Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/190260
ture, such as that which occurs when returning the system to service, can result in the biological growth dying off and the remains being pushed through the system. Cleanliness Codes Most plants have equipment monitoring programs that define lubricant property limits. These limits are usually established for normal operating conditions. One of the parameters typically monitored is particulate levels. The International Organization for Standardization (ISO) has developed a method (ISO 4406) for quantifying the level of particle contamination. The values gathered in a particle count test identify the number of particles in a given volume of fluid that are above a specific size range, which is generally set at 4 microns, 6 microns and 14 microns. The data is normally presented in a format such as 17/15/13, which provides a numeric range value representing the measured quantity of particles greater than 4 microns, 6 microns and 14 microns, respectively. Figure 2 illustrates the change in particulate levels from the time the turbine was on turning gear until the unit was synchronized to the power grid. Notice when the turbine rolled off turning gear and increased its speed to 2,400 revolutions per minute for thermal soaking, a large burst of particulate was released into the lubrication system. This caused all three particle levels to increase above the normal operating limits and remain high for more than two hours. Added filtration was able to bring the particle levels Case Studies In a recent turbine outage, the lubrication system was placed into operation, and the main turbine was placed on turning gear. While the system was operating, an auxiliary filtration skid was connected to the main turbine reservoir to run in parallel with the normal filtration system. The skid had dual 7-micron filters and processed the main turbine reservoir four times per hour. An oil sample recorder pulled samples at 20-minute increments from the center of the turbine oil reservoir and then documented 31 hours of results from the mesh blockage particle counter. As Figure 1 indicates, after approximately 12 hours in operation, a large slug of contaminants must have released into the system, causing the need to change filters. At that point, a decision was made to reduce the filter size and continue. Once the turbine was rolled, the auxiliary filtration unit was secured. Inspection of the last set of filters revealed a significant collection of particulate captured within the filters. In another example, a filtration skid with a particle counter was tied into a turbine reservoir during the plant's startup. This power plant normally only operates during peak summer months in the southern part of the United States, leaving it shut down for at least six months out of the year. The particle counter recorded main turbine reservoir contaminant levels above 4, 6 and 14 microns. www.machinerylubrication.com | September - October 2013 29