Oil Analysis Improves Cooling Tower Problems

K-Reactor at the Savannah River Site

The Savannah River Site is located in the southeastern coastal area of South Carolina near the Savannah River, and operates as a U.S. government Department of Energy nuclear materials management facility. The Site Utilities Department (SUD) is a department within Solid Waste and Infrastructure that is within the Operations business unit of the Savannah River Site.

In November 1999, the SUD implemented an on-site oil analysis program that took baseline particle count readings on cooling tower drives, supply pumps and vertical pump motors. A primary interest was to identify solid particle contaminants that were 10 microns in size or greater. Figure 1 shows the baseline 10-micron particle count for the components tested similar to test results approximately eight months later. As the graph illustrates, baseline particle counts ranged from 300 to 3,300 particles per milliliter on the fan drives and 100 to 7,400 particles per milliliter on the supply and vertical pump drives. Using the crackle test method, moisture was found in all of the cooling tower drives.

Savannah River Site Defense
Waste Processing Facility

The cooling tower drives were of particular concern because of frequent breakdowns. At the time, two mechanics were regularly scheduled to perform overhaul activities every three years.

Time-directed oil changes were scheduled every six months. In trying to identify the source of the wear debris and moisture, the drive oil reservoir located inside the cooling tower cell was observed to have an external air breather vent. Although the oil fill point and oil level site glass were external to the cell, there were no provisions to filter or circulate the oil and it was questionable whether the oil samples taken accurately represented the oil in the drives.

Steps were taken to add fittings to the cooling tower drive’s external oil piping to provide a suction and return connection for a filter cart. Desiccant breathers were added to vent the drives external to the cells. Once the oil circulation piping was in place, the oil in each of the cooling tower drives was replaced and the reservoirs were cleaned using the filtration cart. The six-month oil changes were replaced with quarterly oil sampling and testing. Figure 1 illustrates the improvements made eight months after the program began.

Click Here to See Figure 1.

Within two years of implementing these changes, numerous improvements were observed. Mechanics were no longer scheduled to perform regular routine maintenance and overhaul activities on any of the cooling tower drives on which the oil reservoir piping had been modified. The useful life of the oil in the drives was extended from six months to three years. Even though the oil tests good chemically, is free of contaminants and shows minimal signs of oxidation, some color change has been observed.

Because of this, the oil will be changed at the three-year point. Savings associated with extending oil drains in mechanic labor alone are estimated to be $108,000 annually (using a $40 per hour labor rate). The costs associated with time-directed oil changes and oil replacement/handling costs are considered to be nearly equivalent to the cost of routine sampling, filtering and testing, so there are no savings recognized strictly for oil lifecycle extensions.

Editor’s Note:
The author has identified a practice that should be part of a healthy lubrication management program for every critical sump in a production environment. Drive lifecycles should be measured, and a mean time between failures (MTBF) baseline should be established, with a significant goal for improvement being a primary program objective. These savings can be substantial. For example, gear case rebuilds often include replacement of gears, bearings, seals and occasionally a shaft. Cumulative costs for these components for a medium-sized cooling tower drive could reach $10,000 per rebuild.

More meaningful savings should be attributed to production loss avoidance. If a failure occurs during a production run, and there is no spare cooling capacity, additional costs are incurred through reduced output or reduced effectiveness. Savings in this area can dwarf whatever reasonable savings may be measured for components, rebuild labor and materials consumption. Lubricant-based cost savings may be helpful but will probably not cover the cost of program implementation.