大型抽水蓄能机组顶盖螺栓裂纹原位在线检测技术研究

Research on In-Situ On-Line Inspection Technology for Cracks of Head Cover Bolts of Large Pumped Storage Units

水轮机顶盖螺栓是连接水轮机顶盖与座环的重要连接件,其安全状态对水电站安全运行至关重要。超声波在金属内部具有透射深度大、反射率高的特点,可用于检测螺栓内部疲劳裂纹,但常规的超声检测必须在螺栓解体拆出状态下才能进行,否则无法保证裂纹的检出。为了有效监测运行状态下的顶盖螺栓裂纹和损伤情况,本文提出了一种基于压电阵列的超声波传感器,通过压电晶片的分区非均匀激发,形成偏心扇形超声声场,并通过对接收信号进行数字处理,实现水轮机顶盖大型螺栓裂纹的原位在线检测。该技术具有实时性强、精度高、可靠性好等优点,能够有效地在线监测水轮机顶盖大型螺栓的裂纹和损伤情况,为水电站安全运行提供重要保障。

Hydraulic turbine head cover bolts are important connectors connecting hydraulic turbine head cover and seat ring,and their safety status is crucial to the safe operation of hydropower plants.Ultrasonic wave has the characteristics of large transmission depth and high reflectivity inside the metal,which can be applied to the detection of fatigue cracks inside the bolts.However,the conventional ultrasonic detection must be carried out only in the state of disassembled and dismantled bolts,or else the detection of cracks cannot be guaranteed.In order to monitor the cracks and damages of the head cover bolts in the operating state effectively,this paper proposes a piezoelectric array-based ultrasonic transducer with non-uniformly excited piezoelectric wafers to form an eccentric fan-shaped ultrasonic acoustic field,and the received signals are digitally processed so as to realize in-situ on-line detection of cracks in large bolts of the hydraulic turbine roof cover.This technology has the advantages of strong real-time,high precision and good reliability,which can effectively monitor the cracks and damages of the large bolts of the hydraulic turbine roof cover online and provide important guarantee for the safe operation of the hydropower station.