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, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants.
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 the velocity ratio, because of the lack of both speed and sensitivity, is used only when backscatter shows uniform microstructure (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.
Related Topics
- Acoustic Emission Testing (AET)
- Eddy Current Testing (ECT)
- 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)
- Pulsed Eddy Current (PEC)
- Radiography
- Remote Field Eddy Current (RFEC)
- Ultrasonic Testing (UT)
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