Re: Re-Passifying Stainless Steel

Here is a message from the HBD May 15, 2000 from John Palmer who is a metallurgist. I think we may be going overboard in Will's kegs here. Since I don't brew daily I can just get by with letting atmospheric oxygen do the job for me when I need to scrub the kettle. + Date: Mon, 15 May 2000 08:33:14 -0700 + From: "John Palmer" <jjpalmer(a)gte.net> + Subject: Stainless passivation + + Passivating Stainless Steel + A situation that often comes up is, "Hey, my stainless steel is + rusting! Why? What can I do to fix it?" + + Stainless steel is stainless because of the protective chromium oxides + on the surface. If those oxides are removed by scouring, or by + reaction with bleach, then the iron in the steel is exposed and can be + rusted. Stainless steel is also vulnerable to contamination by plain + carbon steel, the kind found in tools, food cans, and steel wool. This + non-stainless steel tends to rub off on the surface (due to + iron-to-iron affinity), and readily rusts. Once rust has breached the + chromium oxides, the iron in the stainless steel can also rust. Fixing + this condition calls for re-passivation. + + Passivating stainless steel is normally accomplished in industry by + dipping the part in a bath of nitric acid. Nitric acid dissolves any + free iron or other contaminants from the surface, which cleans the + metal, and it re-oxidizes the chromium; all in about 20 minutes. But + you don't need a nitric acid bath to passivate. The key is to clean + the stainless steel to bare metal. Once the metal is clean (and dry), + the oxygen in the atmosphere will form the protective chromium oxides. + The steel will be every bit as passivated as that which was dipped in + acid. The only catch is that it takes longer-- about a week or two. + + To passivate stainless steel at home without using a nitric acid bath, + you need to clean the surface of all dirt, oils and oxides. The best + way to do this is to use an oxalic acid based cleanser like Bar + Keepers Friend, RevereWare Cleanser, or Kleen King, and a non-metallic + green scrubby pad. Don't use steel wool, or any metal pad, even + stainless steel, because this will actually promote rust. Scour the + surface thoroughly and then rinse and dry it with a towel. Leave it + alone for a week or two and it will re-passivate itself. You should + not have to do this procedure more than once, but it can be repeated + as often as necessary. + + John Palmer + www.realbeer.com/jjpalmer/ David H Berg writes: -- Steve Piatz piatz(a)cray.com Cray Inc. 651-605-9049 1340 Mendota Heights Road Mendota Heights, MN 55120