Hot continuous rolling production method for 508mm large-diameter extra-thick-wall seamless steel pipe

The invention discloses a hot continuous rolling production method for a 508mm large-diameter extra-thick-wall seamless steel pipe. The method comprises the following steps that 1) a blank is put intoan annular heating furnace for heating; 2) when the temperature of the blank is increased to 1230 DEG C and 1250 DEG C, the blank is taken out and punched into a tubular billet; 3) PQF three-roller continuous rolling is carried out on the punched tubular billet through a continuous rolling mill; 4) a pierced billet obtained after continuous rolling is subjected to pipe disengaging, reducing and sizing through a pipe disengaging rack; after sizing, the outer diameter of the steel pipe is 508 mm, and the thickness of the steel pipe is larger than 60 mm and smaller than or equal to 80 mm; and 5)the sized steel pipe is transferred to a cooling bed for cooling. It can be known from the process that according to the hot continuous rolling production method for the 508mm large-diameter extra-thick-wall seamless steel pi