Experimental and theoretical study on crack detection in pipes filled with fluid

The possibility of representing a crack with straight front, normal to the axis, and part through-the-thickness in a straight pipe containing fluid under pressure, by a spring for simulating its transverse free vibration has been examined experimentally. The fluid considered is water. Two different materials; aluminium and mild steel have been examined. Crack size to pipe thickness ratio ranging from 0.19 to 0.64 is considered. Within the fluid (gauge) pressure range of 0–0.981 MPa examined, the stiffnesses obtained by deflection- and natural frequency-based methods show good agreement. This indicates that the representation of a crack by the rotational spring is reasonably accurate. The natural frequency-based method can also be used to detect the location of an unknown crack in the pipeline. This has also been examined. The maximum error in prediction is 2.6% for all the cases considered. Data presented on variation of rotational spring stiffness vs. ratio of crack size to thickness can be very useful in crack size detection in pipelines knowing the spring stiffness. The error in the crack size prediction using these plots lies in the range −16.44% to 10.30% for aluminium and −5.83% to 12.04% for mild steel.