核电厂围板螺栓超声检测技术研究

Study on Ultrasonic Inspection of Baffle Bolts in Nuclear Power Plants

围板螺栓是核电厂堆内构件的关键连接部件,长期服役下可能产生辐照应力腐蚀裂纹(IASCC)等缺陷,有必要对其结构完整性进行无损检测。分析围板螺栓的结构特点和在役检查工况,开发针对外六角头结构螺栓的组合晶片超声检测方案,介绍探头设计选型原则和缺陷评定技术,确保良好的声场有效覆盖以及检测出螺栓不同部位的裂纹缺陷。通过对含缺陷试块的试验验证了超声检查工艺的可行性,结果表明该技术能够有效检测30%螺杆横截面当量的裂纹缺陷,信噪比可达12 dB以上,满足在役检查要求。

Baffle bolts are the critical joint parts of the internal structures in nuclear power plants,and it is necessary to perform non-destructive testing on their structural integrity in order to detect the defects such as irradiation assisted stress corrosion cracking(IASCC)which may occur during a long-term service.In this study,the structural characteristics of the baffle bolts and the in-service inspection conditions were analyzed,and a combined-crystal ultrasonic technique(UT)was developed for the external hexagon bolts.The probe design and defect assessment were reviewed to ensure the good sound field coverage,and the cracks in different parts of the bolt can be detected.The practical trials on the flawed samples were performed to verify the feasibility of the ultrasonic process,and the result showed that currently technique is able to detect the flaw on the order of 30%of the shank cross-sectional area and the signal to noise ratio(SNR)can reach more than 12 dB,which meet the requirements for the in-service inspection.