Two Unusual And Catastrophic Bearing Failures Caused By Electrical Arcing In The Oil Film, Their Causes, And The Surprisingly Simple Solutions That Cured Them.

Abstract

Rotating equipment engineers are frequently not prepared to deal with the catastrophic damage that often accompanies electrical arcing in the oil film of high-speed turbomachinery. Electrical engineers at the site are often of little help. This paper deals with two specific examples of unusual and catastrophic bearing failures directly attributable to arcing in the oil film. The cause of each failure is identified, and the successful solutions are discussed. Suggestions are made as to how to handle the organization of a team to effectively address this type of problem. The first example is a 1000 hp (746 kW) motor/gearbox/ centrifugal compressor train installed in a major Gulf Coast petrochemical complex. This unit successfully compressed anhydrous hydrochloric acid vapor for a period of one year after startup. It then began experiencing bearing failures due to electrical arcing. Consultants were called in, components were demagnetize, shaft grounding brushes were installed, and insulated couplings were tried, all with no success. In the end, it took changes in the lubrication oil to solve the problem. The second example is a high-pressure turboexpander operating on a platform in the North Sea. This unit experienced arcing induced failures from the initial startup. Again, consultants were called in, and all parts were demagnetized, but to no avail. While the damage was similar to the first example, the mechanism was believed to be electrostatic in nature, and the solution was once again achieved by changing the lubricating oil characteristics.