Transmission, Distribution & Storage
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.
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