ajdelange wrote:Cliff wrote:Never get a fermenter made in china unless you know that it's not welded but Spun or cold drawn The Chinese can not make sanitary welds.
I have a couple of cylindroconicals from China and the welds are pretty good as far as I can tell.
That's the problem with welds in the first place. They can look great and perform wonderfully for years.
Without very expensive equipment one can't tell whether a weld in SST is sanitary or not unless it was so badly done that it looks crappy - then one can hazard a good guess. You can't tell with the eye nor with a magnifying glass nor with anything that costs less than about 20-Grand.
Ya need high magnification X-ray or Gamma to find the microscopic piping that welding leaves behind.
And there's more.
When dealing with the Chinese, you need an X-ray fluorescence tool costing another 30 Grand or so to tell you what the metal alloy composition is, or else all you can know about it, is that it's shiny and magnets don't stick.
"Oh look it's shiny and my magnet doesn't stick" just happens to be the ONLY test that the reseller of chinese conicals and tanks has available to him. I know 'cause I demanded of him how he'd inspect my tanks If I bought them from him. He uses his eyes and a magnet and that is all he's got. Or stated another way: He's got nuthin'.
So unless you have an X-Ray fluorescence tester the alloy of the metal will be a total mystery to you.
It could be high lead or have Cadmium in it - or both and more. Historically too many Pacific Rim smelters have been willing to take all sorts of shortcuts and they are known to dump otherwise unusable alloys and metals in their product just to bulk it out and get some return on an otherwise useless scrap product. So they might toss in to the smelter whole buckets and barrels of old scrap 1960's era (banned) Cadmium treated nuts and bolts or high lead alloy steels any of which they bought as scrap, and they don't care, so long as the end product looks and feels right.
Mind you not all Chinese metals are like that, but enough are that many vendors won't touch 'em and people like NASA and medical device makers are terribly leery of them. It's also entirely possible that the Chinese welder who welded your products might have been highly skilled, but the guy next to him maybe not so much.
And then there's all the mystery of what a sanitary weld is. Lots of welders don't even know the term. Many will tell you that so long as you are using TIG you can do sanitary welds and there are levels and levels of sanitary. Stainless steel counter tops don't require the same level of precision as do tank welds because of the contact time that food has with the welds. So there's a sanitary weld and then there are sanitary welds.
In weld micro-piping, the problem is that your sanitation fluids can't penetrate the microscopic pipes where bacteria can find safe harbor. The sanitizer might get the bacteria near the opening of the pipe, but not deep in and once the sanitation fluid is diluted with a nice sweet food like wort or milk, or whatever, the bacteria deep in will consume the dead ones near the opening and flood out into your food product.
It can take years of use for the micro-pipes to become fully contaminated. So a person might use his equipment for a very long time before experiencing problems, which will seem as if they are just coming out of the blue.
"How come I can't clean my tank? Is the problem even my tank? Why is there spoilage when I'm doing everything right?"
And all the while it's micro-pipes that took a long time to get all plugged up with bugs.
This is why Blichmann only sells Spun formed tanks and why all better tanks have O-ring & threaded fittings and not welded fittings.
But back to SST conicals.
All hope is not lost even if you have visibly crappy welds or even damn fine looking welds.
If they are crappy you can always take some 56% Cad Free Silver solder and cover them. That's it.
OR you can just take a propane torch to all the welds before you fill the tank as part of your sanitation regimen heat the welds to something above 250F to 300F , but not so hot that you start to make the metal red with heat and you are golden.
Such a sanitation regimen is a perfectly workable and permanent solution taking all of 5 minutes or less each brew day.
As to the problem os suspect metals:
Well you already know how to strip the lead from brass. Use the same procedure
Caustic Magnesia and EDTA can be used to strip Cadmium from the surface of most metals. Follow that with a long soak in a high strength solution of Citric acid in water to re-passivate the SST and you are golden.
Really anything ( acid or base) that causes cadmium to go into ionic solution combined with a chelating agent like EDTA to prevent it from re depositing, will work just fine but ya gotta passivate the SST after.
