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通过分析声波传播特性、检测信号及图像特征,提出20°探头的超声衍射时差法(TOFD)检测模式,并研制20°探头。通过对比5 MHz及2.25 MHz这2种频率下检测效果,进行优化试验。然后通过对不同的内壁模拟缺陷进行检测,制定适合厚壁承压容器内壁缺陷的最佳TOFD检测工艺。试验表明:在核电厂厚壁承压容器内壁缺陷TOFD检测中,20°探头、5 MHz频率是最佳选择;在此检测工艺下,对壁厚120 mm以内的承压容器,能够检出内壁缺陷的最小临界尺寸高为2 mm。
By analyzing the characteristics of acoustic wave propagation, detecting signals and image features, a TOFD detection mode of 20 ° probe was proposed and a 20 ° probe was developed. By comparing the detection results at two frequencies of 5 MHz and 2.25 MHz, the optimization test is carried out. Then, the best TOFD testing technology for the inner wall defects of thick-walled pressure-bearing vessel was developed by testing different kinds of simulated wall defects. The test shows that 20 ° probe and 5 MHz frequency are the best choice for TOFD detection of thick-walled pressure-bearing vessel wall defects in nuclear power plants. Under the detection process, the inner wall can be detected for pressure vessels with a wall thickness of 120 mm The minimum critical dimension of defects is 2 mm high.