Advanced Ultrasonic Back Scatter and Spectrum Analysis (AUBT/ABSA)
IRISNDT is a licensee of the technology and procedures developed by Shell for High Temperature Hydrogen Attack HTHA detection. The Advanced Ultrasonic Backscatter Technique (AUBT) and the associated Angle Beam Spectral Analysis (ABSA) technique for welds were developed for detecting and quantifying damage from high temperature hydrogen attack.
IRISNDT APPLIES AUBT TO INSPECT pressure vessels and piping for High Temperature Hydrogen Attack (HTHA). This damage can develop in steels exposed to high pressure hydrogen at elevated temperatures. Examinations incorporate:
- The backscatter technique used primarily to determine damage progression through the wall. It works with materials of any geometry with or without cladding.
- Spectrum analysis which helps to determine the degree of HTHA; it is sensitive to fissures and is independent of the measurement system.
- The velocity ratio measurement which differentiates between fissures and other internal defects. It is not affected by material geometry, back wall surface condition, or the measuring system.
The technique uses high frequency, broadband UT probes and a digital oscilloscope to provide both an A-Scan display and frequency analysis. Variables such as the ID surface condition, geometry and other internal defects have little effect on backscatter measurements. The method is consistent and reliable so monitoring of hydrogen attack and its progression over time provides meaningful information. Nevertheless, the surfaces to be inspected must have a buffed finish at each measurement location, typically 60 – 120 grit.
The backscatter techniques were developed because conventional UT techniques do not detect micro-fissuring and older methods such as attenuation measurement proved unreliable in the field. The ABSA procedure for weld HAZ inspection utilises the Spectrum Analysis technique
In high pressure hydrogen at elevated temperatures hydrogen atoms can diffuse into steels and react with carbides. The reaction leads to formation of methane and, subsequently, intergranular fissuring and losses of material strength and toughness.