Abstract: The hollow bloom with larger diameter and higher diameter/thickness ratio than that of those produced by the original pass shall be provided by the piercing mill when pipe products with the size over the product outline are to be produced by 460 mm PQF Plant.In order to meet the need of production of the casing pipe with 473.08 mm diameter and 11.05 mm wall thickness, the 488 mm pass has been developed and using it the hollow bloom with 533 mm diameter and 25 mm wall thickness, which is over the design capacity, is successfully produced through optimizing design of the piercing tools(plug and guide shoe) and improving the rolling program.Now the products can be produced by the 488 mm pass in volume production with their quality conforming to related standards.