The production flow sheet for X65 etc. clean pipeline steel at Tianjin Pipe is 100 I UHP EAF-LF-RH- Φ310 ~Φ500 mm CC process. With using the process measures including charging 35% 〜40% hot metal in arc furnace

controlling slag amount no less than 22 kg/1 at Al consumption 1. 85 kg/t

controlling refining slag index ( CaO/SiO

2

/ Al

2

O

3

) 0. 18 〜0. 32. RH powder injection for desulphurization

EAF end [C

]

≥0. 05%

phosphorus content in melting down liquid ≤0.005%

prolonging foaming slag maintaining time

RH high vacuum treated time ≥10 min

soft stirring for 10 ~ 15 min after calcium treatment and using high basicity shielding agent in tundish

the cleanliness of l0MnVNbMo etc seamless steel tube of X65 pipeline steel is ≤0. 001 %S

≤0. 008% P

≤75 x 10

-6

N

≤20 x 10

-6

O

and ≤l. 5 x 10

-6

H.