Image Analysis of Indications in Fillet Welding by Phased Array Ultrasonic Technique

Abstract

The steel frame for carrying boiler in power generation station is usually connected by fillet welding like corner or tee joints. Traditionally, we inspect this type of welding by Magnetic Particle Testing (MT) and Dye Penetration Testing (PT), by which only the surface or near surface defects can be detected, and the internal defects in butt welding is inspected by Ultrasonic Testing (UT) and Radiographic Testing (RT). Though ultrasonic Testing (UT) has various advantage in flat butt weld, it requires a better condition on the detection surface avoiding the interference of being rough, irregular in shape, very small or thin, or not homogeneous. Due to the geometric shape or structural constrains in fillet welding, volumetric defects are sometimes unable to be detected by RT. Currently, there are no effective methods of Non-destructive examination (NDE) for the volumetric flaws in this type of welding which connects the steel column and reinforcing plate. Normally, the volumetric and plannar defects of fillet welding are commonly as: incomplete penetration, slag inclusion, porosity, lack of fusion and cracks, which have a great influence on the welding quality. This paper aims at using the advantages of Phased Array Ultrasonic Testing (PAUT) to detect the fillet weld: • Focal depth is variable. • Scanning range is large, steering beam from −89° to 89°. • Covering large volume at single position of probe. By setting different types of artificial flaws, we carried out the reliability analysis of this kind of welding with PAUT. Through observing the representative images of flaws, we can directly know the location of defects in the weld. According to the data provided by the scan software, we can read its depth and distance from the weld center line, which helps us to locate defects in weld precisely.