Effects On Mechanical Behavior Of Glass Fiber Reinforced Epoxy Pipes

M.V. RAMOS, R. MAZZINA, C.R. BERNAL, P.E. MONTEMARTINI

Viña del Mar, Chile

Simposio; IV Simposio Argentino-Chileno de Polímeros ARCHIPOL IV; 2007

Piping is one of the most rapid expanding areas for composites in the chemical, oil and gas, among other industries. Glass fibre reinforced pipes (GFRP) have applications in pressure pipelines as well as in industrial sewerage systems. The use of GFRP tubing for industrial applications requires the understanding of the degradation processes involve under service conditions. Moreover, GFRP failure in service is mostly attributed to the aging that occurs under particular environment. Several studies have shown the pernicious effect of temperature, light and humidity on the composite mechanical behaviour. The corroding influence of the alkaline environment has also been reported. The main goal of this work is to understand the aging process of GFRP. Commercial glass/epoxy filament-wound pipes were used. The matrix was an anhydride cured epoxy system. Specimens were directly cut from pipes in the longitudinal direction. Four sets of specimens were aged under benzene and distilled water at different temperatures. After absorption, samples were dried in order to evaluate permanent damage. A completely different behaviour of the GFRP aged in different environments was observed. Distilled water seems to reach equilibrium close to 0.23% in W20 and W60 environment. On the other hand, at 80ºC (W80) no equilibrium is reached after 180 days. B20 samples increase their weight up to 1.4% which seems to be close to equilibrium. DSC analysis shows different behaviour for W80 and B20 which is consistent with elastic modulus analysis. In the first run, B20 shows two transitions (55ºC and 117ºC). The low temperature transition could be assigned to plasticized phase with high benzene concentration. After drying, the low temperature transition disappears and material recovers the original Tg. On the other hand, after drying W80 Tg decreases 20ºC (98ºC), this can be associated to permanent damage. B20 elastic modulus recover after drying, while W80 remains constant. The effect of water at 80ºC could be attributed to interface and matrix hydrolysis which deteriorates mechanical behaviour and makes glass transition lower and wider. Benzene deterioration seems to be reversible and related with a diffusion process. The good agreement obtained between “lab aged” and “in service aged” samples allow to go further in explaining the GFRP aging process and proposing monitoring procedures.