Hydrogen Embrittlement Sensitivity Research Articles

Influence of welding defects on hydrogen embrittlement sensitivity of girth welds in X80 pipelines

Hydrogen embrittlement poses a considerable threat to girth welds in high-grade steel pipelines. This study investigated the influence of welding defects on the hydrogen embrittlement sensitivity of girth welds in X80 pipelines through slow strain rate tensile (SSRT) testing, scanning electron microscopy, hydrogen permeation test, and finite element analysis. The findings indicated that regardless of the presence of welding defects, the hydrogen embrittlement sensitivity of pipeline girth welds increases with negative current density. Welding defects can lead to a substantial increase in the hydrogen embrittlement sensitivity of girth welds and can shift crack initiation points from the surface areas of SSRT specimens to the locations of the defects. Stress concentration caused by welding defects results in the redistribution and local enrichment of hydrogen under the effect of stress-induced hydrogen diffusion, thereby leading to a considerable increase in hydrogen embrittlement sensitivity.

Influence of Nb on the hydrogen-assisted cracking behaviour in multiphase stainless steel: Phase fractions, stacking fault energies, and nanosized NbC precipitation

Nb alloying has been reported to deteriorate the hydrogen embrittlement resistance of multiphase steels, which contrasts to the case of single-phase metallic materials. This study clarifies the impact of Nb alloying on the hydrogen embrittlement behaviour of a novel multiphase stainless steel. The findings revealed a 17 % reduction in the hydrogen embrittlement sensitivity upon Nb incorporation. It was found that higher austenite fractions in the Nb-bearing steels impeded hydrogen ingress. The austenite phase in such Nb-bearing steels possesses a higher stacking fault energy, thereby delaying martensitic transformation and crack initiation. The precipitation of nanometre-sized NbC in the matrix obstructed hydrogen diffusion, which indirectly inhibited crack initiation and propagation.

Coupled slow strain rate and acoustic emission tests for gaseous hydrogen embrittlement assessment of API X65 pipeline steel

Hydrogen embrittlement (HE) sensitivity of API X65 pipeline steel was evaluated in this study through the simultaneous application of slow strain rate tests (SSRT) and acoustic emission (AE) monitoring on hollow dog-bone samples. Exposure to hydrogen gas decreased the elongation to fracture percentage with a significant rise in embrittlement index for the higher pressure of 10 MPa. SEM images of the fracture surfaces demonstrated that the fracture mechanism changed from ductile to ductile–brittle under 1 MPa pressure, and to predominantly brittle with quasi-cleavage characteristic when testing under 10 MPa hydrogen gas. Classification of the AE events based on waveform analysis revealed a mainly shear mode fracture for 10 MPa nitrogen sample, while a dominant tensile mode fracture was identified for the hydrogen charged samples.

Characterization of hydrogen embrittlement sensitivity of 18CrNiMo7-6 alloy steel surface-modified layer based on scratch method

PurposeThe purpose of this paper is to assess the hydrogen embrittlement sensitivity of carbon gradient heterostructure materials and to verify the reliability of the scratch method.Design/methodology/approachThe surface-modified layer of 18CrNiMo7-6 alloy steel was delaminated to study its hydrogen embrittlement characteristics via hydrogen permeation, electrochemical hydrogen charging and scratch experiments.FindingsThe results showed that the diffusion coefficients of hydrogen in the surface and matrix layers are 3.28 × 10−7 and 16.67 × 10−7 cm2/s, respectively. The diffusible-hydrogen concentration of the material increases with increasing hydrogen-charging current density. For a given hydrogen-charging current density, the diffusible-hydrogen concentration gradually decreases with increasing depth in the surface-modified layer. Fracture toughness decreases with increasing diffusible-hydrogen concentration, so the susceptibility to hydrogen embrittlement decreases with increasing depth in the surface-modified layer.Originality/valueThe reliability of the scratch method in evaluating the fracture toughness of the surface-modified layer material is verified. An empirical formula is given for fracture toughness as a function of diffused-hydrogen concentration.

Influence of hydrogen volume/specimen surface area ratio on hydrogen embrittlement sensitivity of X52 pipeline steel

In the transition towards green energy, long distance transportation of gaseous hydrogen by pipeline is considered to be an economically attractive solution. For safe transportation of hydrogen, it is important to conduct relevant mechanical tests in representative hydrogen environments and working conditions of pipelines to demonstrate acceptable hydrogen embrittlement resistance of the steel. One important issue is the testing condition for the ratio of gaseous hydrogen volume over specimen surface area required in mechanical testing since this has not been specified in any testing standards and codes or investigated. This study investigated this issue by performing slow strain rate tensile (SSRT) testing of an X52 pipeline steel in gaseous hydrogen with different ratios of hydrogen volume/specimen surface area, Rv/s, ml/mm2. It was found that, with increasing Rv/s ratio, the area reduction of the steel decreased and hydrogen embrittlement sensitivity increased in the range of the Rv/s ratios investigated. The saturating Rv/s ratio appeared to be ∼2.0 beyond which the effect of Rv/s ratio on hydrogen embrittlement sensitivity was relatively small. The macroscopic and microscopic observations on both the fracture and side surfaces of the SSRT tested specimens also found that the tendency to cleavage fracture increased with increasing Rv/s ratio. The results of the ab initio molecular dynamics (AIMD) simulations performed also predicted a dependence of hydrogen embrittlement on hydrogen volume when Rv/s ratio is relatively small.

An ensemble learning strategy for multi‐source hydrogen embrittlement data by introducing missing information

AbstractAccurately and quickly predicting hydrogen embrittlement performance is critical for the service of metal materials. However, due to multi‐source heterogeneity, existing hydrogen embrittlement data are missing, making it impractical to train reliable machine learning models. In this study, we proposed an ensemble learning training strategy for missing data based on the Adaboost algorithm. This method introduced a mask matrix with missing data and enabled each round of training to generate sub‐datasets, considering missing value information. The strategy first trained a subset of features based on the existing dataset and a selected method and continuously focused on the combination of features with the highest error for iterative training, where the mask matrix of the missing data was used as the input to fit the weights of each base learner using a neural network. Compared with directly modeling on highly sparse data, the predictive ability of this strategy was significantly improved by approximately 20%. In addition, in the testing of new samples, the predicted mean absolute error of the new model was successfully reduced from 0.2 to 0.09. This strategy offers good adaptability to the hydrogen embrittlement sensitivity of different sizes and can avoid interference from feature importance caused by filling data.

Change in Hydrogen Trapping Characteristics and Influence on Hydrogen Embrittlement Sensitivity in a Medium-Carbon, High-Strength Steel: The Effects of Heat Treatments.

Medium-carbon, high-strength steels are widely used in the field of hydrogen energy because of their good mechanical properties, and they can be readily tailored by heat treatment processes such as the normalizing-tempering (N&T) and quenching-tempering (Q&T) methods. The hydrogen embrittlement (HE) susceptibility of a medium-carbon, high-strength steel was investigated utilizing microstructural characterization with scanning electron microscopy (SEM), the electron backscatter diffraction (EBSD) technique, and transmission electron microscopy (TEM). A study was also conducted on the steel's hydrogen transport behavior as affected by the N&T and Q&T treatments. The steel contained more hydrogen traps, such as dislocations, grain boundaries, lath boundaries, and carbide interfaces, after the Q&T process, which was associated with a lower HE sensitivity when comparing the two treatments. In comparison, the N&T process produced larger-size and lesser-density carbides distributed along the grain boundaries, and this resulted in a relatively higher HE susceptibility, as revealed by the slow-strain-rate tensile (SSRT) tests of the hydrogen-charged steels and by the fractographic study of the fracture surface.

Effect of water vapour and H2S content on the hydrogen embrittlement sensitivity of low alloy steels for underground storage

A key point for the development of a renewable energy economy at a large scale is the possibility to use the current natural gas network and storage capacity to transport and store hydrogen. This study is dedicated to evaluate the integrity of materials used for underground aquifer storage regarding hydrogen embrittlement in a gaseous environment saturated with water vapour and containing few amounts of H2S. In this environment, the water vapour content in the gas stored may reach saturation at bottom well pressure and temperature. It is known that the presence of impurities in the gas, such as H2O, can promote or inhibit hydrogen embrittlement phenomenon, depending on the nature of the steel. This work investigates mechanical properties of a tempered martensite N80-Q steel, and a ferrite-perlite L360-NB C–Mn steel issued from a completion and a collect tube respectively. The testing environments are NG, NG + H2S, NG + 25%H2 and NG + 25%H2 + H2S saturated in water vapour at 8.5 MPa and room temperature. These environmental conditions aim at replicating the storage service conditions.Fracture toughness and fatigue crack growth properties are assessed. So far, the mechanical behaviour of such steels under hydrogen gas pressure saturated with water vapour and low amount of H2S has poorly been addressed. Regarding toughness properties, the two steels present different behaviour: for the L360 NB crack has not propagated for any testing environments, while cracks propagated in all the tests for the N80 Q. Despite this difference, for the two steels, the toughness does not seem to be affected by hydrogen as the results obtained in NG + 25%H2 + H2O and NG + H2O are similar. Based on the literature C–Mn steels toughness is affected by the presence of dry hydrogen. Hence, the results presented here show that H2O inhibits hydrogen embrittlement as far as toughness is concerned. The L360NB, however, presented a slight decrease in toughness properties with the combination of NG + 25%H2 + H2S + H2O. FCG (fatigue crack growth) results, on the opposite, clearly highlight the influence of hydrogen on the mechanical behaviour of the two steels. The FCG rates are faster from a factor five (resp. 10) in NG + 25%H2 + H2O compared to NG + H2O for the N80 Q (resp. L360). In this article, toughness and FGC results on the two steels are discussed in terms of microstructure and mechanical loading modes, aiming to quantify and better understand the influence of H2O and H2S on the sensitivity of low alloy steels to hydrogen embrittlement.

Iterative multi-objective design of hydrogen embrittlement resistant high-strength steels using Bayesian optimization

The infiltration of hydrogen can weaken the strength and toughness of materials, especially in high-strength steel. Considering the inherent trade-off between strength and toughness in steel design, balancing these two factors with the material's hydrogen embrittlement sensitivity has become a huge challenge in steel design. The long cycle nature of hydrogen embrittlement testing makes the iteration of traditional trial and error methods infeasible for steel development. This work adopts active learning algorithms based on Bayesian and Pareto optimization to iteratively optimize the chemical composition and processing technology of high-strength steel, in order to simultaneously improve its hydrogen filled tensile strength (UTS_H) and hydrogen filled total elongation (TEL_H). After two rounds of iterative optimization, the iterative optimization algorithm significantly improved the strength prediction of materials after hydrogen charging. The machine learning model found 16 types of steel from over 15 million unknown materials. Eight materials showed better comprehensive performance than known data, with one material having a tensile strength exceeding 1800 MPa and an elongation of 12.6%. Subsequent experiments showed that the optimization algorithm demonstrated an understanding of the impact of austenite content on hydrogen embrittlement sensitivity in multiple experiments, and designed high-strength steel resistant to hydrogen embrittlement through the austenite content of martensitic steel.

Experimental study on slow tensile, fatigue, and impact on X42 steel and #20 carburizing steel

Hydrogen embrittlement is a common phenomenon in high-strength steels and presents a significant challenge in the research and development process. This study aims to analyze the mechanism of hydrogen embrittlement, investigate the causes of crack growth in steel, and conduct experiments at mesoscopic and microscopic scales to gain a deep understanding of the relationship between hydrogen embrittlement and defects in high-strength steels. The research includes a slow tensile test to study the shrinkage and ductility of X42 steel and 20# carburizing steel under air and hydrogen environments. Furthermore, fatigue testing is conducted to comparatively investigate the crack growth of CT specimens in nitrogen and hydrogen environments at different pressures. Additionally, impact testing is performed to examine the fracture of V-notched specimens in air and hydrogen at different pressures. The findings reveal that 20# carburizing steel exhibits better fracture toughness than X42 steel during the slow tensile process, and its hydrogen embrittlement sensitivity is lower. Moreover, the fatigue crack growth process of 20# carburizing steel is less affected by hydrogen embrittlement, resulting in better fatigue rupture resistance compared to X42 steel. Furthermore, the impact toughness value of 20# carburizing steel is higher than that of X42 steel in the impact toughness test. Both steels show varying effects on crack growth under different hydrogenation pressures. Importantly, the impact toughness of both steels is less affected by different hydrogenation pressures.

Microstructural Engineering of Mn-Alloyed Austenitic Steel for Hydrogen Storage and Delivery

Austenitic stainless steels are commonly used for hydrogen storage and transportation. These alloys have a high nickel (Ni) content, which increases alloy cost. In this study, high manganese (Mn) austenitic alloys were evaluated as potential lower cost alternatives. Two heats of high Mn alloys with different stacking fault energies (SFE) of ~29 mJ·m-2 and 49 mJ·m-2 were acquired. Additionally, a new vanadium (V)-microalloyed high Mn alloy was designed to achieve a SFE of 47 mJ·m-2 to minimize planar slip deformation mechanisms. Post-processing via cold working in conjunction with aging was also performed on the V-microalloyed high Mn steel. Hydrogen embrittlement sensitivity was investigated using circumferential notch tensile specimens cathodically charged with hydrogen in a 0.05M NaOH electrolytic solution. The alloys were compared to a cold-worked 316L stainless steel, which exhibited no strength loss due to hydrogen. The high Mn alloys with SFE of ~29 mJ·m2 and 49 mJ·m-2 had notch strength losses of 11 and 6 pct, respectively. The V-microalloyed high Mn steel in the as-hot-rolled condition had a notch strength loss of 17 pct. The V-microalloyed high Mn steel in the cold worked and aged condition indicated no notch strength loss in hydrogen, which was comparable to the performance of the 316L stainless steel.

Effects of microstructure and morphological distribution on hydrogen-embrittlement sensitivity of Ti–6Al–4V alloy welded joint

The effects of the organizational characteristics and morphological distribution of Ti–6Al–4V alloy welded joint on their resistance to hydrogen embrittlement were investigated. The β-phase continuity of the base material (BM) was poor, and the large volume of the striped α-phase hindered hydrogen diffusion. Consequently, the BM has low hydrogen embrittlement sensitivity. The basket-like phase distribution of the weld material (WM) had better β-phase continuity and higher phase boundary density compared with the BM, providing a more convenient channel for hydrogen diffusion and more hydrogen absorption sites. Therefore, the WM had a high hydrogen embrittlement sensitivity.

Rapid evaluation of the critical condition for hydrogen-induced cracking in ultrahigh-strength automotive steel sheets: A semiquantitative investigation based on U-bend specimens

The production of automotive steel plates, which involves pickling, electroplating, and welding among other steps, introduces hydrogen. Additionally, during the service life of components fabricated using such plates, electrochemical corrosion occurs, and hydrogen atoms are introduced. The hydrogen atoms are adsorbed and diffused into the interior of the metal, accumulating at any defects. Automotive parts are commonly fabricated using cold forming techniques. The hydrogen embrittlement sensitivity of ultrahigh-strength automotive sheets (UHSSs) is influenced by the stress, concentration of diffusible hydrogen, and plastic strain resulting from the cold forming process. The standard methods for quantitative studies on the UHSS hydrogen embrittlement sensitivity, such as the constant-load testing and low-strain-rate testing, require a specialized equipment and extended experimental period, making them impractical for original automotive equipment manufacturers. This study focuses on the use of the quenching and partitioning (QP) steel QP1180, which contains residual austenite, and martensite steel MS1500, which has a low deformation ability but high strength, as research objects. The equivalent strain and stress were controlled by adjusting the bending radius and U-bend opening distance, while the diffusible hydrogen concentration was charged through immersion. The fracture time of the U-bend sample was recorded, and the critical diffusible hydrogen concentration for hydrogen-induced cracking was measured. Additionally, the stress distribution during the U-bending process was simulated using the finite-element method. To evaluate the hydrogen embrittlement resistances of QP1180 and MS1500, the area enclosed by the load stress and equivalent strain (bending radius) and fracture time were semiquantitatively determined. Finally, the hydrogen-induced delayed fracture space regions of QP1180 and MS1500 were determined in the three-dimensional space, with equivalent strain, load stress, and diffusible hydrogen concentration as coordinate axes. This provided a convenient and reliable means of determination of the critical conditions for a safe service and rapid evaluation of the hydrogen embrittlement sensitivity of ultrahigh-strength automotive sheets.

The hydrogen embrittlement mechanisms and hydrogen induced cracking process of selective laser-melted GH4169

This study investigates the hydrogen embrittlement sensitivity and brittle failure mechanism of selective laser-melted GH4169 alloy under hydrogen precharged conditions. Fractographic analysis reveals that a high concentration of hydrogen facilitates the formation of small quasi-cleavage steps near the fracture edge. Additionally, hydrogen promotes the migration of {111} planar dislocations, resulting in shear failure of the δ phases and the nucleation of microvoids. These microvoids then propagate, leading to the development of hydrogen-assisted transgranular cracks along the dislocation slip bands. The deformation behaviors of the δ and γ" phases were characterized using high-resolution transmission electron microscopy.

Study on the Influence of Surface Integrity on Hydrogen Permeation Resistance of Hydrogen Production Reactor Materials

Hydrogen permeation reduces a material’s properties and increases the risk of brittle fracture, which causes a potential safety hazard. A workpiece’s hydrogen permeation resistance could be improved by improving its surface integrity through surface processing. This paper studies low-alloy steel’s surface integrity and its hydrogen permeation resistance in a hydrogen production reactor, using the electrochemical cathodic hydrogen-charging method to carry out electrochemical hydrogen-charging experiments. After the specimens were pretreated using different surface-grinding methods and shot peening pressure strengthening, they were hydrogen-charged on a self-designed and built electrolytic hydrogen charging platform. Before and after hydrogen charging, the specimens’ section hardness and tensile strength were tested, and the fracture morphology of the specimens was observed. The influence laws of surface roughness and surface residual compressive stress on the distribution of material hardness along the depth, the variation in material hardness, the fracture morphology, and the decline in the tensile properties of the low-alloy steel specimens after 5 h of hydrogen charging were analyzed. The reasons for the influence of surface integrity indexes on the hydrogen permeation resistance of the specimens were also analyzed. Based on the experimental results, a series of mechanical processing parameters were proposed to improve the material’s permeation resistance, which provides a theoretical and practical basis for the processing of materials with high surface integrity and hydrogen permeation resistance. Through the experiments, it was found that the hydrogen permeation resistance of the Ra 0.17 μm surface roughness specimen was the best of all specimens with different surface roughness values, and its hydrogen embrittlement sensitivity index was 20.96%. The specimen had the best hydrogen permeation resistance under 336 MPa surface residual compress stress, and its hydrogen embrittlement sensitivity index was 16.45%.

Effect of additive manufacturing and subsequent heat and/or surface treatment on the hydrogen embrittlement sensitivity of 316L austenitic stainless steel

Austenitic stainless steels (ASS) offer attractive characteristics for use in hydrogen service, such as low hydrogen diffusivity and high solubility. The role of the production process is, however, still unclear. Especially the effect of additive manufacturing (AM) on the hydrogen interaction is not extensively researched yet. The present work compares the hydrogen embrittlement sensitivity of conventional (cold rolled and annealed) and additive manufactured 316L ASS and evaluates the possible advantage of performing a heat treatment and/or reducing the surface roughness post printing. AM increases the hydrogen solubility but the hydrogen diffusivity was only slightly reduced. The heat treatment reduced the hydrogen solubility of the AM materials and significantly increased the hydrogen diffusivity. Despite these observations, the conventional 316L ASS shows a higher hydrogen embrittlement (HE) sensitivity compared to AM316L. This is linked to the increased hydrogen-assisted cracking sensitivity of conventional 316L ASS. The heat treated microstructure behaves similarly as the as-built material in terms of HE sensitivity, while a major improvement is observed when the surface oxide layer formed during the heat treatment is maintained since this reduces hydrogen absorption. Surface polishing intensifies the HE sensitivity which is linked to a higher surface hydrogen concentration leading to more crack initiation.

Hydrogen embrittlement sensitivity of dispersion-strengthened-high-strength steel welded joint under alternating wet-dry marine environment

This paper investigated the effects of welding and alternating wet-dry seawater on the hydrogen embrittlement (HE) susceptibility of a new nanoparticle-reinforced high-strength steel, dispersion-strengthened-high-strength (DSHS) steel. The results show that welding led to the transformation of granular bainite to tempered martensite. It also promotes grain coarsening as well as an increase in inclusions size and irregular changes in shape. This results in increased susceptibility to HE at the welded joint (WJ). After wet-dry cycle corrosion in seawater, corrosion products impede the oxygen transfer and promote the hydrogen evolution reaction, so the hydrogen production increases. The decrease in the protection of corrosion products at the WJ and the decrease in NbC content led to an increase in hydrogen production but a decrease in hydrogen trapping capacity. Therefore, the WJ HE sensitivity of DSHS steel is further increased.

Hydrogen permeation and hydrogen damage behavior of high strength casing steel in acidic environment

To explore the effect of hydrogen permeation on pipes in an acidic environment, the tensile mechanical properties of three types of high strength steels were evaluated before and after hydrogen filling. The hydrogen damage behavior of three kinds of high-strength steels was studied by electrochemical hydrogen permeation test, MTS tensile test, and fracture morphology analysis. First, the basic physical and chemical properties of the materials were analyzed, and then the D-S double electrolytic cell technology was used for hydrogen permeation experiment. Finally, the influence of hydrogen loading on the tensile mechanical properties of the steel was determined by MTS tensile test and fracture morphology analysis. As the hydrogen filling current increases, the system temperature rises and the pH decreases, the hydrogen diffusion coefficient increases and the sensitivity of the steel to hydrogen embrittlement increases. The higher the steel strength, the higher the hydrogen diffusion coefficient, the higher the diffusible hydrogen concentration, the higher the hydrogen embrittlement sensitivity. The hydrogen damage evaluation method of high-strength steel used in this paper can provide a reference for the applicability evaluation of oil well pipe under acidic environment and provide theoretical guidance for the selection of oil well pipe in the field.

Experimental-numerical study on ballistic impact behavior of 316L austenitic stainless steel plates against blunt and ogival projectiles

316L austenitic stainless steel (ASS) is the standard reference material in fabricating pressurized hydrogen storage tanks due to its low hydrogen embrittlement sensitivity and excellent corrosion resistance. Ballistic performance of such tanks is of course a concern of safety. In this study, ballistic impact behavior of 316L ASS was studied against blunt and ogival nose shaped projectiles within impact velocity range of 160.3–324.1 m/s. Ballistic impact behavior of 316L ASS is sensitive to nose shapes of projectiles. For targets against blunt projectile, shear plugging with ejected plugs is observed, and target deflection is limited; for targets against ogival projectile, failure mode is ductile hole enlargement, small bulge and some fragments are observed on front and rear sides of targets, respectively. Ballistic limit velocities (BLVs) for two projectiles are respectively 180.9 m/s and 333.5 m/s, indicating better energy absorption against ogival projectile. Numerical simulations of ballistic impact tests were carried out using either the Lode independent MJC or the Lode dependent modified Mohr-Coulomb (MMC) fracture criterion. Numerical prediction by the latter is more accurate than the former as ballistic impact tests are dominated by stress state where Lode parameter is strong enough to cause a big difference between MMC and MJC criteria, and fracture behavior is accurately predicted by the latter but overestimated by the former.

Mechanism of hydrogen-induced defects and cracking in Ti and Ti–Mo alloy

Mechanism of Hydrogen-induced defects and cracking in Ti and Ti–Mo alloy was systematically analyzed from the perspective of microstructure. Results show that more hydrogen atoms can be dissolved in Ti–Mo alloy due to the existence of β phase, and the precipitation amount of hydride is reduced under the same hydrogen charging conditions. The analysis of positron annihilation results show that the solid solution of Mo element reduces the hydrogen induced defect concentration in the alloy and inhibit the combination of hydrogen and defects. At the same time, Mo atom can affect the electronic structure of Titanium hydrides, and then reduce the bonding between titanium atoms and hydrogen atoms, thereby reducing the formation of brittle titanium hydride. The reduction of hydride and hydrogen induced defect concentration significantly decrease the hardening rate of Ti–Mo alloy, thereby effectively reducing the hydrogen embrittlement sensitivity of titanium and inhibiting its hydrogen absorption cracking tendency.