Corrosion is one of the most important factors leading to damage to butterfly valves. Butterfly valve corrosion protection is an important issue for butterfly valve protection. For metal butterfly valves, surface coating treatment is the most cost effective method of protection.

Epoxy coated butterfly valves

Epoxy coating of butterfly valve bodies has the following characteristics.

Corrosion resistance
Epoxy coated steel has good corrosion resistance and significantly reduced bond strength to concrete. It is suitable for industrial conditions in wet environments or corrosive media.

Strong adhesion
The presence of polar hydroxyl groups and ether bonds inherent in the epoxy resin’s molecular chain makes it highly adhesive to a wide range of substances. The low shrinkage rate of the epoxy resin when cured produces low internal stress and makes the protective surface coating less likely to peel off and fail.

Electrical properties
The cured epoxy resin system is an excellent insulating material with high dielectric properties, surface leakage resistance and arc resistance.

Mould and mildew resistance
The cured epoxy system is resistant to most moulds and can be used in harsh tropical conditions.

Role of butterfly valve surface coating

Shielding
When a metal surface is painted, the metal surface is relatively isolated from the environment. This protective effect can be referred to as shielding. It must be noted, however, that a thin layer of paint does not provide absolute shielding. As polymers have a certain degree of permeability, when the coating is very thin, its structural pores allow water and oxygen molecules to pass freely. Soft seal butterfly valves have strict requirements on the thickness of the epoxy coating on the surface. It can be seen that for many coatings the value is greater than for uncoated steel surfaces. In order to improve the impermeability of the coating, anti-corrosion coatings should use film-forming substances with low permeability and solid fillers with large shielding properties, while the number of coating layers should be increased so that the coating reaches a certain thickness and is dense and non-porous.

Corrosion inhibition
By making the internal components of the coating react with the metal, the metal surface is passivated or a protective substance is produced to improve the protective effect of the coating. Butterfly valves used for special requirements must pay attention to the composition of the coating in order to avoid serious adverse effects. In addition, cast steel butterfly valves used in oil pipelines, the degradation products produced by the action of some oils and the drying effect of metal soaps can also play a role in organic corrosion inhibition.

Electrochemical protection
When a dielectric penetrating coating comes into contact with a metal surface, galvanic corrosion occurs under the film. Use a metal with a higher activity than iron as a filler for the coating, e.g. zinc. It will act as a sacrificial anode for protection. The corrosion products of zinc are alkaline zinc chloride and zinc carbonate, which will fill the gaps in the film and compact the film, thereby greatly reducing corrosion and extending the life of the butterfly valve.

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