Effect of welded joint imperfection on the load-carrying capacity of pipe elbows subjected to in – plane bending moment (original) (raw)
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Effect of Welded Joint Imperfection on the Integrity of Pipe Elbows Subjected to Internal Pressure
Tehnicki Vjesnik
Original scientific paper Since local defects reduce the load-carrying capacity and deformation ability of a piping system, an analysis is undertaken to quantify the influence of weld defects on integrity of the pipe elbows subjected to internal pressure. Incompletely filled groove is examined, because this type of defect was previously detected by ultrasonic measurement on the inner surface of the pipeline from a hydro-power plant. Three-dimensional finite element analysis is conducted using Abaqus software package. The influence of weld defect geometry (its depth, length and location) on the elbow integrity is determined. Additionally, decrease of load carrying capacity is determined for the case when a crack has initiated at the bottom of the defect. The influence of finite element type (hexahedral or tetrahedral) is examined. Utjecaj grešaka u zavarenom spoju na integritet cijevnih lukova izloženih djelovanju unutarnjeg tlaka Izvorni znanstvenu članak Imajući u vidu da lokalna o...
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Tehnicki vjesnik - Technical Gazette, 2020
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The Influence of the Internal Pressure and In-Plane Bending Moment Loadings on Pipe Bends
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Circular thin-walled pipe bends are frequently used as a key part in pipeline connection either in the vertical direction or the horizontal direction due to their high flexibility. The high flexibility of pipe bends is due to the ability of their cross-section to ovalize when subjected to internal pressure and/ or bending moments that lead to high-stress concentrations at bend locations within the pipeline system. Moreover, the surface geometric characteristics of bends may cause some unbalanced outward forces caused by the induced internal pressure loading only which leads to an outward resultant force that tends to straighten out the bend causing a rise within the deformations and stress levels. This phenomenon was known as "The Bourdon effect". In addition to that, external bending moment load acting on the pipe bends may result from either occasional loadings such as; seismic loads, soil settlement, and/ or secondary loadings exerted on the pipe due to thermal expansions resulted in additional stresses. These additional stresses resulting from bending loads acting on the pipe bend are accounted for in the design codes using stress intensification factors (i) and flexibility factors (K). These factors are presented in the current American code ASME B31.3.Although they have been derived for a 90-degree pipe bend subjected to in-plane closing bending moment with long bend radius(R), they cannot be used for other loading cases such as in-plane opening moment or out-of-plane bending moment. Previous studies showed that the direction of bending moment affected the distribution and magnitude of stress levels found on the bend. However, previous studies considered only small pipe sizes of NPS 16 (406mm) and smaller under bend angles of 90 degrees or less. This paper extended the investigation on smooth pipe bends with initial circular cross-sections and uniform wall thickness with large pipe size from NPS20 (508mm) up to NPS 72 (1829mm) under a wide range of bend angles (Ø)(from 30° up to 160°). The loading considered in this study is the internal pressure and the in-plane opening/closing bending moment. In this respect, an extensive parametric study is conducted using a numerical finite element analysis (FEA) simulation using ABAQUS software to model Pipe bends with different nominal pipe sizes (NPS), bend angles (Ø), bend wall thickness (t), and various bend radius (R). The results showed that as the bend angle increases, the flexibility of the bend increases as well leading to higher stresses on the pipe bend. Finally, from the finite element analysis results depicted through curves, it could be concluded that the codes do not cover the stress distribution for large pipe bends accurately.
Elasto-Plastic collapse analysis of pipe bends using finite element analysis
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Conference paper,When an external load is applied to one of its ends, a pipe’s bends cross section tends to deform significantly both in and out of its end plane. This shell type behaviour characteristic of pipe bends and mainly due to their curves geometry accounts for their greater flexibility. This added flexibility is also accompanied by stresses and strains that are much higher than those present in a straight pipe. The primary goal of this research is to study the elastic-plastic behaviour of pipe bends under out of plane moment loading. It is also required to study the effects of changing the value of the pipe bend factor and the value of the internal pressure on that behaviour and to determine the value of the limit moments in each case. The results of these analyses are presented in the form of load deflection plots for each load case belonging to each model. From the load deflection curves, the limit moments of each case are obtained. The limit loads are then compared to...
Mechanical Behavior of Steel Pipe Bends: An Overview
An overview of the mechanical behavior of steel pipe (elbows) is offered, based on previously reported analytical solutions, numerical results, and experimental data. The behavior of pipe bends is characterized by significant deformations and stresses, quite higher than the ones developed in straight pipes with the same cross section. Under bending loading (in-plane and out-of-plane), the main feature of the response is cross-sectional ovalization, which influences bending capacity and is affected by the level of internal pressure. Bends subjected to cyclic in-plane bending exhibit fatigue damage, leading to base metal cracking at the elbow flank. Using advanced finite-element tools, the response of pipe elbows in buried pipelines subjected to ground-induced actions is also addressed, with emphasis on soil-pipeline interaction. Finally, the efficiency of special-purpose finite elements for modeling pipes and elbows is briefly discussed.
Nonlinear analysis and plastic deformation of pipe elbows subjected to in-plane bending
International Journal of Pressure Vessels and Piping, 1998
The purpose of this study is to investigate the large strain and stress analysis for pipe elbows subjected to in-plane bending moments. A finite element model for the bend was constructed and loaded taking geometric and material nonlinearities into account using (ABAQUS) nonlinear finite element code. The initiation of yielding for the opening and closing cases appears at the inside surface of the elbow crown. However, further loading causes a significant difference in strain distribution and deformed shapes. The limit moment for the opening cases is higher than that for closing due to the geometric stiffening effects. ᭧
Pipeline Engineering [Working Title]
Pipelines are one of the most practical and economically efficient ways to transport dangerous and/or flammable substances, for which road or rail transport is often impossible. The evaluation of the processes that can negatively influence the performance of the pipelines is particularly important for assessing the risk associated with the operation of these technical systems and the potential for technical accidents. The anomalies that can be found on the pipes can be classified into two main categories. Imperfections that do not inadmissibly affect their load-bearing capacity and defects with significant negative influences on the correct operation and load-bearing capacity of the piping, which require supervision and maintenance measures. The influence of these anomalies and the processes that lead to the decrease of the pipeline-bearing capacity constitutes the main objectives of the analysis performed. The local elastic-plastic deformation anomalies are considered, for which th...
Evaluation of pipe bending reference stress equations
International Journal Sustainable Construction & Design, 2010
The use of a Failure Assessment Diagram (FAD) is widespread in the assessment of welddefects. To determine whether a defect is acceptable or not, this requires the calculation of a load ratio anda fracture ratio for the defect under consideration. Nowadays, many formulae are available to calculatethese two quantities and no clear guidance is given on which equation(s) should (not) be used. A partialclarification of this problem is achieved by comparing different reference stress equations. This article isconcerned with such comparison, for the specific case of welded pipes subjected to a bending load. A largeset of historical experimental data has been investigated in which defected pipes were subjected to anincreasing bending force until failure occurred. Two kinds of reference stress equations are considered, fullpipes subjected to a bending load and flat plates subjected to a uniform tension load. From the equationsunder consideration, the flat plate solution of Goodall & Webster...
Assessment of the integrity of welded pipes
Zastita materijala, 2014
Assessment of the integrity of welded pipes The subject of the paper is analysis of the integrity of welded pipes made of API J55 steel by high frequency contact welding (HF). Experimental research on the mechanical properties of the base material was conducted on pipes withdrawn from exploatation after 70 000 hours at service. Defect influence of the surface crack on the integrity of pipes was tested using hydrostatic pressure of pipes with axial surface crack in the base material. Fracture behaviour was tested using modified compact specimen (CT), with the initial crack in the base material, welded joint and heat affected zone (HAZ). Critical value of the tensile strength factors K Ic was determined based on the critical value J of the integral J Ic. Apart from the experimental research, based on the derived values of K r and S r and by applying fracture analysis diagram (FAD) an assessment of the integrity of welded pipes with axial surface crack on the outer surface area was conducted.
Numerical study of semi-elliptical cracks in the critical position of pipe elbow
Frattura ed Integrità Strutturale
Pipelines are considered as a major tool to transport hydrocarbons due to its important role in transporting fluids taking into account the operating conditions. Despite the importance of the elbow which considered as a critical part in the pipelines, the repeated failures and defects became a dangerous and enormously costly issue. In this numerical study, the Fluid-Structure Interaction (FSI) analysis was carried out using Ansys software. This work is divided into four main parts: the first part focused on studying and comparing the effect of bending radius of pipe elbow on the maximum of Von-Mises stress values for each radius with the yield stress of the steel of the pipe. The second part focused on the creation of a semi-elliptical crack for different locations along the elbow angles to show the critical position compared to the stress intensity factors. In the third part, the Citation: Muthanna, B. G. N., Bouledroua, O., Meriem-Benziane, M., Hadj Meliani, M.,