Hydrostatic performance and debonding damage monitoring of CFRP reinforced cracked pipes embedded with fiber Bragg grating sensors

Steel pipelines frequently encounter cracking problems due to corrosion, impact, and in ocean service lives. Carbon fiber reinforced polymer (CFRP) composites provide an effective solution for repairing cracked pipes, because of their high strength, corrosion resistance, and ease of construction. In this study, thin-wall cracked-steel pipes (100 mm outer diameter) were strengthened using 2 layers of unidirectional carbon fiber fabric. During the hydrostatic test, the strain distributions of pipes were monitored by embedded multiple fiber Bragg grating (FBG) sensors. Testing results revealed that the CFRP wrapping improves ultimate hydrostatic pressure by 63.3 % compared to adhesive alone. The failure modes were initial debonding at the steel-adhesive interface, followed by tensile fracture of the adhesive and CFRP according to the finite element model. The debonding emergences were detected by the abrupt strain drop in the strain-pressure curves monitored by FBG. The length and width of the debonding region were monitored by the position of FBG sensors and strain drop values. The debonding regions exhibited spindle shapes, and the area increased progressively with the pressure. CFRP wrapping reduced the final width and areas of the debonding region by 17.2 % and 15.6 %, respectively, and increased the residual hydrostatic strength by a factor of 12.9 for adhesive alone.