METHOD OF SURFACE HARDENING OF THREAD JOINTS OF THIN-WALLED DRILLING PIPES Russian patent published in 2019 - IPC C23C8/54 

FIELD: soil or rock drilling.

SUBSTANCE: invention relates to methods for surface hardening of threads by means of which parts of a drill string are connected. Method of hardening threaded surface of lock joint of thin-walled drill pipe includes the following stages: a) preparing a threaded surface of the lock joint, involving preliminary cleaning and degreasing of the threaded surface in the alkaline solution, washing with water and heating the lock joint with the threaded surface, b) chemical-thermal treatment of heated lock joint with threaded surface by liquid carbonitriding in bath containing melt of salts – cyanate and alkali metal carbonate, and extraction of lock connection from threaded surface from bath, cooling in calm air, washing and drying. Heating of threaded surface of lock joint before immersion into bath with molten salt is carried out in melt of nitrates of alkali metals containing 55 % of potassium nitrate KNO₃ and 45 % sodium nitrate NaNO₃ at temperature of 250–300 °C for 15–20 minutes. Said chemical-thermal treatment is carried out at temperature of 540–580 °C for 15–25 minutes, wherein melt of salts of cyanate and alkali metal carbonate used is a melt of the following composition: potassium cyanate KCNO 85–95 %, potassium carbonate (potash) K₂CO₃ 5–15 %.

EFFECT: provides for technological and environmentally safe hardening of threaded surface of locking joint of thin-walled drill pipe.

1 cl, 1 dwg