In the former report, phased array testing which carried out the sector scan using focus beam had discussed and reported to have sufficient ability to detect the surface flaws on the butt-welded joint of the bottom plates in state-oil-stockpiling tank covered with tight coating painted to prevent corrosion of bottom plates. In this report, ultrasonic test system and scanning machine were discussed in order to apply to actual tanks. And confirmation test results for flaw detectability which performed using the test plates with EDM notches on the weld surfaces simulated the actual joint configuration of the bottom plates in state-oil-stockpiling tank and field verification test results which performed using weld line of about 1. 5km in 3 actual tanks were reported.
Simultaneous test system for flaws along the weld direction and flaws vertical to the weld direction were discussed. Two phased array probes were located at both sides of weld line in order to detect flaws along the weld direction from both sides of weld line with sector scans and to use by pitch-and-catch method for coupling check. Two angle probes of refraction angle of 70 degree were located emitting and receiving the ultrasonic beam in the direction of 45 degree to the weld line and crossing two beams at weld center line with 1 skip for vertical flaw detection to weld line. Scanning machine with laser tracking equipment was prototyped and proved to trace the laser beam emitted from over 50m distance through weld centerline by commercial low output laser transmitter with high accuracy.
In the confirmation tests using the test plates simulated the actual tank welds and in the actual 3oil tanks, it was confirmed that scanning system mounted ultrasonic test system was sufficiently functioning under 75mm⁄sec. of traveling speed, and had sufficient flaw detectability.
