Abstract: Described in the paper are the main aspects of the extra-long seamless steel pipe as made with the onetime-forming process for cooling the blast furnace bottom,including the technical requirements,the technical difficulties and the activities concerning the design and development of the extrusion process,etc.Relevant actual practice proves that the 12Cr18Ni9 pipe as produced with the extrusion process has its performance better than requirements as specified under applicable technical specification and technical agreement,being capable of meeting the criteria for bottom-cooling and long service life of the large blast furnace,and worth using as reference for type determination and application of the pipe for bottom-cooling service for the large and medium blast furnaces.