Polyolefins Plant - Gearbox
Cracked Steam Pipe Causes Rainmaker
As already discussed, water is a serious contaminant when present in lubricating oil. This case study illustrates the dramatic effects that water contamination can have on a system. The unit in this case study is a very large gearbox operating in a polyolefins plant. This unit is critical, if the gearbox fails then production stops and the entire plant is essentially shut down.
Figure - This gearbox is a critical component in a chemical manufacturing plant. The gearbox nearly failed due to serious water ingression as the result of a cracked steam pipe.
The gearbox has a capacity of close to 3,500 litres (900 gallons) of oil. Amazingly within a one month span this oil became contaminated with over 9% water. It can be difficult to accurately quantitate a water contamination level over 1% due to separation and settling of the water, and the variance the sampling process can induce as a result, never-the-less a large quantity of water was obviously ingressing into this gearbox in a very short time.
Because the plant was in a planned shutdown period, after the sample on 07-23-2001 the unit underwent a complete oil change and was investigated for obvious leaks. No leaks or sources of water entry were noted at that time. A resample was taken one week later and showed that the water level was close to 0.0%. It was assumed that this water contamination must be an anomaly and that everything had returned back to normal.
Figure - This graph demonstrates how the initial oil change-out removed the water contamination, the root cause was not corrected (cracked steam pipe) so the water contamination level rose back to its original critical level.
The next regularly scheduled sample on 08-23-2001 (only 3 weeks later) again showed close to 9.0% water. This time the plant was in full production, so the unit could not be shut-down to conduct an oil change. A vacuum distillation unit was hooked up to the gearbox, and the unit was monitored more closely during the next several months, but allowed to run. The vacuum distillation unit was able to keep the water level at 9.0% but could not keep up with the ingress of water. At the next planned outage the unit was again investigated, and this time a steam leak was discovered in a pipe that ran next to the unit. The leak was repaired, the oil was filtered and levels returned to normal within a few months.
Figure - The charts above show the effects of the water ingress. A substantial increase in apparent viscosity, but more importantly a rise in the iron level (rust), and copper and lead (corrossion).