Testing & Analysis

Oil Pan Cracking: Part 2

Failure Investigation & History

After being informed of the potential issue with oil pans cracking in the field, Tier II product support engineers from CAT gathered all pertinent information including customer (Williams) inquiry via the Dealer Service Network, engine serial number, engine hours, application, etc.  This information is used by CAT to help troubleshoot the failure and recommend an interim corrective action.  A CAT tech dispatched to the site found a crack on the left of the oil pan about a third of the way back.  It appeared to be located on the weld between the bottom and side plates of the pan.  No other visual damage to the bottom of the pan was found.

The CAT Tier II team reviewed the commissioning report and requested the failed components be sent back to the factory for testing and failure analysis.  The team’s goal was to determine the failure mode of the component and develop a plan to uncover the root cause using the six sigma DMAIC process.

Through their investigation, CAT found only two other pan failures throughout the history of the G3612 in the compression application.  While the failure rate was extremely low, the high cost of replacing a failed pan prompted the launch of an internal continuous product improvement issue.  The investigation at CAT internally along with the support from Williams and 6D (Six D Testing & Analysis) is further discussed below.

Post Commissioning Vibration Survey

A portion of the history that was available was a post commissioning vibration survey, which was performed on all of the CAT 3612 units at the station.  A typical vibration survey consists of measuring locations on the compressor, engine, skid, and piping.  The survey looks for global issues and would not necessarily focus on a localized issue.  Additionally, since the oil pan is difficult to get to it would be unusual for vibration measurements to be taken near the location where the crack occurred.

As expected, the vibration survey identified high vibration on parts of the compressor and piping, but no measurements were taken near the crack.  Speed limits were put in place to protect the vibrating components.   This is a typical approach until remediation efforts can be put in place to correct the vibration levels. Unit 1 could only be operated at 920 RPM, Unit 2 from 945 to 950 RPM, and Unit 3 from 940 to 960 RPM.    In this situation, the speed limits placed the unit in a non-typical operating speed that accelerated the cracks.

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Next up: Nondestructive Testing

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