Crevice Corrosion

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Benz,

There could be another problem as well. Stainless has a different galvanic potential in and out of water. So a stainless fitting that is partially immersed is actually galvanically active itself.

It could also be that because the corrosion was localized, it has a point failure, either a bad fitting, it was tapped up right there, contaminate from tooling ect.