LOW-ALLOYED STEEL FOR BOTTOM OIL PIPES OWNING HIGH RESISTANCE SILENCTING UNDER VOLTAGE IN SULFID-CONTAINING MEDIUM

摘要

Low alloy steel for borehole oil pipes is proposed, which has high resistance to cracking under the action of stress in a sulfide-containing medium and is suitable for casing or laying in oil or gas wells. Specifically described is low alloy steel for borehole oil pipes, containing, in wt.%, C: from 0.2 to 0.35%, Si: from 0.05 to 0.5%, Mn: from 0.05 to 1.0 %, P: 0.025% or less, S: 0.01% or less, Al: 0.005 to 0.10%, Cr: 0.1 to 1.0%, Mo: 0.5 to 1.0 %, Ti: from 0.002 to 0.05%, V: from 0.05 to 0.3%, B: from 0.0001 to 0.005%, N: 0.01% or less, O (oxygen): 0, 01% or less, Nb: from 0 to 0.1%, Ca: from 0 to 0.01%, Mg: from 0 to 0.01% and Zr: from 0 to 0.1%, and having a half width (H ) and the diffusion coefficient of hydrogen (D) (10cm / s), satisfying the following equation (I): 30H + D ≤ 19.5 (1).