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Letter 34079
Galvanized vs. electroplated [Bahrain]
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Dear sir,
We have to supply some fabricated structural members along with
fasteners.The client's specification for the fastners says that HM
8.8 BOLTS, NUTS AND WASHER-Galvanized.
This instant could I supply these fastners which has been
galvanised by electroplating method. And please advice what is the
difference between the hot dip and electroplated.
Thanking you
Velayudham Ravishankar
structural fabricator - Manama, Bahrain, Kingdom of Bahrain
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Hot-dip galvanized coatings are heavier than electroplated zinc
and will exhibit greater corrosion resistance. It is never
permissable to make a substitution without approval, however, because
one never knows for sure the intents of the specifier. For example,
zinc electroplating is also susceptible to whiskering whereas
galvanized coatings are not believed to be. If these items are
intended for a computer room, you could have great liability.
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Ted Mooney, P.E.
finishing.com
Brick, NJ
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+++++
I agree with Ted.
Hot Dip coatings are usually thicker, better bonded and will
probably perform better than electroplated zinc, which are commonly
more used for cosmetic purposes only. We find these fasteners are
only well protected in stored conditions. For structurable
fabrications, if atmospheric corrosion is your concern, I would get
the client to agree on a design change.
But does it ever actually rain in Bahrain?
Martin Rich
- Plymouth, Devon, UK
+++++
Is it really the case that electroplated zinc coating is mostly
cosmetic?
Would you also offer your opinions on fasteners in ACQ-treated
wood in outdoor structures? Does the particular copper-rich formula
of ACQ accelerate corrosion of galvanized nails, screws, and bolts?
I use 1/4" to 3/4" diameter bolts, mostly 3/8". I use either
hot-dipped or electroplated zinc bolts. Should I not use
electroplated any more?
Thanks.
Michael Cohen
Community Built Playground Design - Ithaca, NY USA
+++++
Zinc plating is fine for some applications, mostly indoors, but
it's corrosion resistance isn't enough to provide much corrosion
resistance in rough outdoor service. The ACQ manufacturers have
specific recommendations about fasteners but, yes, copper in the wood
will accelerate corrosion due to the galvanic couple.
 Ted Mooney, P.E. finishing.com Brick, NJ
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Mr Ravishanker
Hot dip galvanising puts a thick zinc layer all over the part and
does protect well. There are Electro Galvanising ( electroplated )
Zinc iron alloys that perform very well and compete with Hot dip
galvanised coatings for Corrosion tesistance. These bear a look .
Regards,
June 4, 2006
I HAVE RECEIVED SOME 3 METER CHANNEL CROSS ARM WHICH IS ELECTRO
GALVANISED. DUE TO HEAVY RAIN IT IS GETTING CORRODED. WHAT MEASURE I
HAVE TO TAKE FOR STOPPING CORROSION AND ANY ZINC SPRAY WILL HELP TO
STOP THE CORROSION. IS ELECTRO GALVANISED OR HOT DIP GALVANISED GETS
CORRODED FAST. AWAITING YOUR EARLY REPLY WITH SOLUTION TO RECTIFY THE
DEFFECT.
N.JAYAKUMAR
- TRIVANDRUM, KERALA, INDIA
June 4, 2006
Investigate replacing it, N. As already stated in this thread,
electrogalvanized is usually inadequate for outdoor service.
 Ted Mooney, P.E. finishing.com Brick, NJ
October 18, 2006
I'm under the impression that the thickness of the zinc coating is
based on the standard or procedures for the specific galvanizing
process. For example, a hot dipped galvanized piece could be
galvanized to a lesser zince coating thickness than an
electrogalvanized piece. (Typically not the case, but as an example.)
Are my assumptions correct? I've spent a little time researching
this...Also, the thickness of the steel must have an effect on the
thickness of the zinc coating, right? Is or are there any studies or
information documenting this?
David Riley
Contracting - Piscataway, NJ
October 17, 2006
The thickness of electroplated zinc on hardware is typically
controlled at anywhere from from .0002" to .0006" according to
specific needs, David. The upper limit is usually based on
practicality in that it takes over an hour of zinc plating time to
reach .0006" in barrel plating and it becomes uneconomic. There is no
real lower limit, but the sloppy and dangerous "specification" of
"commercial zinc plating" is often interpreted to mean .0002". The
thickness of the steel has no effect on the thickness of
electroplated coatings.
Galvanizing is never that thin. Typical thicknesses are .0015" to
almost .004". In general you can't really control the thickness;
rather it depends on the surface condition of the steel. Thicker
steel takes longer to heat up and usually takes a heavier coating.
In all, it may be theoretically possible for an exceptionally
thick electrodeposited zinc coating to be as thick as a very thin hot
dipped coating, but it is nearly unheard of.
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Ted Mooney, P.E.
finishing.com
Brick, NJ
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July 25, 2007
Can we use electroplated Binding wires for construction purpose or
is it better to use hot dipped only???
Prasad A. Haridas
- Pune, Maharashtra, India
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