Experimental and Numerical Study on the Strength of Repaired Steel Pipes with Composite Patches under Internal Pressure

Considering the old methods of maintenance and repair of oil and gas pipelines such as welding or replacing a part of the damaged pipeline which include high costs and spending a lot of time, the important usage of novel methods with lower costs such as the use of composite patches can be highlighted. In this research, the strength of steel cracked pipe with composite patches of glass fibers and epoxy/polyester resins has been studied experimentally. A crack with a length of 15 mm in the longitudinal axis of the pipe is considered. The specimen was subjected to internal pressure by a hydraulic pump to evaluate the strength of the glass/epoxy and glass/polyester composite patches considering the effects of fiber distributions, fiber angles, number of layers, and dimensions. Also, a comparison has been made between glass/polyester composites in two modes of complete curing and initial curing. Finally, the experimental test results were compared with the numerical simulations obtained by Abaqus software and the accuracy and precision of the study were verified. Some of the obtained results indicate that arrangement and number of layers have significant roles in the pressure-bearing capacity of composite patches. In this paper, for the first time, the effect of composite patches with different fiber orientations and the number of layers as well as curing effects are considered for the cracked pipe. The results show that the pressure-bearing capacity of composite patches rises with increasing the number of composite layers. Also, it can be seen that after complete curing of the glass-polyester composites, the pressure-bearing capacity rises about 3 times in 3- and 5-layer composites, and in 7-layer ones, it increases about 2 times.