Radiography Testing On Thick-wall Nozzle Fillet With Linear Accelerator

The development of nuclear power is a major trend to adjust the energy structure.Nuclear power plays an important role in China's "going out" strategy.The safe operation of nuclear power plants is a prerequisite.The welding structure of nozzle fillet is widely used in nuclear power plant,and its quality directly affects the operation of equipment,which is related to the safety of social property.The welding structure of nozzle fillet goes against welding,so it is easy to produce defects.Therefore,it is of great significance to determine the defects in the weld.The commonly used examination methods are conventional ultrasonic testing and radiographic testing.As the nozzle fillet has a large diffrence thickness between main pipe and brantch pipe,the conventional ultrasonic testing is not conducive to the identification and positioning of defects.The radiographic testing result is intuitive and reliable,the individual factor interference is small,and the record can be preserved for a long time.But at the same time,it is limited by the equipment capacity,especially for large thickness parts,the testing time is long and inefficient.For thick-wall nozzle fillet weld structure,in order to make up for the conventional radiographic testing equipment faults and achieve the purpose of high accurate detection of internal defects,this paper uses the high energy linear accelerator to detect nozzle fillet from the outer wall for the radiographic testing technology research.Making simulation test pieces with detects(Intensive poles with length range 30mm/35 mm,lack of penetration with length 25mm/40mm/50 mm,incomplete fusion with length 10mm),the main pipe thickness is 46 mm.In order to improve the detection result of incomplete fusion,based on the experimental comparison of the parameters such as the angle of illumination(the angle of ray beam and groove is 0°,5°,15°,30°,45°),energy selection(2MeV,4MeV),shooting distance(800mm,1000 mm,1500mm),film system(800mm,1000 mm,1500mm)and screens(Pb: 0.25mm/0.1*2mm/0.25 mm,Pb: 0.50mm/0.1*2mm/0.50 mm,Pb: 1.00mm/0.1*2mm/1.00 mm,steel: 0.25mm/0.25mm/0.25 mm,no screens),the detection parameters of the welding structure of nozzle fillet with linear accelerator are optimized.To find all the defects of the simulation test pieces,we used a parameters optimized radiographic detection equipment to test.And using conventional ultrasonic testing results to compare with the former.At the same time,compare the radiographic detection result with dissection result.Finally we found that the detection deviation of poles and lack of penetration is less than 10%,the detection result is good;the detection deviation of incomplete fusion is nearly 30%,the detection result is still low.This paper proved that using the linear accelerator in testing large thickness nozzle fillet weld structure for poles and lack of penetration is feasible.It's good for the optimization of non-destructive testing technology of this structure and providing some guiding significance.