This paper presents a study on the durability of pultruded GFRP tubes subjected to seawater sea sand concrete (SWSSC) and seawater environments. Environmental conditions, time and temperature of conditioning, and the tube thickness were the studied parameters. Tensile and compressive strength tests were conducted to investigate the mechanical properties of tubes after conditioning. SEM and micro-CT were used to investigate the microstructural properties, degradation mechanisms and damage levels. Finally, models were proposed to predict the long-term performance of GFRP tubes under different conditions using Arrhenus theory. The results showed that SWSSC is significantly harsher condition for GFRPs compared to seawater. A reduction factor is recommended for tensile strength and compressive strength of GFRP tubes exposed to SWSSC and seawater environments.