Defects Analysis of a Large Length and High Power S304 Stainless Steel Sheathed Mineral Insulated Heating Cable

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.