High temperature water or steam is flowed inside and high temperature sodium in the outside. A probe with one set of two coils is inserted into the heat transfer pipe. When high-frequency electric current is sent in the coils, eddy current is produced in the pipe by electromagnetic induction and as a result alters the electric current in the coils. If there is a scratch or a crack inside the heat transfer pipe near one of the two coils, the flow of eddy current will be disturbed. Because the electric current in the coil alters when eddy current is disturbed, the existence and the depth etc. of the scratch or crack can be detected by comparing the electric current of the coil positioned in an undamaged area.
False noise make it difficult to discern actual damage.
The detected data must be compared with previously collected data of various artificial scratches and cracks in a test equipment in order to grasp the size and depth of the scratches and cracks. The heat transfer pipe Because the structure of the heat transfer pipe is extremely complex and there are twelve welded areas, it is difficult to insert and position the probe. Quality of the evaporator pipe material Stainless steel cracked easily in water by the stress, and the heat transfer pipes of the evaporator are made out of chromium-molybdenum steel. This brings large noises and makes the discernment of scratches and cracks difficult. Sodium Sodium left and attached on the surface of the pipe following the extraction from the heat transfer pipe during inspections becomes the cause of unwanted noise.