Cleanliness of pipeline steel(≤0.04%C-1.559%~1.78%Mn)produced by two refining processes-RH-LF and LF-VD with liquid steel melting by hot metal pretreatment- 150 t top and bottom blown converter process has been compared. Results showed that after RH-LF or LF-VD refining
the nitrogen content in pipeline decreased to (30~40) x 10
-6
the oxygen content was ≤ 10×10
-6
and the sulphur content was ≤0.0020%;as the basicity of refining slag for LF-VD process was higher than that for RH-LF process
the average phosphorus content in LF-VD refined steel was 0.0090% which was lower by 0.0010% as compared with that in RH-LFrefined steel; the main inclusions in both refining steel were calciun-aluminates inclusion and calcium-aluminate silicon-dioxide compound inclusion; and the size of most inclusions in steel refining by LF-VD was 5~10 μm while that by RH-LF was 5~20 μm.