Tube Wall Thickness Research Articles

Thermal and structural evaluation of composite solar receiver tubes for Gen3 concentrated solar power systems

A composite solar receiver tube containing thermally conductive and high-temperature protective layers is proposed to improve its thermal and structural performances. Two combinations of materials, which are Inconel 718/nickel and 316 stainless steel/GRCop-84, are selected based on the similarity in their coefficients of thermal expansion. The solar-to-thermal energy conversion in conjunction with the fluid flow and heat transfer of supercritical carbon dioxide inside the solar tubes is analyzed by computational fluid dynamics. The thermal stress due to different solar tube designs is solved by finite element analysis based on the derived temperature field and pressure distribution. The results show that both maximum thermal stress and maximum temperature in solar tubes could be reduced by the composite design. The maximum thermal stress decreases by 4.1 MPa and 24.0 MPa respectively in Inconel 718/nickel and 316 stainless steel/GRCop-84 composite solar tubes. The performance improvement becomes more significant as the thickness of tube wall and intensity of solar radiation increase. Due to the surface temperature reduction, the entire thermal efficiency of solar tubes could increase by up to 1.3% and the creep issue of high-temperature protective materials can be alleviated.

A metastable jet model for leaks in steam generator tubes

The modeling and prediction of flow rates through leaks in steam generator tubes requires an understanding of the rapid decompression of a subcooled fluid flowing through a small and short flow path. The thin walls of steam generator tubes may lead to the phenomenon that the coolant water cannot evaporate within the leak flow path, which is a key difference compared to leak flow in thick-walled components. Experimental investigations in the literature were investigated and additional laboratory tests on dedicated specimens were performed, including mass flow measurements and optical measurements, which study the flow pattern at the outlet of the leak. These experiments cover a ratio of flow length (wall thickness) to hydraulic diameter L/dh range from 0.4 to 12. Based on the findings, a metastable jet model is proposed, which is based on the formation of a jet of metastable liquid water. The model parameters are fitted with the experiments. The model is compared with alternative approaches, which demonstrates that it is suitable to approximate the mass flow of leaks in steam generator tubes with a sufficiently large leak width or cross section. Due to the small absolute wall thickness of steam generator tubes only very narrow flaws are found to be successfully modeled with ordinary two-phase flow models.

Analysis of 3D composite preform contour locking parameters based on vibration characteristics

To ensure the smooth insertion of the side rod/fiber bundle during the three-dimensional woven preform contour locking process, the influence of the diameter, speed, and other parameters on the free end vibration displacement response of the side rod and the fiber-carrying needle is analyzed. By calculating the kinetic energy and potential energy of the two separately, the dynamic equations of the side rod and the fiber-carrying needle are established based on Hamilton's principle and discretized. The state equations are solved using the Runge–Kutta method, and the free end vibration displacement responses of the side rod and the fiber-carrying needle for different parameters are obtained. The results show that the equilibrium position and the maximum amplitude of the free end of the side rod and the fiber-carrying needle decrease with the increase of the section diameter and the decrease of the axial speed. And the circular tube wall thickness has less impact on the free end vibration displacement of the fiber-carrying needle. The overall analysis shows that the fiber-carrying needle vibration response is smaller than that of the side rod under the same parameters.

Performance of steel-reinforced square CFST stub columns loaded in axial compression: Experiments

A steel-reinforced concrete-filled steel tubular column is a type of concrete-filled steel tubular (CFST) column reinforced by embedded steel profile. The inner carbon steel tube reinforced square concrete-filled stainless steel tubular column (SR-CFSST) has not been systematically investigated. In this project, stub composite columns with various experimental parameters were tested as loaded in axial monotonic compression, considering the effects of the concrete strength, column size and wall thickness of the steel tubes. The mechanical behaviour of stub columns was analysed in terms of ultimate load-bearing capacity, strength index, ductility, and failure modes. The calculation methods in five codes, including GB 50936, DBJ/T 13–51, Eurocode 4, ANSI/AISC 360 and AIJ, which are widely used for ordinary CFST stub columns, were compared. Finally, a simplified calculation method for the SR-CFSST stub columns was proposed for predicting the ultimate bearing capacity. The predicted results agree well with test results and the simplified calculation method can be used to design SR-CFSST stub columns loaded monotonically in axial compression.

Investigation on the influence of weld position on the deformation behavior of welded tube during free bending process

The plastic deformation behavior of welded tube is affected by the non-uniform distribution of the mechanical properties of welded tube during the free bending process. To explore the influence of weld position on the forming quality and axis dimensional accuracy of welded tube, the free bending experiment and numerical simulation of welded tube were conducted in this paper. First, the principle of free bending was theoretically deduced and the stress distribution of bent tube was analyzed. Then, the hardness test and uniaxial tensile test were conducted to obtain the mechanical properties of weld zone and parent zone of welded tube. The material strength in the weld zone of welded tube is significantly higher than that in the parent zone. Finally, the free bending experiment and numerical simulation with different weld positions were carried out, and the influence of weld position on the bending radius, cross-sectional distortion, and wall thickness of bent tube was discussed. All these findings advance the insight into the free bending deformation behavior of welded tube and help to improve the forming quality of welded tubes and facilitate the application of free bending technology in welded tube.

Parametric study on the crushing performance of a polyurethane foam-filled CFRP/Al composite sandwich structure

Composite structures have drawn growing attention for their outstanding characteristics benefiting from the combination of multi materials. This paper aims to investigate the crushing performance of a hybrid system involving an outer thin-walled tube made of carbon fibre-reinforced plastic (CFRP), a medial polyurethane (PU) foam and an inner thin-walled tube made of aluminium alloy (Al). The elastoplastic model of Al, the continuous damage model of CFRP and the compressible foam model of PU were established with assistance of universal material tests. The finite element model of the composite structure, namely CFRP-PU-Al, was validated by the experimental study. Based upon the reliable numerical modelling, the parametric study was carried out for exploring the effects of the wall thickness, diameter and ply orientation of the outer CFRP tube, namely CFRP-O, on the crushing behaviours of the composite structure. It was found that increasing the diameter or wall thickness of CFRP-O was helpful to increase the mean crushing force and energy absorption of CFRP-PU-Al, however, the overall specific energy absorption of the composite sandwich structure was limited by the characteristics of constitutive materials. Compared with the diameter, the wall thickness had a higher impact on the energy absorption characteristics, and increasing the diameter may decrease the specific energy absorption due to the increase of the overall structural mass. In terms of the ply orientation, the composite structure with stacking sequence of [0°/45°]3 possessed higher mean crushing force and energy absorption than the structure with stacking sequence of [0°/90°]3 under axial compression in this study.

Experimental study on cryogenic chilldown performance through a thick-wall tube

Cryogenic pipeline chilldown is an inevitable process in cryogenic liquid transfer operation, but the researches on chilldown performance through a thick-wall tube are still insufficient. In the present study, a high-pressure cryogenic chilldown test platform is established to study the tube wall thickness influence on chilldown characteristics. Two stainless steel tubes, with 2 mm thickness wall and 5 mm thickness wall, respectively, are manufactured and tested under different inlet Reynolds numbers (Re) conditions. The temperature decrease curves and heat transfer variations are analyzed and compared. The test results show that a thicker wall tube requires an apparently longer chilldown time and a larger liquid consumption to reach the chilldown purpose. In the present experiments, the mass ratio of the two tubes is about 3.0, but the time cost ratio varies within 3.5–6.0 and the liquid consumption ratio is about 4.5. This performance indicates that in a thicker-wall pipe chilldown event, a lower efficient utilization of liquid cold energy could be speculated. Moreover, increasing inlet Re produces temperature rises both at critical heat flux (CHF) and Leidenfrost point (LFP). For the 2 mm wall tube cases, increasing inlet Re from Re = 5500 to Re = 43000 gives rise to a 39 K temperature rise in LFP and a 32 K temperature rise in CHF. Under the similar inlet Re variation, the temperature rises of LFP and CHF in the 5 mm wall tube cases are 28 K and 46 K, respectively. Comparatively, the 5 mm wall tube experiences a shorter transition boiling-dominated range when increasing the inlet Re. In addition, in the present test cases, the chilldown thermal efficiency varies with 8%–23%, and the 5 mm wall tube cases experience lower thermal efficiency than the 2 mm wall tube cases. To realize a high-efficient chilldown purpose, the approaches of increasing chilldown thermal efficiency should be significantly concerned in the chilldown scheme design, especially when a thick wall tube situation is encountered.

Research on the axial elongation and springback law of thick-walled tubes in cold bending forming

Research on the axial elongation and springback law of thick-walled tubes in cold bending forming

Crystalline phase of TiO2 nanotube arrays on Ti–35Nb–4Zr alloy: Surface roughness, electrochemical behavior and cellular response

An investigation was made into the electrochemical, structural and biological properties of self-organized amorphous and anatase/rutile titanium dioxide (TiO 2 ) nanotubes deposited on Ti–35Nb–4Zr alloy through anodization-induced surface modification. The surface of as-anodized and heat-treated TiO 2 nanotubes was analyzed by field emission scanning electron microscopy (FE-SEM), revealing morphological parameters such as tube diameter, wall thickness and cross-sectional length. Glancing angle X-ray diffraction (GAXRD) was employed to identify the structural phases of titanium dioxide, while atomic force microscopy (AFM) was used to measure surface roughness associated with cell interaction properties. The electrochemical stability of TiO 2 was examined by electrochemical impedance spectroscopy (EIS) and the results obtained were correlated with the microstructural characterization. The in vitro bioactivity of as-anodized and crystallized TiO 2 nanotubes was also analyzed as a function of the presence of different TiO 2 polymorphic phases. The results indicated that anatase TiO 2 showed higher surface corrosion resistance and greater cell viability than amorphous TiO 2 , confirming that TiO 2 nanotube crystallization plays an important role in the material's electrochemical behavior and biocompatibility.

Pilot scale fabrication of lanthanum tungstate supports for H2 separation membranes

This paper reports the fabrication of asymmetric tubular geometry lanthanum tungstate-based membranes for high temperature H2 separation applications. As starting materials, powders with the compositions La28-yW4+yO54+δ (y = 0.848), La28-yW4+yO54+δ (y = 1) and La28-y(W1-xMox)4+yO54+δ (x = 0.3, y = 1) were synthesized by solid state reaction method. Porous, thick-wall tubes made of lanthanum tungstate-based powders with high gas permeability (7–8 x10-15 m2 at 2 bar overpressure) and homogeneous porous microstructure were made by combining a cost-effective solid-state synthesis and thermoplastic extrusion method. Deposition of lanthanum tungstate-based dense thin film (∼20 μm) was achieved on top of porous supports through dip coating technique. The influence of conformation routes, thermal debindering and sintering processes were investigated in detail to achieve defect free H2 transport membranes. Asymmetric geometry membranes with ∼20 μm dense layer thickness supported on porous tubular (∼ 7.5 mm diameter and ∼0.8 mm thick) supports.As a result, a procedure for proton conducting ceramics manufacture was established which can be deployed to fabricate high temperature catalytic membrane reactors for synthetic fuel from gas-to-liquid (GTL) processes.

Research on Influence Factors of Bearing Capacity of Concrete-Filled Steel Tubular Arch for Traffic Tunnel

When a traffic tunnel passes through special strata such as soft rock with high geo-stress, expansive rock, and fault fracture zones, the traditional supporting structure is often destroyed due to complicated loads, which threatens the construction and operation safety of tunnel engineering. Concrete-filled steel tubular (CFST) structure gives full play to the respective advantages of steel and concrete and has better bearing capacity and economic benefits than traditional support structure, which has achieved good results in some underground engineering applications. In order to promote the application of CFST in the construction of traffic tunnels with complex geological conditions and improve the bearing capacity of the initial supporting structure of tunnels, the influencing factors of the bearing capacity of CFST arch were studied by numerical simulation. The main achievements are as follows: (1) The load-displacement curves of CFST members under different material parameters are basically consistent. CFST members have significant restrictions on displacement in the elastic stage and have high ultimate bearing capacity. Although the bearing capacity decreases obviously after reaching the peak, it shows good extension performance. (2) The height of the steel tube section, the thickness of the steel tube wall and the grade of the core concrete have an approximately linear positive correlation with the bearing capacity of CFST arch, but the influence of these three factors on the bearing capacity of CFST arch decreases in turn, and when the grade of core concrete increases above C50, it has no significant effect on the bearing capacity of members.

A modified rule for estimating notch root strains in ball defects existing in coiled tubing

Coiled tubing life is predominantly limited by fatigue as it undergoes cyclic bending strains well into the plastic regime leading to cyclic ratchetting due to plastic strain accumulation. Furthermore, small defects occurring in the oil field environment are capable of reducing coiled tubing fatigue life significantly. Small defects are macroscopic flaws that have small dimensions relative to the tubing wall thickness. Very shallow flaws at depths of only a few percent of the wall thickness can have a substantial, detrimental influence on fatigue life. Accordingly, the influence of surface ball defects on the magnitude of the fluctuating strains at the root of these defects was the subject of this investigation. Accurate cyclic strain magnitude predictions are essential to ultimately quantify the fatigue life of coiled tubing. The effects of defect radius and depth were both studied, and the strains at the notch root were evaluated for coiled tubing having a diameter of 2.375 in. and a wall thickness of 0.156 in..A matrix of ball defects with various depths and radii were examined. The defects were introduced at the surface of a model having the same thickness as the actual coiled tubing. The FEA results provided detailed information about the magnitude of cyclic strains at the root of a defect in coiled tubing that were previously unavailable. The notch root strain results were used to bring about a modified Neuber’s rule since conventional notch strain analysis approaches did not lead to accurate notch root strain range predictions. A new modified rule was therefore proposed and validated based on a detailed statistical analysis. This modified rule led to a substantial reduction in the percentage difference between the numerical notch root strain range and the estimated analytical one to within 8%.

STUDY OF ALUMINUM TUBE COLD NOSING PROCESS INTO CONICAL AND HEMISPHERICAL DIES

Theoretical analysis and finite element method were used to simulate the cold nosing process of commercial purity Aluminum tubes into conical and hemispherical dies. The influences of process parameters, namely initial tube wall thickness, conical semi-die angle and coefficient of friction were investigated. The results of the nosing process were obtained in terms of load-displacement curves, thickness distribution of deformed parts, the nosing ratios and strain distributions. According to these finding, the final shape and defects of the product can also be predicted. Experimental work was carried out to verify the simulation results. A new developed setup design was proposed to improve the product quality. Two adjacent punches were used: one with a front plunger and the other was an outer sleeve to constrain the tube. It could be observed that the load increase with increasing the tube wall thickness, semi die angle and coefficient of friction. The nosing ratio increases as wall thickness increases. Comparison between analytical and FE predictions to the experimental results showed good agreement.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ РЕШЕНИЙЗАДАЧ О НЕОСЕСИММЕТРИЧНОЙ ТОЛСТОСТЕННОЙ ТРУБЕ И ТРУБЕ С ЭЛЛИПТИЧЕСКИМ ВНЕШНИМ КОНТУРОМ ПРИ УСТАНОВИВШЕЙСЯ ПОЛЗУЧЕСТИ

This article presents a comparative analysis of the solutions of nonlinear boundary value problems of steady-state creep for a nonaxisymmetric thick-walled tube and for a tube with an elliptical outer contour in the first approximation by the small parameter method. Two problems for the first approximation of the small parameter method are formulated in the article and the results of their solution are considered on the example of two materials with different material nonlinearity characteristics. The differences and similarities in the solution results are shown, which are given in the table and presented in the form of graphs for comparative analysis.

Creep and Long-Term Strength of a Laminated Thick-Walled Tube of Nonlinear Viscoelastic Materials Loaded by External and Internal Pressures

Creep and Long-Term Strength of a Laminated Thick-Walled Tube of Nonlinear Viscoelastic Materials Loaded by External and Internal Pressures

Дослідження причин аварійного руйнування пароперегрівних труб в котельному обладнані

Results of comprehensive studies of samples of prematurely destroyed 57×4 mm steam superheaer tubes of STBA 22 steel used in a boiler unit of Singburi Sugar Co, Ltd factory (Thailand) are presented. The tubes were manufactured at Interpipe Niko Tube Ltd. (Ukraine) according to JIS G 3462 Standard (Japan). They were destroyed in a short (~240 hrs) term of operation. The cause of premature destruction of tubes of the above steel grade and size assortment in the boiler unit has been established. Based on present-day investigation methods (metallography, X-ray diffraction, etc.), it was found that the tubes were operated with violation of fuel combustion conditions and heat-carrying agent circulation. Characteristic features of operation of damaged tubes include high thermal stresses from the side of the fire-chamber and limitation (or absence) of circulation of the heat-carrying agent (blockage in bends, drum heads, etc.). During operation, the tubes were also exposed to significant thermal vibration stresses (unstable combustion conditions). Prolonged overheating occurred at temperatures above 1000 °C because of violation of circulation of heat-carrying agent and unstable combustion mode. High thermal stresses at almost complete absence of a heat-carrying agent, uneven distribution of growing heat flows caused by violation of the combustion mode in the fire-chamber contributed to accelerated degradation of structure and thermal destruction of the tube metal. In a short term of operation (~240 hours), there was a significant change in the tube size (accelerated high-temperature creep) and complete recrystallization of metal structure throughout the entire wall thickness of the damaged tubes. It has been established that the accelerated degradation of metal microstructure in the destroyed tubes was associated with both overheating of the tube wall and the as-delivered metal structure non-recommended for operation at high temperatures and pressures. It was shown that it is necessary to adjust the heat treatment conditions for these tubes at Interpipe Niko Tube Ltd. The study results have made it possible to develop recommendations for eliminating violations of operating conditions and establishing control of actual heat flows in the most thermally loaded sections of the Singburi Sugar Co. Ltd factory’s steam boiler superheater. Taking into account peculiarities of the boiler equipment and its operating conditions, it was also recommended to use a more heat-resistant and refractory steel instead of the currently used material for manufacture of the steam superheater tubes. Keywords: boiler tube, steam superheater, damage, thermal destruction, structure degradation, combustion conditions, heat carrier circulation, overheating.

Plastic behavior of slender circular metal foam-filled tubes under transverse loading

In this paper, the large deflection of the slender circular metal foam-filled tube (FFT) under transverse loading is studied theoretically and numerically. The yield criterion of the circular foam-filled tube is proposed. Using the yield criterion, the analytical solution for the plastic behavior of slender circular metal foam-filled tube under transverse loading is obtained considering the interaction between bending and stretching and foam strength. Large deflection of the circular metal foam-filled tube is numerically calculated. The analytical model captures numerical results. Influences of tube-wall thickness, punch width, foam strength, loading position and the radius of filled foam on the load-carrying capacity and energy absorption (EA) of foam-filled tubes are discussed in detail. The results show the load-carrying capacity and energy absorption of the foam-filled tubes increase with the increase of tube-wall thickness, foam strength, punch width and the radius of filled foam.

A bipotential-based macroscopic fatigue criterion of porous materials with a pressure-sensitive and non-associated plastic solid matrix and comparison with numerical simulation

The formulation of macroscopic strength criteria under cyclic loading of ductile porous media containing a pressure sensitive and non-associated plastic matrix is still a pending issue. In this paper, a new approach is developed by using the bipotential theory. In this framework, non Generalized Standard Materials (GSM) are transformed into a class of Implicit Standard Materials (ISM), allowing the recovery of the flow rule normality in a weak form of an implicit relation. The classical shakedown theorems are extended to the homogenization of ISM. The solution of a thick wall tube under uniform pressure is established with the assumption of vanishing plastic strain increment over a single stabilized cycle. A macroscopic fatigue criterion is further delivered for the first time for porous materials with a non-associated Drucker–Prager type solid matrix. It is now possible to separate the effects of frictional and dilatancy angles. It is found that the shakedown limit load under hydrostatic loading is only related to the friction angle, but not the dilatancy one. The safety domain defined by the established criterion under general cyclic loads is comparatively reduced with the decrease of dilatancy angle. The new criterion is fully assessed by comparing the theoretical predictions to FEM-based step-by-step simulations for different values of porosity and frictional and dilatancy angles. Finally, the new criterion can also be applied to associated solid matrix as a special case and it significantly improves the accuracy of predictions provided by previous works based on the Melan’s static theorem.

Computational bifurcation analysis for hyperelastic residually stressed tubes under combined inflation and extension and aneurysms in arterial tissue

In this investigation, the mechanical modelling of a hyperelastic residually stressed thick-walled circular cylindrical tube under inflation and extension is performed from a numerical standpoint. The constitutive relation is derived for residually stressed solids using an invariant-based free energy approach. A three-dimensional residual stress field is introduced in the argument of the free-energy function. This formulation is incorporated into a numerical procedure using the Finite Element Method (FEM), with the use of a nonlinear solution scheme via the modified Riks method in order to capture bifurcation and post-bifurcation of the tube. The FE implementation of the proposed formulation is carried out in the general purpose code ABAQUS by means of user-defined capabilities. A comprehensive analysis of the structural performance of the tube is conducted with special focus on the effect of the residual stresses on the bifurcation behaviour. Results are analysed mainly in the context of aneurysms formation and propagation in arterial wall tissues, although it has other applications such as in the context of venous tortuosity. Bulging and bending modes are obtained, and post-bifurcation is also captured. Results suggest that the onset and location of the bulge along the axis of the tube depend mainly on the axial stretch and on the residual stress field. Computations also show that for sufficiently large values of axial stretch the onset of bifurcation is bulging while for small values of axial stretch the onset of bifurcation is bending. Post-bifurcation behaviour of this latter case gives rise to bulges on one side of the tube, which is an irregular shape that appears in the advancement of abdominal aortic aneurysms (AAA). • Bifurcation and postbifurcation of an inflated and extended residually-stressed circular cylindrical tube are analysed. • Bending and bulging motion are captured depending on the axial stretch of the structure. • The onset of bifurcation and the motion of the bifurcation are exploited in the context of aneurysm formation and propagation. • The combination of bending and bulging is consistent with the development of abdominal aortic aneurysms (AAA).

Influence of the structural state and crystallographic texture of Zr-2.5% Nb alloy samples on the anisotropy of their thermal expansion

• The thermal linear expansion coefficient of Zr-2.5%Nb channel tubes has been studied. • Crystallographic texture before and after phase transformation has been investigated. • The influence of initial crystallographic texture and structural-phase state on dimension changes after dilatometric measurements has been established. • The physical processes occurring in Zr-alloys during heating and cooling at 20-1200° C temperature interval has been explained. Zirconium remains the main structural material for thermal reactors due to the small capture cross section of thermal neutrons. In the period of stricter safety requirements for reactors with a simultaneous increase in operating parameters, predicting the behavior of the material in emergency situations has gained greater urgency. In this work, we measured the temperature dependence of the thermal expansion of samples cut from thick-walled tubes made of Zr-2.5% Nb alloy that were deformed and annealed in different modes. The analysis of the physical processes responsible for the shaping of the material is carried out. It was found that the anisotropic change in the linear dimensions of cubic samples both during heating and cooling is due to a change in the zirconium content in the β-phase, phase transformations α + β-Zr → α + β-Nb → β → α + β-Zr, as well as the preferred orientation of the grains of the α-phase, characterized by high anisotropy of linear expansion. It is shown that the expansion of the investigated samples upon heating in the α -phase is determined exclusively by the integral texture parameters of Kearns, and the coefficients of thermal linear expansion (TLEC) in different directions vary over a wide range from 3⋅10 -6 to 12⋅10 -6 K −1 . During cooling at the stage of the reverse phase transformation of the β-phase into α, an increase in the size of the cubic samples in the tangential direction up to 2.3 % and a decrease in the radial direction to 1.3 % are noted, which is associated with the orientation of the α-phase grains formed during cooling in the β -matrix and anisotropy of the TLEC of the α -grains. It is shown that the orientation of the α-phase grains in the reverse β → α transformation is determined not only by the orientation of the basal axes in the initial material, but also by the spatial distribution of the prismatic axes relative to the external directions in the tube. Significant size fluctuations in different directions of the samples obtained using the technology of manufacturing channel tubes for CANDU reactors should lead to the development of significant macrostresses both during heating and cooling of the tube. The structural state of the samples deformed or annealed at 400–530 °C does not significantly affect the temperature dependence of the TLEC, but is manifested only in some of its features. In this case, completely recrystallized samples, i.e., with a recrystallization texture, in which the < 11 2 - 0 > directions are oriented along the tube axis, are characterized by a significantly lower variation in dimensions in different directions in the temperature range 20–1200 °C.