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How to stop corrosion between galvanized and 316 stainless

We are installing pipework in a marine environment (major aquarium)where 316SS chemically anchored studs have been set into concrete to support pipe hangers. Hangers are hot dipped or electro-galvanized MS, and have been installed with no insulating washers or sleeves on the 316SS. Specs for valves require galvanized loose flanges on uPVC stub flanges and stainless steel(no spec.) bolts. We are worried about galvanic corrosion in humid 25 degree C environment between stainless steel and galvanized section. The 316SS has not been passivated. Should we cover or spray for corrosion inhibition, - if so, with what? Is this really a problem over 25+ year lifetime?

Robin Clanahan
consulting engineer (civil) - White River, Mpumalanga, South Africa
2003

I would guess that you will certainly have a problem with this in this environment. The 316SS parts should be okay unless they were exposed to some mild steel in process, in which case they will rust. The galvanized parts on their own will probably eventually show some rust in this environment, but the galvanic effect where they come in contact in this warm, humid, marine environment will probably be a problem. Can you still put something between the two metals?

Even with a coating over the joint you could still get a problem at the junction. I can't recommend a coating, but you can go online to see what rust inhibiting coatings are available in South Africa.

Where is Mpumalanga? I will be in South Africa next week.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2003