– Fracture Mechanics Approach for the Maintenance Of Offshore Onil ad Gas Pipeline –
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ABSTRACT
Failure of offshore oil and gas pipelines occurs under certain conditions due to some applied mechanical forces. These conditions constitute a potential threat to the integrity of in-service life span of the pipelines which can lead to loss of resources and environmental pollution.
Several studies have shown that pipelines fail as a result of Welding, Fatigue Crack Growth, Corrosion Fatigue, Stress Corrosion Cracking, and Erosion due to fluid flow.
TABLE OF CONTENTS
DEDICATION ………………………………………………………………………………………………………………………………. iii
ACKNOWLEDGEMENT …………………………………………………………………………………………………………….iv
ABSTRACT ………………………………………………………………………………………………………………………………. v
List of Figure ……………………………………………………………………………………………………………………………. viii
List of Tables ……………………………………………………………………………………………………………………………… ix
CHAPTER ONE: Background and Introduction ……………………………………………………………………………… 1
1.1: Research Background ………………………………………………………………………………………………………… 1
1.2: Problem Statement …………………………………………………………………………………………………………….. 3
1.3: Objective of the study ………………………………………………………………………………………………………… 4
1.4: Scope of the work ……………………………………………………………………………………………………………… 4
CHAPTER TWO: Literature Review …………………………………………………………………………………………….. 6
2.1: Fundamentals of fracture mechanics ……………………………………………………………………………………. 6
2.2: Pipelines and their failures …………………………………………………………………………………………………. 7
2.2.1: Fatigue Crack Growth (FCG) …………………………………………………………………………………………… 7
2.2.2: Corrosion Fatigue (CF) ……………………………………………………………………………………………………. 9
2.2.3: Stress Corrosion Cracking (SCC) ……………………………………………………………………………………. 11
2.2.4: Hydrogen Induced Cracking (HIC) …………………………………………………………………………………. 12
2.2.5: Stress Oriented Hydrogen-Induced Cracking (SOHIC) ……………………………………………………… 14
2.2.6: Erosion due to fluid flow ……………………………………………………………………………………………….. 15
2.3: Welding …………………………………………………………………………………………………………………………. 18
2.3.1: Laps ……………………………………………………………………………………………………………………………. 18
2.3.2: Hook Cracks ………………………………………………………………………………………………………………… 19
2.3.3: Girth Weld Cracks (GWC) …………………………………………………………………………………………….. 19
2.4.4: Narrow Axial External Corrosion (NAEC) ………………………………………………………………………. 19
2.4: Stress Intensity Factor ……………………………………………………………………………………………………… 20
CHAPTER THREE: Modeling ……………………………………………………………………………………………………. 21
3.1 Introduction …………………………………………………………………………………………………………………….. 21
3.2: Analytical Modeling of crack growth …………………………………………………………………………………. 22
3.3: Finite Element Modeling of Pipelines ………………………………………………………………………………… 23
CHAPTER FOUR: Results and Discussions …………………………………………………………………………………. 24
4.1: Introduction ……………………………………………………………………………………………………………………. 24
4.2: Crack Aspect Ratios (a/c) …………………………………………………………………………………………………. 24
4.3: Crack Depth to Pipe Thickness (a/t) …………………………………………………………………………………… 26
4.4: Hole Radius to Pipe Thickness ………………………………………………………………………………………….. 28
4.5.1: Stress Distribution ………………………………………………………………………………………………………… 30
4.5.2: Geometry …………………………………………………………………………………………………………………….. 31
4.5.3: Crack Growth Rate ……………………………………………………………………………………………………….. 32
CHAPTER FIVE: Conclusion and Recommendations for future work …………………………………………….. 36
5.2: Conclusion ……………………………………………………………………………………………………………………… 36
5.3: Recommendations for Future Work …………………………………………………………………………………… 37
REFERENCES …………………………………………………………………………………………………………………………. 38
INTRODUCTION
Oil and Gas Pipelines are used as a medium through which petroleum products are transported from the wells to the tanks. When it is under operation, it fails rarely; meanwhile, it causes extremely serious problems like loss of resources and lives if failure does occur.
Over half of all in-service pipelines fail as a result of some externally applied mechanical forces which must be properly analyzed to prevent reoccurrence. Fractographic examination is to determine the causes of failures by studying the characteristics of a fracture surface.
REFERENCES
[1] Fatigue of Materials 2nd Ed.– – – S. Suresh
[2] Critical Analysis of Crack Propagation — – P. Paris and F Erdogan (1963)
[3] Fatigue Crack Growth Characterization by LEFM parts 1 & 2—R. J. Allen, G. S. Booth and T. Jutla (1988)
[4] Lecture notes on Fatigue and Fracture—-Prof. Wole Soboyejo
[5] WWW. Corrosionpedia
[6] Mechanical behavior of Engineered Materials—-Prof. W.O. Soboyejo
[7] WWW.Ask.com
[8] Stress Intensity Factor Handbook
[9] The behavior of Short fatigue Crack—–Eds K.J Miller and E. R de Los Rios
[10] Stress Intensity Factor Equations for Cracks in Three Dimensional Finite bodies—J.C Neumann Jr and I.S.Raju
[11] WWW. Petrowiki
[12] Multiphase Flow in Pipes———Griffith P. 1984
[13] Engineering Data Book, Nineth Edition 1972
[14] Handbook of Stress Intensity Factor—–G.C. Sir
[15] Compendium of Stress Intensity Factor——-D.P. Rooke and D.J. Cartwright
[16] Stress Intensity Factor Handbook——–Y. Murakami et al
[17] Stress Intensity Factor for corner flaws——-A.F. Liu
[18] Stress Intensity Factor in Hollow Cylinder containing a Radial Crack—–Delale, F and Erdogan, F 1982
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