CHARACTERIZATION OF SURFACE CRACK ON STAINLESS STEEL PLATE BY LIQUID PENETRANT TEST AND PHASED ARRAY ULTRASONIC TEST (PAUT)

Stress Corrosion Cracking is one of the threat for equipment reliability. Particular assessment need to be done in order to decide if that particular equipment is still fit for services. Currently, the method being applied is Liquid Penetrant Test, which only capable in providing the orientation of surface crack, without giving enough detail to aid the decision making. Research has recognized Phased Array Ultrasonic Testing (PAUT) capability in providing realtime discontinuities profiling, but its capability in characterizing surface crack have not been properly tested. This study aimed to characterize and interpret surface crack using Liquid Penetrant Test and Phased Array Ultrasonic Test, before evaluating and comparing the profile produced by both methods. A stainless steel pressure vessel plate has been used as the specimen for the experiment, and the study has divided into four phases. From phase I of this study (Characterization using liquid penetrant test), it is found that the stainless steel pressure vessels plate have 2 major surface crack on the external surface. From phase II (characterization using PAUT), it is found that the PAUT cannot give accurate characterization of surface crack as indicated by liquid penetrant test, when the scanning done on the surface with the crack, as well as from the back side of the crack. From phase III ( assessment of crack characterization of both methods) , it was found that liquid penetrant test can only give orientation of the surface crack without the details of the crack such as the crack depth and internal orientation, while the PAUT can profile subsurface discontinuities in real time. From phase IV ( assessment of intenal crack by specimen sectioning), the subsurface detection accuracy of PAUT is confirmed to be around 1mm. However, few more relevant tests are required to accurately size the subsurface cracks to be compared with the overall subsurface discontinuities profiled by the PAUT as extension from the surface cracks.