Study Effect of Crack on the Properties of Vibration in Pipes of Transporting Oil

This research aims to study the effects of cracks in pipes used to transport fluid oil (crude oil with a density of ρ_f = 895 kg/m³) with varied flow velocities on natural frequencies with various crack sites and depths. Pipes are susceptible to a variety of damage, such as cracking. The consequences of cracks are crucial in pipe structure design because they affect safety and vibration characteristics. The pipe was made of carbon steel with a modulus elasticity of (E = 210 GPa) and a density of ρ = 7850 kg/m³. Research focuses on vibration analysis of a pipe with a longitudinal surface crack for both analytically and numerically, the effect of the ratio of pipe radius to pipe thickness (R/h) on crack length, depth, and location. The results showed that due to a crack and flow velocity, the fundamental natural frequency was reduced, and the system instability onsets at a lower flow velocity in compliant systems compared with an intact pipe. Analytical solutions relied on constructing equations of motion in the state (Simply Support) for a fluid-transporting pipe with a crack. A computer program evaluated the mathematical formulation equation of the models (MATLAB). The crack measures 2 cm in length and depth (0.2h, 0.4h, 0.6h) mm, where h is the thickness of the pipe. Ansys software workbench 17.0 package has been used to perform the finite element method numerical solution. For the velocity of flow 0.75 m/sec, the highest percentage disparity for the fundamental natural frequency between numerical and analytical is 3.02%, whereas for the velocity of 1.5 m/s, the percentage disagreement is 2.10%.