An external through type RA-EMAT for steel pipe inspection

Abstract The online inspection system for pipe rolling production lines is essential for product quality assessment and cost control. The electromagnetic acoustic transducer (EMAT) is contactless and can achieve a rapid quantitative inspection, however, the effective detection range of common portable EMAT is limited. To increase the detection range of a single EMAT without increasing the number of the channels, we propose a different EMAT configuration—ring array EMAT (RA-EMAT). With only one solenoid coil and sufficient permanent magnets, the entire cross section of the steel pipe can be test when using this configuration. Through simulations and experiments, the proposed RA-EMAT is capable of generating ultrasonic waves in multiple positions of the same circumference of the steel pipe simultaneously. The comparison tests show that the RA-EMAT has better inspection ability and accuracy than the piezoelectric ultrasonic transducer. Verification tests were also carried out on the sample pipe with four different wall thicknesses and the boiler water-wall tube with simulated corrosion defects, among which the blind-hole artificial defect with the minimum depth of 0.75 mm is accurately measured.