IADC Dull Grading

Cutting Structure
Inner Rows Outer Rows Dull Char. Location Bearings/Seals Gauge Other Dull Char. Reason Pulled


Inner Cutting Structure   X
Outer Cutting Structure   Gauge
A measure of lost, worn and/or broken cutting structure.
Linear Scale: 0-8
0 - No lost, worn and/or broken cutting structure
8 - All of cutting structure lost, worn and/or broken
  (Measure in fractions of an inch)
I - In Gauge
1 - 1/16" Out of Gauge
2 - 1/8" Out of Gauge
4 - 1/4" Out of Gauge
Dull Characteristics   Other Dull Characteristics
BF - Bond Failure   (Refer to column 3 codes)
BT - Broken Cutters    
BU - Balled Up   Reason Pulled or Run Terminated
CR - Cored   BHA - Change Bottomhole Assembly
CT - Chipped Cutters   CM - Condition Mud
DL - Delaminated Cutters   CP - Core Point
ER - Erosion   DMF - Downhole Motor Failure
HC - Heat Checking   DP - Drill Plug
JD - Junk Damage   DSF - Drill String Failure
LM - Lost Matrix   DST - Drill Stem Test
LN - Lost Nozzle   DTF - Downhole Tool Failure
LT - Lost Cutters   FM - Formation Change
NO - No Dull Characteristics   HP - Hole Problems
NR - Not Rerunnable   HR - Hours on Bit
PN - Plugged Nozzle/Flow Passage   LIH - Left in Hole
RO - Ring Out   LOG - Run Logs
RR - Rerunnable   PP - Pump Pressure
WO - Washed Out   PR - Penetration Rate
WT - Worn Cutters   RIG - Rig Repair
    TD - Total Depth/Casing Depth
Location   TQ - Torque
A - All Areas   TW - Twist Off
C - Cone   WC - Weather Conditions
G - Gauge   WO - Washout - Drill
N - Nose    
S - Shoulder    
T - Taper    


API Fixed Cutter Bit Tolerances


Any fixed cutter bit should be ring gauged prior to running in the hole. Stabilizers should also be calipered or gauged to verify they meet API-approved outside dimension tolerances as shown in the following table. Fixed cutter bits should not be larger than the nominal diameter.

6-3/4 and Smaller -0.015 to +0.00  
6-25/32 to 9 -0.020 to +0.00  
9-1/32 to 13-3/4 -0.030 to +0.00  
13-25/32 to 17-1/2 -0.045 to +0.00  
17-17/32 and Larger -0.063 to +0.00  
A “no go” gauge is used to ensure a bit is not smaller than allowed and, as the name implies, it should not go or slip down the entire length of the bit. A “go” gauge ensures a bit is not larger than allowed and should slip down the entire bit.