Tube Supports Research Articles

Investigations of In-Plane Fluidelastic Instability in a Multispan U-Bend Tube Array—Part I: Tests in Air Flow

Abstract The tubes in the U-bend region of a recirculating type of nuclear steam generator are subjected to cross-flow of a two-phase mixture of steam and water. There is a concern that these tubes may experience flow-induced vibration, including the damaging effects of fluidelastic instability. This two-part series of papers presents the results of flow-induced vibration experiments performed by Canadian Nuclear Laboratories for the Electric Power Research Institute (EPRI) using the Multi-Span U-Bend test rig. The tube bundle is made of 22 U-bend tubes of 12.7 mm (0.5 in.) diameter, arranged in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5. The test rig was equipped with variable clearance flat bar supports at two different locations to investigate a variety of tube and flat-bar support configurations. The primary purpose of the overall project was to study the occurrence of in-plane (or streamwise) fluidelastic instability in a U-tube bundle with flat-bar tube supports with clearances or preloads. Initially, the test rig was configured for tests in air-flow using an industrial air blower. Then tests with two-phase refrigerant (R-134a) were performed. Part I of this two-part series describes the test rig, experimental setup and some of the challenges encountered, and the results of experiments with air flows. Part II will present results of tests using refrigerant two-phase flows.

Annular-flow-induced vibrations of a simply-supported tube in a finite-length narrow-gap support

The stability behavior of a simply-supported tube subjected to narrow annular flow in a finite-length gap support at the mid-length of the tube is experimentally investigated. For the experiments, a simply-supported tube and several finite-length gap supports were made considering different gap sizes. Several diffuser angles at the downstream of the support were also tested, since it is believed that the pressure recovery at the exit of the support is much more important than pressure loss at the entrance of the support. In this study, we observed that the tube lost its stability by flutter, and that the critical flow velocity at which the tube lost stability was dependent on the annular gap size and the diffuser angle. Interestingly, the tube with the diffuser angle of 10° lost stability at a lower flow velocity than with the diffuser angle of 20°, for relatively narrow gaps that are in the range of 0.018 to 0.042 gap-to-tube diameter. Differently, for the largest gap of 0.138 gap-to-tube diameter, the diffuser angle of 20° resulted in a lower instability flow velocity. We concluded that there may be different instability mechanisms depending on diffuser angle and related to the narrowness of the gap.

Novel porous ceramic tube-supported polymer layer membranes for acetic acid/water separation by pervaporation dewatering

New polymer-ceramic hybrid membranes consisting of sulfonated polybenzimidazole (sPBI) coating layer on porous ceramic tube supports have been successfully developed for acetic acid/water separation by selective pervaporation removal of water from the liquid mixtures. The enabling preparation procedure that were critical to form crack/defect-free polymer layer coated intimately on the wall surface of ceramic support tubes is reported. Air humidity during dip coating, the dying method, and pre-mixing of polymer solution were found critical to the intimate adherence, crack-free, and uniformity of the coating membrane layer on the wall of porous ceramic tube. Our hybrid membranes have shown a high-flux selective separation performance data: 2.5–10 times higher flux than previously reported state-of-the-art value (~0.15 LMH) for free-standing sPBI polymer membranes. Also, the ceramic tube-supported membranes provide better mechanical ruggedness, pervaporation stability, and a unique platform for large scale multi-tube membrane module applications.

Experimental study on cross flow induced vibration response of four-span straight tube bundle with TSP or AVB supports

Flow induced vibrations in steam generator and other heat exchangers can result in tube failure and lead to large economic losses. Tube supports such as tube support plates (TSP) or anti-vibration bars (AVB) are commonly used to suppress the flow induced vibration. Knowledge on the tube dynamic characteristics and instability phenomena under these support conditions is therefore essential, when fluid flows across the multi-span tubes. In this paper, flow induced vibration of a four-span rotated triangular tube array with a pitch-to-diameter ratio of 1.4 under three sets of AVB or TSP supports is experimentally studied. Part of the middle segment of the tube is subjected to cross flow. The vibration displacements and frequency spectra of a tube on first row are analyzed. It was found that the vibration mode for four-span tube bundle with TSP is different from that of the tube supported by AVB when fluid elastic instability (FEI) happens. The effective FEI critical velocities for the tube with TSP and that with AVB is 6.8 m/s and 3.0 m/s, respectively. Five correlations for predicting the onset of FEI of the tube bundle tested are compared with experimental results. Weaver and El-Kashlan correlation (1981b) is best. The effective FEI critical velocities predicted by Weaver and El-Kashlan correlation (1981b) are 15% and 27% higher than the experimental results for tube with TSP and tube with AVB, respectively. The vortex shedding responses are analyzed for the two tube-support structures. The Strouhal number for non-resonant vortex shedding response is calculated and compared with expectations from literature. The turbulent buffeting response for tube under different supports are compared with each other and discussed.

Experimental identification of the fluid-elastic coupling forces on a flexible tube within a rigid square bundle subjected to single-phase cross-flow

The importance of fluid-elastic coupling forces in tube bundle vibrations is well documented and can hardly be over-emphasized, in view of their damaging potential. Even when adequate tube supports are provided to suppress fluid-elastic instabilities, the flow-coupling forces still affect the dynamical tube responses and remain a significant issue, in particular concerning the vibro-impact motions of tubes assembled using clearance supports. Therefore, the need remains for more advanced models of fluid-elastic coupling, as well as for experimental flow-coupling coefficients to feed and validate such models. In this work, we report an extensive series of experiments performed at CEA-Saclay leading to the identification of stiffness and damping fluid-elastic coefficients, for a 3×5 square tube bundle (D = 30 mm, P/D = 1.5) subjected to single-phase transverse flow, in a water test-loop. The bundle is rigid, except for the central tube which is mounted on a flexible suspension (two parallel steel blades) allowing for translation motions of the tube in the lift direction. The system is thus single-degree of freedom, allowing fluid-elastic instability to arise through a negative damping mechanism. The flow-coupling stiffness and damping coefficients, Kf(Vr) and Cf(Vr), are experimentally identified as functions of the reduced velocity Vr. The maximum value of the Reynolds number ranged from 105 to 2.16 105 (based on the maximum pitch velocity), according to the tested configuration. Identification is achieved on the basis of changes in tube vibration frequency and reduced damping as a function of flow velocity, assuming a constant fluid added mass. In the present experiments, coefficient identification is performed well beyond the instability boundary, by using active control, thereafter allowing exploration of a significant range of flow velocity. The modal frequency and the modal mass of the system are respectively modified by changing the tube suspension stiffness, and/or by adding a mass to the system. We can thus assert how the fluid-elastic coefficients change, for this configuration, with these two system parameters, all other parameters being kept constant. The results obtained from the configurations tested suggest that formulations for coefficient reduction may be improved, in order to better collapse the identified data.

Design Research and Application of D-shape Expansive Concrete-filled Steel Tube Supports in Roadway Support

In order to perfect the application of concrete-filled steel tube support (CFSTS) in roadway support, aiming at the shortcomings of the existing common CFSTS, this paper put forward the D-shape expansive concrete-filled steel tube support (D-ECFSTS). Firstly, this article uses the numerical simulation to carry on the optimization of circular steel tube, designs the D-shape steel tube, and carries on the comparative analysis of D-shape concrete-filled steel tube support (D-CFSTS) and circular concrete-filled steel tube support (CFSTS). Then, the scheme of expansive concrete is put forward, and the ratio of expansive concrete is tested by the test method. Finally, the D-ECFSTS was made by D-CFSTS and expansive concrete, then used in roadway support. The results show: The deformation of D-CFSTS is much smaller than that of circular CFSTS under the same load; The best ratio of expansive concrete includes that the ratio of cement, sand, gravel is 1:1.31:2.65, water cement ratio is 0.41, expansion agent ratio is 11% and water-reducing agent ratio is 0.5%; In the support of Pingdingshan coal mine roadway, the supporting effect of D-ECFSTS is much better than that of U36 support. So, D-ECFSTS is a good roadway support method.

Fabrication of SiO2–ZrO2 (50/50) membranes on the porous stainless steel-tube support for pervaporation

The SiO2–ZrO2 membranes were fabricated with silica–zirconia sols on a porous stainless steel-tube support (O.D. = 10 mm, length = 20 mm, 316L SUS, Mott Corp. USA) by a dipping–rolling–freezing–fast drying (DRFF) and/or soaking–rolling–freezing–fast drying (SRFF) method. After coating of SiO2–ZrO2 sol, single gas permeation characteristics (He, H2, and N2) for SiO2–ZrO2 membranes were evaluated at room temperature, and the pervaporation experiments were performed at a specified feed isopropyl alcohol concentration of 90 wt% at 50°C with silica–zirconia membranes. The morphology of surface and the cross sections of the membrane were investigated with FE-SEM analysis. Judging from FE-SEM analysis, the surface of silica–zirconia membrane on the PSS tube support was denser, and the number of surface defects considerably reduced than DRFF method, and the additional modification via the SRFF significantly diminished surface defects, which could not be avoided during the DRFF step. The membrane the silica–zirconia membrane showed hydrogen permeability under 10−7 mol m−2 s−1 Pa−1 and low water selectivity in the range of 10–23. The silica–zirconia membranes with a smooth surface on the stainless steel tube supports, was quite well prepared by the DRFF and SRFF method in this study.

Experiment and Application Study on the Load-Bearing Properties of Shallow Arch Circular Concrete Filled Steel Tube Support

Shallow arch circular concrete filled steel tube support has a good load-bearing capacity, which is used in soft rock roadway supporting to solve the problem of supporting instability and to reduce the amount of anti-invert excavation. In this paper, concrete filled steel tube supports of Φ168 ×6 are designed according to shallow arch circular concrete filled steel tube structures and their load-displacement curves, ultimate bearing capacity and support failure mode are especially tested in experiment. This shallow arch circular concrete filled steel tube support is also applied in very soft rock roadway supporting of No. 1 mine well of Chaganzhuoer in Xilinhot, Inner Mongolia and proved to be of good supporting effect. The shallow arch circular concrete filled steel tube support is of higher load-bearing capacity and of outstanding advantages in solving extremely soft rock roadway supporting problems, as is proved in both theoretical test and application.

Characterization of Effect of Support Structures in Laser Additive Manufacturing of Stainless Steel

Abstract Laser additive manufacturing (LAM) of stainless steel is a layer wisetechnology for fabricating 3D parts from metal powder via selectively melting powder with laser beam. Support structures play a significant role in LAM process as they help to remove heat away from the process and on the other hand hold the work piece in its place. A successful design of support structures can help to achievea building process fast and inexpensive with high quality. Aimof this study was to characterize the usability of two types of support structures: web and tube supports. Purpose of this studywas also to analyze how suitable they are in two industrial application cases: case for dental application and case for jewelry application. It was concluded that the removability of web supports was much better than tube supports. It was noticed that support structures are an important part of LAM process and they strongly affect the manufacturability and the end quality of the part.

Case Studies on Field Repairs of Stainless Steel Components in Refinery

Stainless steels (SS) possess excellent corrosion, creep and high temperature oxidation resistance and are invariably used in refinery for construction of heater tubes, tube supports, Heat exchanger bundles, piping and internal lining of pressure vessels. Ferritic stainless steel type 405 is used for column strip-lining, martensitic stainless steel type 410 is used for column trays and heater tubes and austenitic stainless steel family is used very extensively for lining, piping, heat exchanger, heater tubes and tube supports. On-stream and turnaround condition monitoring of plant and equipment are carried out for health assessment and mitigation of premature failure. However, catastrophic failures of stainless steel due to stress corrosion cracking, thermal fatigue and stress relaxation cracking are encountered in addition to bulging and cracking of strip-lining. Field repairs of these components are required to be done. Stainless steels are difficult to weld due to low thermal conductivity, higher coefficient of thermal expansion, fissuring and solidification cracking problem during welding. Lower heat input and fast cooling facilitate the welding process. Welding of service exposed stainless steels is more challenging, as it has already undergone metallurgical degradation. Welding of stainless steels is carried out using TIG and SMAW process with matching electrode after establishing the welding specification procedures and welders qualification. Field repairs of stainless steels components are also attempted with original procedures and in case of difficulties, a buttering layer of inconel (ERNiCr3) or ER 309Mo is provided on the welding surface before using matching electrodes. Quality assurance of weld joint is ensured by stage-wise inspection and non-destructive testing. Dye penetrant test of root run and radiographic examination of final weld joint are most common. Post weld heat treatment is done as per code requirement. This Paper highlights three case studies on field repairs of stainless steel components in refinery. 1. Welding procedure followed for repair of bulged and cracked SS 316 strip-lining and cladding on carbon steel backing material. It is a dissimilar welding of SS 316L with degraded carbon steel. 2. Field welding of SS 347 Piping components, which has undergone thermal relaxation cracking at fillet joints. 3. Welding repair of SS 310 cast heater tube support conforming to A 297 Gr HK 40. The Paper also presents brief failure analysis with reasons and remedies.

Fabrication and Cell Properties of Flattened Tube Segmented-in-Series Solid Oxide Fuel Cell-Stack Using Decalcomania Paper

In the segmented-in-series solid-oxide fuel cells (SIS-SOFCs), fabrication techniques which use decalcomania paper have many advantages, i.e., an increased active area of the electrode; better interfacial adhesion property between the anode, electrolyte and cathode; and improved layer thickness uniformity. In this work, a cell-stack was fabricated on porous ceramic flattened tube supports using decalcomania paper, which consists of an anode, electrolyte, and a cathode. The anode layer was <TEX>$40{\mu}m$</TEX> thick, and was porous. The electrolyte layers exhibited a uniform thickness of about <TEX>$20{\mu}m$</TEX> with a dense structure. Interfacial adhesion was improved due to the dense structure. The cathode layers was <TEX>$30{\mu}m$</TEX> thick with porous structure, good adhesion to the electrolyte. The ohmic resistance levels at 800, 750 and <TEX>$700^{\circ}C$</TEX> were measured, showing values of 1.49, 1.58 and <TEX>$1.65{\Omega}{\cdot}cm^2$</TEX>, respectively. The polarization resistances at 800, 750 and <TEX>$700^{\circ}C$</TEX> were measured to be 1.63, 2.61 and <TEX>$4.17cm^2$</TEX>, respectively. These lower resistance values originated from the excellent interfacial adhesion between the anode, electrolyte and cathode. In a two-cell-stack SOFC, open-circuit voltages(OCVs) of 1.915, 1.942 and 1.957 V and maximum power densities(MPD) of 289.9, 276.1 and <TEX>$220.4mW/cm^2$</TEX> were measured at 800, 750 and <TEX>$700^{\circ}C$</TEX>, respectively. The proposed fabrication technique using decalcomania paper was shown to be feasible for the easy fabrication of segmented-in-series flattened tube SOFCs.

Application Research on Concrete Filled Steel Tube Supports Supporting Technology in Stress Concentration Roadway

Part of the east wing belt roadway in -450 level east, NO.1 mining area, Dashu village coal mine, Jizhong Energy Fengfeng Group was under the 172102 working face’s stop mining coal pillar. The phenomenon of the stress concentration was obvious, the pressure of the roadway was large and the surrounding rock damaged severely. Concrete filled steel tube supports were used in stress concentration region. The supports type was φ194×8mm, and distance between supports was 800mm. They were of rapid construction speed, better supporting effect. The numerical simulation results also showed that the concrete filled steel tube supports can reduce deformation of the roadway surrounding rock in stress concentration region effectively.

250 直交流による円柱群の流れ方向振動に関する研究

The authors have studied the in-flow vibration phenomena of cylinder arrays caused by cross-flow in the low Reynolds number range around Re=800. This Reynolds number has been studied because it is the range where symmetric vortex shedding occurs. This report is our first trial to study the in-line fluidelastic vibration of cylinder arrays. In initial tests, the flow velocity was increased up to the maximum achievable level by the test equipment. However, it was found that the array's cantilever tube supports resulted in large static tube deflections due to static drag forces. The cylinder array tube supports have therefore been replaced by thin plates supported at both ends. The cylinders are set to be flexible both in the streamwise direction and the direction transverse to the flow. The obtained results of these two patterns are also compared with previous cantilevered data. The origin of the observed vibrations whether a self-induced mechanism or vortex shedding is discussed in detail.

Supporting Effect and Economic Benefit Analysis on New Type Concrete-Filled Steel Tube Supports

The finite element contrast model such as concrete filled steel tube support, U-steel support and hollow steel tube support were established with ANSYS software, combining with engineering practice and relative design scheme of concrete filled steel tube test, respectively analysis their influencing factors and mechanical properties such as support effect, bearing capacity and so on. The economic benefit of each support was been analysised by comprehensive comparison of the material using condition and mechanical performance. The results show that, comparing with traditional U-steel support, retractable concrete filled steel tube support is a new style support with high bearing capacity, a large variety of sizes, higher economic benefit, and hence fit to support the deep soft rock broken jointed rock mass.

解体建物における床サポート本数の合理化の提案

Bending moment of the slab caused by a load of a heavy machine under demolition work is usually defined less than allowable moment for temporary loading. The number and arrangement of tube supports are determined to meet the condition. If the plastic deformation of a slab is estimated with accuracy, the reasonable floor support system can be proposed. In this report, the results of measured axial forces of the supports in a 2 way slab are described, and the reasonable support system is proposed.

Short-period segmented-in-series solid oxide fuel cells on flattened tube supports

Segmented-in-series solid oxide fuel cells (SIS-SOFCs) were prepared on flattened-tube partially stabilized zirconia supports. The distinguishing characteristic of these cells was the short repeat period, 2.4 mm, and small active cell length, 1.3 mm, compared to ≈10 mm in previous SIS-SOFCs. The support tubes, formed by gelcasting, were bisque fired and then screen printing was used to sequentially deposit Ni-YSZ anodes, YSZ electrolytes, and Pt-YSZ composite interconnects. After high-temperature co-firing, LSM–YSZ and LSM cathode layers were screen printed and fired. Each flattened tube side had 12–16 individual cells. For testing, the open tube ends were sealed and humidified hydrogen flowed inside of the tubes; air was flowed over the outside of the tubes. Maximum total power at 800 °C was ≈8 W and maximum power density was ≈0.7 W cm −2, calculated using cell active area. Good stability was observed during a ≈650 h steady-state test. Excellent stability was also observed over ≈20 redox cycles.

Failure analysis of superheater tube supports of the primary reformer in a fertilizer factory

A failure analysis of superheater tube supports of the primary reformer in a local fertilizer factory is presented. A number of tube supports failed at approximately half of their designed service life. Following the failure, the factory was visited, and relevant information and samples were collected. The samples were investigated in the laboratory by chemical analysis, macro- and microhardness measurements, macro-and micrometallographic examinations, and X-ray diffractometry. The analysis showed the supports were fabricated from HH-type heat-resisting alloy and that the failure mode was high-temperature creep. The microstructure of the alloy showed the presence of massive intergranular as well as intragranular σ-phase and intragranular needle-shaped M23C6 carbides. It was also concluded from the formation of massive σ-phase in the tube that the failure was hastened because the supports were operating at approximately 800 °C. The alloy composition led to the formation of σ-phase under the operating conditions of the reformer, and the use of an alloy with a higher concentration of austenite-stabilizing element(s) could have avoided the failure.

The Thermal Hydraulics of Tube Support Fouling in Nuclear Steam Generators

It is hypothesized that the thermal-hydraulic environment plays a role in the fouling of tube supports in nuclear steam generators. Experiments were performed to simulate the thermal-hydraulic environment near various designs of supports. Pressure loss, local velocity, turbulence intensity, and local void fraction were measured to characterize the effect of the support. Fouling mechanisms specific to supports were inferred from these experimental data and from actual steam generator inspection results. An analytical model was developed to predict the rate of particulate deposition on the supports, to better understand the complex processes involved.This paper presents the following set of tools for assessing the fouling propensity of a given support design: (1) proposed fouling mechanisms, (2) criteria for support fouling propensity, (3) correlation of fouling with parameters such as mass flux and quality, (4) descriptions of experimental tools such as flow visualization and measurement of pressure-loss profiles, and (5) analytical tools.An important conclusion from this and our previous work is that the fouling propensity is greater with broached support plates, both trefoil and quatrefoil, than with lattice bar supports and formed bar supports, in which significant cross flows occur.

An assessment method for unstable vibration in multispan tube bundles

The flow external to the tubes in a heat exchanger tube bundle may cause large amplitude tube vibration. The most severe mechanism is a fluidelastic instability which can damage tubes in a matter of weeks or months. This mechanism has been the subject of many laboratory experiments and theoretical research over the past 30 years, and consequently, there is a body of data ready to be passed on to those involved in the design of heat exchangers. However, this data is not in a readily usable form because laboratory conditions are very different to those found in a typical heat exchanger where fluid properties vary considerably with location. In order to deal with these variations, an assessment equation is derived which takes into account the changing flow conditions along the length of a heat exchanger, the geometry of the tube support system and the dissipation of energy by the vibrating tubes. The assessment equation uses fluidelastic force coefficients. Unfortunately, there has only been a very limited attempt to measure these coefficients directly. Therefore, a method is developed which shows how these coefficients can be deduced from available measured data. This requires the existing data correlations for fluidelastic instability to be viewed in a fresh and more general manner. The heart of the assessment method is a modal analysis of the tubes. This modal analysis is undertaken in two stages and covers both the fluid forces that cause interactions between neighbouring tubes and the variations in tube amplitude controlled by the tube supports. The assessment equation makes the energy dissipation, expressed by a damping factor, the subject of the assessment equation. This is useful because damping data has a wide statistical spread, which introduces considerable uncertainty, and it is necessary to introduce a probabilistic approach when managing the technical risks of fluidelastic vibration.

On the Assessment of Through-Wall Circumferential Cracks in Steam Generator Tubes With Tube Supports

The assessment of steam generator tubes with defects is of great importance for the life extension of steam generators. Circumferential through-wall cracks are the most severe of all tube circumferential defects, and usually require plugging of the affected tubes. The assessment of the tubes with through-wall circumferential cracks or cracks projected to become through-wall can be conducted using the failure assessment diagram (FAD) approach. This approach requires the calculation of the stress intensity factor and the limit load. The available stress intensity factor and limit load solutions for cracked tubes do not include the constraining effect of the tube supports. In the present paper, it is shown that this can be overly conservative. Solutions for stress intensity factors and limit loads are presented for tubes with circumferential through-wall cracks including the effect from the tube support plates. Different values of support spacing are considered. Based on these solutions, the assessment of a typical steam generator tube is demonstrated.