An eight point dull grading system has been established by the IADC to enable drillers and bit manufacturers to evaluate the performance of a drill bit. This eight point system is described below and is used on both tricones and fixed cutter bits but does not apply to drag bits:
1. Inner Cutting Structure – Inner cutting structure wear is also noted by a number ranging from 0 to 8 with 0 being no wear and 8 being total wear.
2. Outer Cutting Structure – Outer cutting structure wear is also denoted by a number ranging from 0 to 8 with 0 being no wear and 8 being total wear.
Steel Tooth Bits
A measure of lost tooth height due to abrasion and/or damage.
0 – No loss of tooth height
8 – Total loss of tooth height
Insert Bits
A measure of total cutting structure reduction due to lost, worn and/or broken inserts.
0 – No lost, worn and/or broken inserts
8 – All inserts lost, worn and/or broken
Cutting Structure Wear
3. Dull Grading Characteristics – Dull characteristics enables the bit salesperson or driller to determine the overall, distinctive aspect of the dulled drill bit according to IADC standards as follows:
BT – Broken Teeth
BU – Balled Up
CC – Cracked Cone
CD – Cone Drag
CI – Cone Interference
CR – Cored
CT – Chipped Teeth
ER – Erosion
FC – Flat Crested Wear
HC – Heat Checking
JD – Junk Damage
LC – Lost Cone
LN – Lost Nozzle
LT – Lost Teeth
NO – No Dull Characteristics
NR – Not Rerunnable
OC – Off Center Wear
PB – Pinched Bit
PN – Plugged Nozzle/Flow Passage
RG – Rounded Gauge
RR – Rerunnable
SD – Shirttail Damage
SS – Self-Sharpening Wear
TR – Tracking
WO – Wash Out
WT – Worn Teeth
4. Location – Location describes where the damage is on the cone.
N – Nose Row
M – Middle Row
G – Gauge Row
A – All Rows
Cone Number One contains the centermost cutting component. Cones two and three follow in a clockwise manner.
Nose row is the centermost cutting structure.
Gauge row is the outer most cutting structure.
5. Bearings/Seals – For open or roller bearing bits, bearing life is estimated on a scale of 0 to 8.
Non-Sealed Bearings
0 – No life used
8 – All life used,
i.e., no bearing life remaining
Sealed bearings
E – Seals effective
F – Seals failed
N – Not able to grade
“X” indicates fixed cutter.
6. Gauge – Gauge measures the amount of gauge wear a drill bit has suffered.
I- In Gauge
1 – 1/16” out of gauge
2 – 1/8” out of gauge
4 – 1/4” out of gauge
7. Other Dull Characteristics – Any other dull grading characteristics should be noted here using the codes from #3.
8. Reason Pulled – The following codes are used to indicate the reason a bit was pulled from the hole:
CM – Condition Mud
CP – Core Point
DMF – Downhole Motor Failure
DP – Drill Plug
DSF – Drill String Failure
DST – Drill Stem Test
DTF – Downhole Tool Failure
FM – Formation Change
HP – Hole Problems
HR – Hours on Bit
LIH – Left In Hole
LOG – Run Logs
PP – Pump Pressure
PR – Penetration Rate
RIG – Rig Repair
TD – Total Depth/Casing Depth
TQ – Torque
TW – Twist Off
WC – Weather Conditions
WO – Washout – Drill String
