Definitions for PDC Bit Dull Characteristics (Column 3)
Bit Dull Grading Characteristic or column 3 In IADC Bit Dull Grading is used to characterize the predominant failure mode for a bit. For a primary dull characteristic, the following definitions apply:
Broken Teeth – More than 1/2 of the cutter is broken off, and the break occurs in both the diamond layer and the tungsten carbide substrate.
Chipped Teeth – A cutter which has minor breakage. Less than half of the cutter has been broken. The chip is in both the diamond layer and tungsten carbide substrate.
Worn Teeth – Normal PDC wear, with an even wear flat. The diamond layer is for the most part without major chips, spalls, or cracks along the worn edge.
No Dull Grade – No dull grade is performed due to unforeseen reason, such as no blades on the bit by design, all natural diamond cutters, etc.
Junk Damage – Hit junk down hole, usually indicated by rust stains, or actual small pieces of debris stuck between cutters or imbedded in the blade and body.
Erosion -Characterized by a badly worn bit, especially between cutters; often the cutters are barely supported by matrix due to the track lock feature, mud flowing from the nozzles have eroded away regions of the bit or blade; sometimes the diamond layer is intact with the tungsten carbide substrate worn smaller underneath.
LS Bond Failure – Where the braze joint between the PDC cutter and the bonded extension shears or breaks off. Sometimes the bonded extension is still in the cutter pocket, while the rest of the cutter is gone.
Broken Blade – Where an entire blade has broken off of a bit. The fracture must have located between the body and 1/2 the height of the blade.
Broken Matrix – Characterized by a section of the blade which has chipped or broken off of a bit. The fracture must be located between the top of the blade edge and 1/2 the height of the blade. In rare cases, broken matrix will occur in locations other than the blade. This type of failure also falls under broken matrix.
PDC-Delam – Where the diamond layer, or a predominant portion of the layer has cleanly come off the tungsten carbide interface. A delamination always occurs at the interface, where the tungsten carbide substrate is exposed.
PDC-Spall – Where areas of the diamond table have chipped off in thin layers or chips. The chips and fracturing of the diamond layer however, never are deep enough to reach the tungsten carbide interface.
Cracked Diamond Layer – Where there is a hairline crack or multiple cracks in a diamond layer which is still intact and has not actually broken off. The cracks can be radial, parallel with the tungsten carbide, etc.
Heat Check – Generally characterized as a wear flat with many small microcracks in the tungsten carbide. The carbide will have cracks similar to a dry mud bed or spider web like effect. The diamond layer often times will be disintegrated.
Lost Tooth – This is characterized by a cutter which is completely or for the most part gone, from the cutter pocket. There may at times be some residual tungsten carbide remaining in the pocket.
Lost Nozzle – Characterized by a missing nozzle or a nozzle which has been severely damaged.
Off Center – Characterized by excessive bit wear on only one side of the bit, due to off center rotation.
Ring Out – Characterized by a worn ring, or worn region of the bit which especially occurs, but is not limited to the nose and shoulder region. Ring out can occur over the entire bit with the entire nose, shoulder and gauge becoming massively worn. It is often accompanied by heat checking due to the extreme heat build which occurred.
Rounded Gauge – Characterized by a bit which looks like a reaming action of the hole took place. This can be identified by excessive amounts of bit wear in the outer shoulder and gauge regions. The individual blades in the gauge area have become rounded and have lost their sharp corners.
Bearing/Seals – Space 5 is used only for roller cone bits. It will always be marked “X” for fixed cutter bits.
Gauge – Space 6 is used to record the condition of the bit gauge. “I” is used if the bit is still in gauge. Otherwise, the amount the bit is under gauge is recorded to the nearest 1/16th of an inch.
Chipped Cutter
Description: A cutter that has minor breakage. Less than half of the cutter has been broken. The chip is in both the diamond layer and tungsten carbide substrate.
Cause: Impact associated with bit whirl or excessive torque due to change information as well as similar variables.
PDC Delamination
Description: Where the diamond layer or a predominant portion of the layer has cleanly come off the tungsten carbide interface. A delamination always occurs at the interface where the tungsten carbide substrate is exposed.
Cause: Most common cause is due to excessive heat which relates to diamond degradation.
PDC Heat Check
Description: Generally characterized as wear flat with many small microcracks in the tungsten carbide. The carbide will have cracks similar to a dry mud bed or spider web like effect. The diamond layer often time will be disintegrated.
Cause: Excessive heat due to starving bit (not enough cooling) or excessive pressure. (ex) W.O.B. in certain formations and similar variables.
PDC Erosion
Description: Characterized by a badly worn bit especially between cutters, often the cutters are barely supported by matrix due to the track lock feature. Sometimes the diamond layer is intact with the tungsten carbide substrate worn smaller underneath.
Cause: Excessive mud flow which can be amplified by abrasive mud and formation.
Broken Cutter
Description: More than ¾ of the cutter is broken off and the break occurs in both the diamond layer and the tungsten carbide substrate.
Cause: Severe impact against PDC drill bit cutters. Commonly seen with bit whirl and sporadic torque, etc.
Lost Cutter
Description: This is characterized by a cutter which is completely or for the most part gone, from the cutter pocket. There may at times be some residual (insignificant, minuscule, tiny pieces, inconsequential fragments due to localize randomized adhesion) tungsten carbide remaining in the pocket.
Cause: Most commonly occurs when the braze bond fails to retain the carbide substrate.
Worn Cutter/Normal Wear
Description: Normal PDC wear with an even wear flat. The diamond layer is for the most part without major chips, spalls, or cracks along the worn edge.
Cause: When all works well.
LS Bond Failure
Description: Where the braze joint between the PDC cutter and the bonded extension shears or breaks off. Sometimes the bonded extension is still in the cutter pocket while the rest of the cutter is gone.
Cause: Due to LS Bond failure usually relating back to PDC manufacturing.
Broken blade
Description: Where the entire blade has broken off of a bit. The fracture must have located between the body and ¾ the height of the blade.
Cause: Due to severe impact. Variables include: Bit whirl, severe change in formation, excessive torque.
Cracked Diamond Layer
Description: Where there is a hairline crack or multiple cracks in a diamond layer which is still intact and has not actually broken off. The cracks can be radial, parallel with the tungstencarbide, etc.
Cause: Possible variable include: Excessive heat, impact, and/or relating back to diamond integrity.
Ring Out
Description: Characterized by a worn ring or worn region of the bit which especially occurs but is not limited to the nose and shoulder region. Ring out can occur over the entire bit with the entire nose, shoulder, and gauge becoming massively worn. It is often accompanied by heat checking due to the extreme heat builduopo which occurred.
Cause: Usually cause by the loss of a cutting structure at a pinpointed area.
Broken Matrix
Description: Characterized by a section of the blade which has chipped or broken off of a bit. The fracture must be located between the top of the blade edge and one half the height of the blade. In rare cases, broken matrix will occur in locations other than the blade. This type of failure alse falls under broken matrix.
Cause: Most commonly due to impact. Examples of variables include junk in hole, excessive torque, etc.
Spalling
Description: A PDC spall can be charcterized as areas of the diamond table which have chipped off in thin layers or chips. The chips and fracturing of the diamond layer, however never are deep enough to reach the tungsten carbide interface.
Cause: A PDC spall is typically caused by exposure to impact due to the high brittleness of the diamond layer.
Reaming
Description: Characterized by concentrated wear on the gage pads. In many cases, the PDC cutters have very little wear.
Causes: Reaming is usually caused by drilling an undersized hole.