某石油勘探公司在对大长度大功率S304不锈钢护套矿物绝缘加热电缆试运行后，发现加热电缆无法在大功率高温度条件下长期作业,检查发现加热电缆不锈钢外护套表面存在线状缺陷。通过对电缆不锈钢外护套的宏观形貌、化学成分、微观组织和力学性能进行分析，确定了缺陷的性质及产生原因。结果表明：由于焊接和热处理工艺操作不当，使不锈钢外护套产生了多种缺陷,临近焊缝钢管咬边,壁厚出现减薄，钢管未焊透,焊缝根部区域存在裂纹;另制作外护套的不锈钢带存在严重敏化现象，并且有过量的冷加工变形。

When a petroleum exploration company made a running test to a large length and high power S304 stainless steel sheathed mineral insulated heating cable, it was found that the cable could not run for a long time at high temperature and there were linear detects on the stainless steel outer sheath surface. By analyzing the macro morphology, chemical compositions, microstructure and mechanical properties of the stainless steel outer sheath, the nature and causes for the defects were determined. The results show that due to the improper welding and heat treatment process, multiple defects produced to the stainless steel outer sheath. Undercutting and wall thickness thinning appeared near the weld, and incomplete penetration and cracks appeared in the root area of the weld. At the same time, significant sensitization phenomenon and too much cold deformation were found in material of the stainless steel outer sheath.