View previous topic :: View next topic |
Author |
Message |
AstoriaDave
Joined: 31 Oct 2005 Posts: 994 City/Region: Astoria
State or Province: OR
|
Posted: Sun May 03, 2015 3:19 pm Post subject: |
|
|
I'll try. The chromium in the alloy in the form of its oxide forms a protective coating on the underlying alloy. If the stainless is held in an oxygen free environment (aka "anoxic"), it is possible for the chromium oxide to be degraded, exposing the underlying alloy, and allowing it to be eroded away. The technical term I know for this is "crevice corrosion".
That said, my local shipwright claims stainless burried within a wooden structure and not exposed to water will last forever.
One source which explains the corrosion in more formal terms: http://www.corrosionist.com/Pitting_Crevice_Corrosion.htm _________________ Dave Kruger
Astoria, OR |
|
Back to top |
|
|
journey on
Joined: 03 Mar 2005 Posts: 3597 City/Region: Valley Centre
State or Province: CA
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: journey on
Photos: Journey On
|
Posted: Sun May 03, 2015 3:32 pm Post subject: |
|
|
Quote:
"Stainless steel is not resistant to chemical or physical attack. The corrosion resistance of stainless steel depends on the formation of a 'passive surface film' composed of nickel and chromium oxides (Cr203 & Ni0). Passivation involves removing free Fe or 'tramp Fe' from the stainless steel surface."
End quote
Boris |
|
Back to top |
|
|
hardee
Joined: 30 Oct 2006 Posts: 12633 City/Region: Sequim
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sleepy-C
Photos: SleepyC
|
Posted: Sun May 03, 2015 7:44 pm Post subject: |
|
|
smckean (Tosca) wrote: | Quote: | Both need oxygen to delay rust incursion and corrosion |
Harvey, I am confused by this. Can you explain it to me? Thanks |
Dave and Boris are much better at it than I am for the technical side. Practically, if you put tape on a stainless tube, it will corrode or rust under the tape faster than on the rest of the surface.
Harvey
SleepyC
_________________ Though in our sleep we are not conscious of our activity or surroundings, we should not, in our wakefulness, be unconscious of our sleep. |
|
Back to top |
|
|
gulfcoast john
Joined: 14 Dec 2012 Posts: 989 City/Region: PENSACOLA
State or Province: FL
C-Dory Year: 2010
C-Dory Model: 255 Tomcat
Vessel Name: Cat O' Mine
Photos: CAT O' MINE
|
Posted: Tue May 05, 2015 6:55 pm Post subject: |
|
|
Hi Brats!
Sure, Oxalic acid in all its various forms will remove rust tarnish from SS, but also your Poli-Glow clear coat (outlier alert!) or wax if you like wax, and it will stain your aluminum trailer (wet it down first) and it's not good for your skin or eyes.
For years I've been using Woody Wax...a cheap Lowes type cotton glove over a vinyl glove (optional, but it keeps the harmless stuff off your hands), spray the outer cotton glove with Woody Wax. Use some bronze wool in stained areas and just The Glove on nonstained SS rails and bimini supports. The cotton glove allows you to get the liquid around post bases etc without hitting your Poli-Glow and is very, very fast and easy and benign. Leave it on as little as 1 hour or 24 hours for tough stains, then wipe it down with a terry rag (or microfiber cloth) and you will have a shiny protected SS rail for up to 3 months in the Deep South. Stash the Cheap Cotton Glove and the used bronze wool in a zip-lock bag for future use (if you're as cheap as I am). Don't even try to use SS or steel wool. The bronze wool can be re-used many times. I bought a gallon of Woody Wax (half price) at the last day of the 2011 Miami Boat Show we are still using. It's also great to get the wax off the plastic black nav light housings and shine up any plastic/composite plastic, as well as a non-skid cleaner and non-slick wax/protectant for your non-skid areas. Also, it tastes great sprayed on Rocky Road Ice Cream (JUST KIDDING!). I've also liked Miracle Cloth but you can't let it contact water and overall Woody Wax is cheaper.
Here are the West Marine prices, but you may well find better searching elsewhere.
http://www.westmarine.com/buy/western-pacific-trading--bronze-wool-pads-fine--P004_126_004_510
http://www.westmarine.com/buy/woody-wax--fiberglass-non-skid-deck-wax-woody-wax-16-oz--3745320
Cheers!
John _________________ John and Eileen Highsmith
2010 Tom Cat 255, Cat O' Mine
Yamaha F150, LXF150 |
|
Back to top |
|
|
hardee
Joined: 30 Oct 2006 Posts: 12633 City/Region: Sequim
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sleepy-C
Photos: SleepyC
|
Posted: Thu May 07, 2015 12:33 am Post subject: |
|
|
I spent some time with a metal fab shop today. The owner said I need to look into "passivating"
So I found it is a chemical process and not something I can brush on and mask around. Anyone have any practical experience with that?
Harvey
SleepyC
|
|
Back to top |
|
|
Will-C
Joined: 21 Aug 2007 Posts: 2476 City/Region: Temple
State or Province: PA
C-Dory Year: 2008
C-Dory Model: 23 Venture
Vessel Name: Will-C
Photos: Will-C
|
Posted: Thu May 07, 2015 8:30 am Post subject: Cleaning rust from Stainless |
|
|
Prism Polish
Prism Polish
Metal Polish and Fiberglass Deoxidizer
Prism Polish has been formulated to clean, polish and protect all metals in one easy application. Our protective coating is designed to last 3 to 6 months. Prism Polish contains no harsh acids, caustics or abrasives. it is safe to use on all metals fiberglass, gel-coat, plexiglass and painted surfaces. Prism Polish has been developed for use in the marine, aviation, automotive, motorcycle and maintenance industries. Use Prism Polish on bronze, brass, copper, stainless steel, aluminum, pewter, nickel, sterling silver, silver plate and factory blued guns.It offers the finest protection available for any chrome or stainless surface. It cleans and protects in one easy application. It restores tarnished and dull surfaces and protects against salt corrosion and rusting. Prism Polish is excellent to clean and deoxidize fiberglass, It removes cloudiness from plexiglass, clear vinyl, eisenglass or Lexan. www.prismpolish.com you can purchase on Amazon
This stuff seems popular with the Tugnuts. It's what we have been using for years. _________________ Chevrolet The Heart Beat Of America |
|
Back to top |
|
|
AstoriaDave
Joined: 31 Oct 2005 Posts: 994 City/Region: Astoria
State or Province: OR
|
Posted: Thu May 07, 2015 11:34 am Post subject: |
|
|
hardee wrote: | I spent some time with a metal fab shop today. The owner said I need to look into "passivating"
So I found it is a chemical process and not something I can brush on and mask around. Anyone have any practical experience with that? ] | Harvey, no hands on experience here. However, a skim of this article may illustrate why passivation is never going to be a realistic answer for corrosion protection of railing or other stainless hardware installed on the boat. I think it is really only useful for original parts fresh from machining, with rigorous monitoring of the passivating materials and conditions. Too bad. BTW, I have never seen SS treated for passivation with a shiny, mirror finish. Always matte, always sort of gray. I suspect this is due to the need to avoid contamination of the surface.
http://www.mmsonline.com/articles/how-to-passivate-stainless-steel-parts |
|
Back to top |
|
|
thataway
Joined: 02 Nov 2003 Posts: 20841 City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
|
Posted: Thu May 07, 2015 1:02 pm Post subject: |
|
|
I have had SS exhaust fittings fabricated for several boats. These were always passivated. As Dave describes, the surface is dull, and has a gray color. _________________ Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
|
Back to top |
|
|
Sea Wolf
Joined: 01 Nov 2003 Posts: 8650 City/Region: Redding
State or Province: CA
C-Dory Year: 1987
C-Dory Model: 22 Cruiser
Vessel Name: Sea Wolf
Photos: Sea Wolf
|
Posted: Thu May 07, 2015 1:42 pm Post subject: |
|
|
OK, here's what I know:
Stainless steel is Iron + carbon, iron for the matrix/strength, carbon for more strength and hardness.
Nickel, chromium, and (sometimes like in 316) molybdenum, are added, all for anti-corrosive properties, as well as some other properties they give the alloy.
The oxides of Ni, Cr, and Mo are what actually protect the steel. The surface of stainless must consist of these oxides. These three metals readily form the oxides when exposed to air.
Any iron atoms on the surface can rust (form iron oxide or rust) with oxygen and water in the air.
When hardware is made with stainless, the various forming process of cutting, machining, welding, etc., leave loose carbon atoms on the surface.
Passivation consists of removing these iron atoms on the surface by various means, such as chemically removing them, eg., "pickling" them with citric acid, though several other processes exist, such as electro-polishing.
Some of the chemical processes etch the surface, leaving a dull, matte finish, unlike elecro-polishing.
Some polishing compounds you can buy claim to "re-passivate" stainless, although I doubt they match the industrial processes.
Waxing the stainless helps protect it for a limited time.
One thing I do know is that if you use regular steel wool, a steel brush, or a file or a similar tool on a stainless piece and then re-use the hardware piece, the contact with the regular steel will leave untold billions of iron atoms on the surface (microscopic welds are made between the regular steel and the stainless, then broken), and the hardware piece will then rust like crazy. A stainless wire brush/wheel is much better, but without re-passivation of the surface afterward, rust still shows up fairly quickly .
I learned this from a metallurgist/welding fabrication supervisor in our sailing club that worked at the Marine Division of Westinghouse in Sunnyvale, California.
Sorry about the retired science teacher blackboard drill, but still can't shake the habit!
Hope this helps!
Joe. _________________ Sea Wolf, C-Brat #31
Lake Shasta, California
"Most of my money I spent on boats and women. The rest I squandered'. " -Annonymous |
|
Back to top |
|
|
Aurelia
Joined: 21 Aug 2009 Posts: 2331 City/Region: Gig Harbor
State or Province: WA
Photos: Aurelia
|
|
Back to top |
|
|
AstoriaDave
Joined: 31 Oct 2005 Posts: 994 City/Region: Astoria
State or Province: OR
|
Posted: Thu May 07, 2015 4:13 pm Post subject: |
|
|
Joe,
Thats a good summary. The link I posted has more detail for those interested.
Oh, one typo. Your first line describes ordinary steel, aka carbon steel. Not stainless until those other guys get into the act. Then comes the black magic.
That business about steel wool screwing up stainless is worth remembering. I also wonder how someone could repassivate a surface after machining or sanding it. I don't see over the counter polishes as capable of doing that. |
|
Back to top |
|
|
Sea Wolf
Joined: 01 Nov 2003 Posts: 8650 City/Region: Redding
State or Province: CA
C-Dory Year: 1987
C-Dory Model: 22 Cruiser
Vessel Name: Sea Wolf
Photos: Sea Wolf
|
Posted: Thu May 07, 2015 7:27 pm Post subject: |
|
|
AstoriaDave wrote: | Joe,
Thats a good summary. The link I posted has more detail for those interested.
Oh, one typo. Your first line describes ordinary steel, aka carbon steel. Not stainless until those other guys get into the act. Then comes the black magic.
That business about steel wool screwing up stainless is worth remembering. I also wonder how someone could repassivate a surface after machining or sanding it. I don't see over the counter polishes as capable of doing that. |
Dave- That's what I meant:
Iron plus carbon = steel,
then with the other elements it becomes stainless.
Thanks for the positive comments!
Joe. |
|
Back to top |
|
|
AstoriaDave
Joined: 31 Oct 2005 Posts: 994 City/Region: Astoria
State or Province: OR
|
Posted: Thu May 07, 2015 9:41 pm Post subject: |
|
|
Joe, Big DOH here. guess I did not process that very well. |
|
Back to top |
|
|
hardee
Joined: 30 Oct 2006 Posts: 12633 City/Region: Sequim
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sleepy-C
Photos: SleepyC
|
Posted: Fri May 08, 2015 2:04 am Post subject: |
|
|
Joe,
No need to apologize for your methods. They worked for years, so must be perfected, and still works here -- at least for me. Thanks for the explanation.
Lesson being learned: It's good to go with the pro's.
Harvey
SleepyC
|
|
Back to top |
|
|
SEA3PO
Joined: 02 Nov 2003 Posts: 1835 City/Region: Chester
State or Province: CA
C-Dory Year: 2003
C-Dory Model: 22 Cruiser
Vessel Name: SEA3PO
Photos: SEA3PO
|
Posted: Fri May 08, 2015 11:37 am Post subject: |
|
|
I agree about how to polish the stains out of stainless.. I use Bartenders Friend... acid works really easy too.
some stainless hardly shines at all...
It is the Chrome content that really sets the properties of Stainless Steel...a low grade (soft) stainless can have as low as 2% Chrome content, while a very hard, highly bright (ease to polish),very corrosion resistant stainless will have up to 17% Chrome content.
Joel
SEA3PO |
|
Back to top |
|
|
|
|
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You cannot download files in this forum
|
|