Rust around keggle couplings

So, I've been getting my new keggle ready for brewing. This has involved some sanding and some washing with Bar Keepers Friend. I noticed tonight that the welds around the couplings appear to be rusting. I am assuming that this is not normal and is something to cause concern. Thoughts?

SS can have it's protective oxide coating removed by machining. You can help it return.
That's the good news.

The bad news I can't find the reference for this. But you need to clean it and heat it. (I think)
The other bad news is that if they used a low grade wire when welding it will rust. I shouldn't imagine this is the case though.

If the stainless became too hot during the weld, it basically lost it's stainless properties. See if you can sand it off and then be sure to wipe some olive oil on it between uses.

What is described as rust around the weld probably came from use of a carbon steel wire brush on a 4" angle grinder used to clean the area post welding. This is just a surface rust which should go away if a cleaner with oxalic acid is used. A stainless steel passivation method used on stainless steel tanks by a company called Astro Pak used ascorbic acid and citric acid in water heated to 180 degrees and circulated until the free iron test of the solution leveled out, about 6-8 hours.

Since part of my job involves fabricating and welding stainless steel pipe and tubing i am quite familiar with the rust on the weld area problem described. Sometimes the dummies i work with will pick a grinder that was used on carbon steel or a carbon steel wire brush to clean a weld and all looks fine for a day or two until the carbon steel deposited on the stainless steel starts to rust. You might try 1 table spoon of oxalic acid in in 1 cup hot water, brush on affected area and wait for the visible rust to dissapear, you may have to reapply the solution a couple times. This should remove the free iron from the stainless and possibly passivate the weld area. Stainless steel is a poor heat conductor so the heat affected area should only extend about 1/2"- 3/4" away from the weld bead.

OK. I thought some pics might help out with ideas. Larger versions and more angles are in the gallery.

Have you asked the vedor for advice?

Looking at the pictures it looks like who ever welded the coupling used a 4" grinder with a flap disc that had been used on carbon steel. The rust on the outside is just a surface deposit of iron, and the black spots on the inside are whats known as surgaring. There are a couple of ways to prevent the surgaring on the weld area, back purge with argon or use a backup flux like Harris company Solar flux around the weld area.

orfy said:

Have you asked the vedor for advice?

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I have an email in to them now.

It looks as if you have rust on the threads of the coupling too.

It sure appears that someone might have used carbon steel wire in a MIG setup as that would explain the spatter pattern. Even when you use carbon steel as a filler the stainless steel will mix in the weld puddle and form a good joint but will rust after exposure to moisture. A test of the weld material would be to use a magnet, as 304SS (most kegs) will barely hold a magnet and 316SS is not able to hold a magnet at all.

Here is a tidbit I just happened to see in "How to Brew". Not sure if it helps or not.

One thing to keep in mind is that the bluish or straw colored area around the weld joint is no longer passivated. The heat has created different oxides that can corrode, so you will need to use a stainless steel cleanser to discoloration away to bare metal so it can repassivate itself.

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Here's another question for the experts. Is it normal to have a gap such as this between the coupling and the wall of the keg? This is the inside of the keggle.

The gap is where the inside of the keg was not welded to the coupling, Sabco and others have the full and half couplings welded both on the outside and inside. This is a PITA to do so not everyone will weld and polish the inside, which will not matter much on a mash or boil kettle as sanitation is not an issue.

I was also kinda curious after lookin into my HLT and boil keggles-my welder guy did the same-outside welds beautiful....insides well...they have the same voids around the fitting (not welded on the inside) . Question answered. Thanks.Shane

Have worked with a company called ASTRO PAK and we passivated two 500 gallon high purity air tanks for Intel useing Ascorbic and Citric acid in a 50/50 mix 1Lb/5 gallons of water heated to 180 degrees and circulated through the inside of the tank. There criteria for achieving passivation was the lack of change of the dissolved iron in the passivation solution, typically 8 hours of circulation. Lower quantities of acid to water should work as the goal is to remove any soluble iron and restore the oxides, leave the nitric acid process to the industrial folks. The citric and ascorbic acid powder should be available through homebrew/ wine making suppliers.

trinitone:
Your welder did a really nice job. All you need to do is get a green 3M scrubbie pad and some Bar Keepers Friend (oxalic acid). Scrub the rust off. The oxalic acid will repassify the stainless. You may have to scrub it several times over the first month or two - then you will be good to go. I did mine 5 years ago and have not had to repeat the process. Have fun!
steve h