CONTRIBUTION TO DETECTION AND SIZING LINEAR DEFECTS BY CONVENTIONAL
AND PHASED ARRAY ULTRASONIC TECHNIQUES
Ontario Power Generation, Pickering, Ontario, Canada.
The paper presents experimental and field results in detection and sizing small linear defects: elliptical EDM
notches, crack-like EDM notches, fatigue cracks with height between 0.15 mm to 3 mm, and length between
2 mm - 15 mm. The linear defects were located in the test blocks for weld inspection (t = 6 - 50 mm, dia =
100 - 600 mm), in the test blocks for turbine components inspection (t=10 - 130 mm) and in the blade roots
of Siemens low-pressure turbine of 580 MW. Conventional UT techniques (tip-echo, mode-converted, TR
L-waves) and phased array techniques with L-, and T-waves were employed within a frequency range 3.5
MHz-12 MHz. Defect co-ordinates (length, height, location, orientation, pattern recognition) were measured
and analyzed. Ray-tracing and advanced simulation were also used to validate the optimum set-up and
defect pattern. Practical conclusions were derivated for procedure development and in-service inspection of
piping welds and turbine components.