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topic 8075

Conductivity - Galvanized / Galvannealed


A discussion started in 2001 but continuing through 2018

2001

Q. I am a custom job shop, primary product is cabinet and case work for the telecom industry. We have an application for a client requesting galvannealed or galvanized material. I understand that one is more accepting of paint finishing while the other is not.

My question is do both materials carry the same conductivity characteristics? Are they both conductive? I always thought they were but I am told otherwise.

Michael Lozy
- Warwick, Rhode Island, USA


2001

A. Galvanneal is merely galvanized steel which has been annealed. The annealing furnace is downstream, from the zinc bath. Galvanneal is easier to paint. The surface is a smooth, dull grey. Usually, it is lightly oiled or even dry.

Galvanize sheets have a bright zinc finish (like garbage cans). The surface is not smooth. Zinc crystals may show through the paint. The surface is normally treated with a chromate solution which is for rust protection. This solution prevents good paint adhesion.

Terry T. Magyar
steel - Gahanna, Ohio usa


2001

A. The galvanneal process converts most of the zinc and some of the iron at the substrate surface to an intermetallic iron-zinc compound. The electrical conductivity for the intermetallic probably is not as great as that for the zinc or iron metal. Thus, the surface conductivity may not be as high for the galvanneal.

larry hanke
Larry Hanke
Minneapolis, Minnesota



2005 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What is the difference between Galvannealed, Galvanized and pre-galvanized.

Eileen Travis
- S Attleboro, Massachusetts


2005

A. Hi Eileen. We appended your question to a thread where Terry & Larry have already explained what galvannealed means.

Pre-galvanized means that the item in question is made by bending, punching, drilling, and/or otherwise working sheet steel that was galvanized before the fabrication work began, rather than galvanizing the item after the other fabrication steps are completed.

Pregalvanized material is used for economy (because it is far less labor intensive to galvanize a continuous sheet than individual fabricated items, and techniques like wiping can be used to limit the thickness). If pre-galvanizing is integrated correctly into the design, the product might be just as good as a post-galvanized item. But if the design is not so good, there will be rusting at the edges and around any holes because there will be no galvanizing on edges that have been created after the galvanizing process. The sacrificial power of the galvanizing offers some level of protection to those bare edges, but it's not as good as having them covered with zinc :-)

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



Do flanged joints require bonding jumpers?

October 28, 2018

Q. We have two SS 304 pipes with SS 304 flanges ends connected with a non conductive gasket, flanges are bolted together with GI nuts and bolts. Do we still need to have a jump over cable for the static energy to pass?

Vijay Kiran Maddireddy
Chemicals manufacturing - Hyderabad, India


October 2018

A. Hi Vijay. The good part is that your situation is commonplace, so it's pretty easy to get explanations, facts, and opinions even if you are finding nothing in the codes. Some engineering forums which discuss this include:
https://www.eng-tips.com/viewthread.cfm?qid=302126
https://www.eng-tips.com/viewthread.cfm?qid=216646

A good paper is at:
https://www.dairyland.com/images/pdf/Over-Voltage%20Protection%20of%20Insulated%20Joints%20On%20Pipelines.pdf

Another good paper discussing these issues and explaining alternatives such as star washers, spikies, etc., is
http://www.crp.co.uk/UserFiles/Documents/Lined%20Piping%20Systems,%20Static%20Electricity%20and%20Earthing.pdfbr That paper also expounds on what to do when you can't find specific guidance in the codes.

There are countless good discussions of your issue if you google the term "electrical bonding across a flanged joint". A simple thing I learned in my fifteen minutes of study is that if you are relying on the bolts to carry current, make sure you have star washers on the head end as well as the nut end. Best of luck.

Regards,

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



Is galvanized steel conductive enough for capacitive sensing?

November 10, 2018
wikipedia
Capacitive Sensing

I'm wondering if galvanized steel is conductive enough to allow for capacitive sensing? The purpose is so that if someone touches a piece of galvanized steel with a low voltage charge applied, resulting in a uniform electrostatic field, resistance could be detected by someone touching the steel.

Thank you for your advice!

Aaron Kettl
- Austin, Texas, USA



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