Session: DA-02-02 Design and Analysis of Piping Components-2

Paper Number: 121900

121900 - Testing Fracture Toughness of Composite Repair Bonding 

Pipelines, in petroleum industry in particular, are exposed to defects that can result in reducing their capacity of transferring oil. Composite repair wrapping is a new emerging method of repairing defected pipelines. To realize the extent of the load capacity for the repaired defected pipeline, it is important to understand the failure criteria for the composite wrapping. There are mainly three mechanism that can lead to the failure of the composite repair; failure of the metallic pipe, failure of the multi-layered composite laminate and the de-bonding between the repair and the metallic pipe substrate. The third type of composite repair failure is significantly important in the case of repairing a pipe with a through-wall defect.

Two approaches can be adopted to investigate the bonding failure of the composite repair. The first approach is based on studying the stress variation at the interface between the steel substrate and the composite repair, to determine the stress level that can trigger the bonding failure. This method would require testing the adhesive both in tension and in shear, to determine the bonding strength, and to incorporate these results in the stress modeling of the contact interface. The other approach is based on the fracture mechanics and interfacial fracture toughness to determine the critical pressure for the crack initiation and hence the bonding failure. Once a crack in the bonding is initiated, it will continue to propagate across the contact interface leading eventually to the leakage of the pressurized fluid. Because of the high level of stress variation and the complex stress pattern at adhesive interface, some literatures have concluded that the fracture mechanics approach is more appropriate and could be more valuable than shear bonding test.

Pressurizing a  composite repair wrapping, bonded on a metal pipe with through-wall defect, leads to formation a volumetric blister. As the pressure increases the volume of the blister increases until a crack in the bonding resin is initiated. Griffth’s fracture criterion states that a crack is initiated if the strain energy release rate due infinitesimal crack propagation is greater than or equal to the critical fracture toughness. The critical pressure at which the crack is initiated depends on several factors such as strength of the bonding resin, substrate surface preparation, and presence of defects due to operator variability. It is therefore important to investigate the bonding failure of the composite repair and to determine the critical pressure for different repair parameters (defect size, repair thickness, repair fiber orientation, etc.). The aim of this study is to experimentally, determine the failure pressure for a defected pipeline with a through-wall defect and a composite wrapping repair. This can be achieved through pressurizing a metallic plate with a through-wall defect and a multi-layered composite laminate, to have a better understanding for the effect the repair parameters on the onset of the repair de-bonding. This in turn can provide guidelines for designing a better repair that can be both stronger and economical.

Presenting Author: Abdullah Al-Shabibi Sultan Qaboos University

Presenting Author Biography: Associate professor in Department of Mechanical and Industrial Engineering at Sultan Qaboos University, Oman.

Authors:

Abdullah Al-Shabibi Sultan Qaboos University
Abdul-Majeed Al Ismaili Sultan Qaboos University
Mohammed Al Ghatrifi Sultan Qaboos University
Hisham Al Kindi Sultan Qaboos University
Hussam Al Mashrafi Sultan Qaboos University