All it takes is a thin layer of condensation on the pipes to form an electrolyte. If the air is salty, the electrolyte will be that much more efficient and rust more pronounced.
I worked in aerospace for several years, primarily on the F-18 program. Every steel fastener had to be cadmium-plated to be near inert galvanically with aluminum. Every metal surface was painted with a zinc-oxide primer, again to be galvanically inert to any exposed aluminum. Even with all that caution, corrosion of aluminum is still a major on-going problem due to the salt atmosphere.
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