Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1123345
www . machinerylubrication.com | May - June 2019 | 9 contaminants associated with acid-scavenging media. An additional 2.11 percent was found to be wear metals or particles consistent with those expected from wear of metallic equip- ment components, while 1.85 percent was characterized as metal contaminants often associated with foreign lubricant mixing. e fi nal 1.27 percent was classifi ed as halogen contaminants, which can be associated with fl uoropolymer breakdown or seawater. Not all of these materials were thought to be current problems with the new oil after the fl ush. Of course, even with a high-velocity fl ush, there will still be some buildup or residual material from a 30-year run that the new fl uid will clean and remove. Of the fl uid-derived breakdown products, 58.86 percent was carbon. is most likely was caused by microdieseling, which is a pressure-induced thermal degradation. An air bubble transitions from a low-pressure area to a high-pressure zone and through adiabatic compression is heated to very high temperatures. Even though not much heat is transferred between the fl uid and the bubble, the temperature within the bubble can reach 2,000 degrees F. When this occurs, it forms submicron-sized soot particles, which can cause the oil to darken. System Chang es As with any plant, many things were changed, modifi ed and updated over the years. Unfortunately, the lubrication and design engineers did not communicate. Although certain changes to enhance a system might not aff ect its operation, they can be very detri- mental to the fl uid. Among the concerns with phosphate-ester fl uid include a pressure drop within the system, pressure spikes, inadequate residence time in the reservoir for air release, improperly returned fl uid to the tank, and the lack of a downcomer or diff user on the return line. Unfortunately, these problem areas are not easy to locate within a system and usually are diffi cult to fi x. In this case, the reservoir was well-designed with downcomers, diff users, baffl es and a large enough volume for proper air-release residence time. There were three submerged screw pumps, each with a capacity of 175 gallons per minute (GPM), along with a constant-pressure regulating valve and three relief valves, one per pump. ere were no accumulators in the original system, so two pumps were run contin- uously to meet system spikes and swings. With 350 GPM from the two pumps, the residence time in the reservoir was just more than seven minutes. e new oil's air-release time is usually between three to fi ve minutes. After one year, the fl uid had an air-release time of 7.4 minutes and was up to 11 minutes before the removal of submicron debris. If there was a spike in the system, the third pump started automatically but did not shut down automatically. e constant-pressure regulator valve was designed to handle 1,100 GPM. When the valve is not working properly, excess fl ow and pressure are relieved by the relief valves on each pump. is initially was not much of a problem since the relief valves dumped into a common header that drained into the main return line to the bottom of the tank through a diff user. Over time, separate dump lines were placed on the relief valves. One remained in the return header, while the other two were fl anged right to the top of the tank. When the constant-pressure regulator valve stuck, there was excessive heat generation at the relief valves and additional aeration from the returning oil to the tank. Prior to t he chemic a l f lu sh, t he constant-pressure regulator valve and three relief valves were sent for rebuild and cali- bration. ey are now calibrated annually as needed. During the fl ush when the tank was drained, new downcomers with diff users were added to the two relief valves' dump lines. Accumulators were also installed approxi- mately one year after the fl ush, so the plant can now operate on one pump at 175 GPM, thus increasing the residence time for air release in the tank. e rest of the system consists of 10 stop valves, 10 control valves, a couple miles of piping, numerous orifi ces and other fl uid-re- stricting valves. e actuators for the stop and control valves were replaced several years ago. Leak-through had not been checked on the old system. e new system has been measured at approximately 50 GPM bleed- through. is fl ow reduction can only help to diminish the heat-induced problems within the system that are detrimental to the fl uid. Dar kening Fluid e corrected items still did not solve the issue of the darkening fl uid. While the ISO codes were excellent (15/13/10 to 16/13/11), the fl uid continued to get darker. However, the fl uid's color was not the actual problem. e facility needed to know how much submi- cron debris was in its fl uid. Submicron debris has been thought to cause blinding or coating of acid-remediation media, which makes it challenging to control acid generation and maintain the proper acid number. e prior fi lter testing had revealed the type of debris, 58.86 percent carbon, which in this case was soot. Two methods can be used to collect submicron debris: membrane patch colorimetry (MPC) and gravimetric analysis. ese methods utilize a nitro-cellulose patch, which will have a specifi c volume of fl uid passed through it before being dried and weighed. e ML This image shows the changes in oil color when electrostatic fi ltration was started, stopped and restarted. STARTED STOPPED RESTARTED