UT Technique Development and Procedure Writing
Building a defensible technique
A procedure must specify: scope and reference standard, equipment and transducer, calibration blocks, surface preparation, couplant, scanning pattern and coverage, angle/mode, calibration and check intervals, acceptance criteria, and documentation. Technique development starts from the discontinuity type and geometry you must find, then selects frequency, angle, and scan pattern to maximize detection probability.
For angle-beam weld inspection, know skip distance, sound path, and how refracted angle relates to leg length and coverage. Understand the difference between scanning for planar flaws (oriented to reflect) and volumetric ones. Coverage means overlapping passes and multiple directions-single-direction scans miss oriented defects.
Traps
- Writing a procedure that names acceptance criteria without a governing code reference.
- Omitting calibration check intervals or the response to a failed check.
- Confusing scan index/spacing with beam width; spacing should ensure overlap.
- Forgetting surface condition and couplant effects on coupling loss.
- Assuming one angle covers all weld geometries; T-joints and nozzles need tailored approaches.
Rule of thumb
Set scan index at no more than half the effective beam width to guarantee overlap; at the 6 dB beam edge this yields roughly full coverage. Document every parameter so the technique is repeatable by a qualified examiner.