管道弯头缺陷检测外置式远场涡流探头设计

远场涡流技术在金属管道的无损检测中应用广泛,但通常需要设备停机以便将探头放入管内。为满足压力管道在役检测的需求,针对其易腐蚀的弯头部位,设计了一种在管外放置的远场涡流探头。首先,应用有限元软件对探头的结构及其激发磁场的效果进行了仿真设计;而后建立了弯头缺陷远场涡流检测仿真模型,分析了内、外壁缺陷深度与检测信号特征量的定量关系;最后搭建试验平台进行了预制缺陷检测试验。结果表明:探头电压信号的相位随缺陷深度的增加而近似线性减小,可用于缺陷深度的定量;内壁缺陷信号的相位减小得更快,利用相位特征量可对仅有外壁或内壁缺陷时的缺陷深度进行定量,而不能对两种缺陷都存在的情况进行定量。

External remote field eddy current probe for defect detection at pipe elbows

The remote field eddy current (RFEC) technique is widely applied for nondestructive testing of metallic pipes, but it always requires shutting down equipment to place the probe inside the pipe. In order to meet the demands of in service inspection for pressure piping whose elbow regions are prone to corrosion, a novel RFEC probe placed outside the elbow is designed in this paper. Firstly, the probe structure and the pattern of its exciting field are simulated and designed by using finite element software. Then, the simulation model of RFEC testing for elbow defect detection is established, and the quantitative relationship of the inner diameter (ID) and outer diameter (OD) defect depth to the signal characteristics is analyzed. Finally, a test platform is set up and the detecting prefabricated defect experiments are conducted. The results show that: i) the probe signal phase decreases almost linearly with the increase of ID or OD defect depth, which can be used to quantify defect depth; ii) the phase of ID defect signal decreases more rapidly, and therefore, the defect depth can be quantified in the presence of only one type (ID or OD) defect by using the phase feature, but cannot be quantified when both two types of defect exist simultaneously.