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A Re-assessment of Ultrasonic (UT) Indication Ratings and Amplitude Based Acceptance Criteria for Welded Steel Joints in Structures

Since 1969 the American Welding Society has recognized ultrasonic inspection to determine acceptance or rejection of welds in steel structures. For welding in steel building structures governed by the American Welding Society AWS D1.1-Structural Welding Code, Steel, the criteria for acceptance and rejection utilize the measured length of detected ultrasonic reflectors and a comparison between the amplitude of the reflector and that of a standard reference reflector (the former being determined by the so-called “6 dB drop” method and the latter being modified for attenuation due to length of sound path). Then, based on the location of the reflector in the weld, the proximity of other reflectors, and the thickness of the weld, the ultrasonic technician determines from one of tables (as specified by project contract documents) whether the reflector will be accepted or rejected. The difference between acceptance and rejection can be as little as 1dB. Therefore, it’s critical that the consistency across technicians, equipment, and flaws enable 1 dB precision in amplitude determination. Data gathered during qualification of ultrasonic technicians and subsequent experimentation indicates that current training, techniques, and equipment are far from achieving this precision. We engaged in a rigorous training program and were able to achieve much improved precision in a classroom setting utilizing commercially available flawed specimens among a group of technicians with a variety of backgrounds and diverse experience levels, however, we were unable to achieve consistent 1 dB precision even in this controlled environment. We then utilized different ultrasonic instruments and search units with a single technician to evaluate the effects of different equipment and found that the required level of precision was achieved. Thus, we attribute the inconsistent results to technician technique. We recommend either abandonment of the Indication Rating as an acceptance criterion or additional standardized training to achieve sufficient uniformity of evaluation among technicians.


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2. AWS D1.1/D1.1M:2010 Structural Welding Code-Steel (2010 ed.),  Clause 6, Inspection.

3. AWS D1.1/D1.1M:2010 Structural Welding Code-Steel (2010 ed.) Annex S, UT Examination of Welds by

Alternative Techniques.

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7. American Welding Society, “Supplemental Ultrasonic Technician Testing,”  (2009)AWS D1.8/D1.8M:2009

Structural Welding Code-Seismic Supplement (2009 ed.), Annex F (Normative).

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