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Q&As since 1989
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Galvanic compatibility of Stainless steel bolt vs brass nut
Q. I have an application in which I need to assemble an irrigation component with a nut and bolt. We are currently using 316 Stainless steel for both the nut and bolt. My problem is that in a very small number of installations, the bolt is seizing to the nut. I would like to change the material of the nut to brass, but I have a concern about long-term galvanic corrosion between the 316 stainless steel bolt and the brass nut. Can anyone help me find specific information on this subject?
Robert ScifresPlastic irrigation product molder - Brownsville, Tennessee
2003
A. Hi Robert,
If the 'nut' is not buried, what I used to do was to use m.s. bolts and a stainless nut on the premise that they'd never gall and could always be easily undone ... to which I'd add some MoS lubricant on the threads to hopefully reduce any galvanic effect.
This was for large dia. plastic flanges where, obviously, s.s. bolts were quite expensive!
This might not be feasible for you ... but if you use a brass nut (which won't take the torque load of stainless), then at least consider using molybdenum disulfide grease.
Freeman Newton [deceased]
R.I.P. old friend (It is our sad duty to
advise that Freeman passed away 4/21/12)
2003
1/2 lb. Moly Paste Anti-Seize
on
Amazon
(affil links)
A. Anti-seize [on eBay or Amazon] is the answer. It is available thru most industrial catalogues. Freeman's suggestion of using the moly grease will work for stainless on stainless in most situations. It is cheap and certainly worth a trial. I would not use mild steel for your application.
James Watts- Navarre, Florida
2003
A. Use an A286 or 347 nut. The corrosion resistance is excellent, and it won't gall.
Bob Dun- Greensburg, Pennsylvania
August 27, 2008
Brass vs stainless steel for pond drain
Q. My husband ordered a Brass rod to use to cut fittings to hold a bottom drain lid in place in our new pond. The nuts he ordered were stainless steel. (The WLim Drain came with stainless steel fittings but we had to improvise for a stone floor.)
My question is should he go ahead and cut the brass rod and use it with stainless steel nuts or should he return the brass rod and re-order the rod in stainless steel.
The drain is of course submerged - the pond is obviously freshwater.
Pond Builder - Johnson City, New York
2005
A. Hi Carla.
If brass nuts are readily available in that size, I go with all brass.
From my experience as a plumber's helper more than my experience in metal finishing, I doubt that either brass or stainless parts, or any combination, will be a problem. Since you already have the brass, and because it's much easier to cut and machine brass than stainless steel, I wouldn't change the rod.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005
Stainless nuts on high tensile studs in boat bilge
Q. You said "if the nut is not buried". Why would it be any different if it were buried? I am uncertain whether to use stainless nuts on a high tensile stud that is lying in the bilge of a boat? Any advise would be appreciated - I am concerned that a bimetallic reaction could compromise either the stud, or the nut?
Ian Smith- Cape Town, South Africa
January 23, 2011
A. Hi Ian. I can't speak for Freeman, but I think the idea is that "buried" implies "always wet" and "probably electrically conductive" -- two factors that would greatly accentuate galvanic corrosion. Lying in the bilge of a saltwater boat can't be any better; if it's a high tensile stud, I think you should have a high tensile nut of the same material.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Brass grommets connected to stainless screws
Q. I'm installing windscreens around a tennis court. The screens have brass grommets and I would like to use stainless washers and screws to fasten to the wooden posts.
What reaction can I expect to see from the two metals over time?
Thank you,
Eddie.
Owner Upholstery business - Niceville, Florida, USA
January 23, 2013
A. Hi Eddie. Although there are different types of stainless and different grades of brass, they are mostly close to each other in the galvanic series; I don't think I'd expect any significant trouble. But remember that brass will corrode even if not in contact with other metals, so trying to keep it lacquered, or waxed, or lubricated in some fashion is a good idea.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Unrelated to the other solutions, a good resource for compatibility is MIL-STD-889 (dissimilar metals). Provided free of charge from our taxes.
Pay attention to the revision notices, they are relevant to the main document.
- Everett, Washington, USA
March 20, 2013
A. I'VE WORKED FOR A FASTENINGS COMPANY FOR SOME YEARS AND WOULD ADVISE ALSO USING PTFE TAPE AS AN EXTRA 'BARRIER'.
Joe BloggsFastening All - Bristol Avon, Britain
February 5, 2018
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