Modeling the effects of loading scenario and thermal expansion coefficient on potential failure of cryo-compressed hydrogen vessels

A multiscale thermomechanical model for a simplified Type-3 cryogenic, compressed-hydrogen (H₂) storage vessel is described in this paper. The model accounts for the temperature-dependent elastic-plastic behavior of the vessel's carbon/epoxy composite overwrap and aluminum alloy liner. The homogenized thermo-elastic-plastic behavior for the individual laminae of the vessel layup is obtained using an incremental Eshelby-Mori-Tanaka approach associated with a micromechanical failure criterion to predict laminar failure while a standard elastic-plastic constitutive model is used to describe the behavior of the typical aluminum alloy assumed for the liner. The vessel's response to external loadings is modeled using a finite element method. Four loading scenarios, representing four thermomechanical cycles applied to the vessel, are analyzed to evaluate constituent and laminar stresses as well as the associated failure criterion during the cycle according to these scenarios. The model can provide helpful guidance to mitigate thermal stresses by selecting a suitable loading scenario, optimizing the layup, and tailoring the thermomechanical properties of the resin matrix.     

The potential for avoiding hydrogen release from cryogenic pressure vessels after vacuum insulation failure

This paper presents an analysis of vacuum insulation failure in an automotive cryogenic pressure vessel (also known as cryo-compressed vessel) storing hydrogen. Vacuum insulation failure increases heat transfer into cryogenic vessels by about a factor of 100, potentially leading to rapid pressurization and venting of the cryogen to avoid exceeding maximum allowable working pressure (MAWP). Hydrogen release to the environment may be dangerous, especially if the vehicle is located in a closed space (e.g. a garage or tunnel) at the moment of insulation failure. We therefore consider utilization of the hydrogen in the vehicle fuel cell and dissipation of the electricity by operating vehicle accessories or electric resistances as an alternative to releasing hydrogen to the environment. We consider two strategies: initiating hydrogen extraction immediately after vacuum insulation failure or waiting until maximum operating pressure is reached before extraction. The results indicate that cryogenic pressure vessels have thermodynamic advantages that enable slowing down hydrogen release to moderate levels that can be consumed in the fuel cell and dissipated in vehicle accessories supplemented by electric resistances, even in the worst case when the insulation fails at the moment when the vessel stores hydrogen near its maximum density (70 g/L at 300 bar). The two proposed strategies are therefore feasible, and the best alternative can be chosen based on economic and/or implementation constraints.     

Dynamics of cryogenic hydrogen storage in insulated pressure vessels for automotive applications

A dynamic model is used to characterize cryogenic H₂ storage in an insulated pressure vessel that can flexibly hold liquid H₂ and compressed H₂ at 350 bar. A double-flow refueling device is needed to ensure that the tank can be consistently refueled to its theoretical capacity regardless of the initial conditions. Liquid H₂ charged into the tank is stored as supercritical fluid if the initial tank temperature is >120 K and as a subcooled liquid if it is <100 K. An in-tank heater is needed to maintain the tank pressure above the minimum delivery pressure. Even if H₂ is stored as a supercritical fluid, liquid H₂ will form as H₂ is withdrawn and will further transform to a two-phase mixture and ultimately to a superheated gas. The recoverable fraction of the total stored inventory depends on the minimum H₂ delivery pressure and the power rating of the heater. The dormancy of cryogenic H₂ is a function of the maximum allowable pressure and the pressure of stored H₂; the evaporative losses cannot deplete H₂ from the tank beyond 64% of the theoretical storage capacity.     

Release and dispersion modeling of cryogenic under-expanded hydrogen jets

In the present work performed within the framework of the SUSANA EC-project, we address the release and dispersion modeling of hydrogen stored at cryogenic temperatures and high pressures. Due to the high storage pressures the resulting jets are under-expanded. Due to the low temperatures the choked conditions can be two-phase. For the release modeling the homogeneous equilibrium model (HEM) was used combined with NIST equation of state for hydrogen. For the dispersion modeling the 3d CFD methodology was used combined with a) a notional nozzle approach to bridge the expansion to atmospheric pressure region that exists near the nozzle, b) the ideal gas assumption for hydrogen and air and c) the standard (buoyancy included) k–ε turbulence model. Predicted release choked mass fluxes are compared against 37 experiments from literature. Predicted steady state hydrogen concentrations along the jet axis are compared against five dispersion experiments from literature as well as the Chen and Rodi correlation and the behavior of the proposed release and dispersion modeling approaches is assessed.     

Review on optimization design,failure analysis and non-destructive testing of composite hydrogen storage vessel

Composite hydrogen storage vessels have been increasingly applied to hydrogen fuel cell vehicles. This review focuses on optimization design, failure analysis and nondestructive testing for enhancing the safety of composites hydrogen storage vessels in service. The optimization designs of the composite vessel components help to improve the durability and strength of composite vessels subjected to burst pressure and fatigue loads. In complex service environments, composite vessels may suffer from various failure forms (burst failure, fatigue failure and impact failure) which involve different damage processes and influence factors. More importantly, this review discusses the applications of acoustic emission, digital image correlation, optical fiber in studying the residual performance (burst pressure and fatigue life) and damage modes of the composite vessel. It is expected that the combination of nondestructive testing techniques plays an increasingly important role in developing the composite vessel for structural health monitoring.     

Fatigue life evaluation of high pressure hydrogen storage vessel

By combining the micromechanics and continuum damage mechanics, a theoretical model is proposed to perform the fatigue evaluation of high pressure hydrogen storage vessel under cyclic internal pressure, which concentrates on the fatigue properties of the aluminum liner. Results show that the fatigue lifetime of vessel relates to the finite element mesh size, crack density and ratio in an element, cyclic loading amplitude and stress status at the liner. Effects of the mesh size and crack density on the fatigue lifetime of vessel are discussed. In addition, numerical results are also compared with those by experiments.     

Determination of the autofrettage pressure and estimation of material failures of a Type III hydrogen pressure vessel by using finite element analysis

The autofrettage process of a Type III hydrogen pressure vessel for fuel cell vehicles with preset winding pattern was simulated by finite element analysis (FEA). For a precise finite element analysis, the ply based modeling technique was used for the composite layers; a contour function was derived for the fibers at the dome part to determine the exact winding angle; and the exact composite thickness was also considered. In order to determine the most appropriate autofrettage pressure, stress analysis of the pressure vessel according to its internal pressure was carried out with consideration of the international regulations about pressure vessel design. The minimum stress ratio, the permanent volumetric expansion and the generated residual stress were investigated, and the failure of the pressure vessel under minimum burst pressure was predicted by application of various failure criteria of anisotropic composites.     

The isentropic expansion energy of compressed and cryogenic hydrogen

Pressure is often perceived as the single most important parameter when considering the safety of a storage system, for example when calculating the pneumatic energy that could be released in the event of a sudden accidental failure (or burst energy). In this paper, we investigate the role of temperature as another degree of freedom for minimizing the burst energy. Results are first presented for ideal gases, for which the relationship between burst energy as a function of initial and final volumes, temperature and pressures can be expressed analytically. Similar analysis is then derived for the specific case of H₂ using real gas equations of state. Assuming the expansion is isentropic, which holds for an adiabatic and sudden release as in a burst, it is shown that the energy released during a sudden burst is a weak function of pressure, revealing that the effect of increasing pressure is negligible beyond a certain value (∼100 bar); whereas the burst energy is a linear function of temperature. This suggests that temperature controls the burst energy in a much greater way. This analysis is carried out in the frame of onboard H₂ storage systems, for which it is shown that the use of cryogenic temperature for hydrogen vehicles, where risks of collision and impact on the surroundings are high, appears as a safety feature since burst energy is up to 18 times less than room temperature, high pressure storage.     

Characteristic of cryogenic hydrogen flames from high-aspect ratio nozzles

Unintentional leaks at hydrogen fueling stations have the potential to form hydrogen jet flames, which pose a risk to people and infrastructure. The heat flux from these jet flames are often used to develop separation distances between hydrogen components and buildings, lot-lines, etc. The heat flux and visible flame length is well understood for releases from round nozzles, but real unintended leaks would be expected to be from higher aspect-ratio cracks. In this work, we measured the visible flame length and heat-flux characteristics of cryogenic hydrogen flames from high-aspect ratio nozzles. Heat flux measurements from 5 radiometers were used to assess the single-point vs the multi-point methods for interpretation of heat flux sensor data, finding the axial distance of the sensor for a single-point heat flux measurement to be important. We compare the flame length and heat flux data to flames of both cryogenic and compressed hydrogen from round nozzles. The aspect ratio of the release does not affect the flame length or heat flux significantly, for a given mass flow under the range of conditions studied. The engineering correlations presented in this work enable the prediction of flame length and heat flux which can be used to assess risk at hydrogen fueling stations with liquid hydrogen and develop science-based separation distances for these stations.     

Influences of filling process on the thermal-mechanical behavior of composite overwrapped pressure vessel for hydrogen

Temperature rise is an important issue during the fast filling of composite overwrapped pressure vessel for hydrogen. Due to different temperature and thermal expansion coefficients at different parts, thermal-mechanical coupling effects exist. In this work, a fluid-thermal-solid coupling analysis method is proposed for the thermal-mechanical behavior of composite overwrapped pressure vessel in the process of filling. Firstly, a computational fluid dynamics analysis is performed to study the temperature rise and compared with analytical solution. Then a finite element model is set up and validated. The temperature field from the computational fluid dynamics model is exported to the finite element model as boundary condition. By this method, the influences of filling rate, inlet location and geometry on the thermal-mechanical stress field are studied. The results of this work can provide guidance for the design of composite overwrapped pressure vessel and the optimization of filling process.     

Visual indicator for the detection of end-of-life criterion for composite high pressure vessels for hydrogen storage

A model to predict the accumulation of fibre breaks in advanced composites, that takes into account all physical phenomena implicated in fibre failure (i.e. the random nature, stress transfer due to breaks, fibre debonding and viscosity of the matrix) shows clearly that the failure of a unidirectional composite structure results in the formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. This stage of development is followed almost immediately by failure. This has direct application to filament wound pressure vessels of the type used to store hydrogen under high pressure. A novel, cost effective, method of revealing developing unreliability in advanced composite pressure vessels is presented.     

Delivery of cold hydrogen in glass fiber composite pressure vessels

We are proposing to minimize hydrogen delivery cost through utilization of glass fiber tube trailers at 200 K and 70 MPa to produce a synergistic combination of container characteristics with properties of hydrogen gas: (1) hydrogen cooled to 200 K is ∼35% more compact for a small increase in theoretical storage energy (exergy); and (2) these cold temperatures (200 K) strengthen glass fibers by as much as 50%, expanding trailer capacity without the use of much more costly carbon fiber composite vessels.     

Safety approach for composite pressure vessels for road transport of hydrogen. Part 1: Acceptable probability of failure and hydrogen mass

Hydrogen is a promising alternative for current energy carriers. Compressed gas cylinders are the storage systems closest to the commercialization of hydrogen in vehicles. The safety factors in current standards are seen as restrictive for further growth and competitiveness of hydrogen infrastructure. A probabilistic approach can be employed in order to give a rational background to the safety factors. However, an acceptable probability of failure needs to be estimated before calculating the safety factors. The discussion of determining the acceptable probability must include the mass of hydrogen since this determines the consequences of an accident. It is concluded that an annual probability of failure of 10⁻⁷ would be appropriate for small pressure vessels containing a few kilograms of hydrogen. Larger pressure vessels of a few hundred kilograms or more should be designed for an annual probability 10⁻⁸.     

Determination of lifetime probabilities of carbon fibre composite plates and pressure vessels for hydrogen storage

It is shown that an analogy can be made between the failure of unidirectional carbon fibre reinforced epoxy plates and filament wound carbon fibre composite pressure vessels and that their strengths and failure probabilities can be determined. Fibres in filament wound composite structures are placed on geodesic paths around the mandrel, which becomes the liner; so that when the structure is pressurised the fibres are only subjected to tensile forces, as in a unidirectional composite. Multiscale modelling reveals that composite failure is controlled by fibre breakage and that clustering of fibre breaks determines ultimate reliability of the structure. Time dependent relaxation of the matrix leads to delayed failure of the elastic fibres. A statistical study, using the stochastic properties of the fibres, determines the range of lifetimes which will be obtained in a given class of pressure vessel, leading to an evaluation of failure probabilities as a function of internal pressures. In this way the definition of safety factors, based on an understanding of the physical processes governing damage accumulation, becomes possible.     

Fatigue life prediction and verification of high-pressure hydrogen storage vessel

A fatigue life prediction method is developed for the high-pressure hydrogen storage vessel based on theoretical research and experimental verification. Firstly, the finite element model of vessel was built considering wound angle of head, thickness and number of the composite layer, then simulation was performed. The optimum range of autofrettage pressure was obtained by FEA with consideration of the DOT-CFFC and CGH2R standards. The influence of autofrettage pressure, metal liner thickness, and fiber thickness on vessel fatigue life was discussed under internal pressure cyclic load. Finally, the experimental verification was carried out. It was found that fatigue failure first occurred in middle cylinder. The experiment results agree well with theory analysis. Their average error is 6.33%.     

Residual stress analysis of autofrettaged thick-walled spherical pressure vessel

In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the inner surface of the vessel. By performing a parametric study, the optimum autofrettage pressure and corresponding autofrettage percent for creating desirable residual stress state are introduced and determined.     

Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam

The master curve (MC) approach as standardised in the ASTM Standard Test Method E1921 was applied to weld metal of the reactor pressure vessel (RPV) beltline welding seam of Greifswald unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The orientation of the specimens within the welding seam is TL and TS according to ASTM E399.     

Optimal design of high pressure hydrogen storage vessel using an adaptive genetic algorithm

The weight minimum optimization of composite hydrogen storage vessel under the burst pressure constraint is considered. An adaptive genetic algorithm is proposed to perform the optimal design of composite vessels. The proposed optimization algorithm considers the adaptive probabilities of crossover and mutation which change with the fitness values of individuals and proposes a penalty function to deal with the burst pressure constraint. The winding thickness and angles of composite layers are chosen as the design variables. Effects of the population size and the number of generations on the optimal results are explored. The results using the adaptive genetic algorithm are also compared with those using the simple genetic algorithm and the Monte Carlo optimization method.     

Prediction of failure strain and burst pressure in high yield-to-tensile strength ratio linepipe

Failure pressures and strains were predicted for a number of burst tests as part of a project to explore failure strain in high yield-to-tensile strength ratio linepipe. Twenty-three methods for predicting the burst pressure and six methods of predicting the failure strain are compared with test results. Several methods were identified which gave accurate and reliable estimates of burst pressure. No method of accurately predicting the failure strain was found, though the best was noted.     

Design by analysis of deep-sea type III pressure vessel

This paper explores the potential of hydrogen as an energy carrier for deep-sea applications. Finite element analysis of a type III pressurised cylinder to the intended working pressures of 300 bar internal and up to 600 bar external were carried out for different designs and safety factors. Design parameters such as helical angle, liner, helical, and hoop thicknesses were studied and optimised. A buckling analysis was carried out for the optimised designs and recommendations to increase the maximum allowable external pressure are given.