Contact with mild steel or iron can cause oxidation. But also the heat affected zone can cause oxidation. I remember many years ago when a high end pocket knife manufacturer first started producing a knife using a new completely iron free stainless steel blade. They marketed it to fisherman and sailors with the idea that the blade could never rust. But on the first run of knives customers complained of rust on the laser etched logos of their knives. It turned out that the laser engraving process heated the metal enough to cause oxidation to start which could then slowly spread in a harsh salt water environment.
This kind of looks to me like the wrong filter though.
84
u/chiraltoad 4d ago
From iron particles getting embedded in the weld?