Static Internal Pressure Research Articles

Monitoring of inside surface crack growth by strain measurement of the outside surface: A feasibility study

Cracks detected by in-service inspections are not always removed when they are judged to be not hazardous according to fitness-for-service evaluations. In order to secure the integrity of the cracked components, it is important to confirm that the cracks do not grow notably beyond the growth prediction conducted for the judgement. However, due to the limitation of accuracy of size determination by the current inspection techniques such as ultrasonic testing, it is difficult to know how much the cracks have grown since their previous measurement. In this study, feasibility of a crack growth monitoring method (outside strain monitoring method) was evaluated by finite element analyses and experiments. When a pipe deforms elastically due to internal pressure, the strain at its outside surface increases. The magnitude of strain near the crack differs from that at an uncracked portion, and the difference depends on the crack size. Elastic finite element analyses were performed for cracked pipes under internal pressure for various crack sizes. It was shown that, by measuring the change in strain at the outside surface of the cracked pipe, the crack size and how much the crack grew can be identified. In the experiment, cracked pipes were subjected to static internal pressure and strains for eight cracks of different sizes were measured. It was revealed that the maximum error was 0.44 mm for the estimation of crack depth of 4 mm and 0.28 mm for the estimation of 1 mm crack growth in the depth direction.

Characterizing airflow through fabric air dispersion system using a porous media model

No existing diffuser models may be used to effectively describe the fabir air dispersion system (FADS), a new ventilation terminal made of ploymer. A porous media model was proposed to describe FADS in present work. And the corresonpongding mathematical model was developed for the airflow through FADS. The characteristics of airflow through FADS was predicted using the commercial software FLUENT with the standard k − ɛ turbulent model. The simulation results were well matched with the corresponding experimental value suggesting that it is feasible to describe FADS using the porous media model. Results showed that the air in the central zone flows forward with a decreasing velocity along the flow direction, and the air in the porous fibre eventually creeps out through its tiny-size holes at very low speed in the direction perpendicular to the porous fibre. The airflow close to the FADS is evenly distributed along the flow direction with a very low velocity. It is also concluded that the internal total pressure and dynamic pressure decrease slightly, while the internal static pressure increases slightly with a decaying increment along the flow direction of the FADS.

On the prediction of long‐term creep‐failure of GRP pipes in aqueous environment

AbstractThe aim of this work was to study the long‐term failure of GRP (Glass fiber‐reinforced Polymer) pipes under the influence of moisture absorption. These pipes are used in water transportation, which has an important effect on the mechanical properties of the polymeric matrix. The GRP pipes are usually tested under ring deflection or internal pressure conditions. This study presents and analyzes experimental creep‐rupture data obtained from standard test methods under ring deflection conditions. This loading configuration simulates in laboratory the conditions verified in a subsoil installation. The creep testing was carried out under constant dead weight on unconditioned and preconditioned samples in a submerged condition. The diametrical deflection of samples was measured periodically, and the time to failure of each sample was recorded. The main purpose of this work was to determine the short and long‐term rupture energies of GRP pipes and assess the influence of moisture preconditioning on those values. The observed failure mode was always the same. It was concluded that the energy at failure decreases with time. The influence of the preconditioning on the creep‐rupture of GRP pipes was considered negligible. Different time‐dependent failure models were described and used for long‐term extrapolation of the experimental data. The maximum strain at failure decreased about 12% from 0.1 to 1,000 hr of creep testing. Furthermore, data extrapolation to 50 years predicts a reduction of strength of about 60%, founded on the most conservative time‐dependent failure criterion. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

플랜지 형성 액압성형시 공정변수에 따른 성형 특성

Hydroforming is the technology that utilizes hydraulic pressure to form tube or sheet materials into desired shapes inside die cavities. Tube hydroforming provides a number of advantages over the conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength. In many case, hydroformed parts have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. In this study for the numerical process design FE analysis was performed with DYNAFORM 5.5. Die parting angle and circumferential expansion ratio was optimized. With optimized condition, bulge and hydroforming experiments to form flange were performed. Forming characteristic at various pressure conditions was analyzed and optimized internal pressure condition was evaluated. The results show that flanged parts can be successfully produced by tube hydroforming process.

高クロム鋼溶接部のクリープ強度特性と実機溶接配管の内圧曲げクリープ試験(<特集>第14回動力・エネルギー技術シンポジウム)

Creep tests on 9 Cr and 12 Cr steels welded joints were conducted under internal pressure conditions as well as uniaxial stress conditions. For both materials, failure occurs at fine grain HAZ region under long time region, which means type IV damage. SEM observation was carried out on internal pressure test specimens of the welded joints. It was found that density of creep voids is higher in mid-thickness of the HAZ portion than that in outer and inner surfaces. Furthermore, a recently developed demonstration test facility, which can load bending forces and internal pressure on actual boiler pipes at high temperatures, is briefly introduced in this presentation.

Failure analysis of (±55°)3 filament wound composite pipes with an inclined surface crack under static internal pressure

Abstract This study conducts failure analysis of filament wound glass reinforced plastic (GRP) pipes made of E-glass/epoxy with an inclined surface crack under open-ended internal pressure. Test specimens are composed of six antisymmetric layers with (±55°)3 winding angles. Tests have been performed at seven different crack angles: 0 ° , 15 ° , 30 ° , 60 ° , 45 ° , 75 ° , and 90 ° , with crack-to-thickness ratio of a / t = 0.50 . The burst strengths of the specimens were determined, and the dependence of the burst strength on the crack angle was examined.

Dynamics and destruction of internally pressurized incompressible hyper-elastic spherical shells

Dynamical response and destruction of incompressible hyper-elastic spherical shells under a periodic or a constant internal pressure are examined within the framework of finite elasto-dynamics. When a static uniform internal pressure is applied, the spherical shell is subject to an unstable aspherical deformation after the initial stable spherical inflation. When a periodic or a constant internal pressure is applied, an exact differential relation between the deformation of the internal boundary and the pressure is obtained. The displacement response curves, the power spectrum curves, the phase portrait and the Poincaré maps are given by numerical computation. It is shown that the spherical shell will undergo nonlinear periodic oscillation if a constant internal pressure is suddenly applied. It will undergo nonlinear quasi-periodic oscillation if a periodic internal pressure is applied. At the same time, the destruction or the structural catastrophes may be admitted and it is discussed in details.

A Comparison of the Flow Structures and Losses Within Vaned and Vaneless Stators for Radial Turbines

This paper details the numerical analysis of different vaned and vaneless radial inflow turbine stators. Selected results are presented from a test program carried out to determine performance differences between the radial turbines with vaned stators and vaneless volutes under the same operating conditions. A commercial computational fluid dynamics code was used to develop numerical models of each of the turbine configurations, which were validated using the experimental results. From the numerical models, areas of loss generation in the different stators were identified and compared, and the stator losses were quantified. Predictions showed the vaneless turbine stators to incur lower losses than the corresponding vaned stator at matching operating conditions, in line with the trends in measured performance. Flow conditions at rotor inlet were studied and validated with internal static pressure measurements so as to judge the levels of circumferential nonuniformity for each stator design. In each case, the vaneless volutes were found to deliver a higher level of uniformity in the rotor inlet pressure field.

B113 高クロム鋼溶接部のクリープ強度特性と実機溶接配管の内圧曲げクリープ試験(保全管理・補修/材料強度・破壊評価,OS6 保全・設備診断技術)

Creep tests on 9Cr and 12Cr steels welded joints were conducted under internal pressure conditions as well as uniaxial stress conditions. For both materials, failure occurs at fine grain HAZ region under long time region, which means type IV damage. SEM observation was carried out on internal pressure test specimens of the welded joints. It was found that density of creep voids is higher in mid-thickness of the HAZ portion than that in outer and inner surfaces. Furthermore, a recently developed demonstration test facility, which can load bending forces and internal pressure on actual boiler pipes at high temperatures, is briefly introduced in this presentation.

Transient dynamic response of initially stressed composite circular cylindrical shells under radial impulse load

Free and forced vibration of multilayer composite circular cylindrical shells under transverse impulse load as well as combined static axial loads and internal pressure was investigated based on first order shear deformation theory. The boundary condition was considered to be simply supported. Displacement components are the product of functions of position and time. The function of position components of displacement was obtained in the form of double Fourier series. Solution to the equilibrium equations of free vibration of the shell was obtained using Galerkin method. In the analysis of transient dynamic response, the impulse load was in the form of sine pulse, which is applied on a rectangular area. The function of time is obtained using the results of free vibration and convolution integral. Finally time response of displacement components is derived by mode superposition method. The effect of fiber orientation, axial load, internal pressure and some of the geometrical parameters on the time response of the shells has been shown. The results show that the dynamic responses are governed primarily by the natural period of the structure which is affected by applied axial load and internal pressure. The accuracy of the analysis has been examined by comparing the results with those available in the literature.

Stamina of a non-gasketed flange joint under combined internal pressure and axial loading

The performance of a bolted flange joint is characterized mainly by its ‘strength’ and ‘sealing capability’. A number of numerical and experimental studies have been conducted to study these characteristics under internal pressure loading conditions alone. However, limited work is found in the literature under conditions of combined internal pressure and axial loading. The effect of external, axial loading pressure being unknown, the optimal performance of the bolted flange joint cannot be achieved. Current design codes do not address the effects of axial loading on structural integrity and sealing ability. To study joint strength and sealing capability under combined loading conditions, an extensive experimental and numerical study of a non-gasketed flange joint was carried out. Actual joint load capacity was determined at both design and test stages with the maximum external axial loading that can be applied for safe joint performance. Experimental and numerical results have been compared and overall joint performance and behaviour is discussed in detail.

Structural Integrity Estimates of Steam Generator Tubes Containing Wear-Type Defects

It is requested that steam generator tubes with defects exceeding 40% of wall thickness in depth should be plugged to sustain all postulated loads with appropriate margin. This critical defect size has been determined based on a concept of plastic instability, however, which is known to be too conservative for some locations and types of defects. The application of this concept may even cause premature retirement of steam generator tubes. In reality, a reliable structural integrity estimation for steam generator tubes containing a defect has received increasing attention. Although several guidelines have been developed and used for assessing defect containing tubes, most of these guidelines are focused on stress corrosion cracking or wall-thinning phenomena. Because some of steam generator tubes fail due to fretting and so on, specific integrity estimation schemes for relevant defects are required. In this paper, more than a hundred three-dimensional finite element analyses of steam generator tubes under internal pressure condition are carried out to simulate the failure behavior of steam generator tubes with specific defect configurations: elliptical wear-type, tapered wedge-type, and flat wear-type defects. After investigating the effect of key parameters such as defect depth, defect length, and wrap or tapered angle on equivalent stress across the ligament thickness, burst pressure estimation equations are proposed in relation to material strengths. Predicted burst pressures agreeded well with the corresponding experimental data, so the proposed equations can be used to assess the structural integrity of steam generator tubes with wear-type defects.

Residual stress analysis and fatigue of multi-pass welded tubular structures

The purpose of this study is to investigate the residual stresses near the weld root and the weld toe for multi-pass welded tube-to-plates. Two different tubular joint configurations were studied; a three-pass single-U weld groove for maximum weld penetration and a two-pass fillet (no groove) welded tube-to-plates for minimum weld penetration. A 2D axi-symmetric finite element model was developed to calculate the temperature distribution, HAZ, penetration depth and the residual stress distribution for the sequentially coupled thermo-mechanical analysis. The calculated residual stresses was compared with experimental results and showed qualitatively good agreement. Torsion fatigue tests were performed in order to study crack propagation from the weld root, lower and upper weld toe in mode III. Some of the tube structures were loaded with a static internal pressure in order to separate the root crack and initiate the crack growth in mode III. Another batch was PWHT and fatigue tested, in order to study the influence of residual stresses.

Application of a combined heating system for the warm hydroforming of lightweight alloy tubes

A combined heating system – comprised of an induction coil plus a heating element – has been applied to the warm hydroforming of aluminum alloy tubes. For the rapid heating of tubes, a specially designed induction heating system has been developed as the main heating source. The induction heating system uses a high frequency induction coil in order to concentrate the energy into the tube and reduce energy losses. However, heat produced by the induction heating system was unequally distributed over the length and circumference of the tube, and as a result, the temperature distribution was non-uniform. An additional heating element was inserted into the inside of the tube to increase temperature uniformity by maintaining the forming temperature and reducing the heat lost to the tooling. Warm hydroforming tests with the combined heating system exhibit increased hydroformability, producing more uniform bulging in the tubes. The processing parameters such as internal pressure, axial feeding and heating conditions have also been successfully optimized.

Flow and pressure characteristics within a screw compressor

The angle-resolved mean and turbulence characteristics of the axial air flow inside a screw compressor with both male and female rotors have been measured, using a laser Doppler velocimeter (LDV) with high spatial and temporal resolution at different radial and axial locations for speeds of 800-1600 rpm, discharge pressures of 1-1.6 bar and discharge temperatures of 33-90°C. The velocity measurements were performed through a special transparent window fixed near the discharge port. The results confirmed the ability of the LDV technique to characterise the flow inside the compressor working chamber; an angular resolution of 1.5° was able to fully describe the velocity field within the machine. The flow variation between the different working chambers was established as well as the spatial variation of the axial mean velocity and turbulence velocity fluctuation within the working chamber.The effect of discharge port opening on the axial mean and RMS velocities was found to be significant near the leading edge of the rotors causing an increase in the mean and RMS velocities of the order of 4.2Vp in mean (where Vp is the axial pitched velocity) for male rotor and 5.4Vp for, female rotor and this effect is less pronounced on the flow near the root of the rotor. Moreover, to obtain a better understanding of the flow motion, a high sampling rate pressure transducer was used to provide the internal angular static pressure variation. These measurements are used to validate the in-house CFD model of the fluid flow within twin screw compressors which, in turn, allows reliable optimisation of various compressor designs.

A comparative study on energy consumption for HVAC systems of high-tech FABs

The unique system dynamics of five different HVAC designs including the RCU (recirculation air unit) system, the MAU (make-up air unit) + RCU system, the MAU + RCU + FCU (fan coil unit) system, the MAU + axial fan system, and the MAU + FFU (fan-filter unit) system for a typical 200 mm DRAM wafer fabrication plant are discussed and compared. The energy performances of the RCU system, the MAU + RCU system, the MAU + RCU + FCU system, and the MAU + axial fan system are 3.8, 1.19, 1.12 and 1.08, respectively, folds that of the most efficient MAU + FFU system. The MAU + axial fan system exhibits slight less efficient in energy performance, compared with the MAU + FFU system. The most influential factor on energy performance between these two systems is the design of the noise abatement system, especially the pressure drop of the silencer, which dominates almost half of the internal static pressure of axial fan. When the static pressure of silencer of the MAU + axial fan system is reduced to 50 Pa, energy consumption of these two systems is comparable. Bypassing a certain portion of FAB return air to mix with make-up air can maximally reduce 50% of energy consumption of the RCU system.

Influence of moisture absorption on creep of GRP composite pipes

The aim of this work was to study the influence of moisture absorption on long-term creep behavior of composite pipes. These pipes are used in water transportation which has an effect on the mechanical properties and on the polymeric composite matrix. Glass-reinforced thermosetting plastics (GRP) pipes are typically tested under ring deflection and/or internal pressure conditions. In this study, experimental creep data obtained from standard test methods under ring deflection conditions were used. This loading configuration simulates in the laboratory the external loads induced in a sub-soil installation. The creep tests were performed on unconditioned and preconditioned specimens. Long-term mechanical behavior prediction based on short-term test data is necessary for design. For this purpose dynamic mechanical thermal analysis (DMTA) tests were performed on specimens machined from GRP pipes. Ten specimens were tested as delivered. Another 10 specimens were conditioned in water at room temperature and another 10 were conditioned in water at 50 ∘ C , until saturation. The time–temperature superposition principle (TTSP) and extrapolation using a power law relation were applied to DMTA data for long-term creep prediction. Both methods were found to be conservative, i.e. predict higher stiffness reduction than the creep tests. Although creep tests were quite dissimilar from the DMTA tests, extrapolation using a power law relation appeared to be accurate enough to be used as a predictive tool for project design. Finally, comparisons of the DMTA data for different environment conditioning enabled the assessment of the hygrothermal effects on modulus.

High temperature zirconia oxygen sensor with sealed metal/metal oxide internal reference

Potentiometric internal reference oxygen sensors are created by embedding a metal/metal oxide mixture within a yttria-stabilized zirconia oxygen-conducting ceramic superstructure. Three metal/metal oxide systems based on Pd, Ni, and Ru are examined. A static internal reference oxygen pressure is produced inside the reference chamber of the sensor at the target application temperature. The metal/metal oxide-containing reference chamber is sealed within the stabilized zirconia ceramic superstructure by a high pressure (3–6 MPa) and high temperature (1200–1300 °C) bonding method that initiates grain boundary sliding between the ceramic components. The bonding method creates ceramic joints that are pore-free and indistinguishable from the bulk ceramic. The Pd/PdO-based oxygen sensor presented in this study is capable of long-term operation and resistant to the strains of thermal cycling. The current temperature limit of the device is limited at 800 °C. As the sensor does not require reference gas plumbing there is flexibility in placement of sensors in a combustion stream. Furthermore, the sensor assembly process readily lends itself to miniaturization.

표면 마모결함을 고려한 증기발생기 세관의 구조건전성 평가

During the last two decades, several guidelines have been developed and used for assessing the integrity of a defective steam generator (SG) tube that is generally caused by stress corrosion cracking or wall-thinning phenomenon. However, as some of SG tubes are also failed due to fretting and so on, alternative failure estimation schemes are required for relevant defects. In this paper, parametric three-dimensional finite element (FE) analyses are carried out under internal pressure condition to simulate the failure behavior of SG tubes with different defect configurations; elliptical wear, tapered and flat wear type defects. Maximum pressures based on material strengths are obtained from more than a hundred FE results to predict the failure of SG tube. After investigating the effect of key parameters such as defect depth, defect length and wrap angle, simplified failure estimation equations are proposed in relation to the equivalent stress at the deepest point in wear region. Comparison of failure pressures predicted by the proposed estimation scheme with corresponding burst test data showed a good agreement.

Analysis of Titanium-matrix Orthotropic Cylindrical Shell Subjected to Thermomechanical Loading

A titanium-matrix orthotropic cylindrical shell with the principal direction of orthotropy following a parallel constant angle helix, has been studied when it is subjected to uniform loading conditions of internal pressure, axial load and pure twisting moment. Nondimensional parameters pertaining to loading and deformations have been calculated and results plotted. The results obtained can be usefully applied in robotic actuators where lightweight considerations with high strength are of prime importance. The study is further extended to investigate the effect of temperature on the deformations. Through parametric studies, deformation patterns are calculated and plotted that are unique to orthotropy. In most of the cases, it is observed that deformation patterns are same, but deformation is increasing with temperatures.