Analysis Of Hydrogen Diffusion Research Articles

Numerical Simulation Analysis of Hydrogen Leakage and Diffusion in Tunnel

In order to study the actual situation of accidental hydrogen leakage of fuel cell buses in tunnels, and to provide certain safety countermeasures when hydrogen leakage occurs in tunnels, a tunnel in Nanjing was taken as the research object by using the fluid simulation software Fluent, and the influence of external factors on hydrogen leakage and diffusion was explored from the angle of leakage rate. The simulation results show that after hydrogen leaks for a period of time, the distribution of hydrogen concentration will form an obvious layered structure with the increase of time. The higher the leakage rate, the higher the rate of hydrogen concentration rise in space, and the smaller the leakage rate, the smaller the area of explosion danger in space.

Critical assessment of hydrogen pipe diffusion at dislocations in metals

Hydrogen-dislocation interactions have always been a crucial problem in understanding and predicting the long-standing hydrogen embrittlement (HE) phenomenon in structural metals. Particularly with respect to hydrogen diffusion, dislocations have often been assumed with the ability to facilitate hydrogen transport via dislocation pipe diffusion (DPD). Yet the experimental and theoretical studies supporting DPD remain elusive and even controversial. In this work, hydrogen kinetics at dislocations in two representative metal systems, fcc Ni and bcc Fe, were systematically investigated combining comprehensive atomistic and kinetic activation relaxation technique simulations to reveal atomic details while enabling long-time (i.e., microsecond to second) hydrogen diffusion analysis. The dislocations were found to favor hydrogen trapping and provide regions of low migration barriers for hydrogen. However, these regions of low barriers only lead to localized fast short-circuit H diffusion, but do not translate into DPD over long time, which is attributed to fast hydrogen diffusion pathways along the dislocation line direction being periodically bound by high hydrogen migration barriers. Using the polyhedral structural units (PSUs) as an effective tool, we further quantitatively analyzed the correlation between hydrogen diffusion behaviors and local dislocation structures, illustrating the structural origin leading to local short-circuit diffusion and inhibition of DPD at dislocations. The new mechanistic insights gained not only are critical for understanding hydrogen-dislocation interaction, but also advances the general knowledge on hydrogen-microstructure interaction in structural metals.

Experimental study of long-term catalytic effect on hydrogen generation G value of water by gamma-ray irradiation and hydrogen diffusion analysis in Compacted Hulls and End-Piece waste

In this study, it was evaluated the long-term catalytic effect and catalyst poisoning effect of gamma-ray irradiation on zirconium molybdate hydrate in the presence of three-way catalysts. The results indicated that the three-way catalyst was effective in suppressing the increase in hydrogen concentration due to radiolysis without being affected by poisoning. In addition, hydrogen diffusion analysis of the compressed hull and endpiece waste shows that hydrogen flows well through the waste and is suppressed by a three-way catalyst located in the center of the waste headspace.

Hydrogen-assisted localized plasticity driven by dislocation pinning-depinning: Finite element simulations

For the development of a hydrogen energy society, understanding hydrogen-assisted fatigue crack propagation is crucial. Hydrogen-assisted fatigue crack propagation exhibits an exceptionally rapid growth rate, with only small plastic deformation observed at the macroscopic level. Nevertheless, the presence of dislocation structures, typically associated with conventional fatigue failure, has been reported near the crack tip. Explaining this phenomenon solely based on hydrogen-induced softening or hardening is challenging. Therefore, this study focuses on the newly proposed concept of temporary hardening resulting from hydrogen-induced pinning and depinning. In this research, we conducted a numerical analysis using an elastoplastic analysis coupled with hydrogen diffusion analysis to simulate the pinning and depinning effects caused by hydrogen. Our simulation results demonstrated that hydrogen-induced pinning and depinning led to higher strains at the crack tip compared to cases without these effects, resulting in small-scale macroscopic plastic deformation.

Analysis of Hydrogen Distribution and Diffusion in Pre-Strained SUS316L through Scanning Kelvin Probe Force Microscopy and Thermal Desorption Spectroscopy

Austenitic stainless steels (γ-SS) play an important role in the storage of high-pressure hydrogen. However, hydrogen embrittlement (HE) can significantly degrade the mechanical properties of γ-SS. Measuring the distribution of hydrogen in γ-SS is a vital way to learn about HE. In this paper, scanning Kelvin probe force microscopy (SKPFM) and thermal desorption spectroscopy (TDS) have been utilized to analyze the distribution and diffusion of hydrogen in pre-strained SUS316L. Additionally, the McNabb–Foster model is employed to calculate hydrogen in the lattice and phase boundaries along the sample’s thickness direction. The results demonstrate that the combination of SKPFM and TDS is an effective approach for studying hydrogen distribution and diffusion in metals. It was observed that hydrogen segregation occurs at the boundary between the martensitic (α′) and austenite (γ) phases. The inhibitory effect of the oxide film on hydrogen diffusion is more significant at lower temperatures. However, it should be noted that the McNabb–Foster model exhibits relatively high accuracy in predicting hydrogen desorption at higher temperatures while disregarding the influence of the native oxide film.

Research on residual stress and hydrogen diffusion of X80 pipeline welded joint

Hydrogen enrichment induced by pipeline welding residual stress is a key issue affecting the safe service of hydrogen pipelines. In order to explore the influence of welding residual stress on hydrogen diffusion and the effect of heat treatment, an X80 pipeline model with a six-layer girth weld was established using ABAQUS software, and coupling analysis of temperature field, stress field, and hydrogen diffusion was carried out. The distribution of residual stress in the welding area and local inclusion area was analyzed, the relationship between the hydrostatic stress and hydrogen diffusion of the pipeline, and the influence of the direction and shape of the inclusion on hydrogen diffusion were explored, and the effect of post-weld heat treatment on the residual stress and hydrogen diffusion in the welding area and local inclusion area was studied. The hydrostatic stress curve is similar to the hydrogen concentration distribution curve, and hydrostatic stress can be considered the main driving force for hydrogen diffusion in the pipeline. As the angle between the inclusions and the hydrogen diffusion direction increases, the hydrogen diffusion flux will gradually decrease. The more slender the inclusions, the stronger the diffusion ability of parallel or 45° inclusions, and the weaker the diffusion ability of perpendicular inclusions. Hydrogen enrichment occurs in inclusions or inclusion boundaries before and after post-weld heat treatment of the pipeline, and the internal hydrogen concentration of hard inclusions is higher than that of soft inclusions. Post-weld heat treatment can significantly reduce welding residual stress and hydrostatic stress, thereby reducing hydrogen enrichment concentration.

Towards quantitative analysis of deuterium absorption in ferrite and austenite during electrochemical charging by comparing cyclic voltammetry and cryogenic transfer atom probe tomography

Hydrogen embrittlement mechanisms of steels have been studied for several decades. Understanding hydrogen diffusion behavior in steels is crucial towards both developing predictive models for hydrogen embrittlement and identifying mitigation strategies. However, because hydrogen has a low atomic mass, it is extremely challenging to detect by most analytical methods. In recent years, cryogenic-transfer atom probe tomography (APT) of electrochemically-deuterium-charged steels has provided invaluable qualitative analysis of nanoscale deuterium traps such as carbides, dislocations, grain boundaries and interfaces between ferrite and cementite. Independently, cyclic voltammetry (CV) has provided valuable analysis of bulk hydrogen diffusion in steels. In this work, we use a combination of CV and cryogenic-transfer APT for quantitative analysis of deuterium pickup in electrolytically charged pure Fe (ferrite) and a model austenitic Fe18Cr14Ni alloy without any second phase. The high solubility and low diffusivity of hydrogen in austenite versus ferrite and potential influence of oxide layer are highlighted to result in clear observable signatures in CV and cryogenic-transfer APT results. The remaining challenges and pathway for enabling quantitative analysis of hydrogen pick up in steels is also discussed.

Analysis of hydrogen diffusion in the three stage electro-permeation test

The presence of hydrogen traps within a metallic alloy influences the rate of hydrogen diffusion. The electro-permeation (EP) test can be used to assess this: the permeation of hydrogen through a thin metallic sheet is measured by suitable control of hydrogen concentration on the front face and by recording the flux of hydrogen that exits the rear face. Additional insight is achieved by the more sophisticated three stage EP test: the concentration of free lattice hydrogen on the front face is set to an initial level, is then dropped to a lower intermediate value and is then restored to the initial level. The flux of hydrogen exiting the rear face is measured in all three stages of the test. In the present study, a transient analysis is performed of hydrogen permeation in a three stage EP test, assuming that lattice diffusion is accompanied by trapping and de-trapping. The sensitivity of the three stage EP response to the depth and density of hydrogen traps is quantified. A significant difference in permeation response can exist between the first and third stages of the EP test when the alloy contains a high number density of deep traps.

In Situ Investigation of Hydrogen-Induced Cracking Behavior in Linepipe Steel Under Different Environments

NACE MR0175/ISO 15156 provides the severity of a sour environment defined as a function of pH and H2S partial pressure for sulfide stress cracking. Although hydrogen-induced cracking (HIC) is also a major issue of linepipes exposed to a sour environment, the severity diagram does not necessarily correspond to the HIC susceptibility. Recently, from the viewpoint of fitness-of-purpose, the severity diagrams for HIC have been proposed based on the concept of equal hydrogen concentration. From this concept, HIC susceptibility corresponds well to the steady-state hydrogen permeability obtained from the hydrogen permeation test method. In this study, in order to clarify the relationship between HIC susceptibility and hydrogen diffusion behavior, in situ crack inspection during the HIC test and finite element method analysis of hydrogen diffusion were performed. The in situ inspection technique using phased-array ultrasonic testing which can capture the time dependence of crack distribution, and HIC initiation and propagation behaviors were clearly visualized and investigated. It was found that crack initiation and propagation stabilize as hydrogen concentration reaches a steady-state value throughout the specimen and the result was considered evidence that the HIC susceptibility corresponded with the steady value of hydrogen permeability.

Effect of Residual Stress on Hydrogen Diffusion in Thick Butt-Welded High-Strength Steel Plates

Thick high-strength steel plates are increasingly being used for ship structures. Moreover, hydrogen enters the process of manufacturing and service, and large residual tensile stress occurs near the weld. Such stress can facilitate the diffusion and accumulation of hydrogen in the material, leading to hydrogen embrittlement fracture of the shell. Therefore, residual-stress-induced diffusion and accumulation of hydrogen in the stress concentration region of thick butt-welded high-strength steel plate structures need to be studied. In this study, manual metal arc welding was realized by numerical simulation of residual stress in a thick butt-welded high-strength steel plate model using the thermoelastic–plastic theory and a double ellipsoidal heat source model. To analyze residual stress, a set of numerical simulation methods was obtained through comparative analysis of the test results of relevant literature. Residual and hydrostatic stress distributions were determined based on these methods. Then, hydrogen diffusion parameters in each region of the model were obtained through experimental tests. Finally, the results of the residual stress field were used as the predefined field of hydrogen diffusion to conduct a numerical simulation analysis. The distribution of hydrogen diffusion under the influence of residual stress was obtained based on the theory of stress-induced hydrogen diffusion. The weak area of the welding joint was found to be near the weld toe, which exhibited high hydrostatic stress and hydrogen concentration. Further, the maximum hydrogen concentration value of the vertical weld path was approximately 6.1 ppm, and the maximum value of the path parallel to the weld centerline and 31 mm away from the weld centerline was approximately 6.22 ppm. Finally, the hydrostatic tensile stress in the vertical weld path was maximized (~345 MPa), degrading the material properties and causing hydrogen-related cracking. Hence, a reliable method for the analysis of hydrogen diffusion according to residual stress in thick high-strength steel plates was obtained. This work could provide a research basis for controlling and eliminating the adverse effects of hydrogen on the mechanical properties of ship structures and ensuring the safe service of marine equipment.

A novel approach for quantifying hydrogen embrittlement using side-grooved CT samples

Aerospace parts made of high strength steels, such as landing gears and helicopter transmissions, are often electroplated to satisfy various engineering specifications. However, plated parts are occasionally rejected because of hydrogen embrittlement, and the industry has few means of evaluating quantitatively the actual damage caused by hydrogen. In the present article, we developed a novel method to measure the stress intensity threshold for hydrogen embrittlement (Kth) in industrial plating conditions. The method consists in plating side-grooved CT samples in industrial plating baths, and measuring Kth with an incremental step loading methodology. We validated the method with a benchmark case known to produce embrittlement (omitted post-plating bake) and we used the method on a test case for which the level of embrittlement was unknown (delayed bake). For the benchmark case, we measured a Kth of 49.0MPam0.5 for non-baked samples. This value is significantly lower than the fracture toughness of the unplated material, which is 63.8MPam0.5. We conclude that this novel combination of geometry and test method is efficient in quantifying hydrogen embrittlement of samples plated in industrial conditions. For the test case, the Kth are respectively 57.9MPam0.5 and 58.8MPam0.5 for samples baked 100 h and 4 h after plating. We conclude that delaying the post-plating bake does not cause hydrogen embrittlement in the studied conditions. Using a finite element hydrogen diffusion analysis, we argue that the side grooves on CT samples increase the sensitivity to hydrogen embrittlement in comparison to smooth samples. In smooth samples, a zone of plane stress at the surface of the specimen shields hydrogen from penetrating to the center of the specimen, a phenomenon which is alleviated with machining side grooves.

Modeling and analysis of hydrogen diffusion in an enclosed fuel cell vehicle with obstacles

Hydrogen has been utilized in FCV and leakage can cause safety issues. In this study, the vehicle is simplified as a cuboid enclosure with obstacles. The influence of obstacle locations on the hydrogen diffusion behavior is investigated with the iso-surfaces of 1% and 4% volume fraction of hydrogen. The time of the iso-surface of 4% volume fraction to reach the ceiling and the sidewalls without any obstacles is 1.42 and 1.25 times of that with an obstacle, respectively. Both height and the width of the flammable zone in the enclosure with an obstacle are greater than that without obstacles. The distance between the obstacle and the leakage affects significantly the hydrogen diffusion and the influence of the obstacle on the hydrogen diffusion strengthens with the decrease of the distance. Yet as the distance keeps same, the obstacle position relative to the leakage has no significant effect on hydrogen diffusion, and it makes little effect difference whether the obstacle is located in front of leakage or side of leakage.

Present Situation and Prospect of Welding Simulation Technology

In this paper, we mainly introduce the research status and development trend of welding numerical simulation technology. It is mainly reviewed that the simulation of molten pool flow field, welding temperature field and mechanical field, welding deformation and residual stress, hydrogen diffusion analysis, carbon migration of dissimilar steel welded joints, special welding process, microstructure of welded joints and grain growth process of welding heat affected zone. Then we discuss the special welding process simulation technology and special software for welding simulation. Finally, the development of welding numerical simulation technology in China are concerned.

Effects of turbulence models on leaking hydrogen diffusion analysis

Effects of turbulence models on leaking hydrogen diffusion analysis

Prediction Model for Weld Hydrogen Cracking in High Strength Steel Weld

Prediction model for weld hydrogen cracking (so called cold cracking) in high strength steel weld was developed by a coupled thermo-elastic-plastic and hydrogen diffusion analysis in the y-grooved weld joint. Critical conditions of cracking was given as the function of principal stress and accumulated hydrogen concentration in the root region where the cracking occurs. In order to clarify the critical conditions of cold cracking, y-grooved cold cracking tests were first conducted using the steel plate with tensile strength level of 780MPa. Plate thickness of the plates were 25 mm and 50 mm. Hydrogen concentration in the weld metal was changed by applying hydrogen into the shield gas in the gas-metal arc welding (GMAW), and different pre-heating conditions were applied to evaluate the critical pre-heating temperature to prevent cold cracking. It was found that the critical pre-heating temperature was increased with thicker plate thickness and higher hydrogen concentration in the weld metal. The cracks were initiated at the weld metal in the root region which exhibits significant tensile residual stress by the welding. Hydrogen accumulation into the root region may have enhanced cracking. Based on the above y-grooved weld cold cracking tests, a simulation model for estimating the critical pre-heating temperature was developed. The y-grooved weld joints with different plate thickness were modeled by the FEM with the actual weld configuration and material properties in the base metal, heat affected zone (HAZ) and weld metal. Hydrogen was put in the weld metal as an initial condition, then welding simulation was conducted by coupled thermo-elastic-plastic and hydrogen diffusion analysis. In the hydrogen diffusion analysis, the α-multiplication method, which stress gradient term in the diffusion law was multiplied, was applied to express realistic hydrogen diffusion enhanced by hydrostatic stress field. Hydrogen accumulation occurred in the root region where showed highest hydrostatic stress. The point where showed the hydrogen accumulation was well corresponded to the crack initiation site. It was found that cracking was enhanced with thicker plate and higher initial hydrogen concentration because of higher tensile residual stress and higher hydrogen accumulation in the root region, respectively. These models were implemented into the Materials Integration (MI) System to estimate the critical pre-heating temperature in the y-grooved weld tests with different welding conditions. Although, further validation and optimization are needed for the models, this hydrogen cracking prediction system has a lot of potential as a material development support tool for reducing experimentation and speeding up the development.

Cohesive zone modeling of hydrogen-induced delayed intergranular fracture in high strength steels

A sequentially coupled hydrogen diffusion-cohesive zone modeling approach was applied to the simulation of hydrogen-induced delayed intergranular (IG) fracture in high-strength low-alloy steels. The effects of multiple hydrogen trap sites and mechanical deformation on the diffusion and cohesive strength of grain boundaries (GB) were taken account, in order to reveal that the hydrogen trapped at GB play a dominant role in the degradation processes of hydrogen of high-strength low-alloy steels, which leads to the IG fracture. The approach was implemented by Abaqus software in the form of a two-steps procedure including the coupled elastoplastic-transient hydrogen diffusion analysis and cohesive stress analysis. To validate the approach, the constant load tests of hydrogen pre-charged AISI 4135 high-strength low-alloy steel notched bars in literature were analyzed. Good agreement is observed between the simulation and experimental data of time to failure. The results confirm that hydrogen-induced IG fracture of high strength low-alloy steels can be related to the hydrogen concentration trapped at GB. The critical hydrogen concentration at GB for crack initiation is independent of the initial hydrogen concentration but depends strongly on the local stress level and stress triaxiality. The critical hydrogen concentration linearly decreases with increasing normalized peak maximal principal stress normalized by the critical cohesive strength in absence of hydrogen.

Cohesive zone based axisymmetric modelling of hydrogen-assisted cracking in a circumferentially notched tensile specimen

The paper presents an axisymmetric finite element model to study hydrogen-assisted cracking (HAC) in a circumferentially notched tensile (CNT) specimen of a high-strength steel. The model includes an axisymmetric 2-D stress analysis coupled with an axisymmetric 1-D hydrogen diffusion analysis. Crack initiation is handled through cohesive elements whose strength is adjusted depending on the local hydrogen concentration. The model successfully predicted the critical SIFs of tempered AISI 4340 under different hydrogen charging conditions in rising displacement tests. Furthermore, the model is able to simulate of typical delayed failure of specimens under HAC conditions in constant load tests. Reported HAC of three different microstructures of AISI 4340 was simulated under rising displacement condition, and the respective model parameters were then also used to simulate crack initiation in the same microstructures under constant load condition. Closeness of critical SIFs from both the simulations indicates that the model parameters calibrated through slow strain rate tests are transferable to constant load situations. Moreover, it is shown that the present 2-D analysis, while being computationally advantageous, is an acceptable alternative of a 3-D model reported earlier.

Analysis of hydrogen diffusion and trapping in ultra-high strength steel grades

The transport behavior of hydrogen in ultra-high strength steel grades (UHSS) has been analyzed by several test and evaluation methods. In particular, permeation and desorption measurements have been performed to evaluate material specific parameters such as the effective diffusion coefficient, the reversible trap density and the reversible trap activation energy. Subjects of this study were a dual phase steel grade (DP) with a ferritic-martensitic microstructure and a martensitic steel grade (MS). The results of the permeation measurements indicate that the influence of irreversible traps might be negligible for the investigated UHSS compared to other impact factors. The evaluated reversible trap densities were some orders of magnitude higher than those known for pure iron reflecting the more complex microstructure. The major influence on hydrogen trapping is attributed to reversible traps like grain boundaries and dislocations based on the results of desorption measurements.

A methodology for the numerical assessment of autofrettage influence on hydrogen content near a notch in a 4130 steel pressure vessel

The introduction of compressive residual stresses, e.g. by means of an autofrettage process, is a common strategy in industry for the improvement in fatigue life of high-pressure vessels. The application of autofrettage process in a vessel, storing hydrogen at 70MPa, is evaluated here. Compressive stresses make difficult the entry of hydrogen in the metal lattice, however the produced plastic strain might be related to the creation of trapping sites for hydrogen. The balance between these two phenomena is analysed. In addition, the likely presence of notches is considered since stress concentrators increase the level of hydrostatic stress and plastic deformation, thus rising hydrogen content in the vicinity of the notch. A pressure vessel is simulated with the Finite Element method combining a static stress–strain analysis with a steady-state hydrogen diffusion analysis. Both autofrettage process and service life are simulated, and a notch is introduced in the inner surface of the vessel. Results indicate that, for each of the considered notch depths, autofrettage pressure must be limited in order to avoid high hydrogen concentrations, thus reducing the efficiency of the autofrettage process. This phenomenon is strongly dependent on the binding energy of trapping sites created by plastic strain.

FE analysis of hydrogen diffusion around a crack tip in an austenitic stainless steel

Hydrogen-assisted cracking (HAC) is a coupled phenomenon between crack growth rate and hydrogen diffusion to the region ahead of crack tip. To understand the cracking mechanism and to control or predict the HAC rate, knowledge of hydrogen diffusion around a crack tip is essential. Metastable austenitic stainless steels can be severely embrittled by hydrogen due to strain-induced α′ martensite transformation around crack tip, as the hydrogen diffusivity in α′ martensite is much higher than in γ austenite while the solubility is lower. However, the effect of induced α′ martensite on local diffusion of hydrogen around a loaded crack tip has not been intuitively demonstrated. This study first reveals the quantitative relations of hydrogen diffusivity and solubility with induced α′ martensite amount, and then performs FE analysis of hydrogen diffusion around a crack tip in a 304L ASS cylinder storing high pressure gaseous hydrogen with considering the combined effect of α′ martensite transformation and hydrostatic stress on diffusion. The hydrostatic stress exhibits a peak value at a distance away from crack tip, while the peak α′ martensite volume fraction locates at the crack tip. Compared to the analysis only considering stress effect, the presence of induced α′ martensite can not only significantly accelerate the hydrogen transport to the critical region ahead of crack tip, but also markedly elevate the level that the peak hydrogen concentration reaches. The peak hydrogen concentration doesn't locate at the peak hydrostatic stress site as generally expected, but at the site in the γ austenite-rich region abutting the α′ martensite-rich region at crack tip vicinity, because this site possesses very high hydrogen solubility and close to the high hydrogen diffusivity region, consequently accommodating the hydrogen getting off the α′ martensite diffusion “highway”.