How stainless is your stainless steel?

[Organikum]

As the question for usability of certain SS vessels and parts comes up very often, I allow myself to present a simple way to test stainless steel and how to do a so called "passivation" for better chemical resistance:

Testing:

... the sample is placed into a copper sulfate solution.  Any remaining iron will show up as pink spots on the sheet.  This would be considered unacceptable

Passivation:

Passivation describes the treating of a metal with a mild oxidant (such as nitric acid) to remove surface iron or iron compounds by dissolution.  This action forms a protective passive film on the surface of the metal.  The trace iron left behind from machining and fabrication can provide sites for corrosion if left untreated.
    The process is performed by first cleaning the surface with solvents or an alkaline solution to remove organic or metallic residues.  Next, the parts are placed into passivation solutions.  The choice for this solution is usually nitric acid.  The process is controlled by three key variables:  time, temperature, and concentration.

More information on this and other chemical engineering questions:

http://www.cheresources.com/archivezz.shtml

[ribbon13]

I was told by someone ex-military that really knows there shit that that stainless steel that isn't so stainless is because of unequal nickel distrubution. He said 'Steel = iron + carbon , Stainless = iron + carbon + nickel'. He said the military thus found a source of stainless steel that is processed in outer space because lack of gravity aids in the equal distribution of the nickel. Not sure it is true, but most of the info I've gotten from this guy is VERY reliable. He also gave some source for stainless steel labware.

[SPISSHAK]

[SPISSHAK]

[Castortrip]

[cublium]

[roger2003]

all about stainless steel you can read here:

http://www.normen.net/Stahlschluessel-2001-Deutsch-Franzoesisch/3922599176.html

[calcium]

By definition, stainless steel is a steel alloy of iron and at least chromium (10% or more, IIRC). Nickel is very commonly added and there might be some molybdenum or other constituents. The 304 and 316 series are highly corrosion resistant and used widely for tanks and process piping in the dairy and brewing industries. 316 is better, especially if it is going to be welded. Welding can deplete the alloy at the location of the weld with 304 stainless but less so with 316.
     Most vessels that bees may come across to use for reactions such as beer or soda kegs are probably going to be 304 or 316 series stainless steel. The information posted above about passivation is right on the money. I've done it many times on tanks that one walks into to inspect. It doesn't take a very strong concentration of nitric acid to provide a durable "stainless" surface on a tank wall.

[cublium]

Oh well,cub had some SS that contained no iron,not sure about rest of the world,sorry.Maybe it wasn't called SS but it didn't rust,that's for sure.

[praeseodymium]

or some other hi-tech alloy. There's plenty of alloys used in jet engines for example that are not classed as ss but something else.... some of which seem almost inert in even reasonably harsh weather conditions.

[Organikum]

cublium?