Thin Stainless Steel Tubes Research Articles

Enhancing bending buckling strength of hollow tubes using concrete filling

Hollow tubular components are widely used in industries as structural elements which are subjected to bending loads. These tubes are susceptible to bending (transverse) buckling, more so in tubes with thinner cross sections. The presented work investigates the effect of adding an inexpensive core like concrete (with good compressive strength) on the bending buckling strength of thin hollow tubes. This study is based on the results obtained from three-point bend tests performed on hollow and concrete filled thin stainless-steel tubes of small diameter. The size of test specimens was chosen such that the bending buckling mode dominates over the yielding as a failure mode. The experimental results are validated by finite element-based simulations. It was observed that addition of a concrete core significantly improves the bending buckling strength of the thin hollow tubes.

Development of a Langmuir probe array for radial potential profile measurement in the collisional merging formation FRC.

The radial electric field in a field-reversed configuration (FRC) plasma plays an important role in the global stability and confinement properties. Herein, we developed a new Langmuir probe array named "Skewered probe" employed in measuring the radial potential profile in the collisional merging formation of an FRC in the FAT-CM (FRC Amplification via Translation - Collisional Merging) device. Because an FRC has a strong toroidal flow, the skewered probe consists of alternately skewered ring electrodes and ceramic beads on a thin stainless-steel tube to neutralize the effect of plasma flow. The developed array has nine electrodes, one every 2cm from r = 9-25cm, and it measures the FRC boundary in the case when the radius of the excluded flux ranges from 10 to 20cm. The skewered probe also has one additional electrode that measures the potential near the chamber wall as a reference for the other electrodes. The radial potential profile of the FRC formed by the collisional merging method in the FAT-CM device was measured using the probe, and the results showed that the region of negative potential gradually changed to a positive potential after merging the FRCs. It was also shown that a strong outward electric field is formed near the separatrix at n = 2 rotational instability.

Experimental behaviour of a three-stage metal hydride hydrogen compressor

A three-stage metal hydride hydrogen compressor (MHHC) system based in AB2-type alloys has been set-up. Every stage can be considered as a Sieverts-type apparatus. The MHHC system can work in the pressure and temperature ranges comprised from vacuum to 250 bar and from RT to 200 °C, respectively. An efficient thermal management system was set up for the operational ranges of temperature desired. It drops temperature shifts due to hydrogen expansion during stage coupling and hydrogen absorption/desorption in the alloys. Each reactor consists of a single and thin stainless-steel tube to maximize heat transfer. These were filled with similar amount of AB2 alloy. The MHHC system was able to produce a compression ratio as high as 84.7 for inlet and outlet hydrogen pressures of 1.44 and 122 bar for a temperature span of 23 °C – 120 °C.

Investigating the Effect of TIG Welding on the Surface Roughness of the Welded Closure of Thin Stainless Steel Tubes

Tungsten inert gas (TIG) welding of thin stainless steel tubes is an important manufacturing process with many applications, in particular for the closure of sheathed thermocouples tubes and thermocouple wells. During the welding process, the microstructure, properties as well as the surface roughness is directly influenced by the setup of the welding procedure and material properties. For the steel tubes of thermocouples, the surface roughness also influences the appearance as well as the wetting behaviour between the probe surface and liquid, which could affect the response of the probe or the maintenance when the probe is used to measure the temperature of liquid and gaseous mediums. In this work, welding tests with controlled parameters and analysis has been conducted on thin austenite stainless tubes of different sizes, the surface roughness of the welded tube is characterised for different welding settings. The data shows that the surface roughness varies between 1-3.5 microns and oxidation patch significantly reduce the smoothness of the surface. The influence of the surface roughness of the tube is investigated and their influence on the service conditions such as wetting/dripping is discussed with reference to typical results from computational fluid dynamics (CFD) simulation.

Development of adiabatic calorimetry system for enthalpy of gas absorption/adsorption and its application to H2/D2 absorption into palladium nanoparticles

We have developed a new adiabatic calorimetry system for enthalpy of gas absorption/adsorption process. The sample cell is designed to be extremely small as a calorimeter cell with a resistance thermometer; mass: 4.34 g, inner volume: 1.06 cc. A thin stainless steel tube is connected at the lid of the cell to introduce a gas. A gas handling system was also constructed to introduce a gas slowly and measure the amounts of the absorbed/adsorbed gas precisely via a pVT method. As the first work on this system, we measured the enthalpies of H2/D2 absorption into Pd nanoparticles with an average diameter of ca. 8 nm. The obtained values are ΔabsH(H) = –(18.15 ± 0.87) kJmol–1 and ΔabsH(D) = –(18.17 ± 0.38) kJmol–1 at 298 K. These values are considerably smaller than those of bulk Pd. The isotope effect are discussed semi-quantitatively on the basis of the potential energy surfaces at the H/D sites.

Microlayer structure in nucleate boiling of water and ethanol at atmospheric pressure

This study investigates the structure of the microlayer that forms between growing bubbles and the heat transfer surface for nucleate pool boiling in the isolated bubble region. The microlayer thickness was measured for water and ethanol by a specially designed measurement system that employs the laser extinction method. A thin (diameter: 94μm) optical fiber in a thin stainless-steel tube was inserted in a liquid pool. Gas flow was used to prevent the fiber, which was made of fluorinated glass, from becoming wet and to remove the pool liquid from the light path. A method for determining the initial microlayer thickness was developed based on numerical calculations. The microlayer thickness decreased over time due to evaporation. The thickness of the initially formed microlayer was found to be uniquely determined. For water, it was in the approximate range of 0–9μm and it increased linearly with increasing distance between the incipient bubble site and the measurement position; this relation was independent of the heat flux. The initial microlayer structure for ethanol was similar to that for water, but its thickness was about twice that for water.

The Influence of Bending Strain on the Critical Current of ${\rm Nb}_{3}{\rm Sn}$ Strands With Different Filament Twist Pitch

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The effect of bending strain on the transport properties of <formula formulatype="inline"><tex Notation="TeX">${\rm Nb}_{3}{\rm Sn}$</tex></formula> strands has been the object of several investigations in the last years. We report on the performances of internal tin <formula formulatype="inline"><tex Notation="TeX">${\rm Nb}_{3}{\rm Sn}$</tex></formula> strands with different filament twist pitches, pre-compressed by swaging into thin stainless steel tubes before the reaction heat treatment and subject to pure bending strain. We have previously reported on the comparison between the performances of the technological OST-Dipole strand (TW-strand) with those of the same strand, but with untwisted superconducting filaments (UNTW-strand). The critical current, as well as the n-index of the samples with twisted filaments gradually degraded with the applied bending strain, while an enhancement of the performances has been observed on UNTW-strands. Here, results on further experimental measurements carried out on OKSC internal tin strands with different filament twist pitches are discussed, in order to clarify some aspects of the current transfer process within the strands. Finally, we carried out an analysis through the second derivative of the V-I curve, which evidenced a peaked critical current distribution for the UNTW-strands, while TW-strands under bending showed a higher degree of non-homogeneity, proven by broader distributions. </para>

Magnetic characterization of Nb3Sn strands under applied strain conditions

We performed magnetic characterizations, using a vibrating sample magnetometer, of an internal tin-typeNb3Sn technological strand. In order to compare the properties of this sample under differentstrain conditions, the same strand was tested under compression, obtained by swaging andcompacting into thin stainless steel tubes before the heat treatment, as well as after a completerelaxation of the filament strain components, by chemical etching of the Cu and bronzematrix components. In particular, we analysed the Kramer extrapolated upper critical fieldBc2K, and the zero-fieldcritical temperature Tc(0) and its distribution, for all the samples. In order to clarify the effect of the strain due toboth the stainless steel reinforcement and the copper matrix thermal pre-compression, wecompared our experimental results with the predictions from well established scaling lawsbased on uniaxial models. Good agreement has been found with measured critical temperatureTc and extrapolatedupper critical field Bc2K values, with proper choice of fit parameters. On the other hand, we observed a broadening of the superconductingTc transition with increasing strain. This has to be ascribed to the effect of radial straincomponents, which cannot be neglected in the present work.

Performance enhancement under bending of Nb3Sn strands with untwisted filaments

We report on the effect of bending strain on the transport properties of multifilamentary Nb3Sn strands having twisted or untwisted superconducting filaments in order to clarify some aspects of the current transfer process within the wire cross section. Critical current measurements were performed on internal tin Nb3Sn strands, which were inserted and compacted inside thin stainless steel tubes before the heat treatment. With the application of a maximum bending strain of 0.5%, the strands with twisted filaments present a degradation of the critical current and of the n-index, while an enhancement of the performances is observed for the untwisted strands. The experimental results are interpreted in relation to the predictions of Ekin’s model.

Manufacturing of prototype components for the ITER divertor baffle

A program for the supply of baffle prototypes was realised as a demonstration of the manufacturing features for different designs of baffle and limiter modules. The scope of the manufacture was aimed on the fist wall heat sink materials such as DS-copper, carbon fibre reinforced carbon (CFC) monoblocks, and armour materials, such as CFC and tungsten vacuum plasma spray. The supply concerns four baffle prototypes with a quasi-poloidal shape and having different geometries with two cooling channels each. Each panel was attached onto a steel block, as a shield block. Type A panels had a DS-copper heat sink with two thin stainless steel tubes and were either plasma-sprayed tungsten (type A/W), or CFC tiles (type A/CFC). CFC monoblock panels consisted in two assembled single CFC U-shaped prototypes with a rear slot cutting and a CuCrZr tube supported by means of S.S. pads (type B), or monoblocks with CuCrZr tubes, put on a S.S. dove-tail mechanical attachment (type C). The manufacturing routes of the four types baffle fabrication are briefly described.

Investigation of striation formation in thin stainless steel tube during pulsed Nd:YAG laser cutting process by numerical simulation

The formation of a striation pattern in a thin stainless steel tube was investigated by numerical simulation during a pulsed Nd:YAG laser cutting process. The simulated results were compared with the experimental results, which were performed under the same conditions for simulation. The simulated results showed good agreement with the experimental results. Although the formation of the striation pattern was influenced by various laser parameters, the laser power density had become the most important factor in the formation of striation patterns, since the laser power density is the most influential in the heating of metal, and the striation formation is caused by the ejection of molten metal and evaporation during laser cutting process. Although a high power density resulted in clear regular striation patterns, relatively low power density caused the formation of a hot spot, which hindered the formation of regular striation patterns and caused less striation. The numerical simulation calculations can be used to predict the shape of striation patterns and to offer a way to provide a smooth cut wall.