Stainless Steel Grid Deck on Galvanized Stringers
Stainless Steel Grid Deck on Galvanized Stringers
(OP)
Somehow I've gotten sucked into a construction problem:
A walkway over a salt water river. The deck is 1-3/4" thick stainless steel open grating supported on galvanized stringers. The question of galvanic corrosion came up after the project was bid (the project was bid based on 50% plans; details are worked out as the job progresses).
All of the literature I read suggests this is a poor combination of materials. It's too late to order galvanized decking. One solution is to paint the top of the the stringers to create a barrier. However, the contractor's proposed cost is astronomical (even by Federal bailout standards). My concern is that the paint will deteriorate over time and there will be no way to reapply a coating without dismantling the deck, railings, and light poles.
One alternative was to install neoprene sheeting in lieu of painting but the architect said no way.
My question: Is it possible to install some type of cathodic protection system? Is the concern about corrosion overblown? Should we just put the stainless in contact with the galvanizing?
Thanks for your opinions.
A walkway over a salt water river. The deck is 1-3/4" thick stainless steel open grating supported on galvanized stringers. The question of galvanic corrosion came up after the project was bid (the project was bid based on 50% plans; details are worked out as the job progresses).
All of the literature I read suggests this is a poor combination of materials. It's too late to order galvanized decking. One solution is to paint the top of the the stringers to create a barrier. However, the contractor's proposed cost is astronomical (even by Federal bailout standards). My concern is that the paint will deteriorate over time and there will be no way to reapply a coating without dismantling the deck, railings, and light poles.
One alternative was to install neoprene sheeting in lieu of painting but the architect said no way.
My question: Is it possible to install some type of cathodic protection system? Is the concern about corrosion overblown? Should we just put the stainless in contact with the galvanizing?
Thanks for your opinions.





RE: Stainless Steel Grid Deck on Galvanized Stringers
Cheers,
gr2vessels
RE: Stainless Steel Grid Deck on Galvanized Stringers
Separate from the design details, rinsing the walkway periodically with tap water may be helpful to keep any salt from accumulating in the crevices, etc. Some times a small amount of maintenance like this can improve an otherwise undesirable situation.
RE: Stainless Steel Grid Deck on Galvanized Stringers
CM
RE: Stainless Steel Grid Deck on Galvanized Stringers
I got sucked into this when someone in the office said "...we got this with bridge with metal decking and the contractor want to know how to put it in over the splice plates, any ideas?" The plans showed a typical splice for a stringer - top and bottom plate on each flange. Anyway, we changed the top splice plate to a longer thicker plate with countersunk holes, that's when I open big mouth about dissimilar metals.
We proposed sheet neoprene - the landscape architect didn't want it - "unsightly!" We suggested painiting the top flange. I'm not crazy about the idea or painting and galvanizing. Do you think it would be worth it to consult a metallurgist to determine a corrosion rate?
RE: Stainless Steel Grid Deck on Galvanized Stringers
How much does it rain in this location? A lot of rain would help.
You also need to make sure that the joints can drain. I know that people tend to design stuff square and flat, but any trapped water will be a problem.
isolation and drainage should give you a long service life.
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Plymouth Tube
RE: Stainless Steel Grid Deck on Galvanized Stringers
If corrosion is a concern, wouldn't the best cost option be to go fully galvanised? That'd remove the dissimilar metal problem.
I'm also a bit uncomfortable about the stainless in a salt environment. Any high residual stress areas (welding, cold working etc) could become susceptible to cracking if chlorides concentrate up.
The talk of crevices and saltwater doesn't bode well either - even for a galvanised design.
Any rate, eventually the stringers will corrode in isolated locations and that will be unsightly. If the stainless' Chromium oxide layer stays intact, then it will drive CS corrosion if an electrolyte exists.
I think the CP/IP system you'd need would be fairly expensive and complicated (and unsighly) to ensure decent cover.
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RE: Stainless Steel Grid Deck on Galvanized Stringers
RE: Stainless Steel Grid Deck on Galvanized Stringers
If so then use plastic spacer blocks and make sure that it can drain. NO TRAPPED WATER is the key.
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Plymouth Tube
RE: Stainless Steel Grid Deck on Galvanized Stringers