Defect Detection in Submerged Plate Structures Considering Inherent Irregularities

Abstract

Health monitoring for damage detection utilizing ultrasonic waves is an emerging field. It uses transmission of stress waves into a material to detect imperfections, damages or to locate changes in material properties. It becomes even more challenging when the specimen being monitored is submerged in water. But water can be used to advantage, as it acts a natural couplant. This report presents the use of above two techniques to detect the damage in steel plates, submerged in water, with seeded defects in the form of notches, considering the inherent irregularities in the plate specimen. Presence of the seeded defects in the plates has been detected by pulse transmission technique and the pulse echo method is used to localize the same. Negative spike pulse is used as an input signal to sending transducer through Pulser/Receiver system and transmitted pulse is received at the other end by receiving transducer. Ultrasonic waves are introduced at different angles to excite the different modes in the subject specimen in both pulse echo and through transmission technique. The signals thus obtained are digitized using digitizer card. Before scanning a plate seeded with defects, specimen plate is tested in healthy condition, for inherent irregularities in it. These inherent irregularities can lead to misinformation regarding the presence, extent and location of the defect. So a correction factor has been formulated to nullify the effect of the inherent irregularities present. The combination of pulse echo and pulse transmission readings has been successfully used to generate the tomograms of the specimen plate. Application of the correction factor on the readings obtained has been found to significantly improve the tomograms regarding the extent and location of the defect.