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E-mail: [email protected] Whatsapp: +8613647327093 Tel: +86-731-8403-0163
In this week, our 8pcs kelly bars are ready and on their way to our customer.
In pile foundation construction, the Kelly bar often plays the role of an “invisible core.” No matter how powerful the drilling rig is or how good the drilling tools are, if the Kelly bar develops wear, bending, or abnormal engagement, the efficiency and safety of the entire drilling system will be compromised. Regular inspection and maintenance of the Kelly bar can extend its service life by 30%–50%, significantly reduce downtime and safety risks, and ensure smoother, more reliable construction.
Let’s now look at how to inspect and maintain a Kelly bar—starting from the details.
Many major Kelly bar failures actually leave “early signs” on the surface. With careful inspection, potential problems can often be discovered dozens of operating cycles in advance, preventing failures from escalating and causing downtime.
1) Check overall straightness: Is there a slight “bow”?
After long-term torsional and lateral loading, the bar may develop irreversible micro-bending. If the bar is not perfectly straight when viewed from both ends, or if slight “wobbling” occurs during rotation, it usually indicates:
Uneven loading or long-term off-center stress
Impacts during construction or improper mounting/dismounting of tools
Potential risk of fatigue cracking
If slight bending is not corrected, it may eventually cause hole deviation, increased rig vibration, and accelerated wear of the pressure points.
2) Inspect the key strips: Is the wear beyond limits? Any broken edges?
The pressure points and key strips are the most critical wear areas. Once wear exceeds tolerance, engagement accuracy decreases and risks increase. Focus on:
Rounded-off edges on key strips
Broken corners or missing material
Impact-flattened key strips
Fine cracks or bright “fatigue marks”
These signs indicate that the pressure points have entered the accelerated wear phase, requiring more frequent inspection or even replacement.
3) Check welds and reinforcement ribs: Any cracks, weak welds, or local detachment?
Weld cracking is a common precursor to Kelly bar failure.
Watch for:
Fine black lines on the weld surface
Peeling or bulging weld toes
Slight discoloration near the weld (overheated zones)
If any of these appear, stop using the bar immediately and have it inspected professionally.
4) Check interfaces, shoulders, and stops for impact marks
These parts should mainly bear axial load. If you see:
Obvious dents
Metal burrs or rolled edges
Local spalling
Abnormally polished shiny marks
This indicates abnormal impact or improper installation, and the cause must be identified.
Durability is not innate—it is “maintained.” Even the best steel or highest torque rating will wear fast if not maintained.
On the other hand, with just a few minutes of proper routine care, you can ensure stable performance and long service life, keeping the rig in its “best condition.”
Below are the most practical and essential daily maintenance points:
1) Daily quick checks + weekly detailed checks
Maintenance must be routine—not “only when someone remembers.”
Recommended schedule:
Daily check (5–10 minutes):
Pressure point appearance and cracks
Smooth sliding of locking keys
Visual straightness check of bar body
Weekly check (30–60 minutes):
Rough measurement of pressure point dimensions
Key strip wear
Weld surface inspection
Engagement consistency of each Kelly section
This keeps the workload reasonable while preventing major failures.
2) Maintain drilling tools together: Half of Kelly bar life depends on “compatibility”
Even the strongest Kelly bar can bend or wear prematurely if the drilling tools—drilling auger, core barrel, or drilling bucket—are misaligned or worn.
Check along with the Kelly bar:
Core barrel centerline deviation
Auger blade breakage or uneven wear
Alignment between tools and Kelly bar
Wear condition of tool kelly boxs
Tool issues are often the root cause of Kelly bar bending and uneven wear.
3) Adjust torque based on ground conditions
Many Kelly bars are not “worn out” but “twisted out.”
Different strata require different torque strategies:
Soft soil: Light pressure + high speed (protects pressure points)
Medium weathered strata: Moderate pressure + stable torque
Hard interlayers: Low speed + high torque, avoid long peak torque
Cobble layers: Avoid continuous heavy torque; use point drilling
A correct torque pattern significantly extends pressure point life.
Even when contractors know the importance of maintenance, many bad habits still shorten Kelly bar lifespan or create hidden dangers. Below are the most common mistakes and correct practices.
1) Misconception: “Slight bending is no problem—just keep drilling”
The Kelly bar is hollow, and bending concentrates internal stress.
Wrong: Continuing to use a bar exceeding allowable curvature will cause:
Unstable drilling
Off-center pressure points
Rapid fatigue crack growth
Could result in bar breakage.
Correct: Measure straightness immediately; if out of tolerance, straighten or replace.
2) Misconception: Ignoring small cracks
Fine cracks may seem harmless, but they expand rapidly under torque.
Correct practices:
Use MT/PT testing regularly
Stop immediately if cracks are found; repair or replace promptly
3) Misconception: Rough handling when lowering or locking the bar
Rapid dropping and rough engagement increase impact load.
Wrong: Excessive impact causes pressure point dents, deformation, and increased clearance.
Correct: Smooth lowering, keep alignment, prohibit violent impact.
4) Misconception: Mixing different brands or incompatible pressure points
Different brands vary slightly in dimensions.
Wrong:
Uneven engagement
Unstable torque transfer
Risk of jumping lock or tool drop
Correct: Use the same brand, same specification, complete matching system.
5) Misconception: Always running at full torque
Some operators use full load every cycle to “maximize efficiency.”
Wrong: Long-term heavy load causes:
Fatigue at pressure points
Stress concentration in bar body
Shortened service life
Correct:
Adjust torque according to strataAvoid continuous full-torque operation
To know more detials about repair and maintenance of kelly bar, please check our this article:
To know how to prevent a kelly bar from breaking during construction, please check our this article:
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