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Fracture Mechanics Approach for the Maintenance Of Offshore Oil and Gas Pipeline

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Fracture Mechanics Approach for the Maintenance Of Offshore Onil ad Gas Pipeline.

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

CSN Team.

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