Hydrogen-induced Failure Research Articles

Effect of pre-strain on hydrogen-induced delayed cracking and hydrogen trapping behavior in high-strength martensitic steels

Pre-strain is a key factor affecting the critical conditions for hydrogen-induced delayed cracking (HIDC). In this study, the threshold stress and critical hydrogen concentration for HIDC of MS1300 and MS1500 steels with different pre-strains were measured by constant load tensile (CLT) tests. The results demonstrated that although MS1500 has higher strength, its safe service strength is lower than that of MS1300 when the hydrogen content exceeds 0.5 wppm. Additionally, the hydrogen penetration, thermal desorption spectroscopy, and hydrogen microprinting methods were also used to analyze the hydrogen-induced failure mechanism. These studies provide an effective data reference for improving the industrial production process.

Analysis of hydrogen-induced cracking mechanism in quenching and partitioning steels

Quenching and partitioning (Q&P) steels are extensively used in the automotive industry due to their exceptional strength and ductility. However, the impact of hydrogen embrittlement (HE) poses a huge challenge to the safe service of Q&P steels, highlighting the necessity to investigate the hydrogen-induced cracking mechanisms. This study investigates the hydrogen-induced failure mechanisms in Q&P steels through experiments and finite element simulations, focusing on microstructure, local stress heterogeneity, hydrogen distribution characteristics, and hydrogen-induced cracking. The results reveal that hydrogen cracking nucleation in Q&P steel is primarily due to the further accumulation of hydrogen in local high-stress martensitic/austenitic regions.

Hydrogen-induced failure analysis of bimetallic clad pipes

This study investigated the mechanical properties and fracture characteristics of an alloy 825/L360 bimetallic clad pipe after it was subjected to hydrogen charging. The results indicated that the elongation loss of the pipe increased from 12.3% to 50.0% with increasing hydrogen charging time. In addition, results obtained from hydrogen microprinting and scanning Kelvin probe force microscopy indicated that the hydrogen distribution characteristics of the aforementioned material influenced the hydrogen fracture failure mechanism of the clad pipe. Specifically, carbides and TiN initiated hydrogen cracking, and crack extension occurred through brittle cracking at grain boundaries, which was caused by the interaction of hydrogen with dislocation slip bands within the dendritic zone.

Hydrogen diffusion dynamics on [formula omitted] surface: A mechanism of hydrogen-induced failure

Hydrogen-induced failure (embrittlement as the primary source) is a significant concern for retrofitting existing pipelines to transport hydrogen. One of the major factors associated with hydrogen embrittlement of metals is hydrogen diffusion. Therefore, understanding the modes and dynamics of hydrogen diffusion into metals is critical for understanding better and acting to limit hydrogen-induced damage to metals. It is well established that transition metals catalyze the dissociation of molecular hydrogen into atomic hydrogen even at room temperature. The atomic hydrogen diffuses through the metal surface, and this causes degradation. Understanding atomic hydrogen diffusion dynamics is critical to reducing hydrogen embrittlement. This work presents atomic hydrogen diffusion dynamics along and into Fe(100) surfaces. The results indicated that diffusion of atomic hydrogen along the surface is favored over surface-to-subsurface diffusion. Once hydrogen diffuses to the subsurface layer, the barrier for further hydrogen diffusion into the subsequent layers is relatively lower. The methodology presented here of atomic hydrogen diffusion under dynamic relaxation into metal surface can be used to study the effect of the metal's chemical composition and structure on the hydrogen diffusion rate. This allows for screening various strategies to reduce hydrogen diffusion into metals and guide the design of degradation prevention strategies.

A novel method to design Nb(W)–Ti–Co(Fe) alloy membrane with high hydrogen permeability and strong resistance to hydrogen embrittlement

A hydrogen permeable Nb43W5Ti27Co20Fe5 alloy membrane was designed and its microstructure and hydrogen transportation performances were systematically studied. W mainly dissolves into primary body-centered cubic (bcc)-(Nb) phases, while Fe is captured in eutectic structures. Substituting Nb with W leads to a substantial reduction in hydrogen solubility and substituting Co with Fe negligibly affects hydrogen solubility. The W and Fe substitutions contribute to an enhanced intrinsic hydrogen diffusion coefficient D∗. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits lower hydrogen solubility and higher hydrogen permeability at temperatures below 623 K than that of the original Nb48Ti27Co25 alloy membrane. No hydrogen-induced failures were found for the designed Nb43W5Ti27Co20Fe5 alloy membrane during cooling to room temperature and under long-term hydrogen permeation at 673 K for 72 h, whereas the original alloy membrane failed at 444 K during cooling to room temperature and after 19 h during hydrogen permeation at 673 K. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits high hydrogen permeability and strong resistance to hydrogen embrittlement.

Hydrogen-induced failure in a partially-recrystallized Al-Zn-Mg-Cu alloy with different aging conditions: Influence of deformation behavior dominated by microstructures

Hydrogen-induced failure in a partially-recrystallized Al-Zn-Mg-Cu alloy with different aging conditions was studied by in-situ electrochemical hydrogen charging method, and the hydrogen-induced cracking mechanism was elucidated by investigating the microstructure-dominated deformation behavior. It was found that in naturally-aged and peak-aged samples, cracks initiate at sample surfaces, and deformation dominated by shearing facilitates hydrogen diffusion, resulting in a high hydrogen embrittlement susceptibility. However, in the over-aged sample, deformation dominated by bypassing cannot transport hydrogen efficiently, which exerts no effect on crack initiation at the sample center. In addition, the same cracking pattern exists on all samples in silicone oil and in-situ hydrogen charging environments. The grain boundary of recrystallized grains is prone to strain localization, leading to intergranular cracking. In unrecrystallized grains, transgranular cracks propagate along intersections of slip lines and subgrain boundaries. This study improves the understanding of hydrogen embrittlement in new generation Al-Zn-Mg-Cu alloy by linking the existing hydrogen embrittlement mechanism to the deformation behavior dominated by microstructures.

The mechanism of hydride formation during electrochemical hydrogen charging of Ti–6Al–4V

The present work studies experimentally the hydrogen uptake and hydride formation in duplex Ti–6Al–4V. Hydrogen is introduced by electrochemical hydrogen charging at room temperature. The effect of the applied charging conditions is evaluated considering the effect of the charging duration and charging current density. Moderate charging conditions induce solute hydrogen in the lattice, resulting in lattice strains, as revealed by X-ray diffraction. More severe hydrogen exposure results in the formation of titanium hydrides when the hydrogen concentration exceeds the solubility limit of the Ti-α phase, as verified by a combined characterization with X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, and hydrogen melt extraction. A progressive mechanism of hydride formation upon increasing hydrogen content is proposed as the charging conditions clearly influence the hydrogen distribution and hydride formation in the material. Controlling the electrochemical hydrogen charging conditions enables to further understand the role of hydrogen and hydrides in hydrogen-induced failure mechanisms, as well as it offers opportunities for sustainable thermohydrogen processing of titanium.

Prediction of hydrogen concentration responsible for hydrogen-induced mechanical failure in martensitic high-strength steels

Hydrogen, at critical concentrations, responsible for hydrogen-induced mechanical property degradation cannot yet be estimated beforehand and can only be measured experimentally upon fracture with specific specimen sizes. In this work, we develop two deep learning artificial neural network (ANN) models with the ability to predict hydrogen concentration responsible for early mechanical failure in martensitic ultra-high-strength steels. This family of steels is represented by four different steels encompassing different chemical compositions and heat treatments. The mechanical properties of these steels with varying size and morphology of prior austenitic grains in as-supplied state and after hydrogen-induced failure together with their corresponding hydrogen charging conditions were used as inputs. The feed forward back propagation models with network topologies of 12-7-5-3-2-1 (I) and 14-7-5-3-2-1 (II) were validated and tested with unfamiliar data inputs. The models I and II show good hydrogen concentration prediction capabilities with mean absolute errors of 0.28, and 0.33 wt.ppm at test datasets, respectively. A linear correlation of 80% and 77%, between the experimentally measured and ANN predicted hydrogen concentrations, was obtained for Model I and II respectively. This shows that for this family of steels, the estimation of hydrogen concentration versus property degradation is a feasible approach for material safety analysis.

Effects of Mn and Microalloying Composition on Corrosion and Hydrogen-Induced Cracking of API 5L X65 Steels

The corrosion and hydrogen-induced cracking (HIC) resistance as well as hydrogen permeation behavior of two API 5L X65 steels with different amounts of Mn and microalloying elements were compared. The corrosion behavior of both steels, evaluated using electrochemical impedance spectroscopy and polarization curves in solution A of NACE TM0284-16 standard with and without H2S saturation (sour medium), showed no relevant differences in each medium, which can be ascribed to their similar microstructures; however, the corrosion resistance of both steels was lower in the sour medium. The investigation of resistance to hydrogen-induced failures disclosed better performance for the low Mn steel. This was confirmed using a harsher HIC test performed in an HCl acidified sour medium and was ascribed to the presence of Nb carbides nanoprecipitates, as revealed by the scanning transmission electron microsccopy analysis.

Subdiffusive High-Pressure Hydrogen Gas Dynamics in Elastomers

Elastomeric rubber materials serve a vital role as sealing materials in the hydrogen storage and transport infrastructure. With applications including O-rings and hose liners, these components are exposed to pressurized hydrogen at a range of temperatures, cycling rates, and pressure extremes. High-pressure exposure and subsequent rapid decompression often lead to cavitation and stress-induced damage of the elastomer due to localization of the hydrogen gas. Here, we use all-atom classical molecular dynamics simulations to assess the impact of compositional variations on gas diffusion within the commonly used elastomer ethylene–propylene–diene monomer (EPDM). With the aim to build a predictive understanding of precursors to cavitation and to motivate material formulations that are less sensitive to hydrogen-induced failure, we perform systematic simulations of gas dynamics in EPDM as a function of temperature, gas concentration, and cross-link density. Our simulations reveal anomalous, subdiffusive hydrogen motion at pressure and intermediate times. We identify two groups of gas with different mobilities: one group exhibiting high mobility and one group exhibiting low mobility due to their motion being impeded by the polymer. With decreasing temperatures, the low-mobility group shows increased gas localization, the necessary precursor for cavitation damage in these materials. At lower temperatures, increasing cross-link density led to greater hydrogen gas mobility and a lower fraction of caged hydrogen, indicating that increasing cross-link density may reduce precursors to cavitation. Finally, we use a two-state kinetic model to determine the energetics associated with transitions between these two mobility states.

Corrosion characterization of new low manganese microalloyed X65 steels in sour and NON-SOUR synthetic seawater

API 5L X65 microalloyed steels are extensively used for oil and gas transportation. In many cases, reserves of such resources contain H2S, constituting what is called a sour medium, at which hydrogen-induced failures are critical. Even though essential for improving mechanical resistance, the addition of high contents of manganese (Mn) may increase the tendency for segregation and the precipitation of MnS inclusions, increasing the susceptibility to hydrogen-induced failures. In this study, electrochemical techniques were employed to compare the corrosion resistance in the B solution of ASTM D1141−98 (synthetic seawater) of three API 5L X65 microalloyed steels with low Mn content, designed for severe sour service applications. Experiments were performed in naturally aerated (pH 8.0), deaerated (pH 8.0 and 5.0), and H2S-saturated (sour pH 5.0) media. Although the steels exhibit very similar chemical compositions and mechanical properties, it was possible to rank their corrosion resistance. Microstructural characterization allowed associating corrosion susceptibility with the presence of pearlite grains in a ferritic matrix. The results also demonstrated the superior aggressiveness of the sour medium, and that the precipitation of a poorly adherent layer of Mackinawite slightly increases the corrosion resistance with immersion time.

New insight into the role of inclusions in hydrogen-induced degradation of fracture toughness: three-dimensional imaging and modeling

ABSTRACT An in-depth understanding of the role of non-metallic inclusions (NMIs) in the hydrogen-induced failure of structural materials is important in the manufacture and application of steels. In this paper we investigated the type, the amount and the distribution of NMIs in pipeline steels and their relation to the susceptibility to hydrogen-induced cracking (HIC). Scanning Electron Microscope (SEM) observation confirmed the interlinking of the microcracks formed at the inclusion-matrix interfaces. By combining with the nondestructive three-dimensional (3D) mapping of crack propagation paths, based on the synchrotron tomography technique, we obtained direct evidence that the cracking initiation at the NMIs and then interlinking on the (nearly) same plane are the main mechanism of HIC failure in X70 steels. We built an elastic-energy-based model, which can be applied to quantitatively predict the HIC-induced dependence of the fracture toughness on NMIs, based on statistical information of the NMIs. The theoretical results show a good agreement with the experimental observation. We proposed a criterion to determine the susceptibility to HIC by the observation of NMIs. We also developed a thermodynamics-based model to analyze the hydrogen trapping at the inclusion-matrix interface and its dependence on the strength of the steel matrix. For the first time, the direct relationship between NMIs and HIC-induced degradation of fracture toughness is obtained.

Improving hydrogen permeability and sustainability of Nb30Ti35Co35 eutectic alloy membrane by substituting Co using Fe

The microstructure and hydrogen permeation performance of Nb30Ti35Co35-xFex (x = 0, 5, 10, 15, 20) alloys have been investigated. With Fe less than 15 at%, the as-cast Nb30Ti35Co35-xFex ingots exhibit fully eutectic structure. When the Fe content is higher than 15 at%, primary bcc-(Nb, Ti) phase appears in combination with eutectic structure. Substituting Co using Fe leads to slightly increased hydrogen solubility but highly enhanced hydrogen permeability, which comes mainly from the increased hydrogen concentration-independent diffusion coefficient D∗. With Fe content up to 10 at%, Nb30Ti35Co35-xFex membranes exhibit stable and higher hydrogen permeation flux than Nb30Ti35Co35 at 673 K during hydrogen permeation test up to 72 h. Nb30Ti35Co35-xFex alloys of fully eutectic structures exhibit no hydrogen-induced failure when cooled down to room temperature under hydrogen atmosphere, indicating the potential application of the membrane at lower temperature range. An optimal combination of hydrogen permeability and hydrogen embrittlement resistance is achieved at 10 at% Fe, since further increase of Fe leads to comparable D∗ as that of Nb30Ti35Co25Fe10 but higher hydrogen solubility.

Control of hydrogen-induced failure in metastable austenite by grain size refinement

To promote the use of metastable austenite for use in hydrogen structures, grain refinement is used. Fe-16Cr-10Ni is a metastable austenitic alloy whose grain size can be controlled by conventional thermo-mechanical processing. With a minimum grain size just below 1 µm, the material was exposed to hydrogen gas at different pressures and tensile tests were performed. SEM/EBSD in-situ tensile tests were also performed. Hydrogen affected all grain sizes, with evidence of intergranular and transgranular fracture at higher hydrogen contents in the larger grains. Smaller grains retained a high yield stress with good elongation, while the largest grains were most embrittled. Cracking was preceded with significant phase transformation and occurred by microvoid coalescence in fine grains and along grain boundaries in coarse grains (with traces of ductility), without indication of failure of austenite-martensite interfaces.

Material Consequences of Hydrogen Dissolution in Palladium Alloys Observed from First Principles

Hydrogen embrittlement is one of the fundamental material science challenges to be faced under a potential “hydrogen economy”, as hydrogen will interact with the infrastructure for hydrogen production, storage, and transportation. While some embrittlement mechanisms have been proposed (especially for Fe), the behavior of dissolved hydrogen and impact on material properties is not fully understood in many systems relevant to hydrogen technologies. Here, hydrogen binding in pure Pd and alloys of Pd with Ag and Au was examined at a fundamental level from first principles in an attempt to elucidate how hydrogen-induced failure can be reduced in Pd alloys relevant to hydrogen production technologies. We show that PdAg and PdAu alloys (where the alloying metal is under 25%) likely suppress hydrogen-induced mechanical failure due to their reduced hydrogen solubility relative to pure Pd. This conclusion is based on our findings that alloying leads to higher vacancy stabilization and lower elastic constants upon hydrogen dissolution than for pure Pd but to unfavorable hydrogen dissolution beyond 25 at. %. The lowering of hydrogen solubility is strongly related to the combination of a lowering of the overall metal d-band center through alloy incorporation as well as changes to the metal Pauli repulsion factor, which is herein related to the metal matrix coupling element. Additionally, hydrogen loading and unloading were sequentially interrogated to mimic stress in storage materials. We find that permanent plastic deformation to the system is pronounced for alloyed systems, which in some cases made subsequent loading more favorable.

Prediction of the Hydrogen-Induced Damage to Ultra-High Strength Steel Concepts

The hydrogen-induced damage behavior of ultra-high strength steels (UHSS) has been predicted by a combination of experimental and numerical investigations. Firstly, the resistance against hydrogen-induced failure was examined by slow strain rate tests (SSRT) using various sample geometries and hydrogen contents. Secondly, the hydrogen distribution and loading conditions during the tensile test were calculated by means of the finite element method (FEM). Finally, a combination of various damage models was applied and validated by further SSRT. The main result of this study is a failure prediction model, which considers local stress and strain conditions, as well as hydrogen content.

Hydrogen-enhanced-plasticity mediated decohesion for hydrogen-induced intergranular and “quasi-cleavage” fracture of lath martensitic steels

Hydrogen embrittlement of lath martenistic steels is characterized by intergranular and “quasi-cleavage” transgranular fracture. Recent transmission electron microscopy (TEM) analyses (Nagao et al., 2012a, 2014a, 2014b, 2014c) of samples lifted from beneath fracture surfaces through focused ion beam machining (FIB) revealed a failure mechanism that can be termed hydrogen-enhanced-plasticity mediated decohesion. Fracture occurs by the synergistic action of the hydrogen-enhanced localized plasticity and decohesion. In particular, intergranular cracking takes place by dislocation pile-ups impinging on prior austenite grain boundaries and “quasi-cleavage” is the case when dislocation pile-ups impinge on block boundaries. These high-angle boundaries, which have already weakened by the presence of hydrogen, debond by the pile-up stresses. The micromechanical model of Novak et al. (2010) is used to quantitatively describe and predict the hydrogen-induced failure of these steels. The model predictions verify that introduction of nanosized (Ti,Mo)C precipitates in the steel microstructure enhances the resistance to hydrogen embrittlement. The results are used to discuss microstructural designs that are less susceptible to hydrogen-induced failure in systems with fixed hydrogen content (closed systems).

A general model for hydrogen trapping at the inclusion-matrix interface and its relation to crack initiation

The role of non-metallic inclusions in hydrogen-induced failure of structural materials has been a controversial topic for many years. In this paper, hydrogen trapping and its relation to the crack initiation at the inclusion-matrix interfaces are studied by considering the interfacial structure and the interaction between the dissolved hydrogen atoms and the elastic strains produced by lattice matching and misfit dislocations. A model is proposed to analyse the change of interfacial structure with inclusion size and its relation to hydrogen trapping. Hydrogen accumulation at the interfaces is quantitatively analysed. The obtained results are in good agreement with the experimental observations. The multiple factors, such as interfacial structure, chemical composition, elastic properties of matrix and inclusions, crystallographic relationship between inclusions and matrix, inclusion morphology and size, simultaneously control hydrogen trapping. In addition, the mechanism of hydrogen-induced crack initiation at the interface is investigated. A criterion is proposed to determine critical conditions for crack initiation. For the first time, the inherent relationship between hydrogen trapping and hydrogen-induced cracking at the interface is clarified. This work paves a way for an in-depth understanding of the effects of inclusions on hydrogen-induced degradation of mechanical properties.

A REVIEW OF THEORECTICAL CONCEPTS OF HYDROGEN CRACKING IN METALS AND ALLOYS

Today the demand for high-strength metal materials to be used in critical structural elements and facilities that operate under variable temperature and stress conditions is steadily growing economic and engineering tendency. However increased strength features of a metal are opposed by its reduced plasticity so the metal often becomes unfit for large plastic straining. In this case solid body brittle failure starts and this process is quite often of random character, which may result in big financial loss and human injuries. Available literature contains little information on delayed failure issues in principle, however, many research findings demonstrate that the decisive role in this process belongs to hydrogen that interacts with different types of micro-defects in the matrice. In order to understand why a more easy propagation of dislocations from the crack tip down results in embrittlement it is necessary to study the crack growth pattern in inert media for plastic materials. Common features of different hydrogen embrittlement processes make it possible to conclude that a solid theory should be based on consolidated concepts of hydrogen-induced failures with taking into account the synergism of metal-hydrogen systems, i.e. the change in embrittlement mechanism in the process of the material structural self-organization at different structure-scale levels. Here a very important issue is to investigate the response of the material fine structure (structural relaxation) to the influence of a hydrogen medium under various straining temperature and speed conditions. Such investigation should be conducted with the help of electronic microscopes by applying acoustical emission and inner friction methods. Thanks to them it is possible to study the auto-wave nature of metal plastic deformation and to identify the most typical sustainable dissipative structures that emerge during the material self-organizing under combined impact of tensile stress and corrosive media.

Hydrogen-induced failure of TiNi based alloy with coarse-grained and ultrafine-grained structure

The objective of this work is to investigate the effect of hydrogen-induced fracture of TiNi-based alloy. In this report we performed the first studies comparing inelastic properties and fracture of the specimens of the binary alloy of TiNi wire under the action of hydrogen with coarse-grained (CG) and ultrafine-grained (UFG) microstructure. It is shown that hydrogen embrittlement (HE) occurs irrespective of the grain size in the studied specimens at approximately equal strain values. However, compared to the specimens with CG structure, those with UFG structure accumulate two to three times more hydrogen for the same hydrogenation time. It is found that hydrogen has a much smaller effect on the inelastic properties of specimens with UFG structure as compared to those with CG structure.