5. Coupon-Based Qualification of Bonded Composite Repairs for Pressure Equipment

Bonded composite repairs are increasingly installed on degraded pressure equipment and are frequently treated as permanent repairs. These repairs are installed on both external and internal corrosion defects. For external corrosion, the repair is assumed to halt further corrosion and therefore prevents further metal loss. However, for internal corrosion the damage process can continue and eventually lead to complete loss of the pressure vessel wall. In this scenario, the bonded repair failure mode switches from a tensile-based failure to an interfacial fracture scenario. As such, the current repair codes require the characterization of the interfacial fracture energy of the repair for input into a fracture-mechanics-based design approach. Currently these characterizations are performed on test vessels with a simulated through-wall defect. In this paper we describe a simple coupon-based test using a width-tapered-double-cantilevered beam specimen. Using fracture energy values derived from this test we can successfully predict the failure pressure of pressure vessels with simulated through-wall defects.