METHOD OF INCREASING RESISTANCE OF STEEL PIPELINES AGAINST CORROSION BY CASE-HARDENING Russian patent published in 2013 - IPC C23F13/16 B23H9/00 C23C8/36 

FIELD: machine building.

SUBSTANCE: method of steel pipe case-hardening comprises heating to 1200-1400°C in carbon-bearing medium in arc flame between two graphite electrodes of arc torch, curing and cooling. Pipe surface is heated for 5-25 s. Current of 50-250 A is fed to electrodes. Arc flame is displaced on pipe surface in helical line at the rate of 2-20 mm/s and pitch of 0.75-0.8 of heating spot diameter making 20-25 mm. Pipe surface is arranged 10 mm from electrode ends in carbon arc flame area. Pipe surface heated by electric arc at 75-100 mm from arc flame is water cooled. In case-hardening, pressure in pipe is kept at the level of 0.5-0.75 of operating pressure. Pipe surface coat features excellent resistance due to it rules out penetration of atomic hydrogen into steel and boats hardness of 2000 N/mm².

EFFECT: higher antirust properties.