Stainless Steel Tube Research Articles

Cyclic behavior of carbon steel and austenitic stainless steel hollow laminated viscoelastomer-filled steel tube damper under unidirectional and bidirectional loadings

The hollow laminated viscoelastomer-filled steel tube damper (HLVSTD) is a metallic damper with stable working performance and excellent energy dissipation capability. It can exhibit equal mechanical performance in any single horizontal direction based on the geometric features of the circular shape. However, the impact of carbon steel tube material, stainless steel tube material and bidirectional loading on the mechanical behavior of HLVSTD remains unclear. The objective of this study is to analyze the mechanical performance of HLVSTD under bidirectional loading conditions using carbon steel tubes and austenitic stainless steel tubes, which are commonly utilized in China. Experimental tests were conducted using both unidirectional loading and bidirectional loading to comprehensively assess the performance. The results indicate that, under unidirectional and bidirectional loading, HLVSTDs made from both carbon steel and austenitic stainless steel tubes exhibit stable hysteresis curves. In comparison to the carbon steel tube HLVSTD, the counterpart with an austenitic stainless steel tube demonstrates higher equivalent stiffness, ultimate force, energy dissipation and low-cycle fatigue performance. Moreover, HLVSTDs under bidirectional loading exhibit a similar trend in mechanical performance compared to those under unidirectional loading. Regardless of whether the tube material is carbon steel or austenitic stainless steel, the cumulative displacement and cumulative energy under bidirectional loading were found to be twice as much as those observed under unidirectional loading, which demonstrates the excellent mechanical performance of HLVSTD under bidirectional loading.

Experimental study on single- to two-phase flow and heat transfer of water in a small tube

Experimental investigation on flow boiling heat transfer in a small tube under high system pressure has been conducted in this study. The test-section is constructed with a 316L stainless steel tube. The inner diameter and heated length of the test-section are 5 mm and 930 mm, respectively. The working fluid is deionized water. The operating conditions of the experiments are as follows, the mass flux from 548 to 978 kg/(m2·s), the wall heat flux from 136 to 238 kW/m2, and the system pressure from 1.0 to 2.9 MPa. The experimental results showed that the inlet subcooling mainly affects the onset of nucleate boiling, but its impact on the heat transfer coefficient at the same vapor quality is almost negligible. The heat transfer coefficient increases with the increase of mass flux and wall heat flux, especially in the region where xe < 0.02. The average heat transfer coefficient is higher under high system pressure owing to the variation of the thermophysical properties. Additionally, the existing flow and heat transfer correlations cannot predict the flow boiling heat transfer coefficient and frictional pressure drop in the experiments accurately enough. Therefore, the new flow and heat transfer correlations are developed based on the experimental data in this paper, and the mean absolute deviation of the flow boiling heat transfer correlation and frictional pressure drop correlation are 13.3% and 12.1%, respectively.

The Effect of Laser-Resistant Endotracheal Tube Design on Airflow Dynamics: A Benchtop and Clinical Study.

Compare ventilation pressures of 2 endotracheal tube designs used in laser airway surgery in clinical practice and with a benchtop model to elucidate differences and understand the design elements that impact airflow dynamics. Ventilatory and aerodynamic characteristics of the laser resistant stainless-steel endotracheal tube (LRSS-ET) design and the laser resistant aluminum-wrapped silicone endotracheal tube (LRAS-ET) design were compared. Ventilatory parameters were collected for 32 patients undergoing laser-assisted airway surgery through retrospective chart review. An in vitro benchtop simulation measured average resistance and centerline turbulence intensity of both designs at various diameters and physiological frequencies. Baseline patient characteristics did not differ between the 2 groups. Clinically, the median LRAS-ET peak inspiratory pressure (PIP; 21.00 cm H2O) was significantly decreased compared to LRSS-ET PIP (34.67 cm H2O). In benchtop simulation, the average PIP of the LRAS-ET was significantly lower at all sizes and frequencies. The LRSS-ET consistently demonstrated an increased resistance, although no patterns were observed in turbulence intensity data between both designs. The benchtop model demonstrated increased resistance in the LRSS-ET compared to the LRAS-ET at all comparable sizes. This finding is supported by retrospective ventilatory pressures during laser airway surgery, which show significantly increased PIPs when comparing identically sized inner diameters. Given the equivocal turbulence intensity data, these differences in resistance and pressures are likely caused by wall roughness and intraluminal presence of tubing, not inlet or outlet geometries. The decreased PIPs of the LRAS-ET should assist in following lung protective ventilator management strategies and reduce risk of pulmonary injury and hemodynamic instability to the patient.

Fabrication and characterization of zirconium oxide coating on tubular steel by metal organic decomposition

In fusion reactor blankets, multifunctional ceramic coatings fabricated on structural materials have been investigated for tritium permeation reduction, electrical insulation, and corrosion protection. However, it has been challenging to manufacture a homogeneous coating on the complicated components in the blanket breeder, such as ducts. In terms of sustainable development, it is crucial to establish a ceramic coating technique on the inner walls of fuel pipes in liquid blanket systems. In this study, we applied the metal organic decomposition method to fabricate zirconium oxide coatings on 316L austenitic stainless steel tubes and characterized their properties as liquid tritium breeding pipes. Homogeneous zirconium oxide coatings with a thickness of 395 ± 12 nm have formed on the inner walls of SS316L tubes. The compatibility of the coated tubes with liquid lithium-lead was examined under static and flowing conditions at 550–600 °C for prolonged exposure of up to 2000 h. Under static conditions, ZrO2 coatings demonstrated exceptional compatibility with the liquid Li-Pb as they protected structural material from corrosion. At a flow rate of 0.16 m/s, the coatings were partly delaminated due to different thermal expansion coefficients of the coating and substrate and acceleration under a dynamic system. The coating thickness increased up to 650 ± 26 nm after exposure for 2000 h, which indicated ZrO2 coatings reacted with Li-Pb to form corrosion products. Besides, ZrO2 coatings achieved the insulating requirements of magnetohydrodynamic insulators as their electrical resistivities were on the order of 104–106 Ω m at the temperature range of 250–550 °C.

Contact neuro-endoscopy-assisted cerebral hematoma evacuation under direct vision.

Neuro-endoscopic hematoma evacuation is a crucial therapeutic approach for intracerebral hemorrhage. Our research team has developed a portable and contact neuro-endoscopy technique to enhance the conventional endoscopy procedure. compared to traditional endoscopy, this innovative approach involves miniaturizing the lens, light source, and camera system. These components are integrated into a stainless steel tube with a diameter of 4 mm, referred to as the portable endoscopy in this study. The portable endoscopy is powered by a USB cable and the video is displayed on a tablet computer. This portable endoscope facilitates easier operation with both hands by a single surgeon.

Acetone Reclamation: An Affordable and Practical Approach to Recycle Impure Acetone from Plastination

Dehydration of the tissues with acetone is one of the critical phases of the plastination procedure, and much acetone is utilized in this step—the present study aimed at acetone reclamation with essential laboratory equipment cost-effectively. The objective was to use the reclamated acetone and not discard it in the environment. In this experiment, 150 liters of impure (used) acetone was taken for reclamation through a simple distillation method. The Institutional Ethical Committee (IEC) of Symbiosis Medical College for Women, Pune, approved the study. Essential laboratory equipment included two heat-resistant glass jars with stoppers, ½ a diameter stainless steel tube, a cooling chamber, a thermostat-controlled hot water bath, an electrode pH meter, and a laboratory thermometer. The cooling chamber condensed the boiling acetone vapours, and pure acetone was collected in the glass jar. The results were calculated using descriptive statistics. With this acetone reclamation setup, 150 liters of impure acetone were recycled, and 128 liters of acetone with a purity of 97% - 99.3% was recovered. The essential equipment for this study pre-existed in our laboratory. The current study also proposes installing a cost-effective acetone reclamation unit at plastination labs to avoid disposing of the impure acetone as toxic waste, thus preventing it from harming the environment. KEYWORDS: Acetone recycling, acetone reclamation, chemical hazards, cost-effective plastination.

Fabrication of a bio-based polymer adsorbent and its application for extraction and determination of glycosides from Huangqi Liuyi Decoction

Huangqi Liuyi Decoction, a famous classical Chinese prescription, shows significant curative effect on diabetes and its complications, in which calycosin-7-glucoside, liquiritin and glycyrrhizic acid are the main components that playing these mentioned pharmacological activity, under the synergistic action of various other ingredients in the decoction. However, there are significant differences in the content of active compounds in Chinese medicinal materials, which mainly due to origin, picking seasons, and processing methods. Hence, the accurate content of the glycosides is the prerequisite for ensuring the pharmacological efficacy. Aiming at establishing an efficient extraction and determination method for accurate quantitative analysis of calycosin-7-glucoside, liquiritin and glycyrrhizic acid in Huangqi Liuyi Decoction, an on line solid-phase extraction-high-performance liquid chromatography method was developed, using a homemade bio-based monolithic adsorbent. The bio-based adsorbent was prepared in a stainless steel tube, using bio-monomers of methyleugenol and S-allyl-L-cysteine, which effectively reduced the dependence of the polymer field on non-renewable fossil resources and reduced carbon emissions. Furthermore, the prepared adsorbent owned abundant chemical groups, which can produce interactions of hydrogen bond, dipole-dipole, π-π and hydrophobic force with the target glycosides, thus improving the specific recognition ability of the adsorbent. The experiments were carried out on an LC-3000 HPLC instrument with a six-way valve. Methodology validation indicates that the recovery is in the range of 97.0%-103.4% with the RSD in the range of 1.6%-4.0%, due to the specific selectivity of the bio-based monolithic adsorbent for these three glycosides, and good matrix-removal ability for Huangqi Liuyi decoction. The limit of detection is 0.17, 0.50 and 0.33μg/mL for calycosin-7-glucoside, liquiritin and glycyrrhizic acid, respectively, and the limit of quantitation is 0.50, 1.50 and 1.00μg/mL, respectively, with the linear range of 2-200μg/mL for calycosin-7-glucoside, and 5-500μg/mL for liquiritin and glycyrrhizic acid. The present work provided a simple and efficient method for the extraction and determination of glycosides in complex medicinal plants.

Acoustic Emission Time-Space Evolution Characteristics of the Bond Behavior of Recycled Aggregate Concrete-Filled Steel Tubes

In order to effectively observe the damage behavior of the interface between steel tube and concrete, and to reveal the law of time-space evolution and the bond failure mechanism of the bond, the Acoustic Emission (AE) non-destructive monitoring technology was used to monitor the process of repeated push-out tests of concrete-filled carbon steel tube (CFST), recycled aggregate concretefilled carbon steel tube (RACFST), and recycled aggregate concrete filled stainless steel tube (RACFSST) specimens. F-S (force-slip) curve and strain distribution were obtained from the tested specimens, in addition to various acoustic emission (AE) parameters such as hit count, energy release rate, and time difference localization points. To establish a relationship between the acoustic emission characteristic parameters, the normalized characteristic parameters, and the F-S curve, we took into account the time-space evolution process of interface bonding failure and developed a constitutive model incorporating the concept of macro-interlocking. The results show that for peak bonding strength, CFST is slightly lower than the RACFST specimen in the first load cycle, while in the second to fourth load cycles, CFST &gt; RACFST &gt; RACFSST. The AE localization points show a continuous and linear distribution, and the time-space evolution characteristics of AE localization points in the first load cycle show a extension from the two ends-middle-lower middle. In the second and fourth load cycles, the positioning points are concentrated in the elastic stage and the upper intermediate stage. The macro-interlocking directly affects the bonding interface characteristics, and the macro-interlocking coefficient defined can quantitatively describe the macro-interlocking of the steel tube and predict the τ-S curve of the RACFST under repeated load cycles.

An Efficient Low‐Cost Device for Sampling Exhaled Breath Condensate EBC

AbstractWhile exhaled breath condensate EBC is not yet used in routine clinical diagnostics and disease monitoring, recent publications indicate that exhaled air and EBC contain a wide range of molecular biomarkers that are characteristic of various medical conditions. This includes evidently lung disorders such as asthma, COPD, and cystic fibrosis, but also diabetes and several types of cancer go along with specific biomarkers exhaled from the airways. In addition, EBC samples can be collected in a non‐invasive way and, due to their small volume, they can be easily stored frozen between collection and analysis. Several home‐made EBC‐collection systems for research purposes are documented in literature while there are also a few systems from commercial suppliers that are not yet certified as medical products. In this work, a novel collection device is presented in which the EBC is condensed and frozen inside stainless steel tubes, tightly surrounded by an aluminum cylinder that is precooled in a kitchen freezer. The device is low cost, easy to use by patients at home or in a clinic, and its collection efficiency of up to 500 µL min−1 of respiration is on the high side.

Compressive Behavior of Stainless Steel–Concrete–Carbon Steel Double-Skin Tubular (SCCDST) Members Subjected to External Hydraulic Pressure

The new-type stainless steel–concrete–carbon steel double-skin tubular (SCCDST) members, characterized by their exceptional corrosion resistance and mechanical bearing capacity, have promising applications in ocean engineering, particularly in deep-water engineering. The external hydraulic pressure and interfacial action of various materials intensify the complexity of composite performance of SCCDST members. This paper describes an analytical investigation on the concentric compressive performance of SCCDST members under external hydraulic pressure. The full-range mechanism, including load–displacement response, bearing capacity contribution, and contact pressures, was investigated through the finite element (FE) model that was validated by the failure mode, bearing capacity, and response of axial load versus strain. Subsequently, influences of key geometric–physical parameters were analyzed, e.g., diameter-to-thickness ratios (Do/to, Di/ti), material strengths (fyo, fyi, and fc), hollow ratios (χ), and water depths (H). Typical results indicate that: the initial active confinement action derived from the hydraulic pressure can enhance the interfacial contact pressure and axial compression capacity of SCCDST members due to the tri-axial compression state; the enhancement of confinement effect is mainly from the interfacial interaction between outer stainless steel tube and concrete infill; influence of water depth on bearing capacity cannot be ignored, e.g., the bearing capacity of an SCCDST member with larger hollow ratio (χ = 0.849) is not enhanced under a higher hydraulic pressure (H = 900 m) because of the cross-sectional buckling failure risk. Finally, a modified method considering the effect of water depth was proposed and verified for SCCDST members under hydraulic pressure.

Design and experimental study of electromagnetic ultrasonic single-mode guided wave transducer for small-diameter stainless steel tubes

ABSTRACT Small-diameter stainless steel pipes find widespread application in nuclear power systems. In order to detect surface axial wear defects that may occur during their service life, a circular fully enclosed probe has been developed for inspecting these small-diameter stainless steel pipes. The probe is composed of a periodic permanent magnet (PPM) and a racetrack-shaped coil. Through the optimised design of the PPM structure, two probes were devised to excite single flexural and single torsional modes, respectively. Furthermore, employing the non-equivalent concept, the torsional mode guided wave probe underwent optimisation, resulting in a 54% increase in the received signal amplitude. Finally, two types of guided wave probes were utilised to conduct detection experiments on artificially induced defects in an outer diameter 10 mm sample pipe. The results indicate that both T(0,1) and F(1,2) mode guided waves can detect axial defects. Moreover, the detection amplitude of the T(0,1) mode guided wave surpasses that of the F(1,2) mode guided wave by a maximum of 53%.

Experimental study of ammonia nucleation boiling onset in dead-end tube segments at different boundary conditions

The nucleation boiling onset of liquid ammonia in stainless steel, aluminium, and titanium tube segments of ID 4 mm, 6 mm, and 8 mm without flow conditions has been experimentally studied at saturation pressures of 12.5–19.8 bar. It has been shown that heterogeneous nucleation is the determining mechanism for the considered cases. Maximal achievable liquid superheating at 19 K has been observed in the tests at low saturation pressure (12.5 bar), decreasing to 6 K at 19.8 bar. The heating rate in the range of 0.2–60 K min−1 (average heat fluxes of ≈0–4 kW m−2) does not impact much on boiling onset. Internal diameter (4, 6 and 8 mm), roughness (1 and 10 μm) and wettability (10°–50°) do not drastically change the level of maximum achievable superheating before boiling onset. However, quantitatively, the titanium surface with the poorest wettability (≈50°) among considered samples leads to higher overshooting of ammonia bulk temperature by several K. A stainless steel surface with artificial scratches shows a bit higher superheating than a smooth surface. The specific tests showed that ammonia boiling could start at nearly saturation level in the case of a strongly overheated wall. In particular, for ammonia at saturation pressure above 12.5 bar, the required overheating of the wall of 19 K ensures the boiling of ammonia without superheating in the bulk of the liquid.

Experimental and numerical investigation of the effect of alumina on thermite reation propagation for thermal plug and abandonment of oil wells

Thermite has been considered as a potential alternative for the wellbore plug and abandonment process. This new technology, thermal P&A, may substitute cementation as a cheaper and more compelling material. In this way, different thermite systems and additives are being explored in this scenario. The present study aims to examine the effects of diluting the Fe2O3–2Al thermite system with alumina in search of a more controlled reaction by observing effects on total ejected mass, burning velocity, and temperature levels. Small-scale experiments were conducted where stainless-steel tubes were filled with the thermite system. Thermocouples welded to the tube's external surface allowed us to obtain the temperature profiles at different positions and the overall reaction propagation velocity. The 20 % diluted system suppressed the measured peak temperature, burning rate, and expelled mass of about 10%, 60%, and 45%, respectively, compared to a non-diluted system. Simplified numerical simulation assuming a zero-order kinetics mechanism presented consistent results with the experimental peak temperatures at most positions analyzed. The simulation revealed that the diluted system would not reach the aluminum vaporization temperature as observed in the non-diluted system. Still, instead, it would be limited to the alumina melting temperature of 2327 K. In summary, the diluted system showed substantial reductions in peak temperature, burning rate, and expelled mass, indicating potential cost-effective and controlled applications in Thermal P&A processes.

Analysis of Springback Characteristics of Bending Unloading for Stainless Steel tubes

Stainless steel tubes are widely used in piping systems in aviation, aerospace and other high-tech fields because of their high strength, excellent corrosion and high-pressure resistance, and good resistance to high-temperature oxidation. This paper takes 304 stainless steel pipe as the research object, based on ABAQUS finite element platform, the springback behaviour of stainless steel pipe in the process of precise bending and forming has been studied in depth. The results show that: pipe bending unloading bending springback angle increases with the increase of the bending angle. The results of the study have important theoretical and practical significance for improving the accurate forming and springback of stainless steel tube bending.

Impact response of stainless steel tube locally-strengthened by concrete-filled steel tube

This paper proposes a novel stainless-steel tube locally strengthened by a concrete-filled steel tube to resist impact loads. A drop hammer impact test system was used to determine the failure modes, impact forces, and displacement responses of the strengthened tubes under an impact load. The effects of the strengthening length and thickness of the concrete and outer steel tubes on the impact responses of the strengthened tubes were investigated. The impact resistance was found to improve with an increase in the thickness of the concrete and outer steel thickness. The test results also indicated that the strengthened tubes exhibited a flexural failure mode with a combination of local and global deformations. An analytical model for predicting the dynamic responses of the locally strengthened tubes was established based on an equivalent two-degree-of-freedom (TDOF) model. The analytically predicted results were compared with the experimental results, and the good consistency between these two results demonstrated the accuracy of the established analytical model.

A Study of PLA Thin Film on SS 316L Coronary Stents Using a Dip Coating Technique.

The dip coating process is one of the recognized techniques used to generate polymeric coatings on stents in an easy and low-cost way. However, there is a lack of information about the influence of the process parameters of this technique on complex geometries such as stents. This paper studies the dip coating process parameters used to provide a uniform coating of PLA with a 4-10 µm thickness. A stainless-steel tube (AISI 316L) was laser-cut, electropolished, and dip-coated in a polylactic acid (PLA) solution whilst changing the process parameters. The samples were characterized to examine the coating's uniformity, thickness, surface roughness, weight, and chemical composition. FTIR and Raman investigations indicated the presence of PLA on the stent's surface, the chemical stability of PLA during the coating process, and the absence of residual chloroform in the coatings. Additionally, the water contact angle was measured to determine the hydrophilicity of the coating. Our results indicate that, when using entry and withdrawal speeds of 500 mm min-1 and a 15 s immersion time, a uniform coating thickness was achieved throughout the tube and in the stent with an average thickness of 7.8 µm.

Measurements of atmospheric C10–C15 biogenic volatile organic compounds (BVOCs) with sorbent tubes

Abstract. Biogenic volatile organic compounds (BVOCs; e.g. terpenes) are highly reactive compounds typically present at sub-parts-per-billion mole fractions in the air. Due to this, their measurements are challenging and they may suffer losses during sampling, storage and analyses. Even though online measurements of BVOCs are becoming more common, the use of sorbent tubes is expected to continue because they offer greater spatial coverage compared to online measurements, and no infrastructure (e.g. electricity, housing/shelter with stable temperature and humidity, sampling lines) is required for sampling. In this study, the performance of an offline technique for the measurement of BVOCs based on sorbent tube sampling was evaluated. Tested compounds included eight monoterpenes, five sesquiterpenes and five oxygenated BVOCs, which are generally either directly emitted (1,8-cineol, linalool, bornyl acetate) or oxidation products (nopinone and 4-acetyl-1-methylcyclohexene). Two sorbent materials (Tenax TA and Carbopack B) and four tube materials (stainless steel (SS), SilcoNert 1000, glass and glass-coated SS) were used. The laboratory evaluations determined the storage stability, breakthrough volumes, suitable tube materials, recovery from ozone scrubbers and particulate filters, and sampling efficiency. In addition, an intercomparison between two laboratories was conducted. No multibed configurations were tested. Of the sorbent materials Tenax TA showed acceptable results for these BVOCs, while with Carbopack B losses and increases in some compounds were detected. Studied compounds were found to be stable in Tenax TA tubes for at least 1 month at −20 and at +20 ∘C. Breakthrough tests indicated that α- and β-pinene have clearly lower breakthrough volumes in the Tenax TA tubes used (4–7 and 8–26 L, respectively) than other terpenes (&gt; 160 L). SS, SilcoNert 1000 and glass were all shown to be suitable tube materials. Results from Tenax TA sorbent tube sampling agreed with online sampling for most compounds. Heated SS tubes, sodium thiosulfate filters and KI/Cu traps were found to be suitable ozone scrubbers for the studied BVOCs. Tested particle filters had a greater impact on limonene (relative difference &lt; +7 %) than on α- and β-pinene (relative difference ±2 %). The laboratory intercomparison of α- and β-pinene measurements showed that in general, measured values by the two laboratories were in good agreement with Tenax TA.

Circular recycled aggregate concrete-filled stainless steel tube stub columns after exposure to fire: Experiments, simulations, and design

This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions.

A Study on Defect Detection of Dissimilar Joints in Cu-STS Tubes Using Infrared Thermal Imaging of Induction Heating Brazing

We proposed a novel detection method for identifying joint defects in the brazing process between copper tubes and stainless steel using a convolutional neural network (CNN) model. The brazing joints were created using high-frequency induction heating equipment, and infrared thermal imaging cameras were employed to capture the thermal data generated during the jointing process. The experiments involved 15.88 mm diameter copper tubes commonly used in plate heat exchangers, stainless-steel tubes, and filler metal containing 20% Ag. The thermal data were obtained with a resolution of 80 × 80 pixels per frame, resulting in 4796 normal joint data and 5437 defective joint data collected over 100 high-frequency induction-heating brazing experiments. A total of 10,233 thermal imaging data were categorized into 6548 training data, 1638 validation data, and 2047 test data for the development of the predictive model. We designed CNN models with varying hyperparameters, specifically the number of kernel filters and nodes, to evaluate their impact on detection performance. A comparative analysis revealed that a CNN model structure, exhibiting 98.53% accuracy and 99.82% recall on test data, was the most effective. The selected CNN-based defect prediction model demonstrated the potential of using CNN models to discern joint defects in tube configurations that are challenging to identify visually. This study opens avenues for applying CNN-based models for detecting imperfections in complex tube structures.

Post-fire behaviour and resistances of square recycled aggregate concrete-filled stainless steel tube stub columns

Experimental and numerical studies on the cross-section compressive behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns after exposure to fire are reported in this paper. An experimental programme was firstly carried out on twelve stub column specimens with three recycled coarse aggregate replacement ratios (0%, 35% and 70%) after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The test results, including load–end shortening curves, failure loads and failure modes, were presented, with the initial compressive stiffness and confinement effect analysed. The experimental programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions. Based on the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as specified in the European code, Australia/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to square RACFSST stub columns after exposure to fire. The evaluation results generally revealed that the European code and Australian/New Zealand standard led to a good level of design accuracy, while the American specification resulted in slightly conservative post-fire cross-section compression resistance predictions.