Use of NDT computerized ultrasonic method with phased array technique in substitution of radiographic method on butt weids of type C independent tanks

摘要

This paper describes the application of computerized phased array ultrasonic examination (PA) on cargo tanks for ethylene carriers made of 5% nickel steel grade. With reference to provisions of the applicable standard, the IMO "International Code for the Construction and Equipment of Ships Carrying Liquefied Gas in Bulk (IGC Code)", PA has been applied, based on a detailed procedure approved by RINA, in addition to radiographic examination (RT) to verify if the former is at least equivalent to the latter in the detection of weld flaws. Examination results showed the substantial equivalence of the two methods in detecting volumetric flaws such as slag and the high sensitivity of phased array in detecting planar flaws such as lack of fusion. The impact of computerized ultrasonic method on repair working hours reduction has been evaluated also.