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assumed that the underlying substrate does not yield and it is used for the hoop stresses due to internal pressure only. Where, (Equation 4.10) External pipe diameter with circumferential defect, D = 0.2121 m Specified Minimum Yield Strength, S = 241 N/m 2 Tensile Modulus for steel pipe, Es = 209 GPa Tensile Modulus for composite laminate, Ec = 25 GPa Internal design pressure, P = 9.05 MPa Maximum allowable operating pressure (MAOP), Ps = 7.68 MPa From the calculation, the minimum thickness (tmin) required for the composite repair is 5.04 mm and the installed composite repair with eight layers has a thickness of 6.56 mm. This means this repair design is safe to be used in the experimental work. 4.4 Methodology of Experiment In any study of the integrity of oil and gas pipeline repair, it is wise to design and fabricate a test rig on site which mimics the actual pipeline, especially in terms of specifications and operating pressures. Normally, a common diameter of oil and gas pipeline is eight inches as reported by the Department of Resources (2010) and one of the examples, is the Mereenie crude oil pipeline project in South Australia. With this size, the maximum operating pressure is around 90 bar. Likewise, with a similar pipe size, the County of Santa Barbara (2009) reports that the normal operating pressure 136
should be between 20 and 28 bar and the maximum allowable pressure should not be more than 95 bar. Based on the above operating pressures and size, the simulation of a pipe model and an experimental test rig for this PhD study were carried out. The experimental test rig was fabricated from API 5L Grade B carbon steel with an eight inch nominal pipe size (NPS). By referring to the results of detailed calculation for pressure vessel and development of the test rig in Appendix 1, the maximum operating pressure was 90.8 bar. ASME B31.4 and 31.8 standards were followed in this development in terms of design, construction, testing, welding and other quality related factors as referred to by Michalopoulos and Babka (2000). Since one of the objectives of this study was to analyse the integrity of bonding between the damaged pipeline, due to corrosion, and the composite repair, artificial arc- shaped notches were introduced on the outside of the test rig specimens with a groove defect of 40 mm length and 3.5 mm depth. Because of this defect, the maximum operating pressure in this experiment was reduced to 50 bar only, after taking into consideration the safety factor of the pipeline. The metal loss defects were actually machine simulated (by turning machine) or created by the actual corrosion that occurred during the normal operating life of the straight pipeline segments. Other researchers such as Freire et al. (October 2006) and Alexander (2007b) also present artificial metal loss defects but they use different types of defects and methodology. This damaged pipeline was later repaired with eight layers of composite wrap and each ply has a thickness of 0.83 mm. Initially, this study had several technical and commercial constraints during the early stages and that is why some of the parameters were finally changed and simplified, as illustrated in Figures 4.4 and 4.5. This study involves blunt defects due to corrosion damage only. For through-wall corrosion damage, references can be made to other literature, for example work carried out by Da Costa Mattos et al. (2009) and others. 137
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CRANFIELD UNIVERSITY MAHADI ABD MUR
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ABSTRACT One of the most common pro
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TABLE OF CONTENTS ABSTRACT ........
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3.7.1 Introduction ................
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5.6 Summary and Conclusions .......
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Figure 3.1: Schematic diagram of th
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Figure 5.4: The average temperature
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NOMENCLATURES ACFM Alternating Curr
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1 INTRODUCTION One of the most comm
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1.1 Objectives Knowing this backgro
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The methodology of this integrated
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Chapter 6 contains the summary and
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period of the major part of the exi
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Figure 2.2: Reported interest in de
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Figure 2.4: Dent damage caused by v
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presented current practices, recent
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Energy Workforce Sdn Bhd (2011) cla
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available provides real time detect
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2.3.3 Reliability Analysis of Infor
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Figure 2.9: Pipeline failure probab
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2.3.3.1 NDT Reliability and POD cur
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increase in the yield limit of stee
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the SCC assessment in their integri
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Manufacturers such as Walkers Techn
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Company L.P, 2005); Aquawrap ® pro
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monitoring, inspection, and damage
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2.6.2 Aims of Structural Health Mon
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Figure 2.16: Application fields and
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egistered by the piezoelectric sens
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discretization error. Round-off err
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notches and Neuber‘s is better fo
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maximum local stress at discontinui
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De Carvalho (2005) concludes that t
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accurate simulation of loading espe
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Based on the above facts, the opera
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3 FINITE ELEMENT ANALYSIS (FEA) IN
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Figure 3.2: Schematic diagram of th
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In this modelling work (i.e. compos
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This partition toolset also helps u
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Figure 3.6: Mesh control using Swee
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Figure 3.7: Schematic representatio
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discretization. Therefore, in this
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According to Staten et al. (2010b),
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3.5 The influence of pressure on th
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each pressure value remains constan
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Axial Stress, σa (S22) was referre
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Figure 3.14 shows a graph of analyt
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the notch defect is found to be in
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One of the contributions of this st
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Table 3.4: Convergence tests on var
Page 105 and 106: Figures 3.16 and 3.17 show that the
Page 107 and 108: Figure 3.20 shows that as the relat
Page 109 and 110: 3.7.4 Concluding Remarks A biaxial
Page 111 and 112: yarns change and lateral contact be
Page 113 and 114: For predicting E2 and Gl2, a number
Page 115 and 116: Where: Ar = weight of one sheet of
Page 117 and 118: Where; The Stiffness matrix is trad
Page 119 and 120: simulations for the hoop strain at
Page 121 and 122: Figure 3.24: Finding the hoop stres
Page 123 and 124: Table 3.8: The effect of repair len
Page 125 and 126: four up to 18 layers. In this study
Page 127 and 128: hoop and axial stress concentration
Page 129 and 130: Table 3.11: Predicted Elastic Const
Page 131 and 132: Table 3.13: Axial Stress v/s L/W ra
Page 133 and 134: Hoop Stress (MPa) Figure 3.3: Hoop
Page 135 and 136: However, Frost (2008) and Alexander
Page 137 and 138: Table 3.17: Ratio of Axial Stress N
Page 139 and 140: axial load (e.g. buried pipelines t
Page 141 and 142: 3.10 Numerical Strain Analysis of C
Page 143 and 144: Figure 3.36 shows the contours befo
Page 145 and 146: Stress Concentration Factor 2 1.8 1
Page 147 and 148: In fact, for Notch 40 with 18 plies
Page 149 and 150: this second approach (i.e. the expe
Page 151 and 152: 4.2.2 Strain Gauge Selection and Cr
Page 153 and 154: Finally, a method used to calculate
Page 155: Where, and are the maximum and mini
Page 159 and 160: welded weld neck flange at both end
Page 161 and 162: Figure 4.7: Sensor and heating elem
Page 163 and 164: Figure 4.9: A summary of data acqui
Page 165 and 166: One of the objectives of doing this
Page 167 and 168: Figure 4.14: A schematic diagram of
Page 169 and 170: Table 4.1: Strain gauge readings at
Page 171 and 172: microstrain 3.00E-04 2.50E-04 2.00E
Page 173 and 174: However, the axial load transfer is
Page 175 and 176: Mircostrain 500 450 400 350 300 250
Page 177 and 178: Since the defect is not a flat notc
Page 179 and 180: Again, the epoxy resin plays a sign
Page 181 and 182: Table 4.4: Study at the defect area
Page 187 and 188: 14.25% in hoop strain and 23.5% in
Page 189 and 190: consideration for the selection of
Page 191 and 192: 5.4 Methodology of Thermal Expansio
Page 193 and 194: Figure 5.1: Some preventive measure
Page 195 and 196: 5.4.1 The Fundamentals of the Therm
Page 197 and 198: 5.5 Analysis of Results 5.5.1 The t
Page 199 and 200: Thermal Output (strain ) 0.0002 0.0
Page 201 and 202: (Strain ,ε) Figure 5.12: Coefficie
Page 203 and 204: (Strain ,ε) 0.0002 0.00018 0.00016
Page 205 and 206: Table 5.1: The strain readings afte
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maximum shear strain increase as th
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The above results show that shear s
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shear strains becomes more stable a
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for future safe design and operatio
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has been fully cured. Poor surface
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6.3 Primary PhD Achievements The ea
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In Chapter 5, the CTE was determine
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ASM International (2002), "Thermal
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Bucinell, R. B. (2001), Calculating
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Proceedings of OMAE'01 20th Interna
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Greenwood, R. (2002), UKOPA Pipelin
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Kotrechko, S. A., Krasovskii, A. Y.
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Mousavi, S. E., Xiao, H. and Sukuma
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Raju, I. S. and Newman, J. C. (1986
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Tennyson, R. C. and Mufti, A. A. (2
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Xue, L., Widera, G. E. O. and Sang,
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General Technical Specifications: T
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Photos of the Design and Build of t
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Composite Installation Process usin
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APPENDIX 3 - STRAIN GAUGE INSTALLAT
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Figure 7: Mylar tape was stuck onto
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Figure 19: Repeating the above proc
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2) Electrical Insulation Test Resul
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