Stainless Steel Tube Research Articles

Axial compression behavior of CFRP-confined square concrete-filled double skin tube stub columns with stainless steel outer tube

Concrete-filled double skin tube (CFDST) stub columns with a stainless steel outer tube is a new kind of composite columns and potential to be widely utilized in ocean engineering owing to the excellent performance characterized by high corrosion resistance. To improve the ultimate bearing capacity and delay the local buckling of stainless steel tube, confining materials such as carbon fiber reinforced polymer (CFRP) can be adopted in these composite columns. Thus, this study conducted an experimental investigation on the axial compression behavior of CFRP-confined square CFDST stub columns with a stainless steel outer tube. The main variables were the width-to-thickness ratio of stainless tube and the number of CFRP layers. The typical failure modes, load-shortening curves, and load-strain curves of the CFDST and CFRP-confined CFDST columns were obtained. The test results indicated that the local buckling of CFDST columns can be well suppressed with CFRP wrapping, prior to CFRP rupturing. The CFRP can provide an effective confinement on the sandwich concrete and the ultimate bearing capacity enhancement increased with increasing the number of CFRP layers. Based on theoretical analysis a design model for the inner steel tube has been proposed to prevent the premature failure of the inner steel tube which can leads serious ultimate bearing capacity lose. Additionally, new methods for predicting the ultimate bearing capacity of the square CFDST and CFRP-confined CFDST are proposed based on the limit equilibrium method and twin shear unified strength theory. The predicted results are in good agreement with the experimental results and collected test data.

Development, characterization, and applications of a portable analyzer for continuous monitoring of H2S in gas streams

A bench-scale analyzer for continuous monitoring of H2S in gas streams was previously described (2012 Sens. Actuators B 162 377–83). The analyzer was based on the exothermic reaction between the scrubbed H2S, in alkaline solution, with hydrogen peroxide. The analyzer offers several advantages but suffers from a relatively slow response time (i.e. 7 min) and a relatively low sensitivity (limit of detection = 100 ppm). In the present work, a substantially improved detector design and direct mixing of the gas with the liquid reagents are described. The improved detector, in the form of a coiled thin-walled stainless-steel (SS) tube also acts as a compartment for direct gas absorption and reaction with sodium hydroxide and hydrogen peroxide reagents, which eliminates the need for a gas scrubber based on microporous hollow fiber membranes (HFMs). The average temperature of the SS coil was measured by three thermocouples attached to the outer surface of the coil with thermally conductive epoxy. The improved detector design and the simplified scheme proved very successful in achieving six times faster response (i.e. 70 s) and ten times more sensitive response (i.e. 10 ppm) in the gas stream and improved repeatability (coefficient of variation = 0.55%). In addition, the previously reported advantages, such as excellent signal stability, wide dynamic range (up to 5% H2S) and convenient tuning of the sensitivity and linearity by varying the ratio between the gas and reagent flow rates were perfectly retained. The improved detector is utilized to construct a compact portable version of the H2S analyzer (∼6 kg), which provides a stand-alone operation for real-time monitoring of H2S in the gas stream for up to 4 h prior to the need for reagent refill or battery recharge. The applications of the described portable analyzer in monitoring H2S removal from H2S–N2 gas stream using an HFM contactor and absorption solvent, and in the determination of sulfide ions in liquid samples are presented. A comparison between the response of the present portable H2S analyzer and a commercial analyzer is also presented.

Evaluation of subcooled void fraction in downward flow under low mass flux condition by using neutron radiography

In downward flow, complex two-phase flow is caused by buoyancy of bubbles. It affects not only a void fraction profile but also a point of net vapor generation (PNVG). In order to understand the fundamental characteristics of the void fraction on subcooled boiling in downward flow, the void fraction was measured by using neutron radiography. The test sections were made of stainless steel tubes that had 400 mm in heated length with 10 and 15 mm in inner diameters. They were heated by direct Joule heating applying D.C. power. The void fraction characteristics were explained by dividing into three regions: i.e., a wall voidage region, a detached voidage region, and a bulk voidage region. PNVG was defined as the boundary between the detached voidage region and the bulk voidage region. In a downward flow, the thermal equilibrium quality at PNVG is smaller than in an upward flow. “Secondary PNVG” was also observed which was caused by the influence of a reverse flow of bubbles. A difference of thermal equilibrium quality between at primary PNVG and at secondary PNVG is lager in 15 mm in inner diameter than in 10 mm. The void fraction profile and PNVG characteristics in downward flow show dependence of inner diameter as well as mass flux. To demonstrate the void fraction profile involving with the influence of a reverse flow in a downward flow, an empirical void fraction correlation based on a drift-flux model with Lahey’s flow quality model was developed. This correlation well agreed with the experimental results.

Experimental and numerical study on the structural performance of the stainless steel ring strengthened removable dowel bar connection system

ABSTRACT Traditional jointed plain concrete pavement (JPCP) systems cannot be reused after grouting fast-setting materials in the dowel slot. To achieve demountability, a removable dowel bar connection system is proposed in this paper. The severe stress concentration occurring in JPCP systems is mitigated by applying a stainless steel ring at the pavement joint surface. In the monotonic loading tests, different stainless steel ring thicknesses, lengths and the stainless steel tube thicknesses were considered. The effect of the stainless steel ring on the structural performance of the removable dowel bar connection system was studied in terms of the failure mode, the deflection response, ductility and the strain distribution and development. Besides, after being validated against experimental test results, the developed finite element model was used to conduct the extended parametric analysis, in which a close relationship was found between the ultimate load and the stainless steel ring length. To prevent the localised crushing failure, the maximum compressive stress at the joint surface was compared with the allowable bearing stress under service load. By using FEA data, an empirical equation was finally proposed to predict the ultimate loads of specimens with the proposed connection system.

Axial compressive behaviour of stainless steel tube-confined steel-reinforced recycled concrete stub columns

Stainless steel tube-confined steel-reinforced recycled concrete columns (SSTCSRRC) have the potential to be widely used in engineering structures due to their advantages of aesthetic appearance and reutilization of waste materials. However, there is currently little research work on this new type of thin-walled stainless steel composite columns. This paper investigates the behaviour of SSTCSRRC stub columns under axial compression. Tests on seven circular and seven square stub columns were carried out, and the main variables include the thickness of the stainless steel tube, the recycled brick aggregate (RBA) replacement ratio and the specimen type. The results indicate that the confinement effect of the stainless steel tube improves the ultimate strength and ductility of the columns, and the ultimate strength decreases with an increase in RBA placement ratio. A high RBA placement ratio or using cross-shaped section steel can significantly improve the ductility of the columns. A finite element (FE) model was developed to simulate the axial compressive behaviour of SSTCSRRC stub columns. Based on the numerical data of 130 FE models, the design formulas for axial compressive strength and stiffness of SSTCSRRC stub columns were proposed.

Effect of the thickness of Cu interlayer on dissimilar laser welding of 304 stainless steel to tantalum

304 stainless steel (304SS) tube and tantalum (Ta) cylinder were successfully joined by laser welding with copper (Cu) interlayer. The influence of Cu interlayer thickness on the microstructure and mechanical properties of joints was clarified. The intermetallic compounds (IMCs) generated between the 304SS and Ta were determined as Fe2Ta and FeTa in the joint without Cu interlayer. The addition of Cu interlayer could effectively inhibit the atomic diffusion between the base metal and the generation of IMCs. In addition to other laser welding parameters, the thickness of the Cu interlayer also has an extremely important effect on the amount of IMC at the fusion zone (FZ)/Ta interface and the heat input on Ta side. As a result, the formation of Fe2Ta and FeTa was reduced and the weld consisted of Fe-based solid solution and Cu-rich phases. Joints produced with a 0.4 mm thick Cu interlayer exhibited the highest tensile strength of 288.7 MPa, which was 54.1% higher than that without Cu interlayer, due to the excellent metallurgical bond and few IMCs at the FZ/Ta interface. A large amount of IMCs was found at the FZ/Ta interface of the joint with a 0.2-mm Cu interlayer, which reduced the strength of the joint. A weak metallurgical bond was formed due to insufficient heat input, as the thickness of the Cu interlayer reached 0.6 mm. Thermodynamic calculations of the Fe-Ta-Cu ternary system explain the diffusion behavior of Cu atoms at the FZ/Ta interface and its effect on the formation of Fe-Ta reaction layer.

Influence of Heat Treatment of Nickel-Titanium Instruments on Cyclic Fatigue Resistance in Simulated Curved Canals.

The aim of this study was to compare the cyclic fatigue of heat-treated and non-treated instruments. Twenty instruments with and without heat treatment from Bassi Logic were evaluated (n = 10). All instruments were subjected to dynamic cyclic fatigue through continuous rotations inside a stainless-steel tube (1.4-mm diameter, 9-mm curvature with 6-mm radius, and 90° angle) using a custom-made device, which performed 1 axial oscillation every 2 seconds with an amplitude of 3 mm, powered by a torque-controlled motor (Silver Reciproc, VDW, Germany), with speed adjusting to 950 rpm and torque to 4 N, according to manufacturer's guidance. The groups were compared using the Mann-Whitney test. The fracture time of the heat-treated instruments (97.20 ± 39.94 second and non-treated instruments (14.30 ± 6.78 seconds had statistical differences [p < 0.05]). Heat-treated instruments were 6.8 times more resistant to fatigue than non-treated instruments (p < 0.05). Heat treatment provides increased fatigue resistance of NiTi alloy with the same design.

Study on non-monotonic pressure-drop of supercritical n-decane with pyrolysis in heated channels

The non-monotonic relation between pressure-drop and flow-rate leading to the flow instability of fuel with pyrolysis was investigated. A characteristic pressure-drop model of n-decane coupled pyrolysis reactions under supercritical pressure was established. The model includes one-dimensional flow control equation, species equation, RK-PR equation of state, high-pressure viscosity model and a reaction mechanism consisting of 10 species and 15 reactions. The non-isothermal friction factor formula with wall correction coefficient fitted by experimental data was used in the model. To verify the model, the pressure-drops at different flow-rates were measured in a horizontal stainless steel tube with the inner diameter of 1.93 mm under different back pressures (3, 4 and 5 MPa). The results show that the model can accurately capture the non-monotonicity of characteristic pressure-drop. Under 3 MPa condition, the characteristic pressure-drop curve of n-decane has a pseudo-critical negative slope (PCNS) region and a reaction negative slope (RNS) region caused by the pyrolysis. With the increase of pressure, the PCNS region disappears but the RNS region still exists. The high pressure makes the onset of RNS region appear earlier due to the accelerated initial reaction rate. The total pressure-drop is separated and analyzed based on the model mathematically. In the PCNS region, the derivative of acceleration pressure-drop to mass flux is negative, whereas the derivative of friction pressure-drop to mass flux is positive. In the RNS region, the two derivatives are both negative because of the sharp decrease in density and the increase in friction factor caused by the pyrolysis reaction. The two parallel channels’ instability with constant total mass flow rate is analyzed based on the characteristic pressure-drop curves for reacting and non-reactive flow. The results indicate that the fuel pyrolysis reaction not only expands the range where the flow excursion may occur but also makes it difficult for the flow-rate to reach stable state again after the flow excursion caused by pseudo-critical instability.

Phase speed and attenuation determination of a monodisperse liquid at the single bubble resonance using a single and two microphone transfer function method

The phase speed and attenuation of a bubbly liquid were determined. The experimental configuration consisted of a vertical stainless steel tube partially filled with water and pressurized air flowing through a single hypodermic needle at the bottom. The sound source was located in the air-filled portion at the top of the tube. A SRS-785 spectrum analyzer was used to measure and calculate the transfer function. Once the impedance was found, the phase speed and attenuation was calculated from the complex wave number.

Investigation of intergranular stress corrosion cracking in a failed 347H stainless steel furnace tube

A 347H stainless steel tube of a furnace of a hydroprocessing unit was cracked during operation shortly after the last shutdown. Both internal and external surfaces of the tube were exposed to sulfur compounds. Material characterization methods including tensile test, double loop electrochemical potentiodynamic reactivation test and fractography were used to investigate the failure causes. Based on stereo investigations, the external surface of the tube was identified as the crack initiation location. The microstructure evaluation and DL-EPR test showed that sensitization with a high DOS value of 18 occurred in the tube material. The sensitization has resulted in a dramatic reduction in the elongation parameter. Fractography examination exhibited a brittle fracture with presence of sulfide corrosion products on the fracture surface. Finally, due to the combination of the obtained results and additional observations including corrosion within grain boundaries and intergranular cracking, polythionic stress corrosion cracking was determined as the failure mechanism.

Effect of Expansion Deformation on the Mechanical Properties and Corrosion Resistance of an AISI 304 Stainless Steel Tube in Water from an Oilfield

The effects of expansion deformation on the mechanical properties and corrosion resistance of an AISI 304 stainless steel (SS) tube with dimensions of ϕ 108 mm × 6 mm were studied with a full-scale test, a mechanical property test, microstructural analysis and a corrosion property test in order to explore the feasibility of using AISI 304 SS tubes as solid expandable tubes in repairing damaged well casings. The results showed that the AISI 304 SS tube had good expansion performance, suitable strength after expansion and excellent corrosion resistance, and it met the technical requirements for repairing the casings of common oil wells. After ~11% radial expansion, the internal pressure strength and collapsing strength of the tube were 71 and 32 MPa, respectively. The increase in dislocations, and in the formation of strain-induced martensite and twinning stimulated by plastic deformation, led to the yield strength of the AISI 304 SS tube increasing from 249 to 539 MPa; however, the corrosion resistance of the AISI 304 SS tube was somewhat worsened because of the increase in dislocations and strain-induced martensite caused by expansion deformation. However, the corrosion resistance of the AISI 304 SS tube was still much better than that of conventional casings.

Behaviour of eccentrically loaded circular recycled aggregate concrete-filled stainless steel tube stub columns

This paper presents an experimental and numerical study of eccentrically loaded circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. The testing programme was conducted on twelve specimens designed with different stainless steel tube section sizes and recycled coarse aggregate replacement ratios, and included tensile coupon tests, concrete cylinder tests and eccentric compression tests. The test results, including the failure loads and modes, load–mid-height lateral deflection curves and evolution of neutral axis, were reported and discussed. Following the testing programme, a numerical modelling programme was conducted, with finite element models developed and validated against the test results and then employed to perform parametric studies to generate further numerical data. The confinement effects were analysed based on the numerical data. The relevant design interaction curves, as set out in the European code, American specification and Australian/New Zealand standard, were assessed for their applicability to circular RACFSST stub columns under combined compression and bending. On the basis of the quantitative and graphical assessments, it has been found that (i) each set of codified design interaction curve leads to similar assessment results for eccentrically loaded circular RACFSST stub columns with different recycled coarse aggregate replacement ratios and (ii) the failure load predictions from the codified design interaction curves are conservative.

The effect of methanol additive on n-decane cracking and coking over TiN coating

Investigation on cracking and coking of hydrocarbon fuel is of great significance to regenerative cooling technology. In this work, the cracking and coking experiments of pure methanol and n-decane/methanol mixture were carried out in TiN coated tube and blank 304 stainless steel tube, respectively. The purpose is to explore the effect of TiN coating on methanol cracking, and the inhibition effect of methanol on n-decane coking. The gas and liquid phase products were analyzed by gas chromatography. The coke characteristics were analyzed by SEM, EDS and carbon burn-off techniques. The results show that the active sites on the surface of the metal tube will catalyze methanol cracking and coking, and the coking phenomenon is very serious. However, the TiN coating can effectively inhibit the carbon deposition during methanol cracking and ensure methanol cracking in high temperature channels. In the blended cracking experiment of n-decane and methanol in coated tube, methanol can inhibit the cracking and coking of n-decane, and will not reduce the heat sink. When the amount of methanol added is 5 wt%, the inhibition effect on coking is the best. When the outlet temperature is 730℃, the coking inhibition rate is 63.40%. Methanol as a hydrogen donor can inhibit the chain transfer and the formation of coking precursor of the n-decane cracking process, thereby achieve the effect of inhibiting coking.

Crafting Metal Surface Morphology to Prevent Formation of the Carbon–Steel Interfacial Composite

We created a coke-repellent inner surface in a stainless steel (SS-321) tube using an enhanced chemical etching tactic. A water-borne etching solution was formulated by combining an ion sequestering ligand (L), hydrogen peroxide (H), hydrochloric acid (C), and a stabilizing agent (E or N). Three etchants, LHC, LHC-E, and LHC-N, were therefore formulated, respectively. The coke-repellent metal surfaces achieved by these etchants all show a characteristic topographic pattern on a micron scale, specifically with grooved spherulite and ridge-like topographic patterns. Fundamentally, these two topographic patterns prompt overhead micro turbulence fields whose agitation mitigates the surface entrapment of aromatic hydrocarbon flocs generated from the overhead lubricant. The surface entrapment of flocs is the crucial step to trigger coke growth. The coke repellency was assessed by placing an SS-321 tube filled with a lubricant in a heat soak. It was found that the topographic pattern and its surface roughness level have opposite effects on coke development. Hence, the three etchants give rise to different coke-resilient surfaces. Moreover, the plug flow rate of the etchant also affects the anti-coking performance, exhibiting an optimal flow rate that offers the highest coke-proof efficacy.

Size effect of square concrete-filled stainless steel tubular short columns under axial compression

Concrete-filled stainless steel tube (CFSST) members combine the advantages of stainless steel materials and concrete-filled steel tube (CFST) members. Therefore, it has a broad range of applications than CFST members in the marine environment and other scenarios requiring great durability and corrosion resistance. However, there are limited researches on the large-size CFSST members. In this paper, 40 square CFSST members with varying steel ratios (4 % ≤α≤ 10 %), widths (500 mm ≤B≤ 900 mm) and strength of concrete (fcu = 40 MPa, 50 MPa) are studied on the size effect under axial compression. The size effect on the peak axial stress, peak axial strain, composite elastic modulus and ductility coefficient are investigated. Then this paper adopted the two-way analysis of variance test (ANOVA) to analyze the data. According to the results, the peak axial strain, composite elastic modulus and ductility coefficient have size effect, but the size effect in peak axial stress does not significant. It was found that the steel ratio will also affect the size effect of CFSST members, and the size effect decreases with the increase of steel ratio. Compared with the current CFST codes, the size effect coefficient included steel ratio is introduced can better predict the ultimate bearing capacity of square CFSST short columns with low steel ratio of range of 4–10 %.

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.

Effect of Copper Iodide on Selective Corrosion of Duplex Stainless Steel Tubing in Acidizing Environments

Effect of Copper Iodide on Selective Corrosion of Duplex Stainless Steel Tubing in Acidizing Environments

Experimental investigation on the performances of a valve-based and on-demand droplet generator producing droplets in a wide size range

Many aspects of our daily lives are affected by the generation of water droplets, and it is important to controllably produce droplets with a wide size range in various applications. In this paper, we describe an on-demand droplet generating system based on a high-speed two-way solenoid valve. A nozzle made of stainless steel tubing is fit into one port of the valve, and the other port is connected to the fluid reservoir by which the pressure can be controlled via a pressure regulator. When the liquid is pressurized and the valve is opened with a short pulse voltage, trace amounts of liquid will be ejected from the nozzle to form a droplet. Droplet generation is captured using a high-speed camera to measure the dimension and velocity and to evaluate the performances of the generator, such as repeatability and stability. We demonstrate the influences of applied pressure and pulse width of driving voltage on droplet generation. It is shown that the droplet generator is capable of producing droplets in a wide size range for a given nozzle (e.g., about 0.7–2.2 mm for a 1.0 mm diameter nozzle). A single droplet is stably generated at Z = 268.1, obviously higher than the published data and the Weber number of a fluid jet (Wej) ranging from 2.1 to 5.6. The droplet generator presented here will be useful for research related to large droplets, such as freezing rain in atmospheric science and supercooled large drops in aircraft icing.

Experimental method of ammonia decomposition study based on thermal-hydraulic approach

Hydrogen is the promising carbon-free fuel to be used massively in future transport based on fuel cell electric vehicles (FCEV) and internal combustion engines (ICE). The reliable and safe way to store hydrogen in vehicles is an open question. As a promising potential solution, hydrogen storage in liquid ammonia is postulated. In this case, the hydrogen is released due to ammonia decomposition under heat energy supply. In the hydrogen ICE, the ammonia decomposition could be provided at the expense of exhaust gas energy. The current article deals with developing test tools and methods for the experimental study of catalysts and reactor prototypes appropriate to the hydrogen ICE. A thermal-hydraulic approach without chromatography and mass spectrometry has been proposed to determine ammonia decomposition kinetics at different fluid pressure, temperature, and flow rate. The tests have validated the approach with the decomposition of ammonia in catalysts with aluminium shavings in stainless steel tube with an inner diameter of 10 mm. The identified ammonia decomposition rate is 0.0119 mol of H2 per gram of catalysts in 1 h.

Methane pyrolysis on sponge iron powder for sustainable hydrogen production

Methane pyrolysis is one of the possible methods to produce low-carbon hydrogen. One of the most promising catalysts for methane pyrolysis is Fe due to its availability, relatively low cost and high working temperature. In the presented paper, the methane pyrolysis on unsupported (without a carrier) sponge iron in the form of powder was studied in the temperature range of 700–1100 °C. Methane pyrolysis was carried out in a stainless-steel tube reactor with an inner diameter of 10 mm. The reactor was heated locally by propane burner, the length of the heated zone was about 8 cm along the reactor tube. Methane feed rates were about 50, 100, and 200 ml/min, and the residence time of methane in the 8 cm long reaction zone was about 4, 2 and 1 s, respectively. The hydrogen yield increased with an increase in the temperature and a decrease in methane feed rate. At 700–800 °C, the hydrogen yield did not exceed 20%. At 900 °C, the yield reached 28.6% at a residence time of about 4 s. At 1000 °C, hydrogen yield was about 40 and 66.5% at a residence time of about 1 and 4 s, respectively. At 1100 °C, hydrogen yield varied in the range of 70–85%. The use of a catalyst increased the hydrogen yield by 81% compared to the experiment without a catalyst at 1100 °C. The catalytic effect of sponge iron powder can be used in the development of methane pyrolysis plants.