Experimental Study On The Weak Magnetic Detection Of The Brazed Joint Of Water-cooled Rotor For Nuclear Power Station

The double water internal cooling generator set for nuclear power is the key equipment of nuclear power station,the dissimilar metal brazed joint of the water-cooled rotor in the power generator has strict requirements on the quality inspection because of its complex structure and weld-zone materials,and the harsh working environment.However,there are few researches on the non-destructive testing of this structure at home and abroad,in view of this situation,this paper proposes the application of the weak magnetic detection technology to the testing of the brazed joint of water-cooled rotor for nuclear power station to achieve a preliminary judgment of the welding quality from the outside.In this paper,the characteristics of copper-steel brazed joint and the basic principles of weak magnetic detection technology were introduced firstly,the feasibility of applying weak magnetic detection technology to the non-destructive testing of the brazed joint of water-cooled rotor for nuclear power station was theoretically analyzed.In the meantime,the square copper pipe butt brazed joint was used as the research object,and a self-developed weak magnetic detection system was used to test them,it was proved that the weak magnetic detection method can be used to detect the defects of copper material through these experiments.Based on this conclusion,and referring to the defects that often occur during the manufacturing process of the brazed joint of water-cooled rotor for nuclear power station,five holes with different diameters were processed on two specimens of brazed joints of water-cooled rotor,then a single channel flux-gate sensor and a TMR sensor were used respectively to test these two specimens.In addition,the data collected by the flux-gate sensor was processed by using the related theory of magnetic field gradients to realize the identification and determination of the defect signals.The test results showed that two sensors both can effectively detect each defect in these artificial specimens,and the aperture detection sensitivity of the hole reaches 0.5mm.The characteristic quantity of the detection signals was analyzed to study the influence of the size of the round hole defects on the detection results,and the influence of the presence of the defects on the distribution of magnetic lines of force in the weld was analyzed.Through the analysis and study of the above test results,the defect detection effect of the two sensors was compared,and the conclusion that the TMR sensor is more suitable for the weak magnetic detection of the brazed joint of water-cooled rotor for nuclear power station was obtained.Finally,the TMR sensor was used to test the specimen of brazed joint of water-cooled rotor with only natural defects,and the test results were compared with the results of radiographic film detection,which further validated the effectiveness of the weak magnetic detection technology.The experimental researches on this subject provide new ideas and methods for the non-destructive testing of the brazed joint of water-cooled rotor for nuclear power station.