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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Galvanic problem: High carbon steel with stainless steel?
My question is I have SA-789 / 2205 Duplex Stainless Steel tubes 2.50 OD x .120 wall thickness going into a Carbon steel 1" thick tube sheet do you see any issues between the two metals
Charlie Lorusso- Illinois
December 9, 2021
⇩ Related postings, oldest first ⇩
Q. I was told that stainless steel rods and clamps that we use are susceptible to oxidation when they are in contact with a high carbon steel. The person stated that the contact would draw the carbon to the surface. There by allowing the oxidation process to happen. now I'm of the assumption that the rods and sheet metal clamps are not just coated but are stainless, although I don't know the level of stainless. I just thought that the whole thing sounded strange considering the fact that he compared the strength and hardness of brass and stainless to be similar. I hope I'm clear enough.
Thanks for any opinions or factual info you can give me.
Mark A. BlairCity of guelph/ Water dept. - Kitchener, Ont., Canada
2003
A. Mark, it's kind of like leaving a wet steel wool pad on your stainless steel sink- you'll get a galvanic reaction (small battery forming) and the chromium oxide layer which gives stainless steel its corrosion resistance will be compromised. The stainless steel sink will rust where the steel wool pad touches it.
So, yes, leaving stainless steel in contact with high carbon (non-stainless) steel can cause the stainless to corrode (although not by drawing carbon to the surface- your informant is likely confusing galvanic corrosion with sensitization, but that's another long-winded explanation). It's pretty simple to correct the potential problem, by electrically isolating the two metals (nylon washers for fasteners, etc) or plating the carbon steel part. Or just keeping it dry, like by painting the joint, if your paint is good enough.
There's a US Military Standard, MIL-STD-889, which has some useful information on the topic. It's available for free at http://assist2.daps.dla.mil/quicksearch/^quicksearch.dla.mil
Stainless steel is not necessarily very strong- many of the 18-8 grades are similar to many brasses and bronzes in terms of strength. The cutlery grades of stainless, also called the martensitic grades, are quite strong. Try to download a copy of Technical Publication 9014, "Design Guidelines for the Selection and Use of Stainless Steel" from the Nickel Development Institute, at www.nidi.org^www.nickelinstitute.org
It's well worth the time to find and read. If you can't download it, give them a call in Toronto- they've been kind enough to mail out copies for me.
Good luck!
Lee Gearhart
metallurgist - E. Aurora, New York
2003
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Ed. note: URLs updated June 2013
Q. I am replacing an old carbon steel drive shaft that had a 400 series stainless wear sleeve. Is it a good idea to keep the existing material selection? I was concerned about reaction between the different metals, in fact the existing carbon steel shaft is heavily rusted.
Jay Craddock- Ontario, Canada
June 13, 2013
June 21, 2013
A. Jay,
My instinct here is that for a mechanically critical component like that, the original material selection should be honored. You wouldn't want to switch to something that might not stand up to the stresses it will encounter during use. The wear sleeve you probably have some leeway with, although I somewhat doubt that contact between carbon steel and 400 grade stainless causes the carbon steel to rust any faster than it would anyway in given environmental conditions.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
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