多架飞机在地面例行检查过程中发现1Cr18Ni9Ti不锈钢回油导管外表面未喷漆部位存在黄色斑纹。对缺陷导管进行形貌检查，化学成分分析、显微组织形貌检查、显微硬度测试等理化检验，并对缺陷导管及其原材料进行模拟试验，分析了缺陷产生的原因。结果表明：导管外表面缺陷属于在外界环境影响下产生的局部浅腐蚀，其产生与导管原材料外表面状态不佳（存在表面细晶区）有关。

During the routine ground inspection of multiple aircrafts, yellow markings were found on the unpainted parts of the outer surface of 1Cr18Ni9Ti stainless steel oil return tubes. Physical and chemical tests such as morphology inspection, chemical composition analysis, microstructure morphology inspection, and micro-hardness test were performed on a defective tube, and simulation tests were performed on the defective tube and its raw materials to analyze the causes of the defects. The results show that the defects on the outer surface of the tube belonged to localized shallow corrosion under the influence of the external environment, which was related to the poor outer surface condition of the raw material of the tube (there was a surface fine-grained area).