Long-Term Natural Aging Effects on Flexural Properties of E-Glass/Vinyl Ester Filament-Wound Pipes

Flexural tests were performed to investigate the effects of long-term natural aging on flexural stiffness and strength properties of E-glass-fiber-reinforced vinyl ester (GFRV) filament-wound pipes (fiber volume fraction ≈ 68%). The flexural properties were evaluated using three-point bending specimens cut longitudinally from pipes having 150-mm inner diameter and 6-mm wall thickness. Flexural specimens were cut from pipe sections aged under three schemes: un-capped 155-mm-long pipe sections exposed to outdoor conditions, capped 1250-mm-long pipes filled with wet oil and exposed to outdoor conditions, and un-capped 1250-mm-long pipes fully submerged in seawater. The exposure intervals were 12, 24, 36, and 48 months. The results revealed no measurable degradation of the flexural modulus of the un-capped pipes aged in the outdoor for all exposure times. Oil-filled and seawater submerged pipes exhibited continuous reduction in the flexural moduli with exposure time. No significant degradation was detected in the flexural strength of GFRV pipes aged under all exposure conditions for up to 48 months. The flexural strain corresponding to the maximum flexural stress did not show measurable degradation for un-capped pipes aged in the outdoor condition but decreased with exposure time for pipes submerged in seawater. The flexural moduli of GFRV filament-wound pipes carrying wet oil or seawater are susceptible to degradation primarily due to moisture uptake. The experimental correlation of decreasing flexural modulus and the lack of significant deterioration in the flexural strength with exposure time suggests that moisture-induced degradation in filament-wound GFRV pipes could be primarily attributed to intralaminar matrix micro-cracking.