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6 CONCLUSIONS AND RECOMMENDATIONS 6.1 Introduction The work presented in the previous five chapters presents investigations into the integrity of bonding in a composite-based pipeline repair using the integrated approach of structural health monitoring. This chapter summarises the content of these five chapters and salient points are addressed. It draws conclusions from the results of this research work and ends with some recommendations for future research to build on the current Study. 6.2 Summary and Conclusions An overview of the pipeline integrity management programme that involves four main components, namely Assessment, Monitoring, Mitigation and Life Extension, was presented. This management programme covers all the aspects of structural pipeline integrity, especially for ageing pipelines that are subject to several damages. In the process of mitigating these damages, the composite repair has provided to be a reliable and economic solution in extending the life of these ageing pipelines. An integrated SHM that mainly involves FEA (ABAQUS) and experimental work which is represented as an integrated pipeline repair system (i.e. Figure 1.2) have been carried out in the current work. This system interfaces all the above four main components with the main aim of encompassing a reliable and cost-effective life extension programme. The objectives and contributions of this Study were also presented in Chapter 1. In Chapter 2, a thorough literature review that was intended to give the background to the significance of the study in the field of pipeline integrity was carried out. It is important to really understand the scenario of pipeline damage and condition assessment, such as inspection, monitoring and reliability of information, so that enough data information of the damaged pipeline are obtained before making any decision on corrective and preventive actions in pipeline repair. Therefore, cost effective strategies 192
for future safe design and operation can be achieved. In this chapter, the composite repair was shown to be one of the reliable methods in the life extension of ageing pipelines. However, without SHM, the aim of successfully achieving the life extension programme may be difficult. Some SHM literature related to numerical and experimental works were further discussed in depth in this chapter. Despite optical fibre sensors having many advantages over electrical strain gauges, Rectangular Strain Gauge Rosettes were used for this study. Some preliminary studies on this type of sensor were carried out first based on many references, such as from literature, recommendations and advice from manufacturers, etc. prior to the final decision being made. The lack of a report or information on the integrity of the bonding study on composite-based pipeline repairs and the unpredictable quality of the installation of glass epoxy composite (wet wrap application) in the pipeline repair are among the key factors that motivated this PhD study. In Chapter 2 also, the previous and current researches show that stress concentrations in the pipelines refer to various discontinuities and defect geometries. However, none of the studies focus on the circumferentially arc-shaped defect on the pipeline. Hence, after comprehensive numerical works, the final half pipe model with a circumferentially arc-shaped defect has been selected and represents the actual pipe specimen. Stress and strain concentration factors based on a pipe with and without composite repairs were studied and analysed in Chapter 3. One of the significant deliverables of this Study is the establishment of a Pipeline Repair Index (PRI) which was studied in Chapter 3. Through the comprehensive study of stress distribution in the composite-based pipeline repair, the PRI is shown to be very useful in the design optimisation of these repairs. The optimum length of repair obtained from the PRI has been compared and validated analytically with ASME PCC-2 2006 and it can be concluded that the shorter the defect the better the design optimisation will be. Through the numerical strain distribution study, the reduction of strain concentration factor percentage (SCFI %) was analysed and the results were 193
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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
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Figures 3.16 and 3.17 show that the
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Figure 3.20 shows that as the relat
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3.7.4 Concluding Remarks A biaxial
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yarns change and lateral contact be
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For predicting E2 and Gl2, a number
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Where: Ar = weight of one sheet of
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Where; The Stiffness matrix is trad
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simulations for the hoop strain at
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Figure 3.24: Finding the hoop stres
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Table 3.8: The effect of repair len
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four up to 18 layers. In this study
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hoop and axial stress concentration
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Table 3.11: Predicted Elastic Const
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Table 3.13: Axial Stress v/s L/W ra
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Hoop Stress (MPa) Figure 3.3: Hoop
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However, Frost (2008) and Alexander
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Table 3.17: Ratio of Axial Stress N
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axial load (e.g. buried pipelines t
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3.10 Numerical Strain Analysis of C
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Figure 3.36 shows the contours befo
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Stress Concentration Factor 2 1.8 1
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In fact, for Notch 40 with 18 plies
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this second approach (i.e. the expe
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4.2.2 Strain Gauge Selection and Cr
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Finally, a method used to calculate
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Where, and are the maximum and mini
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should be between 20 and 28 bar and
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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
Page 207 and 208: maximum shear strain increase as th
Page 209 and 210: The above results show that shear s
Page 211: shear strains becomes more stable a
Page 215 and 216: has been fully cured. Poor surface
Page 217 and 218: 6.3 Primary PhD Achievements The ea
Page 219 and 220: In Chapter 5, the CTE was determine
Page 221 and 222: ASM International (2002), "Thermal
Page 223 and 224: Bucinell, R. B. (2001), Calculating
Page 225 and 226: Proceedings of OMAE'01 20th Interna
Page 227 and 228: Greenwood, R. (2002), UKOPA Pipelin
Page 229 and 230: Kotrechko, S. A., Krasovskii, A. Y.
Page 231 and 232: Mousavi, S. E., Xiao, H. and Sukuma
Page 233 and 234: Raju, I. S. and Newman, J. C. (1986
Page 235 and 236: Tennyson, R. C. and Mufti, A. A. (2
Page 237 and 238: Xue, L., Widera, G. E. O. and Sang,
Page 239 and 240: General Technical Specifications: T
Page 241 and 242: Photos of the Design and Build of t
Page 243 and 244: Composite Installation Process usin
Page 245 and 246: APPENDIX 3 - STRAIN GAUGE INSTALLAT
Page 247 and 248: Figure 7: Mylar tape was stuck onto
Page 249 and 250: Figure 19: Repeating the above proc
Page 251: 2) Electrical Insulation Test Resul
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