Composite Patch Repairs – A New Qualification Methodology

The maintenance and the repair of offshore corroded metallic structures can be a challenge for operators, especially in ATEX environments (ATmospheres EXplosibles). Currently, the most popular repair technique is the crop and renew, which involves replacing the damaged area by new steel plates and stiffeners. To reduce the maintenance cost, shipyards and operators are seeking alternative efficient repair solutions. A composite patch repair with its high mechanical properties and ease of installation appears to be a promising candidate without compromising the safety. Indeed, such cold and non-intrusive repair technology can be applied in ATEX areas. While some applications have received qualification from Classification Societies, the number of large-area bonded repairs contributing to hull girder strength that have been approved remains limited. In this context, Bureau Veritas and its partners1 launched the Joint Industry Project (JIP) StrengthBond Offshore in 2019 to develop a methodology for the design assessment of bonded repairs. Determining the failure load of such composite/steel assembly is complex, as it involves mixed material interfaces that cannot be represented with standard specimens during the mechanical properties’ characterization phase. When designing bonded assemblies, simple approach involves stress analysis with analytical or numerical models but is limited when studying complex geometries and loadings. For the studied case, fracture mechanics approach utilizing Finite Element models with cohesive zone modeling was adopted to simulate the behavior of the multiple interfaces and identify the interface most susceptible to failure initiation. This approach paves the way for a new methodology for the qualification of composite patch repairs.