Dissimilar Seat Materials

[bcwalsh]

I am considering replacing the seat material on a parallel slide gate disk with a 300 series stainless steel overlay. The seat ring in the valve is a bronze material, vintage 1930. Would you expect any wear or other issues associated with using these dissimilar metals in this design. Valve is not in a severe service or in service where dielectric isolation would be a consideration.

 

[gerhardl]

... A very cautious,no,????? (Others?), perhaps depending on fluid. If seawater for instance, SS might not be the best in itself.

It would probably help your 'answer rate' if you gave more information: existing material replaced, other details, size, apllication, operational pressures etc.

 

[bcwalsh]

Valves are in-line, are vintage 1930 125# class cast iron valves, and have existing bronze seat rings. The bronze seat rings in the valves are in relatively good condition. The existing disc packs however, are not in good condition. The cast iron sections of the discs have extensive corrosion. These must be refurbished or replaced. Due to the current cost and lack of availability of copper based materials, and the difficulties in applying these to mild steel and/or cast iron surfaces, we are considering using stainless overlay. We are looking at fabricating new disc packs from mild steel and overlaying with the stainless materials. Service is filter water influent, effluent, and backwash. All at near ambient and relatively low pressure. Due to the parrallel slide design we are not anticipating any major problems; however, we are cautious enough to at least raise the question. Thoughts?

 

[gerhardl]

... size? Somhow I believe you are talking about fairly large valves, perhaps above 24 inches? Smaller?

For this aplication in Europe, depending on placement/exact service and size, at least for 24 inches and below, a typical modern replacement would be gatevalves with complete rubber-lined gate, body in nodular cast iron, epoxy coated body and top inside and outside (250-300my), selected from top-quality producers and top models.

A good alternative is high-quality knife-gate valves (ss quality knife, nodular cast iron housing, epoxy coated (also here certified surface coating)) which would also be chaper and lighter for sizes 12 inches and up, and if actuated.

Other alternatives for new valves exists, and complete new valves and pipeline should anyway be considered as an alternativ to repair, with cost/lifetime calculations for complete renewal alternatives compared to overhaul and repair.

Apart from this, I do not think you will have problems with your material combination, repair done properly, but I could be wrong. This is more a material/metallurgical/corrosion problem. You could perhaps try to present this in a material-oriented forum?

 

[DLite30]

You may be giving a little in the way of sealing with small particulate matter in the stream, however if you're bronze seats held up that long, the stream must be fairly clean and/or the valve has not been cycled that much.

But I'd say you're okay, as long as you get a good, parallel lap job on the sealing surfaces.