Abstract: Technology method of many time welding was used in assemblage furnace mantle of large-scale smelting converter. For avoiding welding quality problem, welding line must be many times tested by magntic particle testing in welding. The detection showed the carck magnetic vestige was displayed in welding line surface of past welding zone of furnace mantle, and continuous distribution magnetic vestige in trunnion, the potential risk for quality was removed in welding line.