16 May 2003
Warning: Do not try this at home, as it can be extremely dangerous for those lacking professional training in this area. We accept no responsibility if you fail to heed this warning. This article is for informational purposes only. Whenever you work on stainless (like kegs), there is a high chance that the stainless will get iron contamination. On top of that, any time you cut holes or weld on fittings in kegs, you overheat the surrounding metal. Left untreated, this iron contamination will rust your newly fabricated kettle. Many job shops and freelance welders know little about metallurgy and won't passivate your keg when they are done welding it. Months later, when your keg/kettle rusts you don't know what to do. You may even consider junking it - thinking that once stainless gets contaminated by ferrous steel it is irrepairable. Not any more!!! We can help! This information will guide you to understanding what has happened to your kettles! By the way, We perform a full passivation process on all of our systems (described below). Since stainless is actually made up of several different types of metals, it's composition changes as these metals become dissassociated from one another (usually due to welding or high heat processes). So, once you've finished altering your keg and converting it into a kettle, it is no longer all stainless (in a matter of speaking). Your kettle now stands the chance of rusting unless you do a final processing step to remove free iron deposits from your kettles and form an invisible protective oxide film on the surface of the stainless (passivation). There are many different ways of treating stainless to remove free iron & form a protective oxide layer by passivation.
Electropolishing (Using an electrolyte and electricity to remove metal including free iron deposits)
Passivation (using an acid to eat away only the free iron)Lets explore Electropolishing:
The other Brewing Equipment suppliers tell you they have a $2000 machine for passivating stainless welds so they will never rust. Besides the fact that they wasted a whole lot of your money buying a premade unit instead of building their own, they now have to price gouge you for their inefficiencies! They will continue to pay more for premade solutions that work with their machine too (and you will inevitably have to pay more for your brewing equipment if you continue to buy from them). We built our own electropolishing wand for next to nothing so we can afford to save you even more money!!! What is an electropolishing wand? It is basically a piece of copper tubing flattened on one end (and covered with a piece of nylon), with a valve and hose attached to the other end, and a pump & reservoir for pumping the electrolyte (typically phosphoric acid based) to the tip of the wand. We use a 12 volt battery charger to provide the "electro" part of electropolishing.
To imagine what this process is doing, think of the black "ground" cable and how electricity wants to ground itself out. Since the Keg is the anode (positive), and the wand is the cathode (negative), the electricity has to flow outward from the keg and phosphoric solution to reach the wand. This action actually removes small amounts of the stainless because the phosphoric acid is corrosive, but even more so when it combines with the electricity! We connect the red (positive) clamp from the charger to the keg, then the black attaches to the wand. We ALWAYS wear face shield, goggles, gloves and long sleeves. We turn on the battery charger & pump and make the electrolyte come out slowly at a trickle rate. We then rub the flattened nylon covered wand tip against the weld areas to remove Heat Tint from the welds.
We never want the actual copper to contact the stainless, that is why we have the nylon mesh at the tip of the wand. Heat tint is an unprotected layer of stainless in the heat affected zone (HAZ) of a weld. It is darker than the surrounding stainless and is more susceptible to rust because it does not have the invisible protective oxide layer). There are many different types of electropolishing solutions, and recipes can be found online. We use a safer recipe than most, and is made up of fda approved ingredients. Once we are done electropolishing the weld areas, we completely passivate the kettles - here is the process:
Rinse the kettles in Deionized water (to clean off any electropolishing electrolyte)Submerse the kettle in an agitated tank of passivating solution (10% citric acid) for 1/2 hour.
We rinse in deionized water 10 minutes
We perform a salt spray test for free iron for 2 hours (no rust means passivating procedure was done successfully)
Second D.I. water rinse
Second Passivation
Third D.I. rinse
Kettles Packaged in a clean-room environment, boxes sealed shut.
As you can see, we perform a multiple step passivating process to guarantee long life kettles for our brewing systems and system components. If you should have any problems with your own home-made kettles, you can now diagnose and understand how they should be repaired. I hope this article proves to be invaluable, as much of this information is not readily available anywhere. We have provided it as a reference for all homebrewers.
Gerhardt
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