Cure Behavior of Epoxies Used for CFRP Repair of Pipelines

This paper presents the results of a laboratory testing program on the curing behavior of one impregnating epoxy (Tyfo S) and one thickened epoxy (Tyfo WS) that are most commonly used in carbon fiber reinforced polymer (CFRP) repair of pipelines, including progression of cure at various temperatures; relative humidities and relationships between the degree of cure and properties such as hardness, glass transition temperature, and long-term water absorption of these epoxies; and tensile properties of the CFRP. Based on the tests performed, curing schedules can be established to achieve a minimum degree of cure of 85%, which is typically used in practice for newly installed CFRP liners prior to refilling of pipelines. Quality assurance procedures are proposed for verification of the degree of cure achieved in the field, including a project example where the proposed procedures have been used.