Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation



Lubrication- Case Study No. 13: Blown Pump Packing Ruins Oil


Lack of attention by the Lubrication Mechanic? Afraid not. Beware of jumping to conclusions that the oil wasn't changed because it came out looking terrible. Lubrication failures can be the SECONDARY MODE of failure, and not necessarily the primary mode of failure.Pump Bearing Located Opposite Stuffing Box

The bearing to the left has process product all over it. When the oil was drained from the pump it looked terrible. If one isn't right there at the scene of the crime, so to speak, bits of misinformation, or half-truths if you will, tend to spread. The one pertaining to lousy looking oil was one of them. Therefore, to put the claim to rest, the disassembly of the pump was monitored and all components were retrieved.

As it turned out, yes the oil was lousy looking, and yes, the pump packing had blown and shot product into a bearing isolator that was never designed for the likes of this. The failed packing is a showcase failure in the "Machine Design - Case Study No. 20: Thirteen Ways to Ruin Pump Packing" article.

Cage Failure From Poor LubricationThe inboard bearing is shown to the left. It was the furthest away from the blown packing. This pump ran for quite awhile with the blown packing, but in the end the lubricant broke down and allowed metal to metal contact. The contact is well illustrated on the bearing ball cage shown below. It had actually worn itself into the shape of the inner raceway. The carving action on the cage allowed the balls to move further out of their orbit. Higher vibration resulted in excessive heat buildup which further aggravated the oil degradation.

This unit was screaming by the time it was taken out of service.

Worn Ball Cage, Groove Cut By Raceway LandProfile Worn Ball Cage

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