Plunger Failure on a Second Stage Cylinder of a Hyper Compressor

In February 2006 a tungsten carbide plunger of the second stage cilinder of a hyper compressor fractured. The failure occurred on the part of the plunger that is running in the high pressure packing. After the incident a failure and unknown cause analysis (UCA) was conducted. It was concluded that the main cause for the failure were heat cracks that initiated a fatigue crack over 60% of the cross section of the plunger prior to final fracture. It appeared that the use of a more wear resistant sealing ring material and poor lubrication conditions during high leak gas caused the initiation of the heat cracks. The more wear resistant ring material was used in all of our compressors. An operation, monitoring and replacement strategy was developed to assure a safe operation. In this way a scheduled replacement of the rings by a non sensitive ring material was possible and production loss was minimized. In the paper all aspects of this case will be discussed.