Investigating the reliability of ultrasound phased array method and conventional ultrasonic testing for detection of defects in austenitic stainless steels

Akgün, Bahadır
In recent years Phased Array (PA) method has become an alternative to the conventional ultrasonic method for critical tests in aerospace, oil, gas and nuclear industries. There is a challenge for inspection of austenitic stainless steels due to high attenuation, skewing and scattering of sound beam. The aim of this thesis is to investigate and to compare the flaw detection abilities of conventional ultrasonic and PA systems using the probability of detection (PoD) approach for testing of austenitic stainless steel blocks and weldments having both artificial and natural defects. Grain size, micro hardness, attenuation measurements, radioscopic and macroscopic inspections were also performed. Three types of test blocks were prepared from AISI 304 steel. First specimen is the block having ø2 mm side drilled holes at different depths; second specimen has side drilled holes with varying diameters between 0.5 to 5 mm at the same depth; and the third specimen is the welded plate having both artificial and natural defects. Although PA method has automated calibration, beam focusing and steering abilities, the PoD analyses did not show remarkable advantage of PA for detecting artificial flaws, except those in the surface near zone. On the welded specimen, however, the PA inspection is clearly more successful than conventional method based on counts of detected flaw possibilities as well as positioning and sizing of the defects. While the automated PA system has superior vi detection and positioning abilities over the manual PA system, the manual PA system has superiority of faster scanning and swiveling of the probe which also brings the risk of human factor.