Short Range Guided Wave Technique
The Short Range Guided Wave (SRUT) was designed to test the annular plate of above ground storage tanks (AST's) while the tank remains in-service and for detecting corrosion under pipe supports. The technique is based on the concept of pulsing guided laminar waves into the base material from the chime area. The waves propagate up to three feet into the annular plate. When corrosion, pitting, erosion are present the ultrasonic waves mode convert and are received by the same transducer.
The technique is also being used to test for corrosion at soil air interfaces, and similar difficult to access locations.
Figure 1 depicts the transducer placement on the chime plate propagating short range ultrasonic waves into the annular plate.
Figure 2 shows the set up when inspecting under pipe supports. The sound reflects at top side or underside corrosion providing a c-scan image of the defect. The signal strength at the defect provides evidence of the depth and overall morphology of the defects.
Figure 3 provides a visual presentation of the collected data providing distance inspected, with of inspection along with details on the indications identified.
SRUT has become a proven and reliable technique as one method for determining the integrity of difficult to access material and can help to prioritize and plan more intrusive inspections.
Figure 1: Annular Plate Set-up
Corrosion Under Pipe Support Set-up
Figure 3: C-Scan Corrosion Map