METHOD OF HEAT TREATMENT OF HF-WELDED TUBES OF CARBON OR LOW-ALLOY STEELS Russian patent published in 1994 - IPC

FIELD: heat treatment of straight-seam electrically welded tubes, being produced in continuous tube welding installations. SUBSTANCE: method comprises steps of feeding tube, had been welded by HF-current, to a sectional furnace for their heating up to temperature A_c3+50^°C; cooling the tubes, had been removed from the furnace, at three stages; at first stage cooling the tubes up to temperature A_c1-50^°C with rate 4.0-6.0 degree/s; at second stage keeping the tubes in the air over a time period, calculated according to 12-14 s/1 mm of the tube wall thickness; at third stage cooling the tubes with a rate, being 8-12 times less, than cooling rate of the first stage. EFFECT: enhanced quality of tubes. 1 cl, 1 tbl