CRACKED PISTON CASES

 

CAUSE: Bent Drill Pipe

SOLUTION: Straighten Drill Pipe

 

The worn out Piston Case can manifest itself as cracking in the threaded ends and in the areas of the internal porting.  When these conditions are encountered, the dimensions of the Piston case should be compared to the values given in the table for wear allowance in the Operation and Maintenance Manual.  The wear observed on the outside diameter may be found to be greater on the ends than it is in the center, but, nevertheless should be reasonable uniform around the circumference of the Piston Case.  When cracking is found to be predominant on one side of the Piston Case, the variation in wall thickness around the outside diameter should be determined.  An excessive amount of wall variation is generally an indication of drilling with excessive weight on the bit or bent drill pipe.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

CRACKED PISTON CASE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CAUSE: Gripping with Jaw Wrench in wrong location.

SOLUTION: Use Chain or Petol Type Tongs / Use Correct Tong Placement.

 

Many Piston failures (due to cracking located near the ends) can be traced to difficulties in tying to loosen the threaded connections by not following the recommendations for tong placement written in the Operation and Maintenance Manual or using Tongs not equipped with a cylindrical jaw.

 

The use of a pipe wrench or stilsons for loosening the threaded connection can leave deep notches in the side of the Piston Case that will result in stress concentrations that lead to premature failure.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

HOLE IN PISTON CASE

 

CAUSE: Gripping with jaw wrench in wrong place.

 

SOLUTION: Use chain or petol type tongs/ Use correct tong placement.

 

Complaints of a hole being blown through the end of the Piston Case are always found to be the result of the intersection of two cracks that had propagated from notches left from tongs not equipped with cylindrical jaws.  Normal hammer operating pressures are much too low to blow a hole, even a small hole, through a Piston Case.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik

CRACKED PISTON CASE

 

CAUSE: Abuse with sledge hammer.

 

SOLUTION: Use chain or petol type tongs/ Use correct tong placement.

 

In some instances, beating on the end of the Piston Case with a hammer is used to loosen threaded connections.  This abusive practice leaves dents in the piston case that can distort the threads and result in cracking.  The practice of loosening threaded connection on piston cases that are surface hardened for enhanced wear resistance imposes a greater risk due to cracking than encountered with those that are only heat treated by the standard process.  The harder, more wear resistance surface hardened material is less crack resistant to the notches and dents left by poor break-out practices.

 

The photograph below displays the same part undergoing magnetic particle inspection under violet light.  The myriad of cracks are a direct result of this abuse.


Reference:

Trouble shooting manual

Driltech Mission, LLC

Sandvik