Use of Ultrasonic Testing in the Structural Steel Industry

IT IS IMPORTANT to note the distinction between a quality
weld and a reliable weld. Many of the discontinuities which
will be discussed may not be considered defective to a
particular weld joint or structural member. The
discontinuities may not make the weld less reliable, but
merely lower the quality of the weld. When does a
discontinuity become a defect? This is the question which one
must ask when separating quality from reliability. The
quality of a weld can be determined with ultrasonic tests;
however, the reliability of a weld is established from
destructive testing or welding history. Test specifications are
available based on these tests.
It should be mentioned, before proceeding further, that
radiography (still a primary weld inspection method),
magnetic particle, and penetrant techniques are powerful
inspection tools, and should not be overlooked when selecting
NDT methods. It is interesting to note, for example, that a
discontinuity orientated for maximum radiographic detection
is in its poorest position for ultrasonic detection, and vice-
versa.
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