Nondestructive Testing of Nonmetallic Pipelines Using Microwave Reflectometry on an In-Line Inspection Robot

• Published in: IEEE transactions on instrumentation and measurement Vol. 68; no. 2; pp. 586 - 594
• Main Authors: Carrigan, Tobias D., Forrest, Benjamin E., Andem, Hector N., Gui, Kaiyu, Johnson, Lewis, Hibbert, James E., Lennox, Barry, Sloan, Robin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Continuous radiation; Crack detection; Cracks; Crawlers; electromagnetic reflection; electromagnetic scattering; External walls; Ground penetrating radar; High density polyethylenes; Inspection; Microwave imaging; Microwave measurement; microwave reflectometry; Microwave theory and techniques; Millimeter waves; Nondestructive testing; Pipelines; polarization; polyethylene; Probes; Raster scanning; Reflectometry; Robots; Sensitivity analysis; Undersea; Wall thickness
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2018.2847780

Microwave and millimeter-wave reflectometry, a form of continuous-wave surface penetrating radar, is an emerging nondestructive inspection technique that is suitable for nonmetallic pipelines. This paper shows a <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-band microwave reflectometry instrument implemented onto an in-line pipe-crawling robot, which raster-scanned cracks and external wall loss on a high-density polyethylene (HDPE) pipe of diameter 150 mm and wall thickness 9.8 mm. The pipe was scanned with three environments surrounding the pipe that approximated the use cases of overground HDPE pipelines, plastic-lined metal pipes, and undersea HDPE pipelines. The instrument was most sensitive when cracks were oriented parallel to its magnetic (H) plane. Any small variation in the standoff distance between the instrument's probe antenna and the pipe wall, which was not easy to avoid, was found to obscure the image. To mitigate this problem, a sensitivity analysis showed that an optimal frequency can be chosen at which standoff distance can vary by up to ±0.75 mm within a certain range without distorting the indications of defects on the image.