Influence Of Internal Pressure Research Articles

Effect of Pipe Bend Shape Imperfections on Creep-fatigue Crack Growth

This study is concerned with assessing the structural integrity of power plant pipes which operate under creep and fatigue conditions. In the manufacturing process of pipe bends it is difficult to avoid thickening on the inner radius of the pipe bend and thinning on the outer radius of the pipe bend. The cross section of the bend also becomes non circular due to bending process; this tends to cause ovality in pipe bends. The acceptability of pipe bends is based on the induced level of shape imperfections considered. The influence of internal pressure, operation time and shape imperfections of pipe bend on stress-strain redistributions and creep-fatigue crack growth rate was investigated using FE-analysis and experiments at elevated temperature. Full-size stress-strain state analysis of pipe bend was performed for different stage of lifetime under considering loading conditions. As a result it was found that the effect of ovality and thinning cross sections interaction is significant and is a function of creep time. The tensile tests were performed for determination the main mechanical properties of pipe bend's material after loading history. The smooth and compact specimens were cut out from four tension and compression critical zones of the same pipe bend with given ovality and thinning cross sections as well as operating time. The creep-fatigue crack growth rate tests were performed on special designed program test-cycle. Comparison between new and old materials shows tensile properties of 12Cr1MoV steel have degraded by long-term high-temperature service; while comparison between the creep-fatigue crack growth rate characteristics indicates that they are a function of the critical zone positions in the considered pipe bend. A new parameter for characterization of the crack growth resistance for power plant materials and structures under elevated temperature is used in the form of creep stress intensity factor.

Analysis of the vibration behavior of FGM cylindrical shells including internal pressure and ring support effects based on Love-Kirchhoff theory with various boundary conditions

This paper presents the study on vibration behavior of functionally graded material (FGM) cylindrical shell with the effects of internal pressure and ring support. The FGM properties are graded along the thickness direction of the shell. The FGM shell equations with internal pressure and ring support are established based on strain-displacement relationship using Love-Kirchhoff shell theory. The governing equations of motion were solved by using energy functional and by applying Ritz method. The boundary conditions represented by end conditions of the FGM cylindrical shell are simply supported-simply supported (SS-SS), clamped-clamped (C-C), free-free (F-F), clamped-free (C-F), clamped-simply supported (C-SS), free-simply supported (F-SS), free-sliding (F-SL) and clamped-sliding (C-SL). To check the validity and accuracy of the present method, the results obtained are compared with those available in the literature. The influence of internal pressure, ring support position and the effect of the different boundary conditions on natural frequencies characteristics are studied. These results presented can be used as important benchmark for researchers to validate their numerical methods when studying natural frequencies of shells with internal pressure and ring support.

Stress Analysis of Shallow Sea Gas Pipelines

Shallow sea gas pipelines usually operate in complicated and changeable regional environments and can generate corresponding stresses and displacement under the influence of internal pressures, earthquakes, waves and other loadings. An unevenly distributed stress will lead to shallow sea gas pipeline failure easily. In order to ensure the safety of pipeline, it is necessary to research the stress conditions of the shallow sea gas pipeline and check whether it can meet the safety requirements or not. In this study, we analyze the stress conditions of shallow sea gas pipelines of two laying modes in XX areas using stress analysis software CAESAR II, discuss the loading conditions under the operating condition and determine the position of the key point where pipeline damage is most likely to happen, the bend pipe. The comprehensive experiments show that underground method more secure than the sea-bed method, it greatly improves the reliability of the shallow sea pipeline running. Our research provides a theoretical basis for the construction of shallow sea gas pipelines.

Free vibration of functionally graded truncated conical shells under internal pressure

The influence of internal pressure on the free vibration behavior of functionally graded (FG) truncated conical shells are investigated based on the first-order shear deformation theory (FSDT) of shells. The initial mechanical stresses are obtained by solving the static equilibrium equations. Using Hamilton’s principle and by including the influences of initial stresses, the free vibration equations of motion around this equilibrium state together with the related boundary conditions are derived. The material properties are assumed to be graded in the thickness direction. The differential quadrature method (DQM) as an efficient and accurate numerical tool is adopted to discretize the governing equations and the related boundary conditions. The convergence behavior of the method is numerically investigated and its accuracy is demonstrated by comparing the results in the limit cases with existing solutions in literature. Finally, the effects of internal pressure together with the material property graded index, the semi-vertex angle and the other geometrical parameters on the frequency parameters of the FG truncated conical shells subjected to different boundary conditions are studied.

Low Cycle Fatigue Behavior and Seismic Assessment for Pipe Bend Having Local Wall Thinning-Influence of Internal Pressure

One of the concerned technical issues in the nuclear piping under operation is pipe wall thinning caused by flow accelerated corrosion. This paper focuses on influence of internal pressure on low cycle fatigue life of pipe bends with local wall thinning and evaluation of safety margin against seismic loading in order to apply the obtained knowledge to the nuclear piping. In-plane bending fatigue tests under several constant internal pressure magnitudes were carried out using carbon steel pipe bends with local wall thinning at the extrados. Also finite element analysis, code-based seismic evaluation and fatigue analysis based on calculated strain range were carried out. Obtained main conclusions are as follows: (1) the tested pipe bends with local wall thinning at the extrados have a strong resistance against fatigue failure based on nuclear seismic piping design in Japan at least up to 12 MPa. That is, the tested pipe bends with severe local wall thinning (eroded ratio = 0.5 and eroded angle = 180 deg) at the extrados have margins against fatigue failure, even though the wall thickness is less than the code-required minimum value based on the nuclear piping seismic design in Japan. (2) Combination of the conventional B2 index and the Ke factor provided in the JSME Design and Construction Code, which is referred by JEAC 4601-2008 overestimates fictitious stress amplitude, when sum of the primary and secondary stress is much greater than 3 Sm.

Influence of Suspension Length on the Mechanical Response of Submarine Flexible Pipe under Internal Pressure and Transverse Load

According to the actual structure of submarine flexible pipe, considering the combined effect of internal pressure and transverse load by wave-current flow that is based on 50 year return period wave statistics data of Cheng Dao sea area, ANSYS finite element model of flexible pipe is established. The influence of internal pressure and suspension length on the axial stress of steel wire reinforcement layer and the Mises stress of rubber layer was analyzed. Comparatively, suspension is the main cause for the failure of steel submarine pipeline, but could hardly lead to the failure of submarine flexible pipe, which shows that flexible pipe is stronger applicable for submarine pipeline.

Effects of Ring Support and Internal Pressure on the Vibration Behavior of Multiple Layered Cylindrical Shells

This paper presents the study on natural frequency characteristics of a multiple layered cylindrical shell with ring support under internal pressure. The multiple layered cylindrical shell configuration is formed by three layers of isotropic materials where the inner and outer layers are stainless steel and the middle layer is aluminum. The isotropic multiple layered shell equations with ring support and internal pressure are established based on first order shear deformation theory (FSDT). The governing equations of motion were employed by using energy functional and by applying the Ritz method. The boundary conditions represented by end conditions of the multiple cylindrical shell are simply supported-simply supported (SS-SS), clamped-clamped (C-C), free-free (F-F), clamped-free (C-F), clamped-simply supported (C-SS), and free-simply supported (F-SS). The influences of internal pressure and ring support and the effect of the different boundary conditions on natural frequencies characteristics are studied. The results are validated by comparing them with those in the literature.

Numerical Study on Mechanical Response of Steel Wire Wound Reinforced Rubber Flexible Pipe under Internal Pressure

According to the actual structure of steel wire wound reinforced rubber flexible pipe, using the finite element software ANSYS, 3-D finite element model of flexible pipe is established. For the mechanical response of flexible pipe under internal pressure, the comparison on the result by numerical calculation, the static loading test and the result by analytic method shows that the 3-D finite element model of flexible pipe is rational. Moreover, based on the finite element model of flexible pipe, the influence of internal pressure, spanning length and reinforced steel wire diameter on the axial stress of the innerest steel layer and the Mises stress of the innerest rubber layer is analyzed.

Forming Limit of Magnesium Alloy Sheet in Hydromechanical Deep Drawing

The experimental research on the hydromechanical deep drawing of AZ31B magnesium alloy sheet was conducted in this paper. The deformation behaviors and the influence of internal pressure on its formability are investigated, moreover, the fracture behaviors of the obtained workpieces are discussed. The experimental results show that the formability of AZ31B magnesium alloy sheet in hydromechanical deep drawing is poorer than that in mechanical deep drawing at room temperature because the internal pressure fails to work effectively due to the weak plastic deformation capacity and the premature fracture of the kind alloy.

Investigation on Corner Filling Process in Hydroforming of Thin-Walled Aluminum Alloy Tubular Part with Polygonal Sections

Bursting at the corner during calibration stage is a popular failure mode in hydroforming process of tubular part with polygonal sections. Bending of thin-walled tube is also a big obstacle for hydroforming process, especially for aluminum alloy tube. In this paper, a thin-walled aluminum alloy tubular part with polygonal sections was hydroformed with the step of hydro-bending, preforming and hydroforming. The influence of internal pressure during bending was discussed. Corner filling process of a symbol section was analyzed, such as filling sequence, corner shape changing and thickness distribution. The corner with less expansion ratio contacted the die first and thickness reduction is smaller. Bursting occurred in the corner with big expansion ratio. If the corner is located in the outer side of bending arc, danger of bursting is more severe. The key factor is to maintain a sound shape for the section before calibration to keep the expansion distribution evenly. [doi:10.2320/matertrans.MF201114]

Surface Accuracy Measurement of a Novel Inflatable Antenna by Photogrammetry

Surface accuracy measurement of a 1.5m-diameter novel inflatable antenna formed by 18 aluminum-coated Kapton® gores is investigated using digital photogrammetry. More than five hundred 3mm-diameter round retro-targets were glued on the surface of the antenna, and their 3D coordinates at different internal pressures of the antenna were obtained using V-STARS digital photogrammetric system. According to the measured data, the influence of internal pressure of the antenna on its surface accuracy was analyzed, and the deviation of gores’ center line and ribs on the surface were also studied. The results show that the internal pressure has significant influence on the surface accuracy of the antenna, especially near the antenna’s dome.

Analytical and numerical analysis for the FGM thick sphere under combined pressure and temperature loading

Thermo-mechanical analysis of functionally graded hollow sphere subjected to mechanical loads and one-dimensional steady-state thermal stresses is carried out in this study. The material properties are assumed to vary non-linearly in the radial direction, and the Poisson’s ratio is assumed constant. The temperature distribution is assumed to be a function of radius, with general thermal and mechanical boundary conditions on the inside and outside surfaces of the sphere. In the analysis presented here, the effect of non-homogeneity in FGM thick sphere was implemented by choosing a dimensionless parameter, named βi (i = 1, . . . , 3), which could be assigned an arbitrary value affecting the stresses in the sphere. It is observed that the solution process for βi(i = 3) = −1 are different from those obtained for other values of βi (i = 1, . . . , 3). Cases of pressure, temperature, and combined loadings were considered separately. It is concluded that by changing the value of βi (i = 1 . . . 3), the properties of FGM can be so modified that the lowest stress levels are reached. The present results agree well with existing results. Using FEM simulations, the analytical findings for FGM spheres under the influence of internal pressure and temperature gradient were compared to finite element results.

Numerical Simulation of High Inner-Pressure Hydroforming of T-Branch Tube

The paper studies the forming process of high inner-pressure hydroforming of T-branch tube by using DYNAFORM finite element simulation software based on its technology characteristics. First, the effects of different loading paths of key parameters(internal pressure, axial extrusion force, radial back force) on T-branch tube hydroforming process have been studied. The studies show that enough feed rate is essential to obtaining a certain branch height but excess feed rate can lead to the thickness seriously increased. The way of influence of internal pressure is contrary to radial back force, both excess internal pressure and slight radial back force can cause top branch thinned or fractured. If branch height is too low, radial back force will obstruct the extension of tube and productions cannot be compliance with design requirements. Second, the effects of coefficient of friction and radius of round angles on forming quality of T-branch tube have been discussed. The studies show that forming quality is better when the coefficient of friction is smaller or radius of round angles is larger.

The Influence of Internal Pressure on Ductile Fracture from a Circumferential Surface Defect on a Pipe

The Influence of Internal Pressure on Ductile Fracture from a Circumferential Surface Defect on a Pipe

Finite element analysis of buried steel pipelines under strike-slip fault displacements

The present paper investigates the mechanical behavior of buried steel pipelines, crossing an active strike-slip tectonic fault. The fault is normal to the pipeline direction and moves in the horizontal direction, causing stress and deformation in the pipeline. The interacting soil–pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behavior and special conditions of contact and friction on the soil–pipe interface. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80), the paper focuses on the effects of various soil and pipeline parameters on the structural response of the pipe, with particular emphasis on identifying pipeline failure (pipe wall wrinkling/local buckling or rupture). The effects of shear soil strength, soil stiffness, horizontal fault displacement, width of the fault slip zone are investigated. Furthermore, the influence of internal pressure on the structural response is examined. The results from the present investigation are aimed at determining the fault displacement at which the pipeline fails and can be used for pipeline design purposes. The results are presented in diagram form, which depicts the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. A simplified analytical model is also developed to illustrate the counteracting effects of bending and axial stretching. The numerical results for the critical strain are also compared with the recent provisions of EN 1998-4 and ASCE MOP 119.

The effect of hydrostatic pressure fields on the dispersion characteristics of fluid-shell coupled system

The effect of hydrostatic pressure on the vibration dispersion characteristics of fluid-shell coupled structures was studied. Both fluid-loaded cylindrical shells and fluid-filled cylindrical shells were considered. Numerical analysis was applied to solve the dispersion equations for shells filled with or loaded with fluid at various hydrostatic pressures. The results for external pressure showed that non-dimensional axial wave numbers are nearly independent when the pressure is below the critical level. The influence of internal pressure on wave numbers was found significant for the real branch s=1 and the complex branches of dispersion curves. The presence of internal pressure increased the cut on frequencies for the branch s=1 for high order wave modes.

The influence of internal pressure on hardness of a pipe element

The influence of internal pressure on hardness of an elastic finite pipe element has been determined. This hardness increases under pressure under both compressive and stretching axial strains.

New Analysis for The FGM Thick Cylinders Under Combined Pressure and Temperature Loading

An analytical solution for computing the radial and circumferential stresses in a FGM thick cylindrical vessel under the influence of internal pressure and temperature is presented in this paper. It has been assumed that the modulus of elasticity and thermal coefficient of expansion were varying through thickness of the FGM material according to a power law relationship. Nevertheless the value of the Poisson ratio was taken as constant throughout the material. In the analysis presented here the effect of non-homogeneity in FGM thick cylinder was implemented by choosing a dimensionless parameter, named β, which could be assigned an arbitrary value affecting the stresses in the cylinder. Using Maple 9.5, distribution of stresses in radial and circumferential directions for FGM cylinders under the influence of internal pressure and temperature gradient were obtained. Graphs of variations of stress versus radius of the cylinder were plotted for different values of β. Cases of pressure, temperature and combined loadings were considered separately. It was concluded that by changing the value of β, the properties of FGM could be so modified that the lowest stress levels were reached. The stresses which were produced in FGM and homogeneous material with the same boundary conditions were compared to obtain the optimum value of β.

Influence of internal pressure on hydroforming of double handles crankshaft

The hydroforming process of a double handles crankshaft with the biggest expansion ratio up to 54% is studied by means of simulation and experiment in this paper. The effects of loading paths during hydroforming process on the failure modes are analyzed. The simulation results show that the part can be formed successfully with the feeding pressure selected in the range from 65 to 75 MPa. A successful crankshaft component can be manufactured in the experiment as the internal pressure is 70 MPa. Folding back occurs as the internal pressure <65 MPa and bursting occurs as the internal pressure >75 MPa. The most serious thinning occurs in the top of crankshaft handle. The maximum thickness appears in the area of the opposite to crankshaft handle. The maximum of thinning rate by the simulation is about 11%, which is close to 10% that is obtained in experiment.

Limiting equilibrium of a spherical shell nonuniform across the thickness and containing a surface crack

The problem of limiting equilibrium of an elastoplastic spherical shell nonuniform across the thickness and containing a surface crack is reduced to a system of singular integral equations. The algorithm of numerical solution of this system takes into account the conditions of plasticity of thin shells and the conditions of boundedness of stresses in the vicinity of the crack. The influence of internal pressure and the mechanical parameters of functionally inhomogeneous material on the opening displacement of the surface crack and the length of plastic strips on its continuation is investigated.