The research about ultimate load of CFRP repaired pipes under long-term seawater immersion and bending moment

Corrosion is a common failure form for subsea pipes. Corroded pipes are increasingly repaired by the composite material because of the low cost and the simple and quick process. However, the repair will be affected by factors such as long time bending moment and seawater immersion. To study the law of the effect, the bending moment and seawater immersion factors are considered in this paper. For the experiment of CFRP repaired pipes, 14 groups of CFRP-pipe specimens were designed, and 30% bending moment was applied, the seawater concentration 5 times more than that recommended by ASTM D1141-98 (2013) was adopted to accelerate the experiment. The pipe specimens were immersed in seawater for different time period (200 hours, 400 hours, 600 hours and 800 hours). The experimental result showed that the ultimate bending load capacity of the repaired pipe decreases with the increasing of time. To study the reasons for the decrease of the ultimate load of the repaired pipes, CFRP-steel plate and CFRP durability tests were set up, 5 groups of CFRP and 5 groups of CFRP-steel plate specimens were designed. It was found that the decrease of the interfacial bonding strength of CFRP repaired pipe and decrease of the CFRP strength resulted in the decline of ultimate load of repaired pipe.