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  #1  
Old 06-21-2007, 01:44 PM
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Default SS and corrosion

OK, i have come to learn that SS is only rust free if exposed to the air.

I can't remember the term right now for adding a protective oxidation coating to the SS if you are about to bury it in epoxy and glass

any one know the process and can i do it at home? I can get nearly any chemical
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  #2  
Old 06-21-2007, 04:58 PM
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Default Re: SS and corrosion

I don't think it will be a problem unless you use carbon steel nuts, bolts or any other fastener made of carbon steel that will be in constant contact with the stainless.
Stainless steel has a natural barrier against corrosion, it's own oxide on the surface.
An introduction or extended exposure to a corrosive (especially Chloride) can produce corrosion (see this page) and electrical charge can produce some unwanted effects.
But barring those things, I think it would be safe snuggled underneath a nice Cozy layer of protective Epoxy..
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Old 06-21-2007, 06:07 PM
ZG4Me ZG4Me is offline
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Default Re: SS and corrosion

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Originally Posted by Dust View Post
OK, i have come to learn that SS is only rust free if exposed to the air.
Pretty well rust free (iron oxide) when buried too
Quote:
I can't remember the term right now for adding a protective oxidation coating to the SS if you are about to bury it in epoxy and glass
Passivate.
We sent some of the SS parts I used to make out to be passivated. Best I can figure, they were degreased, then dipped in a vat of acid. Nitric rings a bell. Think it's to increase the depth of the oxide coating.

YMMV.

Rick
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Old 06-21-2007, 06:44 PM
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Default Re: SS and corrosion

I'm confused here. Rust = Oxidation correct? No oxygen = no rust. If it's sealed in epoxy then there's no oxygen so no rust.
Quote:
OK, i have come to learn that SS is only rust free if exposed to the air.
......so if it's exposed to ...... oxygen, there's no rust.

Or, as Dennis P. would say ......... win, win!
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Old 06-21-2007, 07:45 PM
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Default Re: SS and corrosion

Stainless steel is a special case, having build and repaired many boats, I can tell you that SS MUST have oxygen to develop a nice protective coating and to keep the metal from corroding! This is well documented!

Yea I know, it doesn't sound right, but there it is.

If there is no oxygen, a condition known as "crevice corrosion" occur. Not a good thing to have happening to you.

Bottom line, if you use SS, have it where air (or water in the case of a boat) can get to it and supply oxygen to it.

If you must bury steel, use normal steel, epoxy coating will keep it from rusting and you should "paint" the exposed part (if any, at least several inches out from the covered part) with the same epoxy before painting it with "real" paint. This will help prevent rust from forming at the line where the metal go into the fiberglass.

Google "crevice corrosion" for more information if you wish.
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Old 06-21-2007, 07:59 PM
Lynn Erickson Lynn Erickson is offline
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Default Re: SS and corrosion

Quote:
Originally Posted by ZG4Me View Post
Pretty well rust free (iron oxide) when buried too

Passivate.
We sent some of the SS parts I used to make out to be passivated. Best I can figure, they were degreased, then dipped in a vat of acid. Nitric rings a bell. Think it's to increase the depth of the oxide coating.

YMMV.

Rick
Passivation: in short uses acid ( nitric and citric are most common ) to remove any iron molecules from the surface and cleans off the chromium oxide from the surface so when the stainless steel is again exposed to the air ( O2) it will form a uniform coating of chromium oxide that is iron free and the oxide protects the ss from corrosion. very much like anodizing but without the pretty colors. scratch it and it will rust. cover it with epoxy and expose it to water and it will corrode. it will corrode very slowly but it will.
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Old 06-22-2007, 09:59 AM
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Default Re: SS and corrosion

I can get just about any alloy locally, 301, 304, 306, 310, etc., would any of them be particularly better?

I have to go to the warehouse shortly for some chrome molly
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Old 06-22-2007, 10:10 AM
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Default Re: SS and corrosion

Quote:
Originally Posted by Dust View Post
I have to go to the warehouse shortly for some chrome molly
Does she have a sister?
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  #9  
Old 06-22-2007, 11:02 AM
Lynn Erickson Lynn Erickson is offline
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Default Re: SS and corrosion

Quote:
Originally Posted by Dust View Post
I can get just about any alloy locally, 301, 304, 306, 310, etc., would any of them be particularly better?

I have to go to the warehouse shortly for some chrome molly
304 or 18-8 is the most common and good for corrosion resistance. 316L is the best for corrosion of the 300 series ss
302 is good mostly found in solid stock not sheet stock
303 is ok easier machining
if it is structural and call for chrome moly do not subtitute SS. SS is not stronger and as good for structural parts unless engineered for the application
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  #10  
Old 06-22-2007, 12:04 PM
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Default Re: SS and corrosion

yep - no chrome moly substitution - just aluminum to ss

on a similar note, the warehouse has 2 chrome moly, i think one was was annealed and one was not, which one? first time the question came up.

the reason i said 310 as i got some and they said it was for nasty furnace environment, thought it might be good stuff.

it is fun to have a SS, chrome moly and aluminum store down the street with a billion pounds of the stuff
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dust

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  #11  
Old 06-22-2007, 11:30 PM
Lynn Erickson Lynn Erickson is offline
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Default Re: SS and corrosion

Quote:
Originally Posted by Dust View Post
yep - no chrome moly substitution - just aluminum to ss

on a similar note, the warehouse has 2 chrome moly, i think one was was annealed and one was not, which one? first time the question came up.
annealed is what you want. what are the other choices? 4130 is used in sheet and tube and 4140 is solid stock for machining ( higher carbon content, it machines better). they both can be heat treated but annealed is plenty strong for our stuff.
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  #12  
Old 06-25-2007, 09:44 AM
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Default Re: SS and corrosion

I was buying sheet for the engine mount pads, small amount
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dust

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  #13  
Old 10-10-2007, 10:44 AM
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Default Re: SS and corrosion

Finally learned what is meant by removing ox and the SS will corrode. It did not make sense, how can you remove oxygen and cause corrosion. Does not the oxygen cause the corrosion!

It is easy, it is corrosion, not oxidation that is caused and the corrosion is from galvanic reaction!

Bury SS in glass and attach it to a dissimilar metal and it will corrode.

Now to find out how to protect SS by creating a layer of oxidation

I just love to understand materials, ss expands with heat, wood shrinks in the winter and expands in the summer from water, chrome moly loves to be welded, and on and on and on the journey goes
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dust

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  #14  
Old 10-11-2007, 11:53 AM
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Default Re: SS and corrosion

OK, I have SS inserts, SS hinge and Titanium screws - anyone see a corrosion problem here?
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  #15  
Old 10-11-2007, 12:51 PM
SteveWrightNZ SteveWrightNZ is offline
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Default Re: SS and corrosion

Quote:
Originally Posted by Dust View Post
[...] it is corrosion, not oxidation that is caused and the corrosion is from galvanic reaction! Bury SS in glass and attach it to a dissimilar metal and it will corrode.
In my opinion, SS won't destroy itself forthwith if you encapsulate it in epoxy. Not so for Aluminum, which will turn itself into a nasty corroded pile of snot if you keep fresh air from it. This does not require a dissimilar metal to do this, IIRC.

S
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