butterfly valve trim material

can any body tell me i have to select a valve trim. As per my spec i require bronze with nbr lining and vendor is providing SG Iron with nylon coating is it acceptalbel ?? my service is cooling water fresh fire water

Trivedi,

I hope you are aware that when the vendor states SG iron for trim material, he has to provide the Special Grade Iron and not Spheroidal gray cast iron as trim material.

Many asian valve manufacturers take their customers for a ride. Hence, their valve prices are cheap.

They indicate SG iron on their data sheets and get customer approval stamp on the data sheets. The Independent third party inspection agency visits the valve vendor works for inspection. The vendor offers for inspection valves with spheroidal gray cast iron as trim material and shows the approved data sheet as proof of acceptance. The unsuspecting inspector approves the valves. The spheroidal gray cast iron tirm valves gets corroded faster causing difficulty in valve opening and closing.

Hence, it is better that you ask the vendor what does SG stand for . An unscruplous vendor shall run away. Whereas, a scruplous vendor shall give the test certificate for the special grade iron. I think the code specifies properties for special grade iron. I think it should be superior to some nickel grade iron ( probably Ni- resist).

Check with your materisl engineer whether the Sg iron offered is equivalent or superior to desired properties in code .If so, attach the test certificate to the data sheet. Indicate on the data sheet against trim material "See enclosed attachment xxxx//yyyy and stamp on both of them. This way you are ensured that the valve inspector accepts on ly correct SG grade trim valves.