| A pipe flowed by a high temperature fluid, the longer it will undergo carburization on the inside of the pipe. Carburization causes the pipe surface on the inside to have a hardening layer, and will cause cracks or leaks when there is excessive vibration. To be able to prevent the occurrence of such damage, it is necessary to measure the thickness of the layer to find out how big the layer, with non-destructive method. In this study nitriding was simulated as carburization on pipes applied to SKD61 steel. This study aims to determine whether NDT Ultrasonic water immersion specifically one probe method, defocusing, and two probe method can be used to measure the different of nitriding thickness. In this study, the measured ripple is rayleigh waves or surface waves generated based on the law of snelius. The result of the nitriding process, obtained different nitriding thickness of 59 µm, 102 µm, and 160 µm, as well as increased surface hardness level at increasing thickness. Fe content on the surface of the specimen also decreases, but not linearly. NDT Ultrasonic test results in the three methods, it was found that the three methods still can not be used to measure the thickness of nitriding. |