PSI - Issue 5

Amr A. Abd-Elhady et al. / Procedia Structural Integrity 5 (2017) 123–130 Amr A. Abd-Elhady et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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Damage is the main cause of crack initiation, and so bonded composite repair can be used to prevent leakage and restore all or part of the maximum allowable operating capacity of the pipeline. Furthermore, fiber reinforced polymer (FRP) materials are highly suited for use as repair material, as they possess a very high specific strength and stiffness, a high formability, an inherent immunity to corrosion, and ease of fabrication (Baker 1999). A number of studies have investigated pipeline with bonded composite patches, notably Shouman and Taheri (2009), Alexander and Ochoa (2010), API (2000), ASME (2006) and Köpple (2013). Failure analysis of pipe made of glass-reinforced plastic with an inclined surface crack under static internal pressure was investigated by Arikan (2010). He concluded that, the crack propagation occurred in Mode II. He mentioned that, the critical stress intensity factor according to mixed mode must be determined in order to study the failure of pipe with crack. Alexander and Ochoa (2010) developed a composite repair system of steel pipeline, formed from unidirectional fibers wrapped in the circumferential direction of the pipe. Moreover, Alexander and Ochoa (2010) deduced a formula to calculate the sufficient thickness of the repair wrap, depending on the ultimate tensile strength of the steel pipe and the ultimate tensile strength of the repair wrap. Alexander and Ochoa (2010) also developed an integrated analytical and experimental method to evaluate the integrity of an onshore composite repair technique. They used a carbon/epoxy- based composite system as a repair for steel pipe. Shouman and Taheri (2009) studied the response of repaired pipelines under internal pressure, axial force, and bending. Shouman and Taheri (2011) also used glass-reinforced polymer to repair steel pipelines based on strain-based design. They found good agreement between their experimental and numerical results. Shouman and Taheri (2011) concluded that the optimized design of composite repaired steel pipelines depends on the fiber orientation of composite repair. The prediction of fracture parameters such as J -integral, stress intensity factors (SIF), and failure strength is one of the most important aspects in the design of composite repair. If steel pipe is exposed to partial damage, the application of composite repair can reduce the spread of this damage. In the present work, the partial damage can be considered as an inclined stationary crack. The present work attempts to predict the path of crack emanating from inclined stationary crack located at the pipeline by the extended Finite Element method X-FEM. Furthermore, the effect of bonded composite repair at the cracked pipeline on the emanating crack path is examined. J -integral values of inclined stationary crack in steel pipe with/without composite repair have been calculated numerically. The effect of the fiber orientation of composite repair on the evolution of the J -integral of inclined stationary crack in steel pipe is examined.

2. Finite element method

2.1 Geometry and mechanical properties

The three-dimensional finite element model for composite repaired steel pipe consists of the pipe and glass fiber reinforced polymer GFRP composite repair. The geometry of composite repaired steel pipe was selected based on Shouman and Taheri (2011) and shown in Table 1. The typical repaired pipe model in the present work is shown in Fig. 1.

Table 1. GFRP composite repaired steel pipelines geometry, Shouman and Taheri (2011) Symbol Value Description L 3000 Steel pipe line length (mm) D 508

Steel pipe line length outer diameter (mm) Steel pipe line length inner diameter (mm)

D i

496

a

5, 35, 75 and 110

Inclined crack length (mm)

D r

540

GFRP composite repair diameter (mm)

0 o , 15 o , 30 o , 45 o , 60 o , 75 o and 90 o

Inclined crack angle

