Frequency-based experimental and theoretical identification of multiple cracks in straight pipes filled with fluid

A technique based on measurement of change of natural frequencies has been employed to detect multiple cracks in long pipes containing fluid at different pressures. The cracks have straight fronts and are non-leaking. Both theoretical and experimental results are presented. Two different materials, aluminium and mild steel, have been examined. The fluid considered is water; three (gauge) pressures in the range 0–981 kPa, and crack size to thickness ratio in the range 0.19–0.64 are studied. Two simultaneous cracks are considered in the experiments. The crack locations are predicted with an error less than 4.3%. Results on crack-equivalent rotational spring stiffness, which can be useful in the calculation of natural frequencies and crack size predictions, are reported.