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topic 19766 p.2

Galvanic Action between Galvanized and Stainless Steel?



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A discussion started in 2001 but continuing through 2019

July 16, 2013

Q. Can I use stainless steel bolt on a grouted and threaded hole on a galvanised frame?

Abayomi Owoeye
- Lagos, Nigeria



May 29, 2015

Q. I'm installing 308 stainless steel rectangular ductwork. Hung on stainless steel unistrut. Using 1/2" Galvanized all thread and hardware that passes through piloted holes in the stainless steel unistrut. Should I worry about electrolysis or corrosion at all?

joseph buelna
Limbach - Rancho cucamonga, california, USA


June 2015

Hi Joseph. If the installation is inside and in a dry area, probably not -- you can't have galvanic corrosion without moisture.

But the question always involves the issue of the seriousness of error or miscalculation, because the fact is that the stainless steel and galvanizing are not galvanically compatible. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



June 1, 2015

Q. Hi

We are working on concrete piles that support timber bearers. We use a stainless steel cable through the concrete pile and galvanised staples to tension the cable onto treated timber. Is there likely to be any corrosion between the two metals?

Many thanks

Paul Cochrane
- Christchurch, New Zealand


June 2015

A. Hi Paul. Corrosion issues are of course complex. But if the cathode area is very large (the stainless cable) and the anode area is small (the staples), that accentuates the seriousness of the corrosion. Another factor is the copper in the pressure treated wood, which is also highly corrosive to the zinc of the galvanizing, and to the steel after the galvanizing is gone. These factors have to be added to a consideration of the environment (wetness and saltiness) and a consideration of the seriousness of failure.

I don't know whether stainless steel staples are available, but if they are, that's probably what I'd be looking into. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



Stainless hardware on stainless cabinet is rusting

July 9, 2015

I have an exterior stainless steel cabinet that was assembled with stainless steel screws, washers & nuts. I am seeing a lot of rust on the assembly hardware. The manufacturer said:

"The corrosion that you refer to is the result of having stainless steel hardware making direct contact with the stainless steel cabinet. Two like metals, especially is a corrosive environment like next to the ocean, is going to result in corrosion. We cannot change that scientific reality."

This doesn't sound right to me.

Don Roney
- Panama City Beach, Florida USA


July 2015

A. Hi. It doesn't sound right to you, and it sounds completely ridiculous to me :-)

Probably the cabinet was passivated and the hardware was not, or the cabinet is of a higher grade of stainless than the assembly hardware.

By installing the hardware with steel tools, it has perhaps lost its passivation. You could either try to repassivate with a citric acid based passivation solution, or try to research if the hardware and cabinet are the same grade. I would guess that the cabinet is 316SS and the hardware is 303SS. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


July 28, 2015

A. Stainless Steel is rusting. No!! That can't happen. Worst name ever for any alloy. CRES (Corrosion REsistant Steel) is a much better name. No metal, under the right conditions, is corrosion proof. Not even Gold.
I think you got it right Ted. Dissimilar alloys in a salt air environment would be the right conditions. Especially after low alloy steel tools were used to assemble the cabinets.

Tim Hamlett
Tim Hamlett, CEF
aerospace metals distributor - Tamarac, Florida, USA



November 2, 2015

Q. Hi,

I am laying a wooden deck on a concrete slab. The frame for the decking is made of galvanized square tube. I am about to attach the wooden boards to the galvanized square tube. I was going to use galvanized screws to avoid corrosion issues. But the stainless steel ones look a much nicer finish. I'm not sure if the ratio's would allow it, but if anyone has any thoughts about drilling in SS screws I'd be interested to hear. The SS screw heads wont touch the gal as they will touch the wood. It's just the screws shafts which are about 4 to 5 mm wide. The galvanized square tube has a wall thickness of about 2 to 2.5 mm.

Thanks for any help!!

al suthy
- Sydney Australia


November 2015

A. Hi Al. I think the stainless screws are the best answer for this situation. Their surface area is small compared to the surface area of the galvanized tubing.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



May 13, 2016

Q. I am installing composite deck boards as a backing to a raised flower bed. I need to span 86' and plan to use tie plates to connect the sections. I was planning to use stainless screws and plates. If I have trouble finding stainless plates, can I use stainless screws with galvanized plates without a corrosion reaction between the two?

Eileen Hall
- Oak Lawn, Illinois, USA


May 2016

A. Hi Eileen. If stainless plates are unavailable or too expensive, you should probably switch to galvanized fasteners for the galvanized plates.

Realistically though, it's probably not a big deal if you already have the stainless screws because, although the galvanizing will corrode to protect the screws, the screws are presumably small compared to the plates.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



April 5, 2017

Q. in our project, we are using SS316L pipes for fire fighting services. and to support this pipes we are suspending with GI clamps.

To avoid di-electric reactions, Do I need to place Rubber Lining in between GI Clamps & Stainless steel pipe.??? or there will be no any di-electric reactions between these two metals...???

please support with your answers.

SHAJAHAN KHADER
- SAUDI ARABIA


April 2017

A. Hi Shajahan. It doesn't sound like a good idea to skip the "rubber lining". The surface area of the pipe is much greater than the hangers, so the galvanizing will probably corrode away quickly if there is any conductive moisture. Also, see the comments regarding zinc embrittlement of stainless steel. It doesn't sound difficult to insulate between the pipe and the hangers though.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



SS Trailer Cladding on Galvanized Frame?

June 22, 2017

Q. Afternoon.
I am currently building a food trailer. The floor and superstructure is out of 1.6 mm galvanised sheet metal and the cladding I want to use is 0.7 mm 430 or 304 SS. The galv. uprights are 90 mm wide and the cladding is 1100 mm x 2000 mm. Reading posts on this forum it looks like this is a bad idea given that I also live at the coast. The other option is to use 0.8 mm Chromadek, but I would prefer to use the SS if at all possible. Any advice other than the obvious and use Chromadek.

Steven Hogg
Product Designer - Port Elizabeth South Africa

----
Ed. note: Chromadek is apparently hot-dip galvanized sheeting with a primer and top coat.




June 8, 2018

Q. I have stainless steel connected to a galvanized piece that is powder coated. Do I still need to worry about corrosion? This is an outdoor structure on a bridge.

John Haenny
Chicago Ornamental Iron - Chicago Illinois USA


June 2018

A. Hi John. Ideally, there shouldn't be a metallic connection between dissimilar metals, and that would solve the problem. But if that isn't possible, then it becomes a question of the severity of the overall circumstances.

- On the negative side is that frequent wetness, and corrosive and ionically conductive de-icers are probably to be expected on a bridge.
- On the positive side is that stainless steel tends to not carry high galvanic currents because its chromic oxide skin isn't conductive, and powder coated materials, except where they are scratched or broken, won't carry any.
- The unknown factors for me are the area of the stainless compared to the galvanized area (if low, then galvanic currents corroding the powder coated and galvanized surface are minimized), and the criticality of corrosion (is the bridge structure at risk, or is there any other realistic threat to life?)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



January 30, 2019

Q. Our condo on the FL Gulf Coast will be replacing the fabric awnings on the top floor of our garage after 19 years. While we do this, we want to replace some or all of the rusted bolts holding the galvanized steel frame together. It would seem hot dip galvanized bolts and nuts would be the best fit [no pun intended] but the fabricator quoting the job is specifying 304 SS because he says the zinc coating spalls off quickly and the bolts rust.
Reading the literature, SS bolts would seem okay since they are small compared to the anodic galv framework but they cost much more. And then, some say it should be 316, not 304.

Open to suggestions.
Dave

david_landsperger
David Landsperger
- Sarasota, Florida, USA


February 2019

A. Hi David. Although I acknowledge that plating & galvanizing can peel if poorly done, I've personally never witnessed the galvanizing flaking or spalling off a nut or bolt in the field in my own experience. Hopefully someone who galvanizes such hardware will reply with some statistics or inside info. Yes, passivated 316SS is ideal, but if a little surface rust/discoloration isn't a big issue, 304 will probably do.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



19766-2
March 19, 2019

Q. Hi, I am repairing a bulkhead on the NC coast and have galvanized tie backs to the deadmen. I was planning on using 316 Ogee washers and bolts, but this does not appear to be such a good idea. Some will below water level at high tide and some will not.

What do you think?

Thanks,

Steve McManimen
- Charlotte, North Carolina USA


March 2019

A. Hi Steve. I'm just the site curator with some limited personal experience in a few topics, not a bulkhead builder. But my experience with my own bulkhead and deck on a salt water lagoon is that the new pressure treated wood (ACQ) is so corrosive to zinc and steel due to its high copper content, that any additional corrosive effect caused by stainless steel is strictly roundoff error and not to be fretted over :-)

But you may find that your stainless nuts won't fit galvanized threads, which are much bigger to allow for the galvanizing thickness.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



April 3, 2019

A. We have G90 coated steel framing an exterior ceiling on a barrier island coast of Florida. Very humid. Would it be acceptable to hang a sheet product using stainless steel drywall screws? This will also be stuccoed.

John Snow
- Jupiter Island, Florida


April 2019

A. Hi John. I see some concerns expressed above regarding issues like "liquid embrittlement" and explosion hazard" which I am unfamiliar with but which sound exaggerated or remote for your particular situation, but you might check building codes to see if there is any prohibition of stainless fasteners with galvanized ceilings. I think galvanized or at least zinc plated or painted drywall screws would be a better idea.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



May 23, 2019

Q. I want to install stainless steel 316 flat sheet to side of gal purlin in swimming pool environment, fixed with class 5 screws any issues ?

Martin Richards
Roofing - Melbourne Vic Australia


June 20, 2019

A. Yes there are issues in using dis-similar metals in contact with each other in such an environment.
You could use insulating washers to insulate the dis-similar metals. The issue isn't proximity, but contact as in electrical contact. Isolate them from each other (plastic washers or similar) and the problem is avoided.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland




June 20, 2019

Q. I'm building a rolling keg cooler. I have a 3/4" stainless steel rod that I was going to use as the axle. My plan has been to run it through 3/4" galvanized standard pipe that is mounted to the bottom of the cooler. Loaded, the cooler will be fairly heavy. I intend to use it occasionally outside, sometimes at the beach. Mostly it will be stored in my garage. Will the stainless rod in the galvanized pipe cause an issue? If so, what would be a good remedy? Thank you!

David McCully
- Orangeburg, South Carolina, U.S.A.


June 24, 2019

A. It is possible to double dip your product to get a thicker coating of galvanization for a little more protection against corrosion.

Zara Lou
- Bradford,Yorkshire


June 26, 2019

A. For this purpose I would not worry about the issue. When you use your carriage on the beach, wash it with fresh water when you get home to reduce the salt.
In theory the SS rod inside the galv pipe will be a dissimilar metals galvanic corrosion issue, but probably not any more noticeable than the wear of a dry axle than is worth worrying about.
You could put in a grease nipple and add some grease!

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland




Stainless steel fasteners on galvanized deck

September 23, 2019

Q. Would there be any concern about using stainless steel screws with sealing washers to fasten a 20 ga. galvanized metal deck to painted structural steel members? We have this situation on a truck canopy that is being built. There is no roofing over the metal deck - the deck and structural steel members are sloped.

Edmond Thayer
- Oak Ridge, Tennessee USA


September 2019

A. Hi Edmond. Galvanized screws seem like a much better idea -- is there a reason you can't use galvanized fasteners? If you can't, is there a reason you can't use insulating bushings along with washers to prevent galvanized surfaces from contacting stainless ones? Between the potential for galvanic corrosion and the dangers in fire situations that Alabbasi mentions, stainless screws contacting galvanized decking sounds troublesome.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


September 23, 2019

thumbs up sign  Thanks for the quick response! You confirmed our thoughts.

Edmond Thayer [returning]
- Oak Ridge, Tennessee USA

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