Proposal of simultaneous measurement of carburization depth and lift-off of heating furnace steel tube

In recent years, the necessity for inspection of the deteriorated oil-refining plant is increased. In the steel tube to be used in a heating furnace has carburizing phenomenon is the cause of the accident. As these carburizing depths increase, so does the steel tube. Therefore, inspection of these depths is important. The conductivity of the carburized layer is higher than that of the non-carburized layer in the steel tube, and it’s magnetic permeability is lower than that of the non-carburized layer. Therefore, studies are being conducted to determine the life of steel tube by applying electromagnetic non-destructive inspection electromagnetic. However, it is difficult to put it to practical use in the field because measurement error occurs due to the effect of lift-off. In this paper, we proposed an inspection method that can measure carburizing depth and lift-off at the same time. This method uses two types of search coil. One is the magnetic flux testing and the other is the eddy current testing.