Issue 63

M. Khaise et alii, Frattura ed Integrità Strutturale, 63 (2023) 153-168; DOI: 10.3221/IGF-ESIS.63.14

PD t

live P D

ext

s

ext

  C





s

(1)







E t

E t

E t

E t

2

2

c min

c min

c min

S s

Eq. (1), P live is the internal pressure in the pipe at the time of repair application, E c and E s are composite and steel module of elasticity, t s is remained pipe wall thickness, t min is minimum required thickness of composite layer, D ext is pipe diameter, P is design pressure and finally  C is the composite allowable strain. The above equation as per standard ISO/TS 24817 and ASME PCC-2 gives a conservative repair thickness, hence it is safer and can sustain higher pressure but it requires more composite materials which incur more repair cost. It is very important to analyse the optimum composite repair thickness for cost effective repair system using numerical and analytical method and it should be validated with the experiment data set for assurance. The primary objective of this study is to develop 3D FE numerical model to evaluate the mechanical behavior of the wall loss defect pipeline and validate with glass fiber reinforced polymer (GFRP) composite repair systems. The numerical results of composite repair thickness are validated with previous experimental results of repaired wall loss defect pipe. The optimization of composite wrap thickness is performed on wall loss defect metallic pipeline for safe and economical composite repair system using numerical model. The proposed numerical model in this research can be used to optimize the composite repair thickness for cost effective repair system. Materials ydrostatic test was performed on composite repair of API-5L X56 steel pipe with 80% wall loss defect and the properties of the polymeric composite material was also determined before used for the damaged pipe. The steel pipe material has the following basic properties: Young’s modulus =210 GPa and yield stress=386 MPa and ultimate tensile stress =625 MPa. Tab. 1 presents the material properties of glass fibre and epoxy resin which used for wrap lamination over defect region of pipe. The experimental results of hydrostatic test and property determination of new polymeric composite material was already published in a previous study [4]. However, further a brief summary of the results is presented. H M ATERIALS AND METHOD

Material

Density (g/cm 3 )

Young´s modulus (GPa)

Poisson’s ration

Tensile strength (MPa)

Fiber glass Epoxy resin

2.55 1.18

72

0.21 0.30

3300

3.5

72

Table 1: Material properties used for manual lamination.

Pipe Testing Tab. 2 presents the geometrical dimension of wall loss defect API 5L X56 steel pipe. The length of pipe specimen is 600 mm and repaired length 300 mm which is half of the pipe length. Composite wrap (glass fibre reinforced) of 16.2 mm thickness calculated based on the design code ISO/TS 24817 is applied over defect region of pipe. Repaired wall loss defect pipeline is as shown in fig. 1. A well detailed hydrostatic test procedure and parameters are explained in [4]. The pressure curve of the hydrostatic test for repaired pipe is presented in Fig. 2. The repaired pipe with 16.2 mm composite thickness sustained the original design pressure of 32.3 MPa.

Parameters

Dimensions (mm)

Pipe thickness (t)

7.11

External diameter (D ext )

168.3 86.82

Defect length (L) Defect Width (W) Depth of defect (d)

39.1

5.65 Table 2: Geometrical parameter of metallic pipe and defect geometry [4].

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