the acids used in brewery for sanitization can wreck metals too. we had some plated brass fittings that got mixed in with the stainless stuff and the acid water turned green and the brass was exposed. some other formerly shiny parts turned grey and chalky and very soft. Some places love their brass but I just want everything to be stainless so I can leave it soaking in sani for as lonng as I'm too lazy to deal with it which is forever.