LUBRICATION

It is recommended that drill rigs used for down the hole drilling be equipped with automatic oilers.  The use of a positive displacement pump for injecting oil into the air steam is preferred to the aspirator type of pump.  Pouring conventional lubricating oil down the drill pipe after various drilling intervals in order to provide lubrication to the hammer is never a recommended practice.

 

The rate of lubrication is a function of hammer air consumption which is dependent on the operating pressure and the choke size being used.  Recommended minimum oil requirements can be founded in tables shown in the Operating and Maintenance Manuals, or can be calculated for a specific application using the "Rule of Thumb"

 

RATE OF LUBRICATION = 0.2 QUARTS PER HOUR PER 100 SCFM

 

Thread lubrication also is essential to the life of the hammer components and drill string in preventing galling and corrosion.  The application of thread lubricant containing at least 40% by weight of zinc particles to the threads and shoulders will insure ease of breakout at the next maintenance disassembly.  In addition, application of the thread lubrication to the stress relief grooves at the base of pin and box threads will also minimise the effects of corrosive drilling fluids.

 

Prior to start up of drilling, the following lubrication practices are recommended:

  1. Coat the inside diameters of the hammer and drill pipe with rock drill oil.
  2. Make sure that all threads, stress relief grooves and make up faces are coated with thread lubricant.
  3. Check the oil level in the lubricator and make sure that it is filled with the recommended grade of rock drill oil for the specific application and location.
  4. Determine the hammer air consumption based on pressure and choke size.  Calculate or look up the lubrication rate for the hammer in the table in the Operating and Maintenance Manual.  Remember to use the next higher grade of rock drill oil when drilling with water injection.
  5. Adjust the lubricator setting to the proper lubrication rate.
  6. To insure that the lubricator is working, the main air valve should be partially open for a couple of minutes with the rotary head set for a low RPM.  After urning the main air valve off, the air hole in the face of the bit should be checked for evidence of a thin film of oil.
While drilling, it is recommended that the level of oil in the lubricator be monitored on a regular basis.  Drilling with the lubricator empty is extemely hazardous.  It is also recommended that air be blown through the inside of the drill pipe and that a quart of oil be poured down each section of pipe.

Scheduled hammer maintenance is extremely important in preventing failures due to galling from the build up of contaminant materials in the hammer.
  1. The hammer should be routinely be disassembled and cleaned.
  2. The frequency depends upon the drilling conditions and use of the hammer.
  3. A new hammer should be disassembled, inspected and cleaned after the first eight hours of operation.
  4. When used with water/foam injection or in wet holes, the hammer should be cleaned as soon as possible after each use with compressed air blasts and coated with rock drill oil.  The hammer should be disassembled, inspected and cleaned every 100 hours of operation.

Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BROKEN PISTON

 

CAUSE: Galling

 

SOLUTION: Check the following: Lubrication system, oil grade, oil quantity being delivered and contamination in hammer.

 

 

The most common cause of piston failure is galling.  When it occurs with a new hammer after only a few minutes of operation, it could indicate a dimensional problem with either the piston or the piston case or that there was a failure in the lubrication system on the drill rig.  More commonly, piston failures are encountered after 30 or so hours of operation.  In addition, the location of failure is gereally found on the bottom end of the piston between the second oil groove and the undercut radius.  In these cases, the outer surface of the piston, particularly in the area of failure, shows evidence of wear and sreaking from galling.

 

 

 

At this point in time, the harmful effects of poor lubrication practices and the build up of contamination in the hammer take their toll.  An examination of the fractured surface of a piston that has failed due to galling on he outside diameter, will show the characteristic conchoidal beach marks of a fatigue failure originating at the surface of the piston and propagating in towards the center like the markings left on the sands of the beach by receding water.  Since cracking can originate from several areas of galling on the surface of the piston, steps or serration's where the cracks meet can sometimes be observe on the fracture surface.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BROKEN PISTON

CAUSE: Galling

 

SOLUTION: Polish Piston Case ID before replacing broken piston.

 

 

 

 

 

 

Galling occurs from the micro welding of two materials in sliding contact such as the piston and piston case.  Replacing the broken piston without polishing the inside diameter of the piston case (in order to remove the build up due to galling) will generally result in the rapid failure of the replacement piston.

 

 

Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BROKEN PISTON INTERNAL

 

 

 

Striking Surface

 

 

CAUSE: Galling with Rigid Valve

SOLUTION: Check minimum makeup space between Top Sub and Piston Case.

 

Failures due to galling can also be observed on the piston upper end without any evidence of wear or streaking on the outer surfaces as with this B53-25 Piston.

 

 

 

 

 

An examination of the fractured surface shows the characteristic conchoidal beach marks of a fatigue failure originating from the inside diameter of the piston and propagating outwardly in a circumferential manner markings left on the (like the sands of the beach by the receding water).  Steps or serrtation's where the cracks from several origins meet can generally be observed on the fractured surface.

 

In this case the piston failure was the result of galling due to contact between the finger of the rigid valve and the bore of the piston.  This type of failure usually results from the loss of the minimum make up spacing between the Top Sub and Piston Case.  This loss of make up spacing could be the result of the permanent set of the rubber make up ring from prolonged storage, frictional heat from trying to free a hammer stuck in the hole or excessive wear on the make up shoulder in the piston case.  Without this makeup spacing, the internal parts of the hammer are free to move with the hammer vibrations.  This may cause wear, heavy galling and component failure. See images below


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

 

CRACKED PISTON CASE

 

 

 

 

CAUSE: Thread Galling

SOLUTION: Regular placement of thread lubrication.

 

Fatigue cracking due to galling can be encountered on the upper threads of piston cases.  In this instance, cracking resulted from the lack of thread lubricant as indicated by the conchoidal beach marks originating from the edge of the thread contact area.  Generally in most drilling applications, there is less need to remove the Top Sub to service the hammer than there is a need to remove the Driver Sub to change bits, therefore, regular application of thread lubricant to the Top Sub Piston Case upper threads and stress relief grooves is equally as important as applying it to the Driver Sub and Piston Case threads and stress relief grooves when replacing bits.

 


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

EXCESSIVE DRIVER SUB SPLINE WEAR

 

 

CAUSE:  Lack of lubrication and/or excessive movement.

SOLUTION:   Check lubrication system and minimum weight on bit

 

Excessive spline wear due to galling on the pressure side can also be observed in driver subs.   This result is either due to a failure in the lubrication system or an excessive sliding motion between the bit and driver sub from insufficient hold down pressure.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BIT SHANKING IN SPLINES

 

CAUSE:  Lack of lubrication and/or excessive movement.

SOLUTION:  Check lubrication system and minimum weight on bit.

 

Corresponding galling on the pressure side of the bit splines is also generally traced to a failure in the lubrication system or an excessive sliding motion between the bit and driver sub from insufficient hold down pressure.  This type of failure generally results in shanking of the bit.

 

An examination of the fractured surface reveals the typical conchoidal beach marks typical of a fatigue failure having their origin on the pressure side on one or two of the bit splines.

 

Again, because galling occurs from the micro welding of two materials in the sliding contact such as the bit and driver sub, replacing only the broken bit without replacing the driver sub or repairing it in order to remove the build up due to galling will generally result in the rapid failure of the replacement bit.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BIT SHANKING IN GUIDE DIAMETERS

CAUSE: Insufficient clearance

SOLUTION: Always use genuine mission parts

 

At times severe galling of bits and driver subs can be obsered on the upper and lower guide diameters of bits and driver subs.  Encountering this type of failure after only a few feet of drilling, might be an indication of insufficient clearance between the guide diameters of the bit and driver sub.  This can sometimes be the case when driver subs not manufactured by sandvik are used.  Here, based on a dimensional inspection of one or two driver subs, the manufacturer of the driver sub, not knowing the dimensional accuracy used by sandvik, must make a guess at the required tolerance.  If the tolerance is too tight, interference and galling will occur, if too loose, a loss of hammer performance will result.

 

 

Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

SEIZURE OF BIT HAMMER

 

 

CAUSE: Sudden lubrication failure or insufficient clearance

 

SOLUTION: Check lubrication system

 

A sudden occurrence of galling in the guide diameters can quite often be traced to a failure in the lubrication system.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BIT SHANKAGE IN SPLINES

CAUSE: Insufficient rotational torque or total weight on bit.

 

SOLUTION: Use plastic drive plates or drive pins and bronze bushings.

 

With larger diameter hammer and bits, the metal damage on the pressure side of the splines (due to galling can become quite large), lubrication and minimum total weight on bit requirements are insufficient to eliminate failures due to galling.  

There are bits and driver subs available with replaceable plastic drive plates and pins to prevent spline galling.  Also available are bronze bushings to prevent galling in the upper and lower guide.

 


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

HEAVY BIT SPLINE WEAR

 

CAUSE: Excessive Movement

 

SOLUTION: Check minimum weight on bit and replace both top and driver sub

 

In those instances of galling where only excessive spline wear is encountered from the movement between the bit and the driver sub, the problem generally results from failure to maintain the minimum total weight on the bit.  This tapered spline wear shows that the hammer has been operated in the drop open position where the shorter spline engagement leads to heavy wear at the top of the splines.

 

This type of failure occurs, primarily, when drilling in loose and unconsolidated formations.  For these applications, the use of the higher hardness, thru-hardened bits and driver subs are recommended.  The Hammerdrill XL type driversub with its large driving area and 12-spine bit will give great improvement over conventional bit designs.  It must be pointed out that prior to replacing a bit due to excessive spline wear, the driver sub splines should be examined for excessive wear.  If both are worn, replacing only the bit will result in repeated rapid bit spline wear.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

BIT SHANKAGE IN LOWER GUIDE DIAMETER

 

 

 

CAUSE: Insufficient minimum weight on bit 

SOLUTION: Check minimum weight on bit and use shot-peened bit

 

Running off bottom due to the failure to maintain the minimum total weight on the bit can also result in galling in the lower guide diameter and shanking of the bit at the radius joining the head to the shank.  Generally, an examination of the fractured surface reveals little about the cause of failure due to the damage from the hammering after failure occurs.  This type of failure occurs, primarily, when drilling in loose and unconsolidated formations.  For these applications, the use of higher hardness bits are recommended because of the shot-peening operation which improves the fatigue resistance over that of standard hardness bits.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik