Detection of the hidden corrosion defect on a L-shaped structural steel using ultrasonic guided waves

Electricity transmission towers situated in open environments are continuously exposed to atmospheric and industrial impacts. Corrosion occurs inevitably under the impacts of these external factors. This study discusses the methodology of detecting and quantifying the internal defect created by corrosion using ultrasonic wave technique. Experimental sample was part of an onsite tower and made of painted steel, it has a slide-shaped corrosion defect. Experimental results reveal that wave energy measured in a particular corroded area is at least 10 times higher than that measured in pristine area. Also, a shift in ultrasonic wave vibration to low frequency range is also recorded in that area. Then the corrosion geometry is profiled and imported to a finite element model for further investigation. However, there is no such effect observed from the simulation with isotropic material. This suggests that the energy amplifying effect is not caused only by the corrosion geometry. As corrosion affects locally the material, further finite element analysis with material constants varying along the defect are performed. The simulations exhibit results close to the experimental measures. Such features are promising for estimating the localization and size of the defect as well as its approximate internal features, for example its depth to the surface and its approximate shape, and mechanical properties.