Alternative methods for fracture energy acquisition in the qualification of composite repair system

Abstract

Composite repair systems for metallic pipelines presenting a through-wall defect must be qualified in accordance with either ISO 24817 or ASME PCC-2 standards. This qualification method requires a number of hydrostatic tests to obtain the failure pressure. In the oil and gas industry, the failure pressure estimation is often performed using a linear fracture mechanics analysis described in both ISO and ASME standards. These standards require the determination of a constant fracture energy, also called the energy release rate. In the case of monotonically increasing loading histories, in the framework of linear fracture mechanics, brutal interfacial debonding occurs when the fracture energy reaches a critical value. This study is an attempt to show that a simpler test, such as, shaft-loaded and pressurized blister test can be employed as an alternative to hydrostatic tests in the qualification of repair systems. The goal is to obtain experimentally the critical fracture energy using blister tests. Results show a reasonable similarity between the critical energy values found using both pressurized and shaft-loaded blister test with the ones obtained with the standard required hydrostatic tests.