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Galvanic corrosion of aluminum by stainless steel

We are supplying 6061-T6 aluminum anodized manifold in an environment where corrosion by water exists. This manifold has standard aluminum cartridge valves, steel plugs, surface valves which are painted steel and steel bolts which are used to mount the painted surface valves to the manifold. In some applications, the steel bolts were experiencing accelerated corrosion, so our customer decided independently to switch to stainless steel screws. Our fear is that he may slow down the corrosion of the screws, but accelerate the corrosion of the manifold and possibly the painted steel surface valves by galvanic corrosion (corrosion by dissimilar metals). We were wondering what would be the optimum screw for this application? If the aluminum block is relatively large and anodized(6 inch by 6 inch x 20 inch long) in comparison to the screws (10-24 x 2 inch long), is our above fear still an issue?

Regards;

Rob Connor
- St. Catharines, Ontario, Canada

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