Red Rust on 316 4

[metalman8357]

Hi all,

I'm just wondering if red rust is possible on 316? I've received a few 316 bolts that were used in coastal applications and they appear to show some slight red rust residue between the 316 washer and 316 bolt, but besides this they appear to be structurally sound. My understanding is that 316 will not show red rust and will undergo pitting instead. I'm wondering if this is due to carbon steel rusting and contamination somewhere in the system, and rainwater brought it the interface between bolt and washer. Any input?

Thanks,
M

 

[EdStainless]

It could be rust rushing onto them from another part.
Or it could be from iron contamination on the surface of the bolt or nut or washer.

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Plymouth Tube

 

[stanweld]

What are the materials connected by the bolts? You seem to indicate contact with carbon steel.

 

[metalman8357]

The bolt and washer are both stainless, and the material that the bolt is connecting two fiberglass panels. These are on the side of a building where iron contamination could be a possibility due to rainfall. My original question was asking if it is possible for 316 stainless to show red rusting.

 

[stanweld]

Because you have indicated that no obsevable corrosion was evident, I would suspect that iron contamination of the bolts/washers was the culprit. Contamination could occur from machining, handling after machining, storage in steel canisters, tools used for bolt up, etc.

As long as oxygen and water are available, iron ions in the iron chloride corrodant solution can be precipitated out as rust.

 

[TVP]

Are you familiar with the term "tea staining"? Here is some good information on the subject:

http://www.assda.asn.au/index.php?option=com_content&task=view&id=85&Itemid=111

316 that has been properly passivated should not show significant red rust unless it has been in service for many years in the splash zone or similar.

 

[EdStainless]

If you have new hardware and you are curious, find some white Head and Shoulders shampoo.
Coat the hardware with a thin layer of shampoo and let it sit.
If you see any blue spots there is free iron on the surface.

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Plymouth Tube

 

[TVP]

Ed,

I have never heard of this trick before. Do you know what the reaction/precipitate is?

 

[arunmrao]

Ed, very ingenious method . Like TVP, I too am wondering the reaction product .

 

[EdStainless]

The active ingredient will complex with Fe. The reason that some H&S is blue is because it is made in plants with steel tubing and they need to dye it to compensate for the tinting.
This used to be a regional issues around the country, some places were white and others were blue.

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Plymouth Tube

 

[NickClark]

Is this a form of the ferroxyl test used for plating porosity? Its common to use copper sulphate also which will plate out copper as a test for steel or stainless.

Nick

 

[TomDOT]

Nick - since the ferroxyl test is one of the ferro-ferricyanide reaction variants, it certainly sounds like it. Ferricyanide reacting with ferrous ions to make Prussian blue (very early synthetic pigment)

I started wondering why there would be ferricyanide in a shampoo - and then I thought about calcium ions. Calcium ions interfere with the action of soaps and some detergents by precipitating out the soap (and building up "soap scum") - typically this is controlled by adding EDTA to shampoo, which will complex with the calcium ions and prevent binding elsewhere. However, I suspect ferricyanide would be more effective than EDTA at calcium control.

Hm.

 

[EdStainless]

The active ingredient is Zn Pyrithione, in this case the ligands are chelated to a Zn, not actually ionic bonding.
The presence of Fe changes the molecule form and hence its color.

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Plymouth Tube

 

[TomDOT]

Ah, often branded as Zinc Omadine. Common antimicrobial - I wasn't familiar with the blue effect for it.

Thanks!

 

[arunmrao]

Thanks Ed, you merit a few stars.

 

[TVP]

Agreed, thank you Ed.

 

[armourian78]

I love this thread. It made me chuckle. I love the idea of testing passivation on components using H&S!
I am already refered to as the mad scientist within my company. I do not need information like this, it will only add fuel to the fire! Now off to find some H&S!!!