Non-magnetic Drill Collars

Non-magnetic drill collars have unusual design requirements, and as a result pose unique problems of corrosion resistance. Drill collars are the bottom components in a drill string, where their weight generates the force on the drill bit allowing it to drill and their stiffness allows the force to be transmitted without buckling.

Non-magnetic drill collars were developed to allow magnetic surveying of the well trajectory using instruments inside the drill string. Magnetic survey instruments (MWD / Magnetic Single Shots / Multi Shots) run in the hole need to be located in a non-magnetic drill collar of sufficient length to allow the measurement of the earth’s magnetic field without magnetic interference. Survey instruments are isolated from magnetic disturbance caused by steel components in the BHA and drill pipe.

Non-magnetic drilling tools of SOKOL include Non-Magnetic Drill Collar in Slick, Flexi and Spiral profiles, Non-magnetic stabilizers and MWD components.

SOKOL Non-magnetic drilling tools are made of special self-engineered steel grade SKL-140HS. The material is chromium – manganese stainless steel, which is developed for long service in corrosive drilling muds with high alternative stresses. Special forging process which is qualified and controlled by our metallurgical experts together with strict control of chemical composition guarantee high mechanical properties and excellent corrosion resistance properties. Roller Burnishing treatment which is applied on ID increases corrosion resistance properties, guarantees the surface hardness of bore up to 400BHN and surface finish of bore at Ra≤3.0 µm.

SKL-140HS provides significantly better performance than is required by API Specification 7.

Available sizes as per API Specification 7 - from 31/8" up to 11" of any type drill collar. Non-standard dimensions can also be supplied as per customer requirements. The collar length is up to 11 m.

Technical specification

Non-magnetic properties

Magnetic permeability (ASTM A 342): Max 1.005

Magnetic Field Variation: 40 gammas Max

Mechanical properties

PROPERTY REQUIREMENT
YIELD STRENGTH (0.2% OFFSET), MIN, KSI 140
Y.S. FOR COLLARS LARGER THAN 9.25”, MIN, KSI 130
ULTIMATE TENSILE STRENGTH, MIN, KSI 150
% ELONGATION IN 4D, MIN 20
% REDUCTION IN AREA, MIN 50
CHARPY V-NOTCH ENERGY, MIN AVERAGE, FT-LBS, @25°C OR BELOW 50
CHARPY V-NOTCH ENERGY, SINGLE VALUE, MIN, FT-LBS 40
HARDNESS, BHN 300 - 425
FATIGUE STRENGTH
(PUSH-PULL OR ROTATING BEND)
AT 10 MILLION CYCLES ± 65 KSI MINIMUM
AT 100 000 CYCLES ± 80 KSI MINIMUM
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