Corrosion is one of the important elements that cause valve damage. In valve protection, valve corrosion prevention is an important consideration. For metal valves, surface coating treatment is the most cost-effective protection method.

The role of surface coatings

1. Shielding effect

After coating the metal surface with paint, it relatively separates the metal surface from the environment, and this protective effect can be called shielding effect. But it must be pointed out that a thin layer of paint cannot have an absolute shielding effect. Because high polymers have a certain degree of breathability, when the coating is very thin, their structural pores allow molecules of water and oxygen to freely pass through. Soft sealing valves have strict requirements for the thickness of the epoxy resin coating on the surface. It can be seen that for many coatings, its value is greater than that of the steel surface without coating. In order to improve the impermeability of the coating, anti-corrosion coatings should use film-forming substances with low permeability and solid fillers with high shielding properties. At the same time, the number of coating layers should be increased to make the coating reach a certain thickness and dense without pores.

2. Corrosion inhibition effect

By utilizing the internal components of the coating to react with the metal, the metal surface can be passivated or protective substances can be generated to enhance the protective effect of the coating. For valves with special requirements, it is necessary to pay attention to the paint composition to avoid serious adverse effects. In addition, cast steel valves used in oil pipelines can also act as organic corrosion inhibitors by generating degradation products under the action of some oils and the drying effect of metal soaps.

3. Electrochemical protection effect

The contact of the medium penetrating coating with the metal surface will form electrochemical corrosion under the film. Use metals with higher activity than iron as fillers in coatings, such as zinc. It will serve as a sacrificial anode for protection, and the corrosion products of zinc are basic zinc chloride and zinc carbonate, which fill the gaps in the membrane, making it tight and greatly reducing corrosion, extending the service life of the valve.