METHOD FOR PRODUCING CASING TUBES FOR THREADING IN TUBE ROLLING AGGREGATES WITH PILGER MILLS Russian patent published in 2007 - IPC B21B21/00 

FIELD: rolled tube production, namely production of casing tubes for thread cutting, possibly in well known tube rolling aggregates with pilger mills and also in tube rolling aggregates with new generation of pilger mills controlled by means of computers.

SUBSTANCE: method comprises steps of heating ingots and continuously cast billets till yielding temperature; piercing them to sleeves in skew rolling mills; rolling tubes on long mandrel in pilger mills and sizing them in calibration mill. Deformation value along rolled tube lengths in pilger mill is cyclically decreased by (n+1) times where n - number of multiple tubes, pieces. Said deformation is decreased due to opening rolls by value determined according to expression Δ = (1.0 - 2.0)H where H - height of initial thread profile, mm. Deformation is decreased in portions of tubes whose lengths are determined according to expression L = L_c + K where L_c - length of coupling, mm; K = 50 - 150 mm, factor taking into account waste value and allowance along length of multiple tubes at working their ends with thickened wall, mm. Tube lengths are cut by multiple tubes along center of thickened portions. Nominal inner diameter of tube end portions is lowered at calibration by value determined with use of expression D_in = D_nom - K₁, where D_nom - nominal inner diameter of tube, mm; K₁ - coefficient taking into account lowered inner diameter of end portions of casing tubes at calibration, mm; K₁ ≤ 3 for tubes with diameter 245 - 340 mm and K₁ ≤ 4 for tubes with diameter 351 - 508 mm. Casing tubes are rolled in such a way that to provide their wall thickness less by 1.0 - 1.5 mm than respective nominal thickness of wall according to standard given in specification. All operations and calculations are performed with use of computer. Invention allows produce for oil and gas industry branches of Russia tubes having high reliability of their threaded joints, lower nominal wall thickness of tubes by 1.0 -1.5 mm.

EFFECT: lowered metal consumption due to reduced number of flaws of threaded joints and reduced wall thickness of tubes, improved efficiency of threading, of cut-off equipment and of hydraulic press, decreased cost of conversion of tubes of given size.

13 cl, 1 tbl