汽轮机高压缸内缸螺栓为高温紧固螺栓，是核电站热动力设备的重要连接部件，由于长期运行于高温及高压的工作环境中，螺栓螺纹区域容易产生疲劳裂纹。针对汽轮机高压缸内缸螺栓螺纹区域产生的内部疲劳裂纹，使用小角度纵波斜探头超声波检测方法，通过现场试验验证和理论分析，该方法提高了螺栓螺纹齿根及疲劳裂纹的检测灵敏度，并有效地发现螺栓螺纹齿根及内部的微小疲劳裂纹。

The bolt of the high pressure inner cylinder of turbine, as a high-temperature fastening bolt, is an important component of the nuclear power plant thermal power equipment. The bolt is prone to fatigue crack in the long run, due to high temperature and high pressure role of bolt material. This article describes the small-angle longitudinal wave angle probe ultrasonic testing of the internal fatigue crack in the threaded portion of the bolt of the high pressure inner cylinder of turbine. Through theoretical analysis and experimental verification, the testing method improves the ultrasonic testing sensitivity about the fatigue cracks.of the root of tooth and inner of the bolt, thus leading to effective detection of small fatigue cracks.of the root of tooth and inner of the bolt.