Why Post-Run Inspection Matters

A PDC bit that runs to destruction and gets thrown away without inspection is a missed learning opportunity. Each wear pattern on the cutters, blades, and gauge section is a record of conditions at the bottom of the hole — conditions that your surface instruments can only approximate.

Systematic dull grading, standardized under SPE/IADC Publication 23939 (first revised 1992 and adapted with industry updates since), provides a shared language between drilling teams, bit engineers, and suppliers. When you record a dull grade accurately, a manufacturer in Zhengzhou can look at the same data as a drilling engineer in Houston and recommend the same design change.

Step 1: Clean Before You Grade

Before any inspection begins, wash the bit thoroughly with fresh water and a soft brush. Mud, cuttings, and formation material can mask cutter condition, obscure blade geometry, and hide erosion patterns. Pay attention to junk slots and nozzle ports — debris here can misrepresent what actually happened downhole.

Take photographs from at least three angles: the face (crown view), the side profile, and a close-up of two or three representative cutters. These images should accompany every dull report filed with the manufacturer.

Step 2: Identify the Wear Pattern — The 14 PDC Dull Types

The IADC system records wear in column three of the dull grade using standardized abbreviations. Understanding what each designation looks like in practice is the difference between a useful dull record and a paperwork formality.

Normal Wear (NW) is what you hope to see: a smooth, uniform wear flat across the diamond table, with no significant chipping, cracking, or delamination. The diamond layer erodes predictably. This indicates appropriate WOB and RPM for the formation, adequate hydraulics, and a well-matched bit.

Chipped Cutter (CT) presents as breakage involving less than half the cutter, with fractures running through both the diamond layer and the tungsten carbide substrate. The most common cause is bit whirl — an eccentric rotation pattern in which the bit orbits around a point other than its own center. Chipped cutters concentrated on one side of the bit often point to lateral shock rather than axial overload.

Broken Cutter (BT) is more severe than chipped: more than three-quarters of the cutter has fractured. When multiple cutters in the same radial position show this pattern, the bit experienced severe impact loading, often from dropping into a hard stringer while rotating, or from torque fluctuations associated with stick-slip. If the breaks are clean and mirror-like, the failure was sudden; rough, jagged fracture faces suggest repeated impact fatigue.

PDC Delamination (DL) is characterized by the diamond layer cleanly separating from the tungsten carbide substrate at the interface, leaving the substrate surface exposed. The most common cause is thermal degradation: diamonds convert to graphite above approximately 750°C (1,382°F) in the presence of iron catalysts, and the resulting volume change breaks the bond. Delamination found in the nose and cone zones, where cutter velocity is lower and heat concentration is higher, typically points to inadequate flowrate or excessive WOB in hard formations.

PDC Heat Check (HC) shows as a network of fine cracks across the wear flat — similar in appearance to dried mud or a cracked glaze. The diamond layer has already converted and the underlying carbide shows thermal stress fractures. This is the downstream result of the same overheating that causes delamination, and usually indicates a drilling parameter problem: flow rates too low, WOB too high for the bit size, or RPM excessive for the formation hardness.

Spalling (SP) presents as thin flakes or chips on the diamond surface that do not reach down to the carbide interface. Unlike delamination, spalling is a surface phenomenon. It typically results from impact on a brittle cutting face rather than thermal failure. Spalling concentrated on the gauge cutters suggests contact with the borehole wall during rotation, possibly from a worn stabilizer allowing lateral bit movement.

Erosion (ER) is material loss from the bit body — blade shoulders, junk slots, nozzle surrounds — caused by abrasive fluid flow. When erosion is severe and localized directly around a nozzle, it often means the jet velocity is higher than 100 m/s (about 330 ft/s), or that the nozzle itself has worn and enlarged, redirecting flow against the body. Matrix body bits are more erosion-resistant than steel body bits for this reason.

Lost Cutter (LC) means the entire cutter is missing from its pocket. A small residue of brazing material or carbide fragments in the pocket usually means the cutter came out intact — a brazing failure. An empty, clean-looking pocket where the cutter shattered and expelled in pieces suggests impact destruction rather than bonding failure. Brazing failures tend to cluster when the bit has run at elevated temperature for extended periods.

Broken Blade (BB) indicates a full blade fracture from the bit body, occurring somewhere between the bit crown and half the blade height. This is typically caused by severe impact loading: encounter with a ledge in an unstabilized wellbore, high-speed rotation into a formation with a sudden hardness contrast, or a fish (dropped object) at bottom. A broken blade almost always terminates the run and requires close inspection of all downstream BHA components for damage.

Broken Matrix (BM) is similar to broken blade but limited to the matrix material at the top of the blade, above the midpoint of the blade height. The most frequent cause is junk in the hole — metallic debris striking the bit while rotating.

Ring Out (RO) describes concentrated wear forming a ring or band at a specific radial position, most commonly the shoulder or nose. Ring out usually results from a localized failure of the cutting structure in that zone — perhaps a cluster of cutters wearing faster due to a harder formation band — causing the remaining cutters in that ring to overload and accelerate wear.

LS Bond Failure (LB) is specific to PDC cutters mounted on a carbide extension post: the braze joint between the PDC table and the extension shears or fractures, separating the diamond element from the post while the post remains in the pocket. This is primarily a manufacturing quality issue and should be reported directly to the bit supplier with photographs.

Cracked Diamond Layer (CD) shows fine linear or radial cracks in the diamond table that have not yet caused separation. The diamond layer is intact but compromised. Continued use would likely lead to delamination or spalling. Cracked layers found after a run suggest the bit is approaching the limit of its thermal or impact tolerance for the formation.

Reaming Wear (RW) is gauge-specific: the primary wear is concentrated on the gauge cutters or gauge pad, while the face cutting structure shows relatively little use. This typically occurs when the bit is used to ream through a tight section — often a previously under-gauge interval — rather than drilling fresh formation. The gauge takes the brunt of the sizing work.

Step 3: Record the IADC Dull Grade

The full IADC dull grade for a fixed cutter bit includes eight columns: inner rows wear (0–8), outer rows wear (0–8), location of dullness, bearings (N/A for PDC), gauge (I/O/G), secondary dull characteristic, primary reason pulled, and remarks.

For wear values, 0 = no wear and 8 = complete wear of the cutting structure. Most runs that pull on schedule without emergency fall in the range of 2–5 for the outer rows.

When recording dull characteristics, use only the standardized abbreviations. A record that reads "BC / BT / O / X / G / NO / TD / —" communicates exactly: outer row broken cutters, no bearing issue, in-gauge, no secondary dull, pulled on total depth, no remarks needed. The same information written in prose takes longer to read and introduces ambiguity.

Step 4: Connect Dull Patterns to Operating Decisions

The inspection has no value unless it feeds back into the next run. The four most common pattern-to-action translations are:

If you see chipped or broken cutters, investigate bit whirl. Review surface torque logs for high-frequency oscillations. Consider a bit with more cutters per blade, larger back-rake angles, or a flatter crown profile that distributes lateral load more evenly.

If you see delamination or heat check, the drilling program over-pushed parameters for that formation. Reduce WOB by 15–20%, increase flowrate to maximum permissible, and consider a thermally stable cutter (TSP) in the nose and shoulder zones for the next run.

If you see lost cutters from brazing failure, document the pocket locations, run depth, and formation interval, and send the full report to the bit manufacturer. This is a quality control issue, not a drilling parameter issue.

If you see uniform normal wear across all zones, the bit-formation match was good. The decision question is whether to re-run the same design at the same depth or go to the next interval. Confirm gauge before re-running.

SUNGOOD's Approach to Bit Inspection Support

At SUNGOOD, we provide post-run analysis support as part of our technical service offering. When you pull a SUNGOOD TECH PDC bit and send us the dull grade and photographs, our engineers evaluate the wear against the original design parameters and the reported formation data. In most cases, we can identify the primary failure mechanism and propose a specific design modification — cutter density, back-rake angle, profile geometry, or cutter type — for the replacement bit.

This process works best when the communication happens within 48 hours of pulling the bit, before the drilling team moves off location and the context is lost. 

Reading a PDC bit after pulling out of hole is a skill that improves with practice and a structured approach. The 14 IADC dull types are not just bureaucratic codes — each one points to a specific physical mechanism that occurred thousands of feet underground. Chipped cutters tell you about whirl. Delamination tells you about heat. Lost cutters tell you about braze quality. Ring out tells you about load distribution.

The 20 minutes spent on a thorough inspection, documented correctly and communicated to your bit supplier, can reduce the next bit's run cost by more than any single parameter optimization. Start with clean cutters, work through the pattern systematically, record the IADC grade accurately, and act on what you find.

For more technical guidance on PDC bit selection, inspection, and performance optimization, visit Our official website.

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