Hydrogen Gas Environment Research Articles

Test Method to Establish Hydrogen Compatibility of Materials in High Pressure Hydrogen Gas Environments for Fuel Cell Vehicles

Test Method to Establish Hydrogen Compatibility of Materials in High Pressure Hydrogen Gas Environments for Fuel Cell Vehicles

Review and Assessment of the Effect of Hydrogen Gas Pressure on the Embrittlement of Steels in Gaseous Hydrogen Environment

Hydrogen gas pressure is an important test parameter when considering materials for high-pressure hydrogen applications. A large set of data on the effect of hydrogen gas pressure on mechanical properties in gaseous hydrogen experiments was reviewed. The data were analyzed by converting pressures into fugacities (f) and by fitting the data using an f|n| power law. For 95% of the data sets, |n| was smaller than 0.37, which was discussed in the context of (i) rate-limiting steps in the hydrogen reaction chain and (ii) statistical aspects. This analysis might contribute to defining the appropriate test fugacities (pressures) to qualify materials for gaseous hydrogen applications.

Pearlite-driven surface-cracking and associated loss of tensile ductility in plain-carbon steels under exposure to high-pressure gaseous hydrogen

Four, hot-rolled, plain-carbon steels with varying carbon content were subjected to slow strain-rate tensile (SSRT) tests in a 95-MPa gaseous hydrogen environment at ambient temperature. The influence of pearlite volume fraction on the magnitude of hydrogen-induced degradation of the materials’ strength and ductility was thereby determined. Hydrogen was seen to significantly affect strain-to-failure and reduction-in-area in all four materials, wherein such a loss of tensile ductility was ascribed to the premature initiation and subsequent propagation of surface micro-cracks as revealed by the quantitative damage evolution analyses on the post-fractured specimens. The pearlite grains on sample surfaces manifestly served as the preferential origins of hydrogen-induced micro-cracks, resulting in more considerable embrittlement in materials possessing a higher percentage of pearlite, due to the rapid coalescence of discrete embryonic damage during tensile straining.

A coupled cohesive modeling approach for predicting fractures in low alloy steel under high-pressure hydrogen gas

Hydrogen-induced fractures usually occur in low alloy steel under the influences of stress concentration and high-pressure hydrogen gas. The purpose of this study was to predict the hydrogen-induced fracture behavior of low alloy steel under a high-pressure hydrogen gas environment. The hydrogen-sensitive cohesive model was used for the prediction of crack propagation, which took into account the influence of high-pressure hydrogen gas. The coupling model between hydrogen diffusion and plastic deformation was also applied by using UMAT and UMATHT subroutines. Disk pressure tests were performed on 4130X steel with different hydrogen pressure rise rates to demonstrate the coupled cohesive modeling approach. The hydrogen-induced fracture behaviors of the 4130X steel disk predicted by the proposed approach showed good agreement with experimental results. Numerical results indicated that hydrogen accumulated at the anchorage of the disk and reduced the maximum cohesive stress with the enhancement of localized plastic deformation. Therefore, the crack growth rate of the disk increased under a high-pressure hydrogen gas environment with relatively low maximum cohesive stress and low fracture energy.

Cold Plasma Treatment of Soybean Oil with Hydrogen Gas

AbstractHigh‐voltage atmospheric cold plasma (HVACP) treatment generates reactive gas species that induce inter‐ and intramolecular reactions in soybean oil. The goal of this study is to analyze the effect of HVACP treatment on the chemical structure of soybean oil in a hydrogen gas environment at atmospheric pressure. HVACP was used to treat soybean oil (15 g) for up to 6 hours by triplicate. Plasma‐generated reactive gas species interact with the sample, producing three distinct fractions identified as a liquid, gel, and solid. Fatty acid profile, Fourier‐transform infrared spectroscopy, proton and carbon nuclear magnetic resonance, size‐exclusion chromatography, thermal properties, and peroxide value were used to characterize the chemical structure. Results indicated a lower content of polyunsaturated fatty acids, increased content of saturated fatty acids, and the presence of isomers. An insoluble portion was observed in the solid fraction and increased with treatment time up to 42% in the 6‐h treated samples. Plasma species may cause two main reactions: polymerization and hydrogenation.

Hydrogen-assisted fatigue crack-propagation in a Ni-based superalloy 718, revealed via crack-path crystallography and deformation microstructures

Fatigue crack-growth (FCG) of Ni-based superalloy 718 was investigated under gaseous hydrogen environment (external hydrogen) and uniformly pre-charged state (internal hydrogen). Under external hydrogen, intergranular fracture predominated, whereas dislocation slip-band or twin boundary fracture were prevalent under internal hydrogen. This failure mode divergence encompassed unique characteristics of macroscale FCG response, leading to both cycle- and time-dependent cracking. The intergranular cracking was ascribed to short-circuit diffusion of hydrogen along grain boundaries. Meanwhile, the material’s inherently inhomogeneous deformation mode exerts harmfulness when hydrogen was uniformly distributed inside the specimen, causing slip-bands or twin boundaries to become the weakest links for fracture.

Tetralin and Decalin H-Donor Effect on Catalytic Upgrading of Heavy Oil Inductively Heated with Steel Balls

The Toe-to-Heel Air Injection (THAI) combined with catalytic upgrading process in situ (CAPRI) has demonstrated it can simultaneously extract and upgrade heavy oil in situ. This paper reports the investigation of augmenting temperature deficit and suppressing coke formation in the CAPRI section through the incorporation of induction heating and H-donor solvents. An induction-heated catalytic reactor was designed and developed, heated with steel balls in a mixed bed of NiMo/Al2O3 catalyst (66% v/v) to 425 °C temperature, 15 bar pressure and 0.75 h−1 LHSV (Liquid Hourly Space Velocity). The catalyst surface area, pore volume and pore size distribution were determined by using nitrogen adsorption–desorption, while the location of coke deposits within the microstructure of the pelleted spent catalyst was analyzed with X-ray nano-Computed Tomography (X-ray nano-CT). Findings showed that induction heating improved the catalyst performance, resulting in a 2.2° American Petroleum Institute (API) gravity increase of the upgraded oil over that achieved with the conventional heating method. The increment in API gravity and viscosity reduction in the upgraded oils with nitrogen gas only, N2 and H-donor solvents, and hydrogen gas environments can be summarized as follows: decalin > H2 gas >= tetralin > N2 gas. Meanwhile, the improvement in naphtha fraction, middle distillate fractions and suppression of coke formation are as follows: decalin > H2 gas > tetralin > N2 gas. The X-ray nano-CT of the spent catalyst revealed that the pellet suffers deactivation due to coke deposit at the external surface and pore-mouth blockage, signifying underutilization of the catalyst interior surface area.

Environment hydrogen embrittlement of pipeline steel X70 under various gas mixture conditions with in situ small punch tests

A series of small punch (SP) tests was conducted to investigate the effect of natural/hydrogen gas mixture conditions on the mechanical properties of X70 pipeline steel. The various gas mixture conditions included 0.1, 0.5, 1, 3, and 5 vol% hydrogen blends and three typical pipeline pressure levels (5, 7, and 10 MPa). The hydrogen embrittlement (HE) susceptibility grades depend on the hydrogen concentration and tend to increase with hydrogen concentration. The hydrogen gas mixture conditions have an insignificant effect on the yield load of the elastic bending region, whereas the maximal load decreases significantly when the hydrogen concentrations increase. Moreover, the quantitative parameters obtained from the SP load displacement curves and fracture morphologies were analyzed to characterize the HE behavior. By evaluating the SP absorption energy as a function of the hydrogen pressure, the ductile–brittle transition and saturated hydrogen pressures of the HE were determined. According to the results, the strength degradation grades of the mechanical properties of X70 pipeline steel in the gaseous hydrogen environment were not affected by the exposure time.

Effect of hydrogen on tensile flow and failure mechanism of low nickel-type 316L austenitic stainless steel

An investigation of the effects of hydrogen on tensile flow, strain-hardening and fracture characteristics of low nickel-type 316L austenitic stainless steel was quantified by means of slow strain rate tensile (SSRT) tests. Both thermal precharged and gaseous hydrogen conditions will be considered. The strain-hardening parameters were derived for an idealized true-stress/true-strain curve expressed by Hollomon’s equation. It was found that hydrogen affects the strain-hardening rate and reduces the overall strain-hardening exponents with a similar tendency for diminution of reduction area and fracture strain. The severity of hydrogen embrittlement was observed to be greater in a gaseous hydrogen environment than when tested in the hydrogen pre-charged specimen. Moreover, the fracture mechanism caused by hydrogen pre-charged and gaseous hydrogen environments were different. Hydrogen-induced cracks in hydrogen were found to appear at the interior of the grain boundary, in which there was a strain-induced martensite transformation phase, and crack formation at the grain boundary was predominant gaseous hydrogen specimens.

Pt8 cluster on alumina under a pressure of hydrogen: Support-dependent reconstruction from first-principles global optimization.

Alumina supported Pt nanoclusters under a hydrogen environment play a crucial role in many heterogeneous catalysis applications. We conducted grand canonical genetic algorithm simulations for supported Pt8 clusters in a hydrogen gas environment to study the intracluster, cluster-support, and cluster-adsorbate interactions. Two alumina surfaces, α-Al2O3(0001) and γ-Al2O3(100), and two conditions, T = 600 °C, pH2 = 0.1 bar and T = 25 °C, pH2 = 1.0 bar, were considered corresponding to low and high hydrogen chemical potential μH, respectively. The low free energy ensemble of Pt8 is decorated by a medium (2-12 H), respectively, high (20-30 H), number of hydrogen atoms under equilibrium at low μH, respectively, high μH, and undergoes different morphological transformations on the two surfaces. On α-Al2O3(0001), Pt8 is mostly 3D but very fluxional in structure at low μH and converts to open one-layer 2D structures with minimal fluxionality at high μH, whereas on γ-Al2O3(100), the exact opposite occurs: Pt8 clusters present one-layer 2D shapes at low μH and switch to compact 3D shapes under high μH, during which the Pt8 cluster preserves moderate fluxionality. Further analysis reveals a similar Pt-Pt bond length increase when switching from low μH to high μH on both surfaces although morphological transformations are different. Electronic structure analysis shows the existence of bonding interactions between Pt and Lewis acidic Al3+ sites along with the Pt-O interaction, which implies the necessity to include Al neighbors to discuss the electronic structure of small Pt clusters.

The inhibitory effect of carbon monoxide contained in hydrogen gas environment on hydrogen-accelerated fatigue crack growth and its loading frequency dependency

The effect of carbon monoxide (CO) contained in H2 gas as an impurity on the hydrogen-accelerated fatigue crack growth of A333 pipe steel was studied in association with loading frequency dependency. The addition of CO to H2 gas inhibited the accelerated fatigue crack growth due to the hydrogen. The inhibitory effect was affected by the CO content in the H2 gas, loading frequency, and crack growth rate. Based on these results, it was revealed that the inhibitory effect of CO was governed by both competition between the rate of fresh surface creation by the crack growth and the rate of coverage of the surface by CO and time for hydrogen diffusion in the material to the crack tip with reduced hydrogen entry by CO.

Pronounced transition of crack initiation and propagation modes in the hydrogen-related failure of a Ni-based superalloy 718 under internal and external hydrogen conditions

The role of hydrogen in tensile ductility loss and on the fracture behaviours of Ni-based superalloy 718 was investigated via tensile tests under hydrogen-charged conditions (internal hydrogen) or in gaseous hydrogen environments (external hydrogen), in combination with post-mortem analyses of fractured samples using electron microscopy techniques. Whereas intergranular fracture was responsible for material degradation under external hydrogen, the failure modes under internal hydrogen conditions were primarily dominated by cracking along slip planes or twin boundaries. The mechanisms of crack initiation and propagation are extensively discussed in terms of hydrogen distribution, intrinsic deformation character of the material and hydrogen-modified dislocation behavior.

Establishment of an in-situ small punch test method for characterizing hydrogen embrittlement behaviors under hydrogen gas environments and new influencing factor

The hydrogen embrittlement (HE) behaviors of structural materials used to handle hydrogen must be tested at their use environments. In this study, an in-situ small punch (SP) test method was established to characterize HE behaviors of SA372 and STS304 steels under hydrogen gas environments at high pressures and low temperatures. In addition, a new influencing factor, relative reduction of thickness (RRT) was proposed to quantify the HE sensitivity of structural steels. Under 10 MPa H2 gas environment, load-displacement curves obtained and fractographic morphologies of the recovered specimens were analyzed to investigate the HE behaviors based on punch velocity and test temperature. When the HE sensitivity was evaluated by RRT, STS304 steel appeared to be vulnerable to HE as compared to SA372 steel across the tested temperature range. As a result, it was found that in-situ SP test and RRT can be used to quantify the HE sensitivity for structural materials screening regardless of test environments.

Assessment of the impact of hydrogen on the stress developed ahead of a fatigue crack

The microstructure generated in a low carbon steel under cyclic loading in air and a 40 MPa gaseous hydrogen environment has been compared as a function of distance from the crack tip. The presence of hydrogen resulted in the formation of a smaller and more equiaxed dislocation cell structure that extended further from the crack tip than the one generated in air. This enhancement and extension of the dislocation structure by hydrogen is consistent with it modifying the generation rate and mobility of dislocations as well as dislocation interactions. Qualitative assessment of the dislocation structure ahead of the crack tip found the stress ahead of the crack tip to vary linearly as ln(1/x), where x is the distance from the crack tip irrespective of the test environment. Hydrogen caused a shift to higher stresses, implying the critical damage level for crack propagation will be achieved more rapidly with a concomitant increase in the crack propagation rate.

Study of excimer laser ablation of photoresist polymer in presence of hydrogen gas environment for micro-fluidic applications

Excimer laser micro-machining has been extensively explored to fabricate micro-patterns in the last few decades in the field of micro-fluidics, precision bearings, optics, micro-electronics etc in their previous work, it was observed by the authors that hydrogen gas has greater impact on the material removal rate and surface quality while ablating photo-resist polymer. In the present work, effect of hydrogen gas on the material removal rate has been mathematically modeled and simulated using finite element technique. In this simulation work, variation of surface temperature as well as ablation depth as a function of laser pulse energy have been analyzed. The simulation result showed an enhanced material removal rate in hydrogen environment due to laser assisted chemical reaction(LACR) involving nascent hydrogen and polymer. Further, a set of laser ablation experiments on polymer using 248 nm KrF Excimer laser has been conducted both with and without Hydrogen environment and under inert gas environment of argon, to validate the mathematical model. Results of the laser ablation experiments have shown the influence of hydrogen gas environment in enhancing both the material removal rate and the excellent edge definition, which is a novel outcome of the present research work and best suited process for the fabrication of micro-fluidic channels. The simulation results have been found in good agreement with the experimental data which supports technical soundness of the proposed model presented and discussed in the paper.

Evaluation of fatigue life and fatigue limit of circumferentially-notched Type 304 stainless steel in air and hydrogen gas based on crack-growth property and cyclic stress-strain response

Fatigue tests were performed using circumferentially-notched, round bar specimens with a stress concentration factor, Kt, of 6.6 for Type 304, metastable, austenitic stainless steel. The tests were carried out in ambient air and in 0.7 MPa hydrogen gas at room temperature. In a relatively higher stress amplitude regime (i.e., the amplitude resulting in Nf < 105), the hydrogen gas environment caused a marked degradation in fatigue life. In contrast, in a relatively lower stress amplitude regime (i.e., the amplitude resulting in Nf > 105), it appeared that fatigue life did not differ between air and hydrogen gas. It was also confirmed that the fatigue limit appeared not have been degraded in the hydrogen environment though there was a slight difference between the data obtained in two environments. The fatigue life curve and fatigue limit were predicted by assuming that the notch was equivalent to a circumferential crack. Consequently, there was a significant disparity between the prediction and the experimental results. As a result of microscopic observations of the fracture process in combination with elastic-plastic finite element analyses, these discrepancies were attributed to (i) complex cyclic plastic deformation behavior under large- and small-scale yielding conditions within the vicinity of the notch root, (ii) the retardation of crack initiation in the finite life regime, and (iii) the absence of non-propagating cracks at the fatigue limit, all of which are typical characteristics of metastable austenitic stainless steel.

Inhibitory effect of oxygen on hydrogen‐induced fracture of A333 pipe steel

AbstractThe effect of oxygen contained in hydrogen gas environment as an impurity on hydrogen environment embrittlement (HEE) of A333 pipe steel was studied through the fracture toughness tests in hydrogen gases. The oxygen contents in the hydrogen gases were 100, 10, and 0.1 vppm. A significant reduction in the J‐Δa curve was observed in the hydrogen with 0.1‐vppm oxygen. Under given loading conditions, the embrittling effect of hydrogen was completely inhibited by 100 vppm of oxygen. In the case of the hydrogen with 10‐vppm oxygen, initially the embrittling effect of hydrogen was fully inhibited, and then subsequently appeared. It was confirmed that 1‐vppm oxygen reduced the embrittling effect of hydrogen. The results can be explained by the predictive model of HEE proposed by Somerday et al.

Evaluation of notch sensitivity on fatigue limit in 70MPa hydrogen gas environment

Evaluation of notch sensitivity on fatigue limit in 70MPa hydrogen gas environment

Hydrogen Effect on the Fatigue Crack Growth in Austenitic Stainless Steel Investigated by a New Method Based on Nanohardness Distribution

A new method of nanohardness distribution for investigating the hydrogen effect on the fatigue crack in austenitic stainless steels was developed. The nanohardness distribution around the fatigue crack tip is dependent on the plastic zone and different microstructures in materials. Nanoindentation could provide a possibility to quantitatively estimate the size of the plastic zone and to expressly identify the strain-induced α′ martensitic transformation around the fatigue crack tip. The results of measured nanohardness distribution reveal that hydrogen reduces the size of the estimated plastic zone around the fatigue crack tip, especially in the specimen tested in hydrogen gas environment, which is attributed to hydrogen-enhanced localized plasticity. Both hydrogen and α′ martensite greatly influence the nanohardness and the gradient of hydrogen concentration near the crack tip, which will have a significant effect on the fatigue crack growth.

The roles of internal and external hydrogen in the deformation and fracture processes at the fatigue crack tip zone of metastable austenitic stainless steels

Fatigue crack growth (FCG) tests were performed with two types of metastable austenitic stainless steels having different austenite phase stabilities under hydrogen-precharged conditions (internal hydrogen) and in gaseous hydrogen environments (external hydrogen). The materials showed a peculiarly slower FCG rate with internal hydrogen than with external hydrogen even though the hydrogen concentration was much higher under the internal hydrogen conditions. The results are interpreted in terms of hydrogen-modified plastic deformation character comprising inhibited cross-slipping or enhanced deformation twinning in combination with the sequence of hydrogen penetration and strain-induced α′ martensite formation in the local region surrounding the fatigue crack tip.