Multiple leakages were found in fillet welds between the nozzle stubs and deaerator spray pipes in a power unit since the plant was put into operation in 2007. Although weld-repair was carried out many times for this fillet welds

defects cannot be eradicated totally

causing serious hidden trouble to safe operation of the power plant. In order to improve the defect detection rate and prevent this kind of accident from occurring frequently

a combination method was proposed using magnetic particle testing and ultrasonic creeping wave. The reason for this defect was analyzed by magnetic memory testing technology. It proposed installing expansion joint to optimize the structure of the deaerator spray pipe and reduce the stress that the spray pipe branch bearing. Through these two methods

the detection rate of crack was improved greatly

and no leakage accident has been reported. This method solves the frequent leaking problem of spray tube fillet welding seats

and also offers references for other power plants.