DUCTILE FAILURE ANALYSIS OF API STEEL PIPE USING STRAIN BASED FAILURE CRITERIA SITI FIRDAUS BINTI MD SALLEH Report submitted in partial fulfillment of the requirement for the award of the degree of Bachelor of Mechanical Engineering BACHELOR OF MECHANICAL ENGINEERING UNIVERSITI MALAYSIA PAHANG JUNE 2013
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DUCTILE FAILURE ANALYSIS OF API STEEL PIPE
USING STRAIN BASED FAILURE CRITERIA
SITI FIRDAUS BINTI MD SALLEH
Report submitted in partial fulfillment of
the requirement for the award of the degree of
Bachelor of Mechanical Engineering
BACHELOR OF MECHANICAL ENGINEERING
UNIVERSITI MALAYSIA PAHANG
JUNE 2013
vii
ABSTRACT
This project was performed to propose ductile failure criteria as a function of the
stress triaxiality for the API X42 steel pipes. The objective of this project is to determine
the burst pressure of modeled pipe using strain based failure criteria. In this project,
uniaxial tension test was performed using three types of specimen. The specimen extracted
from API X42 5L steel pipe. The steel pipe was machined to desired dimension and obeys
the international standard of ASTM-E8 specimen. Three type of specimen which is smooth,
notch radius 1.5 mm, 3 mm and 6 mm prepared and undergoes uniaxial tension test. The
engineering stress-stress data retrieved from the test converted to the true stress-strain
curve. The true stress-strain data become as an input data to the simulation analysis. Initial
and final diameter of specimen was taken to calculate the strain fracture of the pipe. Stress
modified critical strain criteria were proposed by using the strain fracture. The findings of
the main parameter which is burst pressure predictions precede by using FEA software.
Finite Element analysis was performed by using MSC Patran/Marc 2008r1 software. In
MSC Patran, the API X 42 steel pipes was modeled. Burst pressure predicted compared to
the available industrial pipe design assessment in order to validate the obtained results.
viii
ABSTRAK
Projek ini telah dilaksanakan untuk mencadangkan kriteria kegagalan mulur sebagai
tekanan fungsi triaxiality untuk paip keluli API X42. Objektif projek ini adalah untuk
menentukan tekanan pecah paip dimodelkan menggunakan kriteria kegagalan berasaskan
ketegangan. Dalam projek ini, ujian ketegangan ekapaksi dilakukan dengan menggunakan
tiga jenis viiipecimen. Spesimen dikeluarkan dari API 5L X42 paip keluli. Ia telah dimesin
untuk menjadi contoh dan menurut standard antarabangsa ASTM-E8. Tiga jenis
viiipecimen yang licin, jejari bertakuk 1.5 mm, 3 mm dan 6 mm disediakan dan menjalani
ujian ketegangan ekapaksi. Data tegasan-terikan kejuruteraan dari ujian, ditukar kepada
graf tegasan-terikan benar. Data telah ditukar dijadikan sebagai input data untuk analisis
simulasi. Diameter awal dan akhir viiipecimen telah diambil untuk mengira patah tekanan
paip. Terikan kriteria tegasan kritikal yang diubahsuai telah dicadangkan dengan
menggunakan tekanan patah. Hasil parameter utama iaitu tekanan ramalan pecah telah
diteruskan dengan menggunakan perisian FEA. Analisis Unsur Terhingga dilakukan
dengan menggunakan MSC Patran / Marc perisian 2008r1. Dalam MSC Patran, API X 42
paip keluli telah dimodelkan. Bagi mengesahkan keputusan yang diperolehi, tekanan letus
yang diramalkan, dibandingkan dengan penilaian reka bentuk paip industry.
ix
TABLE OF CONTENT
Page
EXAMINER’S DECLARATION ii
SUPERVISOR’S DECLARATION iii
STUDENT’S DECLARATION iv
DEDICATION v
ACKNOWLEDGE MENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENT ix
LIST OF TABLE xii
LIST OF FIGURES xiii
LIST OF SYMBOLS xvi
LIST OF ABBREVIATIONS xvii
CHAPTER 1 INTRODUCTION
1.1 Research Background 1
1.2 Problem Statements 2
1.3 Objectives 2
1.4 Scopes of Study 3
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 4
2.2 Fundamental of API Pipe 4
2.3 Pipelines 5
2.3.1 Defects On Pipes 6
x
2.4 Engineering Stress-Strain Curves 9
2.5 True Stress-Strain curve 11
2.6 Finite Element Analysis 15
2.7 Failure Criteria 17
2.7.1 Stress Modified Failure Strain Criteria 17
CHAPTER 3 METHODOLOGY
3.1 Introduction 20
3.2 Research Flow Chart 20
3.3 Specimen Preparation 23
3.4 Machining Process 24
3.5 Uniaxial Tension Test 27
3.6 Simulation 31
3.6.1 Development of failure criteria equation 33
CHAPTER 4 RESULTS AND DISSCUSSION
4.1 Introduction 36
4.2 Uniaxial Tension Test Result 36
4.2.1 Results from Uniaxial Tension Test 36
4.2.2 Engineering Stress-Strain curve 42
4.2.3 Conversion of Engineering stress-strain curve 44
4.3 Materials 45
4.4 Finite Element Analysis 46
4.4.1 Determination of Stress Modified Critical Strain Criteria 47
4.4.2 FE Analysis Results 51
4.5 Effect of Corrosion Defect on Burst Pressure 56
4.5.1 Burst Pressure on Different Depth Defect 57
4.5.2 Burst Pressure on The Different Length Defect 58
4.5.3 Burst Pressure On The Different Width Defect 58
xi
4.6 Comparison of FEA to the Available Code 59
4.6.1Variation of Burst Pressure on the Different Length Defect 60
4.6.2Variation of Burst Pressure on the Different Depth Defect 61
4.6.3Variation of burst pressure on the Different Width Defect 63
CHAPTER 5 CONCLUSION
5.1 Conclusion 65
5.2 Recommendation 66
REFERENCES 67
APPENDICES
Appendix A 68
Appendix B 69
Appendix C 70
Appendix D 71
Appendix E 72
Appendix F 73
xii
LIST OF TABLES
Table No. Page
2.1 Chemical Composition of API X42 steel pipe 5
2.2 Mechanical Properties of API X42 steel pipe 5
3.1 The standard requirement in ASTM E8 procedures for smooth
specimens
23
3.2 The chemical composition of the material selected 29
3.3 Design of pipe defect for FEA 31
4.1 Final area of the specimen 41
4.2 Chemical Composition 45
4.3 Mechanical properties 46
4.4 Failure results CS1 52
4.5 Failure results CS2 52
4.6 Failure results CS3 53
4.7 Failure results CS4 53
4.8 Failure results CS5 54
4.9 Failure results CS6 54
4.10 Failure results CS7 55
4.11 Failure results CS8 55
4.12 Failure results CS9 56
4.13 Burst pressure result for each case 56
4.14 Variation of burst pressure on selected design code 59
xiii
LIST OF FIGURES
Figure No. Pages
2.1 External corrosion defect on pipe 6
2.2 Corrosion on the pipeline 8
2.3 The irregular length, width and depth of a typical corrosion
defect
9
2.4 Stress-strain curve 10
2.5 True stress-strain curve 14
2.6 FE meshes for notched tensile bars, (a) notch = 0.2R
(b) notch = 1.5R (c) notch 3R
15
2.7 Comparison of experimental engineering stress-strain data for
smooth tensile bars with FE results
16
2.8 Equivalent strain and stress triaxiality distribution of smooth
tensile bars
18
2.9 Stress triaxiality distribution 19
3.1 The process flow chart 22
3.2 The standard dimension for notch specimen 23
3.3 API X42 steel pipe 24
3.4 Band saw machine 24
3.5 Raw material of API X42 25
3.6 Conventional Milling machine for facing purpose 25
3.7 Standard specimen 26
3.8 Lathe machine 26
3.9 Cutting tool for notch shaping 27
3.10 Ready specimens 27
3.11 Profile projector machine 28
3.12 Spectrometer machine 28
3.13 Uniaxial tension test machine, INSTRON 29
3.14 Testing of the smooth specimen 30
xiv
3.15 Testing on the notch specimen 30
3.16 Tested specimen 30
3.17 Selecting the analysis type and start to build the pipe
coordinate
32
3.18 (a)The process of curving the coordinate (b) checking the
element of surface to ensure the next solid extrude will have
no element inside out
32
3.19 Meshed one-four pipe with the simulated corrosion defect 33
3.20 Pipe with simulated corrosion defect 34
4.1 Smooth specimen with d = 5.77mm 37
4.2 Smooth specimen with d = 5.82mm 37
4.3 Notched R1.5 with d = 6.41mm 38
4.4 Notched R1.5 with d = 6.09mm 38
4.5 Notched R3 with d = 6.30mm 39
4.6 Notched R3 with d = 6.2mm 39
4.7 Notched R6 with d = 6.24mm 40
4.8 Notched R6 with d = 6.22mm 40
4.9 Notched R6 d = 6.20mm 41
4.10 Engineering stress-strain graph 42
4.11 (a)Engineering stress-strain graph for notched specimen R1.5
(b) R3 (c) R6
43
4.12 Engineering stress-strain graph for notched R1.5, R3,R6 and
smooth specimen
44
4.13 True plastic stress-strain curve for API X42 45
4.14 Comparison of uniaxial tension test results to FE analysis 46
4.15 (a)Fracture strain vs. stress triaxiality for CS1 (b)CS2 (c)CS3