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Advanced Ultrasonic Backscatter Technique (AUBT)

Overview of Advanced Ultrasonic Backscatter Technique (AUBT)

Advanced Ultrasonic Backscatter Technique (AUBT) involves a collection of ultrasonic techniques used for detecting High Temperature Hydrogen Attack (HTHA) in process equipment. AUBT is well-documented in API RP 941.

Key steps in the AUBT procedure include:

  • A pattern-based backscattering technique is used as the initial screening method on the external surface that has been flapper-wheel (200 grit) prepared.
  • Depending on the backscatter pattern observed, one of several follow-up techniques, including frequency dependent backscatter, velocity ratio, spectral analysis, and spatial averaging, can be used to determine the cause of backscattering signals.
  • Note that velocity ratio, because of the lack of both speed and sensitivity, is used only when backscatter shows uniform microstucture (i.e. this indicates either no damage or near through-wall damage), to determine if damage really exists.
  • Spectrum analysis uses Fast Fourier Transform (FFT) to convert the signal readout from amplitude versus time to amplitude versus frequency. This technique compares spectra of back-wall echoes measured from suspect locations with a "clean" reference spectrum taken from a "no damage" area. This follow-up technique is used because of its speed and sensitivity to HTHA. 
  • A spatial averaging technique may be used where velocity ratio and spectral analysis have difficulty determining whether nearly through-wall HTHA exists (e.g. for clad nozzles, etc.)
  • For weld and heat affected zone (HAZ) inspections, angle-beam techniques based on backscatter and spectral analysis principles are used. These angle beam techniques do not require flush grinding of weld crowns for inspection.

 

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Related Topics

Acoustic Emission Testing (AET) Eddy Current Array (ECA) Electro Magnetic Acoustic Transducers (EMAT) Guided Wave Ultrasonics (GWUT) Infrared Inspection Liquid Penetrant Examination (LPE) Magnetic Flux Leakage (MFL) Magnetic Particle Testing (MPT) Meandering Winding Magnetometer Array (MWMA) Pulse Reflectometry Pulsed Eddy Current (PEC) Radiography Remote Field Eddy Current (RFEC) Ultrasonic Testing (UT)
Articles about Advanced Ultrasonic Backscatter Technique (AUBT)
  • November/December 2010 Inspectioneering Journal
    By John Reynolds at Intertek

    High Temperature Hydrogen Attack (HTHA) is a long known and still occurring degradation issue for fixed equipment construction materials in the hydrocarbon process industry where hydroprocess plants (hydrogen plus hydrocarbons) are in service. Though HTHA failures in these units are the focus of this article, it is important to recognize that HTHA damage can also occur in high pressure boiler tubes, hydrogen producing units, synthetic gas units, ammonia plants and other equipment where hydrocarbons may not be involved but high temperatures are involved.

  • November/December 1995 Inspectioneering Journal
    By Greg Alvarado at Inspectioneering Journal, and Dr. W. David Wang at Shell Oil Products Company

    Nelson Curve changes in the late 1980's provided cause for Shell Oil Company to look at more reliable NDE non-destructive evaluation methods for assessment of materials/equipment in high temperature hydrogen service. The primary change motivating Shell was the lowering of the C-0.5 Mo steel Nelson Curve to the carbon steel level.

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