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Corrosion of the valve stem and corrosion damage of the protective valve body are mainly caused by corrosive media； However, the situation of valve stem corrosion is different, and its main problem is the packing. Not only corrosive media can corrode and damage the valve stem, but general steam and water can also cause spots at the contact between the valve stem and the packing. Particularly problematic is the fact that pitting corrosion of valve stems can also occur in valves stored in warehouses. ； Even stainless steel stems are hard to avoid. why is that? This is the electrochemical corrosion of the valve stem by the packing. The most widely used filler now is asbestos-based packing, such as graphite asbestos packing, oil-impregnated asbestos packing, and rubber asbestos packing. Asbestos materials contain a certain amount of chloride ions, as well as potassium, sodium, magnesium and other ions, and graphite contains iron sulfide and other impurities, which are all factors of corrosion. Chloride ions can penetrate the passivation film on the metal surface, causing corrosion to continue. The presence of other impurities also contributes to the progression of corrosion. Water and steam are electrically conductive substances that enable further communication in circuits that are electrochemically corroded. Valves in warehouses also suffer from electrochemical corrosion due to moisture in the filler or moisture in the air. In addition, there is a lack of oxygen between the packing and the valve stem. Compared with the surroundings, there is a difference in oxygen concentration. This constitutes an oxygen concentration difference battery and becomes another form of electrochemical corrosion. As we all know, valve stems are often made of high-quality materials. Its corrosion damage is a pity and affects production, so anti-corrosion measures must be taken. Measures that can be taken include: (1) Do not add packing during valve storage. Without packing, the electrochemical corrosion factor of the valve stem is lost, and it can be stored for a long time without being corroded. (2) Surface treatment of the valve stem. Such as chromium plating, nickel plating, nitriding, boronizing, zinc plating, etc. (3) Reduce asbestos impurities. Washing with distilled water can reduce the chlorine content in asbestos, thereby reducing its corrosiveness. (4) Add corrosion inhibitor to asbestos packing. This corrosion inhibitor inhibits the corrosive properties of chloride ions. Such as sodium nitrite. (5) Add sacrificial metal to asbestos. This is a sacrifice of a metal with a lower potential than the valve stem. In this way, chloride ion corrosion occurs first on the sacrificial metal, thus protecting the valve stem. Examples of sacrificial metals include zinc powder. (6) Protected by polytetrafluoroethylene. PTFE has excellent chemical stability and dielectric properties, and current cannot pass through it. If the asbestos packing is impregnated with PTFE, corrosion will be reduced. The asbestos packing can also be wrapped with polytetrafluoroethylene raw material tape and then installed into the stuffing box. (7) Improving the processing finish can also reduce electrochemical corrosion.