Originally Posted by GaryHLucas
Interesting little story about stainless steels. This week we got back a wastewater RO filtration unit from a customer. All the stainless on this unit was 316. The sch 40 piping was welded and not subsequently finished in any way. It was all quite corroded at all the welds. The filter canister was a bead blasted finish, and eaten completely through in several places! The high pressure Can pump had an electropolish finish, and was still bright and shiny everywhere. Interestingly, the hot dip galvanized frame still looked great! I don't know what they were processing, but it sure raised hell with stainless steel.
Gary H. Lucas
Not surprised the bead blasted portion and welds got eaten up. Not surprised the electropolished stuff was in good shape. The irregular surface of the bead blasted areas encourage crevice corrosion and that's why it got eaten away so badly. IIRC, the welds tend to be more prone to corrosion because the alloy composition changes due to the high temperatures of the welding process, since the various components of the stainless steel alloy have different melting points. The increased corrosion can be reduced by using low carbon versions of the alloy, 316L, rather than 316.
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