Thick-walled Pressure Vessels Research Articles

Methods for Estimating Hydrogen Fuel Tank Characteristics

Abstract The pressure vessels needed to store hydrogen for next-generation hydrogen fuel cell vehicles are expected to be a substantial portion of the total system mass, volume, and cost. Gravimetric capacity, volumetric capacity, and cost per kilogram of usable hydrogen are key performance metrics that the U.S. Department of Energy (DOE) uses to determine the viability of hydrogen fuel cell systems. Research and development related to hydrogen storage systems covers a wide range of potential operating conditions, from cryogenic temperatures to high temperatures (above ambient) and low pressure to high pressure. Researchers at PNNL have developed methods for estimating these key pressure vessel characteristics to support on-board hydrogen storage system design and performance evaluation and to support decision-making about DOE hydrogen storage system research investments. This article describes the pressure tank estimation methodology that has been used as a stand-alone calculation and has been incorporated into larger system evaluation tools. The methodology estimates the geometry, mass, and material cost of type I, type III, and type IV pressure vessels based on operating pressure and material strength at the system's operating temperature, using classical thin-wall and thick-wall pressure vessel stress calculations. The geometry, mass, and material cost requirements of the pressure vessel have significant impacts on the total system performance. For example, hydrogen storage materials that can separately achieve a very high hydrogen density can be deemed impractical for use in fuel cell vehicle hydrogen storage systems because the pressure tank containing them is too large, heavy, or expensive. This article describes the design philosophy and analytical process of the tank characteristic estimation methodology, which has been implemented in spreadsheet calculation tools and system-level analysis tools used by DOE researchers. Each of the three tank types (type I, type III, and type IV) uses a different analysis methodology with some common elements. This article also provides examples of implementing the methodology to perform parametric studies of all three pressure vessel types. The goal of this article is to present the methodology in sufficient detail so it can be implemented in other hydrogen fuel cell vehicle design and analysis tools.

Fatigue crack propagation in thick-walled pressure vessels under hydraulic testing condition

Fatigue is one of the failure modes in gun barrel. It is still an important problem to understand crack propagation behavior due to fatigue loading of firing cycles. This paper presents a hydraulic fatigue test method to simulate crack propagation in a tube containing a pre-machined defect on its inner surface. A close inherent relation is found between crack propagating rate and hoop strain on the outside surface of the tube, which provides a feasible approach for investigation of fatigue behavior in gun barrel under actual firing condition.

Investigation of stress relief crack susceptibility of CrMoV steels coarse grain HAZ via simulation of uniaxial stress conditions during PWHT

Creep-resistant steels such as the 13CrMoV9-10, used in the construction of thick-walled pressure vessels, are most commonly submerged arc welded (SAW). These steels can develop stress relief cracks (SRC) if the mandatory post weld heat treatment (PWHT) is performed improperly. Current PWHT parameters, such as heating rate and holding time at a specific holding temperature, are based on both empirical experience and conventional free shrinking welding experiments to characterize the SRC-susceptibility of the weld. These cannot adequately depict the higher residual stresses caused by the structurally induced stiffness of the surrounding construction.This study discusses the development of a repeatable, precise, and time-efficient methodology to study the effects of different stress levels and heating rates on the SRC susceptibility of the coarse grain heat-affected zone (CGHAZ). For that purpose, samples were thermically treated to simulate a coarse grain heat-affected zone (CGHAZ) and subsequently exposed to representative levels of stress during the heating phase of a PWHT. The recorded stress and heating rate–dependent strains were mathematically analyzed via curve tracing/calculus to identify interdependent effects. This procedure facilitates the measurement of material characteristics such as carbide growth on grain boundaries at the µm-scale via an integrated value over the entire sample volume. The first and second derivatives show a slight, precipitate-dependent, increase in hardness of the sample, depending on the heating rate and applied stress. This new methodology generates an improved assessment of the SRC susceptibility of SAW microstructures of creep-resistant CrMoV steels.

A parametric finite element study for determining burst strength of thin and thick-walled pressure vessels

To accurately predict the burst strength of both thin and thick-walled pressure vessels (PVs), a parametric study of PV burst strength was performed for a wide range of vessel geometries and materials using elastic-plastic finite element analysis (FEA). A valid FEA model was established through a detailed study of 2D versus 3D FEA models, the critical stress failure criterion versus the limit load criteria, and the thick-wall effect on the FEA simulations. The results show that the stresses and strains at the mean diameter, rather than outside diameter, determines a more accurate burst strength for both thin and thick-walled PVs. On this basis, a parametrized FEA script using the ABAQUS Python application programming interface (API) was used to create a large database of PV burst strengths for a variety of vessel geometries and materials, demonstrating that Python scripting is a powerful technique for performing parametric studies or generating large databases. From the FEA results, using the regression method, a new burst pressure model was developed as a function of the vessel geometry (D/t ratio) and material properties (UTS and n). As validated by a large number of full-scale burst test data, the proposed burst model can very accurately predict the burst strength for both thin and thick-walled PVs.

Material-based modeling of cavatappi artificial muscles

Soft actuators show much promise for use in bioinspired and biomimetic robotics as they share many similarities with actuation systems found in nature. Twisted and coiled actuators are soft actuators that have been shown to outperform many metrics of biological muscles, leading researchers to derive actuation models for future control and implementation. Although models have been proposed for twisted and coiled carbon nanotubes and polymer fibers, cavatappi artificial muscles—a novel twisted and coiled fluidic soft actuator—have not been modeled yet. This work establishes a framework for modeling cavatappi using the thick-wall pressure vessel stress analysis and the spring theory. The presented model uses the mechanical properties of the precursor drawn material used for fabrication, initial twist (internal fiber angle), muscle geometry, and internal pressure to predict the artificial muscles contraction under different external loads. The model predictions agree with the experimental results for cavatappi of different internal fiber angles and load conditions. Given their potential implementation in bioinspired applications, our model can help better design, optimize, and control the actuation response of cavatappi.

Enhanced gaseous hydrogen solubility in ferritic and martensitic steels at low temperatures

Metals that are exposed to high pressure hydrogen gas may undergo detrimental failure by embrittlement. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals is crucial for avoiding hydrogen embrittlement. In this study, the effect of stress-enhanced gaseous hydrogen uptake in bulk metals is investigated in detail. For that purpose, a generalized form of Sievert's law is derived from thermodynamic potentials considering the effect of microstructural trapping sites and multiaxial stresses. This new equation is parametrized and verified using experimental data for carbon steels, which were charged under gaseous hydrogen atmosphere at pressures up to 1000 bar. The role of microstructural trapping sites on the parameter identification is critically discussed. Finally, the parametrized equation is applied to calculate the stress-enhanced hydrogen solubility of thin-walled pipelines and thick-walled pressure vessels during service.

Neutron diffraction, finite element and analytical investigation of residual strains of autofrettaged thick-walled pressure vessels

Residual strain distributions, positions of elastic-plastic juncture and 1st yielding etc. of autofrettaged thick-walled pressure vessels were revealed quantitatively using Neutron Diffraction (ND), Finite Element (FE) and Analytical solution. FE models were validated with ND results. Relationships between autofrettage pressures (Pmii, Pmao, Paopt) and load bearing capacity versus radius ratio K were respectively established via FE parametric study, by which optimal radius ratio K = 3 rather than K = 4 was identified for some existing vessels. Based on ND and FE results, new formula for calculating optimal juncture radius rjopt was deduced which narrowed the gap between analytical and FE results by 0.5 mm. Four coefficients Cj were proposed to modify conventional equations for calculating juncture radius rj, that facilitated a tool to address residual strains of autofrettaged pressure vessels. These results may be referred to for the design, manufacture, and proper application of the autofrettage technique onto pressure vessels and relevant engineering components.

Local creep damage effects on subsequent low temperature fatigue crack growth behaviour of thick-walled pressure vessels

The influence of prior creep damage on the subsequent fatigue cracking behaviour of thick-walled pressure vessels has been thoroughly investigated in this study. Creep damage was introduced into fracture mechanics specimens by performing creep tests at 550 °C and stopping them after reaching a desired crack length. Using this experimental methodology, creep damage was successfully introduced ahead of the crack tip in the form of intergranular voids and microcracks. In order to assess the creep damage effects, in the absence of significant plasticity, on the structural integrity of thick-walled pressure vessels the material was uniformly pre-strained under compressive plastic deformation prior to the specimen manufacture, thus hardening the material. Fatigue tests were performed on specimens with and without creep damage and the results were compared with each other. Moreover, metallurgical investigations were conducted to understand the influence of microstructural damages, as a result of creep loading conditions, on the fatigue cracking behaviour of the material. The results from this study show a clear reduction in the fatigue cracking rate in the presence of creep damage local to the crack tip. The findings have been discussed in terms of the effects of static creep loading conditions and microstructural damages on the subsequent fatigue cracking behaviour under cyclic loading conditions.

Mammary Tumor Organoid Culture in Non-Adhesive Alginate for Luminal Mechanics and High-Throughput Drug Screening.

Mammary tumor organoids have become a promising in vitro model for drug screening and personalized medicine. However, the dependency on the basement membrane extract (BME) as the growth matrices limits their comprehensive application. In this work, mouse mammary tumor organoids are established by encapsulating tumor pieces in non‐adhesive alginate. High‐throughput generation of organoids in alginate microbeads is achieved utilizing microfluidic droplet technology. Tumor pieces within the alginate microbeads developed both luminal‐ and solid‐like structures and displayed a high similarity to the original fresh tumor in cellular phenotypes and lineages. The mechanical forces of the luminal organoids in the alginate capsules are analyzed with the theory of the thick‐wall pressure vessel (TWPV) model. The luminal pressure of the organoids increase with the lumen growth and can reach 2 kPa after two weeks’ culture. Finally, the mammary tumor organoids are treated with doxorubicin and latrunculin A to evaluate their application as a drug screening platform. It is found that the drug response is related to the luminal size and pressures of organoids. This high‐throughput culture for mammary tumor organoids may present a promising tool for preclinical drug target validation and personalized medicine.

Effect of length in rotational autofrettage of long cylinders with free ends

Thick-walled cylindrical and spherical pressure vessels are often subjected to autofrettage, a process in which the vessel is loaded at the inner wall to cause a partial or complete plastic deformation emanating from the inner wall, followed by unloading. This introduces the beneficial compressive residual stresses in the vicinity of the inner wall. Depending on the type of the loading, there are five different types of autofrettage processes— hydraulic, swage, explosive, thermal and rotational. This article analyzes the rotational autofrettage, in which the cylinder to be autofrettaged is loaded by rotating it about its longitudinal axis. The centrifugal forces cause the required plastic deformation in the cylinder. Hence, when the cylinder is unloaded by bringing it to rest, compressive hoop residual stresses are introduced in the vicinity of its inner wall. When long cylinders are rotated about their axes, the distribution of axial stress changes with length of the cylinder and affects the generation of the residual stresses in the autofrettaged cylinder. This effect is investigated here by a finite element method (FEM) analysis of rotational autofrettage of cylinder made up of A723 gun steel. The FEM analysis using ABAQUS® package reveals the presence of tensile axial residual stresses in the vicinity of the inner wall of the cylinder, which increase with length. The tensile residual stresses can be mitigated by constraining the ends of the cylinder during the rotational autofrettage.

Design and Analysis of a Bulge Test Device

The aim of this work is to present the methodological process to design a device capable of performing Bulge tests. This kind of device allows obtaining more information about the plastic behavior of a material than the one provided by a traditional tensile test. The engineering specifications of the device were evaluated through the QFD methodology. Then, a basic design of the device was performed based on available analytical models such as thick-walled pressure vessel theory, annular plate theory, and a basic plasticity model for the biaxial stress state. Later, a detailed design of the device was proposed, which was evaluated by means of a 3D model of finite elements and a linearstatic analysis for the main components. Finally, a 2D axisymmetric model and a dynamic non-linear analysis were performed to validate the proposed design. The main novelty of the work consists of articulating the methodology of the mechanical design process and the conception, design, and validation of a Bulge device while solving the deficiencies found in the literature regarding the design and validation processes of this type of devices.

Numerical Analysis of Filament Wound Cylindrical Composite Pressure Vessels Accounting for Variable Dome Contour

In this work, the stress distribution along cylindrical composite pressure vessels with different dome geometries is investigated. The dome contours are generated through an integral method based on shell stresses. Here, the influence of each dome contour on the stress distribution at the interface of the dome-cylinder is evaluated. At first, the integral formulation for dome curve generation is presented and solved for the different dome contours. An analytical approach for the calculation of the secondary stresses in a cylindrical pressure vessel is introduced. For the analysis, three different cases were investigated: (i) a polymer liner; (ii) a single layer of carbon-epoxy composite wrapped on a polymer liner; and (iii) multilayer carbon-epoxy pressure vessel. Accounting for nonlinear geometry is seen to have an effect on the stress distribution on the pressure vessel, also on the isotropic liner. Significant secondary stresses were observed at the dome-cylinder interface and they reach a maximum at a specific distance from the interface. A discussion on the trend in these stresses is presented. The numerical results are compared with the experimental results of the multilayer pressure vessel. It is observed that the secondary stresses present in the vicinity of the dome-cylinder interface has a significant effect on the failure mechanism, especially for thick walled cylindrical composite pressure vessel. It is critical that these secondary stresses are directly accounted for in the initial design phase.

Thermoelastoplastic response of FGM linearly hardening rotating thick cylindrical pressure vessels

An analytical solution is presented to analyze the thermoelastoplastic response of a rotating thick-walled cylindrical pressure vessel made of functionally graded material (FGM). The analysis is based on Tresca's yield condition, its associated flow rule and linear strain hardening material behaviour. The uncoupled theory of thermoelasticity is used, and the plane strain condition is assumed. The material properties except for Poisson's ratio, are assumed to vary nonlinearly in the radial direction. Elastic, partially plastic, fully plastic, and residual stress states are investigated. The heat conduction equation for the one-dimensional problem in cylindrical coordinates is used to obtain temperature distribution in the vessel. It is assumed that‏ the inner surface is exposed to an airstream and that the outer surface is exposed to a uniform heat flux. Tresca's yield criterion and its associated flow rule are used to formulate six different plastic regions for a linearly hardening‏ condition. All these stages are studied in detail. It is shown that the thermoelastoplastic stress response of a rotating FGM pressure vessel is affected significantly by the nonhomogeneity of the material and temperature gradient. The results are validated with those of other researchers for appropriate values of the system parameters and excellent agreement is observed.

Stress Calculation and Analysis of a 600MW Supercritical Boiler’s Steam-water Separator

The steam-water separator of a 600MW boiler has been chosen as the research object. By theoretical analysis’s method and finite element analysis, the stress and secure research has been carried out in the steam-water separator as the thick-walled pressure vessel. For its start-up and normal operation of the working process and features and considering the internal pressure load and thermal stress loading conditions, the initiation of separation stress and security analysis have been carried out about the steam-water separator. The primary stress at the continuum of the cylinder structure can be calculated by the formula, and the calculated results are basically in agreement with the simulated graphic results. And the research work provides a theoretical basis for on-line stress monitoring and life assessment.

Large deformation of hyperelastic thick-walled vessels under combined extension-torsion-pressure: analytical solution and FEM

The mechanical behavior of a thick-walled pressure vessel composed of an incompressible isotropic nonlinearly elastic material subjected to the combined pressure and extension-torsion loading is investigated. An analytical solution is proposed for the general form of the free strain energy density, and different models including well-known Neo-Hookean, Mooney-Rivlin, and recently presented free energy contained two exponential terms -exp-exp model- which is strongly stable and compatible with experimental data, are employed. Comparing different constitutive models involves compatible calibration for a specific material. Thus, the uniaxial and equi-biaxial experimental data of silicon-rubber are simultaneously considered to be used in a calibration optimization procedure. Regarding the application of extension-torsion problem, e.g., biological application in papillary muscles, it is required to inspect this loading on a hollow cylinder and considering the internal and external pressure make the problem more realistic to be employed as capillary muscle. After proposing a closed-form solution for this problem, the finite element analysis of the same problem is conducted to verify the proposed analytical solution. Comparing the results of non-dimensional stress, force and moment distribution of analytical and finite element methods illustrate excellent agreement which confirms the accuracy of the presented solution. Some designing factors including the value of applied twist, axial stretch and pressure, and radius ratio are studied. Results demonstrate that the exp-exp model is more conservative in a small amount of twist and axial stretch. However, it yields a higher value for the stress, force, and moment in larger twists and stretches.

Micro/Nanocrack Propagation and Fatigue Strength Analysis of Gun Barrel

Micro/nanocrack propagation and fatigue strength have a very important effect on metals used in a wide variety of applications, such as household electrical appliances, automobile engine, aerospace propeller, and munitions. In this paper, to analyze the rule of gun barrel micro/nanocrack propagation and the mechanism of fatigue failure, we simplified the gun as thick-walled pressure vessel, established the barrel fatigue analysis model under the impact force of bore pressure, calculated the transverse/longitudinal micro/nanocrack propagation caused by initial defect point and the corresponding fatigue strength of barrel, which were validated by finite element analysis. The results show that the fatigue danger zone of the barrel mainly distributes in the fore and aft ends of barrel, which affects the micro/nanocrack propagation rate and barrel life. The propagation rate of a longitudinal micro/nanocrack in the radial direction is faster than that of the axial direction, and that of an initial micro/nanocrack in the transverse is slower than a micro/nanocrack in the longitudinal direction. Therefore, the process control of initial defects in the fatigue danger zone, especially the composite strengthening of material properties to control the longitudinal initial micro/nanocracks and to alleviate the radial propagation rate of barrel micro/nanocracks, is the way to improve the fatigue life of the barrel. The model also provides a basis for analyzing the cause and mechanism of barrel bulging.

Etching Methods for the Microstructural Characterization of a Heat Resistant 2.25Cr-1Mo-0.25V Weld Metal

Abstract Submerged arc welded heat resistant 2.25Cr-1Mo-0.25V weld metals are increasingly used for hydrocrackers and thick-walled pressure vessels in the petrochemical industry. They are exposed to high pressures and temperatures of more than 450 °C. In order to satisfy the high demands with respect to strength and toughness, they are typically subjected to a post-welding heat treatment at temperatures in the range of 691 – 719 °C. During heat treatment, a large number of changes take place in the weld's microstructure. These changes can partly be observed during a light microscope examination. Etching studies described in the literature are mostly concerned with determining phase fractions in multi-phase steels. This work shows how selective etching and precipitation etching allow for contrasting various microstructural features. While the etching solutions Klemm I, aqueous sodium metabisulfite, and picric acid are suitable for revealing the former austenitic grain structure, the dendritic solidification structure of samples in as-welded condition can be contrasted using color etching techniques according to LePera, Klemm I, and Beraha I. For an identification of changes in the shape of dendrites, it is recommended to perform picric acid etching. Color etchings according to Klemm I and LePera are recommended for revealing larger carbides, as they provide a good contrast between the carbides which appear bright, while the surrounding microstructure is colored.

Analyzing the Occurrence Probability of Leaks and Ruptures in NPP Equipment Pipelines and Pressure Vessels Based on Physical and Statistical Modeling of Fracture Processes

A software tool (ST) and methodology implemented in it for probabilistically assessing the reliability of reactor thick-walled pressure vessels are described. The basic principles of ST operation, the list of input data used in the computations, and possible objects for analysis are given. The analysis is based on modeling the incipience and growth of cracks in the material. The techniques used for modeling the initial flaws in material are described that take into account the possibility of missing flaws during non-destructive testing, and for modeling the incipience and growth of cracks during operation of the object under consideration. The technique for assessing the pressure vessel wall strength characteristics is described. To illustrate practical application of the ST, the results from probabilistically assessing the destruction of the PGV-1000 steam generator primary circuit header’s perforated zone are given. Graphic dependences of the leak and rupture occurrence probabilities on the steam generator operation time are presented. The list of possible engineering and scientific problems solved using the developed ST is also given.

Fatigue and fracture behavior of A516 steel used in thick-walled pressure vessels

In this paper, the growth of semi elliptical crack in the walls of thick walled cylindrical pressure vessels has been investigated. Considering the importance of the crack growth problem in cylindrical pressure vessels provides a numerical and experimental 3D model for the growth of fatigue crack and estimating the fatigue life of pressure vessels. Because of available geometric geometric and physical parameters, it can be predicted the problem of the fatigue life of these pressure vessels more precisely in comparison with existing standard tests which are experimental and numerical. A most common specimen of thick walled tanks, steel, is analyzed for conducting experimental tests. The mechanical properties and fatigue behavior of A516 steel have been determined experimentally. For estimating the crack growth and calculation of fatigue life, boundary element method and linear fracture mechanics equations have been used. Finally, the experimental results for fatigue crack growth were compared with numerical method, which yielded acceptable results. The overall results show a good agreement between the experimental data and the numerical results.

Editorial

Editorial