To investigate the hydrogen embrittlement susceptibility and hydrogen permeation behavior of 90 mm extra-thick Q690DR steel plate in the thickness direction, samples were taken from three regions: Subsurface layer, 1/4 Thickness layer (1/4T), and 1/2 Thickness layer (1/2T). The results showed that the matrix structure in each region was mainly tempered martensite, and the grain size gradually increased from the Subsurface to 1/2T; a discontinuous banded structure existed in the Subsurface region. In-situ hydrogen permeation and mechanical testing under 6 MPa hydrogen revealed that hydrogen embrittlement susceptibility: Subsurface > 1/2T > 1/4T. The Subsurface region was significantly affected by rolling deformation, with grains elongated along the rolling direction (RD) and forming a banded structure, providing a rapid channel for hydrogen diffusion and making hydrogen more likely to permeate the material interior, resulting in the formation of fine elongated cracks during fracture. Therefore, it exhibited the highest hydrogen embrittlement susceptibility. The 1/2T region formed coarse martensite structure due to a slower cooling rate, and a large number of secondary cracks were generated during fracture. In contrast, the 1/4T region had a homogeneous distribution of tempered martensite and fine grains, with a stronger hindrance effect on hydrogen diffusion, and thus had the best hydrogen embrittlement resistance. In summary, the degree of deformation during the rolling process and the cooling rate during the cooling process are the key factors that cause the microstructure to show a gradient distribution and thereby affect hydrogen embrittlement susceptibility.

Type III hydrogen cylinders with steel liners feature high storage pressure, large single-cylinder capacity and low material cost, making them highly promising for application in large-capacity hydrogen transport systems using long-tube trailers. However, the structural design of such cylinders, in which the liner and the winding layer jointly bear the load, is influenced by a variety of factors, including material costs, cylinder performance and trailer load capacity, and there is currently no specific design method. In this study, considering the structural load-bearing characteristics of Type III hydrogen cylinders and multiple influencing factors, a multi-constraint structural optimization design concept was proposed. A detailed structural design method was established based on genetic algorithms, progressive damage theory and fatigue assessment theory. Furthermore, this method was subsequently applied to the structural design of a cylinder with a design pressure of 55 MPa and a volume of 3318 L. The results show that the proposed optimization design method has excellent convergence and high reliability. It achieves material cost minimization while ensuring the cylinder meets all requirements for strength, fatigue life, trailer load capacity and so on. Compared to the traditional design method that does not consider the liner load-bearing capacity, the material cost of the Type III with the steel liner cylinder designed with this study was reduced by nearly 10%.

In this study, the low cycle fatigue tests of S30408 austenitic stainless steel with a strain ratio of-1 were conducted at 110 K, and the corresponding 110 K cryogenic design fatigue curve (S-N curve) was established. The experimental results demonstrate that within the strain amplitude range of 0.4%-0.8%, the fatigue life of S30408 at 110 K is significantly improved compared to that at 293 K, and the fatigue properties exhibit notable differences. The cyclic stress response under 0.5% strain amplitude at 110 K exhibits three distinct stages: rapid cyclic hardening, cyclic stabilization, and rapid decline, thus featuring a cyclic stabilization phase and a higher cyclic stress amplitude than that at 293 K. Microscopic analysis reveals that the fatigue fracture at 110 K displays distinct ductile fracture characteristics, while under the high strain amplitude, it further exhibits multiple crack sources, fatigue steps, and secondary cracks in the crack initiation region. Based on the experimental data from this study and relevant literature, the 110 K cryogenic S-N curve for austenitic stainless steels was established with a fatigue life safety factor of 20 and a stress amplitude safety factor of 2. Compared with the S-N curves specified in ASME VIII-2 and EN 13445-3, the 110 K cryogenic S-N curve exhibits a higher stress amplitude when the number of cycles exceeds 103. Within the typical fatigue life range of pressure vessels (103 to 106 cycles), it can significantly extend the service life of cryogenic pressure vessels.

The rupture disk opening process has a significant impact on the flow and spontaneous ignition of the released high-pressure hydrogen. This study investigates the characteristics of shock wave and spontaneously combusting flame produced by hydrogen release through C-scored and Cross-scored rupture disks with burst pressures ranging from 8 to 24 MPa, based on their distinct opening manner and opening time. Results show that compared to a Cross-scored rupture disk, the opening of a C-scored rupture disk generates stronger early compression waves, which exhibit a better superposition effect when coalescing to strengthen the leading shock wave. This effect increases with rising burst pressure but decreases with increasing distance from the rupture disk. Conversely, the adverse impact of C-scored rupture disk longer opening time on rapid formation of a strong leading shock wave decreases with rising burst pressure but accumulates over time. The intensity variation of leading shock wave under the competition of these two opening factors makes it easier for the Cross-scored rupture disk to initiate the spontaneous ignition inside the tube at a lower burst pressure, while the C-scored rupture disk could generate a stronger initial flame at a higher burst pressure, which then decays more severely as propagating inside a long release tube. In addition, the fragment generated by the C-scored rupture disk opening could affect the flame stabilization and expansion during its evolution to a jet flame outside the tube by blocking hydrogen jet and destroying combustion core. The hazard of this jet flame produced by a large-capacity tank release is assessed to be fatal, which requires significant attention in safety protection designing.

The degradation of fracture resistance and the associated failure mechanism under the synergistic effect of full-ocean-depth hydrostatic pressure and moisture absorption still remain unclear. Therefore, this study investigates the degradation of CFRP/titanium adhesively bonded structures under full-ocean-depth hydrostatic pressure (20-110MPa) combined with moisture absorption. Systematic experiments on adhesive moisture absorption, adhesive tensile properties and mode I/II fracture resistance reveal distinct degradation mechanisms. High pressure drives water into pre-existing micropores, expanding transport channels and disrupting hydrogen bonds, which accelerates moisture diffusion. Consequently, moisture absorption increases linearly from 2.80% to 4.38% without saturation, glass transition temperature drops by 43.22% and porosity rises by 128.99%. A distinct transition zone identified in the vicinity of 3% moisture content separates mild plasticization from rapid structural‑damage‑dominated degradation. The tensile strength of bulk adhesive degrades linearly by 44.77% (from 22.85MPa to 12.62MPa at 110MPa), accompanied by brittle-to-ductile failure transition. The degradation of fracture toughness exhibits pressure-dependent behavior, transitioning from cohesive failure within the adhesive layer below 50MPa to moisture-driven adhesive failure at the adhesive/titanium interface above 50MPa. At 110MPa, the mode I fracture toughness decreases by 51.45%, while mode II fracture toughness decreases by 74.55%, compared to that of dry condition. The findings can provide experimental data and theoretical basis for performance evaluation and reliability-based design of adhesively bonded structures in deep-sea equipment.

The effect of gaseous hydrogen on the corrosion and stress corrosion cracking behavior of X80 pipeline steel was investigated under a custom-built dual-phase simulation apparatus that replicates internal gas transmission and external seawater immersion conditions. Hydrogen permeation, electrochemical, immersion corrosion, and slow strain rate tensile tests were conducted at 6.3 MPa nitrogen and hydrogen environment coupled with a 3.5 wt% NaCl solution. Hydrogen permeation rate and steady-state current density increase substantially with hydrogen concentration due to enhanced surface interactions. Hydrogen alters the corrosion product film composition, promoting the transformation of gamma-FeOOH to conductive Fe3O4, resulting in an incomplete Fe3O4-rich film. This defective film accelerates localized corrosion and the oxygen reduction reaction, ultimately increasing corrosion current density and reducing impedance. In H2/NaCl solution environment, hydrogen simultaneously promotes the formation of pitting corrosion and corrosion pores on the outer surface of the substrate, as well as hydrogeninduced cracks on the inner surface, thereby increasing the starting points for crack formation and leading to a severe degradation of mechanical properties. This study provides insights into hydrogen-induced degradation mechanisms for pipeline safety in hydrogen transport applications.

This work revealed an experiment of catastrophic rupture of a 70 MPa-48 L high-pressure hydrogen storage tank under a protective barrier in a semi-enclosed test field. Experimental results indicated that during the 1322 s exposure to the GTR 13-II standard fire test, the internal pressure of the tank escalated from an initial 68.6 to 112.3 MPa (63.70 % of increase), ultimately resulting in catastrophic failure due to explosion. The measured peak overpressure along the explosion-venting direction exhibited a significant attenuation from 465.60 to 47.85 kPa as the distance increased from 3 m (P1) to 10.1 m (P4) from the explosion center. The explosion-proof wall could effectively mitigate the overpressure. At the measuring points with the same distance (approximately 5.1, 7.2, and 10.1 m), the overpressure attenuation rates of the measurement points behind the wall compared with those of the diagonal measurement points were 79.61 %, 78.59 %, and 40.02 % respectively. In addition, a numerical simulation of the above case was carried out using AUTODYN. By comparing the simulation results with and without the explosion-proof wall, it was revealed that the wall reduced the peak overpressure behind it by 93.69 %, but increased the peak overpressure at 3 m from the explosion-venting by 19.33 %.

The lack of experimental methods for quantitatively detecting hydrogen distribution at fatigue crack tips has hindered the validation of numerical models. This study proposes a method for determining hydrogen distribution by combining scanning Kelvin probe force microscopy (SKPFM) and thermal desorption spectrometry (TDS). Using this approach, the characteristics of hydrogen distribution at the crack tip of austenitic stainless steel were investigated at various stages of fatigue crack propagation in a high-pressure hydrogen environment. The results revealed dynamic hydrogen uptake at the fatigue crack tip. At each propagation stage, the hydrogen concentration was highest on the surface of the crack tip and decreased rapidly with increasing distance from it, with a hydrogen penetration depth of less than 4 mu m. Furthermore, as crack propagation progressed, both the hydrogen concentration at the crack tip and the penetration depth gradually decreased. The trend in hydrogen distribution at the crack tip across different propagation stages, simulated by a phase-field model, was consistent with the experimental results, demonstrating the model's potential for predicting such distributions. The proposed method offers a new approach for the quantitative characterization of hydrogen concentration at crack tips.

Laser surface nitriding of pure iron was conducted under mixed NH3/N2 atmospheres to suppress hydrogen diffusion while avoiding defects associated with conventional laser remelting. Ammonia addition promoted laser-assisted nitrogen incorporation and nitride formation, thereby enhancing hydrogen trapping capability. However, excessive NH3 unexpectedly deteriorated the hydrogen barrier performance despite the increased Fe2–3N content. Increasing NH3 concentration intensified pore formation induced by hydrogen evolution, creating preferential pathways for hydrogen diffusion. The sample with 10% NH3 exhibited the optimal hydrogen barrier effect, showing a 52.1% reduction in the hydrogen diffusion coefficient and a 109% increase in hydrogen trap density. In contrast, the hydrogen diffusion coefficient of the 30% NH3 sample exceeded that of pure iron due to excessive porosity. The results reveal that hydrogen diffusion during ammonia-assisted laser nitriding is governed by the competition between Fe2–3N-enhanced trapping and pore-assisted diffusion. This work provides new insights into the design of hydrogen-resistant laser-resistant surface nitriding.

In-situ electrochemical hydrogen charging combined with scanning Kelvin probe force microscopy (SKPFM) and electron backscatter diffraction (EBSD) was employed to study hydrogen diffusion and trapping behaviors in the α and γ phases of 2507 duplex stainless steel. It was found that hydrogen diffusion in both phases exhibited a strong dependence on crystallographic orientation. In the γ phase, hydrogen diffusivity in the (111) oriented grain was the slowest among the examined orientations, whereas it was the fastest in the α phase. Additionally, SKPFM measurements revealed pronounced hydrogen trapping at the α/γ phase boundary.

Cryogenic storage tanks are critical equipment in energy systems, where heat ingress during storage induces pressure variation and thermal stratification, posing safety risks. Therefore, experiments are essential to elucidate the pressure and temperature evolution. In this study, a real-time measurement system for pressure, liquid level, and temperature was established on a 5 m3 product-scale liquid nitrogen storage tank. Experiments were conducted under three representative conditions: storage following pressurization, venting, and liquid discharge. The relationship between fluid temperature and wall temperature, the circumferential and axial wall temperature distributions, and pressure evolution were systematically analyzed. The results show that the initial vapor-wall temperature difference gradually diminishes, whereas the liquid temperature remains nearly identical to the wall temperature. The negligible circumferential temperature difference (maximum 4.9 K) indicates that a one-dimensional axial measurement adequately characterizes the overall temperature field. Despite the large initial axial temperature gradient, the system evolves toward a quasi-steady state through internal heat and mass transfer, after which external heat ingress dominates. The ullage wall temperature profile is nearly linear at high liquid levels and concave at low liquid levels, while thermal stratification develops in the liquid-phase region and intensifies over time. Pressure increases during storage following venting due to liquid evaporation, whereas during storage following pressurization and liquid discharge, pressure evolution is governed by the competition between vapor cooling, condensation and liquid evaporation. These findings provide practical guidance for temperature sensor placement, pressure control strategies, and structural design optimization of cryogenic storage tanks.

LNG storage tanks, as core equipment for cryogenic energy storage, are being developed toward the integration of safety, economy, and resource conservation under the guidance of green manufacturing. This necessitates a detailed investigation of their pressure and temperature evolution under multiple operating conditions. In this study, a 5 m3 vacuum-insulated storage tank integrated with an experimental platform was developed for realtime monitoring of pressure, liquid level, and multi-point temperatures under multiple LNG operating conditions. Systematic tests were conducted, and an experimental database covering multi-condition operations was established. The pressure-temperature evolution, fluid-wall temperature relationships, and axial/circumferential wall temperature distributions were analyzed. The results show that wall cooling undergoes three stages (convection, boiling heat transfer, and stabilization) during replacement and filling. During pressurization and liquid discharge, a maximum wall temperature of -30.23 degrees C is observed at 0.31 MPa. The axial wall temperature distribution exhibits saturated/subcooled conditions in the bottom liquid-phase region, while the temperature increases with height in the upper region. Notably, the temperature gradient during storage gradually diminishes, exhibiting a linear profile at high liquid levels and a concave profile at low liquid levels. The wall temperature converges to the liquid temperature under stable liquid contact, while pressurization and discharge may induce abrupt medium temperature changes, with a maximum fluid-wall difference of 26.36 degrees C. The circumferential temperature distribution indicates that single-axis temperature data can reflect the overall temperature variation trends. These findings offer an experimental basis for the safe design, structural optimization, and monitoring system simplification of LNG storage tanks.

This study modifies the texture and precipitation phases of titanium-free maraging steel by adjusting the heat treatment process, thereby enhancing its resistance to hydrogen embrittlement and toughness without compromising the steel's strength. The results revealed three key advancements: (i) omega-precipitates and reversed austenite acted as hydrogen traps, delaying hydrogen diffusion; the subsequent formation of the Laves phase further enhanced this effect, significantly reducing the hydrogen diffusion coefficient by 71.3 %; (ii) incomplete recrystallization of austenite before quenching inhibited the formation of martensite variants, resulting in a pronounced < 110 > //RD fiber texture that effectively altered the crack propagation path-a texture mechanism previously overlooked in hydrogen embrittlement studies; (iii) analysis of the crack path and thermal desorption spectra of SLLA-480 demonstrated that reversed austenite served as a hydrogen trap, inhibiting hydrogen diffusion, while dispersed reversed austenite had limited capacity to impede crack propagation in high-strength maraging steel. Due to these synergistic mechanisms, the SLLA-480 process reduced hydrogen embrittlement sensitivity by 17 % without compromising strength. This work deepens our understanding of the hydrogen embrittlement mechanism in maraging steel and proposes a microstructure design strategy based on the synergistic control of nanoprecipitates and crystal texture-a strategy particularly important for titanium-free maraging steel systems.

This study systematically investigated the influence of loading rates and pre-cracking environment on the fracture toughness of L245 pipeline steel in a 6 MPa hydrogen gas environment. The measured fracture toughness values exhibit a dependence on the loading rate employed during testing. Notably, a critical threshold in loading rate was identified, which significantly exceeding the upper limit specified by standard testing protocols. When the loading rate remains below this critical threshold, the fracture toughness values stabilize and remain virtually unchanged. This critical loading rate can be determined by correlating the hydrogen diffusion rate, obtained from in-situ gas-phase hydrogen permeation experiments, with the crack growth rate observed in fracture toughness tests. It was found that the fracture toughness of specimen pre-cracked in air could not be determined when tested under sufficiently slow loading rates. This phenomenon is attributed to crack tip blunting for stress concentration alleviation and dislocation-mediated hydrogen trapping for mitigation of hydrogen-induced damage.

This study systematically investigates the coupled effects of hydrogen pressure and stress ratio on the fatigue crack growth (FCG) behavior of X80 pipeline steel under high-pressure hydrogen environments. The FCG process presents a two-stage characteristic, including an initial acceleration stage and a subsequent stable stage similar to that in air. Experimental results quantitatively reveal that elevated hydrogen pressure and stress ratio significantly increase the fatigue crack growth rate (FCGR) in both stages, where hydrogen pressure exhibits a more dominant promotion effect in the acceleration stage. By integrating experimental data, two-parameter fatigue theory, the Abel-Noble equation of state, and Sieverts' law, a novel FCGR prediction model is established. Compared with existing models, the proposed model considers the dual influences of pressure and stress ratio, and it is applicable for the integrity evaluation of X80 and lower-grade pipeline steels under hydrogen pressure up to 12 MPa and stress ratio up to 0.7.

Composite overwrapped pressure vessels (COPVs) for storing cryo-compressed hydrogen face significant safety challenges under cryogenic high-pressure conditions. While previous studies have primarily evaluated COPV safety through empirical testing, comprehensive analyses of their failure mechanisms remain limited. This study investigates the cryogenic burst pressure and failure mechanisms of COPVs using a finite element model. The results indicate that under cryogenic conditions, matrix failure in the composite layers occurs at a lower internal pressure, which is detrimental to the vessel's burst pressure. Conversely, at cryogenic temperatures, the composite develops longitudinal compressive stresses that partially offset the tensile stresses induced by internal pressure, and the composite strength is simultaneously enhanced. Ultimately, the combined effect of these three factors leads to an enhanced burst pressure for COPVs at cryogenic temperatures.

This special issue highlights the generation, application, and safe use of low-carbon hydrogen produced from renewable energy sources.

In this paper, the residual strength of carbon fiber reinforced polymer composites (CFRP) for marine applications has been studied. The seawater absorption tests, regular tensile tests, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis of CFRP exposed to seawater at 25 degrees C, 40 degrees C and 60 degrees C respectively were conducted. A hydro-mechanical coupling progressive damage model has also been established to predict the mechanical behavior and damage evolution, considering both hydrothermal- and mechanical load-induced damage. The experimental results show that the seawater immersion significantly affects the transverse mechanical properties, while having little effect on the in-plane shear and longitudinal properties. The micro- structural comparative analysis indicates that the accelerated moisture absorption, induced by high immersion temperature, increases salt deposition and weakens the adhesion between fiber and matrix. The finite element analysis (FEA) results shows good fidelity, with relative errors not exceeding +/- 10 % in predicting residual strength. Seawater immersion significantly accelerates matrix tensile damage, increasing its area, but has minimal effect on fiber tensile damage. This model can assist engineers in predicting the durability of composite load-bearing structures in marine environment.

Carbon Fiber Reinforced Polymer (CFRP) is widely employed in insulated cryogenic pressure vessels (ICPVs) due to their lightweight and superior thermal insulation properties. However, the outgassing behavior of CFRP accelerates interlayer vacuum degradation, compromising thermal insulation performance and the operational safety of these vessels. This study developed a theoretical vacuum outgassing model based on planar specimens and systematically investigated the outgassing characteristics of CFRP (resin volume fraction of 60%) and pure resin materials using the static pressure rise method. Results indicate that CFRP exhibits a lower diffusion coefficient than pure resin, validating the gas diffusion barrier effect of carbon fibers. The total ion current of CFRP represents 62.5% of that of pure resin over the same testing period, further confirming that outgassing originates solely from the resin, with no significant contribution from carbon fibers. Additionally, experiments on ICPV vacuum behavior identify composite outgassing as the primary factor contributing to interlayer vacuum degradation. Over a period of 10 hours, the interlayer pressure increased sharply from 10(-1) Pa to approximately 1.5 Pa, highlighting the significant influence of CFRP outgassing on vacuum degradation and the need for effective mitigation strategies. This research provides a robust theoretical and experimental foundation for optimizing the design and maintenance of cryogenic pressure vessels, offering

High-pressure hydrogen systems' internal load sensors face challenges such as zero drift, creep, and response hysteresis, primarily due to hydrogen infiltration into traditional resistive strain gauges. To address this, we developed a novel polycrystalline FeCrAl film and fabricated an in-situ Cr/AlN/FeCrAl sandwich-structure thinfilm strain gauge (TFSG) on a 316 L stainless steel substrate using magnetron sputtering and a template technique. Results indicate that substrate temperature significantly affects the microstructure and resistance of FeCrAl. At 400 degrees C, the uniform, fine body-centered cubic (bcc) polycrystalline film exhibits higher resistivity and resistance stability, while higher temperatures lead to grain coarsening and defect proliferation. Testing in a 12 MPa hydrogen environment shows that the Cr/AlN/FeCrAl TFSG outperforms traditional Cu-Ni strain gauges in hydrogen resistance, with zero drift and creep below 30 mu epsilon and a strain sensitivity coefficient of approximately 1.62, demonstrating high hydrogen resistance and practicality in high-pressure environments.