Degradation behavior and lifetime estimation of fiber reinforced plastics tanks for hydrochloric acid storage

Fiber reinforced plastics (FRPs) are often used for chemical equipment because of their high chemical resistance, especially their resistance to acidic conditions. However, serious accidents have been reported when using such tanks with hydrochloric acid (HCl). We gathered FRP tanks used for 35% HCl storage from various chemical companies, and analyzed their changes in appearance, HCl penetration and residual flexural strength. We found that residual strength of FRP decreased to < 50 MPa after 24 years of usage. The strength degradation at the tank roofs was more severe than at other positions in the tanks; in these parts the residual strength was 10-25 MPa after 20 years of usage. The strength degradation of FRP is caused by diffusion of HCl into the FRP. If the diffusion of HCl reaches the reinforced layer of the FRP tank, the FRP strength sharply decreases. Based on our comprehensive analysis of FRP tanks, the lifetime of current FRP tanks for 35% HCl storage is estimated at < 20 years.