Passivation of AISI 304SS

[dfaunce]

I'm a young engineer and am still have a lot to learn, so bear with me.

I work in the aerospace industry, specifically water/waste systems. We frequently authorize certain parts to be passivated, seeing that the fabricated parts of our plumbing systems are stainless steel (particularly 304).
(side note: we passivate to AMS 2700 or QQ-P-35).

I understand that when stainless steel is being machined, particulates of iron and other corrosive metals inbed themselves into the stainless steel, so when water runs across our stainless piece, there is potential for corrosion. (correct me if I'm wrong).

I also understand that the result of passivation creates an oxidized film that prevents the metal from corrosion. (correct me if I'm wrong).

I designed a 304SS tube (1.000" OD X .035WT), per AMS5567, 6" long, with a 4" bend radius (45degrees) and both ends are beaded per AS5131, Style A. Water will run through this tube.
I would assume the beading process could possibly create these corrosive particulates, which would mean the tube will require passivation. Is this correct?

If so, what if the tube was NOT beaded. Would it still require passivation

 

[EdStainless]

You basically have it right.
While we passivate in order to assist in building a robust passive layer what we are really doing (actually the only thing that we can test for) is removing free iron from the surface.
If the forming is done with no steel tooling, never put on a steel surface, not cut with steel tools, and so on then there would be no reason for passivation.
I know people that cut under oil and for with bronze tooling just so they don't have to re-passivate.

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Plymouth Tube

 

[Robertmet]

ANY process that may contain contaminents can be a problem. A proper SS shop will have dedicated machines and tooling for use only with SS.All too often a non-dedicated step is used without thought .

 

[EdStainless]

Yes, that nice SS or brass tool is used because it isn't steel, but last week it was used on steel. And you are hosed.

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