Butterfly Valve for Seawater Material

I assume your are referring to rubber lined butterfly valves.

The manufacturer's I'm familiar with claim that the rubber lining will prevent seawater from ever contacting the shaft and therefor they typically provide 304SS or 420SS shafts.

The seals are usually nitrile.

Hi dave2109,
Many thanks for your comment, Yes, it is rubber line Butterfly valve, would you tell me the typically provide material of Valve BODY, DISC and Stuffing as well as valve shaft?

If the valve disc is uncoated it should be made from a seawater compatible material.

Do not use stainless of any grade as it is very suspect to chloride pitting corrosion.(this is not true of super-duplex)

LG2 bronze is acceptable but a much better option would be a cupro-nickel alloy like nickel aluminium bronze or monel 400.If you have lots of money in the budget you could look at incolloy 825

The same applies to the body but as it is rubberlined it shouldnt be in contact with the seawater and couuld be externally epoxy coated.

Hope this helps

Hi macvalsa,
Thanks a lot for your help information, your suggestion will be very useful for me, but I want to confirm except incolloy 825, whether monel 400 also very expensive, as you know it is DN3400 i cannot imagine how big and how weight it is. if the body and disc all use the same material, it will be much expensive. does cupro-nickel alloy like nickel aluminium broze is cheaper? which one is cheaper does it compare with Stainless steel?
Thanks in advance.

Aluminium Bronze bodies with Monel Vanes are a common option for seawater applications. However, you can expect to pay three to fives times more for a monel valve over a stainless steel one.

Hi DeanA,
Many thanks for your information, we will check it and compare the price to decided which one is our best choice.

Body in ductile iron with aspecial 4till5 layer coating
Exotic materials are verry nice but far to expensive fore these applications!
a verry good and widly accepted disc construction is ductile iron with hardrubber coating (+/-6mm)
when the valve is full rubberlined the shaft is not in contact with the fluid 17-4 or aisi431 is sufficient

Hi gervanderpers,
Many thanks for your suggestion, it is the best choice for us, because it is very easy to available for ductile iron, but the problem is as you mentioned how can I achieved 4 till 5 layer coating, what's material of coating I can use? regarding of dis what's the hardrubber coating? how can I dofor +6mm?
our butterfly valve is double eccentric not full rubber lined the shaft we choose SS420 does it is sufficient?
Thanks in advance.