The experts at MRG have extensive experience working in nuclear power plants and with nuclear power plant operators. This experience has translated into innovative solutions for nuclear MOV grease relubrication and analysis.
MOV Stem and Stem Nut In-Service Relubrication
To date, the only practical way of relubricating the stem and stem nut of an MOV requires stroking the valve back and forth or disassembly. There is now a more efficient option offered by MRG Labs called the StemThiefTM.
MRG Labs introduced the StemThief at the 2013 MOV User’s Group meeting. A simple and straightforward design, the patent-pending StemThief uses the stem protector mounting threads in the actuator housing to introduce a device that creates a seal against the stem nut. This allows new fresh grease to be pumped into the stem/stem-nut thread area, purging out the old grease and particulates, establishing a new lubricant film for the threads. The relubricator tube section of the StemThief is sized to slide over the stem grease sampling Lubrication Analysis for Nuclear Facilitiesstem without impacting it, and a Zerk fitting mounted on the tube allows the new grease to be introduced with a manual lever grease gun.
MOV Grease Analysis
To address the other issues raised in IN 2010-03, a grease sample can be obtained from the purged grease at the far end of the stem nut. A special kit is available from MRG that follows the guidance of ASTM D7718, “Standard Practice for Obtaining In-Service Samples of Lubricating Grease” to gather a 1 gram sample of the discharged grease. This sample can be analyzed using the Grease Thief®.
With the one gram of grease, which is approximately the amount that is effectively coating the stem threads in the interface area, analysis can provide insight into particulate levels, both wear and contaminants, consistency changes (hardening or softening from the new fresh grease baseline), and oxidation of the grease. The condition of the grease, as well as wear of the threads can be monitored in this manner, and the NRC guidance to “assess lubricant performance in MOV applications” can be systematically and objectively achieved.