The optimization of flow control device in 38 t expansion tundish from original 29 t for casting 250 mm X 2 000 mm slab at steelworks has been carried out by numerical simulation. The effect of number and position of dam and weir on flow field and residual time distribution ( RTD) curves of liquid in tundish has been studied. With comprehensive consideration of tundish metallurgical effect and production cost

the optimum design for control flow devices- current regulator + dam + weir is proposed. With the optimum structure the volume fraction of plug flow region in tundish is up to 77. 1%

the volume fraction of dead region decreases to 4. 2%. With using this structure in situ the qualified ratio of non- metallic inclusions in pipeline steel produced in non-stable casting condition increases to 95% from original 88%

obviously to increase the metallurgical function of tundish.