Defect detection method for storage tank floors based on SH0 guided waves and frequency-domain SAFT imaging

Objective During long-term service, storage tank floors face structural safety risks from corrosion. Traditional detection methods suffer from low efficiency, require tank shutdowns for cleaning, and incur high costs, hindering online, efficient, and large-area inspection of modern tanks. Thus, there is an urgent need to develop a high-sensitivity, high-resolution, and long-distance detection method suitable for complex operating conditions.

Methods A novel non-destructive testing and imaging method was established by integrating SH0 guided waves with the frequency-domain Synthetic Aperture Focusing Technique (SAFT). Non-dispersive, low-attenuation SH0 guided waves were excited using a self-developed magnetostrictive shear guided-wave transducer, and frequency-domain SAFT was innovatively introduced for signal processing and imaging reconstruction. By comparing the dispersion characteristics of Lamb waves and SH0 guided waves in a 12-mm-thick steel plate, the superior propagation stability and anti-interference capability of SH0 guided waves at frequencies (64 kHz and 128 kHz) were confirmed. Based on these findings, a detection process encompassing excitation design, signal acquisition, frequency-domain compensation, and SAFT imaging was constructed.

Results Experimental verification was conducted on an 8 000 mm-long storage tank floor sample using transducers at 64 kHz and 128 kHz. The established detection method demonstrated excellent performance: 64 kHz low-frequency SH0 guided waves effectively identified defects with a 0.82％ equivalent cross-sectional loss at 2 550 mm, while 128 kHz high-frequency SH0 guided waves detected small defects with 0.32％–0.59％ loss in the near field. The integration of SH0 guided waves with frequency-domain SAFT significantly enhanced defect imaging resolution and reliability.

Conclusion The new method demonstrates superior performance in liquid environments and greater computational efficiency. It offers a novel solution for non-shutdown detection of storage tank floors and serves as a valuable reference for safety monitoring of large plate-type structures such as bridges, ships, and pressure vessels.