Butterfly Valve Question 1

[impeller1]

Good day,

Happy New Year to all of you.

Young Engineer here, and I have a question about the material of a particular valve. We've got 30" butterfly valves that are underwater (seawater) and are currently in need of replacement. Unfortunately, the valves are obsolete and are not manufactured anymore, so I'm trying to find an exact duplicate to the valves we have. I've managed to find one thus far, however, it seems the only materials I can get the body and disc in are cast iron and ductile iron respectively with a coating of 2 part liquid epoxy on the interior (3-5 mils) and disc and universal primer on the exterior (3 mils). I'm a bit skeptical as to whether or not this material would withstand constant submersion in seawater. Also, the existing valves' body and disc are made of Cast Austenitic Gray Iron (Ni resist) and Cast Austenitic Ductile Iron (Ductile Ni resist). What's the difference between the two? And would the alternate valve work?

Thanks

 

[micalbrch]

Ni resist cast iron has a nickel content of more than 20 % and can therefore withstand seawater corrosion. Standard grey cast iron and ductile cast iron cannot. The coating of standard grey and ductile cast iron is not bad but not a permanent protection against seawater corrosion. The difference between the two Ni resists is the microstructure and the shape of the carbon phases.

 

[mtneerbob]

may want to consider a valve made of 316SS ...very common for salt water service...if interested, i can recommend a valve company that specializes in replacement valves.

 

[gerhardl]

This is highly a question of both of two things: what is commercially avilable today, at what price; and what could the enduser be expected to accept, both materialwise and pricewise.

a) A BFL valve is a very broadspectered family of valves, and for the new valve all important aspects (leave material choice out for a moment) should be as close to the original as possible: stem size, sealing constructions bearings, general closing (centric, double or triple eccentric), geometrical forms etc.

b) Depending on size and pressure class, application and end users requirement you have a lot of commercial possibillities.

Lower price end:

Housing: simpler material, clad construction. Disc SS or AlBronze.

Higher end.

SS, special SS, or exotic material for all components.