Purpose/Aim
Once a fire occurs in the cable shaft, it is easy to produce the “chimney effect”, thereby accelerating the spread of fire. As one of the important means to prevent the spread of fire, it is necessary to evaluate the performance of the fireproof sealing system of the cable shaft. Thus, this paper proposed a defect detecting method for the fireproof sealing system of cable shaft based on piezoelectric ultrasonic.
Experimental/Modeling methods
Firstly, the propagation characteristic equation of ultrasonic guided wave in the fireproof sealing system was constructed, and then the frequency dispersion equation of Lamb wave was obtained. By solving the frequency dispersion equation of the Lamb wave, the frequency dispersion curve was obtained. Next, Sparse Representation with Dispersion Based Matching Pursuit (SDMP) was used for processing received ultrasonic guided wave signals, which demonstrates good performance against noise with maximum sparsity. By comparing standard signals and signals processed by SDMP, defects in the fireproof sealing system can be found. Then, an ultrasonic guided wave detection device was developed, which includes a function generator, a power amplifier, piezoelectric plates for generating and receiving ultrasonic guided wave signals, a digital oscilloscope, and a computer for signal control and processing. Finally, a simulated experiment platform for the fireproof sealing system was built. In the construction process of the fireproof sealing system, the foreign materials would be placed in advance and cracks and gas holes would be made artificially. And the performance of the ultrasonic guided wave detection device was verified by detecting the artificial defects.
Results/discussion
The SDMP signal processing method can better extract meaningful information from the original signal. Based on the above defect detecting method, for defects (cracks, gas holes, and foreign material placed in advance) in the fireproof sealing system, the correct recognition rate can be higher than 90%.
Conclusions
In conclusion, as a non-destructive detection method, it can evaluate the performance of the fireproof sealing system without destructive experiments, which has a good application in state evaluation for the fireproof sealing system.
 

Defect detecting,fireproof sealing system,piezoelectric ultrasonic,SDMP