PURPOSE: To obtain a defectless weld zone which obviates the generation of a welding defect in circumferential welding of reaction pipes consisting of a high- Si carburization-resisting and heat-resisting cast steel by forming a single U groove of which the root face has a specific width to the butt surfaces thereof and subjecting to plasma welding.
CONSTITUTION: The single U groove of which the width of the root face is 5W 10mm is formed to the butt surfaces of the reaction pipes consisting of the high- Si carburization-resisting and heat-resisting cast steel for petrochemical industry in such a manner that the root side thereof is on the reaction side of the reaction pipes in the stage of butting said reaction pipes and welding circumferentially the pipes. The root face part is then subjected to plasma arc welding. The under fill part produced by forming the single U groove is welded by TIG welding, etc. and is filled by the weld metal. The weld defect such as crack is thus prevented and the satisfactory weld zone is obtd.
NISHIHARA HISAKATSU
MIHARA TAKAO
ARATA YOSHIAKI