Hydrogen-containing Medium Research Articles

The stress state of a thick-walled shell with allowance for contact with a hydrogen-containing medium

Numerical and experimental methods are used to solve a multidisciplinary problem on determining the stress state of a steel shell of revolution under mechanical loading and thermal effect with allowance for its contact with a hydrogen-containing medium. The study uses a well-developed mathematical tool for solving heat conduction problems in order to solve the problem of hydrogen diffusion into metal. The effective stresses and their invariants are determined by solving the nonlinear boundary value problem of thermoplasticity of a thick-walled shell of revolution in a three-dimensional formulation. The study takes into account the experimentally found effect of changes in the mechanical properties of steel affected by hydrogen. The correctness of the proposed method and the performed calculations is quantitatively estimated by comparison with a well-known problem having an analytical solution. The paper shows that it is possible and necessary to take into account the change in mechanical properties when determining the stress state of steel structures operating in contact with a hydrogen-containing medium.

Modeling of deformation and fracture processes of unevenly heated round plate subjected to high-temperature hydrogen corrosion

The paper considers modeling of deformation and fracture processes of a round plate subjected to high-temperature hydrogen corrosion in a non-uniform temperature field. The influence of hydrogen-containing medium and temperature on the character of creep and fracture processes is taken into account in model building. The derivation of the solving differential equation of a non-uniformly heated circular plate is described.

Research of the influence of the kinetics of a hydrogen-containing medium on the stress-strain state of a cylindrical shell made of titanium alloy

This paper considers a mathematical model of the stress-strain state of a circular cylindrical shell made of titanium alloy VT1-0, operating in an aggressive hydrogen-containing environment. The shell is under the action of an internal evenly distributed pressure. To formulate the problem and carry out calculations, a model with triple nonlinearity is used, formulated within the approach associated with normalized stress spaces. The resulting algorithm for solving the problem of studying the effect of an aggressive medium on titanium alloy shells effectively takes into account the substantially nonlinear change in the parameters of the stress-strain state depending on the time factor. In the study, a system of nonlinear resolving equations for calculating the shell was formulated, results were obtained for the key parameters of the effect of a hydrogen medium on the stress-strain state of a cylindrical shell, taking into account embrittlement.

Modal analysis of a hydrogen-damaged pipe as shell inhomogeneous on thickness

Hydrogen corrosion of main gas and oil pipelines often leads to accidents. It is necessary to assess the life of hydrogen-weakened pipes. An inner layer with deteriorated mechanical characteristics is formed in them under pressure of hydrogen-containing medium. In the paper the calculation of free vibrations of such a tube taking into account the degradation of its material is performed. The tube is modeled as a bilayer cylindrical shell according to the classical theory. Influence of hydrogen-impacted layer is taken into account when calculating stiffnesses and displacement of neutral line of the shell. Three variants of averaging of parameters determining the stiffness of the shell are considered, numerical experiments are carried out and the natural frequencies of the shell are found. Comparison with calculations using the method of finite elements in the ANSYS software made it possible to estimate the degree of applicability of each version of averaging. The method of averaging Young's modulus over the thickness of the shell does not "feel" asymmetry of layers relative to the neutral line. The method of adding a correction for the neutral line radius of the shell works satisfactorily for axisymmetric and beam modes. The next more accurate approximation is to average the shell stiffnesses over its thickness with the reduced radius. This method allows us to obtain satisfactory results in a wide enough frequency range and for the modes related to the deformation of the shell cross section. A method for the principle reconstruction of the parameters characterizing the stiffness of the shell using three experimentally obtained fixed frequencies has been proposed. On the basis of these studies formulas are proposed which allow to reconstruct parameters of weakening of pipe material, as a result of hydrogen corrosion, both in thickness and in time from the frequency characteristics of the pipe.

STUDY OF THE INFLUENCE OF THE KINETICS OF HYDROGEN SATURATION ON THE STRESS-DEFORMED STATE OF A SPHERICAL SHELL MADE FROM TITANIUM ALLOY

In this paper, a mathematical model is considered that allows one to determine the stress-strain state of a spherical shell made of titanium alloy VT1-0, the external load is assumed to be transverse uniformly distributed, acting on the outer surface, the medium is assumed to act on the inner surface of the shell. For this, a nonlinear model was used, presented in normalized stress spaces. Fastening along the contour of the shell is rigid. Nonlinear resolving equations for calculating a spherical shell are obtained. An algorithm for solving the problem of hydrogenation of titanium alloy shells has been developed. A practical solution was made by a two-step method of sequential perturbations of parameters using the MatLab and Maple software packages. To solve the system of the obtained differential equations, the method of finite differences is applied. The calculation of the stress-strain state of the shell is obtained taking into account the diffusion process of an aggressive hydrogen-containing medium, and the obtained solution is compared with the results of the classical nonlinear theory without taking into account the aggressive medium. The results of comparing these solutions demonstrate quantitative differences in the parameters of the shell deformation process, which are explained by a more accurate account of the influence of the type of stress state. This approach has a rather flexible mechanism for considering the initial and induced differential resistance, demonstrates a high accuracy of matching the obtained theoretical results with empirical data on loading a wide range of materials under complex types of stress state.

Фреттинг-изнашивание наводороженного циркониевого сплава Э125, упрочненного диффузионными покрытиями

Protective coatings that improve the corrosion resistance of the E125 zirconium alloy under conditions of the combined effect of a hydrogen-containing medium and friction wear have been investigated. The formation of coatings on the surface of the samples was carried out by thermal diffusion treatment in powder saturating media with halogen activation at temperatures from 400°C to 950°C. The resulting coatings were formed as a result of the processes of oxidation, siliconization, and nitrocarburizing. Wear tests were carried out on a SRV Testsystem multifunctional testing system according to the disk-ball scheme without lubrication. Cathodic hydrogenation of the samples was carried out in an electrolyte solution containing a single normal sulfuric acid solution at room temperature. The cathodic current density was from 20 to 500 mA / cm2. The hydrogen concentration in the samples was determined on a highly sensitive G8 Galileo H gas analyzer by melting the samples in a carrier gas flow. As a result of the study, it was shown that the wear of the coated specimens after siliconizing and nitrocarburizing is three times lower than that of the original uncoated specimen. Oxidation leads to a significant, more than fivefold, increase in the amount of wear, in comparison with the same initial sample. Hydrogenation of the surface of the samples allows not only to reduce the coefficient of friction, but also to reduce the amount of wear in the process of testing samples for fretting wear. This study makes it possible to obtain modified surfaces of zirconium samples that significantly improve the mechanical properties, as well as reduce the level of hydrogenation, and increase the performance of components made of zirconium alloys under conditions of increased friction.

Determination of the limiting state of the muffle shell

Using numerical methods, the problem of determining the limiting state of a metal shell under thermomechanical loading and taking into account contact with an aggressive hydrogen-containing medium is solved. The acting stresses are determined by solving a nonlinear boundary value problem for a shell of revolution. The method is demonstrated on a construction - a muffle designed for high-temperature annealing of electrolytic steel in bell-type furnaces.

Calculation of electric potentials on the surfaces of interaction of deformable metal bodies with hydrogen-containing environment

In most cases the metal structures service under operating conditions results in the fact that these structures or their certain elements are constantly affected not only by mechanical factors (load, residual stresses, etc.), but also by the environment. Elements of pipelines, load-bearing sections of thermal and hydroelectric power stations, metal structures of bridges are all influenced by the environment that fills or surrounds them. Such environment depending on the content of acids and alkalis, a number of hydrogen-containing media can be corrosive. It should be also noted that the influence of such corrosive environment and mechanical factors influence are simultaneous and interrelated resulting very often in brittle or quasi-brittle metal fracture. Therefore, the problem of estimating the basic metal structures engineering parameters (strength, reliability, etc.) that are corroded by the simultaneous action of mechanical force factors, is currently an important problem of industrial operation. The paper presents problems based on the theory of elasticity, electrodynamics, theoretical electrochemistry and equations of mathematical physics. According to the established analytical ratios for the calculations of effective electric potentials and the corresponding numerical experiments, the estimation of electric potentials on the surfaces of interaction of deformable metal bodies with hydrogen-containing medium is carried out.

Influence of the Working Media of Fuel Cells on the Structure and Physicomechanical Characteristics of Ceramics of the ZrO2–Y2O3–NiO System

We study the properties of ZrO2 –Y2O3 –NiO ceramics obtained by using the technologies of sintering of powders and tape casting in the intact state and after one-time reduction both in pure hydrogen and in Ar–5% H2 and N2 –10% H2 –5% CO2 mixtures. It is demonstrated that, by using the technology of tape casting, it is possible to obtain materials for anodes-substrates of solid-oxide fuel cells with smaller grains and a more uniform structure, which improves their strength characteristics. It is shown that, in the hydrogen-containing medium containing carbon dioxide (N2 –10% H2 –5% CO2 ), the strength of 8YSZ–Ni cermet decreases as its electric conductivity increases as compared with the material reduced in the Ar–5% H2 mixture.

Stressed state of a steel construction working in hydrogen containing environment

An approach is proposed to solve the problem of estimating the stress state of a shell structure loaded with a thermomechanical load and in contact with a hydrogen-containing medium. The stress state of the steel housing of the diffusion apparatus for the production of highly pure hydrogen was determined. The object of study is presented in the form of a composite shell of rotation, loaded by internal pressure and operating at elevated temperatures. The purpose of the work is to determine the stress state of the shell at normal and elevated pressure, taking into account changes in the mechanical properties of the combined effect of temperature and hydrogen. In the general case, the task of calculating such a structure under given operating conditions is related. In the phenomenological approach, the relationship between thermal diffusion and mechanical problems is manifested in a change in the parameters of the sample deformation diagram with increasing temperature and hydrogen concentration. The integration of differential equations of a boundary value problem for a shell under pressure is performed by the discrete orthogonalization method S.К. Godunov.

Changing of mechanical characteristics of Co-based amorphous alloy and Fe-based nano-crystalline alloy in the hydrogenous medium under the influence of impulse electric current

Experimentally established the preliminary influence of hydrogen-containing medium (NACE) in cobalt-based amorphous alloys reduces the temperature of the onset of ductility during annealing. The structure of the surface changes forming in the holding of samples in the NACE medium either separate NaCl crystals or branched crystalline structures on the surface. A layer of oxide appears on the nanocrystalline alloy is preventing in heat exchange between the sample and environment. The passing of the impulse electric current j = 108 – 109 A/m2 results increases mechanical stress releases comparing to non-affected samples by the hydrogen-containing medium because of the temperature increase. The amorphous structure proves to be more resistant under simultaneous influence with the impulse electric current to the effect of the hydrogen medium NACE compare to the nanocrystalline one.

Influence of the Modes of Ion Nitriding on the Fretting-Fatigue of 40Kh Steel

We present the results of experimental investigation of the fretting-fatigue with bending for 40Kh steel after ion nitriding in hydrogen-free and hydrogen-containing media. The optimal mode of ion nitriding in hydrogen-free media is determined according to the criterion of maximum service life of 40Kh steel under the conditions of fretting-fatigue. We also establish the effect of hydrogen on steel after nitriding in hydrogen-containing medium.

Structural and morphological characteristics of CuMe2O4 spinels in reductive atmosphere depending on the chemical nature of Mе(III) cations

Mixed copper-containing spinel-type compounds CuCr1Fe1O4, CuCr1Al1O4 and CuFe1Al1O4 were studied by means of XRD and HREM after calcination at 650 °C in the air and treatments in a hydrogen-containing medium at 270–210 °C (H2:He = 5:95; H2:CO:H2O = 50:7:43). The effect of the chemical nature of Mе3+ cation on the structural-morphological characteristics of oxide systems and their transformations in a reducing medium was investigated. It was shown that the nature of Me3+ cation makes it possible to control the structural characteristics, particularly in the reduced state.

Evaluation of Stress-Strain State of Engineering Structures Subject to Damage in Materials under Creep-Based Simulation

This work describes research methods of the complex problem solution to estimate strength and durability of rotation shells with an account of plastic deformations, temperature creep, the hydrogen corrosion and degradation of the material properties in time. The practical calculation of the stressed – strained state accounts of the single-layer conical shell. During the research, the values of the stresses on the shell surface and the destruction time are defined, with the effects of hydrogen-containing medium both taken into account and not. In addition, in the elastic, elastic-plastic the creep deformation statements have been calculated for this shell with ANSYS tools. The results obtained in this work show that the best approach to the modeling of the shell stress - strain state is the use of multiple software products using different material and geometry models and the subsequent joint analysis of the calculation results. Under certain conditions, which are impossible to predict in advance, the shells calculation for strength and durability without the influence of such factors as damage at the creep and at high-temperature hydrogen corrosion may have incorrect results.

Methanation of the carbon supports of ruthenium ammonia synthesis catalysts: A review

The propensity of carbon support for methanation in a hydrogen-containing medium is a problem for active ruthenium ammonia synthesis catalysts, since this leads to the degradation of the support and the sintering of the active component. This review analyses some key works on approaches to methanation inhibition and their results to show that, on the whole, an algorithm for solving the methanation problem has been found, i.e., the graphitization of carbon supports at high temperatures (up to 2000°C) and the introduction of ruthenium promoters, specifically alkali (Cs, K) and alkali-earth (Ba) oxides, whose role is to modify the electron state of ruthenium and block the surface of a carbon support to prevent it from interacting with active hydrogen. The most efficient catalyst not liable to methanation up to 700°C and a hydrogen pressure of 100 atm has been found. The resulting analysis can be useful in selecting and preparing Me/C catalysts in which Me represents metals of the VIII Group and others.

Transformation of organic and inorganic compounds in trifluoroacetic acid

It is established that the effectiveness of fluorine-containing acids in the transformation of organic and inorganic substrates is due to the ability of the acid to perform several functions: to accumulate relatively high concentrations of molecular oxygen, to activate it, and to serve as a hydrogen-containing medium.

Methanation of Carbon Supports of Ruthenium Catalysts for Ammonia Synthesis. Review

Methanation of carbon supports in a hydrogen-containing medium results in degradation of the support and sintering of the active component of ruthenium catalysts for ammonia synthesis. In the review, key publications on approaches to inhibiting methanation are analyzed. It is demonstrated that the solution algorithm is, in general, determined. This is graphitization of the carbon supports at high temperatures (up to 2000 °C) and addition of promoter such as alkali (Cs, K) and alkali-earth (Ba) oxides to modify the ruthenium electron state and to prevent the carbon surface from interaction with active hydrogen. The most effective catalyst that does not suffer from methanation at temperature up to 700 °C and hydrogen pressure of 100 atm is identified. The analysis can be useful to choose and prepare Me/C catalysts, where Me is a 8 group metal.

Effect of hydrogen on the electrical characteristics of structural elements of the Pt/WO x /6H-SiC

The formation conditions of the Pt/WOx/SiC thin-film system on a silicon carbide (6H-SiC) single crystal are optimized. The prepared system possesses stable characteristics and makes it possible to effectively record hydrogen at low concentrations in air at a temperature of ∼350°C, as well as to hold hydrogen in the WOx lattice at room temperature for a long time. The voltage shift of reverse portions of the current–voltage characteristics at a hydrogen concentration of ∼0.2% reach 6.5 V at a current of 0.4 µA because of large series resistance, which is defined by space-charge regions in WOx and SiC. Structural-phase investigations of the oxide layer are performed under various effect modes of the hydrogen-containing medium on the Pt/WOx/SiC system. A correlation in the variations of its electrical properties (ability to accumulate charge and vary the resistivity) and structural state of the oxide layer is revealed. An explanation for the variation in the current transport through the Pt/WOx/SiC and its contact regions (barrier layers) under the effect of hydrogen is proposed.

Influence of Hydrogen on the Initiation of Creep-Fatigue Cracks in Plates Near Stress Concentrators

We formulate a mathematical model for the determination of the effect of hydrogen on the period of initiation of creep-fatigue macrocrack in the vicinity of a stress concentrator in a plate. By using this model, we find the period of initiation of a macrocrack for a strip with two side notches under cyclic loads, high temperatures, and the action of hydrogen-containing medium. It is shown that hydrogen increases the rate of crack initiation in steel plates.

On the features of hydrogen detection by a semiconductor structure grown on a 6H-SiC substrate by the combined method of platinum ion implantation and deposition

The results of a comparative study of the electrical properties of gas-sensitive semiconductor structures grown by the pulsed laser deposition of platinum, platinum ion implantation, and a combined method of platinum implantation and deposition onto an n-6H-SiC substrate are presented. Double-layer structures show a stronger response to hydrogen gas with a more pronounced diode behavior of the currentvoltage characteristics at high temperatures of ∼500°C than single-layer ion-implanted structures. Furthermore, double-layer structures exhibit higher reproducibility of the current-voltage characteristic parameters during thermal cycling in a hydrogen-containing medium than ordinary thin-film structures on SiC substrates. The chemical state of ion-implanted platinum and the structure of thin-film layers after long-term testing are studied under harsh conditions. Possible mechanisms of the effect of platinum on the current flow in the ion-implanted layer and its dependence on the composition of the surrounding gaseous medium are considered.