Gaseous Hydrogen Charging Research Articles

Hydrogen diffusivity, uptake and embrittlement of solution annealed and cold deformed austenitic stainless steel 1.4435 at hydrogen pressures up to 1000 bar and 200 °C

Austenitic stainless steel 1.4435, a candidate material for high-pressure tubing for hydrogen applications, was investigated in two different stages of cold deformation (0 and 27 %) regarding its hydrogen embrittlement tendency. The determination of effective diffusion coefficients revealed slightly increased diffusion kinetics at 60°C for the cold-reduced material (8.0 · 10−15 m²/s) compared to the solution annealed one (5.0 · 10−15 m²/s). High-pressure gaseous hydrogen charging shows no differences regarding the degree of cold deformation with a maximum hydrogen concentration of 112 wt.-ppm. Furthermore, a significant ductility loss expressed by the ratio of the reduction of area was observed.

Safe pipelines for hydrogen transport

The hydrogen compatibility of two X65 pipeline steels for transport of hydrogen gas is investigated through microstructural characterization, hydrogen permeation measurements and fracture mechanical testing. The investigated materials are a quenched and tempered pipeline steel with a fine-grained homogeneously distributed ferrite-bainite microstructure, and hot rolled pipeline steel with a ferrite-pearlite banded microstructure. All tests are performed both under electrochemical and gaseous hydrogen charging conditions. A correlation between electrochemical hydrogen charging and gaseous charging is determined. The results point to inherent differences in the interaction between hydrogen and the two material microstructures. Further research is needed to unveil the influence of material microstructure on hydrogen embrittlement.

On the hydrogen uptake of line pipe steels L80 and P110 under gaseous hydrogen charging up to 1000 bar and 200 °C

Because of increasing demands on hydrogen storage for green energy systems, the applied materials have to withstand severe conditions in terms of hydrogen partial pressure and temperature. The two industrial steel grades L80 and P110 are widely used for pipe line applications and were therefore chosen for this study. To determine the hydrogen uptake and the material performance under a constant load at pressures up to 1000 bar and 200 °C, a new autoclave test bench was established. Hydrogen charging at 1000 bar resulted in hydrogen contents of 1.24 wt.-ppm for L80 and 1.36 wt.-ppm for P110 respectively. Furthermore, the effective diffusion coefficients of both materials were determined as 1.4 · 10−6 cm2/s for L80 and 1.1 · 10−6 cm2/s for P110 by performing electrochemical permeation measurements. Based on the effective diffusion coefficients, numerical simulations were applied to calculate diffusion profiles and to examine the critical hydrogen content for embrittlement, which is 1.73 wt.-ppm for L80 and 1.0 wt.-ppm for P110 respectively. Although at 1000 bar higher hydrogen contents during tests have been obtained than critical hydrogen contents, none of the conducted constant load tests failed under a load of 90 % yield strength, not even for steel P110.

Effect of different hydrogen Fugacities on the microstructure of additively manufactured Ti-6Al-4V

In this study we compared the microstructural changes in the presence of hydrogen of Ti-6Al-4V alloy prepared by two different additive manufacturing (AM) methods: electron beam melting (EBM) and selective laser melting (SLM). Cathodic hydrogenation of AM Ti-6Al-4V resulted in significant expansion of β Ti phases due to the solute hydrogen, increasing of micro-strains, and α → titanium hydride/βH transformation. It was shown that SLM Ti-6Al-4V with acicular martensitic structure is more prone to hydrogen-induced phase transformation and hydrogen-assisted damage, compared to EBM. Moreover, it was revealed that different hydrogen charging environments cause different microstructural changes in EBM Ti-6Al-4V. Unlike cathodic hydrogen charging, gaseous hydrogen charging at elevated temperature reduced the process-induced micro-strains and promoted Al redistribution within the EBM Ti-6Al-4V. This resulted in massive precipitation of brittle α2-Ti3Al intermetallic compound, which act as a strong hydrogen trapping site aside from the Ti hydride phase.

The influence of gaseous hydrogen charging on the microstructural and mechanical behavior of electron beam melted and wrought Ti–6Al–4V alloys using the small punch test

The influence of gaseous hydrogen charging at 600 °C on the microstructure and mechanical behavior of wrought and Electron Beam Melted (EBM) Ti–6Al–4V alloys was investigated for hydrogen contents between 0.14 and 1.0 wt%. The small punch test (SPT) technique was used to characterize the mechanical behavior of all specimens. Both EBM and wrought alloys containing ∼6 wt% β and similar impurity levels showed similar phase content and mechanical property changes at all hydrogen contents, regardless of their original microstructural differences. This similarity can be explained by the high hydrogen diffusivity at the high temperature at which gaseous charging was carried out, and is in contrast to previous reports where EBM Ti–6Al–4V was found to be more sensitive to hydrogen embrittlement due to low-temperature electrochemical charging. After hydrogenation, αH and βH solid solutions were formed. The quantity of the αH phase reduced gradually with hydrogen content, while forming βH, α2, and hydrides. It was found that βH saturated at 0.27 wt% hydrogen content. Both alloys demonstrated relatively high strength and ductility up to hydrogen content of 0.2 wt%, i.e. below the βH saturation concentration. Above the βH saturation concentration, the mechanical properties of the maximum load (Pmax), deflection at maximum load (δmax), and absorbed energy (E), degraded significantly due to hydride formation.

Hydrogen-Accelerated Fatigue of API X60 Pipeline Steel and Its Weld

In this work, the hydrogen fatigue of pipeline steel X60, its girth welds and weld defects were investigated through in situ fatigue testing. A novel in situ gaseous hydrogen charging fatigue set-up was developed, which involves a sample geometry that mimics a small-scale pipeline with high internal hydrogen gas pressure. The effect of hydrogen was investigated by measuring the crack initiation and growth, using a direct current potential drop (DCPD) set-up, which probes the outer surface of the specimen. The base and weld metal specimens both experienced a reduction in fatigue life in the presence of hydrogen. For the base metal, the reduction in fatigue life manifested solely in the crack growth phase; hydrogen accelerated the crack growth by a factor of 4. The crack growth rate for the weld metal accelerated by a factor of 8. However, in contrast to the base metal, the weld metal also experienced a reduction of 57% in resistance to crack initiation. Macropores (>500 µm in size) on the notch surface reduced the fatigue life by a factor of 11. Varying the pressure from 70 barg to 150 barg of hydrogen caused no difference in the hydrogen fatigue behavior of the weld metal. The fracture path of the base and weld metal transitioned from transgranular and ductile in nature to a mixed-mode transgranular and intergranular quasi-cleavage fracture. Hydrogen accelerated the crack growth by decreasing the roughness- and plasticity-induced crack closure. The worst case scenario for pipelines was found in the case of weld defects. This work therefore highlights the necessity to re-evaluate pipelines for existing defects before they can be reused for hydrogen transport.

Experimental comparison of gaseous and electrochemical hydrogen charging in X65 pipeline steel using the permeation technique

Herein, hydrogen uptake and diffusivity in X65 pipeline steel were investigated using the permeation technique under different hydrogen charging conditions. Hydrogen charging was performed using hydrogen gas at different pressures, and electrochemical charging was performed at different cathodic current densities. The results revealed that both the sub-surface hydrogen concentration in lattice and reversible trap sites and the effective hydrogen diffusivity were dependent on the charging conditions. Moreover, the relationship between equivalent hydrogen fugacity and overpotential was determined.

Numerical Modeling for Rapid Charging of Hydrogen Gas Vessel in Fuel Cell Vehicle

As a fuel for power generation, high-pressure hydrogen gas is widely used for transportation, and its efficient storage promotes the development of fuel cell vehicles (FCVs). However, as the filling process takes such a short time, the maximum temperature in the storage tank usually undergoes a rapid increase, which has become a thorny problem and poses great technical challenges to the steady operation of hydrogen FCVs. For security reasons, SAE J2601/ISO 15869 regulates a maximum temperature limit of 85 °C in the specifications for refillable hydrogen tanks. In this paper, a two-dimensional axisymmetric and a three-dimensional numerical model for fast charging of Type III, 35 MPa, and 70 MPa hydrogen vehicle cylinders are proposed in order to effectively evaluate the temperature rise within vehicle tanks. A modified standard k-ε turbulence model is utilized to simulate hydrogen gas charging. The equation of state for hydrogen gas is adopted with the thermodynamic properties taken from the National Institute of Standards and Technology (NIST) database, taking into account the impact of hydrogen gas’ compressibility. To validate the numerical model, three groups of hydrogen rapid refueling experimental data are chosen. After a detailed comparison, it is found that the simulated results calculated by the developed numerical model are in good agreement with the experimental results, with average temperature differences at the end time of 2.56 K, 4.08 K, and 4.3 K. The present study provides a foundation for in-depth investigations on the structural mechanics analysis of hydrogen gas vessels during fast refueling and may supply some technical guidance on the design of charging experiments.

Change in nanoindentation hardness of polycrystalline tungsten irradiated with Fe ions or electrons by hydrogen gas charging

The effects of hydrogen atoms on the hardnesses of unirradiated, ion-irradiated, and electron-irradiated polycrystalline tungsten samples were investigated using nanoindentation tests. The bulk equivalent hardnesses of the unirradiated and electron-irradiated tungsten samples did not change upon hydrogen charging. The bulk equivalent hardness of the ion-irradiated tungsten increased upon the hydrogen charging. The number of hydrogen atoms trapped at dislocation loops was very small. We estimated that the hydrogen occupancy in vacancy clusters was 0.24−0.45 (in the case of tri-vacancies, the number of hydrogen atoms trapped per vacancy (H/V) is 1.04−1.95). Because of the irradiation temperature of 573 K, the density and size of irradiation-induced defects did not change during hydrogen charging at 543 K. Therefore, the hardening was mainly caused by an increase of approximately 8 − 11% in the obstacle strength α of vacancy clusters containing hydrogen atoms. The ion-irradiated area hardened upon the hydrogen charging and changed the configuration of the pile-up. Observation of the dislocation structure is required to clarify the mechanism of hardening caused by hydrogen charging.

Quantitative Evaluation of Hydrogen Effects on Evolutions of Deformation-Induced ε-Martensite and Damage in a High-Mn Steel

We investigated the effects of hydrogen on e-martensite-related damage evolution (crack/void initiation and growth) in Fe-Mn-Si-base austenitic steel using tensile tests after gaseous hydrogen charging at 100 MPa. Specifically, we evaluated the quantitative hydrogen effects on e-martensite fraction and associated damage evolution with different strains and strain rates. Hydrogen charging increased the probability of e-martensite-related damage initiation and deteriorated micro-damage arrestability, which decreased elongation. The primary factor causing the detrimental hydrogen effects on resistance to damage evolution was the promotion of deformation-induced γ-e martensitic transformation. An increasing strain rate from 10−4 to 10−2 s−1 suppressed the γ-e martensitic transformation and correspondingly increased elongation. Interestingly, the e-martensite fraction near the fracture surface did not change with increasing strain rate, but the area fraction of the brittle-like fracture region decreased. This fact implied that the brittle-like fracture at the low strain rate, which had a longer time for damage growth, was assisted by stress-driven hydrogen diffusion near the crack/void tips.

Effects of Mn Content and Grain Size on Hydrogen Embrittlement Susceptibility of Face-Centered Cubic High-Entropy Alloys

The effects of Mn content and grain size on the hydrogen embrittlement resistance of face-centered cubic (FCC) CrCoFeMnNi high-entropy alloys were examined using tensile testing at an initial strain rate of 10−4 s−1. The most important finding of this study was that the combined effect of Mn removal and grain refinement provided nearly complete resistance to hydrogen embrittlement with over 800 MPa tensile strength in FCC high-entropy alloys, even after 100 MPa hydrogen gas charging.

Effect of gaseous hydrogen embrittlement on the mechanical properties of additively manufactured CrMnFeCoNi high-entropy alloy strengthened by in-situ formed oxide

Effect of gaseous hydrogen charging on the mechanical properties of additively-manufactured CrMnFeCoNi high-entropy alloy (HEA) strengthened by in-situ formed oxide was investigated. The results showed that SLM-built HEA exhibited yield strength of ∼729.6 MPa and has an excellent hydrogen embrittlement resistance due to high-hydrogen solubility and easy deformation twin formation.

Influence of charging conditions on simulated temperature-programmed desorption for hydrogen in metals

Failures attributed to hydrogen embrittlement are a major concern for metals so a better understanding of damage micro-mechanisms and hydrogen diffusion within the metal is needed. Local concentrations depend on transport phenomena including trapping effects, which are usually characterised by a temperature-programmed desorption method often referred to as Thermal Desorption Analysis (TDA). When the hydrogen is released from the specimen during the programmed heating, some desorption peaks are observed that are commonly related to detrapping energies by means of an analytical procedure. The limitations of this approach are revisited here and gaseous hydrogen charging at high temperatures is simulated. This popular procedure enables attaining high concentrations due to the higher solubility of hydrogen at high temperatures. However, the segregation behaviour of hydrogen into traps depends on charging time and temperature. This process and the subsequent cooling alter hydrogen distribution are numerically modelled; it is found that TDA spectra are strongly affected by the charging temperature and the charging time, both for weak and strong traps. However, the influence of ageing time at room temperature after cooling and before desorption is only appreciable for weak traps.

Hydrogen-Induced Microstructure Optimization of the Ti-6Al-4V Alloy

To obtain advanced materials through the development of traditional materials without the addition of another alloying element, advanced heat treatment can be used. One such innovative process is a thermo-hydrogen treatment (THT); it facilitates a purposeful adjustment of an improved microstructure using hydrogen as a temporary alloying element within heat treatment. In this paper, the five-step process of homogenization, hydrogenation, solution treatment, dehydrogenation, and aging was used in THT. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), backscattered electron (BSE), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) were utilized to analyze the phases and phase transformations in Ti-6Al-4V. Three different homogeneous microstructures were established for the investigation using different homogenization parameters values. The hydrogenation was carried out for these microstructures via hydrogen gas charging leading to hydrogen concentrations for the formation of hydride (δ TiH2). After the solution treatment at a temperature above β transus temperature (Tβ), the metastable phases of a martensitic structure consisting of a mixture of α ́ (hcp) and α ́ ́ (orthorhombic) was found. Steps 4 and 5 of THT were a vacuum annealing (hydrogen degassing) followed by aging treatment. The aging treatment was applied to complete the martensite phase decomposition and the precipitation of two phases. By means of this THT cycle, very fine equiaxed microstructures could be established. These microstructures consist of the αs phase (secondary α) in the β phase matrix and the α2 phase (Ti3Al) in the αp phase. The precipitation of these phases increases the strength of the Ti-6Al-4V alloy and, consequently, enhances the mechanical properties. No evidence of the δ phase was found.

Comparative Study of Hydrogen Embrittlement of Three Heat-resistant Cr-Mo Steels Subjected to Electrochemical and Gaseous Hydrogen Charging

Hydrogen embrittlement (HE) behaviors of low carbon steel and three heat-resistant Cr-Mo steels having different Cr contents were compared through tensile testing, silver decoration, and blistering observation after electrochemical hydrogen charging and hardness testing after gaseous hydrogen charging. It was observed that higher Cr content caused a longer suppression in charging hydrogen into the steels. However, under hydrogen supersaturation conditions, the higher the strength of the heat-resistant steels, the poorer the HE resistance after electrochemical charging. In contrast, the higher the Cr content, the better the HE resistance under high-temperature gaseous charging conditions.

Understanding the role of hydrogen on creep behaviour of Zircaloy-4 cladding tubes using nanoindentation

The present article investigates the influence of hydrogen concentration on the creep performance of cold-worked stress-relieved unirradiated Zircaloy-4 cladding tube using nanoindentation technique. The as-received Zircaloy-4 tube is hydrided to the concentrations of 600 ppm and 900 ppm using gaseous hydrogen charging method. Constant load indentation creep tests are performed for a dwell period of 600 s in the temperature range of 300°C-500 °C at 1000 μN, 2000 μN, and 3000 μN. The impact of hydrogen is evaluated in terms of steady state power law creep exponent and activation energy. The power law creep exponent decreases with increase in hydrogen concentration, however, it remains fairly constant with increase in temperature up to 500 °C. Moreover, activation energy too decreases significantly with increase in hydrogen concentration. The mean stress exponent and activation energy are found to be 3.58 and 28.67 kJ/mol, respectively, for as-received sample.

Tensile and Fracture Behaviors of Austenitic High-Manganese Steels Subject to Different Hydrogen Embrittlement Test Methods

The hydrogen embrittlement susceptibility of austenitic high-manganese steels according to different hydrogen charging test methods was discussed in terms of hydrogen embrittlement process and fracture mechanism. Ex-situ electrochemical and high-pressure thermal hydrogen charging methods exhibited a difference in hydrogen embrittlement susceptibility because they affect the permeability and diffusivity of hydrogen. Moreover, the in-situ high-pressure gaseous hydrogen charging method showed the most apparent hydrogen embrittlement susceptibility because higher triaxial stress in the necked region caused by plastic instability accelerates hydrogen charging in the specimen during tensile testing in hydrogen environment, thus leading to intergranular fracture at all regions of the specimens.

Effect of radial hydride fraction on fracture toughness of CWSR Zr-2.5%Nb pressure tube material between ambient and 300 °C temperatures

Pressure tube spools fabricated from Zr-2.5%Nb alloy, were subjected to gaseous hydrogen charging and stress reorientation treatment to form radial hydrides in a specially designed fixture. Curved Compact Tension specimens of 17 mm width containing 100 wppm of hydrogen were made using electro discharge machining. Some of the samples were annealed at 300, 325 and 350 °C followed by furnace cooling. Metallographic examination of the samples revealed 100% radial hydride in the samples to which stress reorientation treatment was imparted. The radial hydride fraction decreased with increase in the temperature of annealing that followed stress reorientation. Fracture toughness of samples with variable radial hydride fraction was evaluated as per ASTM E1820-13 procedure between 25 and 300 °C. All the samples exhibited a sharp ductile to brittle transition behavior and the transition temperature was observed to increase with increase in the radial hydride fraction.

Equivalent hydrogen fugacity during electrochemical charging of some martensitic advanced high-strength steels

A new thermal desorption spectroscopy apparatus was used to study hydrogen in four martensitic advanced high-strength steels (designated MS980, MS1180, MS1300 and MS1500) after gaseous hydrogen charging, and after hydrogen charging electrochemically in 0.1M NaOH and in 3.5wt.% NaCl. The hydrogen concentration did not correlate strongly with steel strength. For MS1500, a relationship was derived between equivalent hydrogen fugacity and the applied charging overpotential. Also for MS1500, the trap binding energies were evaluated to be 26.4kJmol−1 and 61.0kJmol−1, which were interpreted as dislocation and interface hydrogen traps.

Microstructure and mechanical properties of Ti44Al6Nb1Cr2V alloy after gaseous hydrogen charging at 1373–1693 K

The hydrogenation behavior of Ti44Al6Nb1Cr2V (at%) alloy at temperature range of 1373–1693 K and its effect on microstructure and room-temperature mechanical properties were studied systematically in this study. The results show that hydrogen content increases with the increase in temperature, and the maximum hydrogen content is 0.126 wt% at 1693 K. The heat of solution of hydrogen is calculated as 82.9 kJ·mol−1 by curve fitting, indicating that hydrogen absorption in TiAl alloys is endothermic. Hydrogen promotes the lamellar colony size because hydrogen promotes the diffusion of elements. Hydrogen stabilizes B2 phase during hydrogenation resulting in more residual B2 phase in the hydrogenated alloy. The nanohardness and elastic modulus decrease after hydrogenation due to that hydrogen weakens the bonds. The Ti44Al6Nb1Cr2V alloy exhibits higher plasticity and lower flow stress hydrogenation with 0.039 wt% H, and the ultimate compressive strength decreases from 1220 to 1130 MPa, while the fracture strain is enhanced by 26%.