某井钻井作业时发生了多次钻杆挤扁现象。采用宏观观察、化学成分分析、力学性能试验、金相检验等方法对钻杆挤扁的原因进行了分析。结果表明：钻杆管体与卡瓦之间的啮合接触不均匀造成应力分布不均匀，当局部的接触应力超过了钻杆管体的屈服强度而使钻杆管体发生塑性变形挤扁，卡瓦牙板磨损较为严重是导致应力分布不均匀的主要原因。

The drill pipe was flattened many times during the drilling operation in a well. The causes of drill pipe flattening were analyzed by means of macro observation, chemical composition analysis, mechanical property test and metallographic examination. The results show that the uneven meshing contact between the drill pipe body and the slip caused the uneven stress distribution, when the local contact stress exceeded the yield strength of the drill pipe body material, the drill pipe body was plastically deformed and flattened. The serious wear of the slip teeth plate was the main reason for the uneven stress distribution.