Stainless versus Carbon Steel in
Construction
Letter 10054
I've been a few different projects as either a Construction
Supervisor, Resident Engineer or Project Engineer and almost always
during the life of a project the question comes up, Is it detrimental
to have stainless steel in contact with carbon steel for the service
life of the contact which could be 20 years or more.
I've been told that stainless steel anchor bolts will cause
premature or accelerated corrosion when used on A36 base plates. I've
seen vendors provide skid mounted equipment with 316 piping isolated
with a rubber pad from the carbon steel supports.
I decided to get on the net to see if I could get my question
answered when I stumbled on this page.
The latest use I've seen of this dissimilar metal has really
piqued my curiosity. The project I'm on now has a proposal to use a
stainless steel, I haven't determined the type or grade yet but it
shines like a mirror, as a shim plate between an A36 steel pier and
an A36 equipment frame.
Is there a problem here for the longevity of this connection? Is
there a rule of thumb to go by to help decide in which situations
this would be acceptable, i.e. stainless with chrome in this range,
17 to 19%, is ok with A36 or A 500 grB. Or is it more simple than
that.
Michael Brown
- Everett, Massachusetts, USA
If the surface area of noble metal (stainless) is small compared
to the surface area of the base metal (steel), galvanic current is
limited by it. Further, the oxide surface of stainless steel is not
highly conductive in most environments. Perhaps for these reasons, my
own experience has been that--even in the very humid and highly
conductive environment of a plating shop--stainless hardware is a
solution, not a problem.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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Hello Michael!
Yes, dissimilar metals in contact can accelerate corrosion of the
more active metal in the pair. Think of it as forming a battery,
which will lead you to the other critical component: the electrolyte.
Having stainless in contact with A36 carbon steel is fine, until some
moisture is also in contact with the joint. So, if you can guarantee
that the joint will always be dry, then there is no problem. If it
can get wet, the carbon steel in the vicinity of the joint will
corrode faster than the surrounding carbon steel.
A nice introduction to the topic is the military standard 889, on
"Dissimilar Metals". It is available free at
http://astimage.daps.dla.mil/quicksearch/, by typing mil-std-889 into
the box.
Good luck!
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Lee Gearhart
metallurgist
East Aurora, NY
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