The Case of the Copper Crisis Diesel
Plato’s Phaedrus observed “Things are not always what they seem; the first appearance deceives many”. Here, impending doom and gloom turned out to be a few leaking O-rings. But, the investigation found impending doom elsewhere.
An annual oil test on a 30-liter, 12- cylinder diesel standby generator set engine showed a large spike in copper which can indicate advanced engine bearing failure. While the generator set was approaching 30 years age it had less than 1,000 hours run time, very little of which was actual run-under-load time.
TI was requested to determine the cause of the elevated copper, and if engine failure was imminent. The generator set had a twin of identical age and hours, and thus it was of similar concern. The engine was partially disassembled. While copper is the major constituent of brass, brass is little used in the engine. One brass component was a crankshaft thrust bearing retaining pin and the pins were found to be badly worn. However, analysis of the pin wear showed it could not be the source of copper in the oil. Accessory drive brass bushings for oil pump and alternator were in normal condition. The oil pan was dropped and inspected. The presence of coolant was noted in the oil. The source of the coolant was found to be age-degraded O-rings that seal tubes which transfer coolant from the engine block to individual cylinder heads and back to the block. Research was conducted and it was learned that certain additives in the engine coolant can react with additives in the engine oil to form compounds that are extremely corrosive of copper. It was found that the oil cooler consisted of brazed copper plates and it was determined that the copper in the engine oil was from the oil cooler. The oil cooler was tested at elevated pressure and found to suitable for continued service.
Part of TI’s investigation included review of periodic maintenance procedures and it was noted that lubrication of the single generator shaft bearing opposite the engine was not in the procedure. Inspection of the bearing grease purge tubes found them dry indicating the bearings might never have been lubricated since the generators were new. The manufacturer’s recommended grease was pumped in until old grease finally emerged from the tubes and samples were sent for analysis. The grease reports showed no abnormal conditions so the bearings were subjected to vibration testing and thermal analysis, with acceptable results. Bearing lubrication was added to the annual preventive maintenance procedure thus preventing a future generator failure.