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2 LITERATURE REVIEW ON STRUCTURAL INTEGRITY 2.1 Introduction This chapter presents an overview of relevant research that has been carried out for the topics proposed in this study. Initially, the scenario of current pipeline problems and condition assessment, which includes inspection, monitoring and reliability of information, is presented. Next, maintenance strategy, and corrective and preventive actions in terms of pipeline repair are also presented. These include the current practice of composite repairs which refers to relevant standards as part of the maintenance strategy. Afterwards, an overview of structural health monitoring as a preventive solution is explored, and a brief discussion on Finite Element Analysis (FEA) and experiments as an integrated Structural Health Monitoring (SHM) approach to the composite based pipeline repair are presented. This chapter ends with a summary and conclusions. 2.2 Pipeline damage scenario One of the most important problems facing pipeline engineers at the beginning of the 21 st century is ensuring the reliability and safety of operating gas and oil pipelines. The large number of pipe ruptures in recent years has led to loss of human life, the destruction of dwellings and industrial facilities, and huge environmental losses (Kaminskii and Bastun, 1997). To meet safety and environmental regulations, and operate cost effectively, striking the right balance between operational costs versus performance and potential failures is the main challenge (www.dnvsoftware.com, 2006). In the North Sea, as highlighted by Clausard (2006), many assets have been in operation more than 20 years and have almost reached the end of their design lives of 25-30 years. Kotrechko et al. (2002) in their study, also mention that the operating 8
period of the major part of the existing pipelines can be estimated as 20-30 years only. But, as oil prices increase, oil companies cannot afford to shut down production despite the threat of ageing problems (Alexander's Gas & Oil Connections, 2005). As a result, this long operating time leads not only to the appearance of macro defects but also affects the mechanical properties of pipelines, as addressed by Thodi et al. (2008), and changes to the material and/or geometric properties of these systems, including changes to the boundary conditions and system connectivity which are defined as damage by Farrar and Worden (2007), adversely affecting the system‘s performance. According to statistics, every second failure has been caused by metal degradation (Lebedev et al., 2003); this is also agreed by Sosnovskii and Vorob'ev (2000) who, in their literature study, list a few main factors as being responsible for the deterioration of material properties and that threaten the integrity of the assets, thus becoming the inducing factors to failures. Normally, this phenomenon occurs during the operation itself and, inevitably, the mechanical properties undergo changes. The main factors are: mechanical loads, temperature and environment. Fatigue is another factor that causes pipeline damage. According to Benham et al. (1996), it happens when a material is subjected to cyclic or fluctuating strains at nominal stresses that have maximum values less than the static yield strength of the material. The resulting stress may be below the ultimate tensile stress, or even the yield stress of the material, yet still cause catastrophic failure. They also mention that fatigue mechanism has influenced the stress concentration to play a major part in causing failure. Brennan (2008) explains that fatigue mechanism has two distinct phases: crack initiation which is based on strain life (e.g. low cycle pressure vessel) and stress life (e.g. high cycle gas turbine blade), and crack propagation. A good example of the crack initiation and propagation study has been carried out by Brennan et al. (2007). They have developed a technique termed controlled stitched cold working which applies different intensities of compressive residual stress at specific regions in a structure. This technique has considerably influenced the fatigue crack propagation by containing crack propagation in one primary direction (i.e. crack growth restricted in one direction); one 9
Page 1: CRANFIELD UNIVERSITY MAHADI ABD MUR
Page 4 and 5: ABSTRACT One of the most common pro
Page 7 and 8: TABLE OF CONTENTS ABSTRACT ........
Page 9 and 10: 3.7.1 Introduction ................
Page 11: 5.6 Summary and Conclusions .......
Page 14 and 15: Figure 3.1: Schematic diagram of th
Page 16 and 17: Figure 5.4: The average temperature
Page 18 and 19: NOMENCLATURES ACFM Alternating Curr
Page 21 and 22: 1 INTRODUCTION One of the most comm
Page 23 and 24: 1.1 Objectives Knowing this backgro
Page 25 and 26: The methodology of this integrated
Page 27: Chapter 6 contains the summary and
Page 31 and 32: Figure 2.2: Reported interest in de
Page 33 and 34: Figure 2.4: Dent damage caused by v
Page 35 and 36: presented current practices, recent
Page 37 and 38: Energy Workforce Sdn Bhd (2011) cla
Page 39 and 40: available provides real time detect
Page 41 and 42: 2.3.3 Reliability Analysis of Infor
Page 43 and 44: Figure 2.9: Pipeline failure probab
Page 45 and 46: 2.3.3.1 NDT Reliability and POD cur
Page 47 and 48: increase in the yield limit of stee
Page 49 and 50: the SCC assessment in their integri
Page 51 and 52: Manufacturers such as Walkers Techn
Page 53 and 54: Company L.P, 2005); Aquawrap ® pro
Page 55 and 56: monitoring, inspection, and damage
Page 57 and 58: 2.6.2 Aims of Structural Health Mon
Page 59 and 60: Figure 2.16: Application fields and
Page 61 and 62: egistered by the piezoelectric sens
Page 63 and 64: discretization error. Round-off err
Page 65 and 66: notches and Neuber‘s is better fo
Page 67 and 68: maximum local stress at discontinui
Page 69 and 70: De Carvalho (2005) concludes that t
Page 71 and 72: accurate simulation of loading espe
Page 73 and 74: Based on the above facts, the opera
Page 75 and 76: 3 FINITE ELEMENT ANALYSIS (FEA) IN
Page 77 and 78: 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
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Figure 4.7: Sensor and heating elem
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Figure 4.9: A summary of data acqui
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One of the objectives of doing this
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Figure 4.14: A schematic diagram of
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Table 4.1: Strain gauge readings at
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microstrain 3.00E-04 2.50E-04 2.00E
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However, the axial load transfer is
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Mircostrain 500 450 400 350 300 250
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Since the defect is not a flat notc
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Again, the epoxy resin plays a sign
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Table 4.4: Study at the defect area
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Mircostrain 300 250 200 150 100 50
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Mircostrain 600 500 400 300 200 100
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14.25% in hoop strain and 23.5% in
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consideration for the selection of
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5.4 Methodology of Thermal Expansio
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Figure 5.1: Some preventive measure
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5.4.1 The Fundamentals of the Therm
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5.5 Analysis of Results 5.5.1 The t
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Thermal Output (strain ) 0.0002 0.0
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(Strain ,ε) Figure 5.12: Coefficie
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(Strain ,ε) 0.0002 0.00018 0.00016
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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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