Bimetallic Tubes Research Articles

Development and Theoretical Justification of an Innovative Process for the Production of Seamless Bilayer Bimetallic Tubes 530, 550, 610, 630, 720, and 820 mm in Diameter with Various Combinations of Steels and Wall Thicknesses

Development and Theoretical Justification of an Innovative Process for the Production of Seamless Bilayer Bimetallic Tubes 530, 550, 610, 630, 720, and 820 mm in Diameter with Various Combinations of Steels and Wall Thicknesses

Behavior of circular bimetallic tube-confined concrete stubs under eccentric compression

This paper aims to investigate the behavior of eccentrically loaded circular stainless steel-carbon steel bimetallic tube-confined concrete stub columns. 15 stub columns including bimetallic tube-confined concrete with and without bars, and concrete filled bimetallic tube were prepared and tested. The results show that the difference in the failure patterns results from the different tube steel ratio of the specimens, even the total steel ratio of the specimens is similar. The ductility of the bimetallic tube-confined concrete is better than that of the concrete filled bimetallic tube with the same parameters. Under the condition of eccentric loading, the performance of the bimetallic tube-confined concrete stub column is lower than those of the concrete filled bimetallic tube with the same parameters. The stainless steel-carbon steel bimetallic tube has a good confinement effect on the core concrete. The strengthening performance of stainless steel can effectively improve the bearing capacity of the stub in the later stage, making up for the bearing capacity reduction of the specimen caused by concrete crash. The results calculated by the traditional code formula for steel tube-confined concrete are more conservative than the test results. The difference between the test results and the calculated results increases with the decrease of diameter-thickness ratio.

Finite Element Simulation of the Parallel Tubular Channel Angular Pressing Process for Al–Cu Bimetallic Tube with Experimental Verification

Finite Element Simulation of the Parallel Tubular Channel Angular Pressing Process for Al–Cu Bimetallic Tube with Experimental Verification

A novel severe plastic deformation method for manufacturing Al/Mg bimetallic tube

A new severe plastic deformation for manufacturing Al/Mg bimetallic tube called the TES (tube extrusion shearing) process, which combines direct extrusion with two-step shearing, has been developed to manufacture Al/Mg bimetallic tube. Load evolution with stroke at different temperatures has been simulated by establishing three-dimensional finite element simulation of the TES process of Al/Mg bimetallic tubes. To explore the deformation mechanisms of the Al/Mg bimetallic tube during the TES process, the microstructures and phase compositions and microhardnesses of the bonded layer have been observed and analyzed. A higher extrusion temperature would decrease the extrusion loads. Defects of bonding layer appear less if the extrusion temperature is higher, and the bonding layer of the bi-metal tube has better quality. Three eutectic compounds, Mg2Al3, MgAl, and Mg17Al12, can be formed in the interface transition zone. The average hardness of the bonding layer is very high. The results indicate that the TES process can produce large plastic deformation and manufacture Al/Mg bimetallic tube and improve the bonding layer.

Performance of concrete-filled bimetallic tube short columns under eccentric compression: Experimental investigation

Concrete-filled bimetallic tubes (CFBTs) combine the mechanical advantages of concrete-filled steel tubes (CFSTs) and the functional features of bimetallic tubes. This paper presents the test results of fifteen circular short column specimens under eccentric compression. The bimetallic tube adopted in the current research was manufactured by combining an inner carbon steel tube and a cladding stainless steel layer, which can improve the corrosion resistance of the conventional carbon steel tube with economic efficiency. A total of fifteen specimens, including seven hollow bimetallic tubes and eight CFBT short columns, were fabricated and tested by considering the nominal load eccentricity (en/D = 0, 0.26, 0.53, or 0.79) as the main testing parameter. The test results indicated that all the CFBT short columns behaved in an improved ductile manner compared to the hollow bimetallic tubes, and the corresponding load-carrying capacity was significantly enhanced. The development of strain in the two tube layers demonstrated the inner and outer steel tube layers worked well together. The influences of load eccentricity on the mechanical behavior of CFBT short columns were discussed. Finally, an improved model was suggested for calculating the N/Nu-M/Mu interaction relationships of CFBT short columns subjected to eccentric compression.

Performance of circular bimetallic tube confined concrete slender columns under eccentric compression

This paper aims to investigate the performance of thin-walled circular stainless steel-carbon steel bimetallic tube confined concrete slender columns under eccentric compression. 14 slender columns including bimetallic tube confined concrete (BTCC) with and without rebar, and concrete-filled bimetallic tube (CFBT) were tested. A parametric analysis is conducted based on the validated finite-element model. The results show that the two steel tube layers worked well together and the thin-walled BTCC specimens behaved in a ductile manner. Under the same parameters, the decrease of the diameter–thickness ratio of bimetallic tube improves the bearing capacity and rigidity of the BTCC slender column, but reduces its ductility in the descending stage. The confinement effect of bimetallic tube on the concrete in BTCC columns is stronger than that in CFBT columns. When the yield strength of stainless steel and carbon steel is similar, the stainless steel–total steel ratio has little effect on the capacity of the column. Provided meeting the requirements of corrosion resistance, relatively thinner stainless steel tube is preferred to reduce the cost. The comparison between the simulation and the calculation results shows that the current design method can predict the bearing capacity of the BTCC slender column with large diameter–thickness ratio.

Towards Manufacturing of Ultrafine-Laminated Structures in Metallic Tubes by Accumulative Extrusion Bonding

A severe plastic deformation process, termed accumulative extrusion bonding (AEB), is conceived to steady-state bond metals in the form of multilayered tubes. It is shown that AEB can facilitate bonding of metals in their solid-state, like the process of accumulative roll bonding (ARB). The AEB steps involve iterative extrusion, cutting, expanding, restacking, and annealing. As the process is iterated, the laminated structure layer thicknesses decrease within the tube wall, while the tube wall thickness and outer diameter remain constant. Multilayered bimetallic tubes with approximately 2 mm wall thickness and 25.25 mm outer diameter of copper-aluminum are produced at 52% radial strain per extrusion pass to contain eight layers. Furthermore, tubes of copper-copper are produced at 52% and 68% strain to contain two layers. The amount of bonding at the metal-to-metal interfaces and grain structure are measured using optical microscopy. After detailed examination, only the copper-copper bimetal deformed to 68% strain is found bonded. The yield strength of the copper-copper tube extruded at 68% improves from 83 MPa to 481 MPa; a 480% increase. Surface preparation, as described by the thin film theory, and the amount of deformation imposed per extrusion pass are identified and discussed as key contributors to enact successful metal-to-metal bonding at the interface. Unlike in ARB, bonding in AEB does not occur at ~50% strain revealing the significant role of more complex geometry of tubes relative to sheets in solid-state bonding.

Тепловая нагрузка биметаллической оребренной трубки

This study is devoted to the problem of numerical modeling of the conjugate heat transfer in a closed-type power installation. The working elements of that are ribbed bimetallic tubes using the openFoam toolbox. The heat transfer process modeling in bimetallic tubes is associated with solving the problem of determining the value of the contact thermal resistance at the metal / metal interface. Considered design of a bimetallic tube involves crimping copper washers on the surface of an aluminum cylindrical tube. Hence, the contact surface of the tube is not isotropic in its properties. A mathematical model of conjugate heat transfer for air / bimetal / coolant medium is proposed. The features of the organization of thermophysical processes at the metal contact interface and at the metal / air and metal / coolant medium are shown. A qualitative comparison of the obtained results with the famous experimental data is carried out. Generalized temperature profiles in the rib longitudinal section are obtained by mathematical modeling. The given distributions of temperature and heat flux make it possible to estimate the contribution of each individual rib to the investigated heat removal process from the air environment. The efficiency of the considered technology of manufacturing a bimetallic finned tube is shown.

Тепловая нагрузка биметаллической оребренной трубки

This study is devoted to the problem of numerical modeling of the conjugate heat transfer in a closed-type power installation. The working elements of that are ribbed bimetallic tubes using the openFoam toolbox. The heat transfer process modeling in bimetallic tubes is associated with solving the problem of determining the value of the contact thermal resistance at the metal / metal interface. Considered design of a bimetallic tube involves crimping copper washers on the surface of an aluminum cylindrical tube. Hence, the contact surface of the tube is not isotropic in its properties. A mathematical model of conjugate heat transfer for air / bimetal / coolant medium is proposed. The features of the organization of thermophysical processes at the metal contact interface and at the metal / air and metal / coolant medium are shown. A qualitative comparison of the obtained results with the famous experimental data is carried out. Generalized temperature profiles in the rib longitudinal section are obtained by mathematical modeling. The given distributions of temperature and heat flux make it possible to estimate the contribution of each individual rib to the investigated heat removal process from the air environment. The efficiency of the considered technology of manufacturing a bimetallic finned tube is shown.

Research Treatment Studies for Cleanable Waste Water for Cleaning Pipes


 
 
 Currently, many methods of treating waste water are known using various lubricating coolant compositions, but there is no universal treatment method. The most suitable ways of reducing the harmful impact of waste water in the metallurgical industry on the water environment are 1) the local treatment of waste water of various compositions, 2) the removal or reduction of the total amount of waste treatment liquid emissions as a result of their regeneration, and 3) reuse of treated waste water in closed water circulation systems and technical water supply to enterprises. During production of bimetallic finned tubes by cold deformation method, alkaline cleaning solutions are used to clean the surface from lubricating-cooling liquid. As a result, there is a need to dispose of spent liquids. The spent detergent solution is a three-phase emulsion. The upper layer is oil-oil products, medium liquid with increased PH index, and aluminates precipitate. A spent emulsion, i.e. an end-of-life emulsion that has lost its functional and operational properties, needs to be decomposed and disposed of.
 Keywords: finned bimetallic tube, air cooler, lubricating coolant, oil – emulsion
 
 

ANALYSIS OF ECONOMIC EFFICIENCY OF USING FLAT-OVAL TUBES WITH INCOMPLETE FINNING IN CONDITIONS OF NATURAL DRAFT

The efficiency of air coolers, working in free convection mode is considered. The expediency of installing an exhaust tower over the heat exchange surface of the air cooler and its transfer to the mode of natural draft has been established. The possibility of using flat-oval tubes with incomplete finning in the designs of air-cooled devices with natural draft is noted. Variant calculations of the aircooling device on the basis of the most widespread in the market of Ukraine finned tubes in which the quantity of air necessary for maintenance of thermal power is provided only by an exhaust tower are carried out. Comparisons of the results of calculations show that the best technical and economic indicators have a variant of the air cooler based on flat-oval tubes with incomplete finning. The amount of capital costs for the manufacture of air cooler based on flat-oval tubes with incomplete finning is 47% less than the heat exchanger based on bimetallic tubes with rolled spiral finning and 2 times cheaper than the option of aircooler based on tubes with welded spiral fins or oval pipes with oval finning.

Profitability of Production of Stainless Steel + Zirconium Metals Combination Adapters

The main difficulty in obtaining adapters from stainless steel + zirconium metal combination lies in the formation of fragile intermetallic compounds at the weld border. By its properties, zirconium is very close to titanium, and therefore the manufacture of tubes from this combination, as well as pure titanium, is considerably difficult. Optimum explosion welding parameters have been developed, ensuring the highest adhesion strength compared to the existing production methods. At the weld border, a structure characteristic of compounds of dissimilar metals was revealed. The permissible heating temperatures for this combination are determined. The fundamental possibility of using the explosion energy as a factor stimulating the connection of dissimilar metals in order to obtain high-quality multilayer tubes, billets and products for various purposes is demonstrated, resulting in the introduction of environmentally friendly technology. Economic analysis of the manufacturing technology of bimetallic tubes by welding explosion was carried out. The cost-effectiveness of manufacturing technology of bimetallic stainless steel + zirconium metal compound nozzles, which is based on the use of high-pressure gradients and loading velocities to create production, was evaluated.

Spring-Back Prediction of the Bi-Layered Metallic Tube under CNC Bending Considering Neutral Layer Shifting Extraction

Bi-layered metallic bending tubes are widely used in extreme environments. The spring-back prediction theory for precise forming of such tube configuration is lacking. The layered coupling causes complex section internal force and new boundary conditions. This work proposed a theoretical prediction model of bimetallic tubes’ spring-back under computer numerically controlled (CNC) bending. This model calculated the spring-back angle by importing two new parameters—the composite elastic modulus (Ec) and the composite strain neutral layer (Dε). To investigate Dε, the neutral layer shifting extraction method was proposed to get the shifting value from finite element simulations. Simulations and full-scale bending experiments were carried out to verify the reliability of this prediction model. The theoretical results are closer to the experimental results than the finite element (FE) results and the theoretical results neglecting neutral layer shifting. The change of spring-back angle with the interlaminar friction coefficient was investigated. The results indicated that the normal mechanical bonding bimetallic tube with an interlaminar friction coefficient below 0.3 can reduce spring-back.

Study on Gas Bulging Forming and Contradictive Cooling Bonding of AZ31/Al7475 Bimetal Composite Tube

Mg/Al bimetallic tubes can give full play to the excellent properties of magnesium alloys and aluminum alloys, such as light weight, high strength and good corrosion resistance. In this study, gas bulging forming and contradictive cooling bonding process was used to form AZ31/Al7475 hexagonal section composite tubes and showed a good result. In addition, the finite element analysis method was utilized to simulate the process and optimize the forming parameters. The results show that the process could be divided into four stages: free bulging stage, sidewall sticking stage, fillet filling stage and contradictive cooling stage. The maximum thinning rate and fillet radius of AZ31/Al7475 composite tube were 10.60% and 7.00 mm, respectively, at 450 °C, 6 MPa, and 600-720 s. And the interface between the inner and outer layers was closely combined. The bonding force of the rounded corner part of the forming part was 2.04, and 2.30 MPa for the straight wall part. The experimental value of the binding force was about 28% higher than the maximum theoretical value.

Study on modalities and microdefects of Al-Cu bimetallic tube by underwater explosive cladding

In this study, a screwed copper tube was cladded an aluminum tube by a new explosive cladding method. To study the modalities of the bonding interface, a light microscope was used to observe the bonding interface. To expose the weak position of the interface, a three-point bending test was conducted under extreme condition. Then the BSE (Backscattering Electron) images of the bent interfaces were obtained. Meanwhile, the EDS (Energy Dispersive Spectrometry) analyses of the melted zone were performed. The results of the light microscopic observations show that there are four bonding modalities on the interface. They can be summarized to two bonding modalities: direct bonding and bonding with the melted zone. There are no macro cracks on the interface of the bent specimens, which represents a reliable joining generally. The elastic modulus of Al-Cu bimetallic tube along the axial direction is 85.2Gpa. The BSE images, the EDS analyses and the microhardness tests show the direct bonding with some characteristics of the micro wavy interface is a pretty nice bonding pattern. The melted zone composed of CuAl2 is a weak bonding pattern, which may affect the mechanical property of the joint.

Thermal and Aerodynamic Researches of Staggered Bundles for Choice of an Effective Spacing of Round-Finned Tubes

The results of an experimental study of local modeling of convective heat transfer and aerodynamic resistance of staggered six-row bundles of bimetallic tubes with spiral knurled aluminum fins under transverse air flow in the range of its velocity alteration in a compressed bundle section of 1.9−11.0 m/s are presented. The velocity range covers the possible modes of operation of industrial air coolers (AVO). The fins with a diameter of approximately 57 mm are rolled on a steel supporting tube with an outer diameter of 25 mm. Tube finning ratio j = 19.26. Such tubes are widely used in the heat exchange sections of AVO of natural gas, in particular, at “Gribanovskii Engineering Plant” JSC (Russia). To measure the reduced heat transfer coefficients, an electric calorimeter had been developed by the authors with a power input of 600−1300 W. The temperature of the wall surface at the base of the fins did not exceed the range of 77–92 °C. The transverse tube spacing in bundles S1was 64.0 or 68.0 mm, while the longitudinal spacing S2 was 54.4 or 50.0 mm. The heat transfer of each transverse row of six-row bundles was measured, as well as the average heat transfer and aerodynamic drag, which are summarized by the similarity equation of a power type. The heat transfer rate of the last transverse row in the direction of air movement is 0–5 % lower than the heat transfer rate of the stabilized rows, and here new features of heat transfer variations in the insufficiently studied area of spacing changes S1 and S2 have been found. The thermal contact resistance (TCR) was measured in the range of the average temperature of the contact surfaces tк = (79–95) оС, and no dependence of the value of TCR on tк for the specified interval was found. The numerical average value of TCR was Rк = 2,13 × 10–4 m2×K/W, which is typical for reliable mechanical connection of the finned aluminum shell with the supporting steel tube made of carbon steel. The results of variant thermal and aerodynamic calculations with the use of the obtained data established the technical and economic feasibility of placing tubes at the vertices of an isosceles triangle with spacing S1 = 68–69 mm and S2 = 55 mm with failure to use the location of the tubes along an equilateral triangle with S1 = S2' = 64 mm (where S2' – is diagonal spacing). With Q = idem and other conditions being equal, the number of tubes on AVO decreases by 5.7 % with a decrease in power consumption to 4.0 %.

Features of Gravitational Flow of Heated Air in an Exhaust Shaft Above a Multirow Finned Bank

The authors have carried out investigations into the introduction of hot-air heating systems in buildings and structures, and also the applicability of mixed convection in calorifers of recirculating air heaters. The heat transfer of two- and four-row staggered air-heater banks consisting of bimetallic finned tubes in mixed convection has been studied. Experimental investigations into the characteristics of a gravitational flow of heated air in an exhaust shaft above a heat-exchange bank in a mixed-convection regime have been presented. An increase of 1.5–3 times in the heat transfer in the mixed-convection regime compared to the heat transfer under conditions of free convection of the air has been established. The dynamics of motion of a geyser flow of heated air in the exhaust shaft above the heatexchange bank under gravity has been described. A decline of 20–50% in the heat transfer of staggered two- and four-row banks because of the presence of geyser air flows has been established. A method to diminish the adverse impact of geyser air flows on the heat transfer of the bank has been proposed.

Comparative analysis of experimental investigations and numericalsimulation of single-row finned tube bundle at mixed convection

Mixed convective heat transfer is very important for a wide class of engineering tasks. However, the experimental study of mixed convection requires significant implementation costs, high-power equipment, as well as large time costs, so it is proposed to expand the scope of experimental studies using numerical simulation. Numerical simulation of the single-row bundle consisting of bimetallic finned tubes at mixed air convection conditions was performed and experimental data were compared. The formulation of the third-dimensional problem for numerical simulation was realized. The conjugated problem for heat exchange modeling from the tube fins to air was solved. In numerical simulation of air momentum it was taken into account that the Reynolds number based on tube diameter and velocity in the space between fins was varied from 100 to 720. Menter’s k–ω shear stress transport model in standard formulation was used to close the Reynolds equations. Flow visualization on the tube surface revealed the transient nature of the air flow. The temperature distribution visualization in the bundle and the exhaust mine made it possible to see the nature of cooling the finned bundle at mixed convection. Results of numerical simulation and experimental investigations are in good agreement and can be used for expansion of the scope of experiments. The experimental data and the numerical simulation results for the single-row bundle consisting of bimetallic finned tubes at mixed air convection are compared in this paper. Flow near tube surfaces was visualized, and the temperature and velocity distributions in a bundle and in the exhaust mine were obtained.

Wall thickness distribution of Cu–Al bimetallic tube based on free bending process

In this study, we focused on bimetallic tube comprising copper and aluminum (Cu–Al) and proposed a theoretical model of its wall thickness distribution by the free bending technology. Compared to the single metal tube, the minimum thickness of the copper tube is smaller than the minimum thickness of the copper layer in the Cu–Al bimetallic tube, whereas the minimum thickness of the aluminum tube is greater than that of the Cu–Al bimetallic tube under different bending radii; the maximum wall thickness of the copper tube is larger than that of the copper layer in the Cu–Al bimetallic tube, whereas the maximum wall thickness of the aluminum tube is smaller than that of the aluminum layer in the Cu–Al bimetallic tube. Further, the reliability of the proposed theoretical model was verified by finite element simulation and experiments. Both of these results showed that the wall thickness distribution of the bimetallic layer of the metal tube tends to be more uniform. The offset rule of the strain neutral layer of Cu–Al bimetallic tube in the free bending process was also revealed. Moreover, the difference between the U–R curve of the Cu–Al bimetallic tube and the single metal tube was also investigated, and the results indicated that the U–R curve of the Cu–Al bimetallic tube is roughly located between the U–R curves of copper and aluminum.

Effect of welding speed on microstructures and mechanical properties of Al/Cu bimetal composite tubes by a novel friction-based welding process

In this work, a novel friction-based welding technology was developed to weld Al/Cu bimetallic tubes. The macrostructure, microstructure evolutions, and mechanical properties of the joint under different welding speeds were investigated. Void defects are observed on the joint interface, especially at the welding speed 60 mm/min. From the Al side to the Cu side, the reaction layer can be divided into five layers. In addition, welding speed has an important influence on the microstructure evolution of reaction layer. Compression-shear testing results show that the shear strength decreases with the increase of the welding speed. The failure of compression-shear samples is first generated at the junction of hypereutectic layer and intermetallic compound (IMC) layer, and then, the crack propagates along the interface of the hypereutectic layer and IMC layer or through the hypereutectic layer to the eutectic layer.