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Corrosion of Ag plated Inconel

2000

We had corrosion problems with a Silver plated Metallic Seal used in sea-water applications (some h2S, CO2 present as well). The base material was either 17-4 ss or Inconel 718 and the Silver plating was only deposited on the sealing area. After a little while in service, the seal was found pitted in the seal area with the Silver plating exfoliating (some seals were also pitted right at the boundary between the Ag plating and the base material). Both 17-4 and Inc718 showed exactly the same typeof damage. I suspect that galvanic corrosion occurred. My questions:

1.Could galvanic corrosion between the Ag and the substrate (resulting in substrate pitting and Ag exfoliation)start because of the fact the Ag was deposited only in the sealing area and not all over the part?

2. If GC occurred, how can one explain the lack of corrosion of the part in contact with the silver plated metallic seal. For the Inc 718 seal this was duplex and for 17-4 it was AISI 410?

I would really appreciate your input. Thanks, Irina

Irina Ward
- Edmonton, Alberta, Canada

Inconel like most valve metals and their alloys are often anodically protected by less electropositive metals. The lack of corrosion adjacent to the silver is an example of this effect.

Gerald Lee Allen
Allen Enterprises - Hayward, California, USA
2001