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(1)AGH University of Science and Technology Faculty of Mechanical Engineering and Robotics . . Doctoral Thesis Welding sequence Analysis By Isaac Hernández Arriaga . Co‐Advisor: Dr. Hab. Piotr Rusek, Prof. AGH Dr. Eduardo Aguilera Gómez September 2009 .

(2) Welding Sequence Analysis. ABSTRACT This thesis has been divided in nine chapters. Chapter 1 provides brief background and general and specific objectives of this work. Chapter 2 presents the methods and advantages of reducing or controlling residual stresses and distortion induced by the welding process as well as a definition and classification of the welding sequence. It also presents a study of the welding sequence analysis, a survey of previous research in the field of welding sequences, and a discussion of its advantages, disadvantages, scope, and limitations. The subject of Chapter 3 is the finite element modeling of the welding processes, defining the boundary and initial conditions of the welding process and studying the effects of the welding sequence on the residual stress distribution and distortion in symmetrical structures. It should be noted that the proposed numerical model has general applicability and is not limited to symmetrical structures. The proposed sequentiallycoupled thermo-mechanical analysis involves two steps. A transient heat transfer analysis is performed followed by a thermal elastic plastic analysis. This numerical simulation is performed in an I-type specimen subject to tension and validated with experimental data [25]. Finally, the chapter presents a numerical simulation of the welding sequence in an L-type structure to demonstrate that the proposed numerical model accurately simulates the effects of the welding sequence on residual stresses and distortion. Chapter 4 presents a study of the effects of the welding sequence on residual stresses and distortion in a stiffened symmetrical flat frame. Selected welding sequences reduce residual stresses, distortion, or the relation between both parameters. These proper welding sequences are obtained from empirical welding rules, axis of symmetry, center of gravity of the frame, and concentric circles. The origin of the circles coincides with the center of gravity of the frame, and the radius of the circles is formed by the center of gravity of the frame with the center of gravity of each of the weld beads. The different welding sequences are analyzed with the numerical model developed in chapter 3. Finally, the chapter presents a procedure to determine the proper welding sequences to reduce residual stress, distortion or the relation between both parameters for 2dimensional symmetrical structures. The main goal chapter 5 is to demonstrate that the procedure to determine the proper welding sequences to reduce residual stress, distortion or the relation between both parameters in 2-dimensional symmetrical structures can be applied to 3-dimensional symmetrical structures. This is done by studying the effects of the i Isaac Hernández Arriaga.

(3) Welding Sequence Analysis welding sequence on the residual stresses and distortion in a 3-dimensional unitary cell-type symmetrical structure. Now the weld bead circles become spheres. To demonstrate the procedure to determine the proper welding sequence for 3-dimensional symmetrical structures, four numerical simulations are performed in the proposed symmetrical structure. Two of these numerical simulations deal with the proper welding sequence to reduce residual stress and the other two deals with the proper welding sequence to reduce distortion. Also, the numerical simulation of a special welding sequence is performed for comparison with the proper welding sequence to reduce distortion. This special welding sequence applies the external weld beads first and the internal weld beads later. All the numerical simulations are based on the proposed numerical model of the welding process developed in Chapter 3. Chapter 6 presents a methodology for the development of the experimental tests. This methodology helps to plan, execute, and control each of the stages of the experimental tests. The methodology starts with the material selection of the specimen, configuration selection, welding process selection, metal transfer mode selection, welding parameter selection, design and fabrication of the equipment needed to run the test, design and fabrication of the mounting locks, residual stresses relief caused by the manufacturing process, transportation, handling, storage and cutting of the plates, measurement of the initial distortion of the plates, design and fabrication of a holder-mounting device to hold the plates, design and fabrication of a squaremounting device to square the holder-mounting device, application of welding tacks, measurement of the distortion after applying the welding tacks, installation of the run-off tabs, application of the welding, removal of the run-off tabs of the welded structure, measurement of the distortion after welding, and measurement of the final distortion induced by the welding process. Chapter 7 covers the results of the experimental tests performed in 3-dimensional unitary cell-type symmetrical specimens. In these experimental tests, the effects of the welding sequence on distortion are studied. Eight symmetrical specimens are prepared. Four welding sequences are considered: two of them are adequate to reduce distortion and the other two reduce residual stresses. The chapter also studies the effects that occur when a welding bead is divided into 3 sub-weld beads, as well as the effects of relieving the residual stresses caused by manufacturing process, transportation, storage and cutting of plates. Welding tacks are applied to all specimens before the actual weld process begins. The measurement of the distortion is periodically performed to observe if rheological effects occur in the specimens after welding. The experimental tests were performed in the Department of Machine Strength and Manufacturing in the Faculty of Mechanical Engineering at the University of Science and Technology in Krakow, Poland. Chapter 8 presents a comparison between the numerical results obtained in Chapter 5 and the experimental results obtained in Chapter 7 for the 3-dimensional unitary cell-type symmetrical structure. The comparison discusses the distortion modes and the distortion in the 24 points of interest. The chapter presents the procedures to determine the proper welding sequences to reduce the residual stresses, distortion, or a relation between both parameters in symmetrical and asymmetrical structures in 2 and 3 ii Isaac Hernández Arriaga.

(4) Welding Sequence Analysis dimensions. These procedures were developed in chapters 4 and 5 to determine the proper welding sequences to reduce residual stresses, distortion, or relation between both parameters in symmetrical structures in 2 and 3 dimensions. Chapter 9 presents the conclusions, contributions and suggestions for future work.. iii Isaac Hernández Arriaga.

(5) Welding Sequence Analysis. ACKNOWLEDGMENTS I am extremely grateful for the support of the University of Guanajuato and AGH University of Science and Technology. They provide employment and resources which made it possible for me to pursue this degree. I wish to express my sincere appreciation to Dr. Eduardo Aguilera for his guidance, encouragement and insight throughout the duration of this research. I would also express my gratitude to Professor Piotr Rusek for his encouragement and support, his influence extends far beyond my academic work. I wish to tanks to Dr. Arturo Lara, Dr. Elias Ledesma, Professor Stanisław Wolny, and Professor Andrzej Skorupa for serving as dissertation committee members and providing positive suggestion and comments. I acknowledge the Consejo Nacional de Ciencia y Tecnología (CONACYT), Dirección de Relaciones Academicas Internacionales e Interinstitucionales (DRAII), and Dirección de Investigación y Posgrado (DINPO) of the University of Guanajuato for the funding of doctoral studies, doctoral research and stay at AGH. I would also like to express my gratitude to Director of the engineering division of the Irapuato-Salamanca Campus; Dr. Oscar Ibarra, for his invaluable support in the completion of my doctoral studies. I would especially like to thank the Authorities of the AGH University of Science and Technology; Rector, Professor Antoni Tajduś, Vice-Rector for Cooperation and Development, Professor Jerzy Lis, and Dean of the faculty of Mechanical Engineering and Robotics, Professor Janusz Kowal for thier invaluable collaboration with the University of Guanajuato. I am also grateful to Dr. Hector Plascencia for his interest and help to my research. Also, I would like to thank to Dr. Pedro de Jesús García and to Dr. Rogelio Navarro for their initial help, interest and advice. I am very grateful to Dr. Tomasz Góral for his help on experimental research. Thanks are also extended to Drs. Jerzy Haduch and Andrzej Tyka for their assistance.. iv Isaac Hernández Arriaga.

(6) Welding Sequence Analysis During my stay at AGH, I was fortunate to have had a number of talented technical workers. Kazimierz Nawrot, Włodzimierz Rusek, and Artur Konopczak all helped with the fabrication of the equipment needed to run the test. My thanks to Salvador Martínez, for his friendly help in the experimental measurements at AGH. The same quality of special thanks goes to Mr. Guadalupe Negrete for his expertise and generous help in welding . My special thanks go to Renato Sánchez for giving me their generous and solidary support. To all my friends and classmates, especilly Hijinio Juárez, Alejandro León, Sergio Pacheco and Mr. Baldomero Lucero, thank you for your warm friendships. To Ms. Ma. Eugenia Gallardo, secretary of our Mechanical Department, for helping me during my studies. My academic achievements would have been impossible without the spiritual support of my family. Special thanks are due to my parents, Beny Arriaga and Daniel Hernández. Their sacrifice for my education made me who I am. Thanks are also extended to my sister and brother; Ruth Hernández and Daniel Hernández, for their understanding and support for my studies. Special love goes to my wife, Maria Victoria Cabrera whose boundless love and encouragement made my time at University of Guanajuato and AGH easy and pleasant. Also, my cute son, Samuel Isaac Hernández, enabled me to periodically escape the academic pressure with his smiles. Finally, I thank an anonymous editor for assisting with the English version of my thesis.. v Isaac Hernández Arriaga.

(7) Welding Sequence Analysis. TABLE OF CONTENTS Abstract Acknowledgments Table of contents List of figures List of tables Nomenclature. i iv vi xii xvii xix. Chapter I INTRODUCTION 1.1 Background 1.2 General objective 1.3 Specific objectives. 1 2 2. Chapter II WELDING SEQUENCE BACKGROUND AND METHODS FOR CONTROLLING RESIDUAL STRESSES AND DISTORTION INDUCED BY WELDING 2.1 Introduction 2.2 Advantages of residual stress and distortion control 2.3 Methods to control welding-induced residual stress and distortion 2.3.1 Welding sequence 2.3.2 Definition of weld parameter 2.3.3 Weld procedure 2.3.4 Fixture design 2.3.5 Precambering 2.3.6 Prebending 2.3.7 Thermal tensioning 2.3.8 Heat sink welding 2.3.9 Preheating 2.10 Post-weld heat treatment 2.11 Post-weld corrective methods 2.4 Welding sequence definition 2.5 Welding sequence classification 2.5.1 Welding sequence for single pass welds 2.5.2 Welding sequence for multiple pass welds. 3 3 4 4 4 5 5 5 6 6 7 7 7 7 8 8 8 9 vi. Isaac Hernández Arriaga.

(8) Welding Sequence Analysis 2.6 2.7 2.8 2.9. Welding sequence selection based on empiric rules Welding sequence background Summary of the welding sequence analysis background Matrix of the welding sequence analysis background. 10 11 43 44. Chapter III PROPOSAL OF A NUMERICAL SIMULATION OF THE WELDING PROCESS AND A NUMERICAL SIMULATION OF THE WELDING SEQUENCE IN AN L-TYPE STRUCTURE 3.1 Introduction 3.2 Heat transfer in welding 3.2.1 Analytical solution for the temperature field 3.2.2 Thermal Initial and boundary Conditions 3.3 Thermal elastic plastic stress analysis in welding 3.3.1 Mechanical equations 3.3.2 Mechanical initial and boundary conditions 3.4 Finite element solution of the welding 3.4.1 Finite element solution of heat transfer in welding 3.4.2 Finite element solution of the thermal elastic plastic stress analysis in welding 3.5 Geometric configuration of I-type specimen subject to tension 3.6 Material selection for the I-type specimen subject to tension 3.7 Temperature-dependent thermal and mechanical properties of ASTM A36 3.8 Finite element model of the I-type specimen subject to tension 3.8.1 Definition and justification of the applied finite elements 3.8.2 Thermal initial and boundary conditions 3.8.3 Mechanical boundary condition 3.8.4 Body load 3.8.5. Solution of the finite element model 3.9 Points of interest in the finite element model of the I-type specimen subject to tension 3.10 Residual stresses in the I-type specimen subject to tension obtained in the numerical simulation 3.11 Comparison between the numerical and experimental results of an I-type specimen subject to tension 3.12 Conclusions of the numerical simulation of the welding process in an I-type specimen subject to tension 3.13 Numerical simulation of the welding sequence in an L-type structure 3.14 Geometric configuration of the L-type structure 3.15 Finite element model of the L-type structure 3.15.1 Thermal initial and boundary conditions 3.15.2 Mechanical boundary conditions. 45 45 46 48 50 50 51 51 51 52 55 56 56 57 58 61 61 61 62 62 62 63 64 65 65 65 66 67 vii. Isaac Hernández Arriaga.

(9) Welding Sequence Analysis. 3.16 3.17 3.18. 3.19. 3.20. 3.15.3 Solution of the finite element model of the L-type structure Configuration of welding sequences for the L-type structure Localization of the point of interest in the L-type structure Numerical results in the L-type structure 3.18.1 Distortion profile in the L-type structure 3.18.2 Residual stress distribution in the L-type structure Experimental tests for the L-type structure 3.19.1 Selection of points of interest in the L-type structure 3.19.2 Configuration of the welding sequences in the L-type specimens 3.19.3 Measurement of distortion on L-type specimens Conclusions of the welding sequence analysis of the L-type structure. 67 67 68 68 70 70 71 72 72 73 75. Chapter IV WELDING SEQUENCE ANALYSIS IN A STIFFENED SYMMETRICAL 2-DIMENSIONAL FRAME 4.1 4.2 4.3 4.4. 4.5. 4.6 4.7 4.8. 4.9 4.10. Introduction Geometric configuration of a stiffened symmetrical flat frame Welding configuration in the stiffened symmetrical flat frame Finite element model of the stiffened symmetrical flat frame 4.4.1 Thermal initial and boundary conditions 4.4.2 Mechanical boundary conditions 4.4.3 Solution of the finite element model of the stiffened symmetrical flat frame Numerical results in the stiffened symmetrical flat frame 4.5.1 Distribution of the residual stresses in the stiffened symmetrical flat frame 4.5.2 Distortion profile in the stiffened symmetrical flat frame Analysis of residual stress-distortion relations analysis Order of importance of the welding sequences to reduce residual stress, distortion, or the relation between them in the stiffened symmetrical flat frame Proper welding sequences to reduce the residual stress, distortion, or a relation between them in the stiffened symmetrical flat frame 4.8.1 Proper welding sequence to reduce the residual stress in the stiffened symmetrical flat frame 4.8.2 Proper welding sequence to reduce distortion in the stiffened symmetrical flat frame 4.8.3 Proper welding sequence to improve the relation between both critical parameters in the stiffened symmetrical flat frame Hypothesis to determine the proper welding sequence to reduce the residual stress, distortion, or a relation between them in symmetrical flat structures Experimental tests in a stiffened symmetrical flat frame specimen 4.10.1 Selection of points of interest in the stiffened symmetrical flat specimen. 76 76 77 80 81 81 82 82 82 83 83 84 84 86 87 87 88 89 90 viii. Isaac Hernández Arriaga.

(10) Welding Sequence Analysis 4.10.2 Configuration of the welding sequence in the stiffened symmetrical flat specimen 4.10.3 Measurement of distortion on the stiffened symmetrical flat specimen 4.11 Conclusions of the welding sequence analysis of stiffened symmetrical flat frame. 90 91 93. Chapter V WELDING SEQUENCE ANALYSIS IN A 3-DIMENSIONAL UNITARY CELL-TYPE SYMMETRICAL STRUCTURE 5.1 Introduction 5.2 Hypothesis to determine the proper welding sequence to reduce the residual stress, distortion, or a relation between them in 3-dimensional symmetrical structures 5.3 Geometric configuration of the 3-dimensional unitary cell 5.4 Selection of the number of weld beads in the 3-dimensional unitary cell 5.5 Symmetry axis selection and formation of the concentric spheres in the 3-dimensional unitary cell 5.6 Proper welding sequence to reduce the residual stress and proper welding sequence to reduce the distortion in the 3-dimensional unitary cell 5.7 Material selection of the 3-dimensional unitary cell 5.8 Fillet weld shape used in the 3-dimensional unitary cell 5.9 Finite element model of the 3-dimensional unitary cell 5.9.1 Thermal initial and boundary conditions 5.9.2 Mechanical boundary conditions 5.9.3 Solution of the finite element model of the 3-dimensional unitary cell 5.10 Localization of the points of interest in the 3-dimensional unitary cell 5.11 Configuration of the numerical simulation for the 3-dimensional unitary cell 5.12 Numerical results of the different welding sequences analyzed in the 3-dimensional unitary cell 5.12.1 Maximum von Mises residual stress in the 3-dimensional unitary cell 5.12.2 Distortion modes in the 3-dimensional unitary cell 5.12.3 Maximum distortion and distortion in 24 points of interest in the 3-dimensional unitary cell 5.13 Numerical comparison between the proper welding sequence to reduce distortion and a special welding sequence in the 3-dimensional unitary cell 5.14 Conclusions of the welding sequence analysis of the 3-dimensional unitary cell. 95 96 97 98 98 100 101 101 101 102 103 103 103 104 105 105 106 106 107 109. Chapter VI METHODOLOGY OF EXPERIMENTAL TESTS 6.1 6.2 6.3 6.4. Introduction Specimen material selection Selection of specimen configuration Selection of the welding process. 110 110 111 111 ix. Isaac Hernández Arriaga.

(11) Welding Sequence Analysis 6.5 Selection of metal transfer mode 6.6 Selection of welding parameters (Operating variables) 6.6.1 Arc voltage and welding current 6.6.2 Welding speed 6.6.3 Wire feed rate 6.6.4 Selecting of contact tip to work distance 6.6.5 Electrode orientation 6.6.6 Electrode diameter 6.6.7 Shielding gas composition 6.6.8 Gas flow rate 6.7 Design and fabrication of the equipment needed to run the test 6.8 Design and fabrication of the mounting locks 6.9 Relief of residual stresses caused by the manufacturing process, transportation, handling, storage and cutting of the plates 6.10 Measurement of the initial plate distortion 6.11 Design and fabrication of a holder-mounting device to hold the plates 6.12 Design and fabrication of a square-mounting device 6.13 Application of the welding tacks 6.14 Distortion measurement after welding tack application 6.15 Installation of the run-off tabs 6.16 Application of the welding 6.17 Removing the run-off tabs from the welded structure 6.18 Measurement of the distortion after applying the welding 6.19 Measurement of the final distortion. 111 112 112 113 113 114 114 115 115 116 116 117 118 119 120 120 121 123 123 124 124 125 126. Chapter VII RESULTS OF THE EXPERIMENTAL TESTS IN 3-DIMENSIONAL UNITARY CELL-TYPE SPECIMENS 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10. Introduction Configuration of the 3-dimensional unitary cell specimens Localization of the points of interest in the 3-dimensional unitary cell specimens Configuration of the experiment Distortion after applying welding tacks in the 3-dimensional unitary cell specimens Distortion after welding in the 3-dimensional unitary cell specimens Distortion modes of the 3-dimensional unitary specimens Final distortion of the 3-dimensional unitary cell specimens Final Remarks for distortion of the 3-dimensional unitary cell specimens Conclusions of the results of the experimental test in 3-dimensional unitary cell specimens. 127 127 128 128 128 129 132 133 135 136. x Isaac Hernández Arriaga.

(12) Welding Sequence Analysis Chapter VIII COMPARISON BETWEEN THE “3- DIMENSIONAL UNITARY CELL”-TYPE STRUCTURES/SPECIMENS 8.1 8.2 8.3 8.4 8.5. Introduction Comparison of distortion modes Comparison of distortion Conclusions of the comparison between numerical and experimental results Procedures to determine the proper welding sequences to reduce residual stress, distortion, or a relation between them in symmetrical and asymmetrical structures in 2 and 3 dimensions 8.5.1 Symmetrical structures in 2 and 3 dimensions 8.5.2 Asymmetrical structures in 2 and 3 dimensions. 137 137 137 140 140 140 142. Chapter IX CONCLUSIONS, CONTRIBUTIONS, AND SUGGESTIONS FOR FUTURE RESEARCH Conclusions Contributions Suggestion for future research. 9.1 9.2 9.3. REFERENCES. 146 147 147 149. APPENDIX 1 2 3 4 5 6 7 8. 9. Plasticity theory applied to welding process and its formulation by finite element method Definition and justification of the applied finite elements Response to critical comments Proper welding sequence to reduce residual stress and distortion in common symmetrical structures in 2 and 3 dimensions based on the hypothesis developed in the sections 4.9 and 5.2. Listing of commands of the numerical simulation of the welding process (I-type specimen subject to tension) Listing of commands of the numerical simulation of the welding sequence in an L-type structure (Welding sequence No.1) Listing of the commands of the numerical simulation of stiffened symmetrical flat frame (welding sequence No.5 with welding tacks) Listing of the commands of the numerical simulation of the 3-dimensional unitary cell-type symmetrical structure (welding sequence most appropriate to reduce distortion with 24 weld beads and welding tacks) Construction drawings. 151 171 179 188 191 194 197 201. 205. xi Isaac Hernández Arriaga.

(13) Welding Sequence Analysis. LIST OF FIGURES CHAPTER II Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.8 Figure 2.9 Figure 2.10 Figure 2.11 Figure 2.12 Figure 2.13 Figure 2.14 Figure 2.15 Figure 2.16 Figure 2.17 Figure 2.18 Figure 2.19 Figure 2.20 Figure 2.21 Figure 2.22. Welded frame distortion [4]: (a) Without considering a proper welding sequence, (b) considering a proper welding sequence Rigid supports [4] Precamber with a curved surface [2] Pre-bending [2] Welding with the thermal tensioning process [11] Heat sink welding [1] Sequences for thin-wall butt-welds [3]: (a) Progressive, (b) backstep, (c) symmetric, and (d) jump Built-Up welding sequence on thick-wall butt-weld [3] Block welding sequence [3] Cascade welding sequence [3] Welding sequences for thin-wall butt-welds [16]: (a) Progressive, (b) backstep, and (c) symmetric Longitudinal residual stress distribution [16]: (a) Along the X-direction and (b) along the Y-direction Different welding sequence for thick-wall butt-welds [16] Residual stresses distribution along the X-direction in various welding sequence for thick-wall butt-welds [16]: (a) Longitudinal and (b) transverse Geometry and various welding sequence for circular patch [16]: (a) Geometry of circular patch welding, (b) Progressive sequence, (c) backstep sequence, and (d) jump sequence Residual stresses distribution for various welding sequence [16]:(a) Circumferential and (b) radial Dimensions of the specimen, mm. [17] Schematic of Weld bead´s delamination [17] Comparison of transverse residual stress between in the same direction and welding in the inverse direction [17] Configuration of welded blocks in a multi-block welding sequence [18] Structural boundary conditions of welded plates (clamp fixture at both sides) [18] Resulted distortion profile for two different block sequences [18]: (a) Welding sequence No. 1 and (b) welding sequence No. 2. 4 5 6 6 6 7 8 9 9 9 11 12 13 14 15 16 17 17 18 19 19 20 xii. Isaac Hernández Arriaga.

(14) Welding Sequence Analysis Figure 2.23 Figure 2.24 Figure 2.25 Figure 2.26 Figure 2.27 Figure 2.28 Figure 2.29 Figure 2.30 Figure 2.31 Figure 2.32 Figure 2.33 Figure 2.34 Figure 2.35 Figure 2.36 Figure 2.37 Figure 2.38 Figure 2.39 Figure 2.40 Figure 2.41 Figure 2.42 Figure 2.43 Figure 2.44 Figure 2.45 Figure 2.46 Figure 2.47 Figure 2.48. Resulted distribution of the Von Mises stress using different block sequences. [18]: (a) Welding sequence No. 1 and (b) welding sequence No. 2 Configuration of a large-diameter multi-pass pass butt-welded pipe joints and its cross section [19] Welding sequences for a multi-pass Welded pipe joint [19] Comparison of circumferential residual stress in multi-pass welded pipe joints [19]: (a) Inner surface and (b) outer surface Comparison of axial residual stress in multi-pass welded pipe joints [19]: (a) Inner surface and (b) outer surface Comparison of residual stress across through-thickness along the heat-affected zone in multi-pass welded pipe joints [19]: (a) Circumferential and (b) axial Configuration of a multi-pass fillet Weld joint, mm. [20] Different welding sequences in multi-pass fillet weld joint [20] Comparison of residual stress in a multi-pass fillet weld joint [20]: (a) Case 1 and (b) case 2 Relation between nominal stress range and fatigue life in multi-pass fillet weld joints [20] Aluminum panel for study on welding sequence effect on angular distortion [21] Welding sequences for angular distortion analysis of aluminum panel structure[21] Distortion displacements at four cross sections of the panel from four welding sequences [21]: (a) At x= 16 inch; (b) at x=32 inch; (c) at y= 9.3 inch; y (d) at y=30 inch. Optimum welding sequence determined by JRM [21] Comparison of distortion resulting from welding sequence and the optimum welding sequence [21]: (a) at x= 16 inch, (b) at x=32 inch, (c) at y= 9.3 inch, and (d) at y=30 inch. T-joint configuration [22]: (a) Finite element model and (b) dimensions of the cross section of the hollow extrusions Different welding sequences [22]: (a) Case 1 and (b) case 2 Comparison of measured (M) and calculated (S) distortion evolution for two welding sequence [22]: (a) Case 1 and (b) case 2 Geometric configuration of a sub-assembly [15] Simplified model with torsion springs [15] Final exaggerated deformed shapes for different sequences [15] Geometric configuration and dimensions of weldment [23] Code to designate the welding sequence and welding direction [23] Radial displacement of the edge of plate with respect to θ for continuous welding and the optimum sequence[23] Tail bearing housing [24] Finite element model of welding process and designation of welding paths showing. 21 22 22 23 24 25 27 27 28 29 30 31 32 33 33 34 34 35 36 36 37 38 39 39 41 41 xiii. Isaac Hernández Arriaga.

(15) Welding Sequence Analysis. Figure 2.49 Figure 2.50. positive orientation of weld and reference number in sequence [24] Run 28 is the optimized displacement with a clamped structure [24] The absolute values of the X displacement for all 28 sequences [24]. 42 42. CHAPTER III Figure 3.1 Figure 3.2 Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 Figure 3.9 Figure 3.10 Figure 3.11 Figure 3.12 Figure 3.13 Figure 3.14 Figure 3.15 Figure 3.16 Figure 3.17 Figure 3.18 Figure 3.19 Figure 3.20. Eulerian frame and thermal initial and boundary conditions Geometric configuration of I-type specimen subject to tension (mm) [25] Thermal and mechanical properties of ASTM A36 as a function of temperature [34] Stress-strain behavior of ASTM A36 carbon steel for different temperatures [Based in figure 3.3] Finite element mesh of the I-type specimen subject to tension Weld thermal cycle of ASTM A36 carbon steel [34-35] Localization of the points of interest on finite element model Distribution of residual stresses in the X-direction in the I-type specimen subject to tension Experimental tests: a) Localization of the points of interest in the I-type specimen subject to tension, mm. b) welding parameters employed [25] Geometric configuration of the L-type structure (mm) Finite element model of the L-type structure Localization of the node 1533 in the L-type structure Maximum distortions in L-type structure for three different welding sequences Maximum Von Mises residual stress in the L-type structure for three different welding sequences Distortion profile in the L-type structure corresponding to welding sequence 3 Distribution of Von Mises residual stress corresponding to the welding sequence 2 Localization of the interest points in the L-type specimen L-type specimen 2 after applying the welding sequence 3 L-type specimen 2 (welding sequence 3) mounted on the coordinate measuring machine Comparison of the welding distortion (exaggerated) between two L-type specimens. 49 55 56 57 58 60 62 63 64 65 66 68 69 69 70 71 72 73 73 75. CHAPTER IV Figure 4.1 Figure 4.2 Figure 4.3. Geometric configuration of the stiffened symmetrical flat frame (mm) Finite element model of the stiffened symmetrical flat frame Distribution of Von Mises residual stresses corresponding to the welding sequence (5 I-O). 77 80 82. xiv Isaac Hernández Arriaga.

(16) Welding Sequence Analysis Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 Figure 4.10. Distortion profile corresponding to the welding sequence 5 O-I WT Centers of gravity of the structure, centers of gravity of the weld beads, axis of symmetry and concentric circles in the stiffened symmetrical flat frame Ranges of the values of P and W for welding sequence 1 I-O and combined welding sequence Localization of the point of interest in the stiffened symmetrical flat specimen Stiffened symmetrical flat specimen after applying the welding sequence 5 O-I WT Stiffened symmetrical flat specimen mounted on the coordinate measuring machine Distortion profile in the stiffened symmetrical flat specimen corresponding to welding sequence 5 O-I WT (exaggerated). 83 86. Panel used in the welding industry Configurations and dimensions of the 3-dimensional unitary cell (mm) Axis of symmetry and concentric spheres of the 3-dimensional unitary cell formed by 24 fillet welds Different welding sequences for the 3-dimensional unitary cell Fillet weld shape used in the 3-dimensional unitary cell Finite element model of the 3-dimensional unitary cell Localization of the points of interest in the 3-dimensional unitary cell Distribution of residual stresses corresponding to numerical simulation 2 Isometric view of the distortion profile corresponding to the numerical simulation 3 Configuration of the special welding sequence. 97 98 99 100 101 102 104 105 106 108. Semiautomatic welding machine OPTYMAG 501 Typical zone of good short circuit welding conditions [37] Contact tip to work distance [40] Positioning of electrode gun with respect to the base metal plate [37] Normal work angle for fillet welds [37] Arm-holder device Welding torch holder device Localization of the locks mounted on the traveler carriage Electric oven used to initial residual stresses relief Measurement of the initial distortion with standard gages Holder-mounting device. 112 113 114 114 115 116 117 118 119 119 120. 87 90 91 91 93. CHAPTER V Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9 Figure 5.10 CHAPTER VI Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure 6.7 Figure 6.8 Figure 6.9 Figure 6.10 Figure 6.11. xv Isaac Hernández Arriaga.

(17) Welding Sequence Analysis Figure 6.12 Figure 6.13 Figure 6.14 Figure 6.15 Figure 6.16 Figure 6.17 Figure 6.18. Square-mounting device C-type clamps mounted on the specimen Welding tacks application in the specimen Installation of the run-off tabs on the specimen Application of the welding to the specimen Removing of the run-off tabs of the specimen Measurement of the distortion after applying welding using standard gages. 121 122 122 123 124 125 125. Distortion (exaggerated) after applying welding tacks and after welding for specimen T9 Distorted shape of the 3-dimensional unitary cell welded specimens Final distortion (exaggerated) for welded specimen T9. 131 132 134. Comparison between numerical (simulation 3) and experimental distortion (specimen T9). Exaggerated distortion. Flow Diagram of the analysis of the welding sequence for symmetrical and asymmetrical structures in 2 and 3 dimensions. 139. CHAPTER VII Figure 7.1 Figure 7.2 Figure 7.3 CHAPTER VIII Figure 8.1 Figure 8.2. 144. xvi Isaac Hernández Arriaga.

(18) Welding Sequence Analysis. LIST OF TABLES CHAPTER II Table 2.1 Table 2.2 Table 2.3 Table 2.4 Table 2.5. Different welding sequences used by Ji and Fang [17] Residual stress´s peak value for several cases [17] Welding sequences and orders applied into the multi-block model [18] Different welding sequence used by Bart, Deepak and Kyoung [15] for various welding conditions [23]. 17 18 19 36 40. Chemical composition of ASTM A36 carbon steel [33] Residual stresses obtained in the numerical simulation of I-type specimen subject to tension Comparison between numerical data and experimental data of two I-type specimen subject to tension Welding sequence configuration in the L-type specimen Distortion at the points of interest in two L-type specimens. 56 63. Welding sequences from the inside to the outside used in the stiffened symmetrical flat frame Welding sequences from the outside to the inside used in the stiffened symmetrical flat frame Order of importance of the analyzed welding sequences in the stiffened symmetrical flat frame Configuration of welding sequence 5 O-I WT used in the stiffened symmetrical flat specimen Distortion at the points of interest (mm) in the stiffened symmetrical flat specimen corresponding to welding sequence 5 O-I WT. 78. CHAPTER III Table 3.1 Table 3.2 Table 3.3 Table 3.4 Table 3.5. 64 68 74. CHAPTER IV Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5. 79 85 90 92. CHAPTER V Table 5.1 Table 5.2. Configuration of the numerical simulations for the 3-dimensional unitary cell Distortion at 24 points of interest (mm) corresponding to different welding sequences In the 3-dimensional unitary cell. 104 107 xvii. Isaac Hernández Arriaga.

(19) Welding Sequence Analysis Table 5.3. Comparison of numerical results between both welding sequences In the 3-dimensional unitary cell. 108. Electric settings used in the short circuit transfer mode [39] Common blends of shielding gas composition for short transfer mode [40]. 113 115. 3-dimensional unitary cell specimen configuration Distortion after application of the welding tacks for the different 3-dimensional unitary cell specimens, mm. Distortion after welding for the different 3-dimensional unitary cell specimens 24 hrs after welding, mm. Final distortion in the 24 points of interest of the 3-dimensional unitary cell specimens, mm.. 128 129. CHAPTER VI Table 6.1 Table 6.2 CHAPTER VII Table 7.1 Table 7.2 Table 7.3 Table 7.4. 130 133. CHAPTER VIII Table 8.1. Difference (%) between numerical and experimental results. 138. xviii Isaac Hernández Arriaga.

(20) Welding Sequence Analysis. NOMENCLATURE Mathematical symbols. Units. Rectangular matrix Column vector, row vector Matrix transpose Matrix inverse Partial differentiation if the following subscript is a letter. -. [ B]. Strain-displacement matrix for each element. -. C. Specific heat Damping matrix. , Latin symbols. [C ]. J/Kg°C Kg/s. Power of viscoplastic straining Increment of; for example , d ε. Tot ij. 1/s -.  D ep . Elastic-plastic stiffness matrix. eije. Deviation component of elastic strain tensor. E Eijkl. Young´s modulus Elastic tensor. N/m2 N/m2. ep Eijkl. Elastic-plastic tensor. N/m2. t Eijkl. Tangent elastic tensor. N/m2. Sum of the body force. N. Elastic forces Inertia forces Damping forces Yield surface. N N N -. Element load vector. N. Global load vector. N. fi. ( )=0 {Fe } {F } f. µε. xix Isaac Hernández Arriaga.

(21) Welding Sequence Analysis. {Ft }. Global load vector corresponding at time t. {F }. Nodal load vector corresponding to the state of stress for the time. i t +∆t. N. ∆t. -. G=. E 2 (1 + v ). Shear modulus. N/m2. G(. )=0. Plastic potential. -. hc. H i kx, ky, kz K=. E 3 (1 − 2v ). [K ] [ Ke ]. Convection heat transfer coefficient Hardening modulus Iteration number Thermal conductivity in the x, y and z directions Bulk modulus. W/m2°C W/m°C N/m2. Global stiffness matrix. N/m. Element stiffness matrices. N/m.  K t . Stiffness matrix in the time. N/m. [M ]. Mass matrix. n. Number of nodal points for each element Shape functions. -. Cosine directors Boundary heat flux Source of heat generation Nodal point force corresponding at time t. W/m2 W/m3 -. N i ( x, y , z ). Nx, Ny, Nz qs Q(x,y,z,t). {Rt } {s} s ij T(x,y,z,t). Stress deviation increment vector. Kg. N/m2 °C °C °C °C. Tm. Stress deviation tensor Current temperature Prescribed surface temperature Surrounding temperature Melting temperature. {α dT }. Thermal dilatation vector. ∆t ∆tcr. Time interval Critical time step. sec sec. Displacement vector Velocity vector Acceleration vector. m m/s m/s2. T∞. -. xx Isaac Hernández Arriaga.

(22) Welding Sequence Analysis ui , j. Displacement gradient. (U r ). Radial distortion with respect to θ. mm. {∆U }. Maximun radial distortion Element nodal increments. mm -. {∆U }. Nodal increment vector in the iteration. -. δ {∆U }. Admissible virtual nodal increase. -. V. Volume of the body Plastic work. i. -. m3. Greek symbols. α χi. Thermal expansion coefficient Parameters that control the yield surface size. δ ij. Kronecker symbol Emissivity Cauchy strain tensor. µε. Power of elastic straining Elastic strain increment. µε. ε kke. Spherical component of elastic strain tensor. µε. d ε ijp. Plastic strain increment. µε. d ε ijtr. Phase transformation strain increment. µε. d ε ijθ. Thermal strain increment. µε. dε p δ d ε ij. Equivalent strain increment Variation in the strain increment. µε µε. κ. Parameter related with the strain hardening effects Plastic multiplier Poisson´s ratio Density Stefan-Boltzmann constant Cauchy stress tensor Hydrostatic stress tensor Spherical invariant. Kg/m3. Radial residual stress. N/m2. dε. e ij. dλ v ρ. σ ij σ kk. µm/m °C -. N/m2 N/m2 N/m2. xxi Isaac Hernández Arriaga.

(23) Welding Sequence Analysis. or σy. or. Von Mises stress Transverse residual stresses Yield stress Longitudinal residual stress Axial residual stress Circumferential residual stress. N/m2 N/m2 N/m2 N/m2 N/m2 N/m2. xxii Isaac Hernández Arriaga.

(24) Welding Sequence Analysis. CHAPTER I INTRODUCTION 1.1 Background During the heating and cooling cycle in the welding process, thermal strain occurs in the filler material and in the base metal regions close to the weld. The strain produced during heating is accompanied by plastic deformation. The non-uniform plastic deformation that occurs in the weld structure is what leads to residual stresses. These residual stresses react to produce internal forces which must be equilibrated and cause distortion [1]. The residual stress and distortion in weldments depend on several interrelated factors such as thermal cycle, material properties, structural restraints, welding conditions and geometry [2]. Of these parameters, the thermal cycle has the greatest influence on the thermal loads in the welded structures. At the same time, the temperature distribution is a function of parameters such as welding sequence, welding speed, energy of the source, and environmental conditions. A high level of tensile residual stresses near the seam can induce brittle fracture, cracking due to corrosion stress, and reduced fatigue strength. Compressive residual stresses in the base metal located some distance away from the weld line can substantially decrease the critical buckling stress [3]. The main effects of distortion are the loss of tolerance in the welded components and deformation of structural elements that results in inadequate support to transfer applied loads [4]. Therefore, residual stresses and distortion should be reduced to meet all geometry and strength requirements. Some of the most popular methods for reducing residual stresses and distortion in weld fabrication are: welding sequence, definition of weld parameters, definition of weld procedure, use of precambering fixtures, prebending, thermal tensioning, heat sink welding, post-weld treatment, control of weld consumables, and post-weld corrective methods [1].. 1 Isaac Hernández Arriaga.

(25) Welding Sequence Analysis 1.2 General objective •. Develop a welding sequence-based methodology to reduce residual stresses, distortion, or a relation between both parameters in symmetrical structures.. 1.3 Specific Objectives • • • •. • • • • • • • • • •. Obtain temperature-dependent material properties of ASTM A36 steel used in this investigation. Conduct a literature survey on welding sequences. Investigate the theory of plasticity applied to the welding process and its finite element formulation. Perform a finite element simulation of the welding process through a thermo-mechanical analysis based on the von Mises criterion and flow rule, assuming a lineal isotropic hardening and temperature dependent materials while neglecting micro-structural evolution. Validate the proposed numerical model of the welding process with experimental data to determine model accuracy. Apply the proposed numerical model of the welding process to determine whether the welding sequence in an L-type structure affects the residual stresses and distortion. Apply the proposed numerical model of the welding process in a welding sequence analysis in 2 and 3 dimensional symmetrical structures. Analyze the effects of the welding sequence on residual stresses and distortion in 2 and 3 dimensional symmetrical structures. Analyze the relationship between residual stress and distortion due to the welding sequence in 2dimensional symmetrical structures. Determine the proper welding sequence to reduce residual stresses, distortion, or a relation between both parameters in 2 and 3 dimensional symmetrical structures. Verify if the proper welding sequence for 2-dimensional symmetrical structures is applicable to 3dimensional symmetrical structures, considering appropriate modifications. Develop a methodology for experimental tests. Perform experimental tests of the proper welding sequence to reduce distortion in a 2-dimensional symmetrical structure. Compare the numerical and experimental results on the proper welding sequence to reduce residual stresses or distortion in a 3-dimensional symmetrical structure.. 2 Isaac Hernández Arriaga.

(26) Welding Sequence Analysis. CHAPTER II WELDING SEQUENCE BACKGROUND AND METHODS FOR CONTROLLING RESIDUAL STRESSES AND DISTORTION INDUCED BY WELDING 2.1 Introduction This chapter presents the methods and advantages of reducing or controlling residual stresses and distortion induced by the welding process as well as a definition and classification of the welding sequence. It also includes a study of the welding sequence analysis, as well as a summary of previous welding sequence research, and a discussion of its advantages, disadvantages, scope, and limitations. 2.2 Advantages of residual stress and distortion control Controlling the residual stress and distortion in weldments provides two main advantages: (1) reduced fabrication costs by minimizing or controlling distortion, and (2) increased service life of the welded structure by controlling the induced residual stress. The benefits of distortion control are [1]: 1. Eliminate the need of expensive distortion correction and loss of accuracy. 2. Reduce machining requirements 3. Improve quality And residual stress control benefits are no less important [2]: 1. Maximize fatigue performance. 2. Minimize costly service problems. 3. Improve resistance to environmental damage.. 3 Isaac Hernández Arriaga.

(27) Welding Sequence Analysis 2.3 Methods to control welding-induced residual stress and distortion Some of the most popular methods used in the industry to control welding-induced residual stress and distortion include: welding sequence, definition of weld parameters, weld procedure, fixture design, precambering, prebending, thermal tensioning, heat sink welding, post-weld heat treatment, control of weld consumables and post-weld corrective methods [2]. 2.3.1 Welding sequence The proper welding sequence can minimize distortion and affect the distribution of the residual stress [4]. Figure 2.1 shows two welded frames. In the first frame (a) a proper welding sequence was not performed and a large distortion was produced. The second frame (a) shows a proper welding sequence which leads to less distortion.. Figure 2.1 Welded frame distortion [4]: (a) without considering a proper welding sequence, (b) considering a proper welding sequence. 2.3.2 Definition of weld parameter This method is based on control of weld parameters such as heat input, weld groove geometry, single-pass versus multiple pass welds, and type of joint [5]. The input heat is the most influential parameter in weldinduced distortion. Reducing welding heat input decreases all kinds of weld-induced distortions [2]. The heat input can be controlled through the welding speed and weld size. Faster welding not only reduces the amount of adjacent material affected by the heat of the arc, but also progressively decreases the residual stress. The important difference lies in the fact that faster welding produces a slightly narrower isotherm. The width of the isotherm influences the transverse shrinkage of butt welds, explaining why faster welding generally result in less residual stress [6]. When the specimen thickness decreases, the weld size also decreases, and a reduction in the volume of weld metal usually results in less residual stresses and distortion. However, when 4 Isaac Hernández Arriaga.

(28) Welding Sequence Analysis the specimen thickness decreases, the tensile residual stress in the areas near the fusion zone and distortion increase [6]. This is because thin weldments absorb more energy per unit volume. The use of small groove angles and root openings decrease the volume of weld metal, resulting in lower transverse shrinkage. For example, the use of a U-groove instead of a V-groove should reduce the amount of weld metal [3]. Welding is frequently performed in one pass, especially for thin plates. However, when welding is performed in multiple passes, particularly when welding thick plates, shrinkage accumulates [3]. 2.3.3 Weld procedure Welding procedures have considerable effect on distortion. Fusion welding often leads to the largest distortion, while laser (LBW), electron beam (EBW), and stir welding (FRW) result in lower distortion. However, friction stir welding can impart large plastic strains to the structure. These large strains, which locally strainharden the material, can influence the fracture response of the structure [8]. In fusion welding, residual stress distributions are similar; this is true when the design and relative size of the weldments are also similar. The most important fusion welding processes are Shield Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding (SAW), and Gas Tungsten Arc Welding (GTAW). However, the automatic or semiautomatic welding processes present more advantages in the residual stresses and distortion control due to their repeatability. 2.3.4 Fixture design This method is based on the design of clamps, jigs and rigid supports that restrain displacements and rotations of some portions of the welded components or the complete structure. However, the use of these devices increases residual stresses [7,9-10]. Figure 2.2 shows a rigid support formed by a back plate and two clamps. The clamps restrain the angular distortion of the welded joint.. Figure 2.2 Rigid supports [4]. 2.3.5 Precambering This method consists on elastically bending some of the components (usually in a specially designed fixture) in a predefined manner before welding. After welding, the precamber is released and the fabricated structure 5 Isaac Hernández Arriaga.

(29) Welding Sequence Analysis “springs back” to minimally distorted shape [2]. Figure 2.3 shows a precamber with a curved surface. The structure is fixed to the device by clamps.. Figure 2.3 Precamber with a curved surface [2]. 2.3.6 Prebending This method consists of plastically bending some of the components before welding, and possibly before placing them in a fixture. After welding, the desired “non-distorted” shape result. The welding is performed with or without a fixture [2]. Figure 2.4 shows a prebending in a fillet weld.. Figure 2.4 Pre-bending [2]. 2.3.7 Thermal tensioning This method consist on strategically moving a heat source ahead of, beside, behind, (or combinations of these) the moving weld torch. This method can control distortions and residual stresses during welding by controlling the heating and cooling rates [11,12]. Figure 2.5 shows thermal tensioning welding.. Figure 2.5 Welding with the thermal tensioning process [11]. 6 Isaac Hernández Arriaga.

(30) Welding Sequence Analysis 2.3.8 Heat sink welding This method is similar to thermal tensioning, except that a cooling source is strategically moved (or kept stationary) during welding (Figure 2.6).. Figure 2.6 Heat sink welding [1]. 2.3.9 Preheating Preheating the components being welded reduces residual stresses and distortion by reducing thermal gradients around the weld bead. Preheating has beneficial effects when welding steels by reducing cracks in the heat affected zones and weld metal [3]. 2.3.10 Post-weld heat treatment Heating all or parts of the welded fabrication to high temperatures (depending on the material) for a period on time may relieve welding stresses. Often the stresses cannot be fully relieved, i.e., some level of residual stress remains. This method is expensive and is often used to prevent service fracture problems such as corrosion, fatigue, creep, or combinations of them. 2.3.11 Post-weld corrective methods Corrective methods may reduce distortion or residual stresses in a welded component. Corrections made “after weld” are often expensive and time consuming. The most important post-weld corrective methods are press straightening, shot peening, laser shock peening, vibratory stresses relief, and hammer peening [3]. Remark: The control methods previously described can increase the production costs due to energy consumption, time, and/or expensive equipment. Other methods slow down production by requiring fixture devices. Welding sequence is inexpensive because it directly affects the temperature field of the welded structure, and consequently the residual stresses and distortion. Therefore, sequence analysis is fundamental for controlling residual stresses and distortion in welded structures. 7 Isaac Hernández Arriaga.

(31) Welding Sequence Analysis 2.4 Welding sequence definition The American Welding Society (AWS) defines welding sequence as the order of making welds in a weldment [13]. 2.5 Welding sequence classification Welding sequences are classified by the number of passes: single pass and multiple pass weld sequences. However, single pass sequences can be applied to multiple pass welds between beads [3]. 2.5.1 Welding sequence for single pass welds For thin components (up to ¼ inch) welding is performed in a single pass [3]. The weld bead is divided in short sections and welded considering the order and direction of the welds [3,14]. The more common welding sequences for single pass welds are: progressive, backstep, symmetric, and jump (Figure 2.7).. Figure 2.7 Sequences for thin-wall butt-welds [3]: (a) Progressive, (b) backstep, (c) symmetric, and (d) jump. Figure 2.7 (a) corresponds to progressive welding, where the weld beads are set down continually from one end of the joint to the other. In the backstep sequence (Figure 2.7 b), the weld beads are deposited in the opposite direction to the welding progress. Figure 2.7 (c) is the symmetric welding sequence, where the weld beads are deposited from the axis of symmetry of the joint. In the jump welding sequence (Figure 2.7 d) the weld beads are deposited in intermittent form. 8 Isaac Hernández Arriaga.

(32) Welding Sequence Analysis 2.5.2 Welding sequence for multiple pass welds For thick components (over 1/4 inch), welding sequences are classified as [3]: •. Built-Up: The first layer is completed along the entire weld length through the previously described single pass sequences (progressive, backstep, symmetric, jump sequences, etc.), followed by the second, third, etc. (Figure 2.8). This sequence applies to large-diameter butt-welded pipe joints frequently used in boiling water reactors, oil pipe transport systems, and steam piping systems.. Figure 2.8 Built-Up welding sequence on thick-wall butt-weld [3]. •. Block welding: A given block of the joint is welded completely and then the next block is welded, and so on. This kind of welding sequence is applied mainly to very long joints (e.g., ship hulls). Figure 2.9 shows the block welding sequence on thick-wall butt-weld, where first the end blocks of the joint are welded in, and later the central block is added to the joint.. Figure 2.9 Block welding sequence [3]. •. Cascade welding: It is similar to the block welding sequence; the main difference is that the ends of the blocks overlap. An application of this sequence is welding of long thick plates (Figure 2.10).. Figure 2.10 Cascade welding sequence [3]. 9 Isaac Hernández Arriaga.

(33) Welding Sequence Analysis 2.6 Welding sequence selection based on empirical rules For complex geometries, several empirical rules useful to decide the welding sequence have been introduced [15]: Rule 1.. The weld bead closest to the previous can be selected next.. Rule 2.. The weld bead farthest from the current can be next.. Rule 3.. Weld beads with greater restraint should be chosen next.. Rule 4.. Weld beads symmetric to the neutral axis are selected next.. Rule 5.. Weld beads originate from the center points of a structure progressing outwards.. Rule 6.. Weld beads that are not adjacent to the current can be next.. Optimizing welding productivity demands minimization of the torch moving distance between weld beads, as in rule 1. However, rule 1 is not appropriate for welding quality because successively welding close beads can generate a very high heat flux that results in serious thermal distortion. Rules 2, 3 and 4 can improve welding quality at the expense of welding time. To tackle both issues simultaneously, rules 5 and 6 are introduced. Remark: The authors in [15] do not clearly define "weld quality,” nor do they mention what specific weld parameters improve or worsen with the previously mentioned algorithms.. 10 Isaac Hernández Arriaga.

(34) Welding Sequence Analysis. 2.7 Welding sequence background Teng and Peng [16] investigated the reduction in residual stresses caused by welding by analyzing the effects of welding sequence on residual stress distribution in single and multi-pass butt-welded plates and circular patch welds. The research was conducted through finite element-based thermo elastic plastic analysis and simulated weld thermal cycles. The test specimen dimensions and the different welding sequences used in the thin-wall butt-weld analysis are shown in figure 2.11. The authors worked with three different welding sequences: (1) progressive, (2) backstep, and (3) symmetric.. Figure 2.11 Welding sequences for thin-wall butt-welds [16]: (a) Progressive, (b) backstep, and (c) symmetric. Figure 2.12 (a) and (b) show the distribution of the longitudinal residual stresses along the X-direction (at Y=150 mm) and Y-direction obtained with progressive, backstep, and symmetric sequences. These figures reveal that the symmetric sequence produced the lowest residual stresses.. 11 Isaac Hernández Arriaga.

(35) Welding Sequence Analysis. Figure 2.12. Longitudinal residual stress distribution [16]: (a) Along the X-direction and (b) along the Y-direction. 12 Isaac Hernández Arriaga.

(36) Welding Sequence Analysis. Reference [16] also considered butt-welded thick plate joints (figure 2.13). Three different cases are considered. Case (A): welding half of the upper groove, the whole lower groove and then the remaining upper groove. Case (B): welding half of the upper groove, half of the lower groove, the remaining of the upper groove and then the remaining lower groove. Case (C): welding the whole lower groove before the whole upper groove.. Figure 2.13 Different welding sequence for thick-wall butt-welds [16]. Figure 2.14 (a) and (b) depict the distribution of the longitudinal and transverse residual stresses obtained with various types of welding sequences. Longitudinal residual stresses between various welding sequences did not appear to differ significantly. However, the transverse residual stresses of case (A) were smaller than those of the other welding sequences. This difference might be attributed to two reasons: (1) the symmetric welding sequence can reduce the residual shrinkage or (2) the symmetric welding sequence has pre-heating and post-heating effects.. 13 Isaac Hernández Arriaga.

(37) Welding Sequence Analysis. Figure 2.14 Residual stresses distribution along the X-direction in various welding sequences for thick-wall butt-welds [16]: (a) Longitudinal and (b) transverse. 14 Isaac Hernández Arriaga.

(38) Welding Sequence Analysis Finally, the effect of sequences on residual stresses for circular plates is reported [16]. Figure 2.15 shows the various welding sequences for circular patch welds.. Figure 2.15 Geometry and various welding sequence for circular patch [16]: (a) Geometry of circular patch welding, (b) Progressive sequence, (c) backstep sequence, and (d) jump sequence. Figure 2.16 (a) depicts the distribution of circumferential residual stresses and reveals that the various welding sequences do not appear to differ significantly. Figure 2.16 (b) depicts the distribution of radial residual stress and reveals that the backstep sequence has smaller radial residual stresses than the other welding sequences. This is because the post-weld treatment and the pre-heating effect of backstep sequence are better than in the other welding sequences. Remark: Reference [16] is applicable only to simple structures, and the numerical simulations do not consider the welding direction. No experiments were conducted for validating the numerical results for the different welding sequences. 15 Isaac Hernández Arriaga.

(39) Welding Sequence Analysis. Figure 2.16 Residual stress distribution for various welding sequences [16]: (a) Circumferential and (b) radial. 16 Isaac Hernández Arriaga.

(40) Welding Sequence Analysis Ji and Fang [17] investigated the influence of welding sequence on the residual stresses of a thick plate. Authors worked with double V-groove multiple-pass butt-welds and adopted the converse welding method between adjacent layers, or between adjacent weld beads in every layer. They analyzed a coupled thermomechanical model using finite element and an ellipsoidal heat source. The numerical results were validated against experimental results (the x-ray method). Figure 2.17 depicts the dimensions of the analyzed specimen and the double V-groove configuration. In the numerical simulation the weld was divided into nine layers (figure 2.18).. Figure 2.17 Dimensions of the specimen, mm. [17]. Figure 2.18 Schematic of Weld bead´s delamination [17]. Table 2.1 displays several welding sequences analyzed to study the effect on residual stresses. The converse welding method, consisting of applying the opposite direction between adjacent layers in multi-layer welds, or between beads in every layer [17], was adopted between adjacent layers. Welding sequence Case (A) 231485967 Case (B) 234158697 Case (C) 231458679 Case (D) 128394567 Case (E) 123845967 Case (F) 123894567 Case (G) 123458697 Case (H) 234516879 Table 2.1 Different welding sequences used by Ji and Fang [17]. Table 2.2 shows the resulting peak value of the residual stresses. It can be seen from the table that the peak values of transverse residual stress or longitudinal residual stress obtained from case (C) are lowest. This 17 Isaac Hernández Arriaga.

(41) Welding Sequence Analysis is because the filler metal is being more uniformly applied, the angular deformation is minimized, and the residual stress is low. Parameter Equivalent residual stress (MPa) Transverse residual stress (MPa) Longitudinal residual stress (MPa). (A). (B). (C). Case (D) (E). 701 623 634. 712 544 636. 571 405 507. 885 718 823. 653 505 592. (F). (G). (H). 658 511 607. 921 829 879. 912 857 865. Table 2.2 Residual stress´s peak value for several cases [17]. To validate if the residual stress obtained by the converse welding method between adjacent layers is the minimum, the authors studied the welding stress of the double V-groove plate under classic and converse welding. The simulation results show that the peak value of the transverse residual stress by the method of converse welding is 18.2 % less than the stress obtained by the method of classic welding (Figure 2.19). Longitudinal residual stresses behave similar to the results shown in figure 2.19, but the peak value decreased by 16.9%. When converse welding is adopted, the residual stresses have an opposite distribution to the previous weld bead, reducing the residual stress value. Therefore, the beads produce a relatively uniform residual stress distribution and a lower residual stress value.. Figure 2.19 Comparison of transverse residual stress between welding in the same direction and welding in the inverse direction [17]. Remark: An important disadvantage of [17] is the computational cost to simulate the welding process because the model considered the effects of phase transformation and the type of heat source. 18 Isaac Hernández Arriaga.

(42) Welding Sequence Analysis. Nami, Kadivar and Jafarpur [18] studied the welding sequence in multiple blocks for the effect on the thermal and mechanical response of thick plate weldments by the use of a 3-D thermo-viscoplastic model. Anand´s viscoplastic model was used to simulate the rate dependent plastic deformation of welded materials. Also, they considered the temperature dependence of thermal and mechanical properties of material, welding speed, welding lag, and the effect of the filling material added to the weld. The model was compared with the results of two analytical and experimental works. Figure 2.20 depicts the configuration and dimensions of the welded blocks. The length of the welded strip was divided into seven parts and welded by different sequences. The arc was allowed to move in a forward (+X3) or in a backward direction (-X3). Figure 2.21 depicts the structural boundary conditions of the welded plates.. Figure 2.20 Configuration of welded blocks in a multi-block welding sequence [18]. Figure 2.21 Structural boundary conditions of welded plates (clamp fixture at both sides) [18]. The selected welding sequences in table 2.3 are commonly used in practice. In the first sequence the joining was done inwardly (toward the center of the plates) and in second sequence the joining happened toward the edge of the plates (outwardly). Welding sequence 1 2. Configuration +1, +7, +2, +6, +3, +5, -4 +2, +4, +6, +1, +3, +5,+7. Table 2.3 Welding sequences and orders applied into the multi-block model [18]. 19 Isaac Hernández Arriaga.

(43) Welding Sequence Analysis Figure 2.22 shows the final distortion profile in weldments, indicating the magnitude and location of the maximum plate distortion. As can be seen, the maximum distortion in sequence 1 is greater than in sequence 2.. Figure 2.22 Resulted distortion profile for two different block sequences [18]: (a) Welding sequence No. 1 and (b) welding sequence No. 2. 20 Isaac Hernández Arriaga.

(44) Welding Sequence Analysis Figure 2.23 shows two very different residual stress contours. The magnitude of the maximum von Mises stress that has been generated by sequence No.2 is greater than produced by sequence No.1. A large stress variation occurs in the region close to the welding pattern. In the region between the welding pattern and the edges, a small variation in the stress value is observed. In the region close to the edges, the boundary conditions introduce large residual stresses with sharp variations.. Figure 2.23 Distribution of the Von Mises stress using different block sequences. [18]: (a) Welding sequence No. 1 and (b) welding sequence No. 2. Remark: Reference [18] does not research the effects of the welding sequence on the relationship between distortion and residual stresses. The proposed methodology is computationally expensive because it considers visco-plastic effects.. 21 Isaac Hernández Arriaga.

(45) Welding Sequence Analysis Mochizuki and Hayashi [19] investigated the residual stress in large-diameter, multi-pass, butt-welded pipe joints for various welding sequences. The pipe joints had an x-shaped groove. The mechanism that produces residual stress in the welded pipe joints was studied in detail using a simple prediction model. The authors worked with a thermo-elastic-plastic analysis using finite element method with an axisymmetric model. Also, they determined an optimum welding sequence for preventing stress-corrosion cracking from the residual stress distribution. The configuration of a large-diameter, multi-pass, butt-welded pipe joint and its cross section is shown in figure 2.24.. Figure 2.24 Configuration of a large-diameter multi-pass pass butt-welded pipe joints and its cross section [19]. Figure 2.25 Welding sequences for a multi-pass Welded pipe joint [19]. The authors [19] proposed six welding sequences (figure 2.25) to study the dependence of the residual stress on the welding sequence. In case 1 the inner side of the groove is welded before the outer surface of the groove. In case 2, the outer side of the groove is welded before the inner surface of the groove. In case 3, half of the inner side of the groove is welded, then the whole outer side, and later the remaining inner side groove. In case 4, half of the outer side of the groove is welded, then the whole inner side of the groove, and later the remaining outer groove. In case 5, half of the inner side of the groove is welded, then half of the outer groove, later the remaining inner groove, and lastly the remaining outer groove. In case 6, half of the outside groove is welded, then half of the inside groove, later the remaining outside groove and at the end the remaining inside groove. Figure 2.26 (a) and (b) show a comparison between the circumferential residual stresses on the inner and outer surfaces of the groove; Figure 2.27 (a) and (b) show a comparison of the axial residual stresses on the inner and outer surfaces of the groove; and Figure 2.28 (a) and (b) show a comparison between the circumferential and axial residual stresses through the plate thickness along the heat-affected zone. All these figures consider multi-pass, butt-welded, pipe joints. 22 Isaac Hernández Arriaga.

(46) Welding Sequence Analysis. Figure 2.26 Comparison of circumferential residual stress in multi-pass welded pipe joints [19]: (a) Inner surface and (b) outer surface. 23 Isaac Hernández Arriaga.

(47) Welding Sequence Analysis. Figure 2.27 Comparison of axial residual stress in multi-pass welded pipe joints [19]: (a) Inner surface and (b) outer surface. 24 Isaac Hernández Arriaga.

(48) Welding Sequence Analysis. Figure 2.28 Comparison of residual stress across through-thickness along the heat-affected zone in multi-pass welded pipe joints [19]: (a) Circumferential and (b) axial. 25 Isaac Hernández Arriaga.

(49) Welding Sequence Analysis. In figures 2.26 (a), 2.26 (b) and 2.28 (a), the circumferential residual stresses behaved similarly: tensile circumferential stresses are distributed near the welding deposit on the inner and outer surfaces. The maximum stress occurs near the welded metal. Tensile stress then decreases and finally becomes compressive about 40 mm from the center of welded metal. In figures 2.27 (a), 2.27 (b) and 2.28 (b), the distribution of the axial residual stress near the welding deposit differs depending on the welding sequence. Stresses in the heat-affected zone vary with the welding sequence, both on the surface and through the thickness, but the axial residual stress distribution away from the welded metal is not affected by the welding sequence. Through-thickness axial residual stresses along the heat-affected zone have a big influence in the generation and propagation of stress-corrosion cracking in multi-pass, welded pipe joints. The inner surface is exposed to a more severe environment than the outer surface because the pipe may contain corrosive substances. There are two steps in selecting an optimum welding sequence for preventing stress-corrosion cracking: (i) lowering the axial residual stress on the inner surface along the heat-affected zone, because crack generation should be prevented first; and (ii) lowering the through-thickness axial stress near the inner surface to reduce or eliminate crack propagation rate, even if a crack begins to propagate. According to figure 2.28 (b), cases 2, 3, and 6 are good candidates since they produced lower stresses on the inner surface of the heat affected zone. Among these, case 6 was the best because the axial throughthickness stress near the inner surface is almost zero up to a depth of 6 mm. This welding sequence should have the lowest probability of generating and propagating stress-corrosion cracking. Remark: In the work performed by Mochizuki and Hayashi [19], the analytical method proposed to determine the residual stresses through-thickness is only applicable to multi-pass, welded pipe joints. Therefore, the method is not valid for pipe joints of small diameter (single pass joints). The method presented has a good qualitative correlation with experimental and numerical data. However, quantitative correlation was not good.. 26 Isaac Hernández Arriaga.

(50) Welding Sequence Analysis Mochizuki, Hattori and Nakakado [20] studied the effect of residual stress on fatigue strength at a weld toe in a multi-pass fillet weld joint. The residual stress in the specimen was varied by controlling the welding sequence. They calculated the residual stresses by thermo-elastic-plastic analysis and compared them to strain gage and X-ray diffraction measurements. A weld joint was fabricated to evaluate the residual stress and fatigue strength. Two attachments were fillet-welded on both sides of a main plate, as shown in figure 2.29.. Figure 2.29 Configuration of a multi-pass fillet Weld joint, mm. [20]. Two joints were fabricated by changing the welding sequence, as shown in figure 2.30. In case 1, the final welding pass was set down in the attachment side, and in case 2 the final welding pass was set down in the main plate side.. Figure 2.30 Different welding sequences in multi-pass fillet weld joint [20]. Figure 2.31 depicts the experimental and numerical results for transverse residual stresses for the two welding sequences. The measured and analytical distributions of residual stress agree well. Therefore, the results from the thermo-elastic-plastic analysis were used to define the residual stress needed to evaluate fatigue strength. The transverse residual stress in the weld toe of the main plate was 170 MPa for the weld 27 Isaac Hernández Arriaga.

(51) Welding Sequence Analysis joint whose final welding pass was deposited on the attachment side (case 1), and 80 MPa for the joint with the final pass on the main plate (case 2).. Figure 2.31 Comparison of residual stress in a multi-pass fillet weld joint [20]: (a) case 1 and (b) case 2. 28 Isaac Hernández Arriaga.

(52) Welding Sequence Analysis Figure 2.32 compares the fatigue strength curves for the two multi-pass fillet weld joints. The vertical axis shows the nominal stress range along the loading direction, ∆σy, and the horizontal axis shows the number of cycles to failure, Nf. It was confirmed from observation during the fatigue test that the initial surface crack nucleated at the center of the weld toe and propagated as a semi-elliptical crack. The fatigue strength resulting from the two welding sequences was nearly the same in the low cycle range. A clear difference appears around 105 cycles, indicating that high cycle fatigue strength can be improved by varying the welding sequence. Therefore, the welding sequence corresponding to case 2 is better for multi-pass, fillet weld joints.. Figure 2.32 Relation between nominal stress range and fatigue life in multi-pass fillet weld joints [20]. Remark: In the work presented by Mochizuki, Hattori and Nakakado [20], the methodology is valid for simple fillet joints only. Two similar welding sequences were used, differing only in the order of application of two weld beads. 29 Isaac Hernández Arriaga.

(53) Welding Sequence Analysis. Tsai and Park [21] studied the distortion mechanisms and the effect of the welding sequence on panel distortion. In this study, distortion behaviors, including local plate bending and buckling, as well as global girder bending, were investigated using finite element analysis. It was found that buckling does not occur in structures with a skin-plate thickness of more than 1.6 mm, unless the stiffening girder bends excessively. They applied the joint rigidity method (JRM) to determine the optimum welding sequence for minimum panel warping. The JRM consists of starting with more rigid joints and progressively moving toward less rigid joints [21]. Figure 2.33 shows the geometrical configuration of the panel structure. This panel is formed by one skin plate, three longitudinal, and three transverse T-stiffeners. The welding sequence simulation includes: i) laying tack welds along the joints and, ii) laying structural welds at various joints with different sequences.. Figure 2.33 Aluminum panel for study on welding sequence effect on angular distortion [21]. Four welding sequences were investigated in this study (figure 2.34). Sequence No. 1 deposits the weld from the inner panels moving outward. Sequence No. 2 lays the weld from the outer panels moving inward. Sequences No. 3 and 4 are respectively similar to sequences 1 and 2. Sequence No. 3 searches for the joint 30 Isaac Hernández Arriaga.

(54) Welding Sequence Analysis with the highest constraint to deposit the next weld as the welding process progresses. Sequence No. 4 lays the next weld at the least constrained joint.. Figure 2.34 Welding sequences for angular distortion analysis of aluminum panel structure [21]. Figure 2.35 shows the vertical displacement along the cross section of the four panels for the four welding sequences being investigated. The origin of the coordinates is at the lower left corner (point A in figure 2.34). The global distortion of the panel in all cases shows a downward movement and tilting toward the unsupported corner due to the structural weight. The high peak values in the displacement curves indicate the location of the stiffeners. 31 Isaac Hernández Arriaga.