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03-31-2006, 08:21 PM
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#1
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4 Rivet Member
1967 30' Sovereign
Leavenworth
, Kansas
Join Date: Jul 2004
Posts: 382
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Chemical reaction?
Both of us having long forgotten all science/chemistry that we ever knew, have a question........... will stainless steel chemically react over time with aluminum?
Inquiring minds want to know
__________________
Beth and/or David
67 Sovereign, double bed, rear bath-"Moby"
2005 Dodge Ram 2500 Hemi, Quad Cab-"Ahab"
"Vintage trailer, vintage owners"
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03-31-2006, 08:28 PM
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#2
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Rivet Master
1979 23' Safari
1954 29' Liner
Orange
, California
Join Date: Feb 2005
Posts: 3,850
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Quote:
Originally Posted by silver 67
Both of us having long forgotten all science/chemistry that we ever knew, have a question........... will stainless steel chemically react over time with aluminum?
Inquiring minds want to know
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Silver 67,
Are you speaking of geological time or human life span? As my geology teacher said "We have all the time in the world"
Bill
__________________
Bill Kerfoot, WBCCI/VAC/CAC/El Camino Real Unit #5223
Just my personal opinion
1973 Dodge W200 PowerWagon, 1977 Lincoln Continental, 2014 Dodge Durango
1979 23' Safari, and 1954 29' Double Door Liner Orange, CA
https://billbethsblog.blogspot.com/
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03-31-2006, 08:36 PM
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#3
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4 Rivet Member
1967 30' Sovereign
Leavenworth
, Kansas
Join Date: Jul 2004
Posts: 382
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What is time?
Time and space - the age old question...
I think we are concerned about the life of either us, or the Airstream, and since it's vintage and we are too, I would guess about 20 years....
__________________
Beth and/or David
67 Sovereign, double bed, rear bath-"Moby"
2005 Dodge Ram 2500 Hemi, Quad Cab-"Ahab"
"Vintage trailer, vintage owners"
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03-31-2006, 08:42 PM
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#4
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Rivet Master
, Minnesota
Join Date: Aug 2003
Posts: 7,721
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If in a dry environment, with large aluminum surface compared to SS, you should be ok. Example: SS screws in aluminum sheet would be OK.
In a wet environment, especially marine, and with the opposite surface area effect (aluminum rivets in SS sheet) the results would be catastrophic.
Looking at the galvanic series, active SS is closer to aluminum than passivated SS. So passivation would not be desirable.
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03-31-2006, 09:02 PM
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#5
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_
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, .
Join Date: Dec 2004
Posts: 8,812
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hi silver67
sure they react but why not desribe the application/issue......
if it's just marker light screws....i wouldn't worry....and the screw threads can be coated with spoke/nipple wax....or other things....not locktite.
if you are thinking about stainless sheet metal...like interior skin....it would be easy to insulate the contact...
cheers
2air'
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03-31-2006, 09:07 PM
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#6
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4 Rivet Member
1967 30' Sovereign
Leavenworth
, Kansas
Join Date: Jul 2004
Posts: 382
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Specifics...
Application - 1/4 stainless steel bolts in exterior door hinge....
__________________
Beth and/or David
67 Sovereign, double bed, rear bath-"Moby"
2005 Dodge Ram 2500 Hemi, Quad Cab-"Ahab"
"Vintage trailer, vintage owners"
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03-31-2006, 09:09 PM
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#7
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2 Rivet Member
1971 25' Tradewind
Boulder
, CO
Join Date: Jan 2006
Posts: 26
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Corosion
Beth-
Al and stainless steal will react over time. In the presents of salt water (or any electrolyte) a galvanic cell will form with Al acting as the anode and suffer from accelerated corrosion. The corrosion rate is strongly influenced by surface area ratios and the amount of oxygen diffusion in the electrolyte as well as the difference in potential between the metals. I don’t remember all the details, but I think this is best shown with the Tafel equation…I’ll post an update after I find my notes…and find the values…
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03-31-2006, 09:11 PM
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#8
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Rivet Master
Join Date: Dec 2002
Posts: 1,335
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One fact that can confuse this matter is that just about every modern production sailboat has an aluminum mast and boom, with stainless steel fittings (tangs for shrouds and stays, gooseneck, crosstree fittings,etc), attached with stainless steel rivets and screws, so why don't they fall apart in the salt spray??
Well, for one thing, the aluminum extrusions are anodized, which coats the outside of the extrusions with a very hard layer of aluminium oxide, and this acts to prevent further corrosion. In addition, between the stainless steel and aluminum, it is good practice to place an electrical insulator such as zinc chromate paste or a gasket, and to dip the fastenings in the paste. The 32 foot aluminum mast on my sea-going yacht shows no visible corrosion, 30 years after I built it.
If we filled a deep swimming pool with the right electrolyte we could anodize a complete Airstream body shell......
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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03-31-2006, 09:20 PM
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#9
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4 Rivet Member
1967 30' Sovereign
Leavenworth
, Kansas
Join Date: Jul 2004
Posts: 382
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Quote:
Originally Posted by JoshuaTonbo
Beth-
Al and stainless steal will react over time. In the presents of salt water (or any electrolyte) a galvanic cell will form with Al acting as the anode and suffer from accelerated corrosion. The corrosion rate is strongly influenced by surface area ratios and the amount of oxygen diffusion in the electrolyte as well as the difference in potential between the metals. I don’t remember all the details, but I think this is best shown with the Tafel equation…I’ll post an update after I find my notes…and find the values…
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All I want to know is should I use stainless steel bolts in an alum. hinge. If not maybe plated bolts?
David
__________________
Beth and/or David
67 Sovereign, double bed, rear bath-"Moby"
2005 Dodge Ram 2500 Hemi, Quad Cab-"Ahab"
"Vintage trailer, vintage owners"
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03-31-2006, 09:23 PM
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#10
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Rivet Master
Join Date: Dec 2002
Posts: 1,335
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Use stainless steel bolts, with a rubber gasket between the skin and the hinge, and coat the shank of the bolts with zinc chromate paste, or dielectric grease, or similar. Fibre washers would be good.You'll be fine.
Nick
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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03-31-2006, 11:24 PM
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#11
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Rivet Master
1973 23' Safari
1977 23' Safari
2018 25' Flying Cloud
Palmer Lake
, Colorado
Join Date: Oct 2005
Posts: 4,092
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Quote:
Originally Posted by silver 67
All I want to know is should I use stainless steel bolts in an alum. hinge. If not maybe plated bolts? David
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the plea of a craftsman who didn't want to build the watch, he just wanted to know what time it was... OK, OK, I'm an engineer, too, but I never miss the humor (if I'm not the one doing the dispensing....).
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04-01-2006, 08:49 AM
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#12
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Retired Moderator
1992 29' Excella
madison
, Wisconsin
Join Date: Aug 2002
Posts: 4,644
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Quote:
Originally Posted by silver 67
Both of us having long forgotten all science/chemistry that we ever knew, have a question........... will stainless steel chemically react over time with aluminum?
Inquiring minds want to know
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with much respect to the sailboat crowd, the answer is NO, not in your lifetime.
at the power company we deal with 3 types of metal for line hardware and conductors.
copper, aluminum and stainless.
i have removed stainless bolts that have been in direct contact with aluminum for over 50 years. no corrosion, no problems.
i think they will hold your door on for how ever long you want with no problems.
john
__________________
you call them ferrets, i call them weasels.
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04-01-2006, 09:11 AM
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#13
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Rivet Master
Join Date: Dec 2002
Posts: 1,335
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John, my supporting reference for this is Wikepedia :
Galvanic corrosion
Galvanic corrosion occurs when a galvanic cell is formed between two dissimilar metals. The resulting electrochemical potential then leads to formation of an electric current that leads to electrolytic dissolving of the less noble material. This effect can be prevented by electrical insulation of the materials, eg. by using rubber or plastic sleeves or washers, keeping the parts dry so there is no electrolyte to form the cell, or keeping the size of the less-noble material significantly larger than the more noble ones (eg. stainless-steel bolts in an aluminum block won't cause corrosion, but aluminum rivets on stainless steel sheet would rapidly corrode.
[ edit]
The whole encyclopedia entry for stainless steel is at:
http://en.wikipedia.org/wiki/Stainless_steel
This accords with my own experience and understanding of this complex subject, particularly with respect to the different grades of stainless steel, the presence of oxygen, and the relative sizes of the dissimilar metals, as Don said earlier.
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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04-01-2006, 09:19 AM
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#14
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Retired Moderator
1992 29' Excella
madison
, Wisconsin
Join Date: Aug 2002
Posts: 4,644
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nick
i don't disagree at all!
i would venture to guess the hardware i use at work is very high grade and non magnetic. therefore the lack of problems.
for trailer use i have replaced all of the zinc plated screws on vents, clips and lights that were rusted with stainless. with no ill effect so far.
the stainless fasteners i buy from ace hardware are non magnetic as well. i know because my handy dandy pick up tool won't grab them when they roll under my workbench!
john
__________________
you call them ferrets, i call them weasels.
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04-01-2006, 09:22 AM
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#15
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Rivet Master
1977 Argosy Minuet 6.0 Metre
1964 26' Overlander
1977 25' Tradewind
Eastern
, Washington
Join Date: Jan 2004
Posts: 865
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Quote:
Originally Posted by john hd
with much respect to the sailboat crowd, the answer is NO, not in your lifetime.
at the power company we deal with 3 types of metal for line hardware and conductors.
copper, aluminum and stainless.
i have removed stainless bolts that have been in direct contact with aluminum for over 50 years. no corrosion, no problems.
i think they will hold your door on for how ever long you want with no problems.
john
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I'm with John on this. I have not experienced any problems in 25 years of work on power systems with aluminum and stainless connections. With current flowing at various rates galvanic erosion is a big problem if the connection is made with the wrong materials.
__________________
Peace
Gary
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04-01-2006, 09:30 AM
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#16
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Rivet Master
Join Date: Dec 2002
Posts: 1,335
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Quote:
Originally Posted by john hd
for trailer use i have replaced all of the zinc plated screws on vents, clips and lights that were rusted with stainless. with no ill effect so far.
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J, that's just what I've done. I just fail to understand why Aistream doesn't do this on assembly. The cost difference in bulk buying would be small, and it would be a marketing point to differentiate a "premium" product from SOBs. Some forum members report corrosion from zinc-plated steel screws on virtually new units. In my UK Screwfix catalogue, some sizes of stainless screws were cheaper than plated!
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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04-01-2006, 10:19 AM
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#17
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The Hawk's Lair
1985 34.5' Airstream 345
BACK WOODS
, Minnesota
Join Date: Dec 2002
Posts: 922
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The process you are worried about is called "dissimilar metals corrosion"! The Military worries about this a great deal on aircraft and they handle it by coating between the metals with "zinc chromate". As used by the military it is a yellow color, but I think you can find it in other colors.
Yes, it can become an issue over very few years. It has nothing to do with the Galvanic Process. No current need be present to cause it.
We once rebuilt an aircraft and prior to painting it OD, we painted it with zinc chromate undercoat and flew it around a while. Looked wierd.
__________________
AKA THE GUNNER
There is no "I" in the word "team," but there are four in "Platitude Quoting Idiot!"
AIRSTREAM 345 TURBO-DIESEL
VFW, LEGION, NRA
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04-01-2006, 10:49 AM
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#18
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Rivet Master
Join Date: Dec 2002
Posts: 1,335
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[quote=cooperhawk]The process you are worried about is called "dissimilar metals corrosion"! The Military worries about this a great deal on aircraft.Yes, it can become an issue over very few years. It has nothing to do with the Galvanic Process.quote]
My humble understanding is that these are two names for the same phenomenon. With respect to airframe corrosion, this is described at http://www.avweb.com/news/columns/189857-1.html
"Another kind of airframe corrosion occurs where dissimilar metals come into contact -- for example, where steel screws are used to fasten aluminum parts, or where a stainless steel firewall is riveted to aluminum structural members. This is known as "galvanic corrosion" or "dissimilar-metals corrosion." "
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
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04-01-2006, 10:59 AM
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#19
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Rivet Master
2003 22' International CCD
Kiln
, Mississippi
Join Date: Dec 2005
Posts: 2,779
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Quote:
Originally Posted by john hd
nick
the stainless fasteners i buy from ace hardware are non magnetic as well. i know because my handy dandy pick up tool won't grab them when they roll under my workbench!
john
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Sorry, but Stainless Steel is never magnetic - all types and grades. The magnetic properties of a metal have nothing to do with the di-electric corrosion between alumnium and stainless steel. It's the electric current produced between two different metals that are in direct contact with each other.
__________________
Michael & Tina with Layla and Preston BZ The family has grown. 2003 22' INTERNATIONAL CCD
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04-01-2006, 11:09 AM
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#20
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Rivet Master
, Minnesota
Join Date: Aug 2003
Posts: 7,721
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Quote:
Originally Posted by clancy_boy
Sorry, but Stainless Steel is never magnetic - all types and grades.
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The martensitic grades are magnetic.
The magnetic properties are a result of the amount of nickel in the alloy, and therefore are related to the corrsion properties.
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