Valve packing is a necessity for plants trying to contain product and meet the latest emission requirements. However, finding a sealing product that works and has longevity can be a challenge. Graphite-based packing can be a good choice for stem sealing when elevated temperature requirements are necessary. This is due to graphite’s ability to maintain its sealing properties at temperatures that cause polytetrafluoroethylene (PTFE) to break down and allow leaks to occur. However, graphite is not an electrical insulator like PTFE; graphite will act as a metal and undergo galvanic corrosion if the environment is right. Maintenance can be a hassle, magnified by the discovery of a corroded valve stem. When a valve stem undergoes galvanic corrosion, the packing is no longer effective and leaks can occur. It also becomes very difficult to continue using the corroded stem when the valve needs to be repacked. However, if the stem is corroding, it is because the conditions are such that it is easier for the system to rust than stay as the perfect stem originally installed.
Learn how different metals react, and how corrosion inhibitors can help avoid downtime.
A.W. Chesterton
10/14/2019
Image 1. Corroded stem. (Images courtesy of FSA)
Image 2. Corroded pump shaft.