Search Results (466)

The pearlitic microstructure, comprising alternating lamellae of ferrite and cementite, provides a favorable combination of strength, toughness, and wear resistance. Consequently, pearlitic steels have been widely utilized in pipeline systems due to their advantageous mechanical properties and cost-effectiveness. These characteristics also render pearlitic steel pipelines promising candidates for hydrogen transport infrastructure, particularly in the context of repurposing existing natural gas networks. However, interactions between hydrogen and the pearlitic microstructure raise significant concerns regarding hydrogen embrittlement, a phenomenon that can substantially degrade mechanical performance and compromise long-term structural integrity. Experimental observations indicate that pearlitic microstructures are particularly susceptible to hydrogen embrittlement, largely due to the high density of ferrite–cementite interfaces, which act as effective hydrogen trapping sites. These detrimental effects motivate the present study, which aims to develop a deeper understanding of nanoscale mechanisms of hydrogen-assisted crack initiation and propagation in pearlitic microstructures. In this work, molecular dynamics simulations are employed to investigate the initiation and propagation of hydrogen-affected cracks in pearlitic microstructures, considering lamellar orientations both parallel and perpendicular to the applied tensile loading direction. The analysis focuses on the synergistic interaction between hydrogen-enhanced decohesion (HEDE), which promotes interfacial separation due to hydrogen segregation, and hydrogen-enhanced localized plasticity (HELP). Full article

The growing adoption of wire arc additive manufacturing (WAAM) requires an understanding of how WAAM-fabricated aluminium alloys respond to environmental factors that may degrade mechanical performance. This study investigates the effects of cathodic charging on the mechanical properties and fracture behaviour of WAAM AA2319 aluminium alloy. Cathodic charging was conducted in an electrolyte containing 3.5 wt.% NaCl and 3 g/L ammonium thiocyanate using different applied current densities. The resulting changes in mechanical performance were assessed through uniaxial tensile and Charpy impact toughness tests. The results demonstrate that cathodic charging led to a progressive reduction in ductility with increasing current density. Elongation decreased by up to approximately 45% relative to the uncharged condition, while ultimate tensile strength and yield strength were marginally affected. Charpy impact testing revealed a corresponding reduction in impact toughness of approximately 40% following hydrogen charging. Fractographic analysis showed a transition from ductile fracture dominated by microvoid coalescence in the uncharged material, to a mixed ductile–brittle fracture in hydrogen-charged specimens, characterised by shallow dimples and quasi-cleavage features. The observed changes in mechanical behaviour and fracture morphology suggest that cathodic charging promoted hydrogen-assisted mechanical degradation, with features consistent with hydrogen-enhanced localised plasticity (HELP) and hydrogen-enhanced decohesion (HEDE). Full article

Marine transportation and storage of liquid hydrogen (LH2) has gained increasing interest, while potential LH2 membrane-type tanks could utilize 316L corrugated austenitic stainless-steel sheets. The corrugation process results in a strain-induced martensitic transformation in the material, introducing rapid diffusion pathways for hydrogen atoms and promoting the formation of hydrogen-trapping sites that alter hydrogen transport and reduce the material’s resistance to hydrogen embrittlement. In this study, 316L sheets were subjected to different levels of uniaxial pre-strain (10, 20, 30, and 40%) with two different strain-rates, to replicate the varying degrees of pre-deformation caused by the corrugation. Microstructural analysis using Electron Backscatter Diffraction (EBSD) (Thermo Fisher Scientific, Waltham, MA, USA) and X-Ray Diffraction (XRD) (Bruker, Billerica, MA, USA) combined with quantitative phase analysis using the Rietveld Method on XRD data, provided valuable insights into the induced phase transformations. Cathodic hydrogen charging method was implemented on as-received and pre-strained material, followed by slow strain rate tensile testing (SSRT) and thermal desorption spectroscopy (TDS) to examine the hydrogen effect on each condition. Experimental results indicated that although 316L exhibits considerable phase stability, it undergoes strain-induced phase transformation resulting in a significant amount of martensite, reaching 5% in the 40% pre-strained condition. Pre-deformation increased hydrogen embrittlement, as evidenced by fractographic analysis which indicated a Relative Reduction of Area (RRA) of 0.83, and by increased hydrogen uptake. These findings contribute to a better understanding of phase transformations and the role of hydrogen in austenitic stainless steels. Full article

Hydrogen energy represents a crucial clean energy carrier and plays a critical role in achieving the national strategic goals of carbon neutrality and peak carbon emissions. Pipeline transportation is currently the most economical and efficient method for hydrogen delivery. However, most existing hydrogen pipelines worldwide utilize low-alloy steels, which are prone to hydrogen embrittlement (HE) during hydrogen transportation, leading to degradation of mechanical properties in pipeline steels. Since material composition and microstructure directly govern pipeline steel performance, this study systematically investigates the effects of compositional variations among three X65-grade pipeline steels on their microstructural evolution and hydrogen embrittlement resistance. Key findings include reducing Mn content enhances hydrogen embrittlement resistance by refining grain size and increasing the proportion of low-angle grain boundaries (LAGBs); cementite phases act as preferential hydrogen trapping sites, significantly reducing hydrogen resistance; and strain rate dependency of HE susceptibility is confirmed, as under slower strain rates, hydrogen interacts with dislocations, promoting brittle fracture mechanisms. This work provides practical mechanism insights for optimizing hydrogen-resistant pipeline steel design through compositional regulation and microstructural engineering. Full article

This study investigates pulsed gas metal arc welding (pGMAW) of API 5L X65 pipeline steel for sour service applications where H₂S exposure is anticipated. Mechanized pGMAW in the 5G downhill position was employed to fabricate girth welds using ER70S-6 filler wire with Ar-20%CO₂ shielding. Comprehensive characterization, including optical microscopy, tensile testing, fractography, EBSD, and fracture toughness evaluation via SENT specimens, was conducted on specimens tested in both air and H₂S-precharged sour conditions. Microstructural analysis revealed ferritic–pearlitic base metal, weld metal with acicular ferrite and bainitic constituents, and a transformed HAZ gradient. Tensile testing demonstrated severe hydrogen embrittlement in sour conditions, with elongation dropping from 22% in air to 4% after H₂S exposure, accompanied by a transition from ductile cup–cone fracture to quasi-cleavage morphology. EBSD showed texture sharpening toward ⟨101⟩ fiber post-deformation, with a broader orientation spread under sour conditions, indicating heterogeneous strain localization. Fracture toughness testing revealed approximately a 50% reduction in CTOD values under sour exposure, with the weld centerline exhibiting greater degradation (0.50 mm to 0.27 mm) compared to the HAZ (0.92 mm to 0.47 mm). Fractography confirmed hydrogen-assisted cracking features, including shallow dimples, cleavage facets, and secondary cracking. These findings establish critical baseline data for engineering a critical assessment of pGMAW-welded X65 pipelines in sour service. Full article

Marine renewable energy systems, including offshore wind, tidal, and wave technologies, are central to global decarbonisation strategies but remain constrained by reliability-driven costs and uncertainty in long-term structural performance. Existing qualification approaches are largely based on empirical methodologies and deterministic safety factors that inadequately capture coupled degradation mechanisms operating in harsh offshore environments. This review presents a mechanism-based perspective on structural integrity in marine renewable energy systems by linking microstructure-sensitive deformation and damage processes with engineering-scale reliability assessment. Key degradation mechanisms, including corrosion–fatigue, hydrogen embrittlement, wear, and manufacturing-induced variability, are critically examined together with their interactions across multiple length scales. The review synthesises recent advances in multiscale modelling frameworks spanning crystal plasticity, damage mechanics, fracture mechanics, probabilistic reliability methods, and digital twin technologies. Particular emphasis is placed on the role of manufacturing variability, inspection-informed updating, and hybrid physics–data approaches in improving predictive capability and reducing uncertainty. The review identifies major limitations in current offshore qualification practice, including uncoupled degradation assumptions, insufficient representation of manufacturing effects, and limited integration of monitoring data within lifecycle assessment. Building on these findings, an integrated framework is proposed that combines multiscale modelling, manufacturing-aware qualification, adaptive inspection, and digital twin-enabled updating to support predictive and reliability-informed structural integrity assessment for next-generation marine renewable energy systems. Full article

Hydrogen energy systems rely extensively on polymeric materials for storage, sealing, transport, and tribological applications; however, their long-term reliability is strongly influenced by hydrogen–polymer interactions. This review presents a comparative analysis of polymers with and without hydrogen bonding, focusing on how molecular architecture governs hydrogen compatibility, transport behavior, and degradation mechanisms under high-pressure environments. Hydrogen-bonded polymers, such as polyamides, polyurethanes (PU), and polyimides, exhibit high mechanical strength and thermal stability due to strong intermolecular interactions but are susceptible to hydrogen-assisted chemical degradation and embrittlement. In contrast, non-hydrogen-bonded polymers, including polyethylene, polypropylene (PP), polytetrafluoroethylene (PTFE), and Polyether ether ketone (PEEK), demonstrate excellent chemical inertness and low hydrogen reactivity, yet experience diffusion-driven damage such as blistering and fatigue softening. This study establishes a unified framework linking molecular structure, hydrogen transport, and failure mechanisms, revealing a fundamental trade-off between mechanical integrity and chemical stability. Advanced strategies, including polymer blending, nanofiller reinforcement, and multilayer composites, are proposed to optimize durability, permeability, and overall hydrogen compatibility. Full article

This study investigates hydrogen embrittlement in welded joints of X52 (L360) pipeline steel obtained from an operating natural gas transmission network after 31 years of service, with particular emphasis on production (longitudinal) and girth (circumferential) welds. The aim is to elucidate the influence of microstructural heterogeneity across the pipe wall and within different welded joint types on hydrogen transport, trapping behavior, and fracture mechanisms. The investigation combines X-ray diffraction, electrochemical hydrogen permeation testing, fractographic analysis, and transmission electron microscopy. X-ray diffraction results show that the base metal and girth weld consist predominantly of body-centered cubic ferrite, whereas the production weld additionally contains retained austenite associated with an elevated manganese content. These phase-related differences are consistent with transmission electron microscopy observations of martensite–austenite constituents within the weld microstructure. Electrochemical hydrogen permeation measurements reveal pronounced microstructure-dependent hydrogen transport behavior. The production weld exhibits a significantly lower apparent diffusion coefficient and a markedly higher hydrogen trap density, approximately five times greater than those of the base metal and girth weld, providing a mechanistic explanation for the observed differences in hydrogen uptake behavior. Fractographic analysis demonstrates a transition from ductile microvoid coalescence in the uncharged condition to predominantly brittle fracture following hydrogen charging. This transition is accompanied by a substantial increase in the fraction of brittle fracture zones, reaching approximately 53% in hydrogen-charged specimens. A pronounced gradient in hydrogen embrittlement susceptibility is observed across the pipe wall thickness, with outer-wall specimens consistently exhibiting greater susceptibility than inner-wall specimens. This behavior reflects the combined influence of long-term soil corrosion and hydrogen-assisted degradation. Transmission electron microscopy reveals that plastic deformation governs dislocation generation, while hydrogen significantly modifies dislocation behavior by promoting dislocation pile-ups near martensite–austenite constituents and non-metallic inclusions. These observations indicate strong interactions between hydrogen, dislocations, and microstructural heterogeneities. A clear size-dependent role of non-metallic inclusions is identified. Sub-micron inclusions act primarily as irreversible hydrogen trapping sites that contribute to hydrogen redistribution within the microstructure, whereas larger inclusions serve as preferential crack initiation sites under hydrogen charging conditions. Overall, the results demonstrate that hydrogen embrittlement behavior is governed by the combined effects of microstructural state, welded joint type, and long-term service-induced degradation, resulting in distinct hydrogen transport characteristics and fracture responses across the pipe wall. Full article

The hydrogen embrittlement (HE) behavior of an Fe–18Mn–8Al–1C–5Ni lightweight steel containing a fine and uniformly distributed B2 phase and κ-carbide was investigated by slow strain rate tensile testing with in situ hydrogen charging. Hydrogen charging reduces the elongation from 28.2% to 11.2%, while preserving an ultimate tensile strength above 1100 MPa and yielding an HE index of 60.2%. A thermal desorption analysis reveals a multi-peak desorption curve corresponding to diffusible hydrogen, hydrogen reversibly trapped at κ-carbides, and hydrogen strongly bound at the B2/γ interfaces, revealing a hierarchical hydrogen trapping behavior. Electron backscatter diffraction and electron channeling contrast imaging analyses near the fracture head region further reveal that localized hydrogen enrichment at the B2/γ boundaries induces severe stress concentration and interfacial weakening, shifting the fracture mode from ductile micro-void coalescence in air to hydrogen assisted intergranular and interphase cracking. This study clarifies the distinct roles of coherent κ-carbide and B2/γ interfaces in hydrogen trapping and crack initiation, offering a microstructure-based perspective for designing high-strength, HE resistant lightweight steels. Full article

Hydrogen embrittlement is a critical degradation mechanism in microalloyed and pipeline steels used in hydrogen-economy infrastructure. We present a physics-informed neural network (PINN) framework that embeds Fick’s second law and the Arrhenius temperature dependence directly into the loss function, trained on 22 temperature-dependent data points spanning pure α-Fe and API X65 pipeline steels (modern and vintage microstructures). The PINN recovered the pure-iron activation energy (4.2 kJ mol⁻¹ vs. literature 4.15 kJ mol⁻¹, R² = 1.00) and yielded Arrhenius activation energies of 28.5 and 45.2 kJ mol⁻¹ for modern and vintage X65, respectively, indicating substantially stronger trapping in older microstructures. McNabb–Foster analysis of ten ternary Fe–Me–C,N alloys revealed flat-trap binding enthalpies of 19 ± 2 kJ mol⁻¹ and deep-trap free energies of 57 ± 2 kJ mol⁻¹, with effective diffusivities spanning three orders of magnitude governed primarily by flat-trap density. The framework provides a computationally efficient and physically consistent tool for hydrogen transport prediction, with a clear roadmap for multi-feature extension incorporating compositional and microstructural descriptors. Full article

Although austenitic steels have been implemented in direct liquid hydrogen (LH₂) contact for decades, detailed microstructural and mechanical studies are still rare at a temperature of 20 K and inexistent for long-term exposure in LH₂. Therefore, austenitic stainless-steel parts, which were in direct contact with LH₂, from a container for LH₂ transport from the company Linde GmbH that has been in service for over 30 years, was chosen as a material model system for this investigation. In the present work, the possible influence of cryogenic gaseous and liquid H₂ (GH₂ and LH₂) on the micro- and macroscopic as well as mechanical properties of the container was investigated. Monitoring the properties after long-term GH₂ and LH₂-exposed material assesses the durability and the failure characteristics of these austenitic steels. A mean content of 2.5 ppm H was detected in the container walls after the long-term exposure. The microhardness of the long-term GH₂ and LH₂ are similar to an H₂ non-exposed sample. Based on the SEM investigations, no microstructural change could be detected in the material after long-term H₂ exposure and the residual tensile properties are still similar to those of ‘fresh’ non-exposed material. The hydrogen embrittlement (HE) occurred in the container material only after additional thermal H-charging, where the ductility reduced to about 50% at 200 K. Full article

High-temperature gaseous deuterium charging was used to investigate hydrogen isotope permeation, retention, microstructural stability, and fracture response in 310S austenitic stainless steel. Gas-driven permeation, thermal desorption spectroscopy, two-dimensional diffusion simulation, XRD/EBSD characterization, tensile testing, and fractographic analysis were combined to correlate isotope transport with mechanical and fracture behavior. The deuterium permeability and diffusion coefficient followed an Arrhenius relationship, and the diffusion coefficient extrapolated at 673 K was 1.11 × 10⁻¹¹ m²/s. With increasing charging time, the deuterium distribution evolved from a surface-enriched unsaturated state to an overall near-saturated state with higher retention. Although deuterium charging had little influence on yield strength, ultimate tensile strength, and elongation under the present room-temperature tensile condition, local quasi-cleavage-like facets, secondary cracks, and serrated fracture edges became more evident after charging. These results indicate that the embrittlement response of 310S stainless steel was mainly characterized by localized hydrogen-assisted damage rather than dominant brittle fracture. Full article

High-manganese steel has emerged as a potential alternative material to austenitic stainless steel for liquid hydrogen storage and transportation environments, owing to its superior mechanical characteristics and limited hydrogen diffusivity. However, its hydrogen embrittlement (HE) susceptibility limits its engineering applications. This study investigates the effect of microstructural regulation through trace titanium (Ti, 0.021 wt%) addition on HE resistance in high-manganese steel. By means of Electron Backscatter Diffraction (EBSD), TEM, SEM, and Slow Strain Rate Tensile (SSRT) tests, the effects of Ti on the microstructure, mechanical properties, and HE susceptibility of high-manganese steel are systematically investigated. The results show that the addition of Ti did not significantly alter the average austenite grain size or phase composition, but it generated a large number of Ti(C,N) nanoscale precipitates with sizes ranging from 20 to 70 nm within the matrix. The elongation loss of the 25Mn-Ti specimen was significantly lower than that of the 25Mn specimen when hydrogen-charged for 72 h, decreasing from 18.4% to 9.3%. The fracture surfaces consistently exhibited ductile dimple morphology, whereas 25Mn steel demonstrated significant cleavage-induced brittle fracture. EBSD analysis revealed that hydrogen-charged 25Mn-Ti steel exhibited higher Kernel Average Misorientation (KAM) value retention rate and more uniform grain strain distribution, indicating enhanced microstructural deformation compatibility. The main mechanism was that Ti pre-formed nanoscale Ti(C,N) precipitates during the preparation of 25Mn high-manganese steel, which played a key role in inhibiting HE. These precipitates altered hydrogen diffusion behavior and distribution patterns, reduced stress concentration levels, and inhibited hydrogen-induced crack initiation. This work is of great significance for improving the HE resistance of high-manganese steels. Full article

The aviation industry is transitioning toward hydrogen propulsion to meet sustainability goals, introducing novel fire safety risks that require updated regulatory frameworks. This study addresses the certification challenges for liquid hydrogen fuel systems by advancing the Certification Readiness Level through a model-driven approach. Using a Model-Based Safety Assessment, this research applies Bow-Tie Diagrams within the NASA AdvoCATE software to analyze in-flight fire risks for a tube-and-wing aircraft architecture. The study models critical threats, including cryogenic embrittlement and leakage, mapping them to specific prevention and protection barriers derived from a regulatory gap analysis. The assessment identifies leakage as the primary failure condition and proposes a safety architecture that emphasizes prevention barriers. Quantitative safety case modeling demonstrates, with proposed means of mitigation and barrier integrity, the feasibility to compute the residual probability of a catastrophic in-flight fire according to EASA CS 25.1309 requirements. These findings validate the use of safety architectures to bridge the gap between design and rulemaking, offering a scalable framework to support early-stage certification and the safe integration of hydrogen technologies into commercial aviation. Full article

A proper understanding of hydrogen–trap interactions in materials is of considerable significance, as it holds the potential to provide promising solutions to the long-standing issue of hydrogen embrittlement. In the present study, we employed a novel integrated approach combining electro-oxidation (EO) technique and thermal desorption spectroscopy (TDS) to characterize both reversible and irreversible deuterium in Fe samples. The samples were deuterium-charged at 500 kPa and temperatures ranged from 25 °C to 500 °C. Deuterium retention was measured by TDS for samples with and without EO treatment. Experimental findings demonstrate that the EO technique not only accelerates the expulsion of spontaneously releasable deuterium but also efficiently removes the majority of non-spontaneously releasable deuterium. It is evidenced that the proportion of reversible deuterium in the non-spontaneously releasable deuterium fraction reaches as high as 70%. Furthermore, an illustrative energy level diagram concerning the different barriers depending on the trap sites was devised to elucidate the trapping and diffusion behaviors of deuterium. Correspondingly, the microstructural trap sites associated with reversible or irreversible states were discussed in detail. This work enhances our understanding of hydrogen-Fe material interactions, thereby strengthening the fundamental theories underlying hydrogen embrittlement. Full article