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.

轧管生产线在线检测系统对于产品质量评估和成本控制至关重要。电磁声换能器（EMAT）是非接触式的，可以实现快速定量检测，但普通便携式EMAT的有效检测范围有限。为了在不增加通道数量的情况下增加单个 EMAT 的检测范围，我们提出了不同的 EMAT 配置——环形阵列EMAT（RA-EMAT）。只需一个螺线管线圈和足够的永磁体，使用这种配置就可以测试钢管的整个横截面。通过模拟和实验，所提出的RA-EMAT能够同时在钢管同一圆周的多个位置产生超声波。对比测试表明，RA-EMAT 比压电超声换能器具有更好的检测能力和精度。还对四种不同壁厚的样管和模拟腐蚀缺陷的锅炉水冷壁管进行了验证试验，其中 精确测量了最小深度为0.75 mm的盲孔人工缺陷。