Addition of silica in the adhesive primer layer of composite systems used to repair leak defects in metallic pipelines

Fibre reinforced polymer composites are often used to repair through-thickness corrosion damage in metal pipes. Usually, a primer adhesive layer is initially applied to the surface of the pipe and then the composite reinforcement is applied in concentric layers. This paper investigates the possibility of adding silica as a low-cost thixotropic thickener to a commercial epoxy resin to facilitate the application of the prime layer while maintaining the strength and effectiveness of the repair after curing. The study of the influence of the silica concentration on the rheological behaviour of the adhesive before fully cured was performed using a rheometer. A preliminary study about the influence of different fractions of silica on the rupture force of metal-composite hybrid bonded joints after full cure showed a good result with the concentration of 1% by weight of epoxy resin. Then, hydrostatic burst tests were carried out on specimens with through-thickness defects, repaired using the same composite, but with two different initial adhesive layers (same surface finish and layer thickness, but with silica and without silica). The study shows that introducing a low fraction of silica facilitates the application of the primer and does not significantly affect the strength of the repair.