Seawater is an electrolyte solution containing various salts, which is strongly corrosive medium to metal butterfly valves. Conventional metal materials can be corroded quickly by seawater and are not suitable as valves for seawater applications. here we explore the general methods to prevent seawater corrosion:
1. Apply anti-corrosion coating to the valve surface. For example, the inside and outside of the valve is sprayed with an anti-seawater corrosion-resistant such as epoxy zinc-rich coating. This is the way with low cost, and it’s limitation is that must be careful and make the coating will not be damaged before install valve to pipeline.
2. Use a corrosion resistant material line for the butterfly valve component that contacts the media. For example, the valve body and the valve disc of the butterfly valve lined with fluorine material such as PTFE , TEFLON , F4 etc. Also can be lined with rubber such as NBR, EPDM, Natural rubber etc. .
3. The butterfly valve component has sufficient corrosion allowance. The wall thickness of the main contact medium such as the valve body of the butterfly valve increases, which can increase the using life.
4. Use a suitable anti-corrosion material. Carbon steel like A216 WCB is not suitable for long-term seawater media. Gray cast iron and ductile iron have better seawater corrosion resistance performance and cost than ordinary austenitic stainless steel, which is a good chooce.
Copper metal is very good for seawater corrosion resistance. Common material grades are: B148 C95800, B148 C95500, Monel K400, Monel K500. Duplex stainless steel also has good seawater corrosion resistance, common material grades. There are: A890 4A, A890 5A, SS904L. Copper, duplex stainless steel cost higher than iron material and have better performance.
The proper material should be chosen according to different conditions.