LAUSR

Owing to their inherent advantages, non-metallic structures such as glass reinforced epoxy (GRE) pipes and high-density polyethylene (HDPE) pipes are rapidly replacing their steel counterparts in pipeline infrastructures. However, non-metallic pipes are vulnerable to a variety of defects which compromise their structural integrity. Hence, periodic inspection of these structures is incumbent to ensure their structural integrity and avoid catastrophic in-service failures. Microwave and millimeter wave non-destructive evaluation techniques have shown great potential for inspecting non-metallic structures due to their high sensitivity, resolution, and cost-effectiveness. However, most of the previous investigations performed on microwave non-destructive testing (NDT) of these particular structures are deemed limited since these investigations considered one probe type and often conducted over narrow frequency band. Furthermore, many of the previous microwave NDT investigations considered unrealistically large defects which renders the reported conclusions about the performance envelope of microwave NDT of non-metallic pipes rather inaccurate. Consequently, an uncertainty still exists in the domain with regards to detection capability of the method when the defects in the pipes are actually small in size. Unlike all previous investigations, a comprehensive and realistic microwave imaging of GRE and HDPE pipes with embedded defects of practical importance is demonstrated in this paper. In order to image these defects, various near-field probes operating at wide range of frequencies are employed and compared herein. The relative performance and the effectiveness of microwave NDT for non-metallic pipe inspection using these probes are quantitatively reported. Furthermore, the images of the HDPE pipe produced by microwave probes are benchmarked to phased array ultrasonic testing.