Abstract
Radiographic test (RT) has been applied to verify the soundness of weld joint of LNG storage tanks made of 9%Ni steel. But recent larger tanks require more radiation for RT to heavy thick plate such as sidewall at the lowest course, resulting in the increase of inspection time. In addition RT is less sensible of planar defects, which may reduce safety margins of strength and toughness, than ultrasonic test (UT) . Several UT techniques have been developed and expected to be rapid and reliable inspection with recordability through the recent advance of data processing.
In this paper these UT techniques were studied for the inspection of LNG storage tanks and the following conclusions were obtained. (1)TOFD technique identified the sizes of several kinds of defects with sufficient accuracy, being applicable to the inspection for the butt weld joint of sidewall plates instead of RT. (2)Phased array UT technique detected defects in the fillet joint connecting annular plate with sidewall plate at the lowest course, being expected as more reliable inspection, and further investigation will be necessary to apply this method to the actual tank.
