Transducers Development And Application For Ultrasound Guided Wave Inspection On Oil Tank Bottom Plate

Aiming to inspect the bottom plate of large oil tank with guided waves, thecritical technique is researched. The emphasis is on designing the special transducersused for testing and the inspection of the complex structures in the bottom plate.(1) A planar coil EMAT (abbr. Electromagnetic Acoustic Transducer) is designedfor the corrosion evaluation and defect imaging. The EMAT can excite single mode S0mode Lamb wave at170kHz with same amplitude at the whole circumferentialdirection. With this EMAT the defects in steel plate can be inspected effectively andimaged.(2) A Chirped SH0mode EMAT is designed. The EMAT can generate a linearchirped SH0mode plate wave in ferromagnetic material. As the receiving sensor hasthe same period varied coil as the exciting sensor, the power of each frequency arrivedat the same time. Thus, the amplitude of the receiving signal can be multipliedwithout any loss of the time domain resolution. An emulator is designed based on thebasic principle of this transducer, each parameter of the Chirped EMAT is studiedwith the results of the emulator.(3) The viscoelastic oil deposition is divided into two types, one type with lowenergy loss and the other type with high energy loss. So that to compensate the resultsof guide wave inspection the thickness of the low energy loss type should be testedwhile the high energy loss type can be ignored in the inspection, As the low loss typedo the same effect to the guided wave as the equivalent elastic material, a bi-layerelastic model is built and the SH wave dispersion curve of the bi-layer is solved. Theguided wave propagating in bi-layer of steel plate and the deposition on it is studied,and the reason for mode jumping is analyzed. Through the researching on thevariation of SH modes dispersion curves at each deposition thickness, a method formeasuring the thickness of deposition with testing the group velocities of SH0modeof bi-layer is developed. The characteristic curves of the water scaling and carbondeposition on plate is extracted, and the experiment study of the steel-water scalingbi-layer is carried out. The results show that the method can be used for thicknessmeasurement of the deposition layer.