Direct answer: DTH bit body wash is excessive loss of the steel matrix around the carbide buttons, flushing holes or face of a down-the-hole bit. The carbide may still look usable while the supporting steel retreats, leaving buttons increasingly exposed and vulnerable to movement, breakage or loss. Body wash is a wear pattern, not a complete root-cause diagnosis.
The practical response is to stop and inspect the pattern, then check rock abrasivity, cuttings return, flushing passages, working airflow, rotation, feed and drill-string condition. Do not automatically add more air: too little cleaning can recirculate abrasive cuttings, while unnecessarily high cuttings velocity can also intensify erosion. Use the hammer and bit manufacturer’s operating and retirement criteria for the actual model.
What DTH Bit Body Wash Looks Like
On a healthy used bit, wear should be judged against the new geometry and the supplier’s inspection limits. Body wash is indicated when steel disappears faster than the adjacent carbide. Typical signs include:
- carbide buttons standing noticeably farther proud of the face than when new;
- scooped, channeled or sandblasted-looking steel around button seats;
- rounded or eroded edges at flushing holes and face grooves;
- a thinned gauge area or loss of steel support behind peripheral buttons;
- button movement, cracking around a seat or a button already missing;
- a falling penetration rate accompanied by heavy fines, poor returns or repeated re-drilling of cuttings.
Do not confuse every scratch with body wash. Normal face polishing, gauge wear, carbide flattening, impact cracks and spline wear have different primary mechanisms. Several can appear together, so record the complete pattern before changing settings or blaming the bit.
Why the Steel Body Erodes Faster Than the Carbide
A DTH bit works in a severe abrasive circuit. Each blow fractures rock, rotation indexes the buttons to fresh contact, and hammer exhaust moves the broken material away. The steel body is tougher but softer than the cemented-carbide inserts. If hard mineral grains repeatedly strike or slide across exposed steel, the matrix can retreat while the carbide remains comparatively prominent.
Rockmore describes body wash as erosion of the bit matrix by rock-chip flow and explains how flushing-groove geometry can change chip velocity at the bit edge. Sandvik likewise treats flushing design as part of cuttings removal and wear control. These sources support an important diagnostic principle: flushing is not merely an air-pressure number; it is a flow system that includes the bit ports, face grooves, annulus, hole condition, cuttings load and actual compressor delivery.
| Possible contributor | Evidence to look for | What to verify |
|---|---|---|
| Abrasive formation or abrasive interbed | Rapid steel loss begins in a quartz-rich, sandy or otherwise abrasive interval; several bits show a similar pattern | Mineralogy, cuttings texture, depth interval and wear per metre |
| Cuttings recirculation | Fine material repeatedly returns late, the hole stops cleaning quickly, or penetration falls while drilling continues | Port blockage, annular clearance, air loss, depth, water entry and cleaning practice |
| High cuttings velocity | Concentrated channel erosion around outlets or grooves despite strong returns | Hammer choke/configuration, bit design and OEM airflow guidance; do not reduce air blindly |
| Excessive rotation for the condition | Polished or directional wear, high gauge wear, heat or small re-ground fines | Actual RPM under load and the rig/bit supplier’s setting range |
| Blocked or damaged flushing geometry | Unequal discharge, packed material, distorted holes or grooves | All passages after safe depressurization and removal |
| Alignment or drill-string problem | One-sided wear rather than a generally even erosion pattern | Bent pipe, rig alignment, chuck guidance, bit shank and hole deviation |
A Safe DTH Bit Body Wash Inspection Sequence
Isolate and depressurize the drilling system before touching the bit or clearing a passage. Secure heavy components against rolling or falling, use the correct lifting and breakout equipment, and follow the rig and hammer manuals. Never probe a flushing hole while the drill string can rotate or receive air.
- Record the bit identity and service interval. Capture the shank, diameter, face design, button layout, supplier part number, drilled metres, rock interval and settings. Without this context, a wear photograph is difficult to interpret.
- Clean without hiding the evidence. Remove loose cuttings and mud so the steel surface, seats and grooves are visible. Avoid aggressive grinding before the condition has been photographed and measured.
- Photograph the face, gauge and shank. Use consistent light and include a scale. Take straight-on and oblique views. Mark the orientation if the wear is one-sided.
- Compare steel support around every button. Look for undercut seats, cracks, looseness and unequal protrusion. A carbide that looks sharp is not serviceable if its supporting steel has been lost.
- Inspect flushing holes and grooves. Confirm that passages are open and edges are not badly eroded, folded or packed. Check the original drawing or an unused bit because face geometries vary.
- Check gauge and symmetry. Measure in more than one direction with the method specified by the supplier. Uneven results may point to alignment, bent-pipe or guidance problems rather than uniform abrasive wear.
- Inspect the shank and hammer interface. Body wash at the face can coexist with spline, chuck, retaining or impact-end wear. Do not return a questionable interface to service merely because the face was dressed.
- Classify the disposition. Continue only if the bit remains within the maker’s limits. Recondition only by an approved procedure. Quarantine a bit with cracks, loose or missing buttons, seriously undercut seats, distorted passages or uncertain structural support.
Flushing Checks Before Changing the Bit Specification
A premature change to button shape or face design can mask a supply problem. Check the system from compressor to collar:
- Compare compressor free-air delivery and working pressure with the hammer maker’s requirement, accounting for altitude, hose and pipe losses, leakage and other tools sharing the supply.
- Observe whether returns are continuous and whether cuttings size or color changes when wear accelerates.
- Check for water inflow, fractures, cavities or an enlarging hole that changes the air path.
- Confirm that drill-pipe bore, bit diameter and actual hole diameter leave a workable return annulus.
- Inspect the bit’s flushing holes, face grooves and hammer passages for restriction or damage.
- Review whether the operator repeatedly re-drills settled cuttings after interruptions or rod changes.
If cleaning is weak, the safe correction is not always maximum compressor output. Find the restriction or air loss and use the hammer manufacturer’s permitted configuration. If returns are forceful but erosion is concentrated in the flow path, ask the supplier to review bit flushing geometry and the approved choke or airflow arrangement for that hammer. Any choke change must follow the hammer manual; an incorrect change can reduce cleaning, affect hammer cycling or create a different failure.
Operating Adjustments: Change One Variable at a Time
Establish a baseline before making adjustments. Record working pressure, compressor load, RPM, penetration rate, hole depth, cuttings return and the measured wear after a known drilled interval. Then change one permitted variable and compare the result.
Rotation
Rotation should index the buttons between impacts, not scrub the face continuously. If the OEM range allows adjustment, a lower setting may reduce abrasive sliding and can produce coarser cuttings that are easier to recognize. But rotation that is too low can cause repeated impacts in the same track and unstable drilling. Judge the outcome with penetration, cuttings and wear—not RPM alone.
Feed
Use enough feed to maintain stable bit contact without forcing the hammer. Excessive feed can increase stress and poor contact can cause bouncing. Neither setting is diagnosed from body wash alone; review the rig’s percussion, rotation and feed guidance together.
Hole cleaning
Clear the hole according to the rig and hammer procedure before adding rods, after interruptions and before withdrawal when cuttings have settled. Persistent cleaning problems in water-bearing, fractured or unstable ground may require a method or drilling-fluid review beyond a simple bit change.
When to Recondition, Quarantine, or Replace the Bit
| Finding | Field decision |
|---|---|
| Even, limited steel wear; buttons and seats secure; dimensions within OEM limits | Document and continue with a shorter inspection interval |
| Grooves need approved dressing but the body remains structurally sound | Recondition only to the supplier’s procedure and re-inspect |
| Wear rate increasing without a clear cause | Quarantine one sample, inspect the air/return system and compare another controlled run |
| Loose or missing button, crack, seriously undercut seat, damaged shank or uncertain support | Remove from service and obtain an engineering or supplier disposition |
| Repeated pattern across bits from different lots | Investigate formation, settings, flushing and drill-string condition before treating it as a lot defect |
| Same abnormal pattern isolated to one lot under controlled conditions | Preserve samples and operating records for supplier failure analysis |
There is no safe universal button-protrusion or steel-loss limit for every DTH bit. Diameter, carbide size, seat design, face geometry, heat treatment and service duty differ. A value from another brand’s manual should not be converted into a PerfoMax or sitewide discard rule.
What to Send in an RFQ or Premature-Wear Review
A useful request allows the supplier to match the bit and diagnose the system rather than quote on diameter alone. Include:
- hammer brand/model and exact bit shank;
- required bit diameter and finished-hole requirement;
- face design, button profile and current flushing layout;
- compressor pressure and free-air delivery, plus altitude and shared demand;
- drill-pipe outside diameter, inside diameter and lengths;
- hole depth, inclination, dry/wet condition and observed air losses;
- rock description, abrasive minerals, fractures and representative cuttings;
- RPM, working pressure, penetration trend and cleaning procedure;
- metres drilled to first visible body wash and to removal;
- clear face, gauge, shank and flushing-port photographs.
For a replacement or controlled trial, review the active PerfoMax DTH drill bit selection pathway. Confirm shank, diameter, face, carbide and flushing requirements in writing before ordering. For a related failure mode, see the published guide on carbide button breakage, cracking and pop-out.
Frequently Asked Questions
Is DTH bit body wash always caused by abrasive rock?
No. Abrasive mineral grains are a major driver, but cuttings recirculation, restricted passages, high local flow velocity, excessive rotation and alignment problems can change the severity or pattern. Diagnose the whole air–bit–hole system.
Can I fix body wash by increasing air pressure?
Not automatically. More usable airflow may help when cuttings are not being lifted, but pressure at the compressor does not prove adequate flow at the bit. Unnecessarily high velocity through a poor flow path may intensify erosion. Stay within the hammer maker’s limits and identify the restriction or loss first.
Why are the carbide buttons still tall when the steel is worn away?
Cemented carbide resists abrasion differently from the heat-treated steel body. In some formations and flow conditions, the steel retreats faster, leaving buttons proud. Tall-looking carbide is not proof of remaining bit life because the seat may no longer support it safely.
Can a body-washed DTH bit be welded or rebuilt on site?
Do not improvise a repair. Welding or heating can alter steel properties, distort the face, damage carbide seats and introduce cracks. Use only a documented supplier-approved reconditioning procedure; otherwise quarantine and replace the bit.
What is the fastest field check for recurring body wash?
Compare wear after a fixed drilled interval while recording rock, working airflow/pressure, RPM, penetration and returns. Photograph the same face positions. A controlled trend is more useful than comparing unrelated bits at end of life.
Technical References
- Rockmore International: CrossFlow bit design and the relationship between flushing geometry, chip velocity and body wash
- Sandvik Mining and Rock Solutions: DTH bit design, flushing and cuttings removal
- Halco Rock Tools: drill-bit handling and inspection guidance for body wash, flushing grooves and button support
Next step: send PerfoMax the hammer model, bit shank, diameter, rock description, compressor delivery and wear photographs. The team can help organize the compatibility and trial-order questions without inventing a universal wear limit for your site.