Elbow Pipe Research Articles

Effect of welded joint imperfection on the load-carrying capacity of pipe elbows subjected to in – plane bending moment

The defects in pipe elbows can, depending on their size and position, affect the integrity and safe service, as well as deformation ability of the piping systems in exploitation. Incompletely filled groove, which is the type of defect examined here, was observed by ultrasonic measurement on the pipeline in the regulation system of the hydro power plant Djerdap. Three-dimensional finite element analysis is performed using Simulia Abaqus software package. First, the models with dimensions of the defects observed by non-destructive examination are formed. Stress and strain fields for different loading types are shown and commented. The influence of the defect dimensions on the pipe elbow load-carrying capacity is determined through plastic collapse loads, which are obtained from bending moment - rotation angle diagrams. Twice elastic slope (TES) technique is applied. Additionally, some more severe defects are considered, in the form of sharp pre-cracks at the bottom of the defect; plastic collapse loads are also determined for these geometries. Both opening and closing bending moments are taken into consideration and the results are discussed and compared to two closed-form solutions from the literature. The influence of the boundary conditions applied for examination of the pipe elbows is commented.

Experimental study on the amplitude characteristics and propagation velocity of dynamic pressure wave for the leakage of gas-liquid two-phase intermittent flow in pipelines

Intermittent flow is one of the most complex flow patterns in gas-liquid two-phase flow in pipelines. The leakage of pipeline intermittent flow poses a threat to the operating safety. In order to improve the application of acoustic method to gas-liquid two-phase leakage detection, the amplitude characteristics and propagation velocity of dynamic pressure wave of intermittent flow for gas-liquid two-phase pipeline leakage were investigated. Experiments with conditions of superficial liquid velocity (vsL) from 0.57 m/s to 1.06 m/s, superficial gas velocity (vsG) from 0.3 m/s to 4.47 m/s, leakage aperture from 4 mm to 9 mm were carried out, and the characteristics were studied by time-domain analysis, frequency-domain analysis and time-frequency analysis. The propagation velocity formula of dynamic pressure wave in two-phase medium was fitted based on Levenberg-Marquardt algorithm, and the propagation velocity of straight pipe and elbow pipe was discussed. The experimental results indicate that the peak-to-peak value of dynamic pressure wave measured by sensor within 4.25 m increases during top or mid sustained leakage when leak aperture is larger than 4 mm in elongated bubble flow and 6 mm in slug flow. The amplitude of sustained leakage dynamic pressure increases as gas flow rate increases. The low frequency energy of signal increases immediately when leakage occurs, the energy of signal mainly concentrates at 0–15 Hz, the frequency amplitude of sustained leakage signal is much higher than normal flow signal and leak occur signal. As the gas volume fraction β increases from 0.23 to 0.75, the dynamic pressure propagation velocity decreases from 33.13 m/s to 26.5 m/s and then increases from 26.5 m/s to 66.25 m/s. The propagation velocity increases when it flows through an elbow pipe section. The results are meaningful for further study of two-phase pipeline slug flow leakage detection and location.

Seismic fragility analysis of a coupled tank-piping system based on artificial ground motions and surrogate modeling

The catastrophic consequences of recent NaTech events triggered by earthquakes highlighted the inadequacy of standard approaches to seismic risk assessment of chemical process plants. To date, the risk assessment of such facilities mainly relies on historical data and focuses on uncoupled process components. As a consequence, the dynamic interaction between process equipment is neglected. In response to this gap, researchers started a progressive integration of the Pacific Earthquake Engineering Research Center (PEER) Performance-Based Earthquake Engineering (PBEE) risk assessment framework. However, a few limitations still prevent a systematic implementation of this framework to chemical process plants. The most significant are: (i) the computational cost of system-level simulations accounting for coupling between process equipment; (ii) the experimental cost for component-level model validation; (iii) a reduced number of hazard-consistent site-specific ground motion records for time history analyses.In response to these challenges, this paper proposes a recently developed uncertainty quantification-based framework to perform seismic fragility assessments of chemical process plants. The framework employs three key elements: (i) a stochastic ground-motion model to supplement scarcity of real records; (ii) surrogate modeling to reduce the computational cost of system-level simulations; (iii) a component-level model validation based on cost-effective hybrid simulation tests. In order to demonstrate the potential of the framework, two fragility functions are computed for a pipe elbow of a coupled tank-piping system.

Assessment by finite element modelling of the mechano-electrochemical interaction at corrosion defect on elbows of oil/gas pipelines

The assessment of corrosion defects to determine their effect on pipeline integrity is essential for pipe managers to develop a scientific maintenance strategy. In this work, a nonlinear finite element (FE) model coupled with multi-physical fields was developed to study the mechano-electrochemical (M-E) synergistic effect at an external corrosion defect on X100 pipeline elbow. The results indicated that bending radius has an apparent effect on the burst pressure of the corroded pipe elbow. However, anodic and cathodic reactions was insensitive to bending radius under normal working pressures. Pipes elbows with corrosion defects located in the intrados have a lower burst pressure than those in the extrados and central line crowns. When the deformation or stress generated at the corrosion defect was elastic, the synergistic mechano-electrochemical interaction effect was insignificant. However, when the depth of the defect or the applied internal pressure of the elbow was sufficient to produce a local plastic strain in the corroded region, the corrosion reaction of the local steel at the defect was remarkably enhanced. Under multiaxial stress, the corrosive behaviour of steel in the defective area involved numerous local galvanic batteries, with the anode located in the high-stress zone and the cathode in the lower-stress zone. Anodic polarisation was found to occur in high-stress zone, which accelerated local corrosion.

Experimental study on the influence of inlet distortion on the performance of single suction centrifugal pump

As a renewable energy source, water energy is indispensable in hydropower generation, and centrifugal pump is widely used in hydroelectric generation. But the centrifugal pump usually uses elbow pipe inflow due to the limitation of installation space, and the inflow distortion will lead to the decrease of pump performance and the increase of vibration. In this paper, the influence rule of inflow distortion on external characteristics and pressure pulsation of centrifugal pump was analyzed. The research results show that the inflow of elbow pipe will lead to the decrease of the head and efficiency of the centrifugal pump, which will decrease by 0.68m and 1.5% at the maximum under the design condition. The increase of bend angle will increase the pressure pulsation at the inlet of the centrifugal pump, which has an influence on the pressure pulsation around the volute at different positions, especially the pressure pulsation intensity at the tongue position significantly increases. The research in this paper can provide reference for the design and safe operation of inlet pipeline in practical engineering.

Rupture of an Industrial GFRP Composite Mitered Elbow Pipe.

This paper examines the immature rupture of glass fiber reinforced plastic composite (GFRP) mitered elbow pipes. The GFRP composite mitered elbow pipe’s lifespan was twenty-five years; however, the pipes in question experienced immature failures, resulting in the reduction of their lifetimes to seven, nine, and ten years, respectively. The GFRP cooling water mitered elbow pipe’s service conditions operate at a pressure of up to 7 bar and temperatures between 15–36 °C. The root cause of failure was determined using visual inspection, analytical, microstructural, mechanical characterizations, and chemical analysis. The initial visualization inspection revealed an improper joint between the composite overwrapped and the straight pipe sections. Mechanical properties along the axial, hoop and 45° from the axial direction were obtained. The results from the analytical analysis indicated that the elbow might withstand the operating pressure depending on the quality factor, which was confirmed to be low due to the elbow joint’s improper fabrication process. As evidence of this, the numerical analyses’ results indicated that the safety factor in withstanding the operating pressure of 5 bar is dropped down in the radial region where the thickness is reduced to simulate the failure zone. This study’s findings recommend that thickness of less than 15 mm be reinforced using overwrapped composites. It is recommended for future installations that the fabrication process be appropriately monitored and controlled and avoids using 45°/−45° fiber orientation and multiple layers of chopped strand mat glass fiber.

Fourier Expansion Number를 적용한 Beam 요소 기반 유한요소해석모델을 이용한 배관계 탄소성 해석 기법

This study proposes a method for confirming the seismic integrity based on the strain of piping systems mainly used in power plants through finite element analysis. The piping system of power plants plays a vital role in connecting the major components of the system. Under earthquake conditions, strain is accumulated due to cyclic loads, and the critical location of strain accumulation due to fatigue failure is found to be the pipe elbows. To confirm the system response, it is necessary to extend the conventional finite element analysis model to the plastic domain and perform seismic transient analysis. Therefore, in this study, a method was proposed for performing an elasto-plastic analysis using the finite element analysis model based on the beam element used in the existing design evaluation. By applying the cross-sectional deformation effect in the elasto-plastic analysis to the existing beam element, the Fourier expansion number could be used to determine the sectional degree of freedom. Through case studies for various pipes, the feasibility of simulating the accumulated plastic strain and critical location using the proposed parameter setting was confirmed. Thereafter, the methodology was verified through application to the surge line geometry of a nuclear power plant. Consequently, using the proposed method, the finite element model containing the beam element with a deformable section effect could well simulate the critical location and determine the accumulated plastic strain value with a difference of 11 % in comparison with the solid element analysis result in the case study and a difference of 26 % in comparison with the surge line analysis result.

Guiding temperature waves with graded metamaterials

Temperature waves exist in many practical scenarios such as pulse heat sources and periodic temperature fluctuations, which have broad applications for thermal nondestructive detection. However, it is still challenging to guide temperature waves in irregularly shaped pipes because temperature waves might be strongly scattered. To solve the problem, we propose a scheme to guide temperature waves with graded metamaterials that have continuous parameter variations in space. Since graded metamaterials can ensure the same phases of thermal wavefronts despite different spatial distances, temperature waves can propagate in irregularly shaped pipes without scattering. We then demonstrate an elementary unit to realize the right-angle bending of temperature waves. Experimental suggestions are also provided to design the elementary unit with common materials and layered structures. We further combine the elementary units together to realize three practical functions including obstacle avoidance, thermal periscope, and reverse bending. These results have potential applications for thermal imaging and sensing in elbow pipes.

Finite element analysis of 90 degree pipe elbow sustained stress indices

Paper deals in-depth with the topic of sustained stress indices applicable to 90° elbows based on non-linear finite element analysis models. A comprehensive overview of the existing literature sources is given in the first part of the paper, showing that there are little sources which deal specifically with this topic and that the ones that do exist result in important scatter of the results. As a result, more than few of the existing sources are non-conservative in their nature. Dedicated non-linear finite element studies have been performed on shell and solid models which are used in conjunction with the regression analysis in order to obtain explicit equations which can be used to calculate both in- and out-plane sustained stress indices in 90° pipe elbows, which can then be used in the typical pipe stress analysis. Newly proposed equations prove to be a good fit for the numerical data, showing little deviation as shown by the correlation parameters presented in the paper. Final part of the paper presents a dedicated section on the high wall thickness elbows and shows the relationship between elbow wall thickness and maximum stress location. It is shown that beyond certain thickness, the maximum stress location shifts from the typical failure location (i.e., side wall) to the locations which are not typically expected (i.e., intrados or even away from elbow). This shifting may have an important effect on the theoretical models which assume failure location.

An implicit numerical scheme for cyclic elastoplasticity and ratcheting under plane stress conditions

The paper reports the development of an implicit numerical scheme for plane stress cyclic elasto-plasticity, capable of integrating a wide range of hardening rules, and simulating multi-axial ratcheting in metal structural components. Constitutive relations account for von Mises yielding in combination with mixed hardening. Emphasis is given to the kinematic hardening part, which is described with an advanced multiple back-stress model suitable for multi-axial material ratcheting simulation. The constitutive equations are integrated implicitly, and the accuracy of the algorithm is assessed via iso-error maps. Two main novelties of the algorithm refer to the incremental update of the internal variables through the solution of a single scalar equation, and the explicit formulation of the consistent tangent moduli. The numerical scheme is implemented within the finite element environment as an external material subroutine, and its computational efficiency is demonstrated through the simulation of large-scale experiments on pipe elbows. Using the proposed computational framework, two kinematic hardening rules are employed to simulate the elbow response with emphasis on local strain amplitude and accumulation (“ratcheting”). The good comparison between numerical and experimental results demonstrates the computational efficiency of the numerical scheme and highlights some key issues concerning multi-axial ratcheting simulation.

Gas–Solid Erosion Wear Characteristics of Elbow Pipe With Corrosion Defects

Abstract Corrosion and erosion are the main factors of pipes failure. Erosion wear characteristics of elbow pipe with corrosion defect are investigated in this paper. Initially, the erosion result of nondefect elbow pipe is calculated and compared to elbow pipe with corrosion defect. An elliptical erosion area with a V-shaped dent occurs at the extrados due to the particles' impact. The uniform corrosion defects change the structure of the pipe's inner surface. Therefore, the defect areas are more prone to be impacted by particles and then more severe erosion occurs. The maximum erosion rates of corrosion defect and noncorrosion area synchronously reach the maximum value as the corrosion defect located at 55 deg. The larger the particle mass flow rate is, the more severe the elbow pipe erosion is. As the flow rate increases, erosion rates of corrosion area and noncorrosion area increase, while the maximum erosion rate of corrosion area occurs at 55 deg. Structural parameters of corrosion defects affect the erosion. As the distance between two corrosion defects increases, the maximum erosion rate of lower corrosion defect increases. Considering the location, structure, and number of corrosion defect, a larger corrosion defect located in the middle of extrados has a worse effect on elbow pipe safety.

방향과 위치에 따른 배관 엘보우의 기계적 물성 불균일성 평가

배관 엘보우에서 기계적 물성의 불균일성을 파악하기 위해서, SA403 WP316 스테인리스강(SS)과 SA234 WPB 탄소강(CS) 엘보우를 대상으로 시편 방향과 원주방향 위치에 따른 인장시험을 상온과 운전온도에서 수행하였다. 시험 결과, 시험온도와 엘보우 종류에 관계없이 방향에 따른 기계적 물성 차이는 크지 않지만, 엘보우에서 원주방향 위치에 따른 기계적 물성 차이는 뚜렷하였다. SA403 WP316 SS 엘보우는 곡관부 측면에서 최대 항복강도와 최소 연신율을 보였으며, 외륜에서 최소 항복강도와 최대 연신율을 보였다. SA234 WPB CS 엘보우는 측면과 외륜에 비해 내륜에서 뚜렷이 높은 항복강도와 낮은 연신율을 보였으며, SA403 WP316 SS 엘보우에 비해 원주방향 위치에 따른 기계적 물성의 편차가 컸다. 원주방향 위치에 따른 기계적 물성의 차이는 각 엘보우의 제작 공정에 따른 미세조직 차이에 기인하는 것으로 확인되었다.

Computational investigation of non-uniform magnetic field on thermal characteristic of nanofluid stream inside 180∘ elbow pipe

The thermal efficiency of the heat exchanger is substantial in chemical and mechanical systems. The presence of the non-homogeny magnetic field considerably enhances the heat rate of nanofluid stream. In this exploration, the presence of the non-uniform magnetic intensity on the heat rate of nanofluid stream is noted inside the [Formula: see text] elbow pipe. FVM is used to model the flow characteristics and temperature distribution through the [Formula: see text] elbow pipe. Our major focus is to demonstrate the main influences of the non-uniform FHD on flow stream and heat transfer of nanofluid in various inlet velocities and magnetic intensities. Achieved outcomes display that growing the magnetic intensity from 1e + 6 to 4e + 6 enhances the average Nusselt number about 30%. Our findings show that increasing the inlet velocity to Re = 100 decreases the magnetic effects about 17% on the heat transfer growth.

Ratcheting assessment of corroded elbow pipes subjected to internal pressure and cyclic bending moment

The present study aimed to study ratcheting strains of corroded stainless steel 304LN elbow pipes subjected to internal pressure and cyclic bending moment. To this aim, spherical and cubical shapes corrosion are applied at two depths of 1 mm and 2 mm in the critical points of elbow pipe such as symmetry sites at intrados, extrados, and crown positions. Then, a Duplex 2205 stainless steel elbow pipe is considered as an alternative to studying the impact of the pipe materials, due to its high corrosion resistance and strength, toughness, and most importantly, the high fatigue strength and other mechanical properties than stainless steel 304LN. In order to perform numerical analyzes, the hardening coefficients of the materials were calculated. The results highlight a significant relationship between the destructive effects of corrosion and the depth and shape of corrosion, so that as corrosion increases, the resulting destructive effects increases as well, also, the ratcheting strains in cubic corrosions have a higher growth rate than spherical corrosions. In addition, the growth rate of the ratcheting strains in the hoop direction is much higher across the studied sample than the axial direction. The highest growth rate of hoop strain was observed at crown and the highest growth rate of axial strains occurred at intrados position. Altogether, Duplex 2205 material has a better performance than SS 304LN.

FBG-Based Nonintrusive Monitoring Method for the Impact Force on 90° Pipe Elbow

Elbow pipe is one of the components in pipeline transportation. The impact force caused by the liquid flow in the pipe elbow produces the strain on the wall. So, the monitoring of impact force can be realized by measuring strain. This article developed a new nonintrusive method to detect the impact force on the 90° horizontal bend pipe by measuring the axial strain and the hoop strain on the outer wall of the pipe elbow. Taking three typical cross-sections (i.e. $\theta = 0^{\circ }$ , $\theta = 45^{\circ }$ , and $\theta = 90^{\circ }$ ) of the pipe elbow as examples, the impact forces were adjusted by the inlet velocity in the bend pipe based on a specific relationship. The nonintrusive method was based on fiber Bragg grating (FBG) sensors, measuring the axial strain and hoop strain on the outer wall of the elbows caused by the impact force accurately. In this article, the theoretical study and numerical analysis by ANSYS Fluent based on the finite-element method were detailed in our initial work. Then, strain gauges were used to verify the effectiveness and accuracy of FBG monitoring. The results demonstrated that the FBG sensors had good performance on the strain measurement and were sensitive to the variation of the impact force caused by different velocity levels. The lightweight and easy networking of this method make it have a wide range of application prospects.

Assessment of corroded API 5L X52 pipe elbow using a modified failure assessment diagram

Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component.

Using XFEM to Predict the Damage with Temperature of the Steel Pipe Elbows under Bending and Pressure loading

The pipes, during their service, are subjected to accumulated loads such as internal pressure and that of the soil. The latter considerably accelerate their damage. In this work, the bending moment stress of API 5L X70 category steel elbows under thermo-mechanical behavior and in the presence of pressure were studied. We used FEM (finite element method) through the numerical calculation code ABAQUS and the XFEM technique for structural damage while using solid elements as a structure. Our objective is to evaluate the response and resistance capacity of the steel elbow by its location in the tube–elbow-tube system under a mixed loading of pressure and moment for all scenarios. It is based on a single standardized dimensioning of the elbow (diameter and thickness). The effect of several parameters has been studied such as the type of loading and the pressure levels, which are clearly conditioned by the level of damage. Numerical damage results are presented by moment-rotation curves. They illustrate the variation in damage as a function of these effects which act simultaneously.

Hybrid Simulation of Structure-Pipe-Structure Interaction within a Gas Processing Plant

AbstractThough often overlooked, the impact of seismic transient ground deformation on natural gas (NG) pipes can be highly adverse. Particularly, pipe elbows may undergo excessive in-plane bending...

Numerical implementation of bounding-surface model for simulating cyclic inelastic response of metal piping components

The present paper describes the numerical implementation of the bounding-surface cyclic-plasticity model in a finite element environment, suitable for simulating the structural behavior of metal components subjected to strong cyclic loading. The model is based on the Dafalias-Popov “bounding surface” concept, equipped with appropriate enhancements that allow for simulation of repeated, alternate inelastic deformation. The numerical implementation is performed using an elastic-predictor/plastic-corrector method. Special features of the model are examined, focusing on the influence of several material parameters on cyclic material response. The model is also employed for simulating laboratory physical experiments. First, stress-controlled and strain-controlled experiments are simulated, in strip specimens made of regular (mild) steel and high-strength steel. Upon appropriate calibration from these material tests, the model is employed in a finite element model for predicting the mechanical response of a large-scale physical experiment on a steel pipe elbow. The very good comparison between the experimental and the numerical results demonstrates the suitability of the numerical model for large-scale structural computations and its capability of predicting the mechanical response of structural metal components under severe repeated loading, with emphasis on the simulation of ratcheting.

Розрахунок просторового турбулентного потоку в каналах авіаційних газотурбінних двигунів

This work is devoted to the development of approaches to the numerical simulation of 3D turbulent gas flows in different ducts of aircraft gas turbine engines, in particular in inlet device ducts. Inlet devices must provide large values of the total pressure recovery factor and flow uniformity at the engine compressor inlet. The aim of this work is the verification of the operability of a technique developed earlier for the calculation of the parameters of a 3D turbulent flow in complex-shape ducts. The basic approach is a numerical simulation of 3D turbulent gas flows on the basis of the complete averaged Navier¬–Stokes equations and a two-parameter turbulence model. The proposed technique of numerical simulation of a 3D gas flow was tested by calculating a 3D laminar flow in a square pipe bent at a right angle. The calculated flow pattern is in satisfactory agreement with the experimental data on the flow structure in a pipe elbow reported in the literature. Based on a numerical simulation of a 3D turbulent flow in the air duct of one of the air intake configurations for an aircraft turboprop engine, the efficiency of that configuration is assessed. The calculated flow parameter nonuniformity at the air intake outlet, i. e., at the compressor inlet, is compared with that obtained earlier for another air intake configuration for the same engine. It is pointed out that the air intake configuration considered earlier provides a much more uniform flow parameter distribution at the engine compressor inlet. On the whole, this work shows that the quality of subsonic air intakes for aircraft gas turbine engines can be assessed using the proposed numerical technique of 3D gas flow simulation. The results obtained may be used in the aerodynamic improvement of inlet devices for aircraft engines of different types.