1. Decoding the 3-Digit IADC Number
The first digit (Series 1–8) defines cutting structure: Series 1–3 denote steel milled tooth bits; Series 4–8 denote Tungsten Carbide Insert (TCI) bits. The second digit (Type 1–4) indicates formation hardness classification from softest to hardest. The third digit specifies bearing and gauge design: open roller bearings, sealed roller bearings, or sealed journal friction bearings.
2. Formation-Matched Selection Strategy
Soft clays and silt formations require long, widely spaced teeth (IADC 111–117) to prevent bit balling and achieve high rate of penetration (ROP). Medium-hard limestone and abrasive sandstones perform best with chisel-shaped TCI bits (IADC 517–537). Hard, abrasive granites, andesite, and quartzites demand compact conical TCI inserts (IADC 617–637) operating under heavy weight-on-bit (WOB) crushing mechanisms.
Engineering Notice: For tailored hook-load ratings, torque calculation, and mud hydraulic modeling matched to your strata, contact KD SONDAJ engineering.
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