Experimental investigation of the structural performance of fiber-reinforced patches in the repair of locally damaged steel pipes

In the present work, we investigate the performance of fiber-reinforced patches in the repair of a locally damaged steel pipe. The specimen of the study was submitted to hydrostatic tests before damage and after repair. Damage was generated as a through-thickness cut acting diagonally to the pipe axis. The repair patch comprised twelve layers of fiberglass plain weave fabric aligned orthogonally to the pipe axis. The layers were divided into four distinct sizes and overlapped in a stepped configuration. The hydrostatic tests were conducted until the maximum admissible pressure for the undamaged steel pipe. Two piezoelectric sensors and four strain gauges were used in the pipe's instrumentation. The signal obtained during the successive tests was processed in terms of acoustic emission. The repair patch successfully survived the test scenario, and acoustic emission detected no significant events. The repair patch robustness was assessed by incrementally degrading its surface and resubmitting the repaired pipe to the hydrostatic test. The repair patch only failed after degrading half of its surface (middle and top layers). A liquid penetrant test was used to demonstrate the patch's failure (surface moisture evidencing leaking), which occurred in the borders of the through-thickness cut. Furthermore, the presence of microcracks or damage propagation in the surroundings of the substrate damage was not detected using a borescope.