采用纵波直探头检测钻铤螺纹时，由于超声波主声束与被检螺纹存在夹角，外螺纹接头大端的第1~2牙处和内螺纹接头小端的2~3牙处的缺陷容易漏检。为了防止缺陷漏检，提出采用小角度探头检测钻铤螺纹，通过计算小角度探头的入射角和对比试块的设计制作等，实现了钻铤螺纹牙底缺陷的有效检测。

When using the longitudinal wave straight probe to detect the drill collar thread, because of the angle between the main ultrasonic beam and the inspected thread, the defects of the first two teeth at the large end of the external thread joint and the second three teeth at the small end of the internal thread joint are easy to be undetected. In order to prevent the defect from being undetected, this paper proposes to use a small angle probe to detect the drill collar thread. By calculating the incident angle of the small angle probe and designing and manufacturing the reference block, the effective detection of the bottom defect of the drill collar thread is realized.