Hydrogen has been postulated to affect fatigue crack growth rates (FCGRs) in Type 304/304L stainless steel during exposure to high purity water (HPW) environments at elevated temperature. To assess this mechanism, FCGR testing was performed at elevated temperature (260°C) in air and pressurized hydrogen gas. Initial results indicate the measured FCGRs in hydrogen are up to 8x lower than those measured in air under comparable fatigue loading conditions. Post-test evaluation of compact tension specimens indicates crack mouth opening displacements and fracture surface morphologies generated in hydrogen that are consistent with those generated in HPW environments. Observations of crack tip blunting suggest the reduced FCGRs in elevated temperature hydrogen occur due to a decrease in the effective ΔK. Finite element plasticity modeling, using a hydrogen-dependent nonlinear kinematic hardening approach, supports the hypothesis that crack tip blunting and retarded FCGRs are due to a hydrogen-based change in cyclic behavior (e.g. cyclic creep) occurring ahead of the fatigue crack tip.

Measurement of the near-threshold fatigue crack growth rate (da/dN) vs. stress-intensity factor range (OK) relationship in hydrogen gas is essential for maximizing the calculated design fatigue life of high-pressure hydrogen storage vessels. However, such measurements are rarely performed, since the low cyclic loading frequencies applied in standard practice lead to prohibitively protracted test durations. The objective of this study was to demonstrate two means for reducing test durations when measuring near-threshold da/dN vs. OKre-lationships under decreasing OK for low-alloy pressure vessel steels in hydrogen gas: 1) imposing steeper Kgradients relative to the recommended limits in standards such as ASTM E647, and 2) increasing cyclic loading frequency relative to typical values applied during fatigue crack growth testing of low-alloy steels in hydrogen gas. Recognizing that steeper K-gradients could amplify loading-history effects, test methods employing this approach were designed to mitigate such effects by either maintaining constant Kmax or gradually increasing the K-gradient as the threshold was approached. Although the varying K-gradient method was vulnerable to loading-history effects in the form of plasticity-induced crack closure, particularly at lower stress ratio (R) and higher starting Kmax values, these effects could be compensated by applying the adjusted compliance ratio (ACR) method. It was demonstrated that steeper K-gradients in concert with increased cyclic loading frequency reduced the duration of near-threshold fatigue crack growth tests in hydrogen gas by more than 99% relative to standard practices.

As the exigency for decarbonizing sectors such as utilities, heavy-duty transportation, and manufacturing has risen, interest in hydrogen technologies has intensified accordingly. Among the safety issues being addressed for hydrogen technologies is the potential for hydrogen embrittlement of steels, which are commonly specified for pressure boundaries in containment components. From an engineering perspective, hydrogen embrittlement of steels can be managed through conventional design and fitness-for-service (FFS) practices provided the mechanical property inputs are measured appropriately, i.e., testing of steels is performed in the hydrogen environment. Given the increasing need for managing hydrogen embrittlement to safely operate high-pressure containment components, the purpose of this review is to comprehensively survey and critically assess the literature on the following mechanical properties of steels in gaseous hydrogen that serve as inputs to design and FFS analyses: threshold stress-intensity factor or threshold J-integral for subcritical, time-dependent cracking, fatigue crack growth rate, and total fatigue life. The review focuses on such mechanical properties in gaseous hydrogen for carbon-manganese (C-Mn) steels, low-alloy steels, austenitic stainless steels, duplex stainless steels, as well as the ferritic and martensitic stainless steels, since these are most pertinent to containment components in hydrogen technology. Three high-level conclusions from the review are the following: 1) mechanical property data for C-Mn and low-alloy steels in hydrogen gas are sufficiently mature so that conservative limits can be specified for design and FFS analyses, 2) mechanical property data for austenitic stainless steels must be supplemented with additional measurements, particularly from specimens tested in high-pressure hydrogen gas, before conservative limits can be defined for design and FFS analyses, and 3) mechanical property data for ferritic, martensitic, and duplex stainless steels in hydrogen gas are so scarce that design and FFS analyses covering wide ranges of steel grades and component service conditions are currently not feasible.

Fracture by hydrogen accelerated fatigue crack growth is a severe type of environmental failure. Although fatigue crack growth has been the subject of intense investigation over several decades, a complete mechanistic and predictive model is still lacking. Such a crack growth model is even more rare in the case of hydrogen in view of the lack also of constitutive models for material deformation under cycling loading that account for the hydrogen effect. In this study, we present a model for fatigue crack propagation induced by alternating crack tip plastic blunting and re-sharpening, which in the presence of hydrogen can be accelerated by hydrogen enhanced dislocation motion and generation. The Chaboche constitutive model, which is a nonlinear kinematic hardening model capable of capturing many features of material behavior under cyclic loading, is used for the calculation of the stress and strain fields at the propagating crack tip. The Chaboche model is calibrated using a sequence of experimental data from uniaxial strain-controlled cyclic loading tests and uniaxial stress-controlled ratcheting tests with a low carbon steel, JIS SM490YB, in the absence and presence of hydrogen. The numerical simulation results indicate that the proposed crack propagation model can predict Paris law behavior and can successfully demonstrate acceleration of fatigue crack growth in the presence of hydrogen. Significantly, the profiles of the steady-state opening stress and strain ahead of the fatigue crack tip in a compact tension (C(T)) specimen were found to have sections over which they vary as ln(1/r) with distance r from the crack tip, consistent with the crack-tip strain field for a non-stationary crack.

It is expected that high-temperature hydrogen technologies, such as the solid oxide fuel cell and high-temperature water electrolysis, will play important roles in the hydrogen society. In this study, creep tests of JIS SUS304, SUS304L and SUS310S austenitic stainless steels and SUY-1 pure iron were carried out in hydrogen and argon at 873 K. For all the materials, the creep rate in the secondary creep region in hydrogen environment was increased. It resulted in reduction of the creep life. In argon, the fracture surface of the SUS304 changed from dimple to intergranular fracture with the increase in the creep life. In hydrogen, this change was delayed. Regarding the mechanism, it was confirmed that the effect of carbide formation, HELP and HTHA were not activated in this study. Instead, enhanced dislocation climb mediated by an increased vacancy density is a plausible mechanism, although further investigation is needed.

Current greenhouse gas emissions suggest that keeping global temperature increase below 1.5 degrees, as espoused in the Paris Agreements will be challenging, and to do so, the achievement of carbon neutrality is of utmost importance. It is also clear that no single solution can meet the carbon neutral challenge, so it is essential for scientific research to cover a broad range of technologies and initiatives which will enable the realization of a carbon free energy system. This study details the broad, yet targeted research themes being pioneered within the International Institute for Carbon-Neutral Energy Research (I2CNER). These approaches include hydrogen materials, bio-mimetic catalysts, electrochemistry, thermal energy and absorption, carbon capture, storage and management and refrigerants. Here we outline the state of the art for this suite of technologies and detail how their deployment, alongside prudent energy policy implementation can engender a carbon neutral Japan by 2050. Recognizing that just as no single technological solution will engender carbon neutrality, no single nation can expect to achieve this goal alone. This study represents a recognition of conducive international policy agendas and is representative of interdisciplinary, international collaboration.

Anomalous and inconsistent results were observed while performing fatigue crack growth tests in hydrogen gas on 4130X Cr-Mo steel when the stress-intensity factor range (ΔK) was less than 10 MPa m1/2. Two particular abnormal characteristics were noted: i) sequential measurements of fatigue crack growth rate (da/dN) vs. ΔK from a single test specimen were not repeatable at lower ΔK, and ii) at constant ΔK ∼8 MPa m1/2, da/dN never reached a steady-state level, as crack growth rates continuously increased as a function of time. It was hypothesized that both of these characteristics could be related to water vapor in the hydrogen gas. This hypothesis was tested by varying the environment in the test chamber through modification of the pressure purging and vacuum evacuation procedures. The resulting water vapor levels in the hydrogen test gas were either higher or lower than the nominal value, and measurements of fatigue crack growth rates in these environments confirmed the hypothesis that water vapor governed da/dN at lower ΔK. One consequence of such water vapor-dominated fatigue crack growth rates is that the da/dN vs. ΔK relationship in dry hydrogen gas at lower ΔK cannot be reliably represented by the da/dN vs. ΔK relationship measured in humid air. As a result, when the lower-ΔK portion of the da/dN vs. ΔK relationship in hydrogen gas is constructed from the da/dN vs. ΔK relationship in air, fatigue crack growth rates can be overestimated by as much as an order of magnitude.

The effect of loading rate (dK/dt) on the hydrogen environment-assisted cracking (HEAC) behavior of Monel K-500 immersed in 0.6 M NaCl and polarized to -950 and -1200 mV(SCE) was assessed via a slow-rising stress intensity (K) testing framework at dK/dt ranging from 0.2 to 20 MPa root m/hr. Comparative testing on Monel K-500 in an inert environment (dry N-2 with RH < 5%) at dK/dt ranging from 0.1 to 4 MPa/m/hr revealed a clear dK/dt-dependence of local plasticity effects on the direct current potential difference (dcPD) signal. A method for decoupling this "false" signal caused by local plasticity from the 'true' crack growth kinetics is presented. Analysis of the corrected data showed that the threshold stress intensity for the onset of HEAC (K-TH) was nominally invariant with dK/dt. The HEAC growth rates (da/dt) were only mildly dependent on dK/dt under severe environmental conditions (-1200 mV(SCE)). However, for moderate conditions (-950 mV(SCE)), a strong influence of dK/dt on HEAC growth rates (da/dt) was observed. For this latter testing environment, two characteristic regimes of behavior were noted depending on the applied dK/dt: (1) a 'plateau' regime where da/dt is independent of dK/dt was observed for dK/dt > 8 MPa root m/hr and (2) a 'linear' regime where log(da/dt) linearly scales with log(dK/dt) was observed for dK/dt < 8 MPa root m/hr. These trends are interpreted using resistance curves calculated from the measured da/dt vs. K-J data. The results of this analysis demonstrate that diffusion-mediated crack growth is only observed for dK/dt > 10 MPa root m/hr at -950 mV scE and all evaluated dK/dt at -1200 mV(SCE), while mechanics-based factors govern the da/dt response for dK/dt < 10 MPa root m/hr at -950 mV(SCE). The influence of dK/dt is considered in the context of current testing standards for evaluating HEAC susceptibility; specifically, rising K-based frameworks consistently yield conservative HEAC metrics.

The service life of high-pressure hydrogen storage vessels at fueling stations is dictated by fatigue crack growth. Standards such as the ASME Boiler and Pressure Vessel Code (BPVC) provide a methodology for calculating the fatigue-limited design life of high-pressure hydrogen storage vessels, in which one essential input is the fatigue crack growth rate (da/dN) vs. stress-intensity factor range (Delta K) relationship measured for the material of construction in the service environment, i.e. hydrogen gas. These measurements must also be conducted at sufficiently slow cyclic loading frequency since decreasing the frequency usually results in faster crack growth rates. Generation of complete fatigue crack growth data sets according to standard test methods becomes very time consuming and expensive when these environment and frequency criteria are met. Two modifications to standard test procedures may reduce the time and associated costs related to this testing. One approach is to accelerate the rate at which Delta K changes with respect to crack extension. This can be accomplished by controlling the normalized K-gradient, C, where C = 1/K.dK/da. In addition, by using negative values of C (i.e. decreasing Delta K), multiple da/dN vs Delta K segments can be generated from a single test specimen. This paper summarizes the status of a project designed to identify the limits to which these two strategies may be employed to measure fatigue crack growth relationships for pressure vessel steels in gaseous hydrogen environments. These limits are defined as the bounds where loading history effects begin to alter the measured da/dN vs Delta K relationships.

The objective of this study is to accumulate creep data in hydrogen of various materials in order to consider the mechanisms that hydrogen affects creep properties. Creep testing was performed in argon and hydrogen gases at 873K. The materials were JIS SUS304, SUS304L and SUS310S austenitic stainless steels and JIS SUY-1 commercial pure iron. For all materials, the creep life was reduced in hydrogen compared to that in argon to a greater or lesser extent. The creep ductility in hydrogen was higher than that in argon except for the pure iron. The mechanism that hydrogen reduced the creep life of the SUS304 we considered was the accelerated dislocation climb mediated by hydrogen increased vacancy concentration. According to the literatures, decarburization, carbide formation and hydrogen enhanced localized plasticity (HELP) were investigated. It was confirmed that these mechanisms were not activated in our creep test for the SUS304.

Fracture resistance of pipeline welds from a range of strength grades and welding techniques was measured in air and 21 MPa hydrogen gas, including electric resistance weld of X52, friction stir weld of X100 and gas metal arc welds (GMAW) of X52, X65 and X100. Welds exhibited a decrease in fracture resistance in hydrogen compared to complementary tests in air. A general trend was observed that fracture resistance in 21 MPa hydrogen gas decreased with increasing yield strength. To accommodate material constraints, two different fracture coupon geometries were used in this study, which were shown to yield similar fracture resistance values in air and 21 MPa hydrogen gas; values using different coupons resulted in less than 15% difference. In addition, fracture coupons were removed from controlled locations in select welds to examine the potential influence of orientation and residual stress. The two orientations examined in the X100 GMAW exhibited negligible differences in fracture resistance in air and, similarly, negligible differences in hydrogen. Residual stress exhibited a modest influence on fracture resistance; however, a consistent trend was not observed between tests in air and hydrogen, suggesting further studies are necessary to better understand the influence of residual stress. A comparison of welds and base metals tested in hydrogen gas showed similar susceptibility to hydrogen-assisted fracture. The overall dominant factor in determining the susceptibility to fracture resistance in hydrogen is the yield strength. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Austenitic stainless steels are used extensively in harsh environments, including for high-pressure gaseous hydrogen service. However, the tensile ductility of this class of materials is very sensitive to materials and environmental variables. While tensile ductility is generally insufficient to qualify a material for hydrogen service, ductility is an effective tool to explore microstructural and environmental variables and their effects on hydrogen susceptibility, to inform understanding of the mechanisms of hydrogen effects in metals, and to provide insight to microstructural variables that may improve relative performance. In this study, hydrogen precharging was used to simulate high-pressure hydrogen environments to evaluate hydrogen effects on tensile properties. Several austenitic stainless steels were considered, including both metastable and stable alloys. Room temperature and subambient temperature tensile properties were evaluated with three different internal hydrogen contents for type 304L and 316L austenitic stainless steels and one hydrogen content for XM-11. Significant ductility loss was observed for both metastable and stable alloys, suggesting the stability of the austenitic phase is not sufficient to characterize the effects of hydrogen. Internal hydrogen does influence the character of deformation, which drives local damage accumulation and ultimately fracture for both metastable and stable alloys. While a quantitative description of hydrogen-assisted fracture in austenitic stainless steels remains elusive, these observations underscore the importance of the hydrogen-defect interactions and the accumulation of damage at deformation length scales.

Hydrogen-accelerated fatigue crack growth is a most severe manifestation of hydrogen embrittlement. A mechanistic and predictive model is still lacking partly due to the lack of a descriptive constitutive model of the hydrogen/material interaction at the macroscale under cyclic loading. Such a model could be used to assess the nature of the stress and strain fields in the neighborhood of a crack, a development that could potentially lead to the association of these fields with proper macroscopic parameters. Toward this goal, a constitutive model for cyclic response should be capable of capturing hardening or softening under cyclic straining or ratcheting under stress-controlled testing. In this work, we attempt a constitutive description by using data from uniaxial strain-controlled cyclic loading and stress-controlled ratcheting tests with a low carbon steel, Japanese Industrial Standard (JIS) SM490YB, conducted in air and 1 MPa H-2 gas environment at room temperature. We explore the Chaboche constitutive model which is a nonlinear kinematic hardening model that was developed as an extension to the Frederick and Armstrong model, and propose an approach to calibrate the parameters involved. From the combined experimental data and the calibrated Chaboche model, we may conclude that hydrogen decreases the yield stress and the amount of cyclic hardening. On the other hand, hydrogen increases ratcheting, the rate of cyclic hardening, and promotes stronger recovery.

The fatigue crack growth behavior of Ti-10V-2Fe-3Al in gaseous hydrogen (H-2) was assessed through comparative experiments conducted in laboratory air and 8.3 MPa H-2. The measured fatigue crack growth rate (da/dN) versus applied stress intensity factor range (DK) relationships and observed fracture morphologies for laboratory air and H-2 were comparable up to Delta K approximate to 6.9 MPa root m, when tested at a load ratio of 0.1 and frequency of 10 Hz. At higher Delta K values, significant crack deflection and subsequent catastrophic failure occurred in the specimen tested in H-2. This degradation was not observed in a specimen pre-exposed to 8.3 MPa H-2 for 96 h and then immediately tested in laboratory air. X-ray diffraction of the failed H-2-tested specimen revealed that the material remnants were predominantly composed of TiH2, suggesting that hydride formation was the catalyst for catastrophic failure in H-2. The mechanistic implications of these results and their impact on current material compatibility assessments for Ti alloys in hydrogen service are then discussed. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The selection of austenitic stainless steels for hydrogen service is challenging since there are few intrinsic metrics that relate alloy composition to hydrogen degradation. One such metric, presented here, is intrinsic stacking fault energy (SFE). This work reviews the exiting literature to use estimated intrinsic SFE values, calculated with a sub-regular solution thermodynamic model, to compare the retention of tensile ductility of γ-austenitic stainless steels in the presence of hydrogen. The goal is to demonstrate SFE as a metric to screen γ-austenitic stainless steels that use diverse alloying strategies for hydrogen compatibility. A transition in the tensile reduction of area of both 300-series and manganese-stabilized stainless steels is observed at a calculated stacking fault energy of approximately 39 mJ m−2, below which pronounced hydrogen degradation on tensile ductility is observed. Calculated intrinsic stacking fault energy is demonstrated as a high-throughput screening metric for a diverse range of austenitic stainless steel compositions with regard to hydrogen compatibility.

The objective of this study is to derive mechanistic insight into the degradation of metals in high-temperature hydrogen in order to enable the safety of evolving hydrogen technologies that operate at elevated temperature. Creep testing was performed in argon and hydrogen gases under absolute pressure of 0.12 MPa at 873 K. The material was JIS SUS304 austenitic stainless steel. Results revealed that the creep life (time to failure) and creep ductility (strain to failure) of the SUS304 in hydrogen gas and in argon displayed opposite trends. While the creep life (time to failure) of the SUS304 in hydrogen gas was significantly shorter than that in argon, creep ductility (strain to failure) was higher in hydrogen. Associated with the relatively higher creep ductility, evidence of transgranular microvoid coalescence was more prevalent on fracture surfaces produced in hydrogen compared to those produced in argon. In addition, analysis of the steady-state creep relationships in hydrogen and argon indicated that the same creep mechanism operated in the two environments, which was deduced as dislocation creep. Regarding the mechanisms governing reduced creep life in hydrogen, the effects of decarburization, carbide formation, and the hydrogen-enhanced localized plasticity mechanism were investigated. It was confirmed that these effects were not responsible for the reduced creep life in hydrogen, at least within the creep life range of this study. Alternately, the plausible role of hydrogen was to enhance the vacancy density, which led to magnified lattice diffusion (self-diffusion) and associated dislocation climb. As a consequence, hydrogen accelerated the creep strain rate and shortened the creep life.

Hydrogen gas accelerates fatigue crack growth and reduces fracture toughness in ferritic structural materials such as pipelines and pressure vessels. The extent to which the crack growth rates are accelerated depends upon environment, mechanical loading conditions, and material. In this work, the effects of loading conditions and environment, specifically oxygen impurities, are examined on an X100 pipeline steel in high pressure hydrogen gas. Fatigue crack growth rates were measured in a gas mixture consisting of nominally 100 ppm O2 in a balance of H2 gas to evaluate the effects of pressure and load ratio (R-ratio) on the manifestation of hydrogen-accelerated fatigue crack growth (HA-FCG). Tests were performed at 21 MPa, 2.1 MPa, and 1.4 MPa and at load ratios of 0.5 and 0.1. The onset of HA-FCG was observed to be dependent on both absolute pressure and load ratio and it will be shown that a critical combination can result in complete mitigation of HA-FCG over the stress intensity factor range (ΔK) examined. Tests were predominantly performed at 10 Hz; however, a single test was performed at 1 Hz which exhibited negligible HA-FCG compared to a test at 10 Hz which did exhibit HA-FCG. Rising load fracture toughness tests were conducted via constant displacement rates to generate J-R curves in both pure H2 and 100 ppm O2 mixed gas. At similar absolute pressures, fracture toughness was measured to be greater in the 100 ppm O2 mixed gas compared to the pure H2. Hydrogen-assisted fracture was completely alleviated at pressures below 2.1 MPa in the 100 ppm O2 mixed gas, in which fracture toughness values were consistent with tests in air.

Oil Country Tubular Goods (OCTG) high strength steels are susceptible to hydrogen assisted cracking (HAC) due to hydrogen ingress as a result of exposure to environmental conditions (cathodic protection (CP) and/or H2S environments) and as such are prone to failure. In order to address the potential cracking susceptibility, a study was performed to understand fundamental parameters such as steady state hydrogen permeation flux, hydrogen concentrations and hydrogen trap binding energies of the high strength steel under charging conditions. Electrochemical permeation testing was performed on unstressed and 80%AYS stressed C110 pipe steel using an applied charging current density of 0.5 mA/cm2 in a 0.5M H2SO4 test solution at 75 F. Comparisons between the stressed and unstressed samples showed that there were no significant differences in steady state flux (Jss) and calculated hydrogen concentration for this charging condition. Further testing was performed to measure hydrogen uptake and time to saturation under the same charging conditions using the Silicone Oil Method. Subsequent laser thermal desorption mass spectrometry (LTDMS) was performed at the saturation point and at several temperature scan rates in order to calculate the apparent activation energy for hydrogen desorption, from which the binding energy for trap sites can be inferred (Eb).