Innovation in Ultrasonic Thickness Gauging for Detecting Corrosion under Insulation


A typical scheme of inspection for insulated equipment consists of ultrasonic thickness gauging (UTG) and corrosion under insulation (CUI) monitoring. There is an opportunity to innovate the conventional ultrasonic testing not only for thickness gauging but also for CUI detection at the adjacent area of the gauging opening. The objective was to modify the standard ultrasonic testing (UT) thickness gauging probe for CUI detection which involved the design and fabrication of the wedge to convert normal longitudinal wave into surface wave for 10 mm and 30 mm probes. The test was done on the surface of 2-inch carbon steel pipe with fabricated CUI defects using two types of UT mode which are single probe testing and dual-probe testing. The characteristics of signal produced were analyzed based on various corrosion profiles and probes distance. The modification to convert the longitudinal wave into surface wave was obtained by machining Perspex wedges with the incident angle of 57.7 o. In both single probe and dual probe testing, the reduction of signal height indicated the presence of CUI and the signal was influenced by the depth of corrosion profile and probe distance. In conclusion, the surface wave produced by the modification on the normal surface probe was proven able to detect CUI with some limitation.

  • Abstract
  • Keywords
  • 1. Introduction
  • 2. Methodology
  • 3. Result and discussion
  • 4. Conclusion
  • 5. Reference

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