FMC allows for the complete time domain signal to be captured from every element of a linear array probe the full set of data is available for post-processing.<br/>Finally the possibility to reconstruct the geometry of the component from the scans including the defects present in its volume represents the ideal solution for a reliable data transferring process to the engineering function for the subsequent FFS analysis.
Is Direct Seawater Splitting Economically Meaningful?
Jun 2021
Publication
Electrocatalytic water splitting is the key process for the formation of green fuels for energy transport and storage in a sustainable energy economy. Besides electricity it requires water an aspect that seldomly has been considered until recently. As freshwater is a limited resource (<1% of earth's water) lately plentiful reports were published on direct seawater (around 96.5% of earth's water) splitting without or with additives (buffers or bases). Alternatively the seawater can be split in two steps where it is first purified by reverse osmosis and then split in a conventional water electrolyser. This quantitative analysis discusses the challenges of the direct usage of non-purified seawater. Further herein we compare the energy requirements and costs of seawater purification with those of conventional water splitting. We find that direct seawater splitting has substantial drawbacks compared to conventional water splitting and bears almost no advantage. In short it is less promising than the two-step scenario as the capital and operating costs of water purification are insignificant compared to those of electrolysis of pure water.
Environmentally-Assisted Cracking of Type 316L Austenitic Stainless Steel in Low Pressure Hydrogen Steam Environments
Aug 2019
Publication
A low pressure superheated hydrogen-steam system has been used to accelerate the oxidation kinetics while keeping the electrochemical conditions similar to those of the primary water in a pressurized water reactor. The initiation has been investigated using a Constant Extension Rate Tensile (CERT) test. Tests were performed on flat tapered specimens made from Type 316L austenitic stainless steel with strain rates of 2×10-6 and 2×10-8 ms-1 at room temperature and at an elevated temperature of 350 °C. R = 1/6 was chosen as a more oxidizing environment and R = 6 was selected as a more reducing environment where the parameter R represents the ratio between the oxygen partial pressure at the Ni/NiO transition and the oxygen partial pressure. Different exposures (1 day and 5 days) prior to loading were investigated post-test evaluation by scanning electron microscopy.
Hydrogen Induced Damage in Heavily Cold-Drawn Wires of Lean Duplex Stainless Steel
Sep 2017
Publication
The paper addresses the sensitivity to hydrogen embrittlement of heavily cold-drawn wires made of the new generation of lower alloyed duplex stainless steels often referred to as lean duplex grades. It includes comparisons with similar data corresponding to cold-drawn eutectoid and duplex stainless steels. For this purpose fracture tests under constant load were carried out with wires in the as-received condition and fatigue-precracked in air and exposed to ammonium thiocyanate solution. Microstructure and fractographic observations were essential means for the cracking analysis. The effect of hydrogen-assisted embrittlement on the damage tolerance of lean duplex steels was assessed regarding two macro-mechanical damage models that provide the upper bounds of damage tolerance and accurately approximate the failure behavior of the eutectoid and duplex stainless steels wires.
Features of the Hydrogen-Assisted Cracking Mechanism in the Low-Carbon Steel at Ex- and In-situ Hydrogen Charging
Dec 2018
Publication
Hydrogen embrittlement has been intensively studied in the past. However its governing mechanism is still under debate. Particularly the details of the formation of specific cleavage-like or quasi-cleavage fracture surfaces related to hydrogen embrittled steels are unclear yet. Recently it has been found that the fracture surface of the hydrogen charged and tensile tested low-carbon steel exhibits quasi-cleavage facets having specific smoothly curved surface which is completely different from common flat cleavage facets. In the present contribution we endeavor to shed light on the origin of such facets. For this purpose the notched flat specimens of the commercial low carbon steel were tensile tested using ex- and in-situ hydrogen charging. It is found that in the ex-situ hydrogen charged specimens the cracks originate primarily inside the specimen bulk and expand radially form the origin to the specimen surface. This process results in formation of “fisheyes” – the round-shape areas with the surface composed of curved quasi-cleavage facets. In contrast during tensile testing with in-situ hydrogen charging the cracks initiate from the surface and propagate to the bulk. This process results in the formation of the completely brittle fracture surface with the quasi-cleavage morphology - the same as that in fisheyes. The examination of the side surface of the in-situ hydrogen charged specimens revealed the straight and S-shaped sharp cracks which path is visually independent of the microstructure and crystallography but is strongly affected by the local stress fields. Nano-voids are readily found at the tips of these cracks. It is concluded that the growth of such cracks occurs by the nano-void coalescence mechanism and is responsible for the formation of fisheyes and smoothly curved quasi-cleavage facets in hydrogen charged low-carbon steel.
Comarine Derivatives Designed as Carbon Dioxide and Hydrogen Storage
Feb 2022
Publication
The growing of fossil fuel burning leads to increase CO2 and H2 emissions which cause increasing of global warming that has brought big attention. As a result enormous researches have been made to reduce CO2 and H2 build up in the environment. One of the most promising approaches for managing CO2 and H2 gases percentage in the atmosphere is capturing and storage them inside proper materials. Therefore the design of new materials for carbon dioxide and hydrogen storage has received increasing research attention. Four derivatives of coumarine linked to thiazolidinone were synthesized in good yields by reacting 3-(2-Phenylaminoacetyl)coumarine and 2-phenylimino thiazolidinone-4-one in a solution of anhydrous sodium acetate /glacial acetic acid at 120° for 5-6 hours. The synthesised organic compounds were identified by using different techniques such as 1H NMR 13C NMR FTIR and energy dispersive X-ray spectra. The agglomeration shape and porosity of the particles were determined utilizing scanning electron microscopy (SEM) and microscopy images analysis. The capacity of carbon dioxide (CO2) and hydrogen (H2) adsorption on the prepared organic materials at 323 K 50 bar ranged from 22 to 31 cm3 /g and hydrogen from 4 to 12 cm3 /g for the four synthesised compounds which contain phenyl substituted with chloro nitro and bromo groups was found to be the most active adsorbent surfaces for carbon dioxide and hydrogen storage.
Effects of Hydrogen Pressure, Test Frequency and Test Temperature on Fatigue Crack Growth Properties of Low-carbon Steel in Gaseous Hydrogen
Jul 2016
Publication
Fatigue crack growth (FCG) tests for compact tension (CT) specimens of an annealed low-carbon steel JIS-SM490B were performed under various combinations of hydrogen pressures ranging from 0.1 to 90 MPa test frequencies from 0.001 to 10 Hz and test temperatures of room temperature (RT) 363 K and 423 K. In the hydrogen pressures of 0.1 0.7 and 10 MPa at RT the FCG rate increased with a decrease in the test frequency; then peaked out. In the lower test frequency regime the FCG rate decreased and became nearly equivalent to the FCG rate in air. Also in hydrogen pressure of 45 MPa at RT the hydrogen-assisted FCG acceleration showed an upper limit around the test frequencies of 0.01 to 0.001 Hz. On the other hand in the hydrogen pressure of 90 MPa at RT the FCG rate monotonically increased with a decrease in the test frequency and eventually the upper limit of FCG acceleration was not confirmed down to the test frequency of 0.001 Hz. In the hydrogen pressure of 0.7 MPa at the test frequency of 1 Hz and temperatures of 363 K and 423 K the stress intensity factor range ΔK for the onset of the FCG acceleration in hydrogen gas was shifted to a higher ΔK with an increase in the test temperature. The laser-microscope observation at specimen surface revealed that the hydrogen-assisted FCG acceleration always accompanied a localization of plastic deformation near crack tip. These results infer that the influencing factor dominating the hydrogen-assisted FCG acceleration is not the presence or absence of hydrogen in material but is how hydrogen localizes near the crack tip. Namely a steep gradient of hydrogen concentration can result in the slip localization at crack tip which enhances the Hydrogen Enhanced Successive Fatigue Crack Growth (HESFCG) proposed by the authors. It is proposed that such a peculiar dependence of FCG rate on hydrogen pressure test frequency and test temperature can be unified by using a novel parameter representing the gradient of hydrogen concentration near crack tip.
On the Concept of Micro-fracture Map (MFM) and its Role in Structural Integrity Evaluations in Materials Science and Engineering: A Tribute to Jorge Manrique
Dec 2020
Publication
This paper deals with the concept of micro-fracture map (MFM) and its role in structural integrity evaluations in materials science and engineering on the basis of previous research by the author on notch-induced fracture and hydrogen embrittlement of progressively cold drawn pearlitic steels and 316L austenitic stainless steel. With regard to this some examples are provided of assembly of MFMs in particular situations.
Ammonia for Power
Sep 2018
Publication
A potential enabler of a low carbon economy is the energy vector hydrogen. However issues associated with hydrogen storage and distribution are currently a barrier for its implementation. Hence other indirect storage media such as ammonia and methanol are currently being considered. Of these ammonia is a carbon free carrier which offers high energy density; higher than compressed air. Hence it is proposed that ammonia with its established transportation network and high flexibility could provide a practical next generation system for energy transportation storage and use for power generation. Therefore this review highlights previous influential studies and ongoing research to use this chemical as a viable energy vector for power applications emphasizing the challenges that each of the reviewed technologies faces before implementation and commercial deployment is achieved at a larger scale. The review covers technologies such as ammonia in cycles either for power or CO2 removal fuel cells reciprocating engines gas turbines and propulsion technologies with emphasis on the challenges of using the molecule and current understanding of the fundamental combustion patterns of ammonia blends.
Interface Instabilities of Growing Hydrides
Jul 2016
Publication
Formation of metal hydrides is a serious complication that occur when hydride forming metals such as zirconium niobium vanadium and magnesium are exposed to long term hydrogen environment. The main concern is that the hydride as being a brittle material has very poor fracture mechanical properties. Formation of hydride is associated with transportation of hydrogen along the gradients of increasing hydrostatic stress which leads to crack tips and other stress concentrators where it forms the hydride. In the present study the thermodynamics of the evolving hydrides is studied. The process is driven by the release of free strain chemical and gradient energies. A phase field model is used to capture the driving forces that the release of the free energy causes. The study gives the conditions that lead to hydride advancement versus retreat and under which conditions the metal-hydride interface becomes unstable and develops a waviness. The spatial frequency spectrum leading to instability is found to depend on the ratio of the elastic strain energy density and parameters related to the interface energy.
The Energy Approach to the Evaluation of Hydrogen Effect on the Damage Accumulation
Aug 2019
Publication
The energy approach for determining the durability of structural elements at high temperature creep and hydrogen activity was proposed. It has been shown that the approach significantly simplifies research compared with the known ones. Approbation of the approach was carried out on the example of determining the indicators of durability of the Bridgman sample under conditions of creep and different levels of hydrogenation of the metal. It was shown that with an increase of hydrogen concentration in the metal from 2 to 10 ppm the durability of the test sample decreased from 22 to 58%.
Notch-induced Anisotropic Fracture of Cold Drawn Pearlitic Steels and the Associated Crack Path Deflection and Mixed-mode Stress State: A Tribute to Masaccio
Jul 2018
Publication
This paper deals with notch-induced anisotropic fracture behavior of progressively cold drawn pearlitic steels on the basis of their microstructural evolution during manufacturing by multi-step cold drawing that produces slenderizing and orientation of the pearlitic colonies together with densification and orientation of the Fe/Fe3C lamellae reviewing previous research by the author. Results of fracture test using notched specimens of cold drawn pearlitic steels with different degrees of cold drawing (distinct levels of strain hardening) in air and hydrogen environment shows: (i) the key impact of the colonies and lamellae alignment and orientation on notch-induced fracture producing anisotropic fracture behavior with its related crack path deflection (or fracture path deviation); (ii) the necessity of both stress triaxiality (constraint) and microstructural orientation (colonies/lamellae) alignment to produce fracture path deflection; (iii) hydrogen presence (the circumstance) promotes crack path deviation in addition to the inherent microstructural anisotropy created by cold drawing; (iv) the anisotropic fracture path with a stepped profile in cold drawn pearlitic steel consisting of deflections and deviations from the initial transverse fracture path in mode I resembles Masaccio’s Tribute Money painting with its mountains at the background so that the present paper can be considered as a Tribute to Masaccio.
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