Short Range Ultrasonic Testing: 
For Inspection of Tank Annular plate

Introduction:
The Short Range Guided Wave Ultrasonic Technique (SRGUT) was designed to test the Annular plate of above ground storage tanks (AST's) while the tank remains in service.  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 under pipe supports,  Corrosion at soil air interfaces, and similar difficult to access locations.

Applications: 

• Tank Floor Annular Plate Testing
• Testing Concrete Coated Interfaces
• Testing Under Pipe Supports
• Tank Dyke Piping Interfaces
• Scan Under Vessel Supports

The graphic below Figure one depicts the transducer placement on the chime plate Propagating long range ultrasonic waves into the annular plate. 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. The next picture provides a visual presentation of the collected data providing distance inspected, with of inspection along with details on the indication identified. 

Limitations of this technique are:

• Top or Bottom Side Differentiation
• Must Have 2” Space for Probe Placement

Short Range Guided Wave Testing has become a proven and reliable technique as one method for determining the integrity of tank annular plates where the highest probability of corrosion exists to help prioritize out of service tank maintenance requirements.