Optimized microwave excitation probe for general application in NDT of wall thinning in metal pipes of arbitrary diameter

highlights•This study develops a long-range inspection of metallic pipe using microwave.•This study proposes a new optimization parameter of microwave exciter probes.•A probe with the large parameter introduces microwaves into pipes largely.•The probe is optimized by numerical analysis on transmission characteristics.•Experiment using pipes with diameter of 19, 39 and 57.5 mm validates the parameter.

Generalized approaches to developing a microwave NDT for flaws inside an arbitrary diameter pipe through optimizing a microwave-exciting probe were investigated. A microwave probe obtained from a parameter-optimizing scheme based on transmission characteristics is proposed. Three-dimensional finite element simulation of five microwave probes indicates that a larger optimization parameter enables reduced microwave reflection, as well as improved single-mode propagation inside the pipe as compared with conventional probes. Experimental verification, using straight brass pipes of various diameters confirmed that the optimized microwave probe exhibits a larger signal-to-noise ratio for internal flaws when compared with conventional probes, thereby validating the new optimization parameter.