某L458M钢管道在无损检测过程中发现检测缺陷，射线和超声检测方法对缺陷复验的结论差别较大，不能确定缺陷种类。采用宏观分析、金相分析及能谱分析等方法对该管段取样进行缺陷原因分析。结果表明：该L485M钢管道无损检测缺陷为裂纹，该位置处进行过管体补焊，裂纹为焊接过程中产生，服役过程中并未发生扩展。原损伤位置在补焊前即存在铜污染，裂纹主要与焊缝金属凝固过程中液体金属不能及时充填收缩位置以及低熔点金属铜引起的结晶裂纹等两方面原因有关。

Testing defect was found in a L458M steel pipeline during nondestructive testing. The conclusion of re inspection of the defect by X-ray and ultrasonic testing methods was quite different, and the type of defect can not be determined. The causes of the defect were analyzed by means of macroscopical analysis, metallographic analysis and energy spectrum analysis. The results show that the defect of the L485M steel pipeline was crack. Repair welding of pipe body has been carried out at this position. The crack was generated during welding and did not propagate during service. Copper pollution existed in the original damage location before repair welding. The crack was mainly caused by the liquid metal can not fill the shrinkage position in time during the solidification process of weld metal and the crystallization cracks caused by low melting point metal copper.