Type IV creep voids detection method for high chromium steel welds using ultrasonic backscattered waves

In high-chromium ferrite heat-resistant steel pipe welds, which are often used in ultra-supercritical pressure boilers Japan, a large number of Type IV creep voids occur the region deep beneath outer surface and then develop into cracks. When crack is detected, main piping power plant judged to have zero remaining life. Since damage areas material there no non-destructive evaluation (NDE) method for dense prior formation, NDE methods cannot be plant-maintenance planning. The authors selected water-immersion acoustic-imaging method, has highest measurement resolution among ultrasonic-measurement that can expected applied actual equipment, searched greatly exceeds existing resolution. And we focused on reception characteristics ultra-high-focused acoustic lens. For purpose, designed an aspherical, angled lens welded part piping. We also developed new system mechanically scan this probe with high accuracy. As result, using system, changes scattered wave amplitude could observed depending presence or absence void density material, led area.