The effect of composite patch in repairing and increasing the strength of cracked gas pipeline under cyclic internal pressure

Due to the presence of initial cracks in gas pipelines and to prevent the increase in replacement and repair costs, the use of composite patches in cracks areas has become popular in recent decades. In this research, the role and performance of composite patch to prevent with fatigue crack growth in steel pipes used in gas pipelines under cyclic internal pressure is investigated. . For this purpose, the method of intelligent growth of a semi-elliptical surface crack has been used for simulation using Ansys software. The findings of the research indicate the predominance of the peripheral sliding separation mode over the normal separation mode, which leads to the separation of the patch from the pipe. The internal crack of the pipe has more critical conditions in terms of stress and stress intensity factor than the external crack. The crack growth in the pipe depends on the type of loading and if the angle of the composite fibers is in the direction of the crack growth, the best reinforcement is provided. Also, with the increase of the internal pressure, the load cycles for crack growth are greatly reduced, and the use of glue between the pipe and the patch leads to a better transfer of strains from the pipe to the outer layers of the composite.