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topic 41658

Galvanize (Hot Dipped) vs. Galvaneal vs. E-coat ... Corrosion Prevention

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A discussion started in 2006 but continuing through 2019

2006

Q. Galvanize, galvanneal, or e-coating? I am making some trailers for boats and other uses. I live by the coast and want to put a protective coating on the axle and frame from the salty air. I know that galvanizing is the common practice but I want to know why the other practices are inferior. Cost wise; which is cheaper? What are the disadvantages to some and in turn advantages to others?

Erwin Hernaez
Entrepreneur - Port Arthur, Texas


2006

A. Hi Erwin. Galvanneal isn't radically different than galvanizing -- the galvanized coating is just annealed to cause a diffusion of zinc and iron, with the result that the surface is more amenable to painting. So, if the item is to be subsequently painted, galvannealing is a good idea; if not, then just galvanize it.

In any event, galvanizing means applying a heavy coating of zinc, which gives sacrificial galvanic protection. E-coating or other organic coatings don't offer sacrificial protection; so if the coating is scratched there is little corrosion resistance. E-coating can be a good finish, but probably not for a salt-water trailer.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



April 8, 2010

Q. I work for a coil steel supplier. I have a customer that is asking if they can use galvanneal instead of electrogalvanized steel.

The end use is for a mounting bracket. For what? I do not know.

What would be the pro's and con's of substituting the galvanneal for the electrogalvanized?

Thank you in advance for any help!

Terri Sommers
Coil Steel Supplier - Fraser, Michigan, USA


April 9, 2010

Hi, Terry. Not trying to be difficult, but you & I are NOT in a position to make a design recommendation when we don't know the use of the item. Trying to list the advantages & disadvantages of something out of context requires a hundred ifs ands & buts, each of which can be misleading, and we can easily miss the most important one for the actual situation. If I'm not sure where I'll be going yet, can you list the pros & cons of driving vs. walking? :-)

Galvanneal is annealed galvanizing. It is ugly, and it is intended to be painted, but once painted is probably more corrosion resistant than zinc electroplated steel. If the bracket will not be painted, galvanneal probably cannot be used. If there is any sort of grounding requirement, galvanneal probably cannot be used. If there are tight tolerances, or threaded areas, galvanneal can probably not be used.

Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



August 9, 2019

Q. Hi,

I have customer who is asking for e-coating paint on equipment that we are selling.

Is there a problem to e-coat galvannealed metal? And if we do so, what the coincidence would be? And how this can be fixed?

Do we really need to e-coat galvannealed metal, or is powder coating good enough?

Most probably the equipment are going to be used in Microwave accessible environment. Does Microwave cause any issue on powder coat paint?

Hootan Goudarzi
Sigma Corporation - Mississauga, Ontario, Canada


August 2019

A. Hi Hootan. Automobile manufacturers feel that galvanneal PLUS e-coat PLUS painting is required, whereas manufacturers of patio and garden equipment feel that e-coat plus powder coating is more than adequate without need for galvannealing.

Many people feel that the biggest problem with powder coating alone is that a pinhole or poor coverage means no protection at all, and that either galvannealing or e-coating will address that problem -- so for most situations I'd probably accept that galvannealing followed by powder coating is a very good finish.

"Handbook of Electropainting Technology"
by W. Machu
from Abe Books
or
Amazon

Per Manchu (and auto industry experience), it seems that galvanneal can be reliably e-coated after proper phosphatization.

Sorry, I have no knowledge of the effect of microwaves on any coating.

Regards,

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



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