Influence of Cold Formed Bending on Strain Based Design Buckling Limits

2016 ◽  
Author(s):  
Tom Oldfield ◽  
Tim Turner ◽  
Andy Young
Keyword(s):  
Sensitivity Analysis ◽  
Finite Element ◽  
Local Buckling ◽  
Forming Process ◽  
Line Pipe ◽  
Cold Forming ◽  
Industry Standard ◽  
Standard Code ◽  
Strain Limit ◽  
Additional Strain

Cold formed bends are regularly used in onshore pipeline design to follow the profile and contours of the ground and to ensure any necessary bending is performed under controlled conditions. The cold forming process induces compressive and tensile plastic strains in the pipe wall which remain in the line pipe throughout the service life of the pipeline. Strain based design of oil and gas pipelines is well established in the offshore environment, where high operating temperatures and pressures have pushed engineers to design more efficient structures through a better understanding of post yield material behaviour and loading mechanisms. The industry standard code DNV-OS-F101 covers the design and limit states for offshore pipeline environments. There is less experience of strain based design in onshore pipelines, and some of the problems unique to the onshore environment have not been fully investigated. Low lateral and vertical soil restraints can be observed on a pipeline operating in a desert environment, this in combination with high operational temperature and pressure loading can result in the potential for displacement of the bends. This displacement can induce significant strains in the pipeline. The compressive strains may be sufficient to develop local buckling. Consequently, the local buckling strain represents a key performance limit for the design of the bends. There is currently no code guidance to include the additional strain component generated by the cold forming process for onshore strain based design. This results in overestimation of the allowable strain capacity of the bends. This paper investigates how the fabrication of cold formed bends affects the local buckling strain limit and how this reduces the structural capacity of the bend. Finite Element analysis has been used to assess how the additional strain components, induced during cold formed bending affects the operational capacity of the pipeline. Sensitivity analysis was carried out on a range of unpressurised line pipe, with a diameter to wall thickness ratio varying between 25 and 60, using a specific material model. Sensitivity analysis indicated a strong correlation between the Finite Element results and those calculated from the local buckling strain limit equation within the industry standard code DNV OS-F-101. The results suggest that an increase in wall thickness, at the bends within a pipeline, could be a solution to offsetting the overestimation in allowable strain capacity due to the cold formed bending process. Fully understanding the effect that cold form bending has on reducing the local buckling strain limit will promote a more robust design of onshore buried bends under high temperature loads.

Finite Element Modeling of Superplastic Sheet Metal Forming for Cavity Sensitive Materials

2003 ◽  
Vol 125 (3) ◽  
pp. 256-259 ◽  
Author(s):  
K. M. Liew ◽  
H. Tan ◽  
M. J. Tan
Keyword(s):  
Finite Element ◽  
Metal Forming ◽  
Present Model ◽  
Cavity Growth ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
The Finite Element Method ◽  
Forming Process ◽  
Strain Limit ◽  
Microstructural Mechanism

In this paper, a constitutive equation for superplasticity, which is based on the microstructural mechanism of superplastic deformation taking into account the effects of deformation damage, is incorporated into the finite element method to simulate the superplastic forming process. The effects of strain rate sensitivity, cavity growth and imposed hydrostatic pressure on the strain limit are studied. The predicted results are validated through the comparison with the existing experimental data. It is found that the present model produces accurate results in all cases.

Nonlinear Finite Element Analysis of Spring-Back Characteristics in the Cold-Forming Process of Three-Dimensionally Curved Thick Metal Plates

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Jeom Kee Paik ◽  
Jeong Hwan Kim ◽  
Bong Ju Kim ◽  
Chang Hyo Tak
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Steel Plates ◽  
Research Centre ◽  
Spring Back ◽  
Forming Process ◽  
Element Analysis ◽  
Cold Forming ◽  
Metal Plates ◽  
National University

The present paper is part of the study to develop the advanced computer aided manufacture (CAM) system called the changeable die system (CDS) that applies the cold-forming technique to produce curved thick metal plates with complex, three-dimensional geometry [Paik et al., 2009, “Development of the Changeable Die System for the Cold-Forming of Three-Dimensionally Curved Metal Plates,” The Lloyd's Register Educational Trust Research Centre of Excellence, Pusan National University, Korea]. This paper focuses on the procedure of predicting the spring-back characteristics using elastic-plastic large deflection finite element method, which is a key technical element within the framework of the CDS process. The validity of the procedure is confirmed by comparison with experimental results obtained by the CDS machine in the cold-forming process of curved steel plates.

scholarly journals Investigating of Mechanical Behavior of AA5083 in the Pressing Process Using Finite Element Analysis

2017 ◽  
Vol 11 (9) ◽  
pp. 51
Author(s):  
Babak Beglarzadeh ◽  
Behnam Davoodi
Keyword(s):  
Mechanical Properties ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Aluminum Alloy ◽  
Friction Stress ◽  
Forming Process ◽  
Element Analysis ◽  
Cold Forming ◽  
Aluminum Alloy 5083 ◽  
And Control

The process of cold forming is considered of the most different industries and the use of such process in the manufacture of components and small parts has expanded. Therefore, analyzing the behavior of metals in this process to identify and control durability that is the main factor of limiting process has particular importance in industrial forming processes. In this study, cold forming process of aluminum metal has been studied and its effect on its mechanical properties has been evaluated. For this purpose, first modeling piece of aluminum alloy 5083 for cold forming process is carried out and using finite element analysis, mechanical properties of considered piece during cold forming processes are investigated. The results show that by reducing friction, stress and strain during the process will reduce, thereby durability of the piece increases, or in other words, ductile fracture occurs in longer life and higher stresses. The results show that by proper forming operations, it can be improved the strength and durability of aluminum alloy. Finally, validation of results, by comparing simulation results with experimental results is carried out.

The Influence of the UOE Forming Process on Material Properties and Collapse of Deepwater Linepipe

2009 ◽  
Author(s):  
Chris Timms ◽  
Luciano Mantovano ◽  
Hugo A. Ernst ◽  
Rita Toscano ◽  
Duane DeGeer ◽  
...  
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Manufacturing Process ◽  
Thermal Ageing ◽  
Full Scale ◽  
Sensitivity Analyses ◽  
Thickness Variation ◽  
Forming Process ◽  
Cold Forming ◽  
Pipe Manufacturing

It has been demonstrated in previous work that, for deepwater applications, the cold forming process involved in UOE pipe manufacturing significantly reduces pipe collapse strength. To improve the understanding of these effects, Tenaris has embarked on a program to model the stages of the UOE manufacturing process using finite element methods. Previous phases of this work formulated the basis for model development and described the 2D approach taken to model the various stages of manufacture. More recent developments included some modeling enhancements, sensitivity analyses, and comparison of predictions to the results of full-scale collapse testing performed at C-FER. This work has shown correlations between manufacturing parameters and collapse pressure predictions. The results of the latest phase of the research program are presented in this paper. This work consists of full-scale collapse testing and extensive coupon testing on samples collected from various stages of the UOE pipe manufacturing process including plate, UO, UOE, and thermally-aged UOE. Four UOE pipe samples manufactured with varying forming parameters were provided by Tenaris for this test program along with associated plate and UO samples. Full-scale collapse and buckle propagation tests were conducted on a sample from each of the four UOE pipes including one that was thermally aged. Additional coupon-scale work included measurement of the through-thickness variation of material properties and a thermal ageing study aimed at better understanding UOE pipe strength recovery. The results of these tests will provide the basis for further refinement of the finite element model as the program proceeds into the next phase.

Investigating the Effect of UOE Forming Process on the Buckling of Line Pipes Using Finite Element Modeling

2006 ◽  
Author(s):  
Samer Adeeb ◽  
Joe Zhou ◽  
Dave Horsley
Keyword(s):  
Finite Element ◽  
Finite Element Modeling ◽  
Tensile Properties ◽  
Material Properties ◽  
Transverse Direction ◽  
Kinematic Hardening ◽  
Material Model ◽  
Forming Process ◽  
Line Pipe ◽  
Hardening Material

Buried line pipe are often subjected to compressive and/or bending loads at locations of ground movements. Those loads might increase the strain of the pipe at some location beyond a critical value and thus a buckle is formed on the pipe wall. Finite element modeling is an excellent numerical technique that can predict the values of the critical strains that a pipe can withstand before buckling. However, these numerical models require an accurate representation of the spatial material behaviour. Tensile specimens taken from the longitudinal and the transverse directions of a line pipe formed using the UOE process often exhibit different behaviour. Finite Element Models of buckling of line pipe often use the tensile properties exhibited by longitudinal specimens without taking into consideration the effect of the different behaviour in the transverse direction. In order to investigate the effect of the forming process a finite element model of forming a plate into a pipe was analyzed. The model was analyzed twice, once with isotropic hardening material properties and the other with kinematic hardening material properties with a constant size for the yield surface. The behaviour under tensile loading of the formed pipe in both the longitudinal direction and the transverse direction were quite different between the two models. The results show that the kinematic hardening material model can predict the difference in the tensile properties often seen between specimens taken from the longitudinal versus the transverse direction of the pipe. The material model is extended further to model the buckling of line pipe. The results show that the buckling of line pipes is dependent on the behaviour of the pipe in both the longitudinal and the transverse direction.

Qualification of Enhanced Collapse Capacity UOE Deepwater Linepipe

2011 ◽  
Author(s):  
Simon Slater ◽  
Robin Devine ◽  
Olav Aamlid ◽  
David Hernandez ◽  
Doug Swanek
Keyword(s):  
Heat Treatment ◽  
Quality Control ◽  
Test Procedure ◽  
Local Buckling ◽  
Small Scale ◽  
Compression Tests ◽  
Forming Process ◽  
Pipe Length ◽  
Cold Forming ◽  
Collapse Resistance

The local buckling of pipelines under external pressure is comprehensively addressed in section 5 of DNV-OS-F101 Rules for Submarine Pipeline Systems. The equations used, calculate the plastic and elastic components to give an overall collapse pressure. These equations include factors that are controlled by the pipe manufacturer. A key feature of the collapse design formula is that the compressive yield stress of UOE pipes is de-rated by 15 per cent through the use of a fabrication factor, αfab. This de-rating is used to account for the Bauschinger effect caused by the pipe forming process, in particular the final expansion. It is well documented that the cold forming (compression & expansion) and light heat treatment can have a beneficial effect on the compressive strength, leading to higher fabrication factors for UOE linepipe. DNV-OS-F101 states, “The fabrication factor may be improved through heat treatment or external cold sizing (compression), if documented”. The standard does not specify what documentation or quality control is required at the pipe mill to ensure every pipe length has the same collapse resistance to allow the increase in fabrication factor. Tata Steel Tubes Europe (Energy), together with Williams Field Services and Det Norske Veritas have recently concluded a technology qualification process, according to DNV-RP-A203 (Qualification Procedures for new Technology), with the specific aim of detailing the documentation and Quality Control needed to satisfy the requirements of DNV OS F101. This would then allow the use of increased fabrication factors in deepwater linepipe design. A key part of the technology qualification was the an extensive testing program that included small-scale compression tests, full-scale collapse tests and the newly developed ring collapse test procedure, which can be utilised as part of the mill quality control system for more representative assessment of the collapse resistance of linepipe material. This paper presents the systematic qualification process; including pipe manufacture, quality control and verification. It also presents some of the key mill capability requirements for producing deepwater UOE linepipe and additional factors that should be considered when optimising for local buckling resistance. Using this approach collapse pressures of above 585bar were achieved for a 457mm diameter × 31.75mm UOE pipe, equivalent to installation depths of over 5000m.

Finite Element Simulation of Bending of Steel Bar Including Plasticity

2015 ◽  
Vol 816 ◽  
pp. 182-187
Author(s):  
Ladislav Novotný
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Plastic Material ◽  
Material Model ◽  
Forming Process ◽  
Cold Forming ◽  
Element Simulation ◽  
Steel Bar ◽  
Elastic Plastic Material ◽  
Element Method

The article presents the use of finite element method for the simulation of cold forming process. The numerical simulation of a real technological operation of bending a rod by an industrial bender. Within the simulation, different types of nonlinearities, namely of material nonlinearity, resulting from the flexible plastic material properties of the rod, are considered, geometric nonlinearities result from large displacement and nonlinear contact. This paper briefly describes the elastic – plastic material model. Numerical analysis confirmed the appropriateness of the use of finite element method in the simulation of technological operations and the eventual possible optimization of these processes.

Residual Stress Evaluation and Buckling Analysis of Carcass Layers in Flexible Pipes Using 3D Finite Element Model

2015 ◽  
Author(s):  
Minggang Tang ◽  
Jun Yan ◽  
Jinlong Chen ◽  
Zhixun Yang ◽  
Qianjin Yue
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Finite Element Model ◽  
Critical Pressure ◽  
Element Model ◽  
Forming Process ◽  
Cold Forming ◽  
3D Finite Element ◽  
3D Finite Element Model ◽  
Flexible Pipes

A carcass layer plays an important role in unbonded flexible pipes to resist the high level of external pressure without buckling collapse. The layer is made of an interlocked helically wound metal wire of profiled section that cold-deformed by a series of rollers. In typical design and analysis process of the carcass layer, the initial stress is always assumed to be zero. During the carcass layer manufacturing (a cold forming process), the metal strap is however subjected to varies of squeezing and bending and deformations to take “S” shape, and then the profiled wire to a cycling sequence of bending, squeezing and twisting deformations, which take it beyond its material elastic limit. The residual stress is therefore introduced and could has effect on the critical pressure of the carcass layer. This paper presents a 3D finite element model to investigate the detailed residual stress distribution and variation during the forming process of the carcass layer. A study case using a 3D ring model is presented to systemically study the influence of imperfections, especially the residual stress, on the critical pressure of carcass layers.

Three Dimensional Finite Element Analysis of Staggered Backward Flow Forming Process

2013 ◽  
Author(s):  
Hemant Shinde ◽  
Pushkar Mahajan ◽  
Ramesh Singh ◽  
K. Narasimhan
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Process Conditions ◽  
State Variables ◽  
Forming Process ◽  
Flow Forming ◽  
Element Analysis ◽  
Cold Forming ◽  
Cylindrical Workpiece ◽  
Backward Flow Forming

Flow forming is one of the cold forming processes which is mainly used to produce thin-walled high-precision tubular components. A three dimensional coupled-field thermo-mechanical finite element model for staggered three-roller backward flow forming of a cylindrical workpiece of MDN-250 maraging steel has been developed using Abaqus/Explicit. In this model, the effect of tip radius of the rollers and friction between the rollers and the workpiece has been considered. The bottom of the workpiece is fixed in the axial direction so that diametral reduction and the axial elongation can be studied. Simulations have been carried out at different process conditions to study the state variables, such as stresses and strains obtained during the deformation. The model has been benchmarked with the experimental results for thickness reduction and the error in the thickness prediction is limited to 4%. The roll forces have been benchmarked against analytical formulation and a difference of 13–20% has been observed. The effect of flow forming process variables, such as feed rate and reduction ratio on the stress/strain distribution and roll forces have been studied. The results show that the roll forces increase at higher feed rates and higher reduction ratios whereas the equivalent strains increase at lower feed rates and higher reduction ratios. In addition, a parametric study has been conducted to study ovality, diametral growth, roll forces, stresses and strains as a function of process parameters.

Application of Ductile Damage Concepts in the Evaluation of Material Formability during Screw Head Cold Forming

2013 ◽  
Vol 577-578 ◽  
pp. 249-252
Author(s):  
Tommaso Coppola ◽  
L. Cortese ◽  
Claudio Guarnaschelli ◽  
I. Salvatori
Keyword(s):  
Finite Element ◽  
Damage Evolution ◽  
Laboratory Tests ◽  
Experimental Tests ◽  
Evolution Theory ◽  
Forming Process ◽  
Screw Head ◽  
Cold Forming ◽  
Fracture Locus ◽  
Plastic Damage

An up to date approach to material cold formability, based on a conventional J2 theory for plasticity together an uncoupled linear plastic damage evolution theory, is applied to the study of steel bolt head cold forming. Specific laboratory tests to characterize the material formability have been used. Finite element simulations have been performed to characterize the strain and stress state both in the forming process and in experimental tests to determine the material ductile fracture locus. The influence of chemical composition and initial microstructure is discussed.

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