Experimental study of guided wave propagation and damage detection in large diameter pipe filled by different fluids

- Large-sized steel pipe with different fluids inside have been studied by damage detection of guided waves.
- The mode conversion exists most serious in water-filled pipe, then oil-filled pipe and weakest in vacant pipe.
- The time-frequency distribution of defect reflecting waves and converted waves are different.
- The relationship of defect length vs. defect signal strength is linear in vacant pipe and nonlinear in liquid-filled pipe.

A series of experiments on damage detection of large-diameter (88 mm diameter) pipe with and without liquid by guided waves have been conducted. Two types of liquid as water and machine oil are chosen to fill in pipe for detecting the influence of filler. The influences of liquid types on guided wave propagation, dispersion and attenuation characteristics have also been studied. The mode conversion phenomenon of reflection waves exists regardless filling state of pipe, but it is most serious in water-filled pipe, and weakest in vacant pipe. The defect wave signal could be distinguished from converted wave mode by time-frequency analysis, and the time-frequency distributions of the two type signals are different. The relationship between defect length and defect reflect signal strength is linear in vacant pipe and nonlinear in liquid-filled pipe. With the defect length increasing, the defect signals of liquid-filled pipe increase too, but the rate of increment are reduced.