Stainless Steel Contamination

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Stainless Steel Contamination

Postby caveman » Thu Aug 16, 2012 1:22 am

Recently ive been asked a few times about stainless steel rusting and contamination of stainless steel. As we all use stainless steel in the process for distilling as in boilers,water cooling fittings and incresingly in columns, bubblers . etc... I thawt i would post some info about this Its something we all should be aware about and keep an eye on as you wouldent want to be mid run when you have a failure and loose good product or at worst have a accident eg fires burns from hot liquids or electrical problems .
cheeres Caveman

Stainless Steel - Surface Contamination in Fabrication

Topics Covered

Background

Contamination by Mild Steel

Contamination by Chloride

Contamination by Carbon
Background

Stainless steels must have clean surfaces, free from contamination to achieve their optimum corrosion resistance. During fabrication care must be taken to either protect the metal surface from contamination or to restore the surface after fabrication is complete.

Three common and undesirable contaminants that are likely to be encountered during fabrication and shipping are mild steel, salt (sodium chloride) and carbon.

Any of these contaminants may imperil the chances of the oxide film protecting the underlying stainless steel.
Contamination by Mild Steel

Corrosion initiation from mild steel contamination may occur in two ways:

1. The protective oxide film on the stainless steel may be broken when the mild steel is brought into contact with the stainless steel. This contact creates a mild steel/stainless steel interface which is a corrosion cell.

2. The mild steel contamination may be at the outer surface of the oxide film on the stainless steel. Then, under moist conditions, the mild steel will corrode and cause both oxygen depletion and ionic concentration beneath the ferrous deposit. These latter effects destabilise the adjacent oxide film on the stainless steel, which then readily corrodes.

Typical causes of contamination by mild steel include:

• Using mild steel hooks, chains, and wire ropes for lifting unprotected steel materials (Suitably placed dunnage, or old fire hose, may be used to cover the lifting tackle to avoid such damage).

• Lifting unprotected stainless steel with forks and coil lifting probes that have previously lifted unprotected carbon steel.

• Dragging stainless steel over mild steel, such as the wearing strips at the back of truck trays.

• Transporting unprotected stainless steel in mild steel railway wagons.

• Contamination from falling particles of mild steel welding and flame cutting dross from higher working levels.

• Grinding dust thrown up by power tools used on mild steel.

• Contamination from tools that have previously been used on mild steel … commonly polishing tools, drills, files, and screwdrivers.
Contamination by Chloride

When contamination by common salt (sodium chloride) occurs the dissolved chloride ions enter the structure of the protective oxide film on the surface of the stainless steel. When moisture evaporates at the surface of the metal, the chloride ions concentrate on the surface and cause the protective film to break down.

Contamination by common salt can occur from:

• Sweaty hands.

• Sea spray and seawater.

• Environmental contamination, such as in butter and cheese plants where air blasting drives salt into the product.

• Salt applied to avert or melt ice (not in Australia).

• Salts added to concrete to aid setting.

• Hydrochloric acid used to clean stonework and chemically etch concrete floors.
Contamination by Carbon

Carbon contamination usually occurs when the metal is heated (e.g. during welding), under which conditions any organic materials may break down on the surface of the metal and contaminate both the solid surface and any molten metal.

Contamination by carbon can occur from:

• Pencil, paint or marking pen markings.

• Combustion of oil films, paper, organic matter, backing strip materials, bonding agents or sooty gas flames in gas welding or heat treating.

• By welding to carbon steel



Source: Atlas Steels Australia

some more links to related s/s
RUST ON STAINLESS STEEL
http://www.sperkoengineering.com/html/Rust.pdf

TUNGSTEN INCLUSION
(This is contamination of stainless steel in the tig welding process)
http://images.slidesharecdn.com/welding ... 1246079870

Pickling and Passivation
(This is a treatment done after the welding process i simply use acetone for this purpose and find it works well and dont have to worry about the other nastys in pickling agents)
http://events.nace.org/library/corrosio ... ckling.asp
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Re: Stainless Steel Contamination

Postby mullamulla » Thu Aug 16, 2012 10:17 am

Cheers for the info Caveman, something to keep in mind :handgestures-thumbupleft:
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Re: Stainless Steel Contamination

Postby Camikaze » Thu Aug 16, 2012 10:38 am

Thanks for that info Caveman, very good.

For someone thats building a 4 - 2 incher out of staino, this is great to know.


Cheers :handgestures-thumbupleft: :handgestures-thumbupleft:

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Re: Stainless Steel Contamination

Postby Granpappy » Thu Aug 16, 2012 11:43 am

i simply use acetone for this purpose and find it works well and dont have to worry about the other nastys in pickling agents)


Hey Caveman - if you look on the tin of acetone, down the bottom where it says - "Repeated exposure to this product may cause sterility" - No need to worry bout 'other nasties' when you got that problem to contend with....
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Re: Stainless Steel Contamination

Postby MacStill » Thu Aug 16, 2012 12:31 pm

Granpappy wrote:
i simply use acetone for this purpose and find it works well and dont have to worry about the other nastys in pickling agents)


Hey Caveman - if you look on the tin of acetone, down the bottom where it says - "Repeated exposure to this product may cause sterility" - No need to worry bout 'other nasties' when you got that problem to contend with....


Keep the crap out of tech threads please :roll:

Obviously caveman has taken a lot of time to make this information available to us, if you have a problem with this information you should contact him via PM so the original post can be amended if the need be.

For your info:

Acetone MSDS

http://www.collectioncare.org/MSDS/Acetonemsds.pdf

Pickling paste MSDS.

http://www.haskellcorp.com/uploads/msds/Cleaners/pickling%20paste,spray.pdf
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Re: Stainless Steel Contamination

Postby googe » Thu Aug 16, 2012 12:59 pm

Thanks for the info Captain Caveman! :). Certainly is delicate stuff hey, i remeber doing a coarse on stainless when i was in the cheese making industry, intereting stuff but i cant remeber a thing about it now haha. One of the welders at work said to use a good stainless brush when cleaning welds to stop cross contemination, is that right?.


Cheers
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Re: Stainless Steel Contamination

Postby emptyglass » Thu Aug 16, 2012 4:06 pm

Some grinding discs are meant for cutting mild steel and have ferrous particles in them. Get stainless steel cutting discs and dont cut mild steel with them while you are doing stainless work. Flap discs or polifans, select the blue ones. The red ones are for mild steel.
Stanless left in the path of grinding sparks from some mild steel work going on nearby is the biggest workshop cause of rusting on stainless.
The other common one is plasma slag from when the welder guy blows a hole in a keg with one. Just need to fill the keg with some water to stop it, and it makes it healthier for the welder man.

Nice post Caveman
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Re: Stainless Steel Contamination

Postby caveman » Thu Aug 16, 2012 9:52 pm

Thanks guys ,
no worries bout the post i put it here to make every one aware of the contamination issues with staino products .
Its the same as anything we do in life if we strive to get the best out of something we do we dont want unforeseen things stuffing it up .
and in our case in this great hobby we do we strive to make the best quality we can. we don't want to go to all the troubble to spend our hard earnt time and money making a nice drink to find out at the end that its tainted with rust or corrosion issues :angry-banghead:
hope this little bit of info helps everyone a nutha step closer to that perfect product we all love to make
cheeres caveman
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Re: Stainless Steel Contamination

Postby MacStill » Thu Aug 16, 2012 9:54 pm

A couple of examples of contamination in SS

2012-08-15 17.01.00.jpg


2012-08-15 17.00.32.jpg
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Re: Stainless Steel Contamination

Postby caveman » Thu Aug 16, 2012 10:00 pm

googe wrote: One of the welders at work said to use a good stainless brush when cleaning welds to stop cross contemination, is that right?.


Cheers

yes googe he's right i allways like to go get a new stainless steel wire brush for this purpose and only use it with staino . then store it in a place it wont get contaminated or picked up to do other work with i normally write stano only in black marker on the handle so i dont forget.
As i think i may have said somewhere before on the forum most stano shops have a dedicated area for doing there cutting, grinding.welding of staino to avoid contamination of there products no other metals are aloud in these areas to avoid the contamination
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Re: Stainless Steel Contamination

Postby Sam. » Thu Aug 16, 2012 10:10 pm

I can see why poeple would use the mild steel cutting discs on angle grinders instead of the stainless ones as recently cutting up some kegs bought 2 stainless discs and thought "yeah that should be plently" about 5 minutes later both discs were gone but worked really well! All I had left was an old red disc (mild) and it took a lot longer to wear but it cut like shit. After reading this probably should not have used it.

Interesting on the passivating as well I know we had some aircraft parts sent away to have this done and it was bullshit fucking expensive :o I'm talking about 2 gorillas to have a couple of little lugs done.
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Re: Stainless Steel Contamination

Postby caveman » Thu Aug 16, 2012 10:21 pm

McStill wrote:A couple of examples of contamination in SS

2012-08-15 17.01.00.jpg


2012-08-15 17.00.32.jpg


The top pic looks to have tungsten inclusion to me and has corroded to the point of a leak .This would have to be ground back out and rewelded to correct this problem as well as pacification or pickiling to avoid this occorring again

In the second pic this looks like the arc area has been contaminated and no pacification has been done after welding sanding back and pacification should resolve the problem

in the case of contamination if left untuched will only get worse untill eventually metal fatigue happens
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Re: Stainless Steel Contamination

Postby caveman » Thu Aug 16, 2012 10:55 pm

hey s and l ive found with the staino discs its a case of steady as it goes just let the disc do the work to much pressure on the disc will chew em up real quick .I no there not real cheep but a few extras around the shed will allways get used or borrowed and there good for cutting most other stuff too just dont cut other shit with em then use em on the staino it will contaminate it .

As the pacification thing goes the aircraft boys are allways a bit anal , which i guess keeps us safe but 2 grand sounds a bit steep
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Re: Stainless Steel Contamination

Postby Sam. » Thu Aug 16, 2012 11:22 pm

Yeah I thought so too, I wasn't part of the money dealings, all I heard was "We can guarantee it will never ever corrode".
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Re: Stainless Steel Contamination

Postby Brendan » Fri Dec 27, 2013 7:27 pm

Just came across this thread, am impressed with the information here.

I had a boily mate cut the top of a keg for me for a mash tun, and there was a heap of slag on the bottom from I think a plasma cutter he used. I used the little metal cutting discs for my dremel to clean it up, but didn't realise I'd probably be introducing mild steel/iron into the staino...filled it with hot water a few days later, and rust spots all over the bottom :angry-banghead:

Now I know a bit more about it, I'll try and clean it up again and avoid this. My boily mate said just put pickling paste on it, but I expect that it is nasty stuff as I know a lot of them are. Will give staino wire brush and acetone a go, and leave it dry for a week hoping it 'seals' itself cleanly.

Thanks for the info :handgestures-thumbupleft:
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