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Stainless Steel vs. Galvanized vs. Zinc Plated Fasteners




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A discussion started in 2002 and continuing through 2017 . . .

October 29, 2014

Q. Which is the most suitable product (S.S. or Zinc plated ) to fasten galvanized metal (20 ga. z-bars) onto a concrete surface.

Brian Mcgee
- Toronto Canada


Hot Dip Galvanizing

November 2014

A. Hi Brian. Best fasteners would be hot dip galvanized if the z-bars are actually hot dip galvanized (I doubt it since the z-bars are only 20 ga.); or zinc plated fasteners if the z-bars are actually just zinc plated (electrogalvanized).

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 23, 2014

Q. Hi,

I'm having issues with the threaded inserts used in some of the plastic components on my motorcycle. The threaded insert appears to be made of Brass and has a hexagonal outer profile. This type of insert is set into the plastic of the air box, fuel tank and some other locations.

The problem seems to be that the bolts are corroding (or in some other way seizing) to the brass insert. When one tries to undo the the bolt from the threaded insert, there is sufficient friction between the mating threads to instead turn the threaded insert inside the plastic housing, preventing the bolt(s) from being removed.

I'm not sure what the current bolts are made from, but it appears to be a some variety of stainless steel. Can you suggest any bolt materials that I might use to prevent this issue?

Note: These particular bolts are not structural or load bearing, just holding on various lightweight plastic bits and pieces.

Kris Hampel
- Sydney, NSW, Australia


November 2014

A. Hi Kris. Before attempting to remove bolts, you should apply WD-40 to the area and tap it to try to vibrate it into the joint, then let it sit for an hour or so. It makes a big difference. When you re-assemble, use some teflon thread sealant. If it's a poor design for a corrosive situation, I think you just want to minimize the problems it causes you, rather than trying a re-design for less corrosion and galvanic issues :-)

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 24, 2014

Good advise from Ted. A dab of anti-seize when reinstalling is a good idea. Plain old Vaseline will do the job.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg,
      South Carolina




December 30, 2014

Q. We are assembling a green house frame (used) and trying to decide whether to use zinc plated bolts or to go the higher $ for the galvanized. If I correctly understand some of the above conversation, it is technically the same material, but the galvanized is hot dipped and thicker vs. (application type) and a thinner coating. So, the zinc plated might last ... how long? Versus almost indefinite on the hot dipped??

Around here it is approximately double the price for the galvanized, and we are on a tight budget -- so just trying to decide if the zinc would get us going for at least a couple years. . .?

Rachael Hallgarth
Produce Grower - Henryetta, Oklahoma, USA


December 2014

A. Hi Rachel. Yes, zinc plating is galvanically similar to galvanizing but thinner. I think the zinc plating will last at least several years in your non-seaside environment (but don't let pressure treated wood be in contact with it).

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



March 27, 2015

Q. Hello: we are designing a 28,000 sf pet adoption facility in the Rio Grande valley located in south Texas. We are using a Varco Pruden pre-engineered building. At the front of the building, we will have (3) large 11'-0" high "animal cut-outs" as a design feature. These will be etched out of 1/4" thick mill-finish aluminum with a water jet, then powder coated with a white color.

16063-1a  16063-1b  16063-1c

I had a question regarding the fasteners that would attach the cutouts to the 24GA steel Varco Pruden "Tech Four" wall panel and into the cold-formed steel Z-girt. This area is very humid and we need a corrosion resistant fastener that is compatible with the aluminum, powder coating, and the VP PEB. please see the attached 3D renderings and the diagrammatic section sketch. Thanks in advance for your help. We appreciate any assistance you are able to provide.

abbie de leon
boultinghouse simpson gates architects - mcallen, Texas, USA



April 20, 2015

Q. Hi,

I am researching on fastener finishes industry. I am just wondering, besides the process involved, what is the real difference between plating and coating. What are the pros and cons of plating vs. coating.

Would appreciate any explanation or references to this.

Thanks and Regards,
Hitesh

Hitesh Kumar
Financial Services - Mumbai, Maharashtra, India


April 2015

A. Hi Hitesh. Those terms are not specifications and it's hard to put a fine point on slang. "Plating" usually is an abbreviation for electroplating, which is the electrodeposition of a metal coating onto a substrate. But coating is a term with almost no delimitations -- fruit can have a coating of chocolate, a road can have a coating of ice, and a fishing net can have a coating of algae or slime.

Fastener Design Manual

Coatings of metal tend to have better adhesion to metal substrates than paints or plastics do. If a metal plating is anodic to the substrate it can afford it sacrificial protection; if a metal plating is cathodic to the substrate it can accelerate the corrosion if there are scratches or porosity. If there is no abrasion or scratching action, an organic coating like paint will often outlast a metallic coating; if there is abrasion or possibility of scratching, a cathodic metal coating will usually offer more corrosion protection than painting.

High quality organic coatings are probably usually better than plating for wood screws, but often aren't applicable for traditional nut & bolt construction because of clearance issues, vibration, a need for repeated unfastening & refastening or other issues.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Ultimate corrosion resistance finish for custom set screws

May 5, 2015

I am looking for the ultimate corrosion resistant material and/or coating to use for custom setscrews we need for our products.

We have a few scenarios and would like to get a single solution if possible, but understand this may not be ideal.

Scenario 1: We have a setscrew going through an aluminium magnesium alloy casting and fastening against a 6106 T6 aluminium extrusion. A 316 stainless setscrew I would think would be the most corrosion resistant but could cause bimetallic corrosion, with the 6106 aluminium. Is there a coating we can use on the 316 setscrew to form a barrier between the two materials, and if there is, is there a worry about cavity corrosion of the stainless setting in? Or could you advise a better material to use.

Scenario 2: We have a setscrew going through a malleable cast iron casting that has been HDG, and fastening against HDG pipe. Again looking for the most corrosive resistance in the setscrew. Is it ok to put a mechanical galv coating over a stainless setscrew? Or again could you advise a better material or coating to use.

Many Thanks

Steve Thrush
- Melbourne Australia


May 2015

A. Hi Steve. I think I'd use the 316SS for the aluminum situation, although you could perhaps order the set screws to be Ivadized or electroplated with aluminum. For the galvanized situation, I'd probably use galvanized steel setscrews. I don't think it's possible to galvanize stainless steel, but it can be electroplated with zinc if you wish. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 8, 2015

? Will the applications allow the use of nylon set screws?
Regards,
Bill

William Doherty
Trainer - Newcastle, NSW Australia


May 10, 2015

Q. Hello Bill, I am interested in your comment on Nylon setscrews. The setscrew is a M12 x 1.75 thread x has to reach and maintain a 30kN holding force. Is there a nylon out there that can do this without stripping the thread or the drive?
Regards
Steve

Steve Thrush
- Melbourne, Australia


May 19, 2015

A. Hi Mate,
I do not have to hand the mechanical properties of nylon fasteners.
Your first point of reference could possibly be a Blackwoods catalogue to identify Aussie manufacturers?
Regards,
Bill

William Doherty
Trainer - Newcastle, NSW Australia



Fasteners for Powder Coated Aluminum

May 27, 2015

Q. Hello,

We are contracting to provide and install a powder coated aluminum railing system constructed with 6061 T 6 aluminum. The designers call out 1/2 Stainless Steel anchors for the base plate connections [and require a bituminous paint on concrete to base plate interface]. They have omitted the fastener call out for the connection between railing panel sections. We have proposed using a 3/8" HDG A307 bolt to connect the railing sections. The application is an outdoor environment next to a busy road along a sidewalk. Each panel has 3 horizontal rails that will connect with a through bolt to a welded aluminum clip on the next post. All aluminum will be powder coated [approximately 6-7 mils]. Is our proposal for the HDG A307 bolts the best choice or will we be better offering stainless steel for the connection bolts?

Thank you in advance.

Jim King
fabricator - Tacoma Washington USA


May 2015

A. Hi Jim. I doubt that it's critical, and suspect that galvanized bolts would be okay, but stainless just sounds like a nicer idea, especially considering that the system is going to have some stainless fasteners anyway.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 29, 2015

A. Mr. Jim King, according to Mr. Mooney hot dip galvanising is okay, but further a 5% H3PO4 dilute coating shall convert zinc into zinc phosphate coating, which has a long shelf life in mud & rough environment.

chennamallu prakasham
consultancy of ep&mf - chennai, tamilnadu, south india



June 4, 2015

Q. Great thread! Question for you experts: I have a custom-made aluminum (alloy of some type I'm sure) door to hand on an outdoor shower. The door weighs ~17 lbs, so I'll need some hefty through-bolts & hinges. Would stainless be the best choice for the hinges and bolts?

Sounds like 'yes' from the previous discussion above, but I see that stainless is quite far from Al on the galvanic chart. Wondering if I should put some rubber or plastic barrier between the Al and mounting h/w wherever possible....
Any suggestions or comments would be much appreciated. Thanks!!

Chris Reynolds
- Ormond Beach, Florida, USA


June 2015

A. Hi Chris. Insulation is always a good idea because if there is no metallic path between the two metals to convey the electrons from one to the other, there can be no true galvanic corrosion. The more common question is whether it is necessary when it isn't easy and practical :-)

Stainless steel fasteners are a commonplace on aluminum and experience seems to show that it's not much of a problem for non-critical applications like shower doors. Galvanic accelerated corrosion is not the only corrosion through. Even anodized aluminum sliding shower doors for indoor use, and all-aluminum patio chairs eventually start corroding.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



June 18, 2015

Q. After reading through these threads, this is a comparatively pedestrian and goofy question. I am working on my screen porch. The house is old, 1888, and I never want to have to go back and replace. So, I am searching for stainless steel, flush, screen clips. I can find zinc cast. I can find galvanized. I can find plastic. And I can find stainless steel from a manufacturer in New Zealand! But, given the material and the shipping, they are a FORTUNE!

16063-2a  16063-2b

Are there any manufacturers in the US that make stainless screen clips? I really don't want to use plastic. Metal appeals to me, much more.

Thanks

P Wood
Flush Screen Clips in Stainless - Woodbury, New Jersey USA


September 9, 2015

Q. @ P Wood,

I'm looking for reasonably priced ss restoration screen hardware also -- did you find any?

Thank you,
greg

Greg Robb
- Oakland, California, USA


September 10, 2015

A. I found stainless bolts, nuts, and cap nuts off the internet. I could not find any stainless turn buttons. I found them in nylon and tried them. Unfortunately, they all broke. I ended up settling for zinc plated turn buttons on ebay from the closing of a hardware store in Florida. They work fine, just not exactly what I wanted.

P Wood
- Woodbury, New Jersey USA



Best hardware/screws/fasteners for installation of aluminum roof in wet/humid climate

September 16, 2015

Hello--Installation of what we hope is a long-lasting roof is scheduled for this weekend.

I'd much appreciate any thoughts regarding whether stainless or galvanized screws/fasteners would be best for aluminum standing seam (.032 aluminum Shur-Lok with Durapon 70 coating by HPM Custom Metal Roofing)? This is for our 2,500 sf residence in a wet/humid tropical climate.

Supplier says galvanized would be better than stainless steel--something to do with positions on a galvanic table. I'd just like more opinion from experts on this question about stainless vs. galvanized fasteners for an aluminum roof. I did read on this forum that there's a difference between zinc coating and hot-dipped, with the latter being superior. Any further counsel would be appreciated! Would stainless be better than galvanized for an aluminum roof?

Thank you.

Elton Johnson
N/A - Honolulu, Hawaii USA


September 2015

A. Hi Elton. Theoretically, aluminum screws or aluminum plated screws would be the first choice because they'd be galvanically compatible, but aluminum screws might not be strong enough and aluminum plated are not very available (pretty much restricted to aerospace uses). Second choice traditionally was cadmium plating, but this is toxic and restricted these days to critical applications (if any).

So you are right that your practical choices are hot dip galvanized or stainless steel. Galvanized would be less expensive and probably approximately as good, so that's what I'd probably use for large fasteners as suggested. But if the hardware is smaller than about 1/4", it's probably zinc electroplated rather than hot-dipped even if it says galvanized because the thickness of the zinc plating on a small screw is limited -- so I'd probably use stainless steel.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


September 18, 2015

Many thanks, Ted.

Looking into the possibility that thin nylon washers (or some other material?), on the pancake screws that will secure the aluminum standing seam to the hot dip galvanized clips, might at least help minimize the area of contact between the stainless steel screws and the aluminum.

I'd really value your opinion on the use of such washers for this purpose.

Elton Johnson [returning]
- Honolulu, Hawaii USA


September 2015

Hi Elton. I am no roofing expert and there seem to be variations in these standing seam roofs -- but isn't it the case that the aluminum roofing snaps directly onto galvanized clips, so there is no preventing the dissimilar metal-to-metal contact anyway? Insulating is not always done in the case of dissimilar materials, but it is always recommended. If you have true insulation (no metal-to-metal contact), you can't get galvanic corrosion -- but a washer alone (no bushing/tubing) will not prevent metal-to-metal contact unless the hole is oversized and the screw is centered with no movement.

I'm having a hard time envisioning how you prevent metal to metal contact, and I thought the idea of pancake screws was to prevent an impression in the panel above it, which a washer under the screw head would seem to aggravate. I can talk about galvanic corrosion, but I can't talk knowledgeably about that roof :-)

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



September 17, 2015

Q. Hi,

We are manufacturers of standing seam metal roofing here in Hawaii, and I often get the question of whether it is better to use stainless steel, or galvanized clips and screws with .032 thick aluminum panels, 3105 alloy. The aluminum is coated with a polyester paint backer, and the top surface is a Kynar 500 paint system. The industry standard is stainless steel clips and screws, but on the galvanic chart, it seems like G90 galvanized clips with zinc plated carbon steel screws would be closer in compatibility. The clips typically should not be exposed to moisture since they are concealed under the panels, however, Hawaii is a damp environment to begin with, and improper installation could allow moisture to get under the panels and contact the clips and screws. In this case, I have seen the screw heads corrode through the aluminum panels when using stainless. Any insight you have on this would be very much appreciated, I am always interested in how to give customers the longest lasting roof possible.

Thanks

Andrew Teter
HPM Building Supply - Honolulu, Hawaii, united states of america


October 2015

A. Hi Andrew. If you could get aluminum or aluminized clips, and aluminum plated or aluminized hardware, that would be the ideal solution. Short of that, or cadmium plating which is no longer available due to toxicity, you have galvanic incompatibility whether you choose galvanizing or stainless, and it becomes a matter of avoiding the one which is worse :-(

The thing is, there is far more aluminum area in the roof than galvanizing or stainless steel, so it's generally considered best to make the larger area component the anode, because that way the corrosive current can be diluted over a large area than concentrated on a small area. That's why stainless (cathodic to aluminum) is probably better for small fasteners and clips -- just book knowledge, and would be happy to hear from roofers with contrary experience.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



August 1, 2016

Q. Dealing with the compatibility of metal fasteners against galvanic corrosion such as galvanized steel, zinc plated and stainless steel, which metal fasteners can be used together? Thought I saw a sign in Home Depot that read "Do not use galvanized steel with stainless and zinc" or one or the other. Found out that using zinc plating in marine use is not good. Used one on a stainless swim platform and one on a jet ski port which have rusted bolt heads. Recently bought two galvanized dock cleats and galvanized lag screws so those should be okay. Stainless steel fasteners are not made in bulk. They mostly come in individual packages and limited to certain sizes.

Richard Brooks
- Montgomery, Alabama U.S.A.


August 2016

A. Hi Richard. Galvanizing and zinc plating are essentially the same material on the surface so they are galvanically compatible. But one problem is that zinc plating tends to be rather thin and therefore not suitable for service in an aggressive environment. Hot dip galvanizing tends to be significantly thicker and therefore significantly more suitable. A second problem (which may relate to the Home Depot sign) is that, because galvanized coatings are so heavy, the threads are cut differently and non-galvanized nuts don't fit galvanized screws and vice versa.

But even hot dip galvanized fasteners may not last long in marine service joining stainless parts together. The zinc is sacrificial to the stainless, and the small amount of zinc on a bolt, even if applied as a heavy coating, cannot sacrificially protect a large stainless item for long. If you must use galvanized hardware on stainless steel in a wet and salty environment you really need to isolate the hardware from the joined parts with plastic washers and bushings so there is no metal-to-metal contact.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



September 21, 2016

Q. We use 304 SS fasteners on aluminum hulls. The tapped holes are painted, however the paint cracks when the fasteners are installed.

As a result, two problems occur.

one being the water starts to get underneath the paint in tight area around the fasteners ( this area is deprived of oxygen), which then causes crevice corrosion.

The second issue is due to the paint failing at the threads, causing the stainless steel fastener to come into contact with the aluminum surface which initiates galvanic corrosion.

So now we have aluminum corroding away and paint that is blistering and peeling off.

Can anyone think of a solution to this problem? We are currently considering aluminum fasteners in low load areas, and using an anti corrosive compound to bed the fasteners such as Duralac.

Any thoughts?

Omar Abdulmajid
- Surrey, BC, Canada



October 19, 2016

Q. I am replacing Mild Steel set screws in a cast iron solid fuel stove [ originals so rusted they had to be chiseled out and holes re taped. What material should the new screws be ? coated mild steel - stainless steel - brass / bronze bearing in mind the high temperature and any reactions to the cast iron

David Bailes
- Sligo Ireland



Best finish for fasteners in heavy truck applications, when trucks are acid washed

December 7, 2016

Q. What plating has the best corrosion protection for use in heavy truck applications, where the trucks are periodically acid washed.

Rob Glass
Quality Manager - Columbus, Ohio US


January 17, 2017

A. I've noticed in the on-going discussion of Fasteners and the subsequent prevention of corrosion in all forms one method of coating isn't mentioned that I've noticed.

Zinc Thermal Diffusion.

Although the process has it's roots in Sherardizing historically, there have been developments to diffuse zinc into substrates below the melting point of zinc. Process temp typically around 300 °C.

When combined with passivation, and if necessary a topcoat, performance is well in excess of 1,000 hours of salt spray and also prevents the following:

- Galvanic Corrosion of dissimilar materials
- Hydrogen embrittlement since the process naturally includes a baking element to it.

Performance per dollar ratio against Stainless and other high grade coatings is quite good as well, typically with sufficient economies of scale (i.e., decent volume).

And to be quite honest I am now working for a company that is bringing their technology to North America so I am biased to a degree, but I also have data that supports the above statements.

Ted Tsikhlakis
- Jackson, Missouri, USA


January 2017

thumbs up signHi Ted. Thanks. Yes, thermal diffusion went unmentioned on this thread previously, as did the very popular zinc-rich dip-spin coatings and a number of other technologies. When "acid washing" is involved, as in the most recent posting, we should probably emphasize electroless nickel plating since zinc coatings have no acid resistance. Each technology has disadvantages to go along with their touted advantages, which is why no method has obsoleted the others.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



March 12, 2017

Q. I need to strap plastic barrels onto my cedar swimming raft. What would be the best strapping material? I was thinking of using galvanized metal strapping with galvanized screws.

Joe Happe
- Buffalo Minnesota


March 2017

A. Hi Joe. Galvanized should be okay, but not as good as stainless.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


March 15, 2017

A. Plastic strapping is strong enough for most purposes, doesn't rust, and is less expensive than steel strapping and much, much less expensive than stainless steel.

tom_rochester
Tom Rochester
Plating Systems & Technologies, Inc.  

Jackson, Michigan, USA



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