Abstract

Repairing cracked pipelines with fiber reinforced polymer is very practical and efficient for subsea pipelines in service. This article aims to study the bearing behavior of thin-walled aluminum-alloy pipes with through-wall crack after carbon fiber reinforced polymer (CFRP) repairing. The experimental investigation of defect-free pipes, cracked pipes and composite repair models of pipes with cracks subjected to compressive load was conducted. The pipe with artificial cracks was wrapped around by composite patches with epoxy. The repair effect was evaluated by comparing the load-displacement curve before and after repair. A finite element model of reinforced pipe wrapped by composite patches based on cohesive behavior was established to compare and verify the experiment. The numerical results are compared well with the corresponding experimental results, which proves that the winding layer can play an obvious bearing role after yielding in the crack region of the pipeline, and the sizes of crack and CFRP have a great impact on the repair effect.

Introduction

Pipelines in service will inevitably produce initial cracks or defects under working load or environmental conditions. The propagation of cracks will cause local or overall fracture failure of the pipeline. Therefore, pipelines with crack should be reinforced and repaired in time to ensure structural integrity and safety. The traditional repair method in engineering is welding or replacement of damaged pipelines, but the welding residual stress always results in the deteriorative property and poor ability to resist brittle fracture. Meanwhile, replacement of pipelines not only is time-consuming, but also has high economic cost. Composite materials for repairing cracked pipelines have been more and more widely used in the maintenance of building structures such as marine structures and aerospace due to the advantages of no welding, simplicity of operation, construction safety and high repair strength. This repair method is mainly to use epoxy to wind carbon fiber, glass fiber and other reinforced composite materials with high-modulus, high-strength and high fatigue resistance on the cracked pipeline to restore the bearing capacity of the damaged pipeline. Seicamv (2007) discussed the application of FRP materials in the reinforcement and repair of submarine damaged pipelines, and conducted a four-point bending quasi-static test on the repaired steel pipes, which proved that the composite materials could better enhance the ultimate strength and bending stiffness of the damaged submarine steel pipe. Zarrinzadeh (2017) studied the effect of glass/epoxy composite patch on fatigue life of cracked aluminum pipe under axial tensile load by extended finite element method. After repairing the pipe, the stress intensity factor decreased and the fatigue life of the repaired pipe increased significantly. Kobayashi (2012) and Liu JX (2017) studied the effect of the laminated thickness of the carbon fiber wrapped on the cylinder on its microscopic damage behavior under impact load. The experimental results showed that the thicker carbon fiber cloth can improve the stiffness of the cylinder and reduce the plastic deformation. Gao (2013) studied the buckling behavior of steel pipe reinforced with carbon fiber based on axial compression experiments. The results showed that CFRP layer can significantly improve the strength and stiffness of steel pipes. The number of carbon fiber layers has a linear relationship with the axial load, and a nonlinear numerical model was established to predict the axial bearing capacity. Sundarraja (2014) carried out a number of tests and analysis on the axial performance of hollow square steel reinforced with CFRP, and pointed out that increasing the width and thickness of CFRP layer could delay the local buckling of the square tube and help to carry additional load. The maximum increase in the bearing capacity of the specimen was 44.32 %.

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